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Lene Aarvelta Hagen, Stuart James Gilson, Rigmor C Baraas; Six-year follow-up of individuals heterozygous for the T190I mutation in the S-cone-opsin gene (OPN1SW). Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4015. doi: https://doi.org/.
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Heterozygotes for the T190I OPN1SW mutation have been reported to have a mild tritan deficiency associated with abnormal S-cone function (Baraas, Hagen et al. 2012). We carried out a follow-up study to investigate whether there was any deterioration of S-cone function six years after the initial examination.
Females (aged 30-42 yrs) heterozygous for the T190I mutation in the S-cone-opsin gene (OPN1SW) with an associated tritan color-vision-deficiency and healthy color normal controls (aged 30-44 yrs) were included in this study. All participated in the initial study (Baraas, Hagen et al. 2012), and all had normal logMAR letter acuity and no observed ocular abnormalities. Color vision was examined with a battery of standard tests, including Moreland anomaloscopy and Cambridge Colour Test.<br /> Achromatic and isolated S-cone spatial acuity were measured in the dominant eye with a Sloan E letter at 90% achromatic contrast and at 23, 46, 69 and 90% S-cone contrast. The Sloan E was presented at 5 deg eccentricity, and fixation was verified by an eye-tracker. Observers were corrected to best logMAR letter acuity and viewed the stimuli monocularly from a distance of 2.3 m. Average luminance of the stimuli was 10 cd m-2.
Observers with the T190I mutation showed poorer performance along the tritan axis on standard color tests, whereas normal controls showed no change six years after the initial test. Achromatic acuity ranged from logMAR 0.26-0.44. S-cone spatial acuity increased with increasing cone contrast for all observers, but those with the T190I mutation could not perceive the S-cone stimuli at the lowest cone contrast. Their performance was more than 2 SD poorer than the controls at 46 and 69% and 1-2 SD poorer at 90% cone contrast.
Tritan color vision deficiency caused by T190I OPN1SW mutation appears not to be stationary. The results from measurements of S-cone acuity at different levels of cone contrast confirm that the T190I mutation is consistent with a loss of function in a single dose.
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