Impact of iris pigment and pupil size in ultraviolet radiation cataract in rat

Purpose: To investigate the effect of iris pigment and pupil size in ultraviolet radiation (UVR)‐induced cataract. Methods: Brown‐Norway rats (pigmented) and Fischer‐344 rats (non‐pigmented) were unilaterally exposed in vivo to 5 kJ/m² UVR. Each strain was split into two groups, each receiving either mydriatic (tropicamide) or miotic (pilocarpine) eye‐drops. One week after exposure, the degree of ocular inflammation and damage in the anterior segment was determined. The lenses were extracted, photographed and the degree of forward light scattering (cataract) was quantified. Results: The cataract types differed between the two strains. All Fischer rats developed macroscopically identifiable UVR cataract while only 41% of Brown‐Norway rats did so. All groups except the miotic Brown‐Norway developed significant light scattering. The Fischer rats developed 3–4‐fold more lens light scattering than the Brown‐Norway rats. The miotic Fischer group exhibited significantly more light scattering than the mydriatic Fischer group. There was no significant difference in light scattering between the two Brown‐Norway groups. There was a correlation between ocular inflammation and degree of light scattering, with Brown‐Norway rats exhibiting less inflammation and lens light scattering. Conclusions: Pigmented rats develop less UVR cataract and less ocular inflammation than non‐pigmented rats. Pupil size plays a smaller role in UVR cataract development in pigmented rats than in non‐pigmented. The role of UVR‐induced ocular inflammation in cataract development is still ambiguous.