Clinical Examination:
Relative Afferent Pupillary Defect

The Relative Afferent Pupillary Defect (RAPD), or Marcus-Gunn Pupil is an extremely significant and highly objective clinical finding in the examination of the visual system. Even in an unconscious patient, the determination of an RAPD can be made. There are many different conditions which lead to this finding, from severe glaucoma to an optic nerve tumor. Also significantly, there are many conditions which lead to a profound loss of vision (such as a complete vitreous hemorrhage), which will not give an RAPD.

This page will describe the pupillary examination itself, and through interactive graphics, a variety of examples of RAPD's and even a reverse RAPD will be shown. Finally a list of possible causes of an RAPD as well as conditions that will not cause an RAPD are presented.

The evaluation of the pupils is best performed in a dimly illuminated room. This allows for some pupillary dilation, while also allowing for the observation of the consensual pupillary response. It is reasonable to test the individual reaction of each pupil initially. In some cases one pupil may not be reactive due to a variety of conditions. In cases where neither pupil reacts to light, no further testing can be done, except for testing the pupillary response to accommodation (focusing at near).

The "swinging flashlight test" is probably the best test for identifying an RAPD (as shown by Enyedi, L.B. et al in Ophthalmology 5/1998; 105:871-873, A Comparison of the Marcus Gunn and Alternating Light Tests for Afferent Pupillary Defects.) In this test, a strong, steady light is used. The light is shined into one eye, and then quickly switched to the other. This is repeated back and forth, until one of four conclusions is reached (listed below). Since light in one pupil causes both pupils to constrict, quickly switching from one eye to the other will give a "relative" indication of the functioning of each eye and optic nerve. If both eyes are equally dysfunctional, no "relative" defect would be found. The results of the test include:

1. No Relative Afferent Pupillary Defect: Both pupils constrict equally without evidence of pupillary re-dilation with the "swinging flashlight test", except possibly for "hippus". Hippus refers to non-rhythmic fluctuations in pupillary size when there is a steady illumination.

2. Mild Relative Afferent Pupillary Defect: The affected pupil shows a weak initial constriction, followed by dilation to a greater size.

3. Moderate Relative Afferent Pupillary Defect: The affected pupil shows a stable or unchanged level of constriction, followed by dilation to a greater size.

4. Severe Relative Afferent Pupillary Defect: The affected pupil shows an immediate dilation to a greater size.

Interactive Clinical Examples To observe these examples, move the mouse pointer over the pupil or each eye as if it were a light pen. In these cases, assume that the testing is being done in a dimly illuminated room. Normal Pupillary Reaction, with Hippus: In this case, there is no RAPD, as each pupil constricts equally with no redilation after the light is switched from pupil to pupil. Hippus is present, which is a normal fluctuation in pupillary size under steady illumination.

Relative Afferent Pupillary Defect, Patient's Left Eye: Clinical Example: A patient with optic neuritis affecting the left eye, and a normal right eye. In this case, the left eye shows an initial weak constriction followed by dilation to a larger size. The right pupil constricts briskly.

Severe Relative Afferent Pupillary Defect, Patient's Left Eye: Clinical Example: A patient with a completely blind left eye following a central retinal artery occlusion. The patient's left eye in this case shows no direct pupillary response, and an immediate full redilation to a larger size.

Reverse Relative Afferent Pupillary Defect, Patient's Right Eye: Clinical Example: This patient is status post multiple surgeries in the left eye for severe glaucoma and cataract, and the pupil is distorted and unreactive. The right eye has had an ischemic optic neuropathy with a severe loss of vision. In this case, the patient's RIGHT eye is the eye with the RAPD. The right pupil reacts briskly consensually to light in the left eye, but then redilates with direct illumination, indicating the presence of an RAPD.

General Points about the Relative Afferent Pupillary Defect

• An RAPD generally occurs with significant optic nerve or retinal disease, when there is a difference in the disease process between the two eyes. If 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.

Conditions leading to a Relative Afferent Pupillary Defect include:

• Optic nerve disorders:
  Unilateral optic neuropathies are common causes of an RAPD. If a condition is bilaterally symmetrical, there will not be an RAPD.

  • Optic neuritis - Even very mild optic neuritis with a minimal loss of vision can lead to a very strong RAPD.

  • Ischemic optic neuropathies - These include arteritic (Giant Cell Arteritis) and non-arteritic causes. Usually there will be a loss of vision or a horizontal cut in the visual field.

  • Glaucoma - While glaucoma normally is a bilateral disease, if one optic nerve has particularly severe damage, an RAPD can be seen.

  • Traumatic optic neuropathy - This includes direct ocular trauma, orbital trauma, and even more remote head injuries which can damage the optic nerve as it passes through the optic canal into the cranial vault.

  • Optic nerve tumor - This is a rare cause, and includes primary tumors of the optic nerve (glioma, meningioma) or tumors compressing the optic nerve (sphenoid wing meningioma, pituitary lesions, etc.)

  • Orbital disease - This could include compressive damage to the optic nerve from thyroid related orbitopathy (compression from enlarged extraocular muscles in the orbit), orbital tumors, or vascular malformations.

  • Radiation optic nerve damage

  • Miscellaneous optic neuropathies, such as Leber's optic neuropathy (usually eventually bilateral) and other inheritable optic neuropathies.

  • Optic nerve infections or inflammations - Cryptococcus can cause a severe optic nerve infection in the immunocompromised. Sarcoidosis can cause inflammation of the optic nerve. Lyme disease can affect the optic nerve.

  • Optic atrophy status-post papilledema - This is usually bilateral.

  • Surgical damage to the optic nerve - This could include damage following retrobulbar anesthesia; damage following orbital hemorrhage related to eye, orbital, sinus, or plastic surgery; damage following neurosurgical procedures such as pituitary tumor resection; and damage related to migration of an orbital plate after surgery to correct a blow-out fracture.

• Retinal Causes of a Relative Afferent Pupillary Defect
  Again, symmetrically bilateral retinal disease will not show an RAPD. Usually retinal disease has to be quite severe for an RAPD to be clinically evident.

  • Ischemic retinal disease - Causes include ischemic central retinal vein occlusion, central retinal artery occlusion, severe ischemic branch retinal or arterial occlusions, severe ischemic diabetic or sickle-cell retinopathy.

  • Ischemic ocular disease (Ocular ischemic syndrome) - This usually arises from obstruction of the ophthalmic or carotid artery on one side.

  • Retinal detachment - An RAPD can often be seen if the macula is detached, or if at least two quadrants of retina are detached.

  • Severe macular degeneration - If unilateral and severe, an RAPD can be seen. Usually the visual acuity would be less than 20/400.

  • Intraocular tumor - Retinal and choroidal tumors including melanoma, retinoblastoma, and metastatic lesion could lead to an RAPD if severe.

  • Retinal infection - Cytomegalovirus, herpes simplex, and other causes of retinitis can lead to an RAPD if there is extensive disease.

• Amblyopia, if severe, can lead to a relative afferent pupillary defect. Usually the visual acuity would be 20/400, or worse.

• Cerebral vascular disease
  Usually, it is an optic nerve disorder that leads to an RAPD, rather than an optic tract or visual cortex disorder. However, there tends to be a higher percentage of crossed vs. uncrossed nerve fibers at the optic chiasm. Thus, in a patient with a homonymous hemianopia from an optic tract disorder, an RAPD could be seen in the eye with the temporal visual field defect. The nasal retina serves the temporal visual field, and these are the fibers that would cross at the chiasm.

• There are certainly other causes of a relative afferent pupillary defect which I have omitted here.

Conditions which will NOT cause a Relative Afferent Pupillary Defect include:

• Refractive Error (even if extreme)

• Media Opacity (a bright enough light will indicate NO RAPD)

  • Cataract (even if completely opaque)

  • Corneal scar

  • Hyphema

  • Vitreous hemorrhage

• Previous eye surgery (unless there is a complication, previous disease, or a new problem)

• Strabismus

• Conditions with an Efferent Pupillary Defect

  • Third Cranial Nerve Palsy

  • Adie's Pupil

  • Horner's Syndrome

• Mild retinal problems, including:

  • Mild background diabetic retinopathy

  • Central serous choroidopathy

  • Non-ischemic vein occlusions

  • Mild macular degeneration

• Conditions which are typically bilaterally symmetrical will not show an RAPD:

  • Bilateral retinitis pigmentosa

  • Bilateral nutritional or metabolic optic neuropathies

• Cerebral infarct usually will not cause an RAPD