The effect of the eye’s surface topography on the total irradiance of ultraviolet radiation on the inner canthus

Basal cell carcinoma is the most commonly occurring skin cancer in sub tropical climates. The link between ultraviolet radiation (UVR) and basal cell carcinomas (BCC) is strong. Numerous studies have investigated the spatial distribution of BCCs over the head and neck region and the relative UVR dose, with little or no correlation found between the UVR dose and occurrence rates. This is particularly noted in the inner canthus region. The inner canthus’ field of view is restricted by the eye brow ridge, eye orbit and the cheek bone. Yet, the occurrence rate here of BCC’s when compared to other regions that are more directly exposed to the environment is significantly higher. A possible causal effect for the increase in occurrence rate in this region is the focussed reflection of UVR from the tear film surface associated with the eye not previously considered in earlier studies. This paper investigates the potential for the surface topography of the eye to reflect focussed radiation towards the inner canthus using a ray tracing programme where the analysis is conducted at a cellular level. Defined hot spots, or striations, of increased irradiation were evidenced across the surface of the inner canthus. This increase in irradiation was not observed with macroscopic detectors which also possibly explain why this increased dose has not previously been detected during environmental measurements with large detectors on manikins or humans.