Why do rats have white eyes? - briefly
White‑eyed rats lack melanin due to albinism or other pigment‑deficiency genetic mutations.
Why do rats have white eyes? - in detail
Rats with white irises lack the pigment melanin, which normally gives the eye its dark coloration. The absence of melanin results from genetic mutations that disrupt the synthesis of this pigment. In most laboratory strains, the mutation occurs in the tyrosinase (Tyr) gene, which encodes an enzyme essential for converting the amino acid tyrosine into melanin. When Tyr function is lost, melanocytes cannot produce pigment, and the iris appears white.
Other genetic alterations can produce a similar phenotype. Mutations in the Oca2, SLC45A2, or MITF genes affect melanin transport or regulation, leading to partial or complete loss of pigmentation in the eye. Some strains carry the c (cataract) or w (white) alleles that specifically affect ocular pigment without influencing coat color.
The lack of pigment in the iris and retina has several physiological consequences. Light entering the eye is not adequately filtered, increasing glare and reducing contrast sensitivity. The retinal pigment epithelium, which normally absorbs scattered light and supports photoreceptor health, is also deficient, often resulting in reduced visual acuity and altered circadian rhythm signaling.
White-eyed rats are deliberately bred for research because their genetic uniformity and visible phenotype simplify the identification of genotypes. They serve as models for:
- Albinism studies – examining the role of melanin in development and vision.
- Ophthalmic research – testing treatments for retinal degeneration and cataracts.
- Behavioral experiments – assessing the impact of visual impairment on learning and navigation.
In summary, the white coloration of the eyes arises from mutations that halt melanin production, chiefly in the tyrosinase pathway, leading to pigment deficiency in ocular tissues and associated visual deficits.