Marcus Gunn Pupil: Causes, Symptoms, Diagnosis & Treatment

Marcus Gunn’s pupil is an eye problem in which each eye responds differently when light is shone into them. It is a type of RAPD (relative afferent pupil defect) and this different response shown by the eyes shows that there is some problem or dysfunction in the retina or the optic nerve.

The pupil of the person exposed to the problem of Marcus Gunn syndrome will get wider. Usually, the pupil becomes small when exposed to bright light but in the case of this problem, it expands. If there is this problem in only one eye then the size of the pupils will become different in both eyes, one will be of the usual size and one will have a bigger size. 

Marcus Gunn test is the basic test that is performed by neurologists, ophthalmologists, optometrists, and other physicians to check whether the patient is having RAPD or not. 

In this test, patients have to look ahead and then the doctor will throw light into the eyes one by one and check the response of pupils to light. If a different response is shown in the pupils then the patient will diagnose with RAPD or Marcus Gunn pupils. 

This test is connected to many eye problems. It looks simple but is very important to take proper measures and make treatment plans for other problems. 

It names after Robert Marcus Gunn. He was a Scottish ophthalmologist. 

This problem is not specific to any age group or gender. It can happen to any person. Now, talking about the chances of the occurrence of the problem; a study was conducted to see how many people face this problem and the results show that 42% of the population show RAPD between 0.08 and 0.22 log units. 

What Are The Symptoms Of Syndrome?

marcus gunn pupil


Patients diagnosed with this problem will face visual impairment in one eye. Obviously, if the pupils are responding differently to light then there will be difficulty viewing different things. 

But now the doctor has to diagnose whether the problem is occurring due to RAPD, cataract, or any other problem. 

There are various RAPD problem types in which you will see the symptoms of Marcus Gunn’s pupil. They are based on the severity of RAPD: mild, moderate, and severe RAPD. 

  • Mild RAPD: In Mild RAPD, pupil size gets small initially and then becomes big. 
  • Moderate RAPD: In Moderate RAPD, you will witness a stable level of constriction in the size of the pupil, and then it will get a big size.  
  • Severe RAPD: This is the most severe form of RAPD in which the size of the pupil gets larger immediately. 
  • No RAPD: There are some other problems in which the symptoms of Marcus Gunn pupil see. 

What Are The Causes of Syndrome?

marcus gunn pupil


  • unilateral optic neuropathy, usually causing loss of vision
  • optic neuritis
  • retinal infection
  • severe lazy eye, otherwise called amblyopia
  • orbital diseases, such as compressive damage to the optic nerve from thyroid-related orbitopathy, orbital tumors, or vascular malformations
  • severe unilateral macular degeneration
  • severe ischemic retinal diseases, such as ischemic central retinal vein occlusion, central retinal artery occlusion, or sickle-cell retinopathy
  • retinal detachment
  • an optic nerve tumor, which is rare
  • optic atrophy, or degeneration of the optic nerve
  • optic nerve infections or inflammation
  • severe glaucoma, which can damage the optic nerve
  • traumatic optic neuropathy, including direct ocular trauma, orbital trauma, and head injuries that damage the optic nerve.

How The Diagnosis Of The Marcus Gunn Pupil Syndrome Is Done? 

marcus gunn pupil


As informed earlier, the doctor shone a light into both eyes one after another to check the case. When a patient goes to the doctor to get the case checked, the doctor will switch off the lights and shine a light into both eyes to check how much response is given by both the pupils. 

In the case where the patient’s eyes are normal, both pupils will respond equally and will get a minor constriction. But, when one eye affects by Marcus Gunn Pupil Syndrome then the eye having the problem won’t respond to the light and won’t get constricted while the other one will get constricted. 

This test knew as the Marcus Gunn test or the “swinging flashlight test.” It performs in a semi-darkened room where the doctor will shine a light for 3 seconds in one eye and the other 3 seconds for the second eye so in total 6 seconds. The penlight threw from a distance of 5 to 10 cm. 

This test is very accurate and the doctor comes to know that the patient is having this problem. The patient also won’t be aware of this problem until he gets this test done.

One other test to diagnose the syndrome is the Modified Gunn test. 

Modified Gunn Syndrome Test 

marcus gunn pupil


In this test, the patient asks to cover one eye and keep the other one open alternatively. Then, prolonged light exposure gives to the eyes. The one with the damaged eye when kept covered and with the normal eye when kept open, the normal eye will constrict.

Now, the damaged eye will keep open and the normal eye will cover and so the damaged eye will dilate. The size of the pupils is measured here. It is very similar to the Marcus Gunn test as lightly used in both the tests and the only difference is that one eye is covered in this test. 

Nowadays, modern computer devices use to get accurate results. Better results and accurate detections are possible with modern pupillography techniques. Binocular pupillometers use to provide information on pupil diameter, pupil diameter vs. time curves, etc. Various parameters are used to measure and quantify the data received with the pupillography technique

Also Read: 6 Best Food For Eyes: Edibles That Improve Your Eyesight

How The Treatment Of Marcus Gunn Pupil Is Done?

marcus gunn pupil


After diagnosing the problem, the next question comes how can we treat it? Now, there are many causes that can lead to this problem as shown earlier so the treatment will differ based on the cause. 

  • If severe unilateral macular degeneration is caused when there is no cure currently so the focus is on slowing down its progression. 
  • Optic nerve tumors treat by checking the status of the tumor, whether it is benign or malignant.
  • If optic neuritis is a cause then it treats with steroids. 
  • If there is severe glaucoma then it treats with laser treatment, eye drops, and surgery. 
  • If a lazy eye is a cause then specific glasses, eye drops, and vision therapy are the treatment options. 
  • If a retinal infection is caused then an injection is used in the eye. Laser eye surgery and treatment are also an option. 

So, here was an overview of Marcus Gunn syndrome. Hope you got an overview of it. If you are facing any eye problem and having a visual problem then contact a good doctor immediately and diagnose the problem so the treatment can be carried out quickly.  

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