Relative afferent pupillary defect
Relative afferent pupillary defect
Description, Causes and Risk Factors:
A relative-afferent-pupillary defect, commonly referred to as the Marcus Gunn pupil, points to asymmetric function of the retina or optic nerve. The anterior midbrain, controlling pupillary size, receives a message from the affected eye that illumination is reduced as compared with the fellow eye, or relative to the fellow eye. The pupillary hallmarks are, therefore, either: (1) pupillary dilatation following a constrictive reaction to a light stimulus applied to the affected side, or (2) the dilation of both pupils when a light stimulus is moved from the non-affected eye to the affected eye.
RAPD is a medical sign observed during the swinging-flashlight test whereupon the patient's pupils constrict less (therefore appearing to dilate) when a bright light is swung from the unaffected eye to the affected eye. The affected eye still senses the light and produces pupillary sphincter constriction to some degree, albeit reduced.
An RAPD generally occurs with significant optic nerve or retinal disease, when there is a difference in the disease process between the two eyes. Each eye has severe but equal disease, there will be no RAPD. Thus, a "bilateral" RAPD does not exist.
Severe disease in one eye leading to an RAPD will not lead to anisocoria. The diseased eye's pupil will appear to be of equal size to the other eye due to the consensual light reaction (unless the iris itself is diseased or unreactive).
Because of the consensual light reaction, only one functioning pupil is needed to determine the presence of an RAPD.
The visual acuity does not necessarily correlate with an RAPD. Some conditions will lead to a marked reduction of visual acuity with an RAPD, while others spare the central vision. Often an extensive loss of peripheral vision correlates with an RAPD.
In an afferent pupillary defect, there is a relative decrease in the direct response. This is most clearly demonstrated by the “swinging flashlight test. Even the flashlight is shined first in the abnormal eye, then in the healthy eye, and then again in the eye with the pupillary defect, the affected pupil becomes larger rather than
An relative afferent pupillary defect is identified by examining the eyes with a bright light. In normal circumstances, when a light is shone in one eye, both pupils constrict. However, when a light is shone in the abnormal eye of a patient with an RAPD, the pupil of the affected eye paradoxically dilates rather than constricts. This abnormal response signifies the brain is not receiving the message properly.
A mild RAPD (slight constriction of the affected pupil), may be a sign of underlying amblyopia, vitreous hemorrhage, retinal scars, severe age related macular degeneration, branch retinal vein or artery occlusion, or retinal detachment. If an RAPD is severe (dilation of the affected pupil), it generally indicates optic nerve disease such as ischemic optic neuropathy, optic neuritis, severe glaucoma, central retinal artery or vein occlusion, or in rare cases, a lesion of the optic chiasm or tract due to a pituitary tumor or stroke.
We suggest taking a stepwise approach when a patient presents with an RAPD.
Ask if the patient is aware of changes in vision. If so, are these changes acute or gradual? An acute optic neuropathy or retinal detachment would be associated with sudden vision loss, while gradual vision loss might support the existence of a compressive lesion.
Elicit significant ocular and medical history. Does the patient have a history of vascular disease, cancer, autoimmune disease, recent infections or trauma?
Carefully examine the patient, and pay special attention to the retina and optic nerve. Optic nerve findings can be subtle or non-existent. For instance, a relatively normal appearing nerve might be present in a retrobulbar optic neuritis. That is why color vision testing and perimetry are so important to the evaluation.
The need to refer for further testing depends on the case. If the patient's history and retinal examination do not offer an obvious explanation for the RAPD, one must assume that a condition affecting the optic nerve or optic tract is causing it. An immediate visual field and color vision test should be performed.
Depending on the condition, the patient may need to be referred for emergent neuroimaging and laboratory testing. For example, an individual who presents with an RAPD as a result of swollen optic nerve and a history of leukemia, would require emergent imaging and radiation treatment if the swollen nerve represented a leukemic infiltrative optic neuropathy.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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