Significant proportion of patients with narrow angle are myopic

COS 2012, July 6 - A significant proportion of patients whose eyes have narrow angles are myopic, according to a retrospective review done by Kingston researchers, suggesting that ophthalmologists need to evaluate angles in all patients regardless of refractive status.

Sarah Simpson, a medical student at Queen's University, Kingston, Ont., and colleagues from Hotel Dieu Hospital described the refractory status in 224 patients with narrow angles who had undergone laser peripheral iridotomy (LPI) at the hospital between August 2006 and March 2011. Patients were classified as myopic if they had a spherical equivalent of < 0 diopters (D) and hyperopic if they had a spherical equivalent > 0 D.

In this cohort, 62 patients were found to be myopic (about 28%) and 161 were found to be hyperopic (about 72%). "Ninety-eight patients (44%) had a refractive status of between 0 and +2 D," Simpson said. Four patients (2%) were highly myopic with a spherical equivalent > 5 D of myopia.

Almost two-thirds of patients' eyes were within 2 D, and over one-third were within 1 D of emmetropia - suggesting they barely needed corrective lenses. Conventional understanding is that patients with narrow angle would be more hyperopic, making this finding unexpected.

Immersion A scans were performed to determine ocular biometry in a small proportion of each group. A-scan results revealed that myopic patients had significantly longer axial lengths than hyperopic patients, "suggesting that myopia was secondary to axial length and not lenticular thickness, as lens thickness did not differ between groups," Simpson said.

Axial lengths appeared to be independent of interior chamber depth. "Interior chamber depth also appeared to be correlated with narrow angles and may be a surrogate for narrow angles," she added.

Evaluation of mean angle opening after LPI showed an average of one Shaffer grade of opening across all refractions, with no differences between groups. This observation suggests it's important to re-evaluate patients' angle status following LPI. It was also observed that the post-procedural angle opening was not very dramatic.

"The implication is that you can't decide to look at a patient's angle solely based on the kind of prescription lenses they are wearing," said co-investigator Dr. Delan Jinapriya, assistant professor of ophthalmology at Queen's.

Traditionally, ophthalmologists only examine angles in hyperopic patients, believing that myopic patients or those who those who don't wear prescription lenses couldn't have narrow angles. However, this is not the case. "When you look at patients' angles, most of them are around neutral on the refractory spectrum from negative to positive," Jinapriya said.