Detection of retinal changes in Parkinson's disease with spectral-domain optical coherence tomography

Abstract

Purpose: This pilot study investigated whether high-resolution spectral-domain optical coherence tomography (SD-OCT) could detect differences in inner retinal layer (IRL), peripapillary retinal nerve fiber layer (RNFL), and macular thickness between patients with Parkinson's disease (PD) and controls.

Methods: Both eyes of patients with PD and age-matched controls were imaged with the Heidelberg Spectralis(®) HRA + OCT. RNFL, IRL, and macular thickness were measured for each eye using Heidelberg software. These measurements were compared with validated, published normal values for macular and RNFL thickness, and compared with matched controls for IRL thickness.

Results: Eighteen eyes from nine subjects with PD and 19 eyes of 16 control subjects were evaluated using SD-OCT. The average age of PD patients was 64 years with a range of 52-75 years. The average age of controls was 67 years with a range of 50-81 years. No significant reduction in IRL thickness was detected between PD patients and age-matched controls at 13 points along a 6 mm horizontal section through the fovea. No significant difference in RNFL thickness was detected between PD patients and published normal values. Overall average RNFL thickness was 97 μm for PD patients, which exactly matched the normative database value. However, significant differences in macular thickness were detected in three of nine subfields between PD subjects and published normal values. In PD subjects, the outer superior subfield was 2.8% thinner (P = 0.026), while the outer nasal and inner inferior subfields were 2.8% (P = 0.016) and 2.7% (P = 0.001) thicker compared to published normal values.

Conclusion: In this pilot study, significant differences in macular thickness were detected in three of nine subfields by SD-OCT. However, SD-OCT did not detect significant reductions in peripapillary RNFL and IRL thickness between PD patients and controls. This suggests that macular thickness measurements by SD-OCT may potentially be used as an objective, noninvasive, and easily quantifiable in vivo biomarker in PD. Larger, longitudinal studies are needed to explore these relationships further.

Keywords: Parkinson’s disease; inner retinal layer thickness; macular thickness; nerve fiber layer thickness; spectral-domain optical coherence tomography.

Figure 1

OCT image of the retina of the left eye. The layers of the inner retinal layer (IRL) are shown: retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), and inner nuclear layer (INL). Dopaminergic cells have been isolated primarily to the INL of the primate retina.

Figure 2

Screen grab from the Heidelberg Eye Explorer software automated analysis of the RNFL thickness. A) Infrared image showing the location of the circular scan (green circle) centered around the optic nerve (green cross) of the right eye. B) Circular optical coherence tomography image of the retina showing the RNFL segmented (red lines). C) RNFL thickness measurements in seven sectors as measured by the software. D) Plot of patient’s RNFL thickness (black line) plotted against normative values (colored lines). Abbreviation: RNFL, retinal nerve fiber layer.

Figure 3

Screen grab from the Heidelberg Eye Explorer software analysis of macular thickness. Infrared image (A) of the posterior pole of the right eye of a Parkinson’s disease patient with superimposed thickness map (multicolored box) and grid corresponding to the nine subfields measured in (B).

Figure 4

High-resolution spectral-domain optical coherence tomography image of a section through the fovea of the right eye of a control patient showing segmentation of the inner retinal layer (red lines). Yellow arrowheads correspond to the 13 points at which the IRL was measured in Parkinson’s disease patients and age-matched controls in the study. These points were equally spaced at 500 μm intervals along a 6 mm horizontal line centered on the fovea.