Reflectivity of the outer retina on spectral-domain optical coherence tomography as a predictor of photoreceptor cone density.

PURPOSE: To investigate the relationship between outer retinal reflectivity on spectral-domain optical coherence tomography and cone density in the corresponding area. DESIGN: Prospective cross-sectional observational study. METHODS: In this institutional-based study, 20 eyes of 10 patients presenting maculopathies with various degrees of impairment of the photoreceptor layer (central serous chorioretinopathy, chronic central serous chorioretinopathy, maculopathy associated with hydroxychloroquine, and healthy eyes) were studied. Selection criteria were intended to ensure good image quality. Inner segment ellipsoid band reflectivity, global retinal reflectivity, and relative inner segment ellipsoid reflectivity (defined as the ratio of inner segment ellipsoid band reflectivity on overall retinal reflectivity) were measured on a longitudinal reflectance profile extracted from the spectral-domain optical coherence tomography B-scan. The cone metrics were measured in the same region of interest, located in the perifoveal area, using an adaptive optics retinal camera. RESULTS: Inner segment ellipsoid and relative ellipsoid reflectivity were closely correlated with cone density (Pearson r: 0.72 and 0.70, respectively, P < .01). CONCLUSION: Outer retinal reflectivity on the transversal optical coherence tomography scan can be correlated to adaptive optics in terms of photoreceptor density. This quantitative approach using optical coherence tomography images could have important implications in the management of maculopathies.

Assessment of parafoveal cone density in patients taking hydroxychloroquine in the absence of clinically documented retinal toxicity.

PURPOSE: To measure cone density in patients taking hydroxychloroquine (HCQ), with no clinical evidence of maculopathy. METHODS: Patients visiting for HCQ macular toxicity screening in the Besançon University Hospital Ophthalmology Department (France) were studied. They underwent routine examination including spectral-domain optical coherence tomography, fundus autofluorescence and multifocal electroretinogram to detect HCQ-induced retinal toxicity. Cone metrics (density, spacing and percentage of cones with six neighbours) were obtained using an adaptive optics camera (RTX1, Imagine Eyes, Orsay, France). The region of interest corresponded to a 0.3° × 0.3° square placed nasally and temporally at 2° of eccentricity from the fovea. RESULTS: Forty eyes of 23 patients were studied. The majority of the patients (21/23) were female. They were aged from 25 to 60 years (mean age ± SD: 40.1 years ± 10). The cumulative dose for HCQ ranged from 24 to 2160 g (777 ± 558 g). None of them displayed HCQ toxicity on screening tests. Bivariate analysis showed moderate cone loss with escalating doses of HCQ (linear regression, r² = 0.23, p = 0.018). Cone spacing also increased with increasing cumulative dose (r² = 0.17, p = 0.008). Cone packing remained unchanged (p > 0.05). Multivariate analysis showed that age and cumulative dose were additive and independent factors of cone dropout. CONCLUSIONS: In this pilot study, we observed moderate cone loss as HCQ cumulative doses increased. The early detection of parafoveal cone metric changes may represent the earliest sign of HCQ macular toxicity during screening.

Reliability of cone counts using an adaptive optics retinal camera.

BACKGROUND: To assess the reproducibility and repeatability of cone imaging in healthy human eyes, using the RTx-1 Adaptive Optics Retinal Camera and its proprietary cone-counting software. DESIGN: Single-centre, prospective study. PARTICIPANTS: Ten healthy adults. METHODS: Macular cones were imaged. Intrasession repeatability was assessed by comparing 10 consecutive acquisitions obtained by the same operator from each subject. For the intersession study, each subject was imaged five consecutive days. Interoperator reproducibility was also evaluated by comparing the images obtained from 10 different subjects by two independent operators. Finally, intergrader agreement was evaluated by comparing the cone counts measured by two masked graders. MAIN OUTCOME MEASURES: Mean cone density (cells/mm(2) ), spacing between cells (µm) and percentage of cones with six neighbours calculated on Voronoi diagrams were measured. Correlation coefficients, intraclass correlation coefficients, and coefficients of variation were calculated. RESULTS: Correlation coefficient and intraclass correlation coefficient were respectively 0.81 and 0.96 between operators, and 0.97 and 0.98 between the two graders. The intrasession and intersession coefficients of variation were under 7%. The percentage of cells with six neighbours and the spacing between cones varied in the same proportion (coefficients of variation ranged from 1.66 to 10.05%). CONCLUSIONS: Overall, the test-retest variability of RTx-1 and its software was good in normal human eyes. Further studies in the normal clinical setting are mandatory.