Argon laser iridoplasty effective in occludable eyes treated with iridotomy

Argon laser peripheral iridoplasty (ALPI) significantly widens the anterior chamber angle circumferentially in eyes with occludable angles treated with laser peripheral iridotomy, researchers say.

ALPI also reduces diurnal IOP fluctuation and might limit damage to the trabecular meshwork, reported Rupert R.A. Bourne, of Anglia Ruskin University in Cambridge, United Kingdom, and colleagues.

They published their finding in the British Journal of Ophthalmology.

In ALPI, clinicians direct an argon laser to create a circle of burns on the peripheral iris, contracting the iris stroma near the angle.

ALPI widens the anterior change angles of eyes presenting with plateau iris syndrome where the angle remains occludable after laser peripheral iridotomy. It has been used in both acute primary angle closure (PAC) and primary angle closure glaucoma (PACG).

Immediately after an angle closure attack, ALPI has proven more effective than systemic medications in lowering IOP.

Diurnal IOP fluctuation decreases with increases in the dimensions of the anterior change angle in untreated patients with a diagnosis of PAC suspect, or PAC in both eyes.

Bourne and colleagues wanted to know how temporal change in anterior chamber angle anatomy and diurnal IOP following ALPI in eyes with gonioscopically occludable angles post laser peripheral iridotomy compared with eyes receiving no further treatment.

They recruited 22 patients whose eyes remained gonioscopically occludable after being treated with laser peripheral iridotomy. They randomly assigned 11 eyes to receive ALPI and 11 to receive no further treatment.

They examined the eyes with swept-source optical coherence tomography (OCT) and measured their IOP with Goldmann tonometry.

They observed a statistically widening effect in 1 week in all parameters and sections following ALPI treatment. The widening of angle parameters at 750 µm from the sclera spur was similar to that observed for all parameters at 500 µm from sclera spur. The change was maintained for 3 months in 7 of the 8 sections.

Inferotemporal angle opening distance (AOD) 500 increased by 0.063 mm (P = 0.004) at 1 day, 0.051 mm (P = 0.029) at 1 week, 0.059 mm (P = 0.006) at 6 weeks, and 0.056 mm (P = 0.011) at 3 months.

The exception was in the inferior sector. AOD500 increased by 0.041 mm, (P = 0.025) at 1 day and 0.029 mm (P = 0.054) at 3 months.

The researchers observed similar results for the trabecular-iris angle (TIA) 500 and the angle recess area (ARA) 500 and the trabecular-iris space area (TISA) 500.

At 3 months, diurnal IOP was significantly reduced (5.04 mm Hg; ±1.61 mm Hg) compared with controls (6.61 mm Hg; ±1.63 mm Hg). Maximum diurnal IOP was significantly greater in the non-ALPI group (1.87 mm Hg, P=0.026), and this accounted for the overall difference in diurnal IOP.

The angle parameters in all the eyes increased following laser peripheral iridotomy prior to the ALPI randomization. And all the eyes that underwent ALPI due to the angle remaining gonioscopically occludable after peripheral iridotomy became non-occludable and stayed that way for 6 weeks.

At 3 months, the researchers observed some regression of angle parameters, but the changes were not statistically significant.

The researchers speculated that a longer follow-up might show eventual decrease of the widening effect of the ALPI, and they acknowledged that the relatively short follow-up for this study was a limitation.

In one previous study, researchers found that only 7 of 11 eyes treated with ALPI maintained IOP reduction at 6 months. In another study of 158 patients with primary angle closure and primary angle closure glaucoma, IOP dropped more in eyes treated with both ALPI and peripheral laser iridotomy 12 months after the treatments. It was not clear in either of these studies whether the measurements were taken at the same time of day.

In a third study, in eyes with persistent appositional angle closure and raised IOP, ALPI reduced IOP on average by 4.9 mm Hg and achieved IOP of <21 mm Hg without medication in 35% of the patient. After a year, ALPI was associated with higher failure rates and lower IOP reduction compared with medical treatment.

“The finding that ALPI significantly widens the anterior chamber angle circumferentially may confer protection from the onset or progression of existing damage to the trabecular network,” the researchers concluded. “The reduction in [diurnal IOP] fluctuation caused by the ALPI is likely to be related to these changes in anterior chamber dimensions.”