Marcus Gunn Pupil

Marcus Gunn pupil is when your pupils don’t change size as much as they should in response to light. It’s also known as relative afferent pupillary defect (RAPD).

Usually, your pupils automatically change in size based on the amount of light around you. They get smaller (constrict) when light shines on them or you move into a bright place. They get bigger (dilate) when you enter a darker place.

These changes are one of your eye reflexes. They happen all the time without you thinking about them. And they happen together. The pupils in both eyes change at the same time to the same size.

If you have relative afferent pupillary defect, when light shines into your affected eye, both pupils won’t constrict like they should. When light shines into the normal eye, both pupils will constrict normally. You probably won’t be able to notice that you have RAPD. But an eye doctor will see it when they shine light in your eyes during an exam.

Your eye doctor will shine a light in both of your eyes, one after the other. They’ll move the light back and forth and watch how your pupils change. This is called a swinging flashlight test. If you have RAPD, your pupils won’t change size like they should when your doctor swings the light to the affected side.

What are the most common causes of RAPD?

Marcus Gunn pupil (RAPD) happens when something stops your retina or your optic nerve from working correctly. These causes of RAPD can include:

• Glaucoma
• Optic neuritis
• Retinal vein occlusion
• Retinitis pigmentosa
• Retinal detachment
• Optic atrophy

Other eye issues may lead to relative afferent pupillary defect, including:

• Amblyopia
• Cataracts
• Eye injuries
• Eye tumors

How is relative afferent pupillary defect treated?

Treatments for RAPD vary widely. That’s because so many issues and conditions can cause it. The specific treatments you need will depend on the cause.

Treatments can include medications, eye drops, laser procedures or surgery. Your eye doctor will suggest treatments for the underlying cause of Marcus Gunn pupil and explain what to expect.

When should this symptom be treated by a healthcare provider?

Visit an eye doctor as soon as you notice any changes in your eyes or vision, especially if you have:

• Eye pain
• Blurry or worsening vision
• Trouble seeing at night
• Trouble adjusting to lighting changes, like going outside on a bright day

Everyone’s eyes take some time to adjust to lighting changes. It’s not instant. But you know what’s normal for you. Visit an eye doctor if it feels like your eyes are taking way longer than usual to adjust.