Seeing functions of sensing a minimum amount of light (light minimum), and the minimum difference in intensity (light difference).

For example impairments such as night blindness as in retinitis pigmentosa.

or light sensitivity due to coloboma of the iris. Without the full ability to control the amount of light entering the eye, a person may have discomfort and poorer vision in bright light. Use of a hat and sunglasses would then be recommended for daytime travel, recreation, or work. A small coloboma or a coloboma of the iris may have little to no impact on vision.