A novel system for the objective classification of iris colour and its correlation with response to 1% tropicamide

Abstract

Iris colour can provide an enormous amount of information about an individual. In addition to changes with pathological conditions, the colour of the iris can be a particularly useful indicator of how well a person will respond to a topically applied ocular drug. Until recently, classification of iris colour has been subjective, ranging from a basic description ('light' and 'dark') to more detailed grading systems, such as a comparison with preset photographic standards. However, variability within observers and differences in the interpretation between observers can influence the results. Objective techniques, in this respect, possess several advantages. They are able to detect differences in colour that subjective techniques are incapable of and they provide continuous data rather than discrete categories, thus improving the accuracy of drug response predictions. This study assessed iris colour by objective means. Slit-lamp photographs of various coloured irides were taken under standardised conditions. The slides were then scanned into a computer and the colour analysed using a calibrated software package. To establish the optimum colour parameter to be used for predictions of drug response, several parameters were calculated and compared with the subject response to 1% tropicamide (maximum change in pupil size, time to maximum change and total duration of effect). Many parameters had strong correlations with drug response, but the parameters 'z', 'b' (the proportion of blue in the image) and 'y' (the proportion of yellow in the image) were found to exhibit the highest correlations. They also showed better correlations with drug response than did a current iris colour grading system.

Towards a colorimetric characterization of the human iris

“…The colour dierence between prostheses and iris set could be attributed to the fact that the manufacture of quality ocular prostheses is currently at a relatively early stage of development, and the iris patterns are usually painted by hand or printed by machine (Port, 1989). The result of the average colour dierence between real observers and iris set should be interpreted with caution, given that our 40 observers were not selected following a rigorous criterion, as in previous works (Seddon et al, 1990;German et al, 1998). Thus, we observe in Figure 3 that there are some rather dark irises (low L Ã ) and only a few bluish irises, as might be expected from a Spanish population (Urtubia, 1991).…”

“…Although, strictly speaking, each human iris is absolutely unique, a quite consistent characterization of the average colour of the iris is possible. With a few exceptions (German et al, 1998), quantitative characterizations of the colour of the human iris are rare in the literature, despite the fact that they would be useful in establishing stronger relationships between iris colour and other parameters in future research. However, from the results provided by iris-recognition technologies or by the visual experiment described here, it is clear that, although colour is an intuitive property of the human iris, it is not the only factor to be considered in characterizing the human iris.…”

“…Although from this result we could conclude that a precise colour measurement of the human iris is not possible, we feel that advances in modern colorimetric instrumentation and colour-image processing oer new possibilities to achieve objective colour measurements of the human iris with increasing accuracy. Thus, an objective technique for measuring iris colour has recently been reported by German et al (1998), who used slit-lamp photographs of the iris scanned into a computer with an appropriate calibration, for an improved correlation between iris colour and drug response.…”

“…Given that until a few years ago quantitative colour measurements of the human iris were not available (German et al, 1998), the main goal of the present paper is to report a new objective method to measure iris colour. Our method has been tested for a set of 72 arti®cial irises, as well as the irises of 25 ocular prostheses and the irises of the right eyes of 40 real observers, without trying to cover the full range of the iris colours of real observers.…”

Colorimetric measurements of iris colour and their significance in East Asian patients with skin cancer

“…[3][4][5][6] However, the validity of this finding in East Asian populations is doubtful. Although objective measurements of iris colour have been performed by several research groups, 1,7 subjective iris-colour classification systems were used. 8,9 Furthermore, these studies were viewed as being unsuitable for the East Asian populations because of a relative homogeneity of iris colour in these populations.…”