Timothy's vision is a focus of interest for many ophthalmologists. he is able to see well when there is low illumination but not so well when there is a lot of light, for instance, if he is outdoors during the day. he is also unable to detect most colors during the day. which poorly-functioning structure of the eye is most likely causing timothy's unusual vision?

Cones.

Explanation:

The eye has two different kind of photoreceptors cells: cones and rod cells.

Cones are the ones who function best in bright light and during the day, the cones can perceive little details.

On the other hand, rod cells are the ones that function when there's dim light or at night, these cells do not perceive details but general forms of the things around and are used in peripheral vision.

Since Timothy can see well in low illumination conditions (function of rod cells) but not so well when there is light or he is outdoors during the day, we can say that the photoreceptors that are likely causing this unusual vision must be cones.