Ripamonti, C; Aboshiha, J; Henning, B; Sergouniotis, PI; Michaelides, M; Moore, AT; Webster, AR; Ripamonti, C; Aboshiha, J; Henning, B; Sergouniotis, PI; Michaelides, M; Moore, AT; Webster, AR; Stockman, A; - view fewer (2014) Vision in observers with enhanced S-cone syndrome: an excess of S-cones connected mainly to conventional S-cone pathways but also a faster pathway. Investigative Ophthalmology & Visual Science , 55 (2) pp. 963-976. 10.1167/iovs.13-12897.

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Abstract

Purpose: The effect of increased numbers of S-cone photoreceptors in enhanced S-cone syndrome (ESCS) was investigated psychophysically in six ESCS observers to understand more about the relative cone sensitivities and postreceptoral organization. Methods: Measures of temporal sensitivity or delay were made: S- and L-cone temporal acuity (critical flicker fusion or cff), S-cone temporal contrast sensitivity, and S-cone delay. Results: ESCS observers showed uniform enhancements of S-cone cff of between 0.85 and 6.25 Hz, but reductions in L-cone cff. They also showed higher S-cone temporal-contrast-sensitivities at medium and high S-cone adaptation levels with sensitivity functions that peaked near 7.5 Hz but fell off at lower and higher frequencies; in contrast, the mean normal function was flat at low frequencies and fell-off only at high frequencies. The S-cone signal, as in the normal, is subject to large phase delays. Conclusions: We interpret the enhancements in cff as increases in S-cone number in ESCS of between 1.39 and 11.32 times normal density (with a mean of 3.48). The peaked ESCS contrast-sensitivity functions are consistent with S-cone signal interactions that increase sensitivity at intermediate frequencies through constructive interference but decrease it at lower and higher frequencies through destructive interference. Measures of S-cone delays relative to L- and M-cone signals show that the predominant S-cone signals in ESCS are negative and delayed as in normal observers, but reveal another faster, positive S-cone signal. This signal is also likely to be the cause of constructive and destructive interference in the contrast-sensitivity data of ESCS observers.

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