Why do white rats have red eyes? - briefly
The absence of melanin in albino rats renders the iris translucent, allowing light to pass through and reflect off the vascular choroid, which appears red. This phenomenon is known as the red‑eye effect.
Why do white rats have red eyes? - in detail
Albino laboratory rats lack melanin because a mutation disables the enzyme tyrosinase, which normally converts the amino acid tyrosine into pigment. The genetic defect is recessive and produces a uniform white coat and unpigmented skin, hair, and ocular structures.
In the eye, melanin normally resides in the iris stroma and the retinal pigment epithelium. Without this pigment, the thin iris tissue becomes translucent. Light entering the eye passes through the iris and reflects off the richly vascularized choroid and retinal blood vessels. The reflected light carries the reddish hue of hemoglobin, which is why the eyes appear red when illuminated.
The red-eye effect results from three anatomical factors:
- Absence of melanin in the iris, making it transparent.
- Presence of a dense network of blood vessels behind the iris.
- External light reflecting off these vessels back toward the observer.
Because the retinal pigment epithelium also lacks melanin, albino rats are more sensitive to bright light and may develop photic damage more readily than pigmented strains. Their visual acuity is reduced, and they rely more on non‑visual cues.
The trait is inherited as an autosomal recessive allele (commonly denoted “c”). Homozygous individuals display the white coat and red eyes, while heterozygotes retain normal pigmentation. Breeders maintain colonies by selecting for the recessive genotype to ensure a consistent supply of albino specimens for biomedical research.
Red-eyed albino rats are employed in studies of genetics, ophthalmology, and behavior because their lack of pigment simplifies certain experimental observations, such as tracking ocular blood flow or assessing the impact of light exposure on retinal health. The characteristic eye coloration thus serves both as a phenotypic marker of the underlying mutation and as a functional factor influencing experimental outcomes.