Blue-cone monochromats

    Blue-cone monochromats (or S-cone monochromats) were first described by Blackwell & Blackwell (1957; 1961), who concluded that they had rods and S-cones, but lacked M- and L-cones. Though two studies suggested that blue-cone monochromats might also possess a second cone type containing the rod photopigment (Pokorny, Smith & Swartley, 1970; Alpern, 1971), subsequent studies have supported the original conclusion of Blackwell & Blackwell that they have only rods and S-cones (Daw & Enoch, 1973; Hess et al., 1989).

    Pedigree studies show that blue-cone monochromacy is an X-linked recessive trait (e.g., Falls, 1960; Spivey, 1965). A molecular genetic analysis of the M and L-cone photopigment gene array on the X-chromosome of blue-cone monochromats shows that the deficit can arise for a number of different reasons, including deletions, or loss of function due to homologous recombination and point mutation (Nathans et al., 1989; Nathans et al., 1993).

    Spectral sensitivities in "classic" blue-cone monochromats have been measured several times before (e.g., Blackwell & Blackwell, 1961; Grützner, 1964; Alpern, Lee & Spivey, 1965; Alpern et al., 1971; Daw & Enoch, 1973; Smith et al., 1983, (patient V-4); Hess et al., 1989), and are typical of the S-cones. A concern about the use of blue-cone monochromats to obtain a standard S-cone spectral sensitivity for central vision, however, is that they usually fixate extrafoveally (but there are exceptions, see Hess et al., 1989).

    Consequently, in order to use blue-cone monochromats to estimate normal S-cone spectral sensitivity, it is necessary to estimate their macular and photopigment optical densities, and, if necessary, correct them to normal density values. Moreover, some individuals in pedigrees with blue-cone monochromacy reveal residual L-cone function if large or even small test fields are used (cf. Smith et al., 1983). Thus, caution must be exercised when selecting candidates, whose genotypes should be known.


Alpern, A., Lee, G. B., & Spivey, B. E. (1965). π1 cone monochromatism. Archives of Ophthalmology, 74, 334-337.

Alpern, M., Lee, G. B., Maaseidvaag, F., & Miller, S. S. (1971). Colour vision in blue-cone 'monochromacy'. Journal of Physiology, 212, 211-233.

Blackwell, H. R., & Blackwell, O. M. (1957). Blue mono-cone monochromacy: a new color vision defect. Journal of the Optical Society of America, 47, 338.

Blackwell, H. R., & Blackwell, O. M. (1961). Rod and cone receptor mechanisms in typical and atypical congenital achromatopsia. Vision Research, 1, 62-107.

Daw, N. W., & Enoch, J. M. (1973). Contrast sensitivity, Westheimer function and Stiles-Crawford effect in a blue cone monochromat. Vision Research, 13, 1669-1680.

Falls, H. F. (1960). Discussion following paper by Alpern, Falls and Lee. American Journal of Ophthalmology, 50, 1012.

Grützner, P. (1964). Der normale Farbensinn und seine abweichungen. Bericht der Deutschen ophthalmologischen Gesellschaft, 66, 161-172.

Hess, R. F., Mullen, K. T., Sharpe, L. T., & Zrenner, E. (1989). The photoreceptors in atypical achromatopsia. Journal of Physiology, 417, 123-149.

Nathans, J., Davenport, C. M., Maunenee, I. H., Lewis, R. A., Hejtmancik, J. F., Litt, M., Lovrien, E., Weleber, R., Bachynski, B., Zwas, F., Klingaman, R., & Fishman, G. (1989). Molecular genetics of human blue cone monochromacy. Science, 245, 831-838.

Nathans, J., Maumenee, I. H., Zrenner, E., Sadowski, B., Sharpe, L. T., Lewis, R. A., Hansen, E., Rosenberg, T., Schwartz, M., Heckenlively, J. R., Traboulsi, E., Klingaman, R., Bech-Hansen, N. T., LaRoche, G. R., Pagon, R. A., Murphey, W. H., & Weleber, R. G. (1993). Genetic heterogenity among blue-cone monochromats. American Journal of Human Genetics, 53, 987-1000.

Pokorny, J., Smith, V. C., & Swartley, R. (1970). Threshold measurements of spectral sensitivity in a blue cone monochromat. Investigative Ophthalmology and Visual Science, 9, 807-813.

Smith, V. C., Pokorny, J., Delleman, J. W., Cozijnsen, M., Houtman, W. A., & Went, L. N. (1983). X-linked incomplete achromatopsia with more than one class of functional cones. Investigative Ophthalmology and Visual Science, 24, 451-457.

Spivey, B. E. (1965). The X-linked recessive inheritance of atypical monochromatism. Archives of Ophthalmology, 74, 327-333