Correlation between residual photoreceptor structure and autofluorescence area in patients with choroideremia

Session Details

Session Title: Free Paper Session 17: Imaging II

Session Date/Time: Saturday 09/09/2017 | 08:00-09:30

Paper Time: 08:30

Venue: Room 120

First Author: : A.Dubis UK

Co Author(s): :    S. Wagner   J. Jolly   K. Xue   R. MacLeran                    

Abstract Details

Purpose:

Choroideremia (CHM) is an X-linked inherited retinal dystrophy characterised by progressive centripetal degeneration of the retinal pigment epithelium (RPE), photoreceptors and choroid. The extent of RPE degeneration can be seen on autofluorescence (AF) imaging as a shrinking ‘island’ of autofluorescence. The aim of this study was to investigate the relationship between the surviving RPE and photoreceptor cells at the advancing edge of degeneration by correlating fundus AF and the photoreceptor mosaic imaged using adaptive optics scanning light ophthalmoscopy (AOSLO).

Setting:

NIHR Biomedical Resource Centre at Moorfields Eye Hospital NHS Trust, London UK and Oxford University Hospitals NHS Trust, UK Outpatients department

Methods:

Fifteen male patients with genetically confirmed CHM were recruited as part of a Phase 2 clinical trial of gene therapy for choroideremia (Clinicaltrials.gov ID: NCT02407678). All subjects underwent 30° and 55° AF imaging (Spectralis, Heidelberg Engineering, Heidelberg, Germany) and AOSLO image using a custom built device based at MEH as previously described [Dubra & Sulai, Biomed Opt Express 2011]. Briefly, this consisted of a Shark-Hartmann wavefront sensor and correction of wave-front aberrations using an 8Hz deformable mirror. The images were acquired at a line rate of 15 kHz and frame rate of 16.6 Hz. The AOSLO images were processed using custom software to visualise photoreceptor mosaics, which were montaged and co-localised onto AF images with Adobe Photoshop CS6 (Adobe Systems Inc, San Jose, California, USA).

Results:

High quality fundus AF and AOSLO images were acquired in 15 subjects (aged 29 – 38 years). Five subjects had general preservation of normal AF pattern within the 55° posterior pole while the rest had significant areas with absent AF, suggestive of RPE cell loss. Confocal AOSLO images showed loss of photoreceptor mosaic which co-localised with areas of absent AF. Split-detection AOSLO images showed that there was decreased cone density in areas of mottled AF (within the residual AF islands) in some but not all locations. Cone density decreased subtly towards the edges of the AF islands. The decrease was no more significant between the edges of AF islands and the pseudo-arms structures protruding from the main AF islands.

Conclusions:

Co-localisation of the cone mosaics as seen by AOSLO and surviving RPE as suggested by AF imaging showed relative preservation of cone photoreceptor density in areas with a disrupted AF pattern. This would suggest that the cone photoreceptor degeneration could lag behind RPE loss in CHM, although it is unclear whether those photoreceptors overlying abnormal RPE have any functional impairment. The findings are consistent with previous observations based on correlation between AF and optical coherence tomography (OCT) in this condition [Xue, Oldani, Jolly, et al, IOVS 2016]. The implication is that a clinical window may exist during which gene replacement therapy to rescue a proportion of RPE cells may be sufficient to slow down or stop the degeneration of overlying photoreceptors. High resolution imaging may be helpful in patient selection for gene and cell therapy trials.

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