What would cause eyes not to dilate?

Several factors can cause eyes not to dilate properly. These include:

1. Medications: Certain medications, such as some antihistamines and antidepressants, can cause the pupils to become constricted and prevent them from dilating.

2. Neurological disorders: Neurological conditions such as Horner's syndrome or third nerve palsy can affect the nerves that control pupil dilation, causing the pupils to remain small or dilated.

3. Eye conditions: Certain eye conditions, such as uveitis (inflammation of the eye) or glaucoma, can also affect pupil dilation.

4. Central nervous system disorders: Conditions that affect the central nervous system, such as brain tumors or strokes, can also impair pupil dilation.

5. Ocular trauma: Injuries to the eye, such as a blunt force trauma, can damage the structures involved in pupil dilation.

6. Diabetes: Diabetic neuropathy, which is nerve damage caused by diabetes, can affect the nerves that control pupil dilation, leading to abnormal pupil responses.

7. Genetic disorders: Some genetic conditions, such as congenital pupil anomalies, can cause the pupils to remain dilated or constricted.

If you notice changes in your pupil size or responsiveness, it's crucial to consult with an eye doctor (ophthalmologist) to determine the underlying cause and receive appropriate treatment.