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Qinyun Wang, William Scott Tuten, Brandon J Lujan, Jennifer Holland, Steven D Schwartz, Jacque L Duncan, Austin Roorda; High-resolution assessment of cone photoreceptor structure and function in macular telangiectasia type 2 (MacTel). Invest. Ophthalmol. Vis. Sci. 2014;55(13):5947. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate visual function in regions of apparent focal cone photoreceptor loss in a patient with MacTel.
Adaptive optics scanning laser ophthalmoscope (AOSLO) imaging and AOSLO microperimetry (AOMP) were used to evaluate the structure and function of cones within the macula of one eye in a woman with MacTel. Cone spacing was estimated using histogram analysis of all intercone distances computed from subsets of cones at 22 locations, including 4 of 10 AOMP test sites, within 0.2 to 3.9 degrees of the fovea. Cone spacing was measured at locations with unambiguous cones and avoided where cones may have been obscured by inner retinal pathology. Cone spacing values were compared with those from 27 healthy eyes. Registered spectral domain optical coherence tomography (SD-OCT) data was used to confirm retinal anatomy consistent with cones in all analyzed regions. AOMP was used to assess photopic visual sensitivity of 10 locations in or around an area of IS/OS junction disruption; these sites were between 15-60 arcminutes from the fovea. Real-time eye tracking enabled delivery of a 3.5 arcmin 550-nm stimulus to targeted retinal loci, and transverse chromatic aberration (TCA) was corrected via image-based methods.
Cone spacing was within normal limits at all 22 locations where unambiguous cones were observed. Of the 10 AOMP test locations, 4 showed normally-reflective cones with increment thresholds of 0.04-0.08 arbitrary units (au). Thresholds in 3 regions with dimly-reflecting, unresolved cones ranged from normal (0.04 au) to markedly elevated (0.26 au). In 2 regions where SD-OCT showed IS/OS junction discontinuity and AOSLO showed RPE cell mosaics, thresholds were measurable at 3.2 times greater than normal, ranging from 0.15-0.16 au, but were lower than some values from dimly-reflecting regions.
AOSLO and AOMP revealed 3 categories of lesions in MacTel. First, most cones showed normal spacing and function. Second, dimly-reflecting cones showed normal to markedly elevated thresholds. Finally, regions with IS/OS junction loss, no reflective cones, and visible RPE cells demonstrated measurable, elevated AOMP thresholds. Residual sensitivity due to ocular scatter or imprecise TCA correction is unlikely, raising the possibility that preserved, abnormally wave-guiding cones reside in these regions of apparent focal cone loss.
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