Table 3.

Direction of effects in the included studies using optical coherence tomography angiography (OCT-A) to assess retinal microvasculature in Parkinson’s disease (PD) and its subgroups compared to healthy controls (HC).

Study (Optovue)	FAZ area	Superficial parafoveal VD	Superficial inferior VD	Superficial superior VD	Superficial whole VD	Superficial foveal PFD	Superficial parafoveal PFD	Superficial inferior PFD	Superficial superior PFD	Deep parafoveal VD	Deep inferior VD	Deep superior VD	Deep Whole VD	Deep parafoveal PFD	Macular VD	Optic Disc	RPC peripapillary VD
Rascuna et al. (2020) [40]	-	-	-	-	∼	-	-	-	-	-	-	-	∼	-	-	-	-
Shi et al. [29]	-	-	-	-	-	-	↓	↓	↓	-	-	-	-	∼	-	-	-
Kwapong et al. [26]	-	↓	↓	↓	-	-	-	-	-	∼	-	-	-	-	-	-	-
Lin et al. [7]	-	-	-	-	-	-	-	-	-	↓H-Y II + III*	-	-	-	-	-	↓H-Y II + III*	-
Li et al. [41]	-	-	-	-	↑	-	-	-	-	-	-	-	↑	-	-	-	∼

Study (Zeiss)	FAZ area	Superficial parafoveal VD	Superficial inferior VD	Superficial superior VD	Superficial whole VD	Superficial foveal PFD	Superficial parafoveal PFD	Superficial inferior PFD	Superficial superior PFD	Deep parafoveal VD	Deep inferior VD	Deep superior VD	Deep Whole VD	Deep parafoveal PFD	Macular VD	Optic Disc	RPC peripapillary VD
Robbins et al. (A) [37]	∼	↓	-	-	↓	-	↓	-	-	-	-	-	-	-	-	-	-
Robbins et al. (B) [38]	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	↑PFD average, sup, inf, temp, nas	-
Zhou et al. [34]	∼	-	-	-	-	-	-	-	-	-	-	-	-	-	↓inner sup sector** ↓all sectors***	-	↓outer sup sector ∼other sectors
Zou et al. [30]	∼	↓	-	-	↓	↓	↓	-	-	-	-	-	-	-	-	-	-
Xu et al. [35]	↓ ↓H-Y III* ↓H-Y I	↓	↓	↓	-	-	-	-	-	-	-	-	-	-	↓ all sectors ↓H-Y III: fovea, SI, II, NI, TI, TO* ∼ SO, IO, NO* ↓ H-Y III: all sectors	-	∼ ∼ between PD subgroups

Study (Heidelberg)	FAZ area	Superficial parafoveal VD	Superficial inferior VD	Superficial superior VD	Superficial whole VD	Superficial foveal PFD	Superficial parafoveal PFD	Superficial inferior PFD	Superficial superior PFD	Deep parafoveal VD	Deep inferior VD	Deep superior VD	Deep Whole VD	Deep parafoveal PFD	Macular VD	Optic Disc	RPC peripapillary VD
Murueta-Goyena et al. [32]	↓ ↓PD-MCI****	-	-	-	-	↑	∼	-	-	-	-	-	-	∼	-	-	-

Study (SS-OCT)	FAZ area	Superficial parafoveal VD	Superficial inferior VD	Superficial superior VD	Superficial whole VD	Superficial foveal PFD	Superficial parafoveal PFD	Superficial inferior PFD	Superficial superior PFD	Deep parafoveal VD	Deep inferior VD	Deep superior VD	Deep Whole VD	Deep parafoveal PFD	Macular VD	Optic Disc	RPC peripapillary VD
Zhang et al. [39]	-	-	-	-	-	↓	↓	↓	↓	-	-	-	-	↓	-	-	-
Satue et al. [23]	-	-	∼	∼	-	-	-	-	-	-	-	-	-	-	∼	-	-

(The information presented in the table is about the comparison of Parkinson’s disease and healthy controls except for the items specified in the table).

VD Vessel density, PFD Perfusion density, FAZ Foveal avascular zone, RPC Radial peripapillary capillary, sup Superior, inf Inferior, temp Temporal, nas Nasal, PD Parkinson’s disease, H-Y Hoehn-Yahr stage scale, SI Superior inner, II Inferior inner, NI Nasal inner, TI Temporal inner, SO Superior outer, IO Inferior outer, NO Nasal outer, TO Temporal outer, MCI Mild cognitive impairment, SS-OCT Swept source optical coherence tomography.

-Data not reported, ∼no significant difference, ↓significant decrease, ↑:significant increase.

*Compared to PD subgroups (H-Y I & II & III), **in 6x6mm2 field of view, ***in 3 x 3 mm2 field of view, ****compared to PD-NC (Normal cognition).