Recent EMGT results support corneal thickness-glaucoma link

Murray Fingeret

SINGAPORE – While most recent clinical trials have shown that thinner corneas are associated with the development of glaucoma, one of the outliers was the Early Manifest Glaucoma Treatment Trial. Newer EMGT results reported here at the World Glaucoma Congress now support the association.

Anders Heijl, MD, discussed new EMGT data involving patients who were followed for 7 to 11 years. These more recent results show that thinner corneas are a risk factor for glaucoma, probably due to an increased number of individuals developing glaucoma. Still, the association was only seen in individuals with high baseline IOPs (hazard ratio 1.45 per 40 µm lower central corneal thickness). These results are now comparable to the Ocular Hypertension Treatment Study.

Meeting objectives

The World Glaucoma Congress (WGC) is the educational arm of the World Glaucoma Association, formerly the Association of the International Glaucoma Societies. This year’s meeting offered the latest research on topics such as angle closure glaucoma, open angle glaucoma and IOP.

The 2007 meeting objectives were as follows:

• To present new developments in diagnosis and treatment of glaucoma to both the glaucoma expert and the general ophthalmologist and optometrist interested in glaucoma.
• To enhance communication about glaucoma among ophthalmologists and optometrists worldwide.
• To enhance exchange of knowledge between the general ophthalmologist, optometrist and glaucoma experts.
• To maintain high scientific and ethical standards. The congress was divided into a series of sessions to allow topics of wide breadth and scope to be delivered.

The morning sessions included talks from many of the world’s glaucoma experts updating topics such as the pathophysiology, epidemiology, genetics, diagnosis and medical and surgical treatment of the different forms of glaucoma. Scientific sessions included a poster session that covered all aspects of glaucoma. Most importantly, the educational courses held in the afternoon ranged in scope — some were for general eye care practitioners and others for glaucoma specialists. Any person could attend any course, depending upon their interest.

Angle closure glaucoma

The meeting offered a series of presentations on angle closure glaucoma (ACG). Individuals with ACG are three times more likely to become blind. As the prevalence of myopia and pseudophakia in urban Asian populations increases, ACG may become more common in rural groups, researchers noted.

ACG has two forms, acute and chronic. Acute ACG is a form of symptomatic ocular hypertension due to the sudden occlusion of the eye’s drainage mechanism by the peripheral iris. Most optometrists associate this type with ACG. Without therapy, optic nerve damage and chronic angle closure glaucoma (CACG) may result. CACG can develop without an acute episode.

There are primary and secondary forms of ACG. The objectives of therapy are to prevent permanent angle closure, reduce the IOP and prevent optic nerve damage. Chronic angle closure is the more common form of ACG; it has an insidious onset in which slow closure of the angle develops, usually without symptoms. It may mimic open angle glaucoma (OAG) and, without gonioscopy, may appear identical to it. It produces the same signs as high-tension glaucoma, but the angle is closed when viewed with gonioscopy.

Another symposium discussed the pathophysiology of OAG. With OAG, abnormally high aqueous humor outflow resistance exists in the trabecular meshwork outflow channels, resulting in elevated IOP. Changes in the extracellular matrix in the juxtacanalicular region of the trabecular meshwork are involved and may be under control of transforming growth factor-beta2 (TGF-beta2). We may be able to modulate TGF-beta2 to reduce the buildup of material in the trabecular meshwork and increase aqueous outflow, researchers said.

IOP symposium

In a symposium on IOP, the first talk described how IOP was regulated. The presenter explained that the aqueous humor inflow and outflow determines IOP, with several pathways interacting to regulate IOP.

The second talk examined IOP over a 24-hour period. The researcher said that a single measurement in the office does not reveal the whole spectrum of pressures. Twenty-four hour peaks tend to occur at night. At bedtime, when a person assumes the recumbent position associated with sleep, IOP immediately increases due to an increase in episcleral venous pressure along with the redistribution of body fluid, leading to peak IOP measurements. Noctural peak IOPs occur regardless of the fact that IOP production is reduced significantly during this period.

Another presentation addressed the influence of IOP fluctuation, a somewhat controversial issue. Some studies point to IOP fluctuation as a risk factor for glaucoma development. Using data from the EMGT study, Dr. Heijl said that high IOP is clearly a risk factor for glaucoma development; however, IOP fluctuation could not be proven to be an independent risk.

Finally, a researcher discussed the need for a continuous IOP monitor. Within several years a contact lens-based pressure sensor may be available that would measure IOP over a 24-hour period intermittently. A more invasive tool is also in development, probably for advanced forms of glaucoma, in which an implanted device wirelessly monitors IOP continuously.

Canadian surgical rates

In one of the research posters, Campbell and associates presented their evaluation of glaucoma laser and surgical procedure rates in Canada. Using health insurance databases, the authors showed that from 2002 to 2005, the rates of laser trabeculoplasty doubled, though the increase varied geographically. Trabeculectomy surgery rates declined by 29% from 1996 to 2005. Glaucoma drainage device usage increased over this period 12-fold and by 2005 accounted for 10% of all glaucoma surgeries.

Glaucoma and heredity

According to another poster, Shoham and colleagues examined glaucoma and heredity. It is well known that primary open angle glaucoma demonstrates a hereditary pattern. In this study, the researchers reviewed data from 17 pairs of first-degree relatives with glaucoma.

Among the parents, 13 had OAG and three had normal tension glaucoma (NTG), while in the children, two had ocular hypertension (OHT), 11 had OAG and three had NTG. In the one group of twins, one had OAG and the other had NTG.

This work highlights that while glaucoma may be hereditary, it can vary from one form to another among individuals in the same family. Individuals with glaucoma should ensure that their first-degree relatives are examined for the condition.

Adult stature may predict occludable angle

Previous research has shown that taller individuals appear to have longer globes and deeper anterior chambers. A study reported in another WGC poster indicates that adult height indeed appears to be related to anterior chamber depth.

An estimated 33 million people have primary angle closure glaucoma worldwide, and the challenge is to detect those at risk and likely to develop an attack.

Chang and colleagues conducted a population-based, cross-sectional survey of adult Chinese living in a certain district in Singapore. The researchers grouped participants based upon height. Other data collected included anterior chamber depth, gonioscopy findings, IOP, refraction and socioeconomic information.

Surprisingly, adult height appears to be related to anterior chamber depth — but not gonioscopic angle width — with shorter stature associated with reduced depth. The use of patient height may be part of a rapid screening assessment to identify those at greatest risk of ACG.

SL-OCT, Visante results comparable

Fan and colleagues measured central corneal thickness and anterior chamber depth with SL-OCT (Heidelberg Engineering, Vista, Calif.) and Visante OCT (Carl Zeiss Meditec, Dublin, Calif.). Both instruments are commercially available and used to evaluate the anterior chamber visually as well as provide depth measurements.

The measurements between the instruments were comparable, showing good agreement. The mean difference between the two instruments was -2.75 µm.

Diabetes, hyperglycemia, CCT

Su and colleagues looked at the relationship between diabetes, hyperglycemia and central corneal thickness (CCT). In this group, the mean CCT was 541.2 µm, with 23 (748) having diabetes. Those with diabetes have significantly greater CCT (547.2 µm) (P < 0.001), and CCT was greater with higher serum glucose levels and HgA1C levels.

After adjusting for age, body mass index, IOP and axial length, patients with diabetes had, on average, CCT 6.5 µm greater than those without diabetes.

World Glaucoma Association

The next World Glaucoma Congress will be held July 8-11, 2009, in Boston. This meeting will appeal to optometrists interested in glaucoma, with an opportunity to listen and learn about glaucoma from the world’s experts. Information on the meeting as well as the World Glaucoma Association (WGA) is available at www.worldglaucoma.org.

The WGA is an umbrella organization comprising societies representing glaucoma specialists worldwide. Member societies include the American Glaucoma Society, Chinese Glaucoma Society, Asian-Oceanic Glaucoma Society, European Glaucoma Society, Latin American Glaucoma Society, Japanese Glaucoma Society and the Optometric Glaucoma Society.

The WGA is “an independent, impartial, ethical, global organization for glaucoma science and care.” The WGA’s mission is to “optimize the quality of glaucoma science and care through communication and cooperation among international glaucoma societies, with glaucoma industries, glaucoma patient organizations and all others in the glaucoma community.”

For more information:

• Murray Fingeret, OD, is chief of the optometry section at the Department of Veterans’ Affairs Medical Center in Brooklyn and Saint Albans, N.Y., and is a professor at SUNY College of Optometry. He is also a member of the Primary Care Optometry News Editorial Board. He may be reached at St. Albans VA Hospital, Linden Blvd. and 179th St., St. Albans, NY 11425; (718) 298-8498; fax: (516) 569-3566; e-mail: murryf@optonline.net. Dr. Fingeret has no direct interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
• Information on the World Glaucoma Association and World Glaucoma Congress is available at www.worldglaucoma.org.