Why do white mice have red eyes? - briefly
White mice are albino, lacking melanin in the iris and retinal pigmented epithelium, which allows blood vessels to be seen as red. The genetic mutation responsible for albinism eliminates pigment production, producing the characteristic eye coloration.
Why do white mice have red eyes? - in detail
Albino rodents lack melanin, the pigment responsible for coloration in skin, fur, and the ocular structures that normally block light. In the absence of melanin, the retinal blood vessels become visible through the thin, unpigmented retina and choroid, producing a reddish appearance of the eyes.
The underlying mechanisms are:
- Genetic mutation: A loss‑of‑function mutation in the Tyrosinase (TYR) gene disables the enzyme needed for melanin synthesis.
- Absence of pigment: Without melanin, the iris and retinal pigment epithelium remain translucent.
- Vascular visibility: Light entering the eye is reflected off the underlying choroidal blood vessels, which are rich in hemoglobin, giving the eye a blood‑red hue.
Additional factors influencing the intensity of the red coloration include:
- Age: Younger mice often display brighter red eyes due to thinner ocular tissues.
- Lighting conditions: Strong illumination enhances the contrast between the blood vessels and the clear iris.
- Strain variations: Some albino strains carry secondary mutations that affect eye size or vascular density, modifying the shade of red.
In contrast, mice with partial pigmentation (e.g., piebald or agouti patterns) retain enough melanin to mask the blood vessels, resulting in normal eye coloration. The red eye phenotype therefore serves as a reliable visual marker for complete albinism in laboratory mouse colonies.