UVR reflections at the surface of the eye.

Sunlight plays an etiological role in the formation of skin cancers [Phys. Med. Biol. 24 (1979) 931]. Non-melanoma skin cancers commonly arise in sun-exposed parts of the body, especially on the head and neck regions [Int. J. Dermatol. 34 (6) (1995) 398] although the amount of sun exposure that is required for the formation of skin cancers is still unknown. It is known that the larger the dose of UVR, and in particular the erythemal action spectrum, the more likely it is to form the non-melanoma skin cancers, basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs). A number of regions on the face exhibit a seemingly high rate of occurrence of BCCs in relation to apparent direct exposure. One of these regions is the inner canthus located next to the eye on the bridge of the nose which has an occurrence rate of 7.1% of all BCCs that occur on the head and neck [Gen. Surg. 51 (6) (1981) 576, Aust. NZ J. Surg. 60 (1990) 855, Malignant Skin Tumours, Longman Singapore Publishers, Singapore, 1991]. The inner canthus seems to be well protected from large direct doses of ultraviolet radiation (UVR) and to explain the higher incidence of BCCs on the inner canthus it is proposed that a significant proportion of the incident UVR on the eye and surrounding areas is reflected onto the inner canthus. This paper presents a preliminary investigation of the contribution of UVR reflected to the inner canthus from the tear film covering the eye using a two-dimensional theoretical model on the horizontal plane (0 degrees elevation angle). Calculations show that up to 30% of the total radiation that is received on the inner canthus on a cellular level in this plane is reflected from the eye. A three-dimensional computer-generated ray tracing model of the eye, surrounding facial features and the inner canthus is being created to investigate the effect that these reflections have on the total dose of UVR.