conjunctival dissection is an important step in glaucoma filtering surgery [ 1 , 2 ] . decreasing the intraoperative conjunctival manipulation may be expected to lead to less subconjunctival fibrosis and better aqueous drainage in the long term [ 35 ] .
an accepted method of maintaining aqueous drainage has been conventional trabeculectomy where , after raising a conjunctival flap , an artificial channel is made between the anterior chamber and the subconjunctival space by means of a scleral flap .
reduction of intraocular pressure ( iop ) has been known to be sustained by this channel over a period [ 69 ] . in this paper , we have presented a modified technique of trabeculectomy for primary open angle glaucoma ( poag ) where a scleral tunnel has been used with decreased conjunctival dissection .
institutional review board ( irb ) approval was obtained and the procedure conformed to declaration of helsinki .
preoperative visual acuity was measured with snellen acuity charts , iop by goldmann applanation tonometer , and anterior chamber depth by optical coherence tomography .
patients with primary open angle glaucoma of age 40 to 70 years , iop more than 21  mmhg , and visual field defects on automated perimetry and who were willing for follow - up were included after informed consent .
patients with previous uveitis , conjunctival scarring , angle closure glaucoma , previous trabeculectomy , and poor visual acuity in fellow eye and one eyed patients were excluded .
the follow - up visits were on day 1 , day 7 , 1 month , 3 months , 6 months , and so on .
a complete success was defined as an intraocular pressure of < 18  mmhg without medications and qualified success was defined as reduction in iop to < 18  mmhg with two or less medications .
intraoperative or postsurgical event which required conversion to conventional trabeculectomy or resurgery to decrease iop was also considered as failure . any ocular adverse effect which required surgical or medical intervention for management
preoperatively , 0.2  ml of 0.01% mitomycin c ( mmc ) was injected subconjunctivally in the area of intended bleb creation .
the speculum was loosened slightly to allow more mobile conjunctiva and to prevent it from being pulled into the fornices .
superior conjunctiva was slid downwards over the cornea and a 2.8  mm bevel - up metal keratome was introduced 1.5  mm behind the limbus ( figures 1(a ) and 1(b ) ) .
the tip of the keratome was passed through the conjunctiva into superficial lamellar sclera ( figure 1(c ) ) .
a superficial lamellar scleral tunnel was then dissected with side to side movements of the keratome till the limbus , keeping the depth of dissection such that the blade could be visualized through the overlying sclera and conjunctiva . at the limbus ,
the blade was angulated more superficially to correspond to the steeper corneal curvature and depth was confirmed by a dimpling of the cornea .
the blade was then introduced 0.5 to 1  mm into clear cornea before entering the anterior chamber ( ac ) in a horizontal plane ( figure 1(d ) ) .
the blade was then withdrawn and viscoelastic instilled into the ac through either a paracentesis or the stab incision glaucoma surgery ( sigs ) tunnel entry ( figure 2(a ) ) .
the 1  mm kelly descemet 's punch ( appasamy associates , india ) was then slid along the tunnel into the ac and with the punch facing downwards , the internal lip of the corneal section was punched ( figures 2(b ) and 2(c ) ) . after pushing the iris away with viscoelastic , the ostium thus initiated was extended posteriorly till the limbus with additional punches under visualization through the overlying clear cornea ( figure 2(d ) ) . a peripheral iridectomy ( pi )
was done with curved vannas scissors by retracting basal iris through the tunnel with nontoothed forceps while the assistant retracted the conjunctiva for visualization ( figure 3(a ) ) .
the iris was gently pushed back into the ac and a simcoe cannula inserted through the tunnel was used to wash out viscoelastic ( figure 3(b ) ) .
balanced salt solution ( bss ) was irrigated through the side port and leakage from the sigs tunnel was assessed .
the 2.8  mm conjunctival cut was sutured with a running 10 - 0 nylon suture ( figure 3(c ) ) .
bss was injected through the side port to balloon the bleb ( figure 3(d ) ) .
subconjunctival garamycin 0.5  ml and dexamethasone 0.5  ml were given in the inferior forniceal conjunctiva ( video file , at supplementary material available online at http://dx.doi.org/10.1155/2016/2837562 ) .
data was entered in a microsoft excel sheet ( microsoft corp . , redmond , washington , usa ) and
continuous variables were expressed as means ( standard deviations ) and categorical variables were expressed as individual counts . after testing for normality distribution of data , the statistical tests were allotted .
seventeen eyes of 17 patients ( 7 males , 10 females ) underwent sigs with preoperative subconjunctival mmc .
the mean preoperative iop was 27.41  5.54  mmhg ( range 2139  mm hg ) and the mean postoperative iop was 16.47  4.81  mmhg ( range 928  mmhg ) .
there was significant reduction in iop from preoperative values ( wilcoxon signed rank test , p < 0.000 ) .
preoperatively 7 out of 17 ( 41.1% ) had advanced glaucomatous field loss and 10 out of 17 ( 58.8% ) had moderate glaucomatous field loss .
there was no significant change in pattern standard deviation ( psd ) in visual field test ( p = 0.068 ) from preoperative to postoperative period .
the mean preoperative and postoperative psd were 6.9  2.7 decibels and 6.97  2.7 decibels .
the number of topical medications was reduced from a mean of 1.35 preoperatively to 0.59 postoperatively .
there was significant reduction in number of medications used from pre- to postoperative period ( p = 0.025 , wilcoxon signed rank test ) . a complete success defined as an intraocular pressure of <
18  mmhg without medications was seen in 64.70% and 82.35% of patients maintaining an iop of < 18  mmhg with 2 medications .
preoperative corrected distance visual acuity ( cdva ) measured by snellen 's distant visual acuity charts was 0.80  0.28 and postoperative cdva was 0.76  0.25 ( wilcoxon signed rank test , p = 0.230 ) .
intraoperative complications encountered were premature entry ( n = 1 ; small basal punch taken ) , trapdoor hinging of internal corneal lip ( n = 1 ; hinged lip excised ) , conjunctival buttonhole ( n = 1 ; small , no intervention ) , descemet 's detachment ( n = 1 ; small , managed with air bubble ) , and nonbasal pi ( n = 1 ; no intervention ) .
postoperative complications encountered were microhyphema ( n = 2 ; medical management ) , more than grade 2 ac reaction ( n = 1 ; medical management ) , hypotony ( n = 1 , managed successfully with transconjunctival tunnel compression suture ) , and uncontrolled iop ( n = 6 ; 3 were managed medically and 3 underwent repeat surgery ) .
there were no sight threatening complications such as bleb inflammation / infection or cystoid macular edema seen in any of the eyes .
traditional trabeculectomy has been a widely adopted procedure of choice [ 1 , 2 ] .
however , a common cause of glaucoma surgery failure is subconjunctival fibrosis of the bleb .
wound - healing response after filtering surgery can present in one of two ways , either as subconjunctival fibrosis or as sub - tenon 's encapsulation leading to lack of filtration and subsequent increase in iop . in an attempt to reduce failure due to fibrosis
, antimetabolites have been used ; however , fibrosis and bleb failure are still reported . reducing excessive intraoperative manipulation of conjunctiva and
nontraumatic subconjunctival dissection has also been tried to prevent inadvertent conjunctival handling [ 1113 ] .
increased conjunctival manipulation can increase chances of buttonhole , tear , and subsequent fibrosis . a reduction in manipulation would help in reducing the same . theoretically , positioning the conjunctival incision and scleral entry apart from each other ( about 4  mm ) may help in preventing direct conduit for microbes .
though there is no exact data on how much the incisions should be spaced for a significant protective effect , there was no inflammation or infection seen in our cases .
however , similar to trabeculectomy , in the presence of a leak or wound dehiscence , this potential advantage may be lost and such situations should be avoided . sliding
the conjunctiva towards the limbus to avoid the conjunctival and scleral wounds from overlapping also decreases the risk of fibrosis between overlapping incisions .
mechanical pressure exerted by the conjunctival sutures is transmitted away from the scleral wound and there is therefore less contact zone between the 2 incisions .
subconjunctival drainage channels are therefore preserved intact to a larger extent as compared to trabeculectomy , thus potentially inducing less subconjunctival fibrosis and allowing better subconjunctival drainage .
bleb elevation is by hydrostatic expansion of largely intact subconjunctival tissue . in our experience ,
the creation of the tunnel was easy and one step and thereby surgery was easier and faster .
larger area of intact conjunctiva also has additional advantage of allowing greater space for a second glaucoma surgery if required .
the single step tunnel approach in sigs offers advantages of posteriorly directed aqueous flow as compared to leakage under a flap where flow occurs to three sides .
once the learning curve is crossed , other potential advantages of this technique include ease of creation , less manipulation compared to a scleral flap , less likelihood of flap tears and buttonholes , and less suture related inflammation . in the extreme event of an expulsive hemorrhage , it can be rapidly closed .
tunnel trabeculectomies that use a scleral tunnel have been described in the past as a successful mode of filtration surgery [ 1416 ] .
however , it differs from these in the absence of conjunctival flap creation and in utilizing a biplanar scleral tunnel .
the entry in sigs is one step and conjunctival incisions as well as subconjunctival dissection are therefore minimized .
a biplanar incision is a more advantageous geometry than a triplanar incision for better aqueous leakage postoperatively .
significant intraoperative complications encountered were premature entry and trapdoor hinging of the posterior corneal lip .
premature entry occurred when the keratome pass was deep and entered the ac directly without a corneal component .
this was managed by taking a single small punch which was sufficient to attain adequate leakage .
a trapdoor hinging occurred when the corneal tunnel was deep and the posterior corneal lip gave way .
this was managed by excising the hinge with vannas scissors and then proceeding as usual .
success rates after trabeculectomy with target pressure between 18 and 22  mmhg have been variously reported to range from 43% to 86% without medications [ 1726 ] and from 59% to 98% with medications [ 17 , 21 , 22 ] . in our study , postoperatively , a complete success was possible in 64.7% with an iop at final follow - up of < 18  mmhg without medication and 82.35% with iop < 18  mmhg with two or less medications .
one patient who had postoperative hypotony was managed by transconjunctival compression suture that compressed the tunnel and decreased flow .
transconjunctival suturing was easy to perform as the scleral tunnel was visible through overlying conjunctiva on stretching conjunctiva out over the tunnel area .
the conjunctiva did not need to be cut for tunnel exposure to apply the suture and the suture was removed after 3 weeks ( figures 4(a)4(d ) ) .
other complications encountered were minor . though we did not put releasable suture in any patient in this case series
, it is possible to do postoperative iop management using laser suture lysis or removable suture technique in the same manner as is done in trabeculectomy .
this can be done by taking a releasable suture in the standard way through the tunnel and releasing it in the postoperative period .
unlike in trabeculectomy where suturing is possible under direct visualization , in sigs visibility is comparatively more difficult .
however , in our experience , the scleral lip of the tunnel is generally visible on pulling the conjunctival incision towards the limbus and this can make application of the releasable suture across the tunnel possible .
a potential disadvantage for this technique is that since all maneuvers are done under the tunnel , the technique appears partially blinded .
however , we were able to visualize the scleral tunnel entrance under the conjunctiva , passage of the keratome , the corneal entry lip , corneal punch , and final diffuse bleb formation in all cases .
another potential disadvantage is the possibility of subconjunctival bleeding as cautery is not applied . in our experience , avoiding visible conjunctival and scleral blood vessels was generally enough to avoid large subconjunctival hemorrhage .
however , patients on oral antiplatelet agents were advised to stop these medications for sufficient duration of time before surgery .
the scleral tunnel incision though hidden underneath the conjunctiva could be visualized in all cases by withdrawing the conjunctival incision towards the limbus . though only a gross assessment of flow was possible , in our experience , free flow of fluid and good ballooning of the bleb on side port irrigation when seen with a soft , yet stable ac lead to better outcomes ( figures 5(a ) and 5(b ) ; figures 6(a)6(c ) ) .
though long term results are still under evaluation , satisfactory iop control was noted by us after sigs in the interim follow - up . the small sample size and the limited follow - up
make it difficult to draw a strong conclusion pertaining to long term outcomes and complication rate .
this pilot study however serves to lay the foundation for further detailed analysis of this technique .
a long term study in a larger population will be required to confirm the anatomical and functional outcomes of this modified technique .
 
 purpose . to describe a modified guarded filtration surgery , stab incision glaucoma surgery ( sigs ) , for primary open angle glaucoma ( poag ) 
 . methods . 
 this prospective , interventional case series included patients with poag ( iop 21  mmhg with glaucomatous visual field defects ) . 
 after sliding superior conjunctiva down over limbus , 2.8  mm bevel - up keratome was used to create conjunctival entry and superficial corneoscleral tunnel in a single step starting 1.5  mm behind limbus . 
 lamellar corneoscleral tunnel was carefully dissected 0.51  mm into cornea and anterior chamber ( ac ) was entered . 
 kelly descemet 's punch ( 1  mm ) was slid along the tunnel into ac to punch internal lip of the tunnel , thereby compromising it . 
 patency of ostium was assessed by injecting fluid in ac and visualizing leakage from tunnel . 
 conjunctival incision alone was sutured . 
 results . 
 mean preoperative iop was 27.41  5.54  mmhg and mean postoperative iop was 16.47  4.81  mmhg ( n = 17 ) . 
 mean reduction in iop was 38.81  16.55% . 
 there was significant reduction of iop ( p < 0.000 ) . 
 64.7% had iop at final follow - up of < 18  mmhg without medication and 82.35% had iop < 18  mmhg with 2 medications . 
 no sight threatening complications were encountered . conclusion . 
 satisfactory iop control was noted after sigs in interim follow - up ( 14.18  1.88 months ) . 
1. Introduction
2. Materials and Methods
3. Results and Discussion
4. Conclusion