Final answer:
A patient with one large pupil may have damage to the oculomotor nerve, optic nerve damage, or other neurological conditions. This phenomenon is called anisocoria and often requires a medical evaluation to determine the underlying cause.
Step-by-step explanation:
If a patient has one large pupil, it suggests a possible issue with the oculomotor nerve, potential optic nerve damage, or other neurological anomalies. This condition is known in the medical field as anisocoria.
When shining light in one eye elicits constriction of both pupils, this normal response is due to the functioning of the pupillary light reflex. If shining light causes only the opposite pupil to constrict, it indicates the direct reflex is lost and the damage is likely in the oculomotor nerve of the non-responding eye.
Conversely, if the light causes no response in the contralateral pupil when light is presented to the opposite eye, the issue could be with the optic nerve. Other conditions, such as unilateral hyperthyroidism or Graves' disease, can also lead to one enlarged pupil and should be considered. Therefore, anisocoria can be a sign of a variety of underlying causes that require medical evaluation.