Dr. Smita Panda, P16507, Dr. Shantha Balekudaru, Dr. George Ronnie J
Comparison of conjunctival complications in Ahmed glaucoma valve (AGV) surgery: Corneal versus scleral patch grafts
Introduction
Glaucoma drainage devices are becoming increasingly popular in the surgical management of glaucoma.These devices are designed to shunt aqueous humor from the anterior chamber to a subconjunctival reservoir formed around a plate to which the tube is connected. The tube is covered by a biologic tissue roofed by the conjunctiva to prevent erosion of the conjunctiva by the tube, and subsequent exposure of the tube. Conjunctival dehiscence with subsequent exposure of the tube and/or plate is a risk factor for the development of endophthalmitis, particularly in the pediatric age group. The materials most frequently used include sclera, pericardium, dura mater andcornea.
The purpose of ourstudy was to compare the conjunctiva related complications in eyes with either scleral or corneal patch grafts used in Ahmed glaucoma valve (AGV) implantation
Materials and methods
A retrospective review of records of patients who underwent AGV implant from January 2000 to December2014 was performed. Inclusion criteria were patients> 18 years of age, with or without prior filtering surgeries, with a minimum follow-up period of 2 months. In eyes with implantation of > one implant, results were censored after the second device was implanted.
The demographic data including age, sex, systemic and ocular medical history, numberof intra ocular pressure (IOP)lowering medications used, and best corrected visual acuity, were recorded. Results of slit lamp biomicrosopy and fundus evaluation were noted. Follow- up data were recorded at 2 months and subsequently at each visit until either the last follow-up visit or until the next glaucoma procedure,were noted. Details of intra operative, post operative complications and their interventions were noted.
Patients were divided into two groups; GroupA included patients who had scleral patch graftand Group B included those who had corneal patch grafts.
Success of AGV surgery was defined as IOP > 6 mmHg and < 21 mm Hg with or without IOP lowering medications.
Failure was defined as IOP < 6 mmHg or > 21mmHg, orrequirement of repeat glaucoma procedures, either surgery or cyclophotocoagulation for IOP control or loss of light perception.
Complications were noted in two phases; early phase; noted within 3 months of surgery and latephase; noted after 3 months from the date of surgery.
Surgical technique
A superior rectus bridle suture was placed improve exposure in the working quadrant. A limbus-based conjunctival incision was made 5-6 mm behind the limbus and sub-conjunctival dissection performedposteriorly to allow adequate exposure for insertion of the plate. Prior to the plate anchorage, the tube was primed with balanced salt solution with a 30-gauge cannula. The implant was anchored between two rectus muscles with the anterior edge approximately 8 to 10 mm posterior to the limbus.The plate was then secured to the globe with two non-absorbable sutures (9-0 monofilament nylon sutures ; Ethilon, Ethicon US). The tube was thentrimmed to create a beveled edge with the opening toward the cornea. A 23-gauge needle was used to create a track through which the tube wasinserted into the anterior chamber just anterior and parallel to the iris or behind it through thepars plana.The tube was secured to the sclera a few millimeters anterior to the plate with 9-0 monofilament nylonsuture(Ethilon, Ethicon US).The tube was covered with partial thickness corneal or scleral patch graft. The patch graft was secured to the globe over the tube either with fibrin glue or with interrupted sutures by using 10-0 monofilament nylonsuture(Ethilon, Ethicon US). Theconjunctiva and Tenoncapsulewere then sutured in separate layers using 8-0 polyglactinsutures(Vicryl, Ethicon US).
Data analysis
SPSS version 21was used for the statistical analysis. The Kolmogorov-Smirnov test was applied to check the distribution of the data. Comparison of continuous data was done by independent samples Student’s T test for normally distributed data. The Mann -Whitney test and the Wilcoxon signed- rank test were applied to non-normally distributed data. Chi-Square and Fisher’s exact tests were used, as appropriate, to analyze categorical data. Apvalue of less than 0.05 was considered to be statistically significant. Univariate and multivariate logistic regression analysis was performed to assess the risk factors for conjunctiva related complications.
Results
280 eyes underwent AGV implantation betweenJanuary 2000 and December 2014.Of these, 208 (74.3%) eyes underwent scleral patch graft and 72(25.7 %) eyesunderwent corneal patch graft. The baseline demographic data is depicted in Table 1.
Theage,sex,mean highest IOP, Number of IOP lowering medicationspre AGV implant surgery,mean number of previous surgeries involving conjunctival dissection and the quadrant of valve placementwere comparable among the two groups.There was significant difference induration between last conjunctival surgery and implant surgery,follow up period,use of glueand the type of valve usedamong the two groups. The details are given in Table no. 2.
Although more number of eyes with scleral patch graft showed conjunctival complications, the difference was not statistically significant. Out of 16 eyes which had conjunctival complications,1 eye showed retraction in early phase and tube exposure in late phase. The details are given in Table no. 4
Dehiscence or retraction occurred as early as 3 days and upto 30 days in some eyes with an average of 15.5±11.4 days.Tube exposure was reported on an average of 22±24.3months with range of 3-73 months.
By logistics regression analysis, S2 type AGV (OR-3.,95% C.I.-1.05-8.9, p=0.04) and superonasalplacementof the AGV(OR-8.,95% C.I.-1.5-52.6,p=0.017) were found to be risk factors for occurrence of conjunctival complication. No significant correlation was found between the type of graft used and conjunctival complication(OR-1.03, CI-0.3-3.3, p=0.957). Other factors such asage(p=0.139), sex(p=0.054),no of conjunctival procedures done previously(p=0.848),duration between last surgery and AGV implant surgery (p=0.759),use of fibrin glue (p=0.791) were found to be insignificantly associated with conjunctiva related complications.
On multiple regression analysis too, S2 type valve(OR-3, 95% CI-1.02-95-, p=0.04) and superonasal placement of valve(OR-7.9,95% C.I.-1.2-48.3, p=0.031)remained as risk factors.
The overall rate of conjunctival complication in the current study was 5.7 %, with 2.9% eyes showing conjunctival dehiscence/retraction and 3.2% eyes showing early or late tube exposure. Equal rates of dehiscence /retraction were seen among the two groups (4 vs. 4) and only 1 eye belonging to group A showed tube exposure in early phase. In late phase all cases of tube exposure were seen only in group A.
DISCUSSION
The follow- up of patients was significantly longer in patients with scleral patch graft than corneal graft,this could attribute to the finding that no patient had tube exposure in the later group
The minimum follow up of patients was 2 months and due to this many cases of retraction / tube exposure would have been missed leading to the low complication rate in this study.
Oriel Spierer et al1 found that corneal grafts followed up for more than 12 months are associated with a 6.7 % rate of corneal graft melting and a 2.2 % rate of tube exposure, which is comparable to the current study.
Fran Smith et al2 however, found patch thinning but no tube exposure in 26.1% eyes and tube exposure in 4.3% eyes,with a follow up of minimum 24 months.
Noa Geffen et al3 in their study noted 33.5% eyes with wound dehiscence and 8.9% rate of device exposures, both being higher than seen in the current study. The inferonasal quadrant was associated with the highest rate of dehiscence in their study but in current series superonasal quadrant AGV placement was found to have higher risk. Their follow up criteria was 12 or more months
Study by Michael S. Kovalet al4 showed that Hispanic ethnicity, neovascular glaucoma, previous trabeculectomy and combined surgery were the risk factors. Type of patch graft used had no effect on conjunctival complications as seen in the current study too.
Corneal patch graft has better cosmetic outcome compared to scleral patch graft without affecting the success rate of AGV. Being a non vascular tissue, theoretically one can assume that complications due to inflammation should be less.
Retrospective nature and short follow up period are the limitations of the present study
Conclusion:
Our rates of conjunctival complications were similar to those reported in the literature. Risk factors included S 2 type of implant and superonasal placement.
References:
- Oriel Spierer, Michael Waisbourd, Yitzhak Golan, Hadas Newman, RonyRachmiel. Partial thickness corneal tissue as a patch graft material for prevention of glaucoma drainage device exposure. BMC Ophthalmology (2016) 16:20
- Smith, M. Fran MD; Doyle, J. William MD, PhD; Ticrney, John W. Jr DD. Comparison of Glaucoma Drainage Implant Tube Coverage. J Glaucoma2002;11:143–147A.
- Geffen N, Buys YM, Smith M, Anraku A, Alasbali T, Rachmiel R,et al. Conjunctival complications related to Ahmed glaucoma valve insertion. J Glaucoma 2014;23:109-114.
- Michael S. Koval, Fouad F. El Sayyad, Nicholas P. Bell, et al., “Risk Factors for Tube Shunt Exposure: A Matched Case-Control Study,”Journal of Ophthalmology, vol. 2013, Article ID 196215, 5 pages, 2013.
Table no. 1. Baseline demographic data.of eyes in group A (sclera patch graft) and group B (corneal patch graft):
| GROUP A | GROUP B | P Value | |
| Age(years) | 46.0±17.3 | 47.2±18.2 | 0.33 |
| Sex M:F | 1.7:1 | 3:1 | 0.06 |
| Pre-operative IOP(mm of Hg) | 33.9±9.6 | 35.8±11.1 | 0.36 |
| Pre-operative number of IOP lowering medications | |||
| mean
median range |
2.5±0.9
3 1-4 |
2.7 ±0.9
3 1-4 |
0.77 |
| Diagnosis
POAG PACG Secondary to uveitis Post trauma Silicon oil induced Secondary OA Glaucoma Secondary AC Glaucoma Congenital glaucoma Neovascular glaucoma
|
39 (18.8%) 25 (12%) 11(5.2%) 5(2.4%) 12(5.7%) 34(16.3%) 67(32.2%) 7(3.3%) 8(3.8%)
|
8(11.1%) 3(4.1%) 5(6.9%) 7(9.7%) 4(5.5%) 12(16.6%) 23(31.9%) 5(6.9%) 5(6.9%) |
0.084
|
| Mean number of surgeries involving conjunctival dissection prior to AGV implantation | |||
| mean | 1.9±9.5 | 1.75±0.9 | 0.45 |
| median | 1 | 1 | |
| range | 1-3 | 1-3 | |
| Duration between previous surgery and AGV(months) | 40.9±5.1 | 94.4±28.5 | 0.004 |
Table no. 2 : Intraoperative details of eyes in group A (sclera patch graft) and group B (corneal patch graft)
| GROUP A | GROUP B | P value | |
| Type of valve
FP7 S2 |
159(76.4%) 49 (23.6%) |
72 (100%) 0 |
< 0.001 |
| Position of valve
superotemporal(ST) superonasal (SN) inferotemporal (IT) inferonasal (IN) |
196(94.2%) 4(1.9%) 7(3.3%) 1(0.4%) |
62(86.1%) 2(2.7%) 2(2.7%) 2(2.7%) |
0.566 |
| Position of tube
AC Sulcus Pars Plana |
177(85%) 15(7.2%) 16(7.6%) |
60(83.3%) 5(6.9%) 7(9.7%) |
0.864 |
| Glue used | 7(3.3%) | 21(29.1%) | <.001 |
TABLE no.3: Post operative details of eyes in group A (sclera patch graft) and group B (corneal patch graft)
| GROUP A | GROUP B | P value | |
| Success rate
absolute relative |
155(74.5%)
28(13.4%) 127(61.5%) |
63(87.5%)
8(11.1%) 55(76.4%) |
0.091 |
| Failure rate | 53(25.5%) | 9(12.5%) | |
| Followup( months) | 28.01±28.5 | 13.05±9.4 | <.001 |
TABLE no.4: No. of eyes with early post-operative Complications (< 3 months)in group A (sclera patch graft) and group B (corneal patch graft)
| Conjunctival complications< 3 m | GROUP A | GROUP B | P value |
| retraction | 3 (1.07%) | 4(1.4%) | 0.19 |
| dehiscence | 1(0.4%) | 0 | |
| Tube exposure | 1(0.4%) | 0 |