Opening the angle and lowering intraocular pressure with peripheral iridotomy and phacoemulsification

Peripheral iridotomy and phacoemulsification are effective in opening the angle and lowering intraocular pressure (IOP) in patients with angle closure and angle-closure glaucoma, but questions remain regarding precisely when to employ either technique, said Augusto Azuara-Blanco MD, Queen’s University Belfast, UK, at a Glaucoma Day session at the XXXIII Congress of the ESCRS in Barcelona, Spain.

He noted that primary angle-closure glaucoma tends to be greatly underdiagnosed. Current estimates are that it occurs overall in about 0.4 per cent of people over the age of 40 and in 0.94 per cent of those over 70 years of age. However, research has not established what percentage of eyes with primary angle closure will go on to develop an elevated IOP or glaucomatous damage.

“Compared with open-angle glaucoma, there are very few trials concerning angle closure and angle-closure glaucoma so we have less direction about what to do,” said Prof Azuara-Blanco.

TREATMENT GUIDELINES

Since primary angle closure suspects have a very low risk of visual loss, their recommended treatment is laser peripheral iridotomy. The question of whether peripheral iridotomy can prevent angle-closure glaucoma in eyes with narrow angles in the long-term remains a topic of research, he said.

He noted that early reports from the Zhongshan Angle Closure Prevention (ZAP) trial indicate that the procedure is safe in primary angle closure suspects, causing only a temporary IOP elevation in around ten per cent of patients. However, the reports also indicate that the opening of the angle achieved through the procedure diminishes over time.

When angle closure progresses to angle-closure glaucoma, the European Glaucoma Society’s Guidelines recommend peripheral iridotomy and topical medication. However, the guidelines leave the options open regarding patients with an inadequate response to iridotomy and medication.

Prof Azuara-Blanco recommended using trabeculectomy if the iridotomy opens the angle but leaves IOP uncontrolled. In eyes where the angle remains closed but IOP is controlled, he recommended monitoring the condition. When the angle remains closed and IOP remains uncontrolled, he recommended phacoemulsification in mild cases and phacotrabeculectomy in more severe cases.

He noted that the rationale behind lens extraction for primary angle-closure glaucoma is based on the phacomorphic pathogenesis of the disease. Lens growth, which is age-related, leads to increased pupillary block which in turn leads to angle closure. Patients who undergo lens extraction for primary angle-closure glaucoma also have a much wider open angle after cataract surgery than they do after laser iridotomy.

Studies indicate that phacoemulsification and trabeculectomy achieve similar reductions in IOP in eyes with angle-closure glaucoma. And although those undergoing trabeculectomy require fewer medications, they also have more complications than those who undergo phacoemulsification. Moreover, around a third of patients undergoing trabeculectomy go on onto develop cataracts as a result.

A study that is now under way, the EAGLE study, asks the question of whether primary lens extraction in primary angle closure and primary angle-closure glaucoma is effective and safe as well as cost-effective. Prof Azuara-Blanco said that he expects to present results from the study at the 12th European Glaucoma Society Congress in Prague in June.

DIFFICULT CASES

There are many special considerations to keep in mind when performing phacoemulsification in eyes of patients with primary angle-closure glaucoma. For example, biometry is less predictable in hyperopic eyes than in emmetropic or myopic eyes, and the inaccuracy increases with the degree of hyperopia. However, the refractive outcome achieved in the first eye can be used to adjust the intraocular lens choice in the second eye.

Some of the surgical difficulties involved in eyes with angle-closure glaucoma include shallow anterior chamber, positive posterior pressure, poor pupil dilation and goniosynechiae. Furthermore, those with previous acute attacks are prone to weak zonules and compromised epitheliums.

Prof Azuara-Blanco recommended using a cohesive viscoelastic or else a spatula under gonioscopic view when performing a goniosynechialysis. He added that clear corneal incisions rather than limbal incisions should be used to avoid iris prolapse.

Augusto Azuara-Blanco: a.azuara-blanco @qub.ac.uk