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Ferenc B Sallo, Adam M Dubis, Irene Leung, Traci E Clemons, Daniel Pauleikhoff, Emily Y. Chew, Alan C Bird; Assessing photoreceptor degeneration in type 2 idiopathic macular telangiectasia.. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3139.
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© ARVO (1962-2015); The Authors (2016-present)
Type 2 Idiopathic Macular Telangiectasia (MacTel) is a disease of the central retina, leading over time to photoreceptor (PR) degeneration and potentially to bilateral loss of central vision. No effective treatment is currently available. SD-OCT 'en face' area measurement of a break in the Ellipsoid Zone (EZ) is an established method for following disease progression in MacTel. An EZ break is however not an early sign in the natural history of MacTel. Finding parameters that provide quantitative measures over a wider range of disease severities may be useful for following disease progression in trials of potential new therapies. Our aim was to assess the feasibility and utility of measuring PR layer thickness in MacTel.
Patients were selected from the cohort of the MacTel Study. Corresponding sets of infrared (IR) and blue reflectance (BLR) images and 15°x10° SD-OCT volume scans centered on the fovea, acquired using Heidelberg Spectralis devices were analyzed. The PR layer was defined as the slab between the inner limit of the Outer Plexiform Layer (OPL) and the outer limit of the Interdigitation Zone (IZ). Boundaries were segmented using Heidelberg Eye Explorer followed by manual correction as necessary. IR, BLR, EZ en face OCT images and contour plots of PR layer thickness were collected in overlays, registered and analyzed.
Sixteen image sets of eyes predominantly with early MacTel were analyzed. A clear focal reduction in PR thickness temporal to the foveal center was present in 14 sets, in 6 sets in the absence of an EZ break. The lateral extent of the PR thinning exceeded that of the EZ break in all cases (PR/EZ area ratio: mean=28.8, SD=38.6 range 3.8-85.2). The BLR hyper-reflective area was present in all sets and consistently larger than the area of PR thinning (BLR/PR area ratio: mean=2.2, SD=0.7, range 1.5-3.1). Differences appear to be lower in more advanced disease. Intra-grader repeatability of PR thickness measurements assessed in 50 B-scans was good (ICC single measures = 0.8841, 95% CI 0.8822 - 0.8860, two-way model).
A thinning of the PR layer appears to precede the incidence and exceed the extent of an EZ break. Measuring PR thickness may offer a tool for quantifying disease severity in the absence of an EZ break. Our results are encouraging and warrant further investigations on a larger sample.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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