High-Resolution Imaging of Parafoveal Cones in Different Stages of Diabetic Retinopathy Using Adaptive Optics Fundus Camera

<div><p>Purpose</p><p>To assess cone density as a marker of early signs of retinopathy in patients with type II diabetes mellitus.</p><p>Methods</p><p>An adaptive optics (AO) retinal camera (rtx1^<b>™</b>; Imagine Eyes, Orsay, France) was used to acquire images of parafoveal cones from patients with type II diabetes mellitus with or without retinopathy and from healthy controls with no known systemic or ocular disease. Cone mosaic was captured at 0° and 2°eccentricities along the horizontal and vertical meridians. The density of the parafoveal cones was calculated within 100×100-μm squares located at 500-μm from the foveal center along the orthogonal meridians. Manual corrections of the automated counting were then performed by 2 masked graders. Cone density measurements were evaluated with ANOVA that consisted of one between-subjects factor, stage of retinopathy and the within-subject factors. The ANOVA model included a complex covariance structure to account for correlations between the levels of the within-subject factors.</p><p>Results</p><p>Ten healthy participants (20 eyes) and 25 patients (29 eyes) with type II diabetes mellitus were recruited in the study. The mean (± standard deviation [SD]) age of the healthy participants (Control group), patients with diabetes without retinopathy (No DR group), and patients with diabetic retinopathy (DR group) was 55 ± 8, 53 ± 8, and 52 ± 9 years, respectively. The cone density was significantly lower in the moderate nonproliferative diabetic retinopathy (NPDR) and severe NPDR/proliferative DR groups compared to the Control, No DR, and mild NPDR groups (<i>P</i> < 0.05). No correlation was found between cone density and the level of hemoglobin A_1c (HbA_1c) or the duration of diabetes.</p><p>Conclusions</p><p>The extent of photoreceptor loss on AO imaging may correlate positively with severity of DR in patients with type II diabetes mellitus. Photoreceptor loss may be more pronounced among patients with advanced stages of DR due to higher risk of macular edema and its sequelae.</p></div

Baseline Characteristics of Study Participants.

<p>Baseline Characteristics of Study Participants.</p

Voronoi (6 tiles) Comparisons at 500-μm Eccentricity^*.

<p>Voronoi (6 tiles) Comparisons at 500-μm Eccentricity^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0152788#t006fn001" target="_blank">*</a>}.</p

Position of the Regions of Interest (ROIs) with Respect to the Fovea.

<p>A: Scanning laser ophthalmoscope (SLO) image of the left eye of a healthy control. AO images (white-bordered cross centered at the fovea), taken at 0° and 2° along the vertical and horizontal meridians, are stitched and superimposed on the SLO image. Four 100×100-μm squares are placed 500-μm (yellow squares) from the foveal center within the 4 retinal quadrants. B: Magnified AO image of the temporal 500-μm eccentricity square. AOdetect^® software recognizes and counts the cells marked by red dots. C: Example of manual correction of the automated counts by one grader (1, missed cones; 2, cones erroneously counted by the automated software). D: Color map of Voronoi tiles.</p

Cone Spacing Comparisons at 500-μm Eccentricity^*.

<p>Cone Spacing Comparisons at 500-μm Eccentricity^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0152788#t005fn001" target="_blank">*</a>}.</p

Cone Density Comparisons at 500-μm Eccentricity.

<p>Cone Density Comparisons at 500-μm Eccentricity.</p

Average Cone Density, Spacing, and Voronoi (Mean ± SD) at 500-μm Eccentricity.

<p>Average Cone Density, Spacing, and Voronoi (Mean ± SD) at 500-μm Eccentricity.</p

Intraocular Variability in the Packing Density of Cones between the both Eyes of the Same Participant.

<p>Intraocular Variability in the Packing Density of Cones between the both Eyes of the Same Participant.</p

Cone Density in Each Quadrant Across the Study Groups.

<p>Cone Density in Each Quadrant Across the Study Groups.</p