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Katherine Mancuso, John L. Barbur, Jay Neitz, Marisa Rodriguez-Carmona, Maureen Neitz; Feasibility of producing sufficient L/M opponency to support red green colour vision by coexpressing an L pigment transgene in a subset of M cone photoreceptors of protanopes. Journal of Vision 2006;6(13):56. doi: https://doi.org/10.1167/6.13.56.
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© ARVO (1962-2015); The Authors (2016-present)
We are developing gene therapy methods in an attempt to expand colour vision in dichromats. A viral vector carrying an L opsin gene is administered by subretinal injection to protanopic squirrel monkeys. To estimate the amount of L photopigment required within a subset of the endogenous M cones to produce an opponent difference equivalent to that of human trichromats, the relationship between L/M spectral separation and colour vision behavior was examined. Chromatic sensitivity was measured using the Colour Assessment and Diagnosis test in normal trichromats and 250 colour-deficient observers. Twenty-three subjects from this group were selected for genetic analysis to determine the spectral separation between L and M pigments. Red-green chromatic sensitivity exhibited a nonlinear relationship with photopigment proximity, indicating that observers would not show a reduction in colour discrimination sensitivity that could be reliably classified as just outside the normal range until the L/M separation is reduced to about 12 nm or less. The size of the L/M opponent response was then extrapolated for the range of L/M separations and these were converted to equivalent differences between an M cone class and one coexpressing L plus M. Accordingly, in a protanope, a subclass of transduced cones with a 1:1 mixture of L and M pigment would produce an amplitude similar to a trichromat with an L/M separation of 15 nm. As few as 1L:3M photopigment molecules within a subset of M cones would produce an opponent difference equivalent to that of anomalous trichromats with 7 nm of separation and hence relatively good colour discrimination sensitivity.
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