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Prophylactic iridotomy effective on ‘occludable’ eyes, surgeon says

ByLauren Wolkoff

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BANGKOK – Laser peripheral iridotomy is effective as a prophylactic tool in eyes that are at risk for angle-closure glaucoma, according to a surgeon here. “Occludable” eyes are those in which the trabecular meshwork cannot be visualized, but there is still an open channel for aqueous egress, the surgeon said.

Prin Rojanapongpun, MD, shared an Asian perspective on angle closure.

“Laser peripheral iridotomy (LPI) is effective as a prophylactic procedure in occludable eyes. However, in primary angle closure and primary angle-closure glaucoma, the effectiveness of LPI is variable and depends on the stage of disease and the mechanisms of angle-closure glaucoma,” Dr. Rojanapongpun said.

Studies in Asian patients have shown distinctions among occludable eyes and those with primary angle closure and primary angle-closure glaucoma in their responses to LPI, he said.

One such study was a population-based survey conducted in Mongolia, he said. In 1987 and 1989, 98 subjects with occludable angle were identified and treated with LPI to keep pressure normal. When these patients were re-examined in 1998, the study concluded that 97% of eyes had responded favorably to the laser treatment, in that they had maintained a normal pressure and had avoided an acute attack.

The outcome among patients with more advanced angle closure was less encouraging, and even less so among a group with primary angle closure with glaucoma, he said.

“In the specific group of primary angle closure (patients), LPI would work about 50% of the time to prevent the rise in IOP, based on the retrospective study,” he said.

Among patients whose angle closure had progressed to glaucoma, the survey showed poor results from LPI. Only about 6% of these eyes had control of IOP from the laser surgery, while 94% failed to respond to the laser treatment, according to Dr. Rojanapongpun.

“If one asks whether LPI eliminates angle closure, I can share with you that, especially in Asian eyes, this does not seem to be necessarily the case,” he said. “This is because most Asian eyes will have more than one angle closure mechanism that contributes to the development of angle closure. This has been evidenced by the fact that 40% of postiridotomy eyes will still have positive provocative tests.”

Terminology is key

Dr. Rojanapongpun stressed the importance of understanding the terminology related to angle closure before trying to address treatment options.

“The terminology used is still variable and lacks consistency,” he said. “However, to comprehend the outcome of treatment in angle-closure glaucoma, it is crucial for practitioners to appreciate the importance of using accurate terminology to describe the different conditions of this disorder.”

He defined angle closure as “an anatomical disorder caused by the abnormal relationship of the anterior segment structures, resulting in a mechanical blockage of the anterior chamber.” With angle closure, IOP can rise acutely or gradually, he added.

Dr. Rojanapongpun drew the distinction between primary angle closure, primary angle-closure glaucoma and occlusion.

“Primary angle closure is not the same as primary angle-closure glaucoma, and the term ‘occludable’ refers to the eye that has the potential for the angle to become occluded. This means the IOP and disc are still normal,” he said.

Occludable eyes may exhibit closure of the trabecular meshwork without peripheral anterior synechiae.

Because occludable eyes are still unaffected by glaucomatous disease, it is not too late to employ prophylactic methods, he said.

“Prophylactic LPI is performed in a case of occludable angle where such structural or functional defect has not yet occurred. Thus prophylactic LPI is reserved to be used in the eye that is labeled as occludable or primary angle-closure suspect,” he said.

Dr. Rojanapongpun cited retrospective data on 80 occludable eyes that underwent prophylactic LPI. None of these patients developed an acute closed-angle attack, he said.

“By investigating the effectiveness of the LPI, by differentiating the stages of the disease, one can get a pretty good idea that it works most of the time on occludable angles, and that it doesn’t work that well on angle-closure glaucoma,” he said.

For Your Information:

• Prin Rojanapongpun, MD, is chief of research and glaucoma service, Ophthalmology Department, Chulalongkorn University, 1873 Rama 4 Road, Bangkok, Thailand 10330; +(66) 2-256-4421; fax: +(66) 2-252-8290; e-mail: rprin@chula.ac.th.