Quantitative analysis of photoreceptor layer reflectivity on en-face optical coherence tomography as an estimator of cone density.

Background: To investigate whether outer retinal reflectivity on en-face Optical coherence tomography (OCT) can be considered as an estimator of cone density measured in the same area.

Methods: Forty-one points of comparisons were studied in 9 eyes (n = 6 patients) presenting maculopathies with various degrees of impairment of the photoreceptor layer. The inner segment ellipsoid zone (EZ), interdigitation zone (IZ), and retinal pigment epithelium (RPE) reflectivity were measured on coronal reconstruction of the photoreceptor layer using homemade dedicated software (Matlab, MathWorks Inc., Natick, USA). The cone metrics were measured in the same perifoveal region of interest using a high-resolution flood illumination adaptive optics camera. A semi-automatic cone counting method was adopted and all photoreceptor densities provided by the manufacturer's software were recounted manually by two experienced readers.

Results: Mean manual cone count was 21,522 ± 6700 (range, 5908-31,233 cells/mm). Both EZ and IZ reflectivity values were closely correlated with cone density in the area studied (r: 0.80 and 0.62, respectively; p < 0.0001).

Conclusion: Outer retinal reflectivity on en-face optical coherence tomography correlates well with photoreceptor density. This cone density estimation method based on retinal reflectivity could have interesting applications in the exploration and management of maculopathies.