Vision outcomes in dogs with primary glaucoma surgically treated with lensectomy and endolaser cyclophotocoagulation after an Ahmed valve gonioimplantation failure
INTRODUCTION Glaucoma is a leading cause of vision loss in canines due to loss of retinal ganglion cells (RGCs) and eventual degeneration of the optic nerve head (ONH) as well as significant ischemic disease of the inner retina and optic nerve due to elevated intraocular pressure (IOP). , , , Glaucoma treatment revolves around medical, surgical, and combined approaches; which work to reduce aqueous humor production, improve aqueous drainage, or both. , While medical treatment plays an important role in glaucoma management, it frequently fails within months, leading to blindness and pain due to uncontrolled IOP. Owner compliance in administering medications and patient tolerance of medications can also influence success of medical therapy. The surgical procedures for canine glaucoma can be divided into: shunt implants (gonioimplants) that divert the aqueous humor from the anterior chamber (AC) to reservoirs created in different anatomical spaces, , cyclodestructive procedures to reduce the aqueous humor production, or a combination of these two procedures. , , , The most utilized shunting device in veterinary medicine is the Ahmed valve gonioimplant (AVG). , , , Two recent studies have reported visual success rate of AVG alone was 89% at 1‐year post‐op and a mean vision preservation time of ~57.5 months. In both of these studies, some patients required additional procedures (e.g., bleb resection and additional AVG). , Common complications leading to valve failure are fibrin occlusion of the intracameral tube, and scar tissue formation around the implant. , , Cyclodestructive procedures have been widely used in veterinary medicine in the past three decades with variable results. Endoscopic diode ciliary body ablation has been used in veterinary ophthalmology over the past decade, with a reported success rate of 71%–85% for vision preservation and IOP control at 1‐year post‐op. , , , , The most noticeable complications encountered include: uveitis leading to secondary glaucoma, delayed IOP lowering effect (2–3 weeks), hypotony, and phthisis bulbi. , , The latter two side effects are encountered less frequently compared with other cyclodestructive procedures due to the relatively low laser energy used and its precise targeting of the ciliary body. , , Prior to the popularity of endolaser, a combination of AVG with a transscleral cyclodestructive (TSC) procedure has been reported as an alternative for glaucoma control with a success rate for vision preservation and IOP control of 41%–57% and 73%–76%, respectively, at 1 year. , Combination of a non‐valved glaucoma drainage device (Baerveltd) valve with a TSC procedure showed a 100% success rates for vision preservation and IOP control in four eyes at the last follow‐up of 19 months. This study describes the use of a two‐stage procedure involving placing an AVG first followed by lensectomy–ECP and bleb resection upon AVG failure. In the author's opinion, staging of the AVG and lensectomy–ECP procedures may decrease post‐op complications compared with performing both procedures at the same time. The purpose of this retrospective study is to evaluate visual outcome, IOP fluctuations, and glaucoma medical therapy in dogs with primary glaucoma using a staged surgical approach. 

MATERIALS AND METHODS 2.1 Ethics compliances This retrospective study abides by the guidelines for Ethical Research in Veterinary Ophthalmology (GERVO). Consent form was signed by owners to allow use of the clinical information from the patients seen after December 1, 2021. The patients seen before the aforementioned date were reported in the aggregate, where a summary of data was used without disclosing client information to protect patient and client privacy in compliance with local and national laws on the use of data in medical records. 2.2 Study design Medical records from canine patients diagnosed with primary angle closure glaucoma (PACG) who underwent surgical treatment: AVG, lensectomy–ECP, and bleb resection at the Animal Eye Center (AEC), or were referred at the AEC after AVG placement, between 2008 and 2021, were reviewed. Fourteen eyes from 13 patients were included in the study. Inclusion criteria were: 1) diagnosed with PACG in one or both eyes; 2) medical management failed or maximum amount of drug therapy (at least three times a day administration of topical carbonic anhydrase inhibitors, topical prostaglandin analogs and two times a day of beta blockers and oral carbonic anhydrase inhibitors) was in use to keep the IOP below 25 mmHg; 3) visual eyes before both of the surgical procedures were performed; 4) at least one recorded IOP consistent with glaucoma prior to AVG surgery. Reviewed and analyzed data included: breed, age when glaucoma was diagnosed, age at the time of lensectomy–ECP surgery, sex, iridocorneal angle evaluation, number of glaucoma medications (topical and oral), IOPs, valve life, valve placement location, surgical complications post‐AVG and lensectomy–ECP, presence of cataracts, additional surgical procedures performed, and vision preservation time post‐AVG implantation. Glaucoma was defined as IOP > 25 mmHg recorded at AEC or at the referring veterinarian. Primary glaucoma diagnosis was based on abnormal iridocorneal angles evaluated by either gonioscopy and/or ultrasound biomicroscopy (UBM) and the absence of a secondary cause based on biomicroscopic examination. Goniodysgenesis was diagnosed based on closed or narrow iridocorneal angle width on gonioscopy, abnormal pectinate ligament morphology, closed or narrow ciliary cleft on UBM, or based on histopathologic results of the previously enucleated contralateral eye. Classification of iridocorneal angle/ciliary cleft width as open, narrow, or closed was subjective. Primary lens instability was determined by breed predisposition and the absence of any underlying secondary cause. Medical treatment for glaucoma included topical and oral medications. The most frequent topical medications used to help control IOP in the preoperative and postoperative period were carbonic anhydrase inhibitors, beta blockers, a combination of both, or prostaglandin analogs. Oral glaucoma medications included carbonic anhydrase inhibitor therapy. Intravenous Mannitol 25% (Hospira, Lake Forest, IL, USA) at a dose of 1–2 g/kg was administered, and if needed, paracentesis was performed in cases where the IOPs were elevated >25 mmHg and the patients did not respond to emergency topical medical management. In addition to glaucoma medications, topical steroids, and oral steroids or NSAIDs were used to control inflammation both pre‐ and postoperatively. Topical and systemic antibiotics were used postoperatively. An IOP value above 25 mmHg was considered valve failure. The frequency of administration of each glaucoma medication (either oral or topical) was recorded at each time point. All patients had full ophthalmic evaluations by at least one board‐certified veterinary ophthalmologists at AEC, or at the referral ophthalmology clinic. Ophthalmic examination included: menace response, dazzle, palpebral, direct and consensual pupillary light reflexes (PLR's), slit‐lamp biomicroscopy examination (Kona SL‐17 portable slit lamp, Kona Company, Torrance, CA, USA), tonometry via Avia Vet Tono‐Pen (Reichert, Depew, NY, USA) or Icare Tono‐Vet (Vantaa, Finland), Schirmer tear testing, and fluorescein staining of the cornea. Fundic examination was performed using a binocular indirect ophthalmoscope (Keeler Vantage Plus, Malvern, PA, USA) and condensing (20D, 28D, and 2.2 Pan retinal) lenses (Volk Optical Inc, Mentor, Ohio, USA). In cases where gonioscopy and UBM were performed, a Koeppe lens (14–17 mm, Ocular instruments, Bellevue, WA, USA) and an ultrasound (Quantel Medical, Bozeman, MT, USA) using a 50 MHz probe (Quantel Medical) were used. Vision was assessed by testing menace response and/or tracking reflex (cotton ball testing) in photopic and scotopic conditions, and obstacle course testing was performed in some of the patients. Vision loss was defined as a lack of menace response, and was confirmed in some of the patients by an abnormal maze test and clinical findings of severe optic nerve and retinal atrophy suggestive of previous IOP elevation. Vision preservation was calculated from the time of the AVG placement until the time of vision loss. 2.3 Surgical procedures Both surgical procedures were performed under general anesthesia. The anesthetic protocol varied for each procedure and for each case. Patients were premedicated with an opioid: Buprenorphine {0.01–0.03 mg/kg, (Par Pharmaceutical, Chestnut Ridge, NY, USA)} or Methadone {0.2–0.3 mg/kg, (Akorn Inc, Lake Forest, IL, USA)} and induced with a combination of either Propofol {1–4 mg/kg (Zoetis, USA)} or Alfaxalone {1–4 mg/kg (Jurox, Kansas City, MO, USA)} and a benzodiazepine: Midazolam {(0.25 mg/kg, (Akorn Inc, Lake Forest, IL, USA)} intravenously (IV). Each patient was intubated and anesthesia maintained with inhalant anesthetic: Isoflurane (Abbott Laboratories, USA) and supportive fluid therapy at a rate of 3–5 mLs/kg/hr was kept for the entire procedure. To allow appropriate globe position, neuromuscular blockade was achieved by administering Atracurium besylate {0.1–0.2 mg/kg IV (Meitheal Pharmaceuticals, Chicago, IL, USA)} every 40 min to 1 h. A mechanical ventilator was connected to all patients to ensure adequate ventilation. Intravenous injection of Cefazolin {22 mg/kg IV (Hikma Farmaceutica, Portugal)} was administered every 90 min in all patients. 2.3.1 Ahmed valve implantation The patients were placed in dorsal recumbency and the affected eye was prepared and draped for surgery in a routine fashion. Topical epinephrine was used to constrict the conjunctival vessels, and diathermy was used to cauterize individual conjunctival and episcleral vessels. Conjunctival incision was performed with tenotomy scissors 6 mm posterior to the limbus. Westcott scissors were used to bluntly dissect down to the sclera and a pocket was formed using tenotomy scissors under Tenon's and the conjunctiva, extending posterior to the equator of the globe. Mitomycin‐C {0.4 mg/mL (Wedgewood Pharmacy, Swedesboro, NJ, USA)} was dripped onto a polyvinyl alcohol sponge (PVA) placed into the pocket and was held on the scleral bed for 5 min, avoiding contact with the conjunctiva. The pocket was copiously flushed with 15–30 mLs of balanced salt solution {BSS (Alcon Laboratories, Fort Worth, Texas, USA)}. An Ahmed valve model: VFP 7, VFP 8, VS 2, or VS3 (Cara life/New World, Rancho Cucamonga, CA, USA) was primed with BSS and placed laterally or medially, between the dorsal and lateral or medial rectus muscles, respectively. The Ahmed valve was pushed into the pocket and the two valve plate eyelets were sutured with two interrupted sutures using Ethilon 8–0 (Johnson & Johnson, USA) on a taper needle, to the sclera 8 to 10 mm behind the limbus. A 22‐ or 23‐gauge needle, with a male adapter attached, was inserted into the anterior chamber starting 1 mm from the limbus. The valve tube was trimmed at a 45‐degree angle and was pushed through the tunnel into the anterior chamber (AC) avoiding crossing the pupillary margins or touching the iris or cornea. Viscoelastic 1.4% (AJL, Spain) was used to facilitate the insertion of the tube in the AC in some cases. The tube was sutured to the sclera midway between the limbus and the valve footplate with an interrupted suture using Ethilon 8–0 (Johnson & Johnson, USA) taking care not to constrict the tube. Tenon's capsule and conjunctiva were closed in two separate layers using 8–0 Vicryl (Jonhson & Johnson, Mexico) in a simple continuous pattern. 2.3.2 Phacoemulsification/ intracapsular lens extraction and endolaser photocoagulation All patients were placed in dorsal recumbency, and the affected eye was prepared and draped for surgery in a routine fashion. For the patients having phacoemulsification (phaco), using a Sapphire blade, a 2.8 mm incision was made into the clear cornea 1–2 mm from the dorsal limbus, to enter the AC. Viscoelastic material was used to maintain the AC and protect the corneal endothelium. Then, 0.2 mLs of 1:10.000 Epinephrine (BPI Labs, Freehold, NJ, USA) was injected intracamerally. An anterior continuous curvilinear capsulorhexis was started with a 23–25 gauge needle and continued with Utrata forceps. The lens was phacoemulsified (Oertli Alexos, Berneck, Switzerland, until 2020 and Oertli Alexos 3 afterward), and the remaining lens material was removed with irrigation/aspiration using heparinized BSS. The anterior capsule was polished with a Singer Sweep. When possible, an artificial lens was inserted into the capsule. Vitrectomy was performed as needed. Viscoelastic 1.8% (An‐Vision, Salt Lake City, Utah, USA) was then instilled in the anterior chamber and ciliary sulcus. An Endo Optiks E2 unit (Beaver‐Visitec International, Waltham, MA, USA) with a curved 19 gauge, 17 K pixels 140 degree Endo Optiks E2 MicroProbe (Beaver‐Visitec International, Waltham, MA, USA) was used. The ECP probe contains a diode laser (810 nm wavelength), a 175 W xenon light source, a helium‐neon aiming beam, and an endoscope. The heads of the ciliary processes were photocoagulated until they shrunk, avoiding visible “pops.” The laser energy was titrated to effect. Irrigation/aspiration was performed to remove all remaining viscoelastic material from the AC. 0.15 mL of Decadron (Somerset Therapeutics, Hollywood, FL, USA) was injected intracamerally. The corneal incision was sutured in a simple interrupted pattern using 8–0 Vicryl (Johnson & Johnson, USA) suture. 2.3.3 Intracapsular lens extraction ( ICLE ) and vitrectomy The cornea was grooved at the limbus for 180 degrees using a 450‐micron restricted depth blade. A 3.2 mm keratome was used to enter the anterior chamber. Corneal scissors were used to complete the corneal incision in the pre‐placed groove. The lens was removed with a cryoprobe and the hyaloideocapsular attachments were sharply transected with Vannas scissors. The corneal incision was closed with 8–0 Vicryl (Johnson & Johnson, USA) interrupted sutures oversewn with an 8–0 Vicryl's simple continuous suture. Just before tying the last sutures, an anterior vitrectomy was performed {using a 20 g continuous flow vitrector unit (Oertli Alexos with Titano handpiece, Berneck, Switzerland}through the pupil to remove anterior vitreous at the pupil margin and anterior chamber. The anterior chamber was reestablished with BSS. 0.15 mL of Decadron (Somerset Therapeutics, Hollywood, FL, USA) was injected intracameral with a 27 g cannula. The ICLE and vitrectomy were performed in the eyes that had significant lens instability, followed by the ECP procedure described above. 2.3.4 Bleb resection A bleb resection was performed at the time of lensectomy–ECP. The location of the bleb was over the Ahmed valve. The conjunctiva was incised with tenotomy scissors and dissection was performed down to the fibrotic capsule over the valve. The fibrous capsule was exposed and removed as completely as possible. It was observed that aqueous flowed freely from the anterior chamber through the valve. No Mitomycin‐C or other antifibrotic agents were used. The incision was closed in two layers: the tenons and conjunctiva with 8/0 Vicryl in a continuous pattern. Postoperative management varied individually for the length of the study. After both procedures, the medications prescribed included a topical steroid: Prednisolone acetate 1% (Sandoz, Alcon Laboratories, Fort Worth, TX, USA) or a topical NSAID either Nevanac (Novartis Pharmaceuticals, Canada) or Keterolac (Micro Labs, Basking Ridge, NJ, USA). Most common topical antibiotics used included fluoroquinolones: Ofloxacin (Akorn, Lake Forest, IL, USA) or Moxifloxacin (Apotex, Ontario, Canada) and/or a triple antibiotic Neomycin Polymyxin B and Bacitracin Zinc (Bausch + Lomb, USA) ointment or a combination of triple antibiotic with a steroid Neomycin Polymyxin B and Dexamethasone (Bausch + Lomb). A topical carbonic anhydrase inhibitor alone or in combination with a beta‐blocker and/or a prostaglandin analog was used to control the IOP postoperatively. Steroid therapy with dexamethasone (Sparhawk Lab., Lenexa, KS, USA) continued with oral prednisone (Jubilant Cadista Pharmaceuticals, Salisbury, MD, USA) or NSAID therapy with either Carprofen (Zoetis Inc., MI, USA) or Meloxicam (Boehringer Ingelheim Animal Health USA Inc.) was used to control post‐op inflammation. Oral cephalosporin (second or third generation) or oral amoxicillin with clavulanic acid was used for antimicrobial prophylaxis for a minimum of 14 days. Intracameral tissue plasminogen activator {TPA (Cathflo activase, San Francisco, CA, USA)} was used once or twice after the Ahmed valve implantation if needed, to break down fibrin around the intracameral tube. Additional surgeries performed at the time of lensectomy–ECP include vitrectomy performed in the eyes that had noticeable vitreous in the anterior chamber. Additional ECP surgery, AVG replacement, or additional AVG placement was performed to reduce elevated IOP and to preserve vision. 2.4 Criteria for success The time of vision preservation was calculated from the time of Ahmed valve implantation until the vision was lost, the last examination date, or death of the patient. The IOPs recorded at the time of AVG implantation, termed “0” in the study, were compared with IOPs post‐lensectomy–ECP at 2, 6, 12, 24, and 36 months. The number of glaucoma medications administered at the time of AVG implantation was compared with post‐lensectomy–ECP at 2, 6, 12, 24, and 36 months. The time to valve failure was calculated from the time of Ahmed valve implantation until IOP was >25 mmHg recorded at AEC or with the referring veterinarian. Minimum follow‐up time was 6 months and the cut‐off time was 36 months. 2.5 Data analysis To facilitate statistical analyses, the data obtained were analyzed using the R Core Team (2021) program. A Kaplan–Meier survival analysis was used to determine the probability of maintaining vision. Because of the relatively low number of the subjects in the study, a non‐parametric paired randomization test was used to compare the IOPs and the number of glaucoma medications before AVG, and after the lensectomy–ECP, to obtain a p ‐value. The mean IOP and the minimal and maximal differences were used to compare the changes in IOPs. A bootstrap confidence interval was used to determine the mean time on the Ahmed valve and binomial distribution was used to construct confidence intervals determining the proportion of cases exhibiting fibrin clots that required TPA injection. A Wilcoxon rank sum test was used to calculate the median time of valve failure. A p ‐value <.05 was considered statistically significant. 

Ethics compliances This retrospective study abides by the guidelines for Ethical Research in Veterinary Ophthalmology (GERVO). Consent form was signed by owners to allow use of the clinical information from the patients seen after December 1, 2021. The patients seen before the aforementioned date were reported in the aggregate, where a summary of data was used without disclosing client information to protect patient and client privacy in compliance with local and national laws on the use of data in medical records. 

Study design Medical records from canine patients diagnosed with primary angle closure glaucoma (PACG) who underwent surgical treatment: AVG, lensectomy–ECP, and bleb resection at the Animal Eye Center (AEC), or were referred at the AEC after AVG placement, between 2008 and 2021, were reviewed. Fourteen eyes from 13 patients were included in the study. Inclusion criteria were: 1) diagnosed with PACG in one or both eyes; 2) medical management failed or maximum amount of drug therapy (at least three times a day administration of topical carbonic anhydrase inhibitors, topical prostaglandin analogs and two times a day of beta blockers and oral carbonic anhydrase inhibitors) was in use to keep the IOP below 25 mmHg; 3) visual eyes before both of the surgical procedures were performed; 4) at least one recorded IOP consistent with glaucoma prior to AVG surgery. Reviewed and analyzed data included: breed, age when glaucoma was diagnosed, age at the time of lensectomy–ECP surgery, sex, iridocorneal angle evaluation, number of glaucoma medications (topical and oral), IOPs, valve life, valve placement location, surgical complications post‐AVG and lensectomy–ECP, presence of cataracts, additional surgical procedures performed, and vision preservation time post‐AVG implantation. Glaucoma was defined as IOP > 25 mmHg recorded at AEC or at the referring veterinarian. Primary glaucoma diagnosis was based on abnormal iridocorneal angles evaluated by either gonioscopy and/or ultrasound biomicroscopy (UBM) and the absence of a secondary cause based on biomicroscopic examination. Goniodysgenesis was diagnosed based on closed or narrow iridocorneal angle width on gonioscopy, abnormal pectinate ligament morphology, closed or narrow ciliary cleft on UBM, or based on histopathologic results of the previously enucleated contralateral eye. Classification of iridocorneal angle/ciliary cleft width as open, narrow, or closed was subjective. Primary lens instability was determined by breed predisposition and the absence of any underlying secondary cause. Medical treatment for glaucoma included topical and oral medications. The most frequent topical medications used to help control IOP in the preoperative and postoperative period were carbonic anhydrase inhibitors, beta blockers, a combination of both, or prostaglandin analogs. Oral glaucoma medications included carbonic anhydrase inhibitor therapy. Intravenous Mannitol 25% (Hospira, Lake Forest, IL, USA) at a dose of 1–2 g/kg was administered, and if needed, paracentesis was performed in cases where the IOPs were elevated >25 mmHg and the patients did not respond to emergency topical medical management. In addition to glaucoma medications, topical steroids, and oral steroids or NSAIDs were used to control inflammation both pre‐ and postoperatively. Topical and systemic antibiotics were used postoperatively. An IOP value above 25 mmHg was considered valve failure. The frequency of administration of each glaucoma medication (either oral or topical) was recorded at each time point. All patients had full ophthalmic evaluations by at least one board‐certified veterinary ophthalmologists at AEC, or at the referral ophthalmology clinic. Ophthalmic examination included: menace response, dazzle, palpebral, direct and consensual pupillary light reflexes (PLR's), slit‐lamp biomicroscopy examination (Kona SL‐17 portable slit lamp, Kona Company, Torrance, CA, USA), tonometry via Avia Vet Tono‐Pen (Reichert, Depew, NY, USA) or Icare Tono‐Vet (Vantaa, Finland), Schirmer tear testing, and fluorescein staining of the cornea. Fundic examination was performed using a binocular indirect ophthalmoscope (Keeler Vantage Plus, Malvern, PA, USA) and condensing (20D, 28D, and 2.2 Pan retinal) lenses (Volk Optical Inc, Mentor, Ohio, USA). In cases where gonioscopy and UBM were performed, a Koeppe lens (14–17 mm, Ocular instruments, Bellevue, WA, USA) and an ultrasound (Quantel Medical, Bozeman, MT, USA) using a 50 MHz probe (Quantel Medical) were used. Vision was assessed by testing menace response and/or tracking reflex (cotton ball testing) in photopic and scotopic conditions, and obstacle course testing was performed in some of the patients. Vision loss was defined as a lack of menace response, and was confirmed in some of the patients by an abnormal maze test and clinical findings of severe optic nerve and retinal atrophy suggestive of previous IOP elevation. Vision preservation was calculated from the time of the AVG placement until the time of vision loss. 

Surgical procedures Both surgical procedures were performed under general anesthesia. The anesthetic protocol varied for each procedure and for each case. Patients were premedicated with an opioid: Buprenorphine {0.01–0.03 mg/kg, (Par Pharmaceutical, Chestnut Ridge, NY, USA)} or Methadone {0.2–0.3 mg/kg, (Akorn Inc, Lake Forest, IL, USA)} and induced with a combination of either Propofol {1–4 mg/kg (Zoetis, USA)} or Alfaxalone {1–4 mg/kg (Jurox, Kansas City, MO, USA)} and a benzodiazepine: Midazolam {(0.25 mg/kg, (Akorn Inc, Lake Forest, IL, USA)} intravenously (IV). Each patient was intubated and anesthesia maintained with inhalant anesthetic: Isoflurane (Abbott Laboratories, USA) and supportive fluid therapy at a rate of 3–5 mLs/kg/hr was kept for the entire procedure. To allow appropriate globe position, neuromuscular blockade was achieved by administering Atracurium besylate {0.1–0.2 mg/kg IV (Meitheal Pharmaceuticals, Chicago, IL, USA)} every 40 min to 1 h. A mechanical ventilator was connected to all patients to ensure adequate ventilation. Intravenous injection of Cefazolin {22 mg/kg IV (Hikma Farmaceutica, Portugal)} was administered every 90 min in all patients. 2.3.1 Ahmed valve implantation The patients were placed in dorsal recumbency and the affected eye was prepared and draped for surgery in a routine fashion. Topical epinephrine was used to constrict the conjunctival vessels, and diathermy was used to cauterize individual conjunctival and episcleral vessels. Conjunctival incision was performed with tenotomy scissors 6 mm posterior to the limbus. Westcott scissors were used to bluntly dissect down to the sclera and a pocket was formed using tenotomy scissors under Tenon's and the conjunctiva, extending posterior to the equator of the globe. Mitomycin‐C {0.4 mg/mL (Wedgewood Pharmacy, Swedesboro, NJ, USA)} was dripped onto a polyvinyl alcohol sponge (PVA) placed into the pocket and was held on the scleral bed for 5 min, avoiding contact with the conjunctiva. The pocket was copiously flushed with 15–30 mLs of balanced salt solution {BSS (Alcon Laboratories, Fort Worth, Texas, USA)}. An Ahmed valve model: VFP 7, VFP 8, VS 2, or VS3 (Cara life/New World, Rancho Cucamonga, CA, USA) was primed with BSS and placed laterally or medially, between the dorsal and lateral or medial rectus muscles, respectively. The Ahmed valve was pushed into the pocket and the two valve plate eyelets were sutured with two interrupted sutures using Ethilon 8–0 (Johnson & Johnson, USA) on a taper needle, to the sclera 8 to 10 mm behind the limbus. A 22‐ or 23‐gauge needle, with a male adapter attached, was inserted into the anterior chamber starting 1 mm from the limbus. The valve tube was trimmed at a 45‐degree angle and was pushed through the tunnel into the anterior chamber (AC) avoiding crossing the pupillary margins or touching the iris or cornea. Viscoelastic 1.4% (AJL, Spain) was used to facilitate the insertion of the tube in the AC in some cases. The tube was sutured to the sclera midway between the limbus and the valve footplate with an interrupted suture using Ethilon 8–0 (Johnson & Johnson, USA) taking care not to constrict the tube. Tenon's capsule and conjunctiva were closed in two separate layers using 8–0 Vicryl (Jonhson & Johnson, Mexico) in a simple continuous pattern. 2.3.2 Phacoemulsification/ intracapsular lens extraction and endolaser photocoagulation All patients were placed in dorsal recumbency, and the affected eye was prepared and draped for surgery in a routine fashion. For the patients having phacoemulsification (phaco), using a Sapphire blade, a 2.8 mm incision was made into the clear cornea 1–2 mm from the dorsal limbus, to enter the AC. Viscoelastic material was used to maintain the AC and protect the corneal endothelium. Then, 0.2 mLs of 1:10.000 Epinephrine (BPI Labs, Freehold, NJ, USA) was injected intracamerally. An anterior continuous curvilinear capsulorhexis was started with a 23–25 gauge needle and continued with Utrata forceps. The lens was phacoemulsified (Oertli Alexos, Berneck, Switzerland, until 2020 and Oertli Alexos 3 afterward), and the remaining lens material was removed with irrigation/aspiration using heparinized BSS. The anterior capsule was polished with a Singer Sweep. When possible, an artificial lens was inserted into the capsule. Vitrectomy was performed as needed. Viscoelastic 1.8% (An‐Vision, Salt Lake City, Utah, USA) was then instilled in the anterior chamber and ciliary sulcus. An Endo Optiks E2 unit (Beaver‐Visitec International, Waltham, MA, USA) with a curved 19 gauge, 17 K pixels 140 degree Endo Optiks E2 MicroProbe (Beaver‐Visitec International, Waltham, MA, USA) was used. The ECP probe contains a diode laser (810 nm wavelength), a 175 W xenon light source, a helium‐neon aiming beam, and an endoscope. The heads of the ciliary processes were photocoagulated until they shrunk, avoiding visible “pops.” The laser energy was titrated to effect. Irrigation/aspiration was performed to remove all remaining viscoelastic material from the AC. 0.15 mL of Decadron (Somerset Therapeutics, Hollywood, FL, USA) was injected intracamerally. The corneal incision was sutured in a simple interrupted pattern using 8–0 Vicryl (Johnson & Johnson, USA) suture. 2.3.3 Intracapsular lens extraction ( ICLE ) and vitrectomy The cornea was grooved at the limbus for 180 degrees using a 450‐micron restricted depth blade. A 3.2 mm keratome was used to enter the anterior chamber. Corneal scissors were used to complete the corneal incision in the pre‐placed groove. The lens was removed with a cryoprobe and the hyaloideocapsular attachments were sharply transected with Vannas scissors. The corneal incision was closed with 8–0 Vicryl (Johnson & Johnson, USA) interrupted sutures oversewn with an 8–0 Vicryl's simple continuous suture. Just before tying the last sutures, an anterior vitrectomy was performed {using a 20 g continuous flow vitrector unit (Oertli Alexos with Titano handpiece, Berneck, Switzerland}through the pupil to remove anterior vitreous at the pupil margin and anterior chamber. The anterior chamber was reestablished with BSS. 0.15 mL of Decadron (Somerset Therapeutics, Hollywood, FL, USA) was injected intracameral with a 27 g cannula. The ICLE and vitrectomy were performed in the eyes that had significant lens instability, followed by the ECP procedure described above. 2.3.4 Bleb resection A bleb resection was performed at the time of lensectomy–ECP. The location of the bleb was over the Ahmed valve. The conjunctiva was incised with tenotomy scissors and dissection was performed down to the fibrotic capsule over the valve. The fibrous capsule was exposed and removed as completely as possible. It was observed that aqueous flowed freely from the anterior chamber through the valve. No Mitomycin‐C or other antifibrotic agents were used. The incision was closed in two layers: the tenons and conjunctiva with 8/0 Vicryl in a continuous pattern. Postoperative management varied individually for the length of the study. After both procedures, the medications prescribed included a topical steroid: Prednisolone acetate 1% (Sandoz, Alcon Laboratories, Fort Worth, TX, USA) or a topical NSAID either Nevanac (Novartis Pharmaceuticals, Canada) or Keterolac (Micro Labs, Basking Ridge, NJ, USA). Most common topical antibiotics used included fluoroquinolones: Ofloxacin (Akorn, Lake Forest, IL, USA) or Moxifloxacin (Apotex, Ontario, Canada) and/or a triple antibiotic Neomycin Polymyxin B and Bacitracin Zinc (Bausch + Lomb, USA) ointment or a combination of triple antibiotic with a steroid Neomycin Polymyxin B and Dexamethasone (Bausch + Lomb). A topical carbonic anhydrase inhibitor alone or in combination with a beta‐blocker and/or a prostaglandin analog was used to control the IOP postoperatively. Steroid therapy with dexamethasone (Sparhawk Lab., Lenexa, KS, USA) continued with oral prednisone (Jubilant Cadista Pharmaceuticals, Salisbury, MD, USA) or NSAID therapy with either Carprofen (Zoetis Inc., MI, USA) or Meloxicam (Boehringer Ingelheim Animal Health USA Inc.) was used to control post‐op inflammation. Oral cephalosporin (second or third generation) or oral amoxicillin with clavulanic acid was used for antimicrobial prophylaxis for a minimum of 14 days. Intracameral tissue plasminogen activator {TPA (Cathflo activase, San Francisco, CA, USA)} was used once or twice after the Ahmed valve implantation if needed, to break down fibrin around the intracameral tube. Additional surgeries performed at the time of lensectomy–ECP include vitrectomy performed in the eyes that had noticeable vitreous in the anterior chamber. Additional ECP surgery, AVG replacement, or additional AVG placement was performed to reduce elevated IOP and to preserve vision. 

Ahmed valve implantation The patients were placed in dorsal recumbency and the affected eye was prepared and draped for surgery in a routine fashion. Topical epinephrine was used to constrict the conjunctival vessels, and diathermy was used to cauterize individual conjunctival and episcleral vessels. Conjunctival incision was performed with tenotomy scissors 6 mm posterior to the limbus. Westcott scissors were used to bluntly dissect down to the sclera and a pocket was formed using tenotomy scissors under Tenon's and the conjunctiva, extending posterior to the equator of the globe. Mitomycin‐C {0.4 mg/mL (Wedgewood Pharmacy, Swedesboro, NJ, USA)} was dripped onto a polyvinyl alcohol sponge (PVA) placed into the pocket and was held on the scleral bed for 5 min, avoiding contact with the conjunctiva. The pocket was copiously flushed with 15–30 mLs of balanced salt solution {BSS (Alcon Laboratories, Fort Worth, Texas, USA)}. An Ahmed valve model: VFP 7, VFP 8, VS 2, or VS3 (Cara life/New World, Rancho Cucamonga, CA, USA) was primed with BSS and placed laterally or medially, between the dorsal and lateral or medial rectus muscles, respectively. The Ahmed valve was pushed into the pocket and the two valve plate eyelets were sutured with two interrupted sutures using Ethilon 8–0 (Johnson & Johnson, USA) on a taper needle, to the sclera 8 to 10 mm behind the limbus. A 22‐ or 23‐gauge needle, with a male adapter attached, was inserted into the anterior chamber starting 1 mm from the limbus. The valve tube was trimmed at a 45‐degree angle and was pushed through the tunnel into the anterior chamber (AC) avoiding crossing the pupillary margins or touching the iris or cornea. Viscoelastic 1.4% (AJL, Spain) was used to facilitate the insertion of the tube in the AC in some cases. The tube was sutured to the sclera midway between the limbus and the valve footplate with an interrupted suture using Ethilon 8–0 (Johnson & Johnson, USA) taking care not to constrict the tube. Tenon's capsule and conjunctiva were closed in two separate layers using 8–0 Vicryl (Jonhson & Johnson, Mexico) in a simple continuous pattern. 

Phacoemulsification/ intracapsular lens extraction and endolaser photocoagulation All patients were placed in dorsal recumbency, and the affected eye was prepared and draped for surgery in a routine fashion. For the patients having phacoemulsification (phaco), using a Sapphire blade, a 2.8 mm incision was made into the clear cornea 1–2 mm from the dorsal limbus, to enter the AC. Viscoelastic material was used to maintain the AC and protect the corneal endothelium. Then, 0.2 mLs of 1:10.000 Epinephrine (BPI Labs, Freehold, NJ, USA) was injected intracamerally. An anterior continuous curvilinear capsulorhexis was started with a 23–25 gauge needle and continued with Utrata forceps. The lens was phacoemulsified (Oertli Alexos, Berneck, Switzerland, until 2020 and Oertli Alexos 3 afterward), and the remaining lens material was removed with irrigation/aspiration using heparinized BSS. The anterior capsule was polished with a Singer Sweep. When possible, an artificial lens was inserted into the capsule. Vitrectomy was performed as needed. Viscoelastic 1.8% (An‐Vision, Salt Lake City, Utah, USA) was then instilled in the anterior chamber and ciliary sulcus. An Endo Optiks E2 unit (Beaver‐Visitec International, Waltham, MA, USA) with a curved 19 gauge, 17 K pixels 140 degree Endo Optiks E2 MicroProbe (Beaver‐Visitec International, Waltham, MA, USA) was used. The ECP probe contains a diode laser (810 nm wavelength), a 175 W xenon light source, a helium‐neon aiming beam, and an endoscope. The heads of the ciliary processes were photocoagulated until they shrunk, avoiding visible “pops.” The laser energy was titrated to effect. Irrigation/aspiration was performed to remove all remaining viscoelastic material from the AC. 0.15 mL of Decadron (Somerset Therapeutics, Hollywood, FL, USA) was injected intracamerally. The corneal incision was sutured in a simple interrupted pattern using 8–0 Vicryl (Johnson & Johnson, USA) suture. 

Intracapsular lens extraction ( ICLE ) and vitrectomy The cornea was grooved at the limbus for 180 degrees using a 450‐micron restricted depth blade. A 3.2 mm keratome was used to enter the anterior chamber. Corneal scissors were used to complete the corneal incision in the pre‐placed groove. The lens was removed with a cryoprobe and the hyaloideocapsular attachments were sharply transected with Vannas scissors. The corneal incision was closed with 8–0 Vicryl (Johnson & Johnson, USA) interrupted sutures oversewn with an 8–0 Vicryl's simple continuous suture. Just before tying the last sutures, an anterior vitrectomy was performed {using a 20 g continuous flow vitrector unit (Oertli Alexos with Titano handpiece, Berneck, Switzerland}through the pupil to remove anterior vitreous at the pupil margin and anterior chamber. The anterior chamber was reestablished with BSS. 0.15 mL of Decadron (Somerset Therapeutics, Hollywood, FL, USA) was injected intracameral with a 27 g cannula. The ICLE and vitrectomy were performed in the eyes that had significant lens instability, followed by the ECP procedure described above. 

Bleb resection A bleb resection was performed at the time of lensectomy–ECP. The location of the bleb was over the Ahmed valve. The conjunctiva was incised with tenotomy scissors and dissection was performed down to the fibrotic capsule over the valve. The fibrous capsule was exposed and removed as completely as possible. It was observed that aqueous flowed freely from the anterior chamber through the valve. No Mitomycin‐C or other antifibrotic agents were used. The incision was closed in two layers: the tenons and conjunctiva with 8/0 Vicryl in a continuous pattern. Postoperative management varied individually for the length of the study. After both procedures, the medications prescribed included a topical steroid: Prednisolone acetate 1% (Sandoz, Alcon Laboratories, Fort Worth, TX, USA) or a topical NSAID either Nevanac (Novartis Pharmaceuticals, Canada) or Keterolac (Micro Labs, Basking Ridge, NJ, USA). Most common topical antibiotics used included fluoroquinolones: Ofloxacin (Akorn, Lake Forest, IL, USA) or Moxifloxacin (Apotex, Ontario, Canada) and/or a triple antibiotic Neomycin Polymyxin B and Bacitracin Zinc (Bausch + Lomb, USA) ointment or a combination of triple antibiotic with a steroid Neomycin Polymyxin B and Dexamethasone (Bausch + Lomb). A topical carbonic anhydrase inhibitor alone or in combination with a beta‐blocker and/or a prostaglandin analog was used to control the IOP postoperatively. Steroid therapy with dexamethasone (Sparhawk Lab., Lenexa, KS, USA) continued with oral prednisone (Jubilant Cadista Pharmaceuticals, Salisbury, MD, USA) or NSAID therapy with either Carprofen (Zoetis Inc., MI, USA) or Meloxicam (Boehringer Ingelheim Animal Health USA Inc.) was used to control post‐op inflammation. Oral cephalosporin (second or third generation) or oral amoxicillin with clavulanic acid was used for antimicrobial prophylaxis for a minimum of 14 days. Intracameral tissue plasminogen activator {TPA (Cathflo activase, San Francisco, CA, USA)} was used once or twice after the Ahmed valve implantation if needed, to break down fibrin around the intracameral tube. Additional surgeries performed at the time of lensectomy–ECP include vitrectomy performed in the eyes that had noticeable vitreous in the anterior chamber. Additional ECP surgery, AVG replacement, or additional AVG placement was performed to reduce elevated IOP and to preserve vision. 

Criteria for success The time of vision preservation was calculated from the time of Ahmed valve implantation until the vision was lost, the last examination date, or death of the patient. The IOPs recorded at the time of AVG implantation, termed “0” in the study, were compared with IOPs post‐lensectomy–ECP at 2, 6, 12, 24, and 36 months. The number of glaucoma medications administered at the time of AVG implantation was compared with post‐lensectomy–ECP at 2, 6, 12, 24, and 36 months. The time to valve failure was calculated from the time of Ahmed valve implantation until IOP was >25 mmHg recorded at AEC or with the referring veterinarian. Minimum follow‐up time was 6 months and the cut‐off time was 36 months. 

Data analysis To facilitate statistical analyses, the data obtained were analyzed using the R Core Team (2021) program. A Kaplan–Meier survival analysis was used to determine the probability of maintaining vision. Because of the relatively low number of the subjects in the study, a non‐parametric paired randomization test was used to compare the IOPs and the number of glaucoma medications before AVG, and after the lensectomy–ECP, to obtain a p ‐value. The mean IOP and the minimal and maximal differences were used to compare the changes in IOPs. A bootstrap confidence interval was used to determine the mean time on the Ahmed valve and binomial distribution was used to construct confidence intervals determining the proportion of cases exhibiting fibrin clots that required TPA injection. A Wilcoxon rank sum test was used to calculate the median time of valve failure. A p ‐value <.05 was considered statistically significant. 

RESULTS Fourteen eyes from 13 patients were included in the study. One patient underwent simultaneous bilateral procedures. Demographic analysis showed females were overrepresented ( n = 9) compared with males ( n = 4) ( p = .267). Participating breeds included: Labrador Retriever ( n = 2), Chihuahua ( n = 2), and one each of the following breeds: Beagle mix, Basset Hound, American Cocker Spaniel, Maltese, Great Pyrenees, Boston Terrier, Shih Tzu, Australian Shepherd, and Bouvier des Flandres. The mean age when glaucoma was initially diagnosed was 6.82 years (range: 0.53–14.12 yrs), and the mean age when ECP was performed was 7.97 years (range: 2.48–14.17 yrs). The right eye was operated on in five patients and the left eye in nine patients. All patients were visual before both of the surgical procedures. One patient (1 eye) had two AVG surgeries at a different clinic, {Ophthalmology for Animals (OFA)}, 10 months apart, and was referred to AEC for phaco‐ECP, 6 months after the latest valve placement. All lensectomy–ECP surgeries were performed at AEC. The iridocorneal angle and ciliary cleft were assessed prior to AVG placement. The iridocorneal angle was assessed in 13 of the 14 eyes, as one eye had an anterior lens luxation. Gonioscopy alone was performed in 5/13 eyes, with 4/5 eyes showing narrow angles in three quadrants (the dorsal quadrant was difficult to examine in all patients) and 1/5 eyes showing a closed angle. UBM alone was done in 4/13 eyes, revealing closed ciliary cleft in three quadrants in 3/4 eyes and open ciliary cleft in two quadrants in 1/4 eyes. Both gonioscopy and UBM were performed in 4/13 eyes, showing narrow angles in 2/4 eyes and closed angles in 2/4 eyes, while UBM showed closed ciliary cleft in three quadrants in 4/4 eyes. Enucleation of the contralateral eye was performed on 6/13 patients, while one eye underwent chemical ciliary body ablation. Goniodysgenesis was diagnosed histopathologically from the enucleated contralateral eye in 4/6 cases; 2/6 eyes were not submitted for histopathology. 3.1 Vision preservation, IOP, and medication Of 14 eyes included in the study, 12 eyes were still available for follow‐up at 1 year, 10 eyes at 2 years, and five eyes at 3 years postoperatively. Vision was preserved in 93% of the eyes at 1 year, 84% at 2 years, 60% at 3 years, and 48% at 4 years, with three eyes retaining vision up to 5.2, 7.1, and 8.3 years, respectively (Figure ). IOP had a statistically significant decrease at 2 and 6 months ( p = .0157 and p = .0163) post‐lensectomy–ECP compared with the IOP before both of the procedures. No significant difference was noted at the rest of the studied time points (12, 24, and 36 months) (Figure ). Mean IOP at the time of Ahmed valve implantation (baseline or “0”) was 21.7 mmHg (range of 5–54 mmHg). Comparison between mean IOPs at baseline relative to post‐lensectomy–ECP showed a reduction of 9.64 mmHg at 2 months, 9.71, 2.45, 7.25, and 12.25 mmHg at 6, 12, 24, and 36 months, respectively (Figures and ). The mean number of glaucoma medications was compared before the AVG placement and after the lensectomy–ECP. There was a reduction in the mean number of glaucoma medications of 4.35 at 2 months, 4.85, 4.09, 3.5, and 4.5 at 6, 12, 24, and 36 months, respectively. The reduction in the number of glaucoma medications administered was statistically significant at 2, 6, and 12 months with a p ‐value of 0.0005, 0.0000, and 0.0065, respectively. At 24 months, the decrease was not significant ( p = .1219) and at 36 months, due to the low number of patients remaining, the p ‐value of 0.0000 is unreliable (Figures and ). 3.2 Surgery and complications In this study, recorded Ahmed valve models used were: VFP 8 ( n = 5), VS2 ( n = 2), VFP 7, and VS3 ( n = 1). In six patients, the model type was not recorded. From the total number of Ahmed valves, 10 were placed laterally and five were placed medially. The median time to valve failure was 131 days (~ 4.3 months). The median time on the valves placed laterally was 131 days (range: 9 to 588) compared with 120 days (range: 84 to 204) on the valves placed medially. The median time to valve failure in different placement locations was not significant ( p = .85; Figure ). Most common complications post‐AVG implantation were fibrin in the anterior chamber obstructing the Ahmed tube, and scar tissue formation around the Ahmed footplate causing valve failure. In this study, 5/14 eyes (35.7%) developed fibrin clots and required TPA injections. The mean time to develop fibrin clots and requiring TPA injection was 3.2 days (range 1.2 to 5.8 days). One of the five eyes that developed fibrin clots required TPA injections twice. Scar tissue around the gonioimplant that required surgery formed in 11 out of the 14 eyes included in the study and a bleb resection was performed at the time of lensectomy–ECP. The three eyes that did not have the bleb resection performed had undergone AVG surgery shortly before the phaco‐ECP (9 and 5 days). One patient (one eye) had 3 bleb resection surgeries: two before, and one at the time of the lensectomy–ECP. The laser power utilized, ranged between 0.1 and 0.4 watts with 270 degrees of treatment. Seven out of 14 eyes had cataract diagnosed before the lensectomy–ECP. Incipient cataracts were present in 4/7 patients, an immature cataract in 1/7 patients, and mature cataracts in 2/7 patients. A lens subluxation was noted in one eye prior to lensectomy–ECP and lens instability was noted at the time of the surgery in 2 out of 14 eyes. In all three of these eyes, an intracapsular lens extraction (ICLE) and anterior vitrectomy was performed. One of the patients developed hypotony, retinal detachment, and lost vision 16 days after surgery. The other two cases maintained vision for 2.5 and 3 years. Phaco‐ECP was performed in the remaining 11/14 eyes. An artificial intraocular lens (IOL) was inserted into the lens capsule in 6/11 of the eyes. Complications occurring in the first 2 months following lensectomy–ECP were recorded. The most common postoperative complication after lensectomy–ECP was anterior chamber fibrin formation in six out of 14 eyes. 2/6 required one TPA injection, 4/6 required multiple injections, additionally one eye required aspiration of the fibrin from the anterior chamber (using an irrigation/aspiration tip) under general anesthesia. Mean time to fibrin formation was 4.5 days (range 2.6 to 6.8 days). Other complications affecting only one eye included: replacement of AVG implant (9 months after the initial placement due to malfunctioning of the valve), epithelial ulcer, and retinal detachment (occurring 16 days post‐op) with subsequent phthisis bulbi. IOP spikes occurred in 3/14 eyes and led to vision loss in one of three eyes 7 days post‐op. Long‐term complications included the need for additional surgery, a second ECP in 1/14 eyes 1 year after the first procedure to control IOPs, removal of the AVG 4 years after initial placement due to irritation of the corneal endothelium; retinal degeneration in 3/14 eyes that lead to vision loss at 2.3, 2.5, and 4.8 years, respectively, post‐lensectomy–ECP. An increasing trend in the IOP and number of glaucoma medications was noted in 2/5 eyes at the 36‐month recheck. Four out of 14 eyes available for follow‐up remained visual at the time of data collection. 

Vision preservation, IOP, and medication Of 14 eyes included in the study, 12 eyes were still available for follow‐up at 1 year, 10 eyes at 2 years, and five eyes at 3 years postoperatively. Vision was preserved in 93% of the eyes at 1 year, 84% at 2 years, 60% at 3 years, and 48% at 4 years, with three eyes retaining vision up to 5.2, 7.1, and 8.3 years, respectively (Figure ). IOP had a statistically significant decrease at 2 and 6 months ( p = .0157 and p = .0163) post‐lensectomy–ECP compared with the IOP before both of the procedures. No significant difference was noted at the rest of the studied time points (12, 24, and 36 months) (Figure ). Mean IOP at the time of Ahmed valve implantation (baseline or “0”) was 21.7 mmHg (range of 5–54 mmHg). Comparison between mean IOPs at baseline relative to post‐lensectomy–ECP showed a reduction of 9.64 mmHg at 2 months, 9.71, 2.45, 7.25, and 12.25 mmHg at 6, 12, 24, and 36 months, respectively (Figures and ). The mean number of glaucoma medications was compared before the AVG placement and after the lensectomy–ECP. There was a reduction in the mean number of glaucoma medications of 4.35 at 2 months, 4.85, 4.09, 3.5, and 4.5 at 6, 12, 24, and 36 months, respectively. The reduction in the number of glaucoma medications administered was statistically significant at 2, 6, and 12 months with a p ‐value of 0.0005, 0.0000, and 0.0065, respectively. At 24 months, the decrease was not significant ( p = .1219) and at 36 months, due to the low number of patients remaining, the p ‐value of 0.0000 is unreliable (Figures and ). 

Surgery and complications In this study, recorded Ahmed valve models used were: VFP 8 ( n = 5), VS2 ( n = 2), VFP 7, and VS3 ( n = 1). In six patients, the model type was not recorded. From the total number of Ahmed valves, 10 were placed laterally and five were placed medially. The median time to valve failure was 131 days (~ 4.3 months). The median time on the valves placed laterally was 131 days (range: 9 to 588) compared with 120 days (range: 84 to 204) on the valves placed medially. The median time to valve failure in different placement locations was not significant ( p = .85; Figure ). Most common complications post‐AVG implantation were fibrin in the anterior chamber obstructing the Ahmed tube, and scar tissue formation around the Ahmed footplate causing valve failure. In this study, 5/14 eyes (35.7%) developed fibrin clots and required TPA injections. The mean time to develop fibrin clots and requiring TPA injection was 3.2 days (range 1.2 to 5.8 days). One of the five eyes that developed fibrin clots required TPA injections twice. Scar tissue around the gonioimplant that required surgery formed in 11 out of the 14 eyes included in the study and a bleb resection was performed at the time of lensectomy–ECP. The three eyes that did not have the bleb resection performed had undergone AVG surgery shortly before the phaco‐ECP (9 and 5 days). One patient (one eye) had 3 bleb resection surgeries: two before, and one at the time of the lensectomy–ECP. The laser power utilized, ranged between 0.1 and 0.4 watts with 270 degrees of treatment. Seven out of 14 eyes had cataract diagnosed before the lensectomy–ECP. Incipient cataracts were present in 4/7 patients, an immature cataract in 1/7 patients, and mature cataracts in 2/7 patients. A lens subluxation was noted in one eye prior to lensectomy–ECP and lens instability was noted at the time of the surgery in 2 out of 14 eyes. In all three of these eyes, an intracapsular lens extraction (ICLE) and anterior vitrectomy was performed. One of the patients developed hypotony, retinal detachment, and lost vision 16 days after surgery. The other two cases maintained vision for 2.5 and 3 years. Phaco‐ECP was performed in the remaining 11/14 eyes. An artificial intraocular lens (IOL) was inserted into the lens capsule in 6/11 of the eyes. Complications occurring in the first 2 months following lensectomy–ECP were recorded. The most common postoperative complication after lensectomy–ECP was anterior chamber fibrin formation in six out of 14 eyes. 2/6 required one TPA injection, 4/6 required multiple injections, additionally one eye required aspiration of the fibrin from the anterior chamber (using an irrigation/aspiration tip) under general anesthesia. Mean time to fibrin formation was 4.5 days (range 2.6 to 6.8 days). Other complications affecting only one eye included: replacement of AVG implant (9 months after the initial placement due to malfunctioning of the valve), epithelial ulcer, and retinal detachment (occurring 16 days post‐op) with subsequent phthisis bulbi. IOP spikes occurred in 3/14 eyes and led to vision loss in one of three eyes 7 days post‐op. Long‐term complications included the need for additional surgery, a second ECP in 1/14 eyes 1 year after the first procedure to control IOPs, removal of the AVG 4 years after initial placement due to irritation of the corneal endothelium; retinal degeneration in 3/14 eyes that lead to vision loss at 2.3, 2.5, and 4.8 years, respectively, post‐lensectomy–ECP. An increasing trend in the IOP and number of glaucoma medications was noted in 2/5 eyes at the 36‐month recheck. Four out of 14 eyes available for follow‐up remained visual at the time of data collection. 

DISCUSSION This retrospective study evaluates cases of canine patients diagnosed with primary glaucoma that underwent an initial AVG placement followed at a later date with lensectomy–ECP, with some patients requiring additional surgical interventions based on responsiveness of glaucoma to the first two surgical treatments. This retrospective study shows that the combination of the two studied surgical procedures prolongs vision preservation, reduces IOP, and lowers medication burden. Vision preservation was 93%, 84%, 60%, and 48% at 1, 2, 3, and 4 years, respectively. The longest vision retention time in our population was 8.3 years after the two surgical procedures. ECP alone has shown a comparable vision preservation success rate; , , , , however, an accurate correlation is difficult to make since there is no peer‐reviewed published data in veterinary medicine describing the combination of the two procedures utilized in this study, in cases of primary glaucoma. One recent study that combined AVG placement followed by ECP (pars plana approach) in one case of secondary glaucoma, showed greater than 1 year vision retention, IOP control, and reduction in glaucoma medications. The findings in this study span a period of 14 years. It is well documented that POH and glaucoma are significant postoperative complications following cataract surgery. In a large study including 138 canine eyes, POH and glaucoma were documented in 42% and 13.8% of the cases, respectively, after cataract surgery. The advantage of approaching surgical treatment for glaucoma with a two‐staged surgical approach is that the complications of the phaco‐ECP that could lead to post‐op inflammation, IOP spikes (POH), and glaucoma are counteracted by the functional Ahmed valve, lowering the IOP until the full effect of the ECP is achieved a few weeks post‐op. A transient but severe increase in IOP could impair vision and may cause dramatic damage to the retina and optic nerve. The combination of phaco‐ECP showed immediate postoperative spike in IOP in 14.4% of the cases in a large study of 368 human eyes. ECPs ability to help with IOP control was demonstrated in a recent study comparing 15 canine eyes that had preventive phaco‐ECP and 36 eyes with phaco alone, showed a significantly higher elevation of IOP in the phaco group versus the phaco‐ECP group, within the first week after surgery. Compared with other cyclodestructive procedures, ECP allows direct visualization of the ciliary processes facilitating a controlled ablation and titration of the laser power to effect. Direct visualization also allows control of the intensity of laser burns to avoid micro‐explosions which lead to secondary inflammation. In human medicine, histological findings comparing tissue injury between transscleral procedures and ECP, showed sparing of the ciliary muscle and stromal tissue surrounding the ciliary processes with ECP in contrast with transscleral cyclodestructive procedures. , It is the authors' opinion that doing both of the surgical procedures in a non‐inflamed eye is part of the key to a successful outcome. Therefore, every effort is made to control inflammation with topical and systemic steroids or NSAIDs. It is preferable, in our opinion, to do the second procedure prior to the patient becoming dependent on prostaglandin analogs that induce miosis and need to be discontinued 24–48 h prior to an ECP procedure. When the IOP reached 18 mmHg or greater (author's preference), we believed the AVG valve was headed to failure. At this time, carbonic anhydrase inhibitors were started and phaco‐ECP and bleb resection surgery was recommended. IOP was significantly reduced at 2 and 6 months post‐lensectomy–ECP, and there was a mean drop from baseline IOP of ⪆ 9 mmHG at 2 and 6 months, ⪆ 2 mmHg at 1 year and ⪆ 7 and 12 mmHg at 2 and 3 years, respectively. The reduction in glaucoma medication before and after the lensectomy–ECP was significant in all periods except at 24 months. A recent review paper of several studies in different human ethnic categories comparing the outcome of phaco‐ECP treatment for glaucoma found a similar reduction in IOP and glaucoma medication from baseline compared with the follow‐up visits post‐treatment; however, in this large retrospective human study, patients were being treated for primary open‐angle glaucoma. Therefore, extrapolation to canine patients should be done with caution. In the current study, three of the eyes had an ICLE at the time of the ECP. Primary lens luxation was suspected in one of the patients based on the breed predisposition (Australian cattle dog). In the other two cases, it was an incidental intraoperative finding. Retinal detachment is the second most common complication after ICLE with an incidence of 38% in veterinary medicine. , We presume the vision loss in one patient 16 days post‐op occurred as a complication of the ICLE; however, hypotony following ECP cannot be completely ruled out. Females were predominant in this study ( n = 9) compared with males ( n = 4). This finding is in concordance with a previous study showing that the females had a 5.5 times increased risk of developing glaucoma post‐cataract surgery. The pathophysiology behind this sex‐based predilection for glaucoma could be explained by a smaller angle opening distance in females compared with males, noticed on ultrasound biomicroscopy of the ciliary cleft, making them more prone to PACG. The circumference of ciliary processes lasered, and the outcome on IOP and medication reduction was reviewed in the human literature. One study compared the efficacy of 240 degrees compared with 360 degrees circumference and showed an additional reduction in IOP of 3.9 mmHg and in glaucoma medication of 1.5 times in the 360 degrees group without increasing the postoperative complication rate; however, a second corneal incision is necessary adding to the surgical time. A study in rabbits randomized in three groups of ECP treatment: A, B, and C corresponding to 180, 270, and 360 degrees, respectively, showed significant lowering IOP effect in the C group at 1, 3, and 6 months post‐op compared with A group and similar lowering effects with the B group. In our study, the radius of burns was 270 degrees in all patients to reduce the adverse effect of hypotony. It is postulated that ECP‐treated ciliary processes might reperfuse several years post‐treatment, leading to an IOP increase and the need for repeated ECP or more aggressive medical management. An alternate explanation is that outflow is further compromised resulting in an increase in IOP. In our study, we noted a mild rise in IOP and glaucoma medications 3 years post‐lensectomy–ECP in 2/5 patients; however, due to the small patient size in this study, it is difficult to accurately determine whether those changes signify ciliary process reperfusion. The placement of the Ahmed valve medially versus laterally had no significant effect on time to valve failure (median 4.3 months). This is in contrast with a recent study where the valve was functional ~11 months after implantation in 81/132 eyes, and medial implantation showed a significant increase in vision preservation time (~ 62 months vs ~ 45 months). These differences could be explained by the small patient size with the valve placed medially in our study ( n = 5), compared with 93 in the other study. Another explanation is the difference in the surgical technique used and breed selection, Shiba Inu and American Cocker Spaniel being the most prevalent breeds compared with a mixed breed population in our study. In the study by Saito et al paper, a large conjunctival tenon flap was created from 9 to 3 o'clock position, with a purpose of creating a large drainage space for aqueous humor. In our study, the conjunctival tenon flap was from 9 to 12 or 12 to 3 o'clock for the lateral or medial positioning, respectively. Limitations of this study are those inherent to a retrospective study, including inconsistent, and limited medical record are data available for some cases. Some of the patients’ follow‐ups were 2–3 weeks earlier or later of the planned regular rechecks. Sample size was limited by: infrequent cases of primary glaucoma, owner financial constraints, and willingness of owners to pursue two surgical therapies. Future aims are to perform a prospective study to eliminate unknown factors that could have influenced this study results. In this study, combined AVG and lensectomy–ECP proved to be a successful surgical method in preserving vision, controlling IOP, and decreasing the number of glaucoma medications in canine patients with primary glaucoma. A future study looking at the outcomes of the two procedures in canine eyes both predisposed to glaucoma and those with secondary glaucoma would help give a more complete picture of the protocol used in managing a broader patient population with glaucoma. 

Bactelius Turicea: Conceptualization; data curation; project administration; writing – original draft; writing – review and editing. Christian L. Munevar: Conceptualization; data curation; methodology; writing – review and editing. Sydney G. Edwards: Resources; supervision; writing – review and editing. Lana L. Linton: Investigation; methodology; resources; supervision; writing – review and editing. 

This statement is to certify that all authors have no conflict of interest to declare related to this retrospective study. 

