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Results of Nonpenetrating Glaucoma Surgery
Introduction
A number of studies on nonpenetrating glaucoma surgery (NPGS) have been published in recent years. This is a fact to be celebrated, in view of the need for objective evaluations of these procedures in terms of efficacy, safety, and advantages in quality of life. Besides, these studies may be a means to adequately place this surgical option into the armamentarium of glaucoma.
Not only the amount but specially the quality of the outcome reports is of paramount importance. The Third Consensus of the World Glaucoma Association (WGA) has made it clear that many aspects should be improved in this field. This implies studies aiming at high-level evidence. The needs are distinct: long follow-ups (preferably more than 1 year), the inclusion of cumulative survival analyses, the use of success criteria including target intraocular pressure (IOP) levels required for advanced glaucoma, the inclusion of data on visual function, the exclusion of cases suffering devastating complications, and the uptake of useful data for measuring quality of life.
Two basic NPGS techniques are commonly used: viscocanalostomy and deep sclerectomy (DS). The first one does not usually depend on external filtration and, therefore, its function should not usually be interfered with by Tenon–conjunctiva scarring, although it may be impaired by healing at the edges of the superficial scleral flap and at the trabeculo-Descemet's membrane. DS, on the other hand, takes full advantage of a filtering bleb.
Peeling of the internal wall of Schlemm's canal (removal of juxtacanalicular trabecula) is a surgical step that influences the amount of aqueous filtration and hence, the hypotensive effect of NPGS ( Fig. 101-1 ). Originally described in DS, it may also be applied in viscocanalostomy (Video Visco plus MMC Zanutigh, MD; Video Removal of JCT).
Measures aiming to enhance or to restore aqueous filtration are diverse and are being used at different rates and combinations in studies on NPGS. They comprise intraoperative antimetabolites, postoperative antimetabolites, and needling procedures (the latter only applied when an external bleb has been produced), YAG laser goniopuncture ( Fig. 101-2 ), and implantation of intrascleral devices ( Fig. 101-3 ).
Outcomes of Long-Term Studies
Retrospective
Two recent retrospective studies on DS include various combinations of NPGS procedures. Lachkar et al. reported a 6-year experience on 247 eyes, of which 157 received an intrascleral collagen implant, and 90 intraoperative 5-fluorouracil (5-FU). YAG laser goniopuncture was performed in 47.3% of cases. At 6 years, the average IOP was 15.81 ± 3.79 mmHg. The number of preoperative glaucoma medications decreased from 2.01 ± 0.58 to 0.8 ± 0.92. Complete success rate (IOP < 21 mmHg) was 66.46% at 60 months.
A 5-year trial including 171 eyes with different interventions (DS with Healon GV, DS with an implant, DS with antimetabolite application, and DS with antimetabolite plus implant) reported a similar average final IOP (15.3 ± 5.3 mmHg) at 5 years. The complete success rate (individual target IOP achieved without medication) was 52% at 4 years. Ninety-three eyes reached a final IOP of 15 mmHg.
Prospective
Two prospective studies, both with a follow-up of 5 years or more, also showed a lasting effect and addressed the subject of whether NPGS may achieve IOPs in the low teens.
A 10-year prospective, nonrandomized, unmasked study, evaluated the success rate and complications of deep sclerectomy with collagen implant (DSCI) in POAG. It included 105 patients with a mean follow-up of 101.5 ± 43.1 months (range 3 to 144). Ten years after surgery IOP was 12.2 ± 4.7 (6 to 20) mmHg and best-corrected visual acuity 0.63 ± 0.34 (0.01 to 1.2). Complete success (IOP ≤ 21 mmHg without medication) at 10 years was achieved by 44.6% and qualified success (IOP ≤ 21 mmHg with medication) was 77.6%. Goniopuncture was performed in 61 eyes (59.8%), 5-fluorouracil treatment was given to 25 patients postoperatively and five cases required a needling procedure.
Shaarawy et al., in a 5-year non-randomized trial including 57 eyes which underwent viscocanalostomy with a loosely sutured scleral flap, obtained an interesting average IOP of 13.9 mmHg at 36 months with a complete success rate (IOP < 21 mmHg without treatment) of 60% at 60 months. The rate of YAG laser goniopuncture was 33.8% and the rate of 5-FU subconjunctival injections was 2.9 ± 1.9.
Nonpenetrating Glaucoma Surgery with Use of Antimetabolites
The benefits of using mitomycin C (MMC) on DS became evident in two controlled trials. In a prospective, controlled study on 90 eyes and a 36-month follow-up period, the use of MMC during DS at a concentration of 0.2 mg/mL and an application time of 2.5 min significantly reduced the postoperative IOP and increased the success rate. An ongoing prospective database was the source of a controlled report in which this same concentration of MMC applied for 2 minutes significantly increased the probability of achieving the target IOP and also IOPs below 14 mmHg at 1 year.
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