World glaucoma congress leaders discuss ways to improve research and treatment

VIENNA — Forming a better understanding of IOP and its role in causing and preventing glaucomatous damage is one of many challenges facing glaucoma specialists in the future, according to Robert N. Weinreb, MD, PhD.

Dr. Weinreb, president of the Association of International Glaucoma Societies, listed some of the challenges for glaucoma researchers in the future in his speech during the World Glaucoma Congress here.

As a method for creating a better understanding of the dynamics of IOP, Dr. Weinreb said he looks forward to the introduction of a 24-hour continuous IOP compliance-monitoring device within the next 5 years.

He said easier-to-use experimental models that mimic human glaucoma, such as the transgenic mouse, will be important for future disease research.

He said he would like to see “the establishment of clinical methods for assessing the entire visual pathway,” as well as a method for clinically imaging the retinal ganglion cells to detect accelerated cell loss.

“I expect that in the future we won’t have arguments about structure or function because we’ll be able to quantitate the number of retinal ganglion cells and determine whether glaucoma is progressing or stable and whether our therapies are effective or not,” Dr. Weinreb said.

Another challenge facing glaucoma specialists, Dr. Weinreb said, is refining risk factor information to better determine who needs which treatment. He cited the work of Felipe A. Medeiros, MD, who reported on the development of a 5-year risk calculator in a poster at the meeting. Dr. Weinreb called his risk calculation model a “promising turn” in understanding risk factors.

Glaucoma specialists also must understand “the cellular and molecular mechanisms that regulate aqueous humor outflow through the trabecular meshwork and the uveoscleral outflow pathway,” he said.

Dr. Weinreb said he expects to see progress in the future “with a number of drugs that can directly affect the trabecular meshwork and open up the uveoscleral outflow pathway.”

Understanding and improving patients’ lifestyles – through factors such as smoking cessation, exercise and reducing obesity – is another challenge Dr. Weinreb said will need more attention from the glaucoma research community.

“Not only is it important to understand these risk factors, but these are modifiable risk factors that might improve the prognosis of patients with glaucoma,” he said.

Another challenge is finding a practical method or methods for drug delivery to the retina, he said.

“It’s obvious we have wonderful neuroprotective agents, … however, we still don’t have the means for delivering them. This is a very important challenge for glaucoma in the next decade,” Dr. Weinreb said.

He said glaucoma specialists must learn more about protecting healthy retinal ganglion cells, develop the ability to rescue damaged cells and design safer, more titratable and more predictable IOP-lowering surgical treatments.

Open-angle glaucoma surgery consensus

Newer surgical and laser therapies for open-angle glaucoma may have merit, but some glaucoma experts say these procedures still lack long-term evidence of efficacy. This was one of the conclusions of a panel discussion here.

An international panel of glaucoma experts debated the merits of a range of issues in the surgical management of glaucoma, including indications for glaucoma surgery, laser trabeculoplasty, wound healing and the future of wound modulation, nonpenetrating glaucoma surgery and glaucoma drainage devices.

The panel discussed these topics in the context of a previously approved document, a consensus on open-angle glaucoma from the Association of International Glaucoma Societies, which was reached during a special meeting in April 2005. The panel then opened the floor to take live votes from the audience on each subject, the results of which were immediately tallied and projected for discussion by the whole panel.

Topics discussed included a comparison of trabeculectomy vs. glaucoma drainage devices, and a comparison of glaucoma drainage devices vs. cyclodestruction.

Two topics in the consensus that generated considerable discussion were the merits of argon laser trabeculoplasty (ALT) vs. selective laser trabeculoplasty (SLT) and the efficacy of nonpenetrating glaucoma surgery techniques.

Donald S. Minckler, MD, addresses attendees in a panel discussion on a consensus document of the AIGS. Image: Mullin DW, OSN

In a refrain that was common to both controversies, Donald S. Minckler, MD, said that long-term evidence of the efficacy of the newer procedures does not yet exist.

“There’s really very little convincing evidence SLT works any better than ALT, and it just hasn’t been around long enough or studied well enough to be sure it’s a better option in terms of pressure-lowering, which is the goal of the procedure,” said Dr. Minckler, of Los Angeles.

Added Dr. Weinreb, “So don’t throw out your argon laser. It’s still the preferred method of many experienced glaucoma surgeons.”

Some panel members noted that the nonpenetrating filtering procedures are more skill-dependent than trabeculectomy, which may account for some surgeons’ reluctance to adopt them.

“Glaucoma surgery worldwide is decreasing in frequency, and it becomes a difficult point for us to decide how often you need to perform a procedure in order to remain at a high enough competency level to offer patients the best chance of success,” said Ivan Goldberg, MBBS, FRANZCO, FRACS, of Sydney, Australia.

If surgeons are performing fewer trabeculectomies, Dr. Goldberg said, they are going to be more reluctant to switch to a nonpenetrating technique that is more skill-dependent.

Prof. Dennis S.C. Lam told Ocular Surgery News in a separate interview that by its nature a consensus tends to be more conservative, which is why newer techniques without much data were excluded.

“Because it’s a consensus, for procedures where we don’t have the evidence – although we may have a case series or some preliminary data or whatnot – that will not be put on the consensus.” Prof. Lam said.

Even though not all procedures were approved as primary treatment by consensus, Prof. Lam said the fact that they were brought up for a vote in the consensus, “gives us a lot of good areas for further research.”

Gold shunt holds promise for nonpenetrating filtering surgery

A 24-karat gold micro-shunt developed by Solx Inc. is showing promise as an adjunct device for use in nonpenetrating glaucoma filtering procedures.

According to Gabriel Simon, MD, PhD, gold is biocompatible enough to remain inert in the suprachoroidal space. Titration of outflow for controlled IOP reduction is achieved by selectively opening and closing flow holes in the Gold Micro Shunt with a 790-nm titanium-sapphire laser.

In a study performed by Dr. Simon and Shlomo Melamed, MD, using the gold micro-shunt, the mean preoperative IOP of 59 patients was 28 mm Hg. At 24 hours IOP, the mean IOP had fallen to a mean of 12 mm Hg. At 3 months, 46 patients had a mean IOP of 19 mm Hg. In seven patients followed to 24 months, mean IOP was 18 mm Hg.

Unlike other devices used in nonpenetrating procedures, the gold micro-shunt is inserted between the sclera and the suprachoroidal space through a 4-mm incision made at the limbus, Dr. Simon told Ocular Surgery News.

After the 4-mm incision is made, the surgeon creates a pocket into the suprachoroidal space, and the shunt is inserted into the pocket. The insertion tool is removed, and one end of the shunt is placed into the anterior chamber.

A spokesman for Solx said the company anticipates European CE approval for the shunt by the end of this year.

Large glaucoma screening shows association with myopia

The risk of glaucoma development is associated with myopia, according to data from a large screening study. Further analysis of data from the screening will focus on quality-of-life and visual impairment issues, said one investigator speaking here.

Anders Heijl, MD, noted that the Early Manifest Glaucoma Trial has already helped identify some risk factors for early glaucoma development as well as determining the benefits of therapy vs. no therapy for disease management. That trial was based on data from Sweden’s Malmo Eye Survey, which screened 44,000 subjects for glaucoma between 1992 and 1997 — making it the world’s largest screening, he said.

Data from that survey shows that the relationship between refractive error and glaucoma is very strong, Dr. Heijl said.

“Not only is glaucoma more common in myopes, but it is less common in hyperopes,” he said. “Every diopter seems to count.”

Continuing to follow these subjects will “answer the most important question of whether immediate treatment offers an advantage, which will in turn answer the question of whether there is a need for early screening and diagnosis,” he said.

Deep sclerectomy maintains low IOP over long term

Deep sclerectomy with a collagen implant can “effectively lower IOP over the long-term,” said one surgeon.

Swiss ophthalmologist André Mermoud, MD, PhD, who has performed more than 3,000 deep sclerectomies over the past 12 years, shared his most recent follow-up data with attendees.

With 8 years’ follow-up, he said, patients had a mean IOP of 12 mm Hg. The procedure achieved complete success in 57% of cases and qualified success in 91% of the patients. Qualified success was defined as an IOP of less than 21 mm Hg. Dr. Mermoud also said 45% of the patients had an IOP of less than 15 mm Hg at the final follow-up.

Dr. Mermoud uses the AquaFlow (STAAR Surgical) collagen implant, which is implanted in the intrascleral space during deep sclerectomy. The implant dissolves within 6 to 9 months, he said. After years of perfecting his technique, he prefers to remove the inner scleral wall, which he said “helps to dramatically decrease IOP immediately postoperatively and keeps the pressure down long term.”

Dr. Mermoud said the implant helps maintain the intrascleral space, which is important to outflow of aqueous.

“If you don’t use the implant, the space will collapse and you will lose that intrascleral space,” he said.

Because every patient has a different scleral depth, it is crucial that surgeons determine the correct depth early in the procedure, he warned.

Dr. Mermoud said that if the patient has an IOP of 19 mm Hg immediately postop, the surgeon probably has not removed the outer wall of Schlemm’s canal, and therefore the IOP will not be lowered over the long term either.

“In the first day, if you did it right, [IOP] should be 3 mm Hg to 4 mm Hg,” Dr. Mermoud said.

Calculation developed for risk of glaucoma from hypertension

A predictive model for calculating the risk of glaucoma development from ocular hypertension was described in a poster presentation.

Felipe A. Medeiros, MD, said he applied the Cox proportional hazards regression model to published results from the Ocular Hypertension Treatment Study (OHTS). The formula calculates the 5-year risk of glaucoma development in patients with ocular hypertension.

“OHTS-derived predictive models performed well in assessing the risk of glaucoma development in an independent population of OHTS subjects,” Dr. Medeiros said in the poster. “A simple risk-scoring system was developed which allows calculation of the 5-year risk of glaucoma development for an individual patient.”

The study looked at 252 eyes of 126 untreated patients in OHTS who had an IOP of at least 24 mm Hg in one eye and at least 21 mm Hg in the fellow eye. Of that population, 31 patients developed glaucoma at follow-up.