Small pupils

Small Pupils

Small pupils, medically referred to as miosis, occur when the pupils of the eyes constrict to a size smaller than normal. This condition can be physiological, pharmacological, or pathological in nature. Understanding the causes and implications of small pupils is crucial for medical professionals, particularly those in ophthalmology and neurology.

Anatomy and Physiology

The pupil is the opening in the center of the iris that regulates the amount of light entering the eye. The size of the pupil is controlled by two sets of muscles: the sphincter pupillae, which constricts the pupil, and the dilator pupillae, which dilates it. These muscles are innervated by the autonomic nervous system, with the parasympathetic nervous system causing constriction and the sympathetic nervous system causing dilation.

Causes of Small Pupils

Physiological Miosis

Physiological miosis can occur in response to bright light, a process known as the pupillary light reflex. This reflex is a protective mechanism to prevent excessive light from damaging the retina.

Pharmacological Miosis

Certain medications can induce miosis. These include:

• Opioids: Drugs such as morphine and heroin can cause pinpoint pupils.
• Pilocarpine: A medication used to treat glaucoma that acts as a muscarinic receptor agonist.
• Cholinergic drugs: These drugs stimulate the parasympathetic nervous system, leading to pupil constriction.

Pathological Miosis

Pathological causes of miosis include:

• Horner's syndrome: A condition caused by disruption of the sympathetic nerves supplying the eye, leading to miosis, ptosis, and anhidrosis.
• Uveitis: Inflammation of the uvea can lead to miosis as a result of irritation and spasm of the sphincter pupillae.
• Argyll Robertson pupil: A condition associated with neurosyphilis, where the pupils are small and do not react to light but constrict during accommodation.

Diagnosis

The diagnosis of miosis involves a thorough clinical examination and history taking. Important aspects include:

• Assessing the pupillary light reflex and accommodation response.
• Reviewing medication history for drugs that may cause miosis.
• Evaluating for signs of systemic conditions such as Horner's syndrome.

Treatment

Treatment of miosis depends on the underlying cause. For pharmacological miosis, discontinuation or adjustment of the causative medication may be necessary. In cases of pathological miosis, addressing the underlying condition, such as treating uveitis or managing Horner's syndrome, is essential.

Also see

• Pupil
• Mydriasis
• Pupillary light reflex
• Horner's syndrome
• Argyll Robertson pupil

External

• Age-Related Macular Degeneration

• Amblyopia (Lazy Eye)

• Anophthalmia and Microphthalmia

• Astigmatism

B

• Behçet's Disease* Bietti's Crystalline Dystrophy

• Blepharitis* Blepharospasm

C

• Cataracts

• Coloboma

• Color Blindness

• Corneal Conditions

D

• Diabetic Retinopathy

• Dry Eye

F

• Floaters

G

• Glaucoma

I

• Idiopathic Intracranial Hypertension

L

• Low Vision

M

• Macular Edema

• Macular Hole

• Macular Pucker

P

• Pink Eye

R

• Rare Diseases

• Refractive Errors

• Retinal Detachment

• Retinitis Pigmentosa

• Retinoblastoma

• Retinopathy of Prematurity

S

• Stargardt Disease

U

• Usher Syndrome

• Uveitis

V

• Vitreous Detachment