Table 1.
Characteristics and quality of studies included in the meta-analysis.
| Author(s) year | Country | Diagnostic criteria | Mean duration (months) | Motor and cognitive function | Number of eyes | Mean age (years) | Sex (men/women) | Newcastle-Ottawa Scale (NOS) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PD | HC | PD | HC | PD | HC | Selection | Comparability | Exposure | Total score | |||||
| Altintaş 2008 [15] | Turkey | UKBB | 54.96 | UPDRS | 34 | 22 | 59.29 | 58.09 | 9/8 | 6/5 | 3 | 1 | 3 | 7 |
| Antal 2000 [16] | Austria | NR | 58.1 | UPDRS, H&Y, ADL, MMSE | 40 | 40 | 65.3 | 59.8 | 13/7 | 13/7 | 2 | 2 | 3 | 7 |
| Bodis-Wollner 1978 [2] | USA | NR | 97.8 | NR | 70 | 52 | 62 | 60 | NR | NR | 2 | 1 | 2 | 5 |
| Buttner 1996 [18] | Germany | NR | 64.8 | UPDRS, H&Y | 78 | 86 | 64.0 | 62.8 | 20/19 | 18/25 | 2 | 1 | 3 | 6 |
| Cubo 2014 [19] | Spain | UKBB | 98.4 | SPES/SCOPA, H&Y, MMSE | 60 | 60 | 65.4 | 62.9 | 18/12 | 15/15 | 3 | 1 | 3 | 7 |
| Daniels 1994 [9] | UK | NR | NR | NR | 32 | 40 | 64.36 | 66.95 | NR | NR | 2 | 1 | 3 | 6 |
| Deng 2006 [25] | China | CMA | NR | NR | 64 | 60 | 64 | 64 | 20/12 | 19/11 | 2 | 1 | 2 | 5 |
| Ehle 1982 [8] | USA | NR | 65 | H&Y | 50 | 36 | 64 | 56 | NR | NR | 2 | 1 | 3 | 6 |
| Garcia-Martin, Elena 2014 [20] | Spain | UKBB | 92.4 | H&Y, SE-ADL | 46 | 33 | 70.72 | 69.67 | 29/17 | 21/12 | 3 | 2 | 3 | 8 |
| Gawel 1981 [7] | England | NR | NR | NR | 94 | 52 | 67 | 63 | 30/17 | 11/15 | 2 | 1 | 3 | 6 |
| Kaur, Marpreet 2015 [21] | India | UKBB | 69.6 | H&Y, UPDRS | 40 | 40 | 58.6 | 58.4 | NR | NR | 3 | 1 | 3 | 7 |
| Kuporsmith 1982 [23] | USA | NR | NR | H&Y | 28 | 28 | 62 | 58 | NR | NR | 2 | 1 | 2 | 5 |
| Li 2004 [26] | China | CNCESD | 56.4 | UPDRS, H&Y, HDS | 140 | 120 | 62.2 | 59.9 | 32/38 | 28/32 | 3 | 1 | 3 | 7 |
| Miri 2016 [22] | USA | UKBB | NR | MMSE | 20 | 16 | 66.3 | 66.5 | NR | NR | 3 | 2 | 3 | 8 |
| Okuda 1995 [10] | Japan | NR | 52.4 | H&Y, MMSE | 42 | 44 | 67.4 | 70.3 | 8/14 | 11/11 | 2 | 1 | 3 | 6 |
| Okuda 1996 [24] | Japan | NR | 52.9 | H&Y, MMSE | 36 | 24 | 65.7 | 67.3 | NR | NR | 2 | 1 | 3 | 6 |
| Peppe 1995 [27] | Italy | NR | 13.3 | UPDRS, H&Y | 36 | 16 | 62.5 | 61.2 | NR | NR | 2 | 1 | 3 | 6 |
| Quagliato 2014 [28] | Brazil | UKBB | 83.76 | UPDRS, H&Y | 86 | 76 | 63.1 | 62.4 | 27/16 | 17/21 | 3 | 1 | 3 | 7 |
| Sagliocco 1997 [17] | Austria | NR | 31.25 | H&Y, MMSE | 34 | 33 | 61.94 | 54.53 | 8/9 | 9/8 | 2 | 1 | 3 | 6 |
| Sartucci 2006 [3] | USA | UKBB | 26.4 | UPDRS, H&Y | 21 | 24 | 60.1 | 46.8 | 6/6 | 6/6 | 3 | 1 | 3 | 7 |
PD = Parkinson's disease; HC = healthy controls; NR = not reported; UKBB = United Kingdom Brain Bank clinical diagnostic criteria; UPDRS = Unified Parkinson's Disease Rating Scale; H&Y = Hoehn and Yahr Scale; SE-ADL = Schwab and England Activities of Daily Living Scale; MMSE = Mini-Mental State Examination; SPES/SCOPA = Short Parkinson's Evaluation Scale/Scales for Outcomes in Parkinson's disease; CMA = Chinese Medical Association clinical diagnostic criteria; CNCESD = Chinese National Conference on Extra-Pyramidal System Disease diagnostic criteria; HDS = Hasegawa Dementia Scale.