The Amazing Eye, and I Even Like the Color

Some of the simplest eyes are just passive holes with a semi-clear membrane, such is the reptilian ‘pineal eye.’ This does little more than allow light to enter and thus allow the animal to determine whether it is light or dark outside. Even if their two main eyes are closed, they can still ‘see’ that it is light outside.

This pineal eye is sufficient to regulate their circadian rhythms. Knowing when it’s time to sleep and when it’s time to wake is about the main function of this simple unblinking eye, a simple clear dot which is about the size of a match head. It function  involves a multitude of health benefits to the animal however. Reptiles kept as pets have a particular need to not only have artificial light of a certain wavelength to simulate the sun for UV absorption, but they also require a sufficient period of darkness as well. Unable to close or ‘hide’ their unblinking pineal eye, they perceive perpetual daytime in an enclosure that maintains 24-hour continuous light or even the irregular human-dictated cycles of ‘day’ versus ‘night.’

This would be sheer torture for a wild mammal; it must also be unpleasant at best for a reptile too. While they will survive this unnatural circadian aberration they can become temperamental over time, moody and aggressive. Lethargy and weight loss can be the norm. Surviving but not thriving, breeding in captivity can become almost impossible. Often, returning to proper regulation of diurnal cycles is all it takes in an otherwise acceptable breeding program to induce reptiles to breed successfully in captivity.

Iguana Eye

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Cold and uncaring, the brightly-colored eye of a reptile while beautiful is also a bit scary for some. If they were glass marbles they would be a highly sought-after collectible. Prized like jewels for their colors, patterns and variations, they would be coveted and praised more than even the most brilliant gemstones.

Both animals and humans have phenotypic variations of eye color that are attributed to ratios of eumelanin, a substance produced by melanocytic cells in the iris. More, less, that is what makes all the difference.

Bright eyes of many bird species employ a different process determined by other pigments and possibly dietary preferences have lead to or contributed to this differentiation. If they are regularly consuming something that provides some element or micro-nutrient that favors a particular gene, that gene will be more effective at producing its specific pigment and thus it may manifest itself in very brightly colored eyes of that particular specie over time. Just as removing poison dart frogs from their environment causes them to eventually cease to be ‘toxic’ themselves, it is possible that wild birds removed from their exotic environment (and from their natural food selections) will in time cause their eyes to not be so brilliant and colorful.