Pupillary dilation

Pupillary dilation is a physiological response that varies the size of the pupil, the opening at the centre of the iris. It can be caused by a variety of factors, including exposure to light, certain emotions, and the use of certain drugs. Pupillary dilation is an important aspect of the eye examination process, as it allows for a more thorough examination of the retina and other internal structures of the eye.

Physiology

The size of the pupil is controlled by two groups of smooth muscles in the iris: the sphincter pupillae and the dilator pupillae. The sphincter pupillae contract to constrict the pupil, while the dilator pupillae contract to dilate or enlarge the pupil. This process is regulated by the autonomic nervous system, with the parasympathetic nervous system controlling constriction and the sympathetic nervous system controlling dilation.

Causes

Pupillary dilation can be caused by a variety of factors. These include:

• Light: The pupils naturally dilate in low light conditions to allow more light to reach the retina, and constrict in bright light to reduce the amount of light that reaches the retina.
• Emotions: Certain emotions, such as fear or excitement, can cause the pupils to dilate.
• Drugs: Certain drugs, including mydriatics and psychoactive drugs, can cause pupillary dilation.

Clinical significance

Pupillary dilation is an important part of the eye examination process. By dilating the pupils, healthcare professionals can examine the retina and other internal structures of the eye more thoroughly. This can help to identify a range of eye conditions, including retinal detachment, macular degeneration, and glaucoma.

Pupillary dilation can also be a sign of certain medical conditions. For example, one pupil that is significantly larger than the other (a condition known as anisocoria) can be a sign of a serious condition such as a brain aneurysm or stroke.

See also

• Pupillary light reflex
• Pupillary response
• Adie syndrome
• Holmes-Adie syndrome
• Argyll Robertson pupil

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