Evaluation of Retinal Vessel Morphology in Patients with Parkinson's Disease Using Optical Coherence Tomography

Abstract

Purpose: The retina has been found affected in Parkinson's disease (PD). It is unclear if this is due to neurodegeneration of local dopamine-dependent retinal cells, a result of central nervous degeneration including the optic nerve or retinal small vessel disease. This study aimed to detect changes of the retinal vasculature in PD patients compared to controls.

Methods: We examined 49 PD patients and 49 age- and sex-matched healthy controls by spectral domain optical coherence tomography (SD-OCT) with a circular scan centred at the optic disc. Vessels within the retinal nerve fibre layer were identified by an automated algorithm and thereafter manually labelled as artery or vein. Layer segmentation, vessel lumen and direct surrounding tissue were marked automatically with a grey value and the contrast between both values in relation to the surrounding tissue was calculated. The differences in these grey value ratios among subjects were determined and used as an indicator for differences in vessel morphology. Furthermore, the diameters of the veins and arteries were measured and then compared between the groups.

Results: The contrast of retinal veins was significantly lower in PD patients compared to controls, which indicates changes in vessel morphology in PD. The contrast of arteries was not significantly different. Disease duration, disease stage according to Hoehn and Yahr or age did not influence the grey value ratios in PD patients. Vessel diameter in either veins or arteries did not differ between subject groups. The contrast of retinal veins contralateral to the clinically predominant and first affected side was significantly lower compared to the ipsilateral side.

Conclusion: Our data show a potential difference of the retinal vasculature in PD patients compared to controls. Vascular changes in the retina of PD patients might contribute to vision-related complaints in PD.

Fig 1. Schematic illustration of the SD-OCT-based analysis.

The approaching light is reflected and scattered by the vessels. The hypothesis is that the characteristics of the change in contrast resemble the vessel morphology. In this image the simplified calculation of the change in grey value is achieved by comparing the mean grey value of the blue boxes with that of the green box.

Fig 2. SD-OCT-based vessel analysis.

The red line symbolises the detected vessels; the line drops when there is a vessel in the SD-OCT scan. The grey value of the vessel is measured, and depicted as the green box. This is compared to the grey value of the surrounding tissue, represented as blue boxes.

Fig 3. Comparison of the SD-OCT-based vessel analysis between patients with Parkinson’s disease (PD) and healthy control patients.

Using a paired t-test, PD patients had a significantly lower grey value contrast for veins compared to controls (mean of differences = -3.877±4.464; p-value<0.0001). The grey value contrast for arteries was not different between the groups (p-value = 0.2926).

Fig 4. Correlation of the vessel contrast change in patients with PD with parameters of disease progression and age.

(A) Disease duration did not correlate with the vessel contrast (p-value>0.05). (B) The clinical progression chart Hoehn and Yahr did not correlate with the vessel contrast (p-value>0.05). (C) The age of the patients did not correlate with the vessel contrast (p-value>0.05).

Fig 5. Comparison of the vessel contrast change between the dominant and non-dominant side of PD patients.

The grey value vessel ratio for veins was significantly different (p-value = 0.0060), while arteries showed no significant difference (p-value>0.05).