Why do laboratory rats have red eyes? - briefly
Albino laboratory rats lack melanin in their irises, allowing the blood vessels behind the eye to be seen as red. This phenotype stems from a genetic mutation that blocks pigment synthesis.
Why do laboratory rats have red eyes? - in detail
Laboratory rats that appear with pink or ruby‑colored eyes are typically albino. In these animals the gene responsible for melanin production—most often a mutation in the Tyrosinase (Tyrc) locus—is non‑functional. Without melanin, the iris lacks the dark pigment that normally masks the underlying vasculature, so the thin layers of blood vessels become visible through the translucent tissue, producing the characteristic red coloration.
The red eye phenotype results from several interconnected factors:
- Genetic mutation – a loss‑of‑function allele eliminates enzymatic activity needed for melanin synthesis.
- Lack of ocular pigment – the iris, choroid, and retinal pigment epithelium contain minimal melanin, reducing light absorption.
- Visible vasculature – blood in the iris and choroid reflects ambient light, giving a reddish hue.
- Selective breeding – research facilities often maintain albino strains because their lack of pigment simplifies visual assessments and gene‑targeting experiments.
Albino rats differ from pigmented counterparts in several physiological respects:
- Increased photosensitivity – the absence of melanin allows more light to reach the retina, making albinos more prone to glare and retinal damage under intense illumination.
- Altered visual acuity – studies show reduced contrast detection compared to pigmented strains, although basic visual function remains adequate for most laboratory tasks.
- Higher susceptibility to certain diseases – melanin deficiency can affect immune responses and skin integrity, influencing experimental outcomes.
Researchers monitor eye health in albino colonies through regular ophthalmic examinations, ensuring that the red‑eye trait does not confound experimental data. When visual performance is critical, pigmented strains such as Long‑Evans or Brown Norway are preferred to avoid the limitations associated with the lack of ocular pigment.