A standardized tool to measure and describe scleral colour in osteogenesis imperfecta.

Background:  Blue colouration of the sclera is a distinctive feature of unknown aetiology in osteogenesis imperfecta (OI). It has value as a diagnostic marker, for distinguishing prognostically distinct subtypes of the condition, and has been reported to undergo rapid unexplained changes concurrently to fractures. Description of the feature is currently hampered by lack of a clinical tool. Methods:  A range of blue reference colour chips from an internationally recognized standard (the Munsell system) was used under standardized viewing conditions, by two independent observers with normal colour perception, to classify the scleral colour of affected individuals. Results:  A total of 43 individuals affected by OI of a wide variety of severity with ages from 5 to 63 years were observed. All individuals in the sample had blue sclerae, and all colours seen could be matched to a Munsell standard within the hue range of 7.5B (blue) to 5PB (purple-blue). There was little variation in observed chroma (saturation), and observations of hue showed poor inter-observer reliability (r = 0.17 ± 0.34: 95% CI). However, levels of value (lightness) showed wide variability and good inter-observer reliability (r = 0.63 ± 0.14: 95% CI). Conclusions:  A practical tool for the description of the colour of the sclera in individuals with OI can be constructed using the colours from the Munsell system varying in value (lightness) with hue: 2.5 PB and chroma: 2.