Introduction
The eyes are one of the human body's most vulnerable and fragile parts. There are various diseases related to the eyes, such as myopia (nearsightedness), astigmatism (blurred vision), and eye injuries. One of the rare conditions associated with the eyes is Marcus Gunn pupil; as the name suggests, it is related to the pupil of the eye.
What Is Marcus Gunn Pupil?
Marcus Gunn pupil is also known as a relative afferent pupillary defect, or RAPD, which means that the pupil gets slightly smaller in response to the light instead of dilating as normal.
This condition was named after a Scottish ophthalmologist, Robert Marcus Gunn, in the 1800s, who introduced systematized teaching of various eye disorders.
It is a rare condition that indicates a dysfunction or disease in the optic nerve or retina. Due to the irregular functioning of the pupil, both pupils acquire different sizes. However, a person with this disorder is not at any risk, but the condition can signal other eye problems which need to be treated.
What Are the Different Parts of the Eye?
Before understanding this condition, one should know about the different parts of the eyes, which are as follows:
What Is the Function of the Pupil?
The pupil allows light to enter the eye; it gets bigger or dilated in low-light conditions, such as in a dark room or at night, to allow more light into the eyes. And when there is a lot of bright light, the pupils tend to get smaller or constricted; this helps prevent any damage to the lens or retina that is sensitive to bright light.
The fully dilated pupil usually is four to eight millimeters in size, and it can constrict up to two to four millimeters.
What Are the Causes of a Marcus Gunn Pupil?
There are various causes of Marcus Gunn pupil; the most common causes are given below:
-
Optic neuritis occurs when inflammation or swelling damages the optic nerve.
-
Severe glaucoma - A condition when the nerve connecting the eye to the brain is damaged, usually due to high eye pressure.
-
Orbital trauma and head injuries can damage the optic nerve.
-
Tumor in the optic nerve is a rare condition.
-
The optic atrophy or degeneration of the optic nerve.
-
Retinal detachment and retinal infection.
-
A severe lazy eye is also known as amblyopia (reduced vision in one eye caused by abnormal visual development in the early stage of life).
-
Retinal artery occlusion or sickle-cell retinopathy.
What Are the Different Types of Marcus Gunn Pupils?
Visual impairment in either one of the eyes could be due to Marcus Gunn pupil or other non-relative afferent pupillary defect conditions (RAPD).
There are different types of relative afferent pupillary defect (RAPD) conditions as well as non-relative afferent pupillary defect conditions that can lead to the occurrence of symptoms related to Marcus Gunn pupil, which are as follows:
-
No RAPD: There are some other conditions, like hippus (fluctuation in pupil size) and non-reactive pupils, which can make the RAPD diagnosis difficult.
-
Mild RAPD: The pupil shows a weak initial constriction before dilating.
-
Moderate RAPD: The pupil shows a stable constriction before dilating.
-
Severe RAPD: The pupil dilates to a larger size immediately.
What Are the Symptoms of Marcus Gunn Pupil?
Generally, Marcus Gunn Pupil does not have any signs, and its only symptoms are because of the underlying conditions. Few patients may experience blurry vision, vision loss, and headaches.
How Is Marcus Gunn Pupil Diagnosed?
Marcus Gunn pupils can be diagnosed by doing a swinging light test, a flashlight test, or a Marcus Gunn test. In this test, the doctor sways a light back and forth in front of the patient's eyes and compares the stimulation in both eyes.
The pupils may respond in two ways to the light:
-
Direct Response: In direct response, the pupil becomes smaller or constricted when light is shone on it.
-
Consensual Response: The pupil constricts reflectively when the light is shone directly into the other eye, indicating that the eyes are linked.
So, during a normal swinging test, the pupils of both eyes constrict equally, whichever eye receives the direct light. But in Marcus Gunn pupil, the affected eye or pupil will constrict minimally compared to the other pupil. And in many cases, the patient is unaware that they have Marcus Gunn pupil unless the doctor performs a swinging light test.
What Is the Treatment for Marcus Gunn Pupil?
There is no specific treatment for Marcus Gunn pupil as it occurs due to an underlying condition. Therefore, the treatment primarily focuses on correcting the underlying cause. Enlisted below are appropriate treatment protocols for the associated conditions:
-
Glaucoma: Treatment involves medication like eye drops, laser surgery, or other types of non-laser surgical procedures.
-
Orbital Cellulitis: Treatment involves intravenous antibiotics or surgical procedures, including drainage of the sinuses or an abscess of orbital fat.
-
Retinal Infection: Usually treated with an injection in the eye and may sometimes require oral or intravenous drugs.
-
Retinal Detachment: Treatment might include a freeze treatment, laser surgery, or a more advanced surgery to move the retina back in place.
-
Optic Nerve Lesion or Optic Neuritis: Treatment involves a short course of steroids that may be injected directly into the veins (intravenous).
Conclusion:
Marcus Gunn pupil is a rare disease and is not that commonly seen; however certain individuals may require medical intervention. A routine examination may reveal certain medical conditions that could be associated with this rare disease. Hence it is imperative to consult an ophthalmologist and undergo routine eye checkups for early diagnosis and prompt treatment. So, it is always beneficial for the patient to consult a healthcare provider before reaching any conclusion and starting with proper treatment.
