Chinese Medical Journal 2004;117(7):1006-1010
Efficacy of non-penetrating trabecular surgery for open angle glaucoma: a meta-analysis

CHENG Jin-wei 程金伟,  MA Xiao-ye 马晓晔 ,  WEI Rui-li 魏锐利

CHENG Jin-wei 程金伟 (Department of Ophthalmology, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China)

MA Xiao-ye 马晓晔 (Department of Ophthalmology, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China)

WEI Rui-li 魏锐利 (Department of Ophthalmology, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China)

Correspondence to:Wei Rui-li,Department of Ophthalmology, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China (Tel: 86-21-63610109 ext 73451. Fax:. E-mail:ruili@sh163b.sta.net.cn)
Keywords
non-penetrating trabecular surgery;open angle glaucoma;intraocular pressure;meta-analysis
Abstract
Background Non-penetrating trabecular surgery is a new filtrating surgery without opening in ternal trabecular structures. This study was to estimate the overall efficacy of non-penetrating trabecular surgery for open angle glaucoma.
Methods The published articles selected for this study were obtained by a computerised Medline and China Biological Medicine Disk search of the literature and a manual search of the bibliographies of relevant articles. Articles meeting the inclusion criteria were reviewed systematically, and the reported data were aggregated using the statistical techniques of meta-analysis.
Results A total of 37 articles were included in the meta-analysis. The pooled complete success rates of non-penetrating trabecular surgery with different techniques were: deep sclerectomy single, 69.7% (95% CI: 58.5%-81.0%); deep sclerectomy with collagen implant, 59.4% (95% CI: 47.0%-71.8%); deep sclerectomy with reticulated hyaluronic acid implant, 71.1% (95% CI: 56.8%-85.3%); and viscocanalostomy, 72.0% (95% CI: 57.6%-86.4%). The overall weighted complete success rate of non-penetrating trabecular surgery was 67.8% (95% CI: 61.4%-74.3%).
Conclusions Non-penetrating trabecular surgery is the best available therapy method for medically uncontrolled open angle glaucoma with a complete success rate of over 60%. But the different techniques cannot belie the complete success rate of non-penetrating trabecular surgery.
Non-penetrating trabecular surgery aims at improving aqueous outflow without opening internal trabecular structures as in trabeculectomy or trabeculotomy. Since Zimmerman et al[1] published their report in 1984, several non-perforating approaches have been presented. Simple removal of the scleral and corneal tissue overlying trabecular structures risks inducing secondary fibrosis and subsequent failure to control intraocular pressure (IOP). The sclerocorneal space created by non-penetrating trabecular surgery acts as an aqueous decompression space that should be kept open. From there, the outflow channels transport fluid and lower the IOP. To maintain the aqueous decompression space, several different biological materials are implanted. Non-penetrating trabecular surgery is not associated with serious complications. Flat anterior chambers, severe choroidal detachments, and severe inflammation are much less frequent because the anterior region is not penetrated compared to classic penetrating trabeculectomy.[1]

During the past ten years, non-penetrating trabecular surgery has been proved to be an effective and safer filtration surgery for open angle glaucoma. To estimate the overall efficacy of non-penetrating trabecular surgery for open angle glaucoma, we performed a meta-analysis, across several techniques, of studies that addressed the efficacy of this non-perforating filtration surgery.

METHODS

The meta-analysis was performed according to a protocol determined before the study, and widely accepted methodological recommendations were followed.[2-5] Measurement of treatment effectiveness was determined on the basis of the clinically relevant outcome: namely, the complete success rate defined as IOP below 21 mmHg without medication.

Selection of trials
Studies that fulfilled the following criteria were included in the present meta-analysis: patients with medically uncontrolled open angle glaucoma who had been treated with NPFS; the complete success rates were assessed; and the results were published as a clinical study.

Study identification
Pertinent studies were retrieved from Medline and China Biological Medicine Disk database (from 1996 to 2002) by using the search terms of “non-penetrating trabecular surgery”, “deep sclerectomy”, and “viscocanalostomy”, and by limiting the search to studies with human patients. In addition, a manual search was performed by checking the reference lists from articles or reviews to identify studies not yet included in the computerised database. When the results of a particular study were reported in more than one publication, only the most recent and complete data were included in the meta-analysis. Thus, a total of thirty-seven articles were used for the analysis.[6-42]

Statistical analysis
A published meta-analytic technique was used to calculate the pooled complete success rate.[43] The chi-square test performed for homogeneity of proportions using the method outlined by the Cochrane Collabrative Center to determine whether there was greater variability among the results of studies than was compatible with the play of chance. Then the pooled success rates and their corresponding 95% CI were estimated. The general method of the weighted average was used to obtain a pooled estimate of the complete success rate.

The statistical method, used to obtain a pooled estimate of the complete success rate (r) from the observed rates (ri) of a number of studies (i=1 to i) of size ni, is the weighted average: r= ∑(ri×wi)/∑wi where the weights (wi) were equal to the inverse of the sum of the study variance and the among-study variance.

If the studies were relatively homogeneous, each study provided an estimate of a single underlying “true” rate, and the variance among individual studies (T) approaches zero. However, in practice, some hetero-geneity is almost always present. In the heterogeneous case, each study population was assumed to have a different true underlying rate. These rates, in turn, varied about a true overall rate according to a normal distribution with variance equal to the among-study variance. One measure of among-study heterogeneity, Q, could be calculated as: Q=∑(wi×[ri-r]2) for i studies, where the weights used to calculate each ri were equal to the inverse of the study variance (Si=[ri×(1-ri)]/ni). When the sample sizes (ni) were relatively large, the distribution of Q under the assumption of homogeneity approximated a χ2 distribution with i-1 degrees of freedom. The among-study variance (T) then could be estimated using the method of moments: T=max{0, [Q-(i-1)]/(∑wi-∑wi2/∑wi)}.

Given this estimate, the pooled rate could be calculated using weights (wi*) equal to the inverse of sum of the individual study variance (Si) and the among-study variance (T), with the standard error (SE) estimated by SE=(∑wi*)-1/2.

RESULTS

Of the 37 studies included in this analysis, 14 articles were involved in deep sclerectomy alone, 10 in deep sclerectomy with collagen implant, 9 in deep sclerectomy with reticulated hyaluronic acid implant, and 8 in viscocanalostomy. The Chi-square test for heterogeneity of proportions confirmed the graphical impression of significant heterogeneity in the reported success rate of non-penetrating trabecular surgery with different techniques (each P<0.01).

Of the 14 articles included in the analysis of deep sclerectomy single, 595 eyes were involved, and overall 378 eyes had an IOP below 21 mmHg without medication. There were two trials in one articles, so 15 trials were included this analysis. The pooled complete success rate of deep sclerectomy single was 69.7% (95% CI: 58.5%-81.0%).

A total of 625 eyes were involved in the analysis of deep sclerectomy with collagen implant, and the number with an IOP below 21 mmHg without medication were 370. Of the 10 articles included in this analysis, there was one article with two trials, and so 11 trials were involved. The pooled complete success rate of deep sclerectomy with collagen implant was 59.4% (95%CI: 47.0%-71.8%).

A total of 251 cases were involved in the analysis of deep sclerectomy with reticulated hyaluronic acid implant, and overall 173 eyes had an IOP below 21 mmHg without medication. The pooled complete success rate of deep sclerectomy with reticulated hyaluronic acid implant was 71.1% (95% CI: 56.8%-85.3%).The complete success rates of viscocanalostomy reported in 8 articles were summarised. After treatment with viscocanalostomy, 322 of 447 eyes had an IOP below 21 mmHg without medication. The pooled complete success rate of viscocanalostomy was 72.0% (95% CI: 57.6%-86.4%).

The minor difference in pooled complete success rates between the different techniques of non-penetrating trabecular surgery was not statistically significant. If one therefore assumed that the success rates of the different techniques were homogeneous, then the overall weighted complete success rate of non-penetrating trabecular surgery was 67.8% (95% CI: 61.4%-74.3%).

DISCUSSION

To avoid the numerous postoperative complications of trabeculectomy (e.g. hypotony, flat anterior chamber, and choroidal detachment), several techniques of non-penetrating filtration surgery have been described.[15] In 1990, Fyodorov et al[44] proposed an equivalent operation, which they called deep sclerectomy. Kozlov et al[45] proposed a collagen drain kept in the deep sclerectomy procedure to improve external filtration and hence lower IOP. In 1991, Stegmann[46] modified the surgical technique, under the name of viscocanalostomy, with injection of hyaluronic acid in both ends of unroofed Schlemm’s canal and the surgical “lack” or surgically created space. Sickenberg and co-authors[47] then reported a similar IOP reduction and fewer complications after deep sclerectomy with a collagen implant compared with trabeculectomy. Recently, a reticulated hyaluronic acid implant was added during deep sclerectomy to maintain the aqueous decompression space.

Over the past ten years, non-penetrating filtration surgery had been proved to be an effective and safer filtration surgery for open angle glaucoma than earlier procedures. But the reported efficacy of non-penetrating filtration surgery for open angle glaucoma is widely different among the studies with complete success rates from 25% to 100%.[7,28] The estimates provided by this meta-analysis indicate a steady complete success rate of non-penetrating trabecular surgery with different techniques: deep sclerectomy single 69.7%, deep sclerectomy with collagen implant 59.4%, deep sclerectomy with reticulated hyaluronic acid implant 71.1%, and viscocanalostomy 72.0%. There were no statistically significant differences in complete success rates between the different techniques of non-penetrating trabecular surgery.All non-perforating approaches are guarded procedures that begin with the fashioning of a one-third thickness limbal-based flap, brought forward as far as 1.5 mm into clear cornea, and dissected under a conjunctival flap. All procedures involve the removal of a second deep scleral flap, dissected in the shape of an equilateral triangle, at a depth that allows the visualisation of the darker colour of the ciliary body below the scleral fibres. In all procedures, the removal of the deep scleral flap leads to formation of an empty space called “aqueous decompression space”, wherein the aqueous humor will be collected before its drainage. This dissection is located in the plane of the scleral spur and the Schlemm canal. Then the Schlemm canal is externalised and the external wall removed. The dissection is then carried anteriorly until only a thin layer of the Descemet membrane separates the anterior chamber from the outside and acts as an outflow resistance site.

In order to keep the aqueous decompression space open, different implant devices have been proposed such as collagen Aquaflow implants, reticulated hyaluronic acid implants and the T Flux implant. Some surgeons use a sponge soaked in 5-fluorouracil directly applied to the bleeding so that fibrosis might be inhibited at the level of the superficial scleral flap. Other surgeons use mitomycin C to inhibit the fibrosis.

In non-penetrating filtration surgery, the removal of both deep scleral flap and corneal stroma behind the anterior trabecula and the Descemet membrane allow the aqueous humor to leave the anterior chamber through the intact trabeculodescemetic membrane, i.e. at the level of anterior trabecula from where it reaches the aqueous decompression space. From the decompression space, the aqueous humor also may reach the uveoscleral pathway through the floor of the deep sclerectomy. The aqueous humor may also be drained through a transscleral pathway. In viscocanalostomy, the enlargement of the Schlemm canal with viscoelastic is designed to enhance aqueous egress through the cut ends of the Schlemm canal.

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