## 4 Literature Review Sections
### Investigating Retinal Parameters among Patients with PD versus PSP  
With regard to the utility of OCT in differentiating between individuals presenting with PD and those being diagnosed with PSP, both with a disease duration of at least three years, [PERSON] et al. evaluated retinal measurements of a total of 23 patients with PD and PSP and reported a significant reduction in mean RNFL thickness in eyes from patients with PSP as compared with those with PD, while the total macular volume was not found to markedly differ between the groups of Parkinsonian patients. Interestingly, an RNFL thickness threshold of 93 \(\upmu\)m among patients with a long duration of disease (>3 years) seems able to distinguish between patients with PD and PSP, yielding a diagnostic sensitivity and specificity around 70%. It should be noted that the durations since symptom onset or since diagnosis were not correlated with either RNFL thickness or with total macular volume. On the contrary, the researchers concluded that the severity of the disease, as assessed by the Unified Parkinson Disease Rating scale (UPDRS), was positively correlated with the RNFL thickness within the group with PD, although negatively associated with total macular volume among all patients' groups [21]. Exploring the role of OCT in delineating PSP from PD patients, [PERSON] et al., having enrolled 39 patients diagnosed with either PSP or PD with a mean disease duration over 3 years, examined the potential linkage between retinal parameters, included pRNFL value, macular volume and single retinal layers' thickness, and the nature of Parkinsonian syndrome, duration of disease, and therapeutic use of levodopa. They observed a marked thinning of pRNFL among patients with PSP when compared with the group with PD in all sectors, a difference that reached statistical significance only as far as the superior quadrant is concerned. Moreover, in patients with PSP, the total macular volume was shown to be reduced, while GCL, IPL, and INL, as well as the inner retinal layer (IRL), were found to be thinner versus patients with PD. Regarding the impact of levodopa use among patients with PD on retinal morphology, a significantly decreased ONL/OPL ratio and an average pRNFL thinning in the inferotemporal sector were reported among levodopa non-users compared with levodopa users. It is of great interest that significant correlations were demonstrated between the duration of disease and retinal measures, both in groups of patients with PSP and PD [22]. Furthermore, in a study conducted by [PERSON] et al., the relationship between patterns of retinal changes and neurodegeneration in PD versus PSP was investigated, studying a total of 53 patients. The researchers exhibited significant differences between the two groups of patients, with a thicker mean average RNFL and a higher mean macular volume among patients with PD than a group with PSP. Notably, it was observed that a minimum GCIPL thickness cut-off value of 69 \(\upmu\)m seems able to distinguish PSP from PD with high sensitivity and specificity values [23]. Examining Retinal Changes in a Setting of Dementia Associated with the Presence of Lewy Bodies or Parkinson's Disease  
In an attempt to provide further insight into the potential role of OCT as a candidate biomarker among patients with dementia other than Alzheimer's disease, [PERSON] et al. explored retinal morphology as well as subtle retinal changes in both settings of dementia with Lewy bodies and dementia coupled with PD. Having enrolled 20 patients presenting with the aforementioned types of dementia, the researchers observed a greater reduction in RNFL thickness in cases of patients with Lewy body dementia compared with a group with PD dementia, although this difference failed to reach statistical significance.