Slow Cone Reflectance Changes during Bleaching Determined by Adaptive Optics Scanning Laser Ophthalmoscope in Living Human Eyes

Photoreceptor-Based Biomarkers in AOSLO Retinal Imaging

Improved understanding of the mechanisms underlying inherited retinal degenerations has created the possibility of developing much needed treatments for these relentless, blinding diseases. However, standard clinical indicators of retinal health (such as visual acuity and visual field sensitivity) are insensitive measures of photoreceptor survival. In many retinal degenerations, significant photoreceptor loss must occur before measurable differences in visual function are observed. Thus, there is a recognized need for more sensitive outcome measures to assess therapeutic efficacy as numerous clinical trials are getting underway. Adaptive optics (AO) retinal imaging techniques correct for the monochromatic aberrations of the eye and can be used to provide nearly diffraction-limited images of the retina. Many groups routinely are using AO imaging tools to obtain in vivo images of the rod and cone photoreceptor mosaic, and it now is possible to monitor photoreceptor structure over time with single cell resolution. Highlighting recent work using AO scanning light ophthalmoscopy (AOSLO) across a range of patient populations, we review the development of photoreceptor-based metrics (e.g., density/geometry, reflectivity, and size) as candidate biomarkers. Going forward, there is a need for further development of automated tools and normative databases, with the latter facilitating the comparison of data sets across research groups and devices. Ongoing and future clinical trials for inherited retinal diseases will benefit from the improved resolution and sensitivity that multimodal AO retinal imaging affords to evaluate safety and efficacy of emerging therapies.

Evaluation of Photoreceptors in Bietti Crystalline Dystrophy with CYP4V2 Mutations Using Adaptive Optics Scanning Laser Ophthalmoscopy

PURPOSE

To evaluate photoreceptors in Bietti crystalline dystrophy patients with CYP4V2 mutations using high-resolution images of the macula obtained with adaptive optics scanning laser ophthalmoscopy (AO-SLO).

DESIGN

Prospective observational case series with comparison to healthy controls.

METHODS

Seven eyes of 7 Bietti crystalline dystrophy patients with CYP4V2 mutations and 12 normal eyes of 12 age- and axial length-matched healthy volunteers were studied. All participants underwent ophthalmologic examinations and AO-SLO assessments. All patients underwent spectral-domain optical coherence tomography, fundus autofluorescence, Humphrey field analysis, and electroretinography. AO-SLO images were analyzed 0.5 mm and 1.0 mm from the center of the fovea in the superior, inferior, nasal, and temporal quadrants.

RESULTS

Mean ± standard deviation cone density (cells/mm(2)) 0.5 mm from the center of the fovea was 17,209 ± 2276 in patients and 20 493 ± 2758 in controls, which was statistically different (P = .001); however, mean cone density 1.0 mm from the center of the fovea was 15 685 ± 2302 in patients and 15 705 ± 1848 in controls, which was not statistically different (P = .20). There was no correlation between cone density and mean deviation measured using a Humphrey field analysis or visual acuity in patients.

CONCLUSIONS

In Bietti crystalline dystrophy patients with CYP4V2 mutations, cone density remained for visual dysfunction by evaluation using high-resolution AO-SLO. These findings support the theory that disorder of the retinal pigment epithelium and the photoreceptors in the patients are the primary and secondary pathologic changes, respectively. This is consistent with results from previous basic studies.