Why does a rat have red eyes? - briefly
Rats look red‑eyed because their irises are tiny and the overlying tissue is largely transparent, so the blood vessels of the retina are visible, particularly in albino specimens. The absence of pigmented layers lets the underlying vasculature show through, producing the red appearance.
Why does a rat have red eyes? - in detail
Rats that display a vivid pink or reddish hue in their eyes lack the pigment melanin that normally masks the underlying blood vessels. In the absence of melanin, the thin layers of the retina and sclera become translucent, allowing the rich network of capillaries to be seen through the pupil. This condition is most common in albino strains, where a mutation in the tyrosinase gene prevents the synthesis of melanin throughout the body, including the iris and retinal pigment epithelium.
The visual system of a rodent consists of several layers that normally absorb and filter incoming light. In pigmented individuals, melanin granules in the iris absorb excess light and protect the retina from phototoxic damage. When melanin is missing, the iris appears pale, and the choroidal blood supply—rich in hemoglobin—creates the characteristic red glare. The phenomenon is not limited to the eyes; albino rats also exhibit pink skin and white fur because the same pigment deficiency affects all melanized tissues.
Genetically, the lack of melanin results from recessive alleles; breeding two carriers produces offspring with the albino phenotype in approximately 25 % of litters. The mutation is stable across generations, making red‑eyed rats a predictable outcome in laboratory colonies that use albino strains for research.
Physiologically, the exposed vasculature does not impair visual acuity under normal lighting conditions, but it reduces the eye's ability to filter ultraviolet radiation. Consequently, albino rats are more sensitive to bright environments and may exhibit heightened stress responses when exposed to intense light sources.
In summary, the red coloration of a rat’s eyes originates from a genetic deficiency of melanin, which renders the ocular tissues translucent and reveals the underlying blood vessels. This trait is a hallmark of albino phenotypes and carries implications for light sensitivity and experimental use.