Glaucoma Surgery: A Paradox
(Note that this was commentary originally authored in 2011-2012)
I recently examined a patient with a long history of glaucoma. A num-ber of years ago, I had performed a trabeculectomy in each eye. The sur-gery was uncomplicated and successfully controlled her intraocular pres-sure (IOP) in the 8- to 12 -mm Hg range without drops. A few years later, a bleb infection developed in one eye; endophthalmitis ensued and she lost functional vision. The other eye served her well until recently. Despite low IOP, her glaucomatous cupping and visual field loss progressed. She was encouraged to discontinue driving and curtail her activities; she was declared legally blind. Unfortunately, this is not an atypical story.
Filtering procedures, in its various iterations, have been the mainstay of glaucoma surgery for over a century. Interestingly, trabeculectomy has changed little from what I learned during my fellowship in 1982. Efficacy of trabeculectomy has always been very good. However, despite various advancements in surgical technique and our enhanced understanding of wound healing, troubling short- and long-term side effects jeopardize the outcome. To a great extent, this limitation is due to the problems of directing intra-aqueous flow through the sclera to the subconjunctival space. It is not a natural space or reservoir; and despite all of our attempts with modulating use of anti-fibrotics and refined surgical technique, problems ensue.
Although directing flow to the subconjunctival space has been the pri-mary target in glaucoma surgery, innovative and more physiologic approach-es to lowering IOP utilizing the canal of Schlemm and the suprachoroidal space are actively being investigated. This recent period of innovation is not by coincidence. Various factors (including enhanced technology, fund-ing, and broad international interest) have converged to develop a safer yet equally efficacious glaucoma operation.
Of the new procedures, the space in and around the canal is the most physiologic. The new devices are well tolerated and safe. The extent of the IOP reduction is, however, not quite to the level achieved by the subconjunctival approach but perhaps close enough. Working in the suprachoroidal space offers the chance of greater IOP reduction but raises more concern about long-term scarring and efficacy. The various devices and procedures are currently entering into phase 3 international random-ized trials, and results are pending. In all likelihood, the current scope of new devices will broaden the indications for a safer surgical means of lower-ing IOP for glaucoma. They will also usher in the day for surgically placed drug delivery systems. Not only will this help stem the problem of patient’s medication adherence but it will also open the door to posterior segment glaucoma treatment.
However, the big therapeutic advance will come in conjunction with a better understanding of the pathophysiology of the disease. We remain poorly informed of why IOP increases in selected individuals and why glaucoma patients (with and without high IOP) lose vision. Along the way, we need a better, more definitive way of classifying glaucoma. Getting away from the phenotypic or gonioscopic-defined angle classification (ie, open- versus closed-angle) in favor of a genotypic-specific diagnosis would greatly help our understanding of the disease as well as help direct custom-ized therapy for specific glaucomas. We need a means of preventing nerve damage in susceptible patients. We need a way to protect and regenerate the optic nerve.
To say we have not made progress in the last 30 years is a misstatement. To say we have not made the progress noted in other ophthalmic special-ties, such as cornea, retina, and cataract, is unmistakable. Yet, the door has begun to open for treating the complications of glaucoma, and innovation is on its way. The next few years will be like no other in the diagnosis and management of this frustrating disease.