## 3 Results
### Study Characteristics  
Seven publications fulfilled our inclusion criteria. They were classified into three groups, according to the nature of the compared disease entities. The first group consisted of three studies focusing on the differentiation between patients with typical (PD) and atypical Parkinsonism (PSP, MSA, and CBS) based on retinal parameters, as assessed with OCT [9; 19; 20]. The second group comprised three studies investigating the retinal morphology and its potential role in distinguishing patients with PD versus patients with PSP [21; 22; 23]. Finally, one study explored the value of retinal parameters through OCT in a setting of dementia associated with the presence of Lewy bodies or Parkinson's disease [24] (Table 1).  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Authors,** & **Number of** & **Type of** & **Assessed Retinal** & **Cutoff Values;** & \\
**Year of** & **Participants** & **Implemented** & **Parameters** & **(Specificity);** & **Main Results** \\ \hline
**Application** & & & & & ONL/OPL ratio & The mean total macular \\  & 35 healthy controls & & & & cutoff of 3.1 for & thickness and volume of \\  & 84 patients & Spectral domain & pRNFL, & differentiation & & patients with PSP \\ Albrecht & - 40 PD & optical coherence & paramacular & between PSP and & reduced compared with \\  & - 40 PD & tomography with & thickness and & PD (96\%); [59\%], & & patients with PD, while \\  & - 19 MSA & manual & volume, thickness & ONL/OPL ratio & the ONL/OPL ratio & combined with INL \\  & - 10 CBS & segmentation & of all retinal layers & with INL cutoff of & changes within group \\  & - 15 PSP & & & & [70\%] & with PSP may serve as a \\  & & & & & & diagnostic marker \\ \hline
**Application** & & & & & Retinal parameters of \\  & 41 healthy controls & Spectral domain & & ONL/OPL ratio & & not significantly \\ Schneider & 93 patients & OCT with a & RNFL, GCL + IPL, & cutoff of 5.03 for & different that those of \\  & - 65 PD & semiautomatic & INL, OPL, ONL, & discrimination & healthy individuals, \\
[19] & - 16 PSP & algorithm & WRT & between PSP and & while opposite changes \\  & - 12 MSA & algorithm & & MSA (88\%); [91\%] & of ONL/OPL ratios \\  & & & & MSA & were reported between \\  & & & & & patients’ groups with \\  & & & & & PSP and MSA \\ \hline
**Application** & & & & & Specific patterns of \\  & & & & & & retina alterations were \\  & & & & & reported among patients \\  & 14 healthy controls & & & & with PD and atypical \\  & 52 patients & & & & Parkinsonism with a \\  & - 24 PD & Spectral domain & macular thickness & & macular thinning in \\  & - 19 MSA & OCT & and volume & & patients with PD and \\  & - 9 PSP & & & MSA and a higher \\  & & & & & repairapillary RNFL \\  & & & & thickness in patients \\  & & & & & with PSP \\ \hline
**Application** & & & & & RNFL thickness \\  & & & & & cutoff of 93 \(\mu\)m in \\  & & & & patients with & was observed in eyes \\  & 12 healthy controls & & & disease duration of & from patients with PSP \\  & & & & & as compared with those \\  & 23 patients & Spectral domain & & & of patients with PD with \\  & - 12 PD & OCT & & & a disease duration of \\  & - 11 PSP & & & & \\  & \end{tabular}
\end{table}
Table 1: Characteristics of the 7 included studies.