Neovascular glaucoma associated with increased risk for hypotony after TCP

The total laser energy delivered did not appear to influence the rate of postop hypotony.

Issue: July 25, 2012

Preoperative diagnosis of neovascular glaucoma was associated with an increased risk for developing hypotony after transscleral diode cyclophotocoagulation, or TCP, according to a study. Furthermore, the rate of hypotony after treatment with TCP did not appear to be influenced by the total laser energy delivered.

“A preoperative diagnosis of neovascular glaucoma was associated with an increased risk of developing hypotony after TCP by a factor of nine,” study co-author Shamira Perera, MBBS, BSc, FRCOphth, a consultant ophthalmologist at Singapore National Eye Centre, said. “We looked into other factors that conventionally one would think might increase hypotony rates, such as higher energy levels used, older patient age or a history of previous failed glaucoma operations, but our univariate analysis of these factors was not found to be significant. Even patients who had repeat treatment with TCP were not found to be at higher risk for hypotony.”

The retrospective case series consisted of 90 eyes of 90 patients (mean age: 59.1 years) who underwent TCP at the Singapore National Eye Centre between 2005 and 2007. The most common underlying diagnosis was neovascular glaucoma (38.9%), followed by post-pars plana vitrectomy or silicone oil-induced glaucoma (12.2%) and other secondary glaucomas (10%).

All TCP treatment was delivered with an 810-nm semiconductor diode laser. The mean preoperative IOP was 41.8 mm Hg, which decreased to 20.7 mm Hg at 1 month and 17.8 mm Hg at 1 year.

Success rate, defined as the percentage of patients who attained an IOP of 5 mm Hg to 21 mm Hg, with or without medication, by 1 year was 54%. However, hypotony developed in 39% of patients.

The mean total energy per session was 83.3 J and the re-treatment rate was 13.3%.

The study was published in the Journal of Glaucoma.

Energy levels

The authors expected similar findings as in a study by Kaushik and colleagues in which lower energy levels were needed for TCP in an Asian population, Dr. Perera told Ocular Surgery News.

“Despite using on average even lower energy levels than in that study, 87.8 J, we had higher rates of hypotony,” Dr. Perera said.

In another study, Spencer and colleagues concluded that no cases of hypotony occurred after using less than 60 J of energy.

“However, our study did not find a safe level of total energy at which hypotony would not occur,” Dr. Perera said. “This is the first study at Singapore National Eye Centre to assess how patients fared, despite it being a relatively common glaucoma procedure.”

Hypotony

The study also found the rate of hypotony after TCP to be much higher than reported in the literature, which ranges up to 18%.

“The major factor for our high 39% rate of hypotony seems to be the case mix,” Dr. Perera said. “We included patients with more severe refractory disease. More than half of the eyes had a baseline visual acuity of no perception to light, far greater than other studies. Plus, almost 40% carried a diagnosis of neovascular glaucoma. The major indication for TCP in these eyes was purely palliative — in other words, to treat a painful blind eye. Prior studies in the literature involved a less severe spectrum of patients with better baseline visual acuities on average.”

Occasionally the hypotony is transient, but trying to salvage these eyes once hypotony is established is challenging, Dr. Perera said.

“Be wary of eyes with neovascular glaucoma, as there may be an element of ocular ischemia and aqueous hyposecretion present,” Dr. Perera advised. “Use conservative energy levels during TCP because the dose-response relationship is unpredictable. Patients should also be counseled about the risk of hypotony, as well as the possibility of re-treatment should the IOP control be inadequate in the longer term.”

A prospective follow-up study with a well-defined approach for neovascular glaucoma eyes could help determine a safe level of energy at which hypotony may be prevented, Dr. Perera said. – by Bob Kronemyer

For more information:

Kaushik S, Pandav SS, Jain R, Bansal S, Gupta A. Lower energy levels adequate for effective transcleral diode laser cyclophotocoagulation in Asian eyes with refractory glaucoma. Eye (Lond). 2008;22(3):398-405.
Ramli N, Htoon HM, Ho CL, Aung T, Perera S. Risk factors for hypotony after transscleral diode cyclophotocoagulation. J Glaucoma. 2012;21(3):169-173.
Spencer AF, Vernon SA. “Cyclodiode”: results of a standard protocol. Br J Ophthalmol. 1999;83(3):311-316.

For more information:

Shamira Perera, MBBS, BSc, FRCOphth, can be reached at Singapore National Eye Centre, 11 Third Hospital Ave., Singapore 168751; 65- 96312157; email: shamiraperera@hotmail.com.
Disclosure: Dr. Perera has no relevant financial disclosures.