Retinal changes detected by diffuse reflectance spectroscopy in parkinsonian monkeys

Significance: Parkinson's disease (PD) is diagnosed when 50% neurodegeneration has occurred. The retina could provide biomarkers that would allow for earlier diagnosis. Retinal spectroscopy is a technique that could be used to find such biomarkers. Aim: We aimed to find new diagnostic biomarkers for PD following detailed spectral examinations of the retina. Approach: ) before and after the administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin used to produce the gold-standard animal model of PD. From the spectrometric data, the blood oximetry was calculated, and the diffuse reflectance spectra (DRS) were analyzed to find variations between the two experimental conditions. Post-mortem analyses were also performed on the retina of the four parkinsonian monkeys and four additional control animals. Results: The analysis of the DRS indicated a lower slope between the 480- and 525-nm wavelengths in both the ONH and the retina. Post-mortem measurements of the retinal layer thicknesses showed that the outer nuclear layer was significantly thinner in MPTP-intoxicated monkeys, compared with controls. Altogether, these results indicate that MPTP altered the optical properties of the ONH and the retina and show that these variations might be explained by MPTP-induced structural changes in the eye fundus, as observed post-mortem. Conclusions: Overall, our results indicate that spectroscopy could be used as a noninvasive method to detect changes in the retina that occur in PD and that such changes could represent retinal biomarkers for improved diagnosis.