Temporal placement of a laser peripheral iridotomy is safe and is less likely to result in linear dysphotopsia than if the PI is placed superiorly

The Science behind the Tip

To prevent pupil block, a laser peripheral iridotomy (PI) is the initial treatment for patients with primary angle-closure/glaucoma. When placed superiorly, 2-4% of patients subsequently report linear dysphotopsia (1) (2). This is described as a hazy, hair-like horizontal line, silver or blue-grey in colour, worse in bright light and less pronounced in dim light. The cause is thought to be an optical aberration secondary to the base-up prismatic effect of the tear meniscus, particularly when the PI is partially covered by the upper lid (2).

In a recent trial, 10.7% of patients had linear dysphotopsia after a superiorly placed PI (6.5% despite complete lid coverage) compared with 2.4% of patients after a temporal PI (3). Ophthalmologists should warn patients of this visual consequence of laser PI and should consider placing the PI in the temporal peripheral iris.

Contributor: John Salmon, Oxford, UK

References

1. Murphy PH, Trope GE Monocular blurring. A complication of YAG laser iritotomy. Ophthalmology 1991; 98: 1539-42

2. Spaeth GL, Idowu O, Seligson A et al. The effect of iridotomy size and positions or symptoms following laser peripheral iridotomy. J Glaucoma 2005; 14:364-7.

3. Vera V, Naqi A, Belovay GW et al. Dysphotopsia after temporal versus superior laser peripheral iridotomy: a prospective, randomised paired eye trial. Am J Ophthalmol 2014; 157: 929-35

Tip Reviewer: Roger Hitchings
Tip Editors: John Salmon and Gordana Sunaric Mégevand