The C‐100:a new dichotomiser of colour vision defectives

Abstract

This paper evaluates a new instrument (G100) which employs flicker photometry or silent substitution to determine the type of colour vision defect (protan or deutan). Specifically, this study addresses the unit’s capacity to: 1. detect colour vision defects; 2. differentiate protans from deutans; and 3. produce reliable measurements under different viewing conditions. We find that an average of five readings enables protans to be clearly separated from deutans in all cases (p < O.OOOl), but that the distinction between these groups and normals is less clear. Dichromats are not distinguished from anomalous trichromats, so the instrument cannot be used as an index of severity. The results are shown to be robust to most of the test conditions likely to be encountered during normal clinical use. A clinical protocol is suggested that utilises the ClOO for classification of colour defective observers. It is concluded that normal, and some anomalous, trichromat settings are performed using flicker photometry, whereas dichromatic observers appear to utilise silent substitution. Accepted for publication: 30 June 1992