Vascular density evaluated by SS-OCTA and microperimetry in RP
Reviewed by Sofia Rokerya

The aim of this retrospective, observational cross-sectional one-year study was to evaluate the retinal and choroidal vessel density in the macular area with swept-source optical coherence tomography angiography (SS-OCTA) in patients of retinitis pigmentosa (RP), to compare this data with a control group of healthy subjects, and to study a possible morpho-functional correlation by microperimetry (MP-1). The study cohort comprised of 40 eyes of 40 RP patients and 24 eyes of 24 healthy individuals. The demographics of the RP groups were as follows: age in years: 51.73 ±13.46; M:F ratio: 16:24; axial length: 23.96 ±1.36mm; best corrected visual acuity (BCVA): 69.56 ±20.83. Those of the healthy control group were as follows: age in years: 63.73 ±1.79; M:F ratio: 9:13; axial length: 22.54 ±1.86mm; and BCVA: 85 ±0.12. Linear regression analyses were performed between the metrics of retinal structure and function (mean retinal thickness by OCT, as well as mean microperimetry sensitivity) and the mean capillary density as measured by OCTA for the superficial retinal, deep retinal, choriocapillaris, and deep choroidal vascular complexes. No significant correlation was detected in any case (R2=0, p>0.05). A comparison between RP and healthy controls revealed a significant reduction in SS-OCTA mean capillary density in the RP group (p=0.0011). This relationship was consistent across vascular layers (p=0.2413). A significant association between the capillary density of the various vascular complexes was detected within individual eyes (p<0.0001). Overall, vessel density was found to be reduced in RP compared to control patients, with the greatest effect being seen in the deep retinal plexus. The comparison of MP-1 and SS-OCTA data in this cohort of patients concluded that RP patients showed a reduction in both the retinal and the choroidal vascular network in the macular area compared to healthy subjects. Limitations: In this study, the diagnosis of RP was based upon clinical features and electro diagnostics and not on genotype data. The cohort was also too small to yield adequate statistical power for subgroup analysis. This was a cross-sectional analysis and therefore included patients at a variety of stages of the disease and hence it was not possible to ascertain whether changes in vascular density as measured by OCTA could be detected over time within individual patients. Strengths: SS-OCTA is deemed to be a useful non-invasive tool for the detection of microvascular alterations in RP. The measurement of vascular density was based upon pixel counts in OCTA images, and which although gave only an approximation of vascular density, did not however require any image manipulation and eliminated potential source further of error and bias.

Vascular density and retinal function in patients with retinitis pigmentosa evaluated by SS-OCTA and microperimetry.
Corazza P, Cirafici P, Testa V, et al.
OPHTHALMOLOGICA
2021;244:27–33.