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Daniel J Lee, Melissa A Wilk, Brandon J Lujan, Bhavna J Antony, Joseph Carroll; Assessing the Henle Fiber Layer in Albinism Using Directional OCT. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5996.
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© ARVO (1962-2015); The Authors (2016-present)
The Henle fiber layer (HFL) is comprised of extended photoreceptor axons resulting from the process of foveal cone packing and concomitant displacement of the inner retina during foveal pit formation. Directional optical coherence tomography (D-OCT) allows visualization of the HFL in vivo. Here we use D-OCT to measure HFL thickness in subjects with albinism and normal controls to assess relationships between the HFL and peak cone density.
Horizontal D-OCT B-scans were acquired, registered and averaged as previously described (Lujan et al, 2015) for 9 subjects with albinism, 2 carriers of ocular albinism and 39 controls. Averaged images were manually segmented to extract HFL thickness and true outer nuclear layer (ONL) thickness. An adaptive optics scanning light ophthalmoscope (AOSLO) was used to acquire images of the foveal cone mosaic, from which peak cone density was assessed.
HFL was observable in all subjects, and the topography of the HFL layer was dramatically different in albinism compared to normal controls (see Figure). Mean HFL thickness at the incipient fovea in subjects with albinism ranged from 7.59 to 66.86μm (avg ± stdev 51.20±18.00μm) while HFL thickness at the foveal center in controls ranged from 0.45 to 31.56μm (avg ± stdev 10.61±7.87μm). Peak cone density was negatively correlated with central HFL thickness (Spearman r = -0.54, p < 0.01) but positively correlated with the eccentricity of peak HFL thickness (Spearman r = 0.62, p < 0.001).
Higher foveal cone densities are associated with thinner foveal HFL and increased displacement of peak HFL thickness, consistent with foveal cone density playing an important role in establishing HFL topography. The presence of HFL in subjects with albinism is consistent with there being extensive foveal cone packing even in the absence of a normal foveal pit contour. This data may be useful in understanding the anatomical basis for visual acuity deficits in albinism.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
D-OCT images revealing the true ONL (shaded blue) and HFL (immediately above the ONL) in a normal control (top) and a subject with albinism (bottom).
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