This study was approved by the ethics committee of Kartal Dr. Lütfi Kırdar City Hospital with 2021/514/215/3 decision number and was performed in accordance with the Declaration of Helsinki. All patients were informed about the purpose of the study and informed consent was obtained.
Patients with genetic neuropathy meeting the clinical and/or electromyography (EMG) diagnostic criteria defined by Piscotta et al. were included in the study . Patients with the following clinical presentation were included in the study: Patients with normal early developmental process followed by gradual weakness and sensory loss during the first two decades of life, positive family history and/or presentations in childhood, slow progression, the presence of foot deformities, and no positive sensory symptoms (e.g. dysesthesias, paresthesias) in the presence of sensory signs. Inflammatory, toxic, or infectious polyneuropathies and those accompanying other genetic diseases (such as metachromatic leukodystrophy, Refsum disease) were not included in the study.
All patients underwent a comprehensive neuro-ophthalmologic examination including color vision, visual field (30−2 SITA program, Humphrey VFA; Carl Zeiss, USA), visual acuity, intraocular pressure measurement, and fundus examinations. Snellen chart was used for visual acuity [evaluated as logarithm of the minimum angle of resolution (LogMAR)] and color vision was assessed using Ishihara color plate testing.
Secondary optic nerve or retinal diseases such as glaucoma, papillitis, optic neuropathies of different etiologies, or age-related macular degeneration were considered as exclusion criteria.
Optical coherence tomography
The GCC and RNFL thicknesses were obtained using SD-OCT (Nidek RS-3000 Advance, Japan). The peripapillary RNFL thickness in each 90-degree quadrant (superior, inferior, temporal, and nasal) was calculated within a 3.45-mm diameter scan circle around the optic disc. The GCC thickness was accepted as between the internal limiting membrane and the inner plexiform layer in the macular region. In the GCC chart (Nidek RS3000), the macular region was divided into two sectors around the fovea as superior and inferior (in 9 mm size). Only high-quality scans with high reliability were assessed in the analysis. All SD-OCT parameters were analyzed by the same experienced technician.
Visual evoked potential
Visual evoked potential recordings (EMG/EP MEB-2300K, Nihon Kohden, Tokyo, Japan) were performed according to International Society for Clinical Electrophysiology of Vision (ISCEV) standards . The study was done in a dark and quiet room at a 1 m distance by the same technician. According to the International 10-20 system, the active electrode was at Oz and the reference electrode was at Fz location. Visual stimulation was performed using a white and black checkerboard, using a pattern-reversal method at 1/sec frequency with a check size 50′. The recordings were evaluated separately for each eye. At least 100 stimuli from two recordings were averaged. The P100 wave was defined as the first major positive peak response with a latency of approximately 100 milliseconds (ms). The latency of P100 wave and amplitude were evaluated. For our laboratory, the normal ranges were 98-115 ms for the P100 latency and 5.8-16 microvolts (µV) for the P100 amplitude. Abnormal P100 latency was considered as values above the mean ± 2SD of the normal group.
All data were evaluated using the IBM SPSS Statistics Standard Concurrent User V 26 statistical package program (IBM Corp., Armonk, New York, USA). Descriptive statistics are given as the number of units (n), percent (%), mean ± standard deviation, median (M), minimum (min), maximum (max), and interquartile range (IQR). The normality of data distribution of the numerical variables was evaluated using the Shapiro-Wilk test of normality. Age comparisons were made using the Mann-Whitney U test. A comparison of eye parameters was performed using the Kruskal-Wallis H test. Dunn-Bonferroni test was used as a multiple comparison test. Chi-square and Fisher’s exact tests were used to compare groups with categorical variables. Correlations between age variables and eye parameters were evaluated using Spearman correlation analysis. The results were rated according to the variation of the rho range as weak (0.0-0.19), low (0.20-0.39), moderate (0.40-0.59), strong (0.60-0.79), and very strong (0.80–1.00) correlations. A p-value of <0.05 was accepted statistically significant.