Adaptive optics ophthalmoscopy in retinitis pigmentosa (RP): Typical patterns

Adaptive optics retinal imaging in patients with usher syndrome

Purpose

To determine the structure of the cone photoreceptor mosaic in the macula in eyes with retinitis pigmentosa related to Usher syndrome using adaptive optics fundus (AO) imaging and to correlate these findings with those of the standard clinical diagnostics.

Methods

Ten patients with a genetically confirmed retinitis pigmentosa in Usher syndrome due to biallelic variants in MYO7A or USH2A were enrolled in the study. All patients underwent a complete ophthalmological examination including best corrected visual acuity (BCVA), spectral-domain optical coherence tomography (SD-OCT) with fundus autofluorescence photography (FAF), full-field (ffERG) and multifocal electroretinography (mfERG) and Adaptive Optics Flood Illuminated Ophthalmoscopy (AO, rtx1™, Imagine Eyes, Orsay, France). The cone density was assessed centrally and at each 0.5 degree horizontally and vertically from 1-4 degree of eccentricity.

Results

In the AO images, photoreceptor cell death was visualized as a disruption of the cone mosaic and low cone density. In the early stage of the disease, cones were still visible in the fovea, whereas outside the fovea a loss of cones was recognizable by blurry, dark patches. The blurry patches corresponded to the parafoveal hypofluorescent ring in the FAF images and the beginning loss of the IS/OS line and external limiting membrane in the SD-OCT images. FfERGs were non-recordable in 7 patients and reduced in 3. The mfERG was reduced in all patients and correlated significantly (p <0.001) with the cone density. The kinetic visual field area, measured with III4e and I4e, did not correlate with the cone density.

Conclusion

The structure of the photoreceptors in Usher syndrome patients were detectable by AO fundus imaging. The approach of using high-resolution technique to assess the photoreceptor structure complements the established clinical examinations and allows a more sensitive monitoring of early stages of retinitis pigmentosa in Usher syndrome.

Adaptive Optics Imaging of Inherited Retinal Disease

The human retina is amenable to direct, noninvasive visualization using a wide array of imaging modalities. In the ∼140 years since the publication of the first image of the living human retina, there has been a continued evolution of retinal imaging technology. Advances in image acquisition and processing speed now allow real-time visualization of retinal structure, which has revolutionized the diagnosis and management of eye disease. Enormous advances have come in image resolution, with adaptive optics (AO)-based systems capable of imaging the retina with single-cell resolution. In addition, newer functional imaging techniques provide the ability to assess function with exquisite spatial and temporal resolution. These imaging advances have had an especially profound impact on the field of inherited retinal disease research. Here we will review some of the advances and applications of AO retinal imaging in patients with inherited retinal disease.

Therapy with voretigene neparvovec. How to measure success?

Retinal gene supplementation therapy such as the first approved one, voretigene neparvovec, delivers a functioning copy of the missing gene enabling the protein transcription in retinal cells and restore visual functions. After gene supplementation for the genetic defect, a complex network of functional regeneration is the consequence, whereas the extent is very individualized. Diagnostic and functional testings that have been used routinely by ophthalmologists so far to define the correct diagnosis, cannot be applied in the new context of defining small, sometimes subtle changes in visual functions. New view on retinal diagnostics is needed to understand this processes that define safety and efficacy of the treatment. Not only does vision have many aspects that must be addressed by specific evaluations and imaging techniques, but objective readouts of local retinal function for rods and cones separately have been an unmet need until recently. A reliable test-retest variability is necessary in rare diseases such as inherited retinal dystrophies, because statistics are often not applicable due to a low number of participants. Methods for a reliable individual evaluation of the therapy success are needed. In this manuscript we present an elaboration on retinal diagnostics combining psychophysics (eg. full-field stimulus threshold or dark adapted perimetry) as well as objective measures for local retinal function (eg. photopic and scotopic chromatic pupil campimetry) and retinal imaging for a meaningful workflow to apply in evaluation of the individual success in patients receiving gene therapy for photoreceptor diseases.