When a normal eye encounters bright light, the pupil contracts to cause less light to enter the eye. The pupil is actually a hole in a structure called the iris, and it is the iris which causes the pupil to change shape. In dim light, the pupil gets bigger, or dilates, so that more light can come in.
Conditions affecting the iris may cause a person to experience photophobia, or sensitivity to bright light, or to have difficulty seeing at all if the pupil is obstructed. Some conditions, such as iritis, can be very painful.
The iris may be important in the treatment of other conditions as well. After a surgery, dilating drops may be prescribed for a few weeks so that the dilation and constriction of the pupil will not cause pain. During this time, the patient may see things differently from the way he/she will see them after the dilating drops are discontinued.
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