Preferred Retinal Loci and Fixation Stability in Patients with Bilateral Ischemic Optic Neuropathy

Abstract

Purpose: To determine if patients with a bilateral ischemic optic neuropathy develop a preferred retinal locus (PRL) and asess their fixation stability.

Methods: A retrospective review of 11 patients with bilateral ischemic optic neuropathy, seen in Vision Rehabilitation clinic. These patients underwent a history, ophthalmic examination and SLO microperimetry (Optos). A suprathreshold strategy was used for microperimetry testing and static fixation testing was performed with the patient fixating on a cross for 5-20 seconds. A template was made marking the fovea and disc margin in a healthy patient. This was used to identify the approximate position of the fovea, and determine if there was a PRL present. Fixation stability was assessed by two methods. The first was the clinical classification proposed by Fujii et al. (2002) which categorizes the dynamic fixation data captured during microperimetery testing. Fixation is classified as being either "stable", "relatively unstable" or "unstable". The second method was using a 68% bivariate contour ellipse area (BCEA), which is based on the static fixation data obtained when the patient fixates on a cross.

Results: There were 21 eyes included in the study. A no light perception eye was excluded from the study as no microperimetry data could be obtained. The mean age in this group was 63.9 years of age (SD 10.8 years), and the mean visual acuity was logMar 0.70 (SD 0.55). The mean duration of disease was 17 months (SD 26 months). PRLs were found in 11/21 eyes (52%) and were bilateral in 4/7 patients (57%). The odds of developing a PRL increased 1.51 times for every 0.1 unit increase in logMAR (p = 0.04) and decreased by 2% for every 1 month increase in duration. By Fujii classification 10/21 (48%) of eyes had "stable" fixation and 11/21 (52%) had "relatively unstable" fixation. The odds of a "relatively unstable" Fujii classification increased 3.52 times (p= 0.09) for patients who had a PRL compared to patients who did not have one. The mean BCEA was 1.66 deg² (SD 2.49 deg²) and there was no effect of the presence of a PRL on the BCEA.

Conclusions: Patients with bilateral ischemic optic neuropathy can develop a PRL and this is more likely to occur in eyes with a worse visual acuity. There were no patients who were classified as having "unstable" dynamic fixation and patients with a PRL were more likely to have "relatively unstable" fixation.