Table 1 Demographics and clinical assessments.

Characteristic	Controls n = 30	PD high visual performers n = 58	PD low visual performers n = 30	Statistic
Age (years)	66.8 (9.3)	66.8 (9.3)	64.4 (8.0)	0.001^b
Male (%)	13 (43.3)	13 (43.3)	48 (54.5)	0.334
Years of education	17.7 (2.5)	17.7 (2.5)	17.1 (2.9)	0.098
Vision
Contrast sensitivity (Pelli–Robson)^a	1.8 (0.2)	1.8 (0.2)	1.7 (0.1)	<0.001^b
Acuity (LogMar)^a	−0.08 (0.2)	−0.08 (0.2)	−0.08 (0.1)	0.441
Colour vision (D15)	1.3 (1.3)	1.1 (0.8)	1.6 (1.8)	0.334
General cognition
MOCA	28.8 (1.3)	28.8 (1.3)	27.9 (2.4)	0.003^b
MMSE	29 (1.1)	29 (1.1)	28.9 (1.3)	0.573
Mood
HADS anxiety	3.7 (3.4)	3.7 (3.4)	5.9 (3.1)	0.023^b,c
HADS depression	1.9 (1.4)	1.9 (1.4)	4.1 (3.1)	<0.001^b,c
Disease-specific measures
Years from diagnosis	–	3.7 (2.6)	4.5 (2.6)	0.061
UPDRS total score	–	44.2 (25.5)	49.9 (26.8)	0.315
UPDRS motor score	–	23. 2 (14.1)	24.3 (14.8)	0.785
LEDD	–	411.1 (273.5)	479.4 (201.2)	0.099
RBDSQ	–	4.4 (2.7)	4.0 (2.1)	0.832
Image quality metrics
Coefficient of joint variation^d	0.69 (0.3)	0.69 (0.3)	0.67 (0.2)	0.925
Entropy focus criterion^d	0.59 (0.1)	0.59 (0.1)	0.59 (0.1)	0.167
Total Signal to noise ratio^e	1.89 (0.2)	1.89 (0.2)	1.85 (0.2)	0.314
Mean framewise displacement^e	0.17 (0.1)	0.17 (0.1)	0.19 (0.1)	0.056

All data shown are mean (SD) except gender.
In bold characteristics that significantly differed between groups.
HADS Hospital anxiety and depression scale, MMSE Mini-mental state examination, MOCA Montreal cognitive assessment, UPDRS Unified Parkinson’s Disease Rating Scale, LEDD Levodopa Equivalent Dose, RBDSQ REM sleep behaviour disorder scale.
^aBest binocular score used; LogMAR: lower score implies better performance, Pelli–Robson: higher score implies better performance.
^bStatistically significant difference between PD and controls.
^cStatistically significant difference between PD high visual performers and PD low visual performers.
^dHigher values imply worse image quality.
^eHigher values imply better image quality.

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