Afferent pupillary defect is an eye condition where one eye is less sensitive to light, indicating optic nerve damage or other eye problems. The oscillating light test can identify this defect, and doctors must be careful in the exam. Treatment may include glaucoma medications or surgery. Patients may not be aware of the condition before the exam.
An afferent pupillary defect is an eye condition in which one eye is less sensitive to light and does not contract as sharply in response to light as the healthy eye. This can be a sign of optic nerve damage, a tumor, glaucoma, and a number of other eye problems. A doctor can identify this defect with the oscillating light test, in which he rapidly moves a light back and forth between the eyes to monitor pupillary response.
The neurological circuitry that controls pupil dilation and contraction works simultaneously in both eyes. For example, when a doctor shines a bright light on the left eye, the right eye also twitches. In a patient with an afferent pupillary defect, shining light into the healthy eye will cause both pupils to contract tightly. If the doctor shines light on the injured eye quickly, the pupils will appear to dilate, because the optic nerve gets less light and thinks it needs to open the pupils for visibility.
Anisocoria, in which the pupils dilate and contract at different rates, is not seen in patients with afferent pupillary defect. The pupils still respond to stimuli simultaneously, but one of the eyes receives garbled signals and does not contract as much as it should in response to light. This can be seen in patients with severe visual impairment caused by a variety of ophthalmic conditions.
Doctors need to be careful in an eye exam, as how fast they move light can impact the outcome of the test. If the light moves too slowly, your doctor may get an incorrect reading. If afferent pupillary defect is suspected, the doctor will repeat the test to confirm. This clinical sign, also known as Marcus Gunn pupil, requires further investigation to learn more about the cause. Treatments may include glaucoma medications or surgery to remove a tumor that is interfering with the optic nerve.
Patients with this condition may not be aware of it before the exam. In bright light, the healthy eye will readily contract, bringing the pupil of the damaged eye with it to a small size. Similarly, in dark conditions, the eyes dilate the same way. Rapidly flashing a bright light back and forth between the eyes is the only way to see the differential response, illustrating that one eye has difficulty with interpreting visual information while the other does not.
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