Abstract
Purpose :
Choroideremia (CHM) is an X-linked retinal degeneration which causes progressive dysfunction of photoreceptors, retinal pigment epithelium, and choroid, ultimately leading to cell death and vision loss. The recent development of optoretinography allows non-invasive assessment of photoreceptor function. Here, we assess cone function in CHM using optoretinography.
Methods :
The cone mosaic of 14 study participants (4 control, 10 CHM) were imaged 0.5-1° from the fovea using a custom-built, multimodal adaptive optics scanning light ophthalmoscope (795nm super luminescent diode imaging beam, 1°x1° field). Each imaging session consisted of 1-6 stimulus trials, and each trial included 1-13 video acquisitions. Non-stimulated trials were also collected. Subjects were dark adapted for 2 minutes prior to each trial. During each acquisition, a 2-second 450nW 550Δ10nm stimulus was presented to the subject 4 seconds after the recording started. Each video was registered, cones were identified, and the intensity of all cones throughout the videos were extracted, normalized, standardized, and aggregated over the cone mosaic to yield the population optoretinogram (ORG) as previously described (Cooper et al., 2017). A gamma probability density function was fit to the ORG and the peak of the fit within 6 seconds of stimulus onset was taken as the ORG amplitude. ORG amplitudes were compared between CHM and control participants using unbalanced one-way ANOVA. We correlated ORG amplitude with bound cone density and foveal sensitivity measured using the Nidek MP-1 microperimeter in CHM participants [Pearson correlation coefficient (PCC)].
Results :
ORG amplitudes were significantly lower in CHM (mean ± standard deviation, 0.22±0.14, arbitrary units, range 0.04-0.48) compared to control (1.34±0.31, range 0.91-1.57, p<0.001). Cone density was reduced in CHM (53,900 ± 19,500 cones/mm2, control: 77,300 ± 8,800 cones/mm2, p=0.045). Microperimetry revealed constricted visual fields and reduced retinal sensitivities in CHM. CHM ORG amplitude was positively correlated with cone density (PCC=0.69) and foveal sensitivity (PCC=0.73).
Conclusions :
Parafoveal cone function is reduced in CHM patients despite the tested locations remaining within the centrally intact retinal area. The correlation between ORG amplitude and retinal sensitivity shows promise for using ORG as an objective biomarker of photoreceptor function in disease.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.