Ganglion cell-inner plexiform layer thickness in patients with Parkinson disease and association with disease severity and duration.

BACKGROUND: To evaluate the average, minimum, and 6-sectoral macular ganglion cell-inner plexiform layer (GC-IPL) thickness measured by spectral domain optical coherence tomography (SD-OCT) in patients with Parkinson disease (PD), as well as average and 4-sectoral retinal nerve fiber layer (RNFL) thickness and to determine whether thickness parameters are correlated to disease severity and duration.
METHODS: Patients with PD (n = 54) and age-matched healthy controls (n = 54) were prospectively examined with SD-OCT. Randomly selected eyes of all subjects were included. The average, minimum, and 6-sectoral (superior, superotemporal, superonasal, inferonasal, inferior, and inferotemporal) GC-IPL thickness values were analyzed. Average and 4-sectoral (inferior, superior, temporal, and nasal) peripapillary RNFL thicknesses were also evaluated. Each parameter was compared between patients with PD and age-matched healthy controls. PD severity was quantified with the Hoehn and Yahr (HY) scale. A correlation analysis was performed to evaluate the association between SD-OCT measurements and the duration and severity of PD.
RESULTS: The mean age of patients with PD and age-matched healthy controls was 66.62 ± 8.71 years and 66.68 ± 7.85 years, respectively. Disease duration ranged from 1 to 15 years with a mean of 5.12 years. The mean PD severity, according to the HY scale, was 2.26 (range, 1-5). SD-OCT measurements revealed significant differences in inferior and temporal peripapillary RNFL values between groups (P = 0.018 and P = 0.031, respectively). All GC-IPL thickness parameters were statistically lower in the patients with PD when compared with the healthy controls (P < 0.001). PD duration was not correlated to any of the RNFL thicknesses, but PD severity was correlated inversely only with inferior peripapillary RNFL thickness (P = 0.006). Average, inferior (P = 0.011), inferotemporal (P = 0.007), and superotemporal (P = 0.007) GC-IPL thicknesses were correlated inversely with both PD severity and duration.
CONCLUSIONS: Retinal dopaminergic neurodegeneration in patients with PD can be detected with macular GC-IPL thickness measurements. Macular GC-IPL thickness was correlated with PD severity and duration. It may be used to follow disease progression and efficacy of the neuroprotective treatment in patients with PD.