The sight of a pure white rabbit with striking red eyes is common in domestic breeds, and the reason for this appearance is purely biological. The color is not an actual pigment but rather a visual effect caused by a complete lack of color-producing cells in the eyes. This absence of pigment allows the underlying circulatory system to become visible, creating the distinct ruby-red hue. This phenomenon stems from albinism, a genetic condition that affects the body’s ability to produce the primary coloring agent found in mammals.
The Role of Melanin in Coloration
Melanin is the natural pigment responsible for providing color to the hair, skin, and eyes of nearly all mammals. This substance is produced by specialized cells called melanocytes, which distribute two main types of melanin: eumelanin (black and brown) and pheomelanin (yellow and reddish). The concentration and ratio of these two forms dictate the color palette of a rabbit’s coat and its eye color.
Melanin also serves a protective function, particularly in the eyes. It helps absorb harmful ultraviolet (UV) radiation and acts as a neutral-density filter to protect delicate tissues from excessive light exposure. Melanin lines structures like the iris and the retina, preventing light from scattering internally and contributing to clear vision. The standard dark eye color seen in most animals is the visual result of a high concentration of this light-absorbing pigment.
Albinism The Genetic Explanation
The condition causing the lack of pigment is albinism, which results from a genetic mutation that prevents the production or distribution of melanin. In rabbits, this trait is linked to the C locus, where a specific recessive allele, denoted as ‘c’, is responsible for complete albinism. A rabbit must inherit two copies of this recessive gene—one from each parent—to exhibit the albino phenotype.
When both copies of the C locus gene are the recessive ‘c’ allele (genotype ‘cc’), the rabbit’s system cannot produce the enzyme necessary for melanin synthesis. This leads to a coat that is entirely white, as all other potential color genes are functionally masked. This complete genetic shutdown of pigment production defines a true albino rabbit.
The Mechanism of Red Coloration
The ruby-red eye color is a direct consequence of the complete lack of melanin in the ocular structures. A normally pigmented eye has melanin in the iris, choroid layer, and retina, which absorbs light and gives the eye its color. In an albino rabbit, the iris is translucent because it contains no pigment to block or absorb light.
When light enters the albino rabbit’s eye, it passes straight through the transparent iris and clear ocular tissues without being absorbed. The light then reflects off the blood-rich capillary beds located in the back of the eye, specifically in the retina and the choroid. The bright red color observed is the visual presentation of the rabbit’s own circulating blood, made visible through the uncolored tissues. This effect is similar to the “red eye” phenomenon seen in flash photography, where the flash illuminates the blood vessels at the back of the eye.
Not All White Rabbits Are Albino
It is a common misconception that every rabbit with a white coat is an albino. Other genetic conditions result in white fur but allow for normal eye coloration. These non-albino white rabbits have blue, brown, or other eye colors because the genetic mechanism affecting their coat differs from true albinism.
The Blue-Eyed White (BEW) rabbit, for example, results from a different recessive gene at the V locus, often called the Vienna gene. This gene restricts pigment production in the fur, resulting in a white coat, but it does not completely eliminate melanin from the eyes. The eyes of a BEW rabbit appear blue due to the way light scatters across the low concentration of pigment still present in the eye’s stroma. The presence of color in the eye determines if a rabbit is a true albino or simply a white rabbit.