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# Strabismus and amblyopia

Strabismus is misaligned eyes; amblyopia (lazy eye) is weak vision in an eye that did not develop normally in childhood, often because of strabismus.

Updated 2026-10-29

## Structures involved

Tap one to see what it is and open it in 3D.

- [Medial rectus](https://durgical.com/en/anatomy/medial-rectus-muscle/)
- [Lateral rectus](https://durgical.com/en/anatomy/lateral-rectus-muscle/)
- [Visual cortex](https://durgical.com/en/anatomy/cuneus/)
- [Superior oblique](https://durgical.com/en/anatomy/superior-oblique-muscle/)
- [Inferior oblique](https://durgical.com/en/anatomy/inferior-oblique-muscle/)
- [Abducens nerve (VI)](https://durgical.com/en/anatomy/abducens-nerve/)
- [Oculomotor nerve (III)](https://durgical.com/en/anatomy/oculomotor-nerve/)
- [Geniculate bodies](https://durgical.com/en/anatomy/lateral-geniculate-body/)
- [Lens](https://durgical.com/en/anatomy/lens/)

## In embryology

- [Coloboma, congenital cataract and congenital glaucoma](https://durgical.com/en/embryology/coloboma-congenital-cataract-and-congenital-glaucoma/)

## In the clinical exam

- [Eye exam: visual acuity, visual fields and eye movements](https://durgical.com/en/clinical-exam/eye-exam-visual-acuity-visual-fields-and-eye-movements/)

## In physiology

- [Optics of the eye, accommodation and refractive errors](https://durgical.com/en/physiology/optics-of-the-eye-accommodation-and-refractive-errors/)
- [The visual pathway, pupillary reflexes and eye movements](https://durgical.com/en/physiology/the-visual-pathway-pupillary-reflexes-and-eye-movements/)

## What it is

Strabismus is misalignment of the eyes; amblyopia («lazy eye») is reduced vision in an eye whose visual pathway did not develop normally in childhood. Strabismus is one of the main causes of amblyopia.

## Who gets it

Both are common in childhood and are among the main causes of poor vision in one eye in children and young adults. Early vision screening is part of child health programmes.

## Causes

- Strabismus: infantile or accommodative esotropia, intermittent exotropia, cranial nerve III, IV or VI palsies, restrictive disease (thyroid eye disease, orbital fracture)
- Amblyopia, strabismic: the deviating eye is suppressed
- Amblyopia, refractive: unequal or high refractive errors (anisometropia, high hyperopia or astigmatism)
- Amblyopia, deprivation: congenital cataract, ptosis, corneal opacity

## Risk factors

- Prematurity and low birth weight
- Family history of strabismus or amblyopia
- Hyperopia (accommodative esotropia)
- Neurological conditions (cerebral palsy, hydrocephalus)
- Genetic syndromes such as Down syndrome
- Congenital cataract or ptosis

## Pathophysiology

In infancy the [visual cortex](https://durgical.com/en/anatomy/cuneus/) needs clear, aligned images from both eyes to develop binocular vision. If one eye deviates or sees a blurred image, the brain suppresses it to avoid double vision, and the pathway from that eye develops poorly. This sensitive period ends in childhood, so amblyopia treated late responds less.

## Classification

- Strabismus by direction: esotropia (in), exotropia (out), hypertropia or hypotropia (vertical)
- Constant or intermittent; tropia (manifest) or phoria (latent)
- Comitant (same in all gazes) or incomitant (paralytic or restrictive)
- Amblyopia: strabismic, refractive (anisometropic or isoametropic), deprivation

## Symptoms and signs

- An eye that turns in, out, up or down
- Head tilt or turn
- Closing one eye in bright light (intermittent exotropia)
- Amblyopia: often no symptoms; reduced vision in one eye found on screening
- Acquired strabismus in adults: double vision

## Red flags

- Absent or white red reflex (cataract or retinoblastoma)
- New strabismus with headache, vomiting or other neurological signs
- Sudden onset of double vision in an adult
- Painful eye movements or a dilated pupil with a third nerve palsy (possible aneurysm)

## Diagnosis

**Clinical**
Corneal light reflex (Hirschberg) and cover–uncover and alternate cover tests detect and measure deviations. Visual acuity is tested with age-appropriate charts; a difference of two or more lines between eyes suggests amblyopia. Eye movements and the red reflex are examined.

**Tests**
Cycloplegic refraction to find hyperopia and anisometropia. Instrument-based photoscreening in young children. Prism cover test to measure the angle.

**Imaging**
Not routine. Brain and orbit MRI for acquired paralytic strabismus or neurological signs; orbital CT for suspected restrictive or traumatic causes.

## Differential diagnosis

- Pseudostrabismus (broad nasal bridge, epicanthal folds)
- Cranial nerve palsies
- Thyroid eye disease
- Retinoblastoma or other causes of poor vision
- Duane syndrome and other congenital motility disorders

## Goal of treatment

Give the brain a clear image from each eye during the sensitive period, restore vision in the amblyopic eye, and align the eyes to allow binocular vision and normal appearance.

## Treatment

**Conservative**
Glasses that correct the full refractive error; they alone improve amblyopia and can straighten accommodative esotropia.

**Conservative**
Occlusion of the better eye with a patch, or penalisation with atropine-class cycloplegic drops, to force use of the amblyopic eye.

**Surgical**
Strabismus surgery: weakening or tightening extraocular muscles (recession, resection) to align the eyes, after amblyopia treatment has started.

**Medical**
Removing the cause of deprivation early, such as congenital cataract surgery or ptosis repair.

**Follow-up**
Frequent visual acuity checks during treatment, as amblyopia can recur and patching can affect the better eye.

## Complications

- Permanent reduced vision in one eye
- Loss of stereoscopic (3D) vision
- Higher risk of severe disability if the good eye is later injured or diseased
- Psychosocial effects of visible strabismus
- Recurrence after treatment

## Prognosis

Amblyopia treated early in childhood often improves markedly; response falls with age, though some older children still benefit. Surgery aligns most eyes, but more than one operation may be needed.

## Prevention

- Red reflex check in newborns and infants
- Vision screening in preschool children
- Early treatment of refractive errors, cataract and ptosis

## Test yourself

Think of the answer, then tap the question to see it.

## What is amblyopia?

Reduced best-corrected vision in one or both eyes from abnormal visual development in childhood, without a structural cause that explains it.

## Which test detects a manifest strabismus at the bedside?

The cover–uncover test: covering the fixing eye makes the deviating eye move to take up fixation.

## Which type of esotropia is caused by uncorrected hyperopia?

Accommodative esotropia; full hyperopic correction with glasses often straightens the eyes.

## What is the main treatment for amblyopia once refraction is corrected?

Occlusion (patching) or atropine penalisation of the better eye.

## Why must a child with strabismus have the red reflex checked?

Strabismus can be the first sign of a cataract or retinoblastoma, which change the red reflex.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/conditions/strabismus-and-amblyopia/)

## Related conditions

- [Cataract](https://durgical.com/en/conditions/cataract/)
- [Retinal detachment](https://durgical.com/en/conditions/retinal-detachment/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Amblyopia](https://www.ncbi.nlm.nih.gov/books/NBK430890/) (StatPearls (NCBI Bookshelf), 2024); [Esotropia](https://www.ncbi.nlm.nih.gov/books/NBK578207/) (StatPearls (NCBI Bookshelf), 2023).

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Source: https://durgical.com/en/conditions/strabismus-and-amblyopia/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/strabismus-and-amblyopia/