• Standard methods for screening color vision defects may be expected to underestimate a color defective's complete chromatic discrimination abilities because the viewing field is confined to the fovea (central 2°). Large-field (8°) Farnsworth-Munsell 100-hue and dichotomous (D-15) tests were constructed. The 100-hue test, along with its small-field counterpart, was administered to five deuteranopes (green defectives) and four protanopes (red defectives). The D-15 small- and large-field tests were given to these same subjects with the addition of two deuteranopes and one protanope. Both deuteranopes and protanopes showed marked improvement on the large-field D-15 and 100-hue tests. This improvement in performance for largefield over small-field viewing is consistent with color-matching data, which show large-field trichromacy in observers who have been demonstrated to be small-field red-green dichromats. These results suggest that tests confined to central fovea viewing provide an incomplete functional description of the color vision of an appreciable number of classic dichromats.
Breton ME, Tansley BW. Improved Color Test Results With Large-Field Viewing in Dichromats. Arch Ophthalmol. 1985;103(10):1490-1495. doi:10.1001/archopht.1985.01050100066021