For most people, eye colour will remain consistent throughout a lifetime, since the colour of one's eyes matures in infancy and generally stays the same colour. In a small percentage of people, however, various factors can cause eye colour to change in old age, while ailments such as glaucoma can also alter the eyes' appearance.
Changes in Eye Color
The colour of our eyes is determined by the amount and colour of pigment granules, called melanin. These granules vary in colour from a neutral tone to very dark brown, with darker eyes caused by darker melanin or a greater degree of melanin, and vice-versa. The colour of the iris is caused by pigment in the stroma (the connective tissue of the front layer of the iris), and this colour can lighten if the amount of pigment granules in the stroma decreases, or if the granules produce lighter pigment. Unlike skin and hair, eyes don't synthesise colour pigment all the time, but retain the accumulated pigment in the stroma. If the pigment degrades over time, this can result in a lightening of eye colour.
One typical factor that can cause a person's eyes to change colour is disease. In fact, a change in eye colour could be a symptom of an eye disease, so any noticeable colour changes should be examined by a doctor. Some of the most common diseases that can lead to a change in eye colour are Horner's Syndrome, pigmentary glaucoma and Fuch's heterochromic iridocyclitis, which generally occur most often in the elderly.
Genetics has much to do with whether or not your eyes will change colour as you age, and 10 to and 15 per cent of Caucasians will experience change in eye colour (races with darker eyes generally experience little change as they get older). This occurs because the amount of melanin in the iris will decrease over time, causing the colour of the iris to alter. This is the same principle that causes hair to change colour as we age, and the rate and age at which is this occurs can vary due to genetic determination.
Another change that can happen to eyes as we age is the appearance of yellowing, a fairly common occurrence among the elderly. This occurs because the chemical composition of the eye's variable lens can change over the course of time as proteins are produced in different proportions than they used to be. These chemical changes can cause the lens to take on a yellow appearance, reducing the lens' transparency and causing it to become somewhat opaque.