Have you looked in the mirror and noticed your pupils changing size? It's not by chance – your pupils constantly react to both your surroundings and your internal states. But when is it normal – and when is it a warning sign when your pupils dilate? Read on to find out the typical reasons why your pupils get big.
What are pupils?
The pupil is the black, circular opening in the center of your eye, located within the iris. It acts as a kind of 'light aperture' in your eye, controlling how much light enters the inner part of the eye (the retina), where visual impressions are formed. Pupils are usually the same size in both the right and left eye, but approximately 8-10% of us have pupils with a slight difference in size.
Why do your pupils get big?
Your pupils get larger when more light needs to enter your eye, for example, when you are in a dark room or a dimly lit space. When you return to normal light, your pupils will return to their normal size by constricting to reduce the amount of light entering your eye.
How does your pupil work?
The pupil's main function is to control how much light enters your eye – just like the aperture of a camera. It does this by changing size:
• In dark environments, the pupil gets larger – it dilates by approximately 4 to 8 mm, a process called mydriasis, to let in more light.
• In bright environments, the pupil gets smaller – it constricts from approximately 2 to 4 mm, a process called constriction or miosis, to protect the eye from overexposure.
How are your pupils controlled?
Your pupil size is controlled by two small muscles in the iris:
• The sphincter muscle closes the pupil (controlled by the parasympathetic nervous system).
• The dilator muscle opens the pupil (controlled by the sympathetic nervous system).
These two muscles are controlled entirely automatically by the autonomic nervous system – that is, the nervous system that regulates unconscious bodily functions such as heart rate, breathing, and digestion.
What affects your pupil size?
The pupil functions as the eye's 'light aperture' and adapts to protect vision and help you see as best as possible. However, it's not just light that dilates your pupils. Everything from emotions, medication, and drugs to concentration and illness can cause pupils to dilate or constrict. Discover the 4 most common reasons for large pupils:
1. Light conditions: The most obvious reason is light. When you move from dark to light, your pupils constrict to protect the eye from too much light. Conversely, they dilate in the dark to allow more light in and improve your night vision.
2. Emotions and stress: Your emotions can also play a role. When you are surprised, scared, or excited, your sympathetic nervous system is activated – and this can cause your pupils to dilate. The same happens when you see something you find exciting or attractive.
3. Medication and drugs: Certain types of medication and drugs can also affect pupil size. Stimulants like caffeine, amphetamines, or certain antidepressants can cause pupils to get larger. Conversely, sedatives, alcohol, or opioids can cause them to constrict.
4. Neurological causes (rare): Injuries or diseases of the nervous system – such as brain injury, stroke, or inflammation – can affect the nerves that control the pupils. This can lead to abnormal pupil sizes, often accompanied by other symptoms such as headache, dizziness, or double vision. If you experience sudden changes in your pupil size, you should contact your ophthalmologist.
Psst… pupils tell us much more than we might think – about both your body and your state of mind. That's why pupils are often called 'windows to the soul' – because they reveal how you are doing both physically and psychologically.
Are sunglasses good for your pupils?
Yes, sunglasses are very good for your pupils – and for your eyes in general. When you are in strong light, especially sunlight, your pupils try to protect your eye by constricting. But in very bright or prolonged UV light, this is not always enough, and a pair of sunglasses is important here.
• Sunglasses relieve your pupils. With sunglasses, your pupils don't have to constrict unnaturally all the time, because the glasses already dim the light. This means less strain on the eye and less effort.
• Sunglasses protect against UV radiation. Sunglasses with 100% UV protection shield against harmful UVA, UVB, and UVC radiation, which can otherwise damage the inner parts of the eye – including the lens and retina.
• Sunglasses prevent long-term damage. Prolonged UV exposure can increase the risk of eye diseases such as cataracts, macular degeneration (AMD) and photokeratitis (eye sunburn). Sunglasses significantly reduce this risk.
• Sunglasses reduce headaches and fatigue. When pupils do not constantly have to regulate light, it reduces the risk of light sensitivity and tension headaches.
REMEMBER! Sunglasses must have 100% UV protection to be effective. Sunglasses without a UV filter can actually be more dangerous, because the pupils dilate in the dark, allowing more UV light to enter – without protection. All OjeOje sunglasses have 100% UV protection against harmful UVA, UVB, and UVC radiation.
Should you worry about large pupils?
Although large pupils are usually completely natural, there are also situations where they can be a sign of something serious. This is especially true if:
• The pupil in one eye is much larger than the other (anisocoria).
• The pupils are large and do not react to light.
• Large pupils appear suddenly along with other symptoms such as headache, confusion, nausea, or blurred vision.
Get your pupils checked
If you experience a change in pupil size without any explanation – and especially if it occurs in combination with neurological symptoms – you should consult an ophthalmologist.
Quick facts about the pupil:
What is the pupil?
• The pupil is the black circle in the center of the eye, which is actually a hole in the iris.
• It acts as an aperture that regulates how much light enters the eye.
How does the pupil work?
• In the dark, the pupil dilates (gets larger) to let in more light.
• In bright light, the pupil constricts (gets smaller) to protect the eye.
• This process is called the pupillary reflex and happens automatically and very quickly.
What controls the pupil?
The pupil is controlled by two muscles in the iris – and is controlled by the autonomic nervous system. The parasympathetic system causes the pupil to constrict, and the sympathetic system causes the pupil to dilate.
Pupils can reveal a lot:
• Level of consciousness
• Brain injury or intracranial pressure
• Poisoning (e.g., drugs)
• Eye diseases and nerve involvement
Fun and nerdy facts:
• The pupil can vary in size from approximately 2 to 8 mm.
• Both pupils should normally react equally – if not, it could indicate a problem.
• Animals have different pupil shapes: cats have vertical, cows have horizontal, and octopuses have W-shaped ones!
FAQ
What does it mean when pupils are large (mydriasis)?
Large pupils, also called mydriasis, means that the pupil dilates to let more light into the eye. This is a completely normal reaction in dark environments but can also be caused by emotions, stress, medication, or in rare cases, neurological conditions.
When are large pupils completely normal?
Large pupils are normal when you are in the dark, in dim lighting, or in situations with strong emotions such as surprise, fear, or excitement. In these cases, the sympathetic nervous system is activated, which automatically causes the pupils to dilate.
What things, besides light, can cause pupils to dilate?
Pupils can get larger due to emotions and stress, concentration, caffeine, certain types of medication, and stimulants. In rare cases, diseases or injuries to the nervous system can also affect pupil size.
When can large pupils be a warning sign?
You should react if one pupil is significantly larger than the other, if the pupils do not react to light, or if large pupils appear suddenly along with symptoms such as headache, dizziness, confusion, nausea, or blurred vision. In these cases, you should contact an ophthalmologist.
Are sunglasses good for your pupils?
Yes, sunglasses protect the pupils and eyes from strong light and harmful UV radiation. Sunglasses with 100% UV protection reduce strain on the pupils, lower the risk of eye diseases, and can prevent headaches and eye fatigue.
