New research published in Investigative Ophthalmology & Visual Science assessed the longitudinal rate of change of retinal microvascular and structural parameters in Parkinson’s disease (PD) compared to controls.
Give me some background first.
There has been an increasing interest in leveraging optical coherence tomography (OCT) to identify ophthalmic biomarkers related to Parkinson’s disease progression.
Prior studies have demonstrated that decreased macular perfusion density (PFD) and increased peripapillary capillary PFD are linked with PD.
Now talk about the study.
This longitudinal study was led by the Eye Multimodal Imaging in Neurodegenerative Disease (iMIND) group from the Duke University School of Medicine.
The research group compared 74 eyes of 40 patients with PD (60% male, mean age = 67.4±7.9 years) to 149 eyes of 78 controls (28% male, mean age = 70.3±5.8 years).
How did they evaluate ophthalmic biomarkers?
Investigators utilized OCT angiography (OCT-A), specifically Early Treatment for Diabetic Retinopathy Study (ETDRS) 6x6 zones (circle, inner ring, and outer ring), and 3x3 zones (circle and inner ring) to measure changes in retinal microvasculature.
Key ophthalmic biomarkers that were assessed with OCT-A included:
- Superficial capillary plexus PFD
- Vessel density (VD)
- Foveal avascular zone (FAZ)
These results were compared with OCT imaging of:
- Peripapillary retinal nerve fiber layer (RNFL) thickness
- Ganglion cell-inner plexiform layer (GC-IPL) thickness
- Central subfield thickness (CST)
How often did they evaluate ophthalmic biomarkers?
These ophthalmic biomarkers were measured at two time points roughly 1 year apart over a mean interval of 22.8 months.
Of note, 2 years is a relatively short amount of time to measure PD progression.
Researchers noted that PD was associated with a greater decline in macular PFD in the:
- 6x6 circle (mean change/year in PD -0.021 vs. control 0.00, p=0.001)
- 6x6 inner ring (PD -0.018 vs. control 0.001, p=0.007)
- 6x6 outer ring (PD -0.022 vs. control 0.00, p=0.001)
- 3x3 circle (PD -0.016 vs. control 0.002, p<0.001)
- 3x3 inner ring (PD -0.016 vs. control 0.002, p<0.001)
What about vascular density?
Similarly, investigators observed PD patients had a greater decline in VD in the:
- 6x6 circle (mean change/year in PD -0.072/mm vs. control -0.054/mm, p=0.006)
- 6x6 inner ring (PD -0.636/mm vs. control -0.048/mm, p=0.03)
- 6x6 outer ring (PD -0.746/mm vs. control -0.054/mm, p=0.005)
- 3x3 circle (PD -0.939/mm vs. control 0.006/mm, p<0.001)
- 3x3 inner ring (PD -0.942/mm vs. control 0.013/mm, p<0.001)
And GC-IPL thickness?
Additionally, PD was linked with a greater decrease in GC-IPL thickness (mean change/year in PD -0.403μm vs. control 0.128μm, p=0.01).
No statistically significant differences in the rate of change were observed in FAZ, CST, and RNFL thickness, as well as when stratified by PD severity.
This study demonstrates that over the span of 2 years, PD patients experience more rapid loss of superficial capillary plexus PFD and VD— as well as accelerated GC-IPL thinning—compared to healthy controls with normal cognition.
The study authors stated that this data potentially indicates that the velocity of decline may be higher in patients with more severe PD, though further studies with larger sample sizes are required to validate this observation.