Marcus Gunn Pupil

Submit your comment about Marcus Gunn Pupil at the bottom of the page

Marcus Gunn Pupil or relative afferent pupillary defect is an important sign that can be tested by swinging light from one eye to another.

This test is very important to assess the optic nerve and the anterior part of visual pathway such as optic chiasm and optic tract.

Optic nerve consists of 1.2 million axons. These axons start in the retina and pass through optic disc to form optic nerve. At optic chiasm, fibers from optic nerves of both eyes will connect. Optic tract starts from optic chiasm and consists of fibers from optic nerve of both eyes. Each optic tract has fibers from both eyes, in contrast to optic nerve which has fibers only from on eye.

When normal eye is stimulated by light, the pupil in this eye will constrict and this is called a direct pupillary reflex and also the pupil in the other eye will constrict and this is called consensual pupillary reflex. Pupil should constrict to a normal size. Once the light stimulator is removed, the pupil in both eyes will return to its normal size.

In relative afferent pupillary reflex test, light is focused in one eye and in response to that; there will be direct and consensual pupillary reflex. The light stimulator then switched to the second eye quickly, the pupil in this eye should be constricted and remain constricted once stimulated by light. This is the normal response.

Example of Normal Response

1- Light focused in right eye, pupil in right and left eye will constrict to the same amount.

2- Light switched to left eye quickly. Pupil will remain constricted in both left and right eye.

Example of Abnormal Response

1- Light is focused in right eye. Pupil in right and left eyes will constrict to the same amount.

2- Light switched to the left eye quickly. Pupil in both eyes will dilute instead of constriction.

3- Light switched again to right eye quickly. Pupil in both eyes will constrict again.

4- Light switched again to the left eye quickly. Pupil in both eye will dilute instead of constrict.

These results will tell us that the optic nerve in the left eye is weaker than that in the right eye. It doesn’t mean that the optic nerve in the right is healthy and that in the left is not healthy. It compares between both optic nerve and shows that one eye is weaker than the other eye.

In this example there is left relative afferent pupillary defect or left marcus gunn pupil.

Causes of Marcus Gunn Pupil

1- Before optic disc such as total retinal detachments

2- At or after optic disc. Any diseases that affect optic disc and nerve such as glaucoma, optic neuritis, compressive lesions, autoimmune diseases and ischemic lesions that affect optic nerve, optic chiasm and optic tract.

Watch this video about Relative Afferent Pupillary reflex test

Do You Have A comment or A question to ask the eye doctor about Marcus Gunn Pupil?

Do you have some questions you would like answered about Marcus Gunn Pupil. Or maybe you'd like to share your story about Marcus Gunn Pupil.

Then here is the place to do it. Simply complete the form below and you can either ask us a question or share your experiences.

Enter Your Title

Leave Marcus Gunn Pupil and go to Ophthalmology Terminology M

Go to HomePage

Privacy Policy

Recent Articles

  1. احمرار بسيط

    Mar 01, 15 03:52 AM

    السلام عليكم، انا جاتني قرحه في عيني الاسبوع اللي قبل اللي فات و الحمدلله شفيت شفاء تام منها و خلصت العلاج . وسألت طبيب في هذا الموقع اذا اقدر البس عدسات

    Read More

  2. pseudopakic negative dysphotopsia

    Feb 22, 15 12:20 AM

    I had cataract surgery jan 2015 dr implanted the acrysoft iq. I see a dark crescent shape on the outside corner of my eye. It pulsates sometimes. Bright

    Read More

  3. متى اقدر البس العدسات

    Feb 22, 15 12:13 AM

    انا جاتني قرحه في عيني اليمين الاسبوع اللي قبل اللي فات، والحمدلله اخدت العلاج يومين ورجعت راجعت والحمدلله قالتلي الدكتوره انو التئم الجرح و شفيت ماشاء

    Read More