Evaluation of visual field metrics in patients with central scotomas from LHON

Abstract

Purpose: Patients with large and dense central scotomas may be unable to reliably complete Stimulus size III (Stim III) Humphrey Visual Fields (HVF). These patients, however, do considerably better with Stimulus size V (Stim V) HVF. In Leber’s Hereditary Optic Neuropathy (LHON) the reliability of the HVF varies over the course of the disease. The purpose of this study was to determine if Stim III and Stim V mean deviation (MD) calculations are equivalent in patients with central scotomas from LHON.

Methods: 10 patients with LHON were administered Stim III and Stim V HVF tests on the same day during multiple patient visits. Stim III MD values were obtained from the HVF algorithm. In addition, separate Stim III and Stim V MD values were obtained from an investigative algorithm (IA). This IA, developed by the University of Iowa Visual Field Reading Center, was used to derive patients' MD from Stim III and Stim V HVF raw numerical data. The MD values from the HVF and IA were compared using a Pearson’s product-moment correlation coefficient.

Results: A total of 72 observations, 10 patients and 18 eyes were analyzed. Stim III HVF and IA: r^2=0.99, HVF mean MD=-26.1 with standard deviation (STD)=+/-6.72. IA mean MD=24.1 with STD=+/-6.30. Mean absolute difference between HVF and IA =1.98 with STD=+/-0.769. IA Stim III MD and Stim V MD: r^2=0.415, Stim V mean MD=-21.2 with STD=+/-5.52. Mean absolute difference between IA Stim III and Stim V MD=1.98 with STD=+/-2.97.

Conclusions: There was near perfect correlation of Stim III MD between HVF and IA, validating the algorithm. MD values for Stim III and Stim V, however, were not interchangeable. This may reflect the variability that comes from visualizing the smaller stimulus in subjects with a dense central scotoma.