Retinal measurements associated with Parkinson’s disease duration

By Sarah Pritchard, medwireNews Reporter

The inner retinal layers in the eyes of patients with Parkinson’s disease (PD) are thinner than those of healthy people’s eyes, except for the inner nuclear layer, which is thicker, show the results of a prospective study involving the latest optical coherence tomography (OCT) methods.

Inner retinal layers were also more greatly affected in PD patients with a disease duration of 10 years or more versus those who were diagnosed more recently, report the researchers in the American Journal of Ophthalmology.

“OCT technology allows for precise measurements of retinal layer thickness, and these measurements may reflect the number of human retinal cells with dopaminergic activity”, explain Elena Garcia-Martin (Miguel Servet University Hospital, Zaragoza, Spain) and colleagues.

They examined the retinal layers in the eyes of 129 patients with PD and 129 age- and gender-matched healthy controls. The PD patients had a mean 8.4-year disease duration and were aged a mean 68.8 years. Controls were 69.0 years old on average.

Using OCT with an automated system that separates the retina into 10 layers, the team observed significant reductions in the thickness of the retinal nerve fibre layer (RNFL) in PD patients compared with controls, at 6.06 versus 6.26 µm, in the ganglion cell layer, at 6.30 versus 6.49 µm, and the inner and outer plexiform layers, at 6.64 and 7.17 µm, respectively, versus 6.77 and 7.31 µm.

By contrast, the inner nuclear layer was significantly thicker in PD patients versus controls, at 7.39 versus 7.14 µm.

RNFL, ganglion cell layer and inner plexiform measurements were all significantly thinner in PD patients with at least 10 years’ disease duration compared with those who were diagnosed more recently, at 5.89 versus 6.06 µm, 5.96 versus 6.40 µm and 6.11 versus 6.47 µm.

“This could be attributable to primary neurodegeneration of the retinal ganglion cells and their axons in [PD] patients or to retrograde trans-synaptic degeneration of the retinal ganglion cell layer and its axons owing to [PD] lesions of the posterior visual pathways”, note Garcia-Martin et al.

They add that ganglion cell layer thickness was borderline significantly inversely associated with PD duration, and in regression analysis, only ganglion cell layer thickness predicted PD axonal damage.

The team suggests that future research using OCT is needed to determine the extent to which each retinal layer could predict PD in its early stages.

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