Monday Medical Issues: Da Boyz are Albinos! Part 2

Yep, da boyz are albinos, as we discussed last week. Temperature-sensitive albinos, to be exact. That's what causes breeds like Siamese, Burmese, Himalayans and Tonkinese to have pointed coats - darker in the extremities and lighter in the torso.

But did you know this albinism extends to eye color, too?

There are two layers in the iris of the eye that determine what color your eyes are (both in humans and cats) – the stroma and the epithelium.

In most cats, pigmented cells are scattered throughout both layers. 

But for cats who have Siamese or Burmese alleles, (that gene pair we discussed last week that causes temperature-sensitive albinism) there is no pigmentation in the stroma.

And, whereas other cat breeds with blue eyes have pigment in that lower epithelial layer, the blue of a Siamese is due to the absence of pigment in both layers.




Whoa… if there's no color in Maxwell's eyes, why do they appear blue?

For the same reason the sky is blue.

(here you go, moms! the answer to the age-old question kids everywhere ask.)

In really basic terms it has to do with the fact that, of all the colors in the visible light spectrum, blue has the shortest wavelength, and colors with shorter wavelengths scatter more than colors with longer wavelengths – it's called Rayleigh Scattering. Since blue light is the predominant light that is bouncing around in the stroma layer, that is the color you see (shown by the cool red arrows in the diagram above!).

You can read more about it at Science Made Simple.

So there you have it, folks. Siamese cats: living out the answer to the age-old question of why the sky is blue.

Oh, and yeah. Da boyz are albinos!

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source:
"Ocular pigmentation in white and Siamese cats", Invest Ophthalmol Vis Sci. 1980 May;19(5):475-86. Thibos LN, Levick WR, Morstyn R.


Comparative Opthalmology, Chapter 11, UC Davis School of Veterinary Medicine