Counterphase modulation photometry: comparison of two instruments.

The ratio of long-wavelength to medium-wavelength sensitive cones varies significantly among people. In order to investigate the possible effect of this variation in large numbers of participants, a quick and efficient method to estimate the ratio is required. The OSCAR test has been utilized previously for this purpose, but it is no longer available commercially. Having access to one of the few remaining OSCAR instruments, we compared the observers' mean settings to those obtained with the Medmont C100, a newer but apparently similar device. We also obtained Rayleigh matches for each participant. One hundred volunteers took part in the study. Settings on the OSCAR test were highly correlated with those on the Medmont C100. Both tests appeared to be influenced not only by L∶M cone ratios but also by the spectral positions of the cone photopigments, since anomaloscope midmatch points accounted for a significant proportion of the variance. We conclude that the Medmont C100 can be used as a suitable replacement for the OSCAR test and has a role in the rapid estimation of L∶M cone ratios.