Studying retinal changes has been revolutionized with the advent of OCT, especially spectral-domain OCT. Recently, the new emerging SS-OCT is being assessed clinically and may add new insights to the current understanding of retinal diseases.
In this study, the average age at examination is 26.1 (6–78); younger than those reported in other studies; 33.4–49.3 years [17, 18]. This can be explained by higher prevalence of inherited disease in the Palestinian population due to higher consanguinity rates; reaching up to 45%, according to the Palestinian Central Bureau of Statistics, which are considered to be among the highest in the Middle East region.
. A wide range of CME prevalence in RP patients has been reported in previous studies, where some reported as small as 5.5% by Hagiwara , Adackapara  has reported 47%, using time-domain OCT, compared to a 17.4% prevalence of CME in our cohort. However, researchers using the spectral domain OCT identified a variety of CME prevalence; 50.9% by Liew et al. , 25.9% by Kim et al. , 12.5% by Triolo et al. , and 14.5% by Chebil et al. . This large variance in CME prevalence can be due to the range of sample size and baseline characteristics and the OCT device’s sensitivity. Nevertheless, CME is still the most frequent OCT change in RP patients .. ERM (10.6%) was the second most frequent change noted. This is in line with the findings of Chebil et al. , which documented EMR in 8.2% of RP patients. Others reported varying proportions, ranging from 0.6 to 28% [18, 19, 22,23,24]. Overall, ERM represented the second most frequent change noted in these studies. We found that ERM had no significant correlation with VA. A similar finding was reported by Ibrahim et al. ; However, when ERM is studied as part of Vitreomacular Interface Disorders (VMIAs), the prevalence was over 40% of the eyes, but its direct association with VA was not examined .
Macular holes were found less frequently, with only one eye (0.6%) displaying a lamellar hole, similar to those recorded by Hagiwara et al. (0.5%) . Previous studies reported a higher prevalence of macular holes [22, 24]. Employing the American Association of ophthalmology classification, no cases of VMT were encountered in this study, whereas 5 of 622 eyes (0.8%) and 58 of 1161 eyes (5%) with VMT reported in other studies [23, 25]. Similarly, no cases of CNV have been identified in this study, as also noted by Ibrahim et al. , whereas 1.7% of eyes with CNV have been reported by Triolo et al. 
This study identified a higher percentage of eyes having an absent EZ (35%) compared to other studies [18, 25,26,27]. We found a highly significant correlation between EZ status and BCVA, as describes in other studies [16, 24, 27,28,29].. The improvement in SS-OCT’ s ability to delineate EZ from other hyper reflexive OCT lines as opposed to other OCT systems for other studies can also explain this. Absent ELM was observed in 37.5% of eyes, much higher than reported others, 13.6% by Triolo et al. , and 25% by Battaglia et al.  using spectral-domain OCT. This may be explained by the more severe disease status of our sample, but also, it may relate to the higher image resolution of SS-OCT. The degeneration of the ELM was also shown to be highly correlated with BCVA (P < 0.001). Indeed, Battaglia et al. showed that ELM remains significantly associated with BCVA after multivariate regression, whereas EZ did not .
In this study, BCVA was found to be significantly correlated with several variables. The first is gender; females, in this study, had a worse BCVA than males. (0.873 vs. 0.545, p = 0.007). This may be related to the cultural beliefs of the studied population, and females are less likely to seek medical attention at an earlier stage . The second is CME, with a highly significant correlation with BCVA (p < 0.001). This contrasts with the non-significant relationship reported by others [16, 23, 24, 27]. It may relate to the noteworthy finding in this study, that eyes without CME had a worse BCVA than eyes with CME (LogMAR 0.73 vs. 0.33). This may indicate that the non-CME eyes may be atrophic, thereby eyes with more advanced disease status rather than an earlier stage, at which stage CME is not a manifestation.
In this study, the average CMT for RP patients was marginally above the healthy population (230.0 ± 85.649 μm) and correlated with decreased BCVA (p = 0.005) .The average CMT decreases to 210 ± 63.1 μm when eyes with CME are excluded, leading to worse visual outcomes in terms of (LogMAR =0.73 ± 0.79). This is likely due to CME being indicative of earlier disease status and thereby better BCVA. A comparison between CMT of CME & non-CME eyes was also made by Kim et al., who found no significant difference in BCVA between groups . A significant relationship between CMT (avg of 180 μm) and BCVA was observed by Ibrahim et al. . This suggests a bidirectional relationship between CMT and vision; both thickened and atrophic maculae showed decreased vision.
It has been hypothesized that the factor involved in photoreceptor degeneration is choroidal thinning caused by decreased blood flow . Our study showed that the subfoveal CVT was 289.3 ± 103.3, almost similar to others’ findings [33,34,35], but still lower than the normal range. This correlates significantly with age (p = 0.039), as expected, and negatively with BCVA (p = 0.015). Similar significant relationships were noted by Aknin et al.  and Ayton et al.  but inconsistent with the results of Dhoot et al. (33)and Sodi Et al.  using Enhanced Depth Imaging OCT. This supports the observation that the greater the choroidal thinning at the subfoveal area, the worse the BCVA.
HRF has been identified in other retinal diseases composed of macrophages, migrating RPE cells, and extravasated lipoprotein. This study is the first to describe HRF in the vitreous, thereby increasing our limited current understanding of their role in the disease process. Although vitreous HRF was present in 43.8% of studied eyes, this was non-significantly correlated with BCVA (p = 0.551). Interestingly, eyes without vitreous HRF had a worse BCVA than eyes with HRF (LogMAR 0.684 vs. LogMAR 0.590). This may indicate that their presence reflects an early or intermediate stage of the disease, rather than an advanced stage. This is also supported by the fact that they were more likely to be found when the EZ was shortened and abnormal (60%) rather than when absent. To date, HRF has been studied in other retinal layers, but not in the vitreous. And vitreous HRF was only studied in diabetic retinopathy and uveitis.
Although previous articles in the literature have studied retinal changes in patients with RP and their correlation with BCVA, this study is one of the first to do so using SS-OCT. Moreover, this is perhaps the most comprehensive study involving the assessment of changes in the vitreous, retina, and choroid, including vitreous HRF being studied for the first time. However, this study has some limitations that should be taken into consideration when interpreting its findings. First limitation is the lack of genetic diagnosis in these patients, and so no genotype-phenotype correlation could be explored. Another limitation is that the generalizability is limited to other populations of high rates of consanguinity similar to the Palestinian population.