5. Visual evoked potentials, contrast sensitivity and foveal optical coherence tomography in Parkinson’s disease patients

Abstract

Background and objective Impaired vision and remodeled foveal pit are demonstrated in Parkinson’s disease (PD) patients. Visual evoked potentials (VEPs) reflect abnormality anywhere in the retina to cortex pathways. We evaluated the correlation between the VEP, contrast sensitivity (CS) and foveal thickness in PD and assessed diagnostic yield of their combination. Methods Ten PD (20 eyes) and eight HC subjects (16 eyes) were enrolled in the study. The two groups were matched for age, gender and ethnicity ( P > 0.05). All subjects underwent standard neurological and ophthalmological examination to exclude any pathology. CS was evaluated using Pelli-Robson chart. Two-channel VEP was recorded on each subject with two different stimuli (pattern reversal, frequency of 2.3 cpd; and on/off pattern frequency of 4.6 cpd). N70 and P100 were recorded. Macular optical coherence tomography (OCT) scans were obtained using Zeiss-HD OCT and macular thickness, volume and ganglion cell layer-inner plexiform layer (GCL-IPL) thickness were extracted. Statistical analysis was performed using SPSS software (version 21.0). Results PD patients had a significantly longer N70 (reversal pattern) and P100 (on/off pattern) latency (86.7 ± 10.2 and 132.9 ± 8.7 ms, respectively) compared to healthy controls (78.8 ± 6.6 and 125.5 ± 11.5 ms, respectively) ( P = 0.01 and P = 0.03). CS score was significantly lower in PD patients (1.66 ± 0.21 vs. 1.89 ± 0.15; P = 0.001). PD patients had decreased thickness at the distance of 1.5–2.5 mm from the foveola (perifovea) (255.0 ± 6.5μ vs. 264.9 ± 18.7μ; P = 0.03). N70 latency was negatively correlated with CS ( R = −0.419, P = 0.01) and average GCL-IPL thickness ( R = −0.529, P = 0.001). CS was positively correlated with parafoveal thickness ( R = 0.490, P = 0.002). A combination of parafoveal thickness and CS score yielded an AUC of 0.784, which increased to 0.844 when combined with N70 and P100 measures. Conclusion Visual function is correlated with foveal morphology. A combination of VEP parameters, CS score, and foveal thickness has a high diagnostic yield for PD.