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Michel Paques, Chahira Miloudi, Laurent Mugnier, José Sahel, Isabelle Bloch, Florence Rossant, Sarah Mrejen; The optical Stiles-Crawford effect strongly affects photoreceptor imaging in diseased retina.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4934.
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© ARVO (1962-2015); The Authors (2016-present)
The optical Stiles-Crawford effect (oSCE) describes the directional reflectance of cone photoreceptors. To which extent does it affect cone photoreceptor imaging in diseased eyes is poorly documented. Here we investigated by adaptive optics (AO) en face imaging and optical coherence tomography (OCT) the directional reflectance of photoreceptors in patients recovering from macular edema.
AO fundus images were obtained through dilated pupils with a commercially available flood imaging AO camera (rtx1™ camera; Imagine Eyes, Orsay, France) in normal eyes (n=6) and eyes recovering from macular edema (n=6). Cone density counts were compared in sets of three images with three different entrance pupils: one through the central cornea (termed here coaxial image) and two after laterally shifting the entry pupil by 2.3° in both directions. Fusion maps were constructed after realignment of the three maps. The optical characteristics of control and diseased retina were analyzed in homologous areas. In parallel, OCT scans taken through these different entry pupils were aligned and fused.
In patients, coaxial AO images and OCT scans both showed patchy defects of photoreceptor structures. Comparison of AO images at different entrance pupils showed that, in diseased areas, 65% (range, 47-79%) of cones were detected only through one of the 3 entry pupil versus 34% (range, 23-41%) in controls. Fusion maps increased the amount of detected cones by a mean of 69% (range, 26-113%) versus 24% (range, 5-56%) in controls. Final cone counts on fusion maps ranged from 31% to 56% of controls. On OCT scans of the same areas, the interdigitation line showed the most important directional reflectance; fusion of multiangle OCT scans markedly reduced the extent of outer layer destructuration.
Following retinal edema, photoreceptors show striking modifications of their optical properties which may lead to an overestimate of destructuration of the outer retina. Integration of AO images as well as OCT scans taken at different entry pupils improves the characterization of photoreceptor density and structure. These changes may participate to visual impairment. Further investigations are needed to determine if this is due to increased oSCE and/or to cone misalignment, the evolution of these changes over time and their presence in other retinal diseases.
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