Marcus Gunn Pupil: Causes and Treatment

Marcus Gunn (RAPD) has no treatments because it’s a symptom of a larger or serious issue that might be glaucoma, optic neuropathy, optic inflammations, etc.

close up image of pupil

Marcus Gunn pupil is an eye defect characterized by a non-delating pupil when exposed to light. Normally, pupils constrict when exposed to light. Marcus Gunn pupil is also known as Relative afferent pupillary defect (RAPD) and named after a Scottish doctor of the same name in the 1800s.

An Overview of Pupil Contraction

Your eye normally contracts upon light exposure that is in other words called a consensual light reflex. The eye restricts the incoming bright light by reducing the pupil size to avoid overexposure and damage to retina and cornea.

Marcus Gunn Pupil: What Causes It How To Treat It

Marcus Gunn pupil is caused by several conditions and has no treatments because it’s a symptom of a larger or serious issue that might be glaucoma, optic neuropathy, optic inflammations, etc. The treatment for RAPD lies upon treating the following eye ailments:






This refers to the condition caused by increased eyeball pressure. If not treated, it often leads to blindness and a symptom.Laser treatment and surgery

Optic nerve tumor

Or neurofibromatosis, optic nerve tumor is a non-cancerous brain tumor that arises from the surrounding optic nerve sheath or the nerve itself. Surgery on the tumor site

Optic nerve inflammations

Also known as papilledema, optic nerve inflammations characterize nausea, vomiting, and headache.Intravenous or oral corticosteroid

Cerebrovascular disease

This refers to the bleeding of a brain area and symptoms such as aneurysms, stenosis and vascular malformations.Anti-hypertensives and blood thinners

Optic nerve infections

Associated with multiple sclerosis, optic nerve involves optic nerve injury and autoimmune disease and symptoms such as pain, vision loss, and reduced color vision.Often heal on its own but steroids can be used to reduce inflammation

Optic neuropathy

Involves inflammation to the optic nerve, loss of the myelin or protective sheath and symptoms like distorted vision, blind spots, and blurring. The treatment focuses to stop the progression before the illness becomes irreversible.

Amblyopia or severe lazy eye

Amblyopia characterizes a reduced or blurry vision not corrected by contact lenses, eye surgery, and glasses.Eye patches, surgery, glasses and atropine drops

Retinal detachment

If Retina, a visual transmitter to the brain, is detached or lifted from its normal position might result in permanent vision loss. Surgery such as freezing or cryopexy and laser surgery

Sickle-cell retinopathy (SCR)

The eye illness manifests floaters, flashes,  blurry vision, peripheral vision loss, eye redness, decreased vision, and eye pain. Laser surgery

What are the Types?

Marcus Gunn pupil or RAPD has no symptoms of its own but rather it’s caused by these severities. 

  • Severe RAPD: The pupil delates immediately to a larger size.
  • Moderate RAPD: The pupil doesn’t contract before dilating.
  • Mild RAPD: The pupil contracts weakly before it dilates to a larger size.

What Should I Do to Avoid Marcus Gunn Pupil?

Because Marcus pupil is a symptom of a larger eye ailment, you’ll need to avoid getting eye ailments: glaucoma, retinal detachment, etc. For instance, for each eye ailment below, you should do the following:


Avoid smoking, wear protective eyewear and exercise with moderation.

Optic atrophy

Reduce the risk factors associated with a related illness such as glaucoma, infection and inflammation before a progression occurs.

How Doctors Diagnose it?

Your eye specialist will carry out a test called swinging flashlight. He/she will shine a narrow beam of light into your eyes in a semi-darkened room. After 3 seconds,  he/she will shine your next eye. When your pupil does not constrict, you got a Marcus Gunn pupil.

How can I Take Care of my Eye?

Eating food sources

These foods might help your eye health:

Nuts and legumes

  • cashews, lentils, walnuts, brazil nuts, peanuts


  • contains vitamin A and beta carotene – both important for the protein rhodopsin (a protein that aids retina to absorb light).


  • Necessary to prevent dry eyes and dehydration.


  • High in omega 3s. It includes chia, hemp, and flax seeds.


  • Includes omega-3-rich fish such as trout, salmon, herring, mackerel, sardines, anchovies, and herring. 


  • Rich in lutein, zeaxanthin, zinc, vitamins C and E.

Leafy green vegetable

  • Rich in lutein, vitamin C and zeaxanthin. Sources include collards, kale, and spinach.

Following good habits for eye health

These good habits can reduce the risk of contracting such as eye illness and its symptoms Marcus Gunn Pupil.

  • Avoid smoking
  • Wear sunglasses especially during summertime.
  • Control cholesterol, blood pressure, and blood sugar levels. When these three blood levels go unchecked, you’ll risk getting hypertension and increased diabetic symptoms all can affect your eye. 
  • Break after using a computer. Staring at a laptop can cause eye strain. Relax and take eye exercises.
  • Breath fresh air. Your cornea gets oxygen directly from fresh air. 
  • Research and look for signs of eye problems. Floaters, hazy vision, double vision, red eyes after prolonged time periods, constant eye swelling and eye pain signal a problem. If you got a check for all of these symptoms, visit your eye specialist immediately.
  • Avoid smoking. Smoking can increase the risk of your blood vessels.
  • A regular visit to an eye doctor. Your eye doctor may perform a vision test, eye, and optic nerve pressure tests.
  • Check the history of your family health. Your family might have a history of diabetes, high blood pressure and genetic diseases that might impact your eye health. 
  • Check your eye health early. The sooner the better you visit a doctor, the less you suffer a progressed eye disease.

The Bottom line: Should I Worry about Having a Marcus Gunn Pupil?

Marcus Gunn pupil does not cause symptoms on its own. What you should worry about is the associated bigger issue of Marcus Gunn pupil. That might be glaucoma, retinal detachment, optic atrophy, etc – all need serious and immediate attention.

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