When eye colour changes…
Melanin production generally does not begin at birth. This is one reason why many babies born to Caucasian people have blue or blue-grey eyes. Once melanin production starts, a baby’s eyes may darken within the first few years, and the colour could change to become darker blue, green, hazel or shades of brown. Some babies are born with brown eyes and this colour doesn’t typically change over time. Usually by the age of 3, a permanent colour settles, which a person will likely have for the remainder of their life.
Eye colour, however, can appear to change for various reasons thereafter. Subtle changes can occur which alters colour a little. Sometimes, different lighting can have an effect on the colour of a person’s eyes. The reason a person’s eye colour may appear to change in different lighting is due to the pigment contained in each of the two layers in the iris. The front layer, in a person with blue or green eyes, for example, may have very little to no melanin at all. With diffraction of light and enough melanin in the other layer, a person’s eyes can appear as different colours in certain lighting conditions.
Other factors which influence eye colour during a person’s lifetime include:
- Emotions: Intense emotions such as anger can alter the size of the pupil and thus influence colour as well. Eye colour can change slightly when the iris expands and contracts in order to control the pupil size. When lighting is dimmer, the pupil enlarges. In brighter lighting conditions, the pupil contracts and becomes smaller. During the process of expansion and contraction, the pigment in the iris spreads or compresses, which alters the colour of the eyes somewhat.
- Age: For many, eye colour tends to lighten after a certain age. Generally, those with lighter colour eyes will notice that their colour lightens during their later years – for instance, colour can change from a hazel green to a shade of grey. Others may note that their dark eyes, darken instead. A small percentage of people (about 10% to 15%) can experience change in eye colour beyond their toddler years, and this is most commonly seen in people of Caucasian descent. Change is usually subtle though. Studies have noted that people with lighter colour eyes tend to experience more noticeable changes than those with darker coloured eyes.
When should you be concerned about eye colour changes?
Not every colour change is part of a normal functioning process. There are some instances where colour changes will need to be assessed / monitored by a medical doctor.
Abnormal changes could be a result of one of the following:
- Fuchs uveitis syndrome (Fuchs heterochromic uveitis / Fuchs heterochromic iridocyclitis): A condition which most commonly affects one eye, mild inflammation (usually chronic) alters the state of the middle portion of the eyes, including the iris. One of the resulting signs is a lightening of the iris (of the affected eye), which creates a difference in colour between a person’s eyes (heterochromia). This can increase a person’s risk of developing cataracts or glaucoma.
- Pigmentary glaucoma / pigment dispersion syndrome: When the pigment in the iris becomes disrupted, loose granules accumulate in the front chamber (layer) of the eye. This can lead to one of two things – glaucoma (where vision loss occurs due to increased pressure in the eye) or dispersion (causing colour changes), which results in a person having two different colour eyes.
- Horner syndrome: When an impairment of fibres in the third cranial nerve occurs, one of the signs of Horner syndrome is a lighter colour in the affected eye than the other. This is most commonly seen in children with the condition (most often before a child’s first birthday), but can also happen in adults (although rare). A key sign is a drooping eyelid. The pupil in the affected eye also contracts, becoming smaller than normal.
- Medication usage: Prescribed medications for the treatment of glaucoma can also result in subtle changes in eye colour. Eye drops can help to reduce internal pressure in an affected eye and sometimes result in colour changes – lighter eyes may darken with an increased amount of pigment in the iris. In many instances, darkening as a result of medication use may be permanent.
It is also possible for traumatic injury to the eyes or a tumour of the iris (benign or malignant) to cause changes in eyes colour. Any abnormal change in one or both eyes must be evaluated by a medical professional (eye specialist) as soon as possible, especially if there are symptoms of pain, redness or vision changes (blurry or limited ability).