Table 1.

Main characteristics of eligible studies^a.

Author, country, year	Study design	No. of participants/no. of eyes	Males/females	Mean age ± SD	Mean disease severity score ± SD	Mean PD duration	Mean UPDRS score ± SD	Adjustments	NOS
Kwapong et al., China, 2018	Cross- sectional	38/49 PD 28/34 controls	NR NR	62.95 ± 7.97 61.18 ± 5.74	NR NR	3.84 ± 2.80 NA	NR NR	Age and IOP	9/10
Berkowitz et al., USA, 2020	Cross- sectional	7/14 PD NR/135 controls	NR NR	NR NR	NR NR	NR NR	NR NR	Age matching	8/10
Rascunà et al., Italy, 2020	Cross- sectional	21/41 PD 17/33 controls	12/9 9/8	61.5 ± 6.5 65.1 ± 10.7	HY: 1.9 ± 0.4 NA	2.28 ± 1.19 NA	25.0 ± 6.9 3.2 ± 2.7	None	7/10
Shi et al., China, 2020	Cross- sectional	25/50 PD 25/50 controls	13/12 13/12	61.9 ± 7.6 59.0 ± 5.8	HY: 2.2 ± 1.0 NA	3.7 ± 2.4 NA	NR NR	Age and sex matching	9/10
Zou et al., China, 2020	Cross- sectional	35/35 PD 35/35 controls	16/19 20/15	61.86 ± 5.46 60.20 ± 6.75	HY: 1.7 ± 0.7 NA	3.2 ± 2.0 NA	NR NR	Age matching	8/10
Robbins et al., USA, 2020	Cross- sectional	69/124 PD 137/248 controls	15/14 10/16	71.7 ± 7.0 70.9 ± 6.7	MMSE: 28.4 ± 2.4 MMSE: 29.0 ± 2.8	NR NA	30.9 ± 6.7 NA	Age and sex matching	9/10
Zhang et al., China, 2021	Cross- sectional	42/75 PD 75/150 controls	NR 32/43	55.92 ± 7.53 54.68 ± 6.66	HY: 1.42 ± 0.55 NA	3.2 ± 2.0 NA	16.92 ± 7.6 NA	Age, sex, IOP, inter-eye correlation	9/10
Murueta-Goyena et al., Spain, 2021	Cross- sectional	49/87 PD 40/73 controls	33/16 13/27	64.6 ± 7.9 62.1 ± 8.0	MoCA: 24.4 ± 4.1 MoCA: 25.7 ± 2.5	7.1 ± 4.1 NA	16.92 ± 7.6 NA	Age, sex, and hypertension	9/10
Zhou et al., China, 2021	Cross- sectional	24/24 PD 23/23 controls	18/6 11/12	65.88 ± 6.50 63.43 ± 7.11	HY: 2.0 ± 0.3 MMSE: 28.5 ± 1.6 NA	5.3 ± 4.2 NA	26.5 ± 12.3 NA	Age, sex, and hypertension	9/10

^aPD Parkinson’s disease, HY Hoehn and Yahr, MMSE Mini-Mental State Exam, MoCA Montreal Cognitive Assessment, NOS Newcastle-Ottawa Scale, NR not reported, NA not applicable, SD standard deviation.