Impaired Ganglion Cell Function Objectively Assessed by the Photopic Negative Response in Affected and Asymptomatic Members From Brazilian Families With Leber's Hereditary Optic Neuropathy

Abstract

Purpose: The photopic negative response (PhNR) is an electrophysiological method that provides retinal ganglion cell function assessment using full-field stimulation that does not require clear optics or refractive correction. The purpose of this study was to assess ganglion cell function by PhNR in affected and asymptomatic carriers from Brazilian families with LHON. Methods: Individuals either under suspicion or previously diagnosed with LHON and their family members were invited to participate in this cross-sectional study. Screening for the most frequent LHON mtDNA mutations was performed. Visual acuity, color discrimination, visual fields, pattern-reversal visual evoked potentials (PRVEP), full-field electroretinography and PhNR were tested. A control group of healthy subjects was included. Full-field ERG PhNR were recorded using red (640 nm) flashes at 1 cd.s/m², on blue (470 nm) rod saturating background. PhNR amplitude (μV) was measured using baseline-to-trough (BT). Optical coherence tomography scans of both the retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC) were measured. PhNR amplitudes among affected, carriers and controls were compared by Kruskal-Wallis test followed by post-hoc Dunn test. The associations between PhNR amplitude and OCT parameters were analyzed by Spearman rank correlation. Results: Participants were 24 LHON affected patients (23 males, mean age=30.5 ± 11.4 yrs) from 19 families with the following genotype: m.11778G>A [N = 15 (62%), 14 males]; m.14484T>C [N = 5 (21%), all males] and m.3460G>A [N = 4 (17%), all males] and 14 carriers [13 females, mean age: 43.2 ± 13.3 yrs; m.11778G>A (N = 11); m.3460G>A (N = 2) and m.14484T>C (N = 1)]. Controls were eight females and seven males (mean age: 32.6 ± 11.5 yrs). PhNR amplitudes were significantly reduced (p = 0.0001) in LHON affected (-5.96 ± 3.37 μV) compared to carriers (-16.53 ± 3.40 μV) and controls (-23.91 ± 4.83; p < 0.0001) and in carriers compared to controls (p = 0.01). A significant negative correlation was found between PhNR amplitude and total macular ganglion cell thickness (r = -0.62, p < 0.05). Severe abnormalities in color discrimination, visual fields and PRVEPs were found in affected and subclinical abnormalities in carriers. Conclusions: In this cohort of Brazilian families with LHON the photopic negative response was severely reduced in affected patients and mildly reduced in asymptomatic carriers suggesting possible subclinical abnormalities in the latter. These findings were similar among pathogenic mutations.

Keywords: electroretinography; leber's hereditary optic neuropathy; photopic negative response; retinal ganglion cell; visual evoked cortical potentials.

Figure 1

Photopic negative response amplitude (BT) from LHON affected patients, LHON asymptomatic carriers and controls (each box shows the median, quartiles, and extreme values; circles represent the subjects).

Figure 2

Representative PhNR recordings with amplitudes measured by both BT (left panels) and PT (right panels) from an m.11778G>A LHON affected (A13–upper panels), his unaffected carrier sister (C 5–middle panels) and a healthy 41-year-old male control (lower panels).

Figure 3

Receiver Operating Characteristic (ROC) curve for affected vs. controls plotted at best cut-off at 11.72 μV for PhNR amplitude (BT) showing high sensitivity and specificity with area under the curve (AUC) = 0.997 (95%CI: 0.990–1.000).

Figure 4

There was a significant correlation between PhNR (BT) and total macular ganglion cell complex (GCC) from LHON affected patients (N = 24), asymptomatic carriers (N = 14) and controls (N = 8).

Figure 5

(A) Retinal nerve fiber layer thickness in the 360-degree average from LHON affected patients, LHON asymptomatic carriers and controls (each box shows the median, quartiles, and extreme values; circles represent individual subjects); (B) Total macular ganglion cell complex thickness from LHON affected (each box shows the median, quartiles, and extreme values; circles represent individual subjects).

Figure 6

RNFL thickness in each quadrant of LHON affected, LHON asymptomatic carriers and controls, showing a significantly thinner RNFL in all quadrants for LHON affected compared to carriers and controls (p < 0.0001).

Figure 7

Foveal OCT scan from subject A8's right eye. Segmentation identifies macular microcysts of inner nuclear layer (INL) as pointed by the yellow arrow. Retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL) and outer plexiform layer (OPL) are shown on the right panel.