ARE BABY'S EYES ALWAYS BLUE?
What makes your eyes blue? Why are my pupils so big? Can my eyes change color?
Nearly all Caucasian infants have blue eyes. This is mainly due to the fact that there are very few "melanocytes", or pigment cells, in the iris. And those melanocytes that are present contain very little pigment. In black and brown races the iris stroma is more dense and the melanocytes contain more pigment, giving rise to a blue-gray appearance. In all races, the pigment cells multiply as the child grows but if the cells contain little to no pigment the eye will stay relatively blue. So, in reality, there are no REAL blue-eyed people, just those that failed to develop brown pigmented melanocytes!
Most of you with light-colored eyes have probably noticed a "spot" or two of brown on your eyes. These are clumps of melanocytes that happen to contain more pigment. These may be called "nevi" or just plain "freckles". They are not unlike those spots on your skin that you call freckles; just a clump of more highly pigmented melanocytes.
Now we know that a lot of pigment will produce a brown eye and that a lack of pigment will produce a blue eye. What about those green eyes? And the hazel? This is a little trickier. A light dusting of brown melanin cells on the iris will produce a yellowish color. Combine the natural blue with the fine scatter of melanin (yellow) and you'll get from a green to hazel color.
Can your eyes really change color? Well, not really, but they certainly can appear to change. All of what we see around us is REFLECTED light. When you look at an object or even another person, you are actually receiving reflected light into your eyes. If that object was illuminated with red light, you would see that object as red, even though it may in fact be white. The melanocytes of the iris do not change (except in infants and the elderly) and therefore are not responsible for periodic eye color changes. The light around you does change, however, especially reflected light....from the color of the room, the sky, and your clothes.
Why are my pupils so big? There is a normal range of pupil size from around 2-9 millimeters. Although a nine millimeter pupil is quite large in normal room light, it is a NORMAL condition. Anisocoria, or unequal pupil size between the eyes is also quite normal, to a certain degree. One study found that 80% of the population showed anisocoria of 0.2 mm or greater at some point in the day. This normal variation is usually not noticeable from casual observation. There are certain pathologies that affect pupil size, however, and if you notice a sudden, significant difference in the two eyes you should consult your eye doctor.
The pupil, as you probably know, is simply a "hole" in the middle of the iris that allows light to enter the eye. In the dark, the small muscle that dilates the eye contracts and the muscle that constricts the pupil relaxes, resulting in a larger pupil. This allows us to see better in the dark. The opposite occurs in bright light so as to restrict the amount of light entering the eye. Pupillary diameter decreases with fatigue, and sleep is accompanied by even smaller pupils. Arousal induced by fear, interest, pain, or excitement causes pupillary dilation. The reason for this is unclear.
I'll look for more "trivia" for you in the columns ahead.