Classification of iris colour: review and refinement of a classification schema

Abstract

Eye colour or, more accurately, iris colour is one of the most obvious physical characteristics of a person. European parents frequently ask the colour of their newborn's eyes, only to see the iris change dramatically during their child's first year of life. Genetic and epidemiological findings have uncovered further details about the basis for iris colour, which may have important implications for further research and treatment of some eye diseases and ocular characteristics. Surprisingly there is no widely recognized classification system for eye colour. An added difficulty when trying to devise an international system is that subtle differences in colour description exist between languages (e.g. hazel vs. auburn). We reviewed the recent and very early literature pertaining to eye colour classification. Recent genetic investigations of eye colour have tended to either use simple (three-category grading systems) or more complex digital colour grading. We present a nine-category grading system. Categories in this novel schema include: (i) light blue; (ii) darker blue; (iii) blue with brown peripupillary ring; (iv) green; (v) green with brown iris ring; (vi) peripheral green central brown; (vii) brown with some peripheral green; (viii) brown; and (ix) dark brown. Although different observers may categorize a person's eye colour differently, it is generally only by an adjacent category. We also describe a continuum of iris pigmentation from a small ring of brown around the pupil to almost complete brown with small peripheral flecks. Digital publishing and assessment of iris colour will result in more standardized classification of iris colour and investigation of its role in eye disease.

Precautions in ophthalmic practice in a hospital with the risk of COVID‐19: experience from China

“…While families tend to identify the iris colour of their newborns, physicians should also monitor the iris colour of their patients. Changes in iris colour may reveal signs of pathology such as neurofibromatosis, Down syndrome, herpes simplex, pigment dispersion, albinism or primary melanocytic tumours of the iris (Mackey et al 2011).…”

Myopia Outcome Study of Atropine in Children (MOSAIC): an investigator-led, double-masked, placebo-controlled, randomised clinical trial protocol

“…A second drop of 1.0% cyclopentolate is instilled in each eye for participants with iris classification green with brown iris ring (v), peripheral green central brown (vi), brown with some peripheral green (vii), brown (viii), and dark brown (ix). [3] 15 minutes post cyclopentolate insertion, the subject is examined to ensure both pupils are dilating and amplitude of accommodation is reducing compared to their pre cycloplegia assessment. If the onset of cycloplegia is not apparent at 15 minutes, another drop of cyclopentolate hydrochloride 1% is instilled.…”

“…Myopia is expected to affect 2.5 billion people by 2020 and close to 5 billion by 2050 1,2 . Developed countries in East and Southeast Asia have the highest prevalence of adolescent myopia, with over 90% of 18 year olds in Singapore and 72% in China affected 3 . There is also evidence that myopia prevalence is increasing in Europe, with myopia affecting almost 50% of 25 to 29 year olds, and the proportion of myopic children more than doubling in the UK over the last 50 years [4][5][6] .…”

Biophysical chemistry of the ageing eye lens

“…The iris consists of two layers, an inner layer of highly pigmented epithelial cells and an outer non-pigmented layer that projects the dilator muscles. The colour of the lens is determined by the concentration of melanin in the epithelium and the scattering of light by the stroma (Mackey et al 2011).…”