Is retina affected in Huntington's disease? Is optical coherence tomography a good biomarker?

Prospective cross-sectional measurement of peripapillary retinal nerve fiber layer thickness (RNFL) and total macular volume (TMV) measured by spectral domain optical coherence tomography (OCT) of retina, Pelli-Robson Contrast Sensitivity test, Farnsworth 15 Hue Color discrimination test, and Unified Huntington’s disease Rating Scale (UHDRS).

Methods
Patients were assessed by Unified Huntington's disease Rating Scale (UHDRS). Pelli-Robson Contrast Sensitivity test Chart 4K, which uses a single large letter size (20/60 optotype) with contrast varying across groups of letters, was used to evaluate Contrast Sensivity. A Pelli-Robson score of 1.5 to 2.25 indicates normal Contrast Sensitivity, a score of 0.9 to 1.35 indicates moderate contrast loss, a score of 0.3 to 0.75 severe contrast loss and a score of 0.15 and less indicates profound contrast loss. Farnsworth D-15 Color test was performed to evaluate Color Discrimination. The results of the Farnworth D-15 test determine color perception or defects in deutan, protan or tritan discrimination.

Using a spectral-domain OCT machine (Heidelberg Spectralis), without pupil dilation, we obtained a circular scan manually centered on the optic nerve head (diameter 3.4mm, Automated Real-Time - ART 100) and a macular volume scan centered on the fovea (63 lines, ART 20). The thickness of the peripapillary retinal nerve fiber layer (RNFL) in µm and total macular volume (TMV) in mm3 was automatically determined by the instrument (Heyex version 5.8). All retinal images were checked for scan quality. We analyzed the mean peripapillary RNFL thickness (RNFL-G) as the main measure of axonal health in the retina and the thickness of RNFL in the temporal peripapillary segment (RNFL-T) that represents the most vulnerable retinal fibers. We also used total macular volume (TMV) measured in the area of a 6 mm wide circular mask to represent global retinal changes.