Why do rats have red eyes? - briefly
Rats show red eyes because their irises lack melanin, making the underlying blood vessels visible through a thin, translucent tissue. This lack of pigment, typical of albino or hypopigmented strains, produces the characteristic reddish appearance.
Why do rats have red eyes? - in detail
Rats display red eyes primarily because the iris lacks melanin, allowing the blood-rich choroid to show through the pupil. This condition is most common in albino strains, where a mutation in the tyrosinase gene blocks pigment production throughout the body, including the eye. The absence of pigment also makes the retina more sensitive to light, so albino rats often exhibit heightened photophobia and may develop ocular pathologies such as cataracts or retinal degeneration.
Key factors contributing to the phenomenon:
- Genetic mutation – a loss‑of‑function allele in the tyrosinase enzyme prevents conversion of tyrosine to melanin.
- Lack of iris pigmentation – without melanin, the iris appears translucent, revealing underlying vasculature.
- Visible choroidal vessels – the dense network of blood vessels beneath the retina reflects red light, producing the characteristic hue.
- Breed prevalence – laboratory and pet albino rats are selectively bred for this trait, reinforcing its frequency in captive populations.
- Physiological consequences – reduced ocular protection can lead to increased susceptibility to UV damage and visual impairments.
In contrast, pigmented rat strains possess melanin in the iris, resulting in brown, black, or amber eye colors. The red appearance is therefore a direct visual indicator of albinism and the associated absence of ocular pigment.