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Grace Han, Jan Kristine Bayabo, Brandon Lujan, Jessica Morgan; Quantification and Comparison of Cone density, Outer Nuclear Layer and Henle’s Fiber Layer Thickness Using High-Resolution Imaging. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3435.
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© ARVO (1962-2015); The Authors (2016-present)
To quantify and compare cone photoreceptor density as measured with adaptive optics scanning laser ophthalmoscopy (AOSLO) to the thicknesses of the outer nuclear layer (ONL) and Henle’s fiber layer (HFL) as measured by directional optical coherence tomography (D-OCT).
Retinal images from 8 normal sighted subjects (age 15-22) with no known retinal pathology were acquired along the nasal-temporal meridian with an AOSLO developed by Canon Inc. Horizontal D-OCTs through the fovea were acquired using the Heidelberg Spectralis OCT. During D-OCT imaging the entry position of the beam was modified horizontally through the pupil to reveal HFL. AOSLO cone images were registered using custom software from Canon, and manually montaged for precise alignment to the Spectralis fundus images and D-OCT sets. Cone density was measured at precise locations along the horizontal meridian using a semi-automated, custom Matlab program. D-OCTs were registered and the ONL and HFL were manually segmented. The thicknesses of these layers were measured at locations where cone density was measured.
Cone density was highest in the central most measured location and decreased with increasing eccentricity. The cone densities measured in this study agreed with previously reported densities for normal controls. From ~0.75-1.5mm cone density positively correlated with HFL thickness (R2=0.46). ONL thickness was highest in the fovea and decreased with eccentricity until reaching a local minimum at ~0.8mm. From ~ 0.8-1.3mm there was a slight increase in ONL thickness, beyond which ONL thickness leveled off. Cone density did not correlate with ONL thickness from 0.75-1.5mm (R2=0.02). The variability in cone density between subjects was less than the variability of ONL and the variability of HFL thickness at all locations measured between 0.75-1.5mm eccentricities.
HFL can be imaged and quantified separate from the ONL by using directional OCT. ONL thickness did not correlate with cone density in the imaged regions, likely due to the increasing rod contribution at these eccentricities. Cone density measurements show less variability between subjects than ONL measurements, which may be a reflection of variability in the contribution of rods. Further studies will examine total photoreceptor densities in comparison with ONL and HFL thicknesses.
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