Prospective evaluation of iris-trabecular contact using anterior segment optical coherence tomography and early intraocular pressure changes in eyes following penetrating keratoplasty
Elevated intraocular pressure (IOP) and secondary glaucoma are common complications following penetrating keratoplasty (PK), potentially leading to significant endothelial cell loss and corneal graft failure . Thus, IOP monitoring and control are critical in post-PK management. The reported incidence of post-PK glaucoma ranged from 9 to 34% . Though most secondary glaucoma occurred at 3 to 6 months after PK , the incidence of early postoperative glaucoma varies from 5.5 to 31% in previous researches [ , , ]. Considering the limited effect of topical corticosteroid use in the early post-PK period , the investigation of factors contributing to raised IOP in the early period helps to clarify etiology. The generally accepted risk factors of post-PK glaucoma encompass preoperative glaucoma, peripheral anterior synechia (PAS), repeat keratoplasty and preoperative diagnosis of inflammatory ocular diseases. However, the effects of age of patients, lens status, graft-host size disparity and additional surgeries combined with PK were controversial [ , , ]. PAS is a crucial factor relating to high IOP or glaucoma either in early or late period after PK . So far, only a few retrospective studies quantified the PAS after PK, manifesting that PAS was very common and highly related to original corneal diseases . However, none of them investigated the preoperative PAS or its changes during early post-PK period, which we think is vital for clarifying the formation and timing of PAS, since PK itself is a procedure to reconstruct anterior chamber. Thus, we would like to prospectively evaluate the PAS changes, to elucidate the effect of PAS on IOP during early post-PK period. Though gonioscopy was the gold standard for evaluating PAS, peripheral corneal opacity before or after PK often hinders the clarity of the anterior chamber angles, and the contact during the examinations brings discomfort for patients as well as potential risk for corneal grafts. Anterior segment optical coherence tomography (AS-OCT) has become a valuable tool to evaluate anterior chamber in the setting of corneal opacity, without contact and immersion . In recent years, the swept-source OCT (SS-OCT) can even afford a 360-degree scans, reliable anterior segment evaluations and quantification of iris-trabecular contact (ITC), which almost represents PAS . Therefore, this study aims to prospectively track the anterior chamber morphology and ITC variations before and after PK using SS-OCT, and to seek their relation with early IOP elevation. 

Participants enrolled Patients who were prepared to accept PK or triple surgery at the Eye & ENT Hospital of Fudan University in Shanghai, China, were recruited. The inclusion criteria for participants included: (1) Asian ethnicity and aged over 18 years; (2) patients with corneal diseases that needed PK or triple surgery (PK combined with other surgeries) to improve visual acuity. The exclusion criteria were as follows: (1) patients diagnosed with acute keratitis, corneal ulcers or perforations, because of their difficulty to cooperate with AS-OCT examinations and IOP measurements; (2) patients with preoperative glaucoma diagnosed by elevated IOP together with glaucomatous optic nerve damage; (3) patients with poor compliance during follow-ups. This study was approved by the Ethics Committee of the Eye & ENT Hospital of Fudan University, and it conformed to the tenets of the Declaration of Helsinki. Before surgery, written informed consent was obtained from all subjects. PK procedure and triple surgery All the PK procedures were performed by a single experienced surgeon (Dr. Xu) under topical anesthesia or general anesthesia. Topical pilocarpine eye drops 3 times before surgery were prescribed for subjects who accepted PK only. The recipient corneas were trephined and excised, and the donor cornea buttons prepared by a Barron donor punch were sutured onto the recipient beds using interrupted 10 − 0 nylon sutures. In addition, a gonioplasty was performed by a blunt cyclodialysis spatula for patients with preoperative ITC, with the help of viscoelastic material to open ITC. The operator confirmed the PAS had been eliminated as much as possible, and the gonioplasty was attempted if needed. The viscoelastic material was aspirated at the end of operation. Triple surgery includes extracapsular cataract extraction (ECCE), intraocular lens (IOL) implantation and IOL replacement. In brief, after the excision of patient’s cornea, continuous curvilinear capsulorhexis was complete using forceps. The lens nucleus was removed and the cortex was aspirated by the irrigation-aspiration tip. When the donor cornea was almost completely sutured, the injectable IOL was inserted into the capsular bag. Finally, the final sutures were finished and then the remaining viscoelastic substance were aspirated. The IOL replacement referred to the removal of anterior chamber phakic IOL and following implantation of IOL in the ciliary groove. Patient postsurgical management Every subject was examined with slit lamp examination, IOP, and AS-OCT scans the day before surgery, as well as one day, one week, and one month after surgery. During the follow-up period, 0.3% tobramycin and 0.1% dexamethasone eye drops were used 4 times daily. Besides, patients with previous viral keratitis were prescribed the antiviral drops (0.15% ganciclovir) 4 times a day. If a high IOP was observed, suitable anti-glaucoma eye drops were added. IOP measurements and AS-OCT examinations The Goldman Applanation Tonometry (GAT), as the golden standard for IOP measurements, was measured at least twice and the average values were recorded. However, sometimes, only the non-contact tonometer or even estimation by doctors were obtained owing to the failures of GAT measurements. High IOP was defined as IOP value > 21 mmHg or an postoperative increase from preoperative value ≥ 10mmHg. All the scans were accomplished through SS-OCT (CASIA SS-1000 OCT; Tomey, Nagoya, Aichi, Japan) by the same two operators, with the upper and lower eyelid gently pulled up and down, and the lighting conditions for all the scans kept the same. For anterior parameters, we chose the cross section of 0 and 180 degrees for analysis: after marking the two scleral spurs (SS) on each angle, the software could automatically calculate the anterior chamber depth (ACD), lens vault (LV), anterior chamber width (ACW), and central corneal thickness (CCT), as well as angle parameters on each side (namely, the angle opening distance at 500 μm from the SS [AOD500], the angle recess area at 500 μm from the SS [ARA500], the trabecular iris space area at 500 μm from the SS [TISA500], and the trabecular iris angle at 500 μm from the SS [TIA500]). The averages of the angle parameters were calculated. At the same time, pupil diameter was manually measured. For ITC range, the same analyzer marked each SS and peripheral end point of the iris (EP) on all the 128 cross-sections scanned in the “Angle Analysis” mode of each eye at every follow-up. When the EP was located more proximally than the SS, it was assumed that there was ITC occurrence. Once all the visible SSs and EPs were identified, the data of ITC range could be automatically calculated. Statistical analysis Quantitative variables were described as mean ± standard deviation in Tables and mean ± 95% CI in Figures, while categorical values were expressed in absolute numbers and as percentages of the total. Chi-squared test, Yates’ correction and Fisher’s precise test were performed to compare rates and proportions. Normality was verified by Shapiro-Wilk test combined with histogram, and homogeneity was checked by Levene’s test. We used univariate analyses of variance method to compare the differences among different time points, and Bonferroni tests for multiple comparisons for the data normally distributed. Otherwise, non-parameter test (Kruskal-Wallis test) was conducted. In addition, Pearson correlation coefficient and logistic regression model were applied for correlation analysis. All the calculations above were accomplished by SPSS 20.0 (IBM Corp. Armonk, NY, USA), and a p value < 0.05 was considered statistically significant. 

Patients who were prepared to accept PK or triple surgery at the Eye & ENT Hospital of Fudan University in Shanghai, China, were recruited. The inclusion criteria for participants included: (1) Asian ethnicity and aged over 18 years; (2) patients with corneal diseases that needed PK or triple surgery (PK combined with other surgeries) to improve visual acuity. The exclusion criteria were as follows: (1) patients diagnosed with acute keratitis, corneal ulcers or perforations, because of their difficulty to cooperate with AS-OCT examinations and IOP measurements; (2) patients with preoperative glaucoma diagnosed by elevated IOP together with glaucomatous optic nerve damage; (3) patients with poor compliance during follow-ups. This study was approved by the Ethics Committee of the Eye & ENT Hospital of Fudan University, and it conformed to the tenets of the Declaration of Helsinki. Before surgery, written informed consent was obtained from all subjects. 

All the PK procedures were performed by a single experienced surgeon (Dr. Xu) under topical anesthesia or general anesthesia. Topical pilocarpine eye drops 3 times before surgery were prescribed for subjects who accepted PK only. The recipient corneas were trephined and excised, and the donor cornea buttons prepared by a Barron donor punch were sutured onto the recipient beds using interrupted 10 − 0 nylon sutures. In addition, a gonioplasty was performed by a blunt cyclodialysis spatula for patients with preoperative ITC, with the help of viscoelastic material to open ITC. The operator confirmed the PAS had been eliminated as much as possible, and the gonioplasty was attempted if needed. The viscoelastic material was aspirated at the end of operation. Triple surgery includes extracapsular cataract extraction (ECCE), intraocular lens (IOL) implantation and IOL replacement. In brief, after the excision of patient’s cornea, continuous curvilinear capsulorhexis was complete using forceps. The lens nucleus was removed and the cortex was aspirated by the irrigation-aspiration tip. When the donor cornea was almost completely sutured, the injectable IOL was inserted into the capsular bag. Finally, the final sutures were finished and then the remaining viscoelastic substance were aspirated. The IOL replacement referred to the removal of anterior chamber phakic IOL and following implantation of IOL in the ciliary groove. 

Every subject was examined with slit lamp examination, IOP, and AS-OCT scans the day before surgery, as well as one day, one week, and one month after surgery. During the follow-up period, 0.3% tobramycin and 0.1% dexamethasone eye drops were used 4 times daily. Besides, patients with previous viral keratitis were prescribed the antiviral drops (0.15% ganciclovir) 4 times a day. If a high IOP was observed, suitable anti-glaucoma eye drops were added. 

The Goldman Applanation Tonometry (GAT), as the golden standard for IOP measurements, was measured at least twice and the average values were recorded. However, sometimes, only the non-contact tonometer or even estimation by doctors were obtained owing to the failures of GAT measurements. High IOP was defined as IOP value > 21 mmHg or an postoperative increase from preoperative value ≥ 10mmHg. All the scans were accomplished through SS-OCT (CASIA SS-1000 OCT; Tomey, Nagoya, Aichi, Japan) by the same two operators, with the upper and lower eyelid gently pulled up and down, and the lighting conditions for all the scans kept the same. For anterior parameters, we chose the cross section of 0 and 180 degrees for analysis: after marking the two scleral spurs (SS) on each angle, the software could automatically calculate the anterior chamber depth (ACD), lens vault (LV), anterior chamber width (ACW), and central corneal thickness (CCT), as well as angle parameters on each side (namely, the angle opening distance at 500 μm from the SS [AOD500], the angle recess area at 500 μm from the SS [ARA500], the trabecular iris space area at 500 μm from the SS [TISA500], and the trabecular iris angle at 500 μm from the SS [TIA500]). The averages of the angle parameters were calculated. At the same time, pupil diameter was manually measured. For ITC range, the same analyzer marked each SS and peripheral end point of the iris (EP) on all the 128 cross-sections scanned in the “Angle Analysis” mode of each eye at every follow-up. When the EP was located more proximally than the SS, it was assumed that there was ITC occurrence. Once all the visible SSs and EPs were identified, the data of ITC range could be automatically calculated. 

Quantitative variables were described as mean ± standard deviation in Tables and mean ± 95% CI in Figures, while categorical values were expressed in absolute numbers and as percentages of the total. Chi-squared test, Yates’ correction and Fisher’s precise test were performed to compare rates and proportions. Normality was verified by Shapiro-Wilk test combined with histogram, and homogeneity was checked by Levene’s test. We used univariate analyses of variance method to compare the differences among different time points, and Bonferroni tests for multiple comparisons for the data normally distributed. Otherwise, non-parameter test (Kruskal-Wallis test) was conducted. In addition, Pearson correlation coefficient and logistic regression model were applied for correlation analysis. All the calculations above were accomplished by SPSS 20.0 (IBM Corp. Armonk, NY, USA), and a p value < 0.05 was considered statistically significant. 

Patient demographics 46 eyes of 46 patients were finally enrolled in this study. Most of the participants were male, and their age ranged from 18 to 78 years old. Preoperative diagnoses included corneal dystrophy, leukoma, graft failure, keratoconus and endothelial dysfunction, respectively. Finally, 9 participants underwent triple surgeries, including ECCE, IOL implantation and IOL replacement coupled with PK (Table ). Anterior segment morphology changes following surgery PK caused a significant reduction in ACD, from 2.803 ± 0.874 mm preoperatively to 1.974 ± 0.587 mm on the first postoperative day ( p < 0.001). ACD then continually rose to 2.450 ± 0.567 mm at the final visit, remaining significant difference from the baseline ( p = 0.005). Since many subjects suffered from endothelial dysfunction, leukoma and graft failure, the CCT at baseline reached 763.5 ± 326.8 μm. However, the edema of cornea faded away with time, and ultimately PK afforded a normal CCT at one-month follow-up ( p < 0.001). Additionally, the changes of PD were attributed to the perioperative use of miotic drug. Although there were no statistical differences in LV and anterior chamber angles in total, it was worth noting that the variation trends of LV were opposite between PK alone group and triple surgery group (Table ; Fig. A, B, C). Hence, the anterior chamber suffered a big transition during early postoperative period. ITC changes following surgery Before surgery, 16 patients had ITC, with the average range of 110.2 ± 106.9 degrees. It was unstartling to find that patients diagnosed with leukoma and with ocular surgery history were tended to have preoperative ITC. Nevertheless, preoperative ITC was also detected in 5 patients diagnosed with corneal dystrophy, despite that two of them only had 5 degrees of ITC. According to the preoperative presence of ITC, we divided these subjects to With ITC group ( n = 16) and Without ITC group ( n = 30), to compare the angle parameters differences and ITC changes. Most patients with preoperative ITC still presented postoperative ITC (13/16), the same as those who accepted PK alone (10/11) (Supplementary Table ). On the first postoperative day, gonioplasty in PK dramatically lessened the ITC range to only 40.0 ± 45.1 degrees in With ITC group. However, unfortunately, most ITC reappeared within the first week, returning to the similar but smaller levels one month after surgery (Table ; Fig. D). Interestingly, a small range of ITC in 3 subjects (5, 30, and 15 degrees respectively) did disappear during the one-month follow-up, and two of them underwent triple surgery. As for Without ITC group, new ITC was observed in 3 patients (10%) following PK alone: Patient 1 diagnosed with keratoconus had a severe suture reaction in the first week after surgery, and then the 10-degree ITC was discovered at one-month follow-up, whose locations were identical to those of the loose sutures; Patient 2 diagnosed with corneal dystrophy presented an extremely shallow anterior chamber of only 0.609 mm on the first day without leakage, when 220 degrees of ITC were detected. With the recovery of ACD, the ITC range gradually decreased to 55 degrees at the last visit; Patient 3 diagnosed with endothelial dysfunction experienced a high IOP on the first postoperative day, and a 10-degree new ITC was observed since one week. As shown in Table ; Fig. E, the two groups had opposite trends on anterior angles: In With ITC group, the anterior chamber angles substantially widened on the first day and gradually narrowed till last visit, in coordination with the ITC change, while the parameters in Without ITC group had no statistical variation. Collectively, PK induced a widening of anterior chamber angle and a dramatic drop of ITC range on the first postoperative day in patients with preoperative ITC, but the ITC inclined to recur since one week after surgery. IOP outcomes The mean preoperative IOP value was 14.3 ± 4.0 mmHg, and only one patient with high myopia had a high IOP of 26mmHg without any sign of glaucoma (CCT = 637 μm). After surgery, 15 patients were recorded to develop high IOP (32.6%) during one-month follow-up, including 7 subjects in triple surgery group (Table ). There was no statistical difference in IOP levels among different time points. All the high IOPs were carefully controlled by anti-glaucoma drugs. Correlation analysis The correlation analyses were performed between the presence of postoperative ITC and high IOP with multiple factors, covering age, gender, graft size, disparity of donor size, accept of triple surgery, preoperative ITC, ITC range, visiting time, and various anterior chamber parameters. Multivariate logistic analysis exhibited that the postoperative ITC occurrence had notably positive relevance to preoperative ITC ( p = 0.002) and negative relevance to AOD500 after surgery ( p < 0.001). High IOP was more likely to happen in triple surgery group ( p = 0.001) and on the first postoperative day ( p = 0.021). No correlation was identified between ITC and high IOP during this period. Moreover, the greater changes of anterior chamber angle (represented by Changed AOD500) was a risk factor for developing elevated IOP ( p = 0.046) (Table ). Complications There was no complication during surgeries. Apart from the high IOP occurrence, there was another complication as mentioned before: one patient diagnosed with keratoconus had a severe suture reaction from 1 week to 3 weeks after PK, and the inflammation reaction gradually subsided with the removal of loose sutures. 

46 eyes of 46 patients were finally enrolled in this study. Most of the participants were male, and their age ranged from 18 to 78 years old. Preoperative diagnoses included corneal dystrophy, leukoma, graft failure, keratoconus and endothelial dysfunction, respectively. Finally, 9 participants underwent triple surgeries, including ECCE, IOL implantation and IOL replacement coupled with PK (Table ). 

PK caused a significant reduction in ACD, from 2.803 ± 0.874 mm preoperatively to 1.974 ± 0.587 mm on the first postoperative day ( p < 0.001). ACD then continually rose to 2.450 ± 0.567 mm at the final visit, remaining significant difference from the baseline ( p = 0.005). Since many subjects suffered from endothelial dysfunction, leukoma and graft failure, the CCT at baseline reached 763.5 ± 326.8 μm. However, the edema of cornea faded away with time, and ultimately PK afforded a normal CCT at one-month follow-up ( p < 0.001). Additionally, the changes of PD were attributed to the perioperative use of miotic drug. Although there were no statistical differences in LV and anterior chamber angles in total, it was worth noting that the variation trends of LV were opposite between PK alone group and triple surgery group (Table ; Fig. A, B, C). Hence, the anterior chamber suffered a big transition during early postoperative period. 

Before surgery, 16 patients had ITC, with the average range of 110.2 ± 106.9 degrees. It was unstartling to find that patients diagnosed with leukoma and with ocular surgery history were tended to have preoperative ITC. Nevertheless, preoperative ITC was also detected in 5 patients diagnosed with corneal dystrophy, despite that two of them only had 5 degrees of ITC. According to the preoperative presence of ITC, we divided these subjects to With ITC group ( n = 16) and Without ITC group ( n = 30), to compare the angle parameters differences and ITC changes. Most patients with preoperative ITC still presented postoperative ITC (13/16), the same as those who accepted PK alone (10/11) (Supplementary Table ). On the first postoperative day, gonioplasty in PK dramatically lessened the ITC range to only 40.0 ± 45.1 degrees in With ITC group. However, unfortunately, most ITC reappeared within the first week, returning to the similar but smaller levels one month after surgery (Table ; Fig. D). Interestingly, a small range of ITC in 3 subjects (5, 30, and 15 degrees respectively) did disappear during the one-month follow-up, and two of them underwent triple surgery. As for Without ITC group, new ITC was observed in 3 patients (10%) following PK alone: Patient 1 diagnosed with keratoconus had a severe suture reaction in the first week after surgery, and then the 10-degree ITC was discovered at one-month follow-up, whose locations were identical to those of the loose sutures; Patient 2 diagnosed with corneal dystrophy presented an extremely shallow anterior chamber of only 0.609 mm on the first day without leakage, when 220 degrees of ITC were detected. With the recovery of ACD, the ITC range gradually decreased to 55 degrees at the last visit; Patient 3 diagnosed with endothelial dysfunction experienced a high IOP on the first postoperative day, and a 10-degree new ITC was observed since one week. As shown in Table ; Fig. E, the two groups had opposite trends on anterior angles: In With ITC group, the anterior chamber angles substantially widened on the first day and gradually narrowed till last visit, in coordination with the ITC change, while the parameters in Without ITC group had no statistical variation. Collectively, PK induced a widening of anterior chamber angle and a dramatic drop of ITC range on the first postoperative day in patients with preoperative ITC, but the ITC inclined to recur since one week after surgery. 

The mean preoperative IOP value was 14.3 ± 4.0 mmHg, and only one patient with high myopia had a high IOP of 26mmHg without any sign of glaucoma (CCT = 637 μm). After surgery, 15 patients were recorded to develop high IOP (32.6%) during one-month follow-up, including 7 subjects in triple surgery group (Table ). There was no statistical difference in IOP levels among different time points. All the high IOPs were carefully controlled by anti-glaucoma drugs. 

The correlation analyses were performed between the presence of postoperative ITC and high IOP with multiple factors, covering age, gender, graft size, disparity of donor size, accept of triple surgery, preoperative ITC, ITC range, visiting time, and various anterior chamber parameters. Multivariate logistic analysis exhibited that the postoperative ITC occurrence had notably positive relevance to preoperative ITC ( p = 0.002) and negative relevance to AOD500 after surgery ( p < 0.001). High IOP was more likely to happen in triple surgery group ( p = 0.001) and on the first postoperative day ( p = 0.021). No correlation was identified between ITC and high IOP during this period. Moreover, the greater changes of anterior chamber angle (represented by Changed AOD500) was a risk factor for developing elevated IOP ( p = 0.046) (Table ). 

There was no complication during surgeries. Apart from the high IOP occurrence, there was another complication as mentioned before: one patient diagnosed with keratoconus had a severe suture reaction from 1 week to 3 weeks after PK, and the inflammation reaction gradually subsided with the removal of loose sutures. 

PK still dominates in keratoplasty, especially in developing countries including China [ – ]. The procedures of PK involve the full-thickness replacement of the pathological cornea, inevitably bringing a dramatic transformation and remodeling to anterior segment. However, there was a vacancy in prospective research on comprehensive anterior morphology changes during the early postoperative period [ , , ], and the development of AS-OCT made it extremely convenient and concise to monitor these changes without contact and harm to corneal grafts, which facilitated this study. In the current study, the parameters measured by SS-OCT indicated that ACD had an evident reduction by almost 1 mm ( p < 0.001) on the first postoperative day. CCT value sustained high within the first week caused by corneal edema, and returned to the normal value at one-month follow-up. Although no substantial changes of LV and anterior angles in all subjects were detected, ECCE and IOL replacement predisposed to a relatively wider space of anterior segment. Finally, PK reconstructed a normal anterior segment within one month after surgery. More importantly, for the first time, this study prospectively followed the ITC change during the early post-PK period. ITC involves PAS and appositional contact of iris with the trabecular meshwork , but concerning the range and height of ITC in this study, ITC was nearly equal to PAS. PAS had a high incidence after PK, ranging from 8.3 to 46.7%, and it was closely related to elevated IOP as well as graft failure [ , , , ]. The rate of preoperative ITC in this study reached 34.8%, without including cases of acute infectious keratitis or corneal perforation. It always occurred in patients diagnosed with leukoma and with ocular surgery history, partially aligning with the result of Fukuda’s research on postoperative ITC . Besides, patients with ocular surgery history were more likely to display a large range of ITC (156.9 ± 130.5 degrees). Surprisingly, although two patients only had 5-degree ITC, half of patients diagnosed with corneal dystrophy had preoperative ITC, which was similar to the postoperative ITC prevalence in this type of patients previously . Whether it meant the ITC after PK existed previously needed to be verified in a larger sample of patients with corneal dystrophy. Taken together, these facts demonstrated that the rate of preoperative ITC was high and closely related to the original diseases and history of ocular surgery. Although preoperative ITC significantly decreased on the first postoperative day, it unfortunately recurred in most patients within one month. The strongest risk factor for postoperative ITC was the presence of preoperative ITC ( p = 0.002). Gonioplasty performed after PK was similar to the procedure of goniosynechialysis (GSL) performed for angle closure glaucoma patients, except for the confirmation by the gonioscopic visualization. In previous studies, there were some controversies on the benefits of GSL alone, whose effect may be restricted by the duration of PAS presence or be dubious when combined with other surgeries [ – ]. So, the disappointing results of ITC in this study might be attribute to the long-standing PAS caused by previous corneal infection or trauma. For patients without preoperative ITC, the incidence of new ITC occurrence was relatively low (10%), and it all happened in patients who accepted PK alone. We believed the emergence of the large range of ITC of one patient with keratoconus was related to the suture reaction, given the consistency of positions. Meanwhile, the new ITC in the other two subjects might be respectively associated with an extremely shallow anterior chamber and high IOP. Hence, new ITC could occur even in the early postoperative period, and more frequent IOP monitoring was needed on these patients. Unfortunately, restricted by the low incidence of new ITC and small sample size, the risk factors of new ITC could not be analyzed. The prevalence of high IOP in the early postoperative period was 32.6%, lower than the previous result with 83.8% rate of high IOP in PK group, perhaps because they included IOP measurement at postoperative hours 6 . In line with the tendency of high IOP occurrence at postoperative hours 6 and 24, most high IOP in this study occurred on the first postoperative day. At this time, when the ITC range was at its lowest, the factors contributing to high IOP mainly included inflammation, retained viscoelastic, and distortion of trabecular meshwork and Schlemm’s canal . Therefore, we found there was no relation between high IOP and ITC during the early postoperative period for patients without preoperative glaucoma. Although this study included only 9 patients who accepted triple surgery, certain facts were revealed: elevated IOP was prone to present in these patients, particularly on the first postoperative day, in line with Maier’s study . The greater postoperative change of anterior angle was associated with high IOP, which we considered as a reflection of the potential relation between high IOP and triple surgery. In the previous study, 76.9% of patients who underwent PK combined with ECCE had ITC, and thus combined surgery was regarded as a risk factor of ITC . However, in the current study, the prevalence of ITC in triple surgery group was 55.6% (5/9) before surgery, and even preoperative ITC of two patients vanished after surgery. Moreover, none of these patients exhibited new postoperative ITC. Hence, the triple surgery was not a risk factor of postoperative ITC in this study. The discrepancy might be attributed to the lack of preoperative data in the previous study, the different constitute of original diseases, the difference in surgeons’ technique, the relatively small sample size or the short following time of this study. Interestingly, a small range ITC (15 and 30 degrees, respectively) of two patients accepted triple surgery did disappear after surgery, which was coincident with the fact that phacoemulsification combined with GSL significantly reduced PAS in patients with angle closure glaucoma [ , – ]. They believed the mechanical forces in phacoemulsification such as the viscoelastic injection, removal of the bulky lens and positive flushing pressure by infusion could help to strip some PAS . In the current study, the reduced LV after triple surgery meant more space in the anterior chamber, partially explaining the fact. Other reasons of disappearance of ITC included temporary contact between iris and trabecular meshwork, the short duration of synechia or the short follow-up time. Accordingly, patients in triple surgery group had a higher incidence on high IOP in the early postoperative time, but the combined surgery might provide a larger space to help reduce ITC. The merit of this study was the elaboration of comprehensive anterior segment parameters changes as well as ITC changes in eyes following PK in a prospective manner. The limitations included the relatively small sample size, especially the small number in triple surgery group. Studies with a larger sample and long-term follow-up were required to determine the long-term outcomes of these ITCs and to identify the possible risk factors for new ITC. In addition, the exclusion of the acute corneal infection or perforation might introduce some bias to this study, such as underestimating the rate of ITC or high IOP. Lastly, the static scan of SS-OCT could only decide the ITC presence, but not the identification of appositional contact or the real PAS, which might overestimate the range of ITC. In conclusion, PK reconstructed a normal anterior segment within one month after surgery, after going through the relatively shallow anterior chamber and cornea edema. ITC have existed in more than one third of the subjects before surgery, and most preoperative ITC recurred within one month. The most related risk factor for postoperative ITC was the presence of preoperative ITC. Correspondingly, the incidence of new ITC was 10%, and all of them happened in patients who accepted PK alone. High IOP after surgery was common and tented to occur in patients who underwent triple surgery and on the first postoperative day. This study underscored that the evaluations of anterior segment and ITC preoperatively through SS-OCT were conducive in predicting the occurrence of postoperative ITC, guiding a targeted gonioplasty during PK, and controlling IOP precisely on patients at high risk. 

Below is the link to the electronic supplementary material. Supplementary Material 1 

