Have you ever looked at your eyes in a mirror? You can see the black circle in the middle of the colored part of the eye (we call it the iris). That's what we call the pupil. Its size changes from time to time. But sometimes, if this pupil remains small no matter how much light changes, it can be a sign of a health problem. That's what we medically call Miosis .
Simply put, what is Miosis?
Miosis is when the pupil of the eye becomes smaller than normal, resembling a spider. The size of the pupil is controlled by muscles in the colored part of our eye, the iris.
Just like you squint when you go into bright sunlight, our pupils also get smaller in bright light. Also, in dark places, the pupils get bigger (dilate) to see better. This is a normal process. However , in someone with miosis, the pupils remain small no matter how much light changes . Some people call them 'pinpoint pupils' because they look exactly like the tip of a needle.
This condition can occur in only one eye (unilateral) or in both eyes (bilateral).
Difference Between Miosis and Mydriasis
These two are opposite conditions. Miosis is when the iris is narrowed. Mydriasis is when the iris is abnormally large (dilated).
What are the main causes of miosis?
There can be several reasons why the eyelid may be small. While some are common, others can be more serious.
| Cause | Effect |
|---|---|
| Some medications (e.g., opioids) | Usually affects both eyes . |
| Horner's Syndrome | Only one side of the face is affected. |
| Poisoning | It often affects both eyes . |
| Eye inflammation (Uveitis/Iritis) | It usually affects one eye , but can sometimes affect both. |
| Pontine Stroke | Both eyes are affected. |
| Cluster Headaches | It only affects one side . |
1. Some medications
Some medications, especially opioids, used for severe pain can cause the iris to become smaller in both eyes. Some eye drops used for glaucoma, such as pilocarpine, can also cause this.
2. Horner's Syndrome
This is a condition caused by a disruption in the sympathetic nerves that run from our brain to the eyes and face. In this condition, symptoms such as drooping eyelids and drooping eyelids can be seen on only one side of the face.
3. Poisoning
This condition can be caused by the ingestion of certain pesticides, especially organophosphates . It can also be caused by an overdose of other drugs, such as benzodiazepines.
If there is even the slightest suspicion of such a thing, the patient should be taken to the nearest hospital Emergency Treatment Unit (ETU) immediately. It is also very important to call the National Poisons Information Centre at the Colombo National Hospital for further advice.
4. Eye Inflammations
Inflammation within the eye, which causes redness and pain, can also cause iris dysfunction. Uveitis and iritis are two such conditions.
5. Brain or Eye Injury
This can also happen when something hits the eye and causes an injury, or due to a stroke that affects certain parts of the brain, especially the brainstem (Pontine stroke).
6. Other reasons
In addition, miosis can also be seen in conditions such as Argyll Robertson pupils, which occur in the final stages of untreated syphilis, and cluster headaches.
Let's also learn about Miosis that occurs during cataract surgery.
During cataract surgery, the iris needs to be dilated to make the surgery easier. However, sometimes the iris can suddenly contract during surgery. This is called intraoperative miosis. Some medications, such as alpha-1 antagonists for high blood pressure or prostate enlargement, are at increased risk. Therefore, it is important to tell your doctor about all the medications you are taking before having any surgery.
What are the treatments for this?
Miosis is a symptom, not a disease, so treatment is directed at the underlying condition that caused it.
- If it's due to a medication: Your doctor will decide whether to stop or change the medication.
- If it is an eye infection: anti-inflammatory drugs or anti-infectives will be given.
- Horner's syndrome: Surgery may be required if it is caused by something like a tumor.
- In the event of a stroke: Emergency treatment must be provided at a hospital.
Can Miosis be prevented?
We can prevent miosis caused by certain causes.
- Staying away from drugs: Completely avoiding the use of drugs, especially opioids.
- Wearing protective equipment: It is very important to wear appropriate eye protection, such as goggles, when playing sports or doing hazardous work.
- Informing your doctor correctly: Always inform your doctor about all medications you are taking.
Remember, this type of change in your eye color, especially if it happens suddenly or is accompanied by other symptoms (such as numbness on one side of the face, severe headache, red eyes), can be a sign of a serious medical condition. So don't ignore it.
Take-Home Message
- Miosis is an abnormally small pupil, which may not respond properly to light.
- This is not a disease, but a symptom of another condition.
- Causes can range from simple to serious conditions such as medications, poisoning, neurological diseases, strokes, and eye infections.
- If you notice this kind of change in your iris, especially if it comes with other symptoms, see a doctor as soon as possible.
- Always inform your doctor about all medications you are taking.
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