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Ayoub Lassoued, Furu Zhang, Kazuhiro Kurokawa, James A Crowell, Donald Thomas Miller; Dysfunction precedes density changes of the cone photoreceptors in retinitis pigmentosa as revealed by AO-OCT. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1129.
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© ARVO (1962-2015); The Authors (2016-present)
Retinitis Pigmentosa (RP) is the most common group of inherited retinal degenerative diseases and causes cone photoreceptors to die in its most debilitating phase. Traditional clinical methods such as perimetry and electroretinography are gold standards for diagnosing and monitoring RP and indirectly assessing cone function. Both methods, however, lack the spatial resolution and sensitivity to assess disease progression in individual photoreceptor cells, where the disease starts. Here, we used phase-sensitive adaptive optics optical coherence tomography (PS-AO-OCT) as a novel method to measure dysfunction of single cone cells in RP subjects.
We recruited three RP subjects (early-, mid- and late-stage) and two healthy age/gender-matched controls. We imaged each RP subject with Spectralis OCT to locate the transition zone (TZ) separating central healthy from diseased retinal tissue, then imaged across the healthy zone and into TZ with PS-AO-OCT at 4 retinal eccentricities: 2°, 4°, 6°, and 8°. At each location we measured cone function by delivering a 5 ms flash of visible light (at 450 nm, 528 nm, or 637 nm) to the retina midway through each AO-OCT video acquisition. Reconstructed volumes were registered and averaged. We extracted phase differences between reflections at opposing ends of individual cones’ outer segments and converted them into optical path length changes (ΔOPL). We analyzed ΔOPL cone responses in principal component (PC) space to identify the S-, M-, and L-cone clusters and to determine displacement of each cluster relative to controls.
In control subjects, we saw three distinct clusters in PC space corresponding to the three cone spectral types (S, M, and L). In RP1 where TZ starts at 6°, M and L cone responses were reduced relative to the controls by 0% (M) and 19% (L) at 2°, 1% and 20% at 4°, 28% and 39% at 6°, and ~100% at 8°. In RP2 where TZ starts at 4°, M and L cone responses were reduced by 25% and 33% at 2°, 47% and 83% at 4°, and N/A yet at 6° and 8°. In RP3 where TZ starts at the fovea, the responses of all 3 cone types were reduced by ~100% at 2° and no cones were apparent at 4°-8°. Cone density was normal in the healthy zone of RP subjects.
Cone dysfunction was detected even in the healthy zone and increased with disease severity as measured by Spectralis OCT. L cones were more vulnerable than M cones to RP.
This is a 2020 ARVO Annual Meeting abstract.
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