Functional evaluation of retina, macula, and optic nerve in high myopia

Purpose The aim of this study was to evaluate the retinal and postretinal function in the patients with high myopia using a battery of visual electrophysiological tests. Patients and methods A retrospective cross-sectional study was conducted on 120 eyes of 120 participants, who were divided into two groups: 60 patients with high myopia [spherical equivalent more than −6.0 diopters and/or axial length (AL) of 26.5 mm or more] and 60 participants of age and sex matched emmetropic controls. Only one eye per participant in each group was included in the analysis. All participants underwent a full-field electroretinography, multifocal electroretinography (mfERG), pattern electroretinography (PERG), and visual evoked potentials (VEP) according to the International Society for Clinical Electrophysiology of Vision standards. Optical coherence tomography (OCT) was performed to correlate the structural parameters with the functional outcomes. Results All electrophysiological responses were significantly reduced in the high myopic eyes in comparison to the control group ( P <0.05). The full-field electroretinography illustrated a significantly reduced scotopic combined dark-adapted 3.0 a-wave and b-wave responses in the high myopia group compared with the controls (a-wave: 242±48 vs. 280±44 μV, P =0.009, b-wave: 438±85 vs. 510±72 μV, P =0.002) and significantly reduced photopic 30 Hz flicker amplitudes (146±34 vs. 180±32 μV, P =0.002). In comparison to controls, the high myopia patients exhibited significantly reduced mfERG P1 central amplitudes (15.2±4.8 vs. 28.9±6.0 μV, P <0.001) and peripheral amplitudes (25.4±7.1 vs. 39.7±7.5 μV, P <0.001), along with a significantly delayed mfERG P1 implicit time (38.6±3.2 vs. 36.1±2.8 ms, P =0.002). In addition, the PERG P50 amplitude was significantly reduced in the high myopia group than in the controls (2.4±0.6 vs 3.2±0.5 μV, P <0.001). Similarly, the PERG N95 amplitudes were markedly reduced in the myopia group compared with the controls (3.6±1.1 vs. 6.1±1.3 μV, P <0.001) with a significant prolongation of the N95 implicit time (103.2±7.8 vs. 98.4±6.2 ms, P =0.011). The VEP results also revealed a significant delay in the P100 latency (118.7±7.9 vs. 103.2±5.6 ms, P <0.001) and reduced P100 amplitude in the high myopia group compared with the controls (7.4±2.0 vs. 9.1±2.1 μV, P =0.008). The mfERG P1 amplitude showed significant correlations with the AL (r=–0.58, P <0.001), subfoveal choroidal thickness (SFCT) (r=+0.58, P <0.001), and central macular thickness (r=+0.42, P =0.006). In addition, the PERG N95 amplitude showed significant correlations with the AL (r=–0.56, P <0.001), SFCT (r=+0.47, P =0.003), central macular thickness (r=+0.35, P =0.021), as well as the retinal nerve fiber layer (RNFL) thickness (r=+0.51, P =0.001). The VEP P100 latency showed significant correlations with the SFCT (r=–0.28, P =0.047), RNFL thickness (r=–0.39, P =0.012), and AL (r=+0.49, P =0.002). Conclusion The electrophysiological tests demonstrated a multi-layer dysfunction in high myopia, affecting the photoreceptor, macular, and ganglion cell function. The combined ERG and VEP testing provided sensitive biomarkers for the functional impairment in high myopia and complemented the structural imaging.