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What Is Dilated Pupils (Dilated Pupils)?

مركز إبصار التخصصي > Ibsar > What Is Dilated Pupils (Dilated Pupils)?

Pupil dilatation occurs when the pupil remains dilated (dilated) and does not respond to light changes in the environment. It can be caused by injury, medications or psychological factors. Usually, the pupil becomes wider to allow more light to enter your eye in dark environments and becomes smaller to prevent light from entering your eye in bright places. The pupil also expands in response to factors such as touch, sound, and emotion. In people with dilated pupils, the pupil will remain dilated even in bright places and in the absence of any stimulus.

In many cases, pupil dilatation is benign and can occur by the drops used during an eye exam or health condition. Constant mydriasis in one eye can also be a red flag for severe brain injury.


How pupils change size

  • The pupil is the round black circle in the center of the iris. It controls the amount of light that enters the eye before it reaches the retina. Standard pupil size varies between 2mm (mm) and 8mm, depending on lighting
  • Two muscles control the size of the pupil. One of them is the peripheral sphincter, which is located on the margin of the iris and is innervated by the parasympathetic nervous system. The other muscle is the iris dilated muscle, which contains fibers that extend across the iris and expand or contract in response to light.
  • Stimulation of the sympathetic nervous system, known for triggering a fight-or-flight response when the body is under stress, can cause pupils to dilate.

What is pupillary constriction?

  • While dilated pupils cause dilated pupils, the opposite can also happen. Pupillary constriction occurs when there is excessive pupil contraction in one or both eyes. Similar to mydriasis, it can be caused by medications such as opioids but also by inflammation and chemicals such as pesticides.

Causes of dilated pupils

Eye injury

Eye injuries can damage the nerves responsible for controlling the pupil and iris, leading to dilated pupils. This form of mydriasis is often followed by other symptoms, such as eye pain, discomfort when reading, photophobia (photosensitivity).

Brain injuries

  • Pupilasia can occur in people with traumatic brain injury. These often increase intracranial pressure, which can put pressure on and affect the eye system. They tend to occur on only one side, and this type of pupil dilatation is called a unilateral constant pupil, or inflated pupil. The presence of dilated pupils on only one side indicates the possibility of a large lump or lesion
  • Permanent pupil dilatation and the absence of mild pupil reflex after a severe brain injury are signs of irreversible brain stem damage and have been strongly associated with poor outcomes.


Medications

Pupilation can also be a side effect of various medications. While systemic drugs cause bilateral dilation, direct eye insemination with topical medications can cause unilateral dilated pupils.

Some medications that can cause problems are:

  • Antihistamines
  • Botox
  • atropine
  • Scopolamine plasters
  • Amphetamines
  • Serotonergic drugs
  • Muscle relaxants
  • Anticholinergics

Exposure to certain plants

Some plants contain substances such as scopolamine and atropine that can cause mydriasis. The angel’s trumpet plant, for example, contains hyosciamine, atropine, and scopolamine, which can expand the pupil. Plants of the belladonna family and Jimson grass can also cause mydriasis.

Substance abuse

Medications can expand or contract the eye muscles, causing pupil dilation. Substances such as cocaine increase the level of serotonin, which can lead to dilated pupils. LSD has a direct effect on serotonin receptors in the brain, which can also cause mydriasis. Other drugs that have similar side effects are crystal methamphetamine and ecstasy.

Increased oxytocin levels

Oxytocin is a hormone. High levels of oxytocin can lead to mild or moderate pupillary dilation.

Migraine

Migraines can sometimes cause benign symptomatic unilateral dilatation due to overactive sympathetic nervous system or sympathetic system inactivity5 which is a temporary condition and is more common in young women.

  • Recognize the symptoms and complications of a migraine attack
  • Cranial neuropathy
  • Neuropathy is a disorder that impairs the ability to feel and move. When it affects the third cranial nerve, also known as the motor nerve of the eye, the pupil becomes fixed and dilated due to paralysis of the iris sphincter.


Pupil dilation in eye examinations

  • Not all causes of mydriasis are problematic. Optometrists and ophthalmologists often use drops to dilate the pupil during an eye exam. This allows them to examine the optic nerve and retina. This dilation usually lasts four to six hours, but sometimes the doctor uses a drop that can last for 24 hours or more. However, other causes may be serious and require treatment.
  • Two types of eye drops are used during eye exams. One dilates the pupil by contracting the muscles of the iris, while the other relaxes the muscles that contract the pupils, allowing the eye to focus the lens inside the eye.
  • It often takes up to 30 minutes for the pupil to expand after receiving the drops. Your eye doctor can’t tell you how blurry your vision is and for how long. This depends on the type of dilated eye drops used and how your eyes react to them
  • When your eyes widen, they are often very sensitive to light. Your vision becomes blurry and you will find it difficult to focus on nearby objects.

Treatment

  • Treatment depends on the causes of mydriasis. When the prescribed medications cause this, the pupils will return to normal after the effect diminishes and they stop taking the drug. No treatment is required in this case.