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Ari Schuman, Rithambara Ramachandran, Xian Zhang, David Birch, Donald Hood; The cone outer segment termination (COST) line appears abnormal on OCT scans of patients with stationary and progressive forms of cone dysfunction. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3634.
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On frequency domain optical coherence tomography (fdOCT) scans, a line is often present between the inner segment ellipsoid (ISe) and retinal pigment epithelium (RPE), and is sometimes called the cone outer segment termination (COST) or misnamed Verhoeff’s membrane. To better understand this feature, we examined fdOCT scans in patients with diminished cone function.
Horizontal line scans through the fovea were obtained with fdOCT (Heidelberg) from 30 healthy control eyes, 10 eyes with achromatopsia (ACHM), and 8 eyes with cone dystrophy (CD). All patient eyes had reduced or absent cone full-field ERGs. Scans were qualitatively examined for the presence and appearance of a COST line. The ISe (aka IS/OS) line and RPE borders were marked using a computer-aided manual procedure. The intensity of the COST region (Fig. 1), the area between ISe line and proximal retinal RPE border, was divided by RPE intensity. The central fovea (±1mm) was not included as the ISe is often abnormal in these patients.[2,3]
Of 30 control scans, 29 had a distinct COST line in part of the temporal and/or nasal retina (Fig. 1A). 9 of 10 ACHM, and all CD patients, showed some sign of a COST line. However, in 8 of 9 ACHM  and all CD patients, this line appeared abnormal. The COST line was “blurred” (Fig. 1B) in 1 ACHM and 2 CD. The COST region was diffuse (Fig. 1C) in 9 ACHM and 4 CD. There was little to no COST line (Fig. 1D) in 1 ACHM. The RPE thickness was greater than the mean of controls in 9 of 10 ACHM (Fig. 1D) and 5 of 8 CD, although not in a statistically significant way. The COST regions in CD (0.79±0.06, p <0.01) and ACHM (0.78±0.06, p<0.001) were significantly less intense than in controls (0.94±0.05), but not different from each other. The intensity of the RPE was not significantly different among groups.
The COST line is absent, blurred, or diffuse in patients with abnormal cone receptor function, and these abnormalities can be quantified with an intensity measure. Although the COST line is typically not visible in all portions of scans from controls, its complete absence or abnormal appearance may be a useful clinical indicator of abnormal cone receptors. 1. Spaide & Curcio Retina, 2011, 2. Hood et al. IOVS, 2011, 3. Birch et al. IOVS, 2011, 4. Thomas et al. Ophthalmol, 2011.
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