Final answer:
Prisms are used to diagnose strabismus to determine the amount and direction of eye misalignment. The cover test, which involves observing eye movements while one eye is covered, is also used to diagnose strabismus.
Step-by-step explanation:
Strabismus, also known as crossed eyes or squint, is a condition where the eyes do not align properly. To diagnose strabismus, an eye doctor may use prisms to determine the amount and direction of eye misalignment. These prisms can help the doctor assess the severity of the condition and prescribe the appropriate treatment.
On the other hand, diagnosing strabismus using light involves a procedure called the cover test. In this test, the eye doctor covers one eye at a time and observes the movements of the uncovered eye. If the uncovered eye shifts to fixate on an object, while the covered eye remains misaligned, it indicates the presence of strabismus.