Purpose: Macular edema is a common retinal disease which may leave important anatomical and functional sequelaes. Directional fundus imaging consists of comparing on- and off-axis images to reveal angle-dependent reflectance properties of fundus structures, which may be related to misaligned photoreceptors. Here, we analyzed directional optical coherence tomography (OCT) and flood-illumination adaptive optics ophthalmoscopy images to detect evidence of misaligned photoreceptors following macular edema.
Methods: Transversal, observational study. Nine patients having recovered a normal macular profile after macular edema due to retinal vein occlusion were included. For each patient, a reference OCT scan (i.e., with the incident beam normal to the fovea) was acquired, and off-axis scans were then acquired by laterally shifting the entry pupil. In addition, in four of these eyes, directional adaptive optics ophthalmoscopy documented the directional variations of cone metrics.
Results: Included patients comprised two women and seven men (age range, 19-76 years). Reference OCT scans showed patchy attenuation of the cone outer segment tips and to a lesser extent of the inner segment/outer segment lines in all, but two eyes; these. Increased intensity of the cone outer segment tips and inner segment/outer segment lines could be observed on off-axis scans. Accordingly, fusion images showed 66% average reduction of the length of cone outer segment tips attenuation. In two cases, although reference scans showed continuity of outer bands, focal attenuation was evidenced in off-axis images. Directional adaptive optics ophthalmoscopy imaging showed a strong directional variability of cone counts in these areas, ranging from near absence to roughly two-third of reference values. In each case, directional variations of cone counts paralleled those of the reflectance of outer bands.
Conclusion: After macular edema, focal attenuations of the inner segment/outer segment and of the cone outer segment tips lines may be present on OCT. These areas may show a strong directional variability by both OCT and adaptive optics ophthalmoscopy, suggesting that misaligned photoreceptor outer segments contribute to such features. The evaluation of outer retinal damage following macular edema should therefore take into account the optical Stiles-Crawford effect to disambiguate missing from misaligned cones.