Fixation parameter test-retest repeatability of the worse eye in central field loss

Objective

Patients with bilateral central field loss develop peripheral retinal loci (PRLs) in the functional eccentric retina. PRL characteristics and visual performance in the better-seeing eye (BE) of these patients have previously been reported. In this study, we determined the test-retest repeatability of fixation parameters, including fixation stability, PRL eccentricity, and PRL span in the worse-seeing eye (WE).

Design

Retrospective consecutive case series.

Participants

Thirty-six patients with bilateral central field loss referred from the Toronto Western Hospital Retina Clinic, who had completed 2 consecutive fixation examinations on the same day.

Methods

Fixation stability was recorded using the Nidek MP-1 microperimeter (Nidek Technologies Srl., Padova, Italy). For each fixation recording, the following parameters were retrieved: (i) 68.2% bivariate contour ellipse area (BCEA), (ii) PRL span (major and minor axes of the BCEA), (iii) PRL meridian (polar angle), and (iv) PRL eccentricity. Test-retest repeatability for each parameter was assessed using Bland-Altman plots to determine 95% limits of agreement.

Results

The mean difference between the fixation trial pairs and the 95% limits of agreement for fixation stability, PRL major axis, PRL minor axis, PRL meridian, and PRL eccentricity were 0.06 ± 0.47 log deg², 0.05° ± 1.42°, 0.07° ± 0.63°, ?0.44° ± 66.0°, and ?0.23° ±1.56°, respectively.

Conclusions

The fixation parameters in the WE showed robust repeatability, comparable to that of the BE as determined from previous studies. The WE’s fixation repeatability should be considered in the interpretation of fixation outcome measures subsequent to treatment interventions.