Nomenclature
| Suffix | AKA | Description | Features |
|---|---|---|---|
| -tropia | Manifest deviation | Binocular vision cannot be obtained. These patients have persistent symptoms. | Persistent symptoms |
| -phoria | Latent deviation | Binocular gaze may be obtained when both eyes are open and fixating, but when the strabismus eye is covered it deviates. | Symptoms only when the eye is tired |
Referring to Horizontal Direction
| Prefix | Description |
|---|---|
| Eso- | Refers to abnormal deviation of an eye towards the midline |
| Exo- | Refers to an abnormal deviation of an eye away from the midline |
Referring to Vertical Direction
| Prefix | Description |
|---|---|
| Hypo | Refers to an abnormal deviation of an eye in the downwards direction |
| Hyper- | Refers to an abnormal deviation of an eye in the upwards direction |
Referring to Cause
| Term | Definition |
|---|---|
| Paretic | Due to paralysis of an extraocular muscle |
| Non-paretic | Not due to paralysis of an extraocular muscle |
Referring to Pattern
| Term | Definition |
|---|---|
| Comitant | Deviation is same magnitude regardless of gaze position |
| Noncomitant | Degree of deviation varies with gaze position |
Overview
Strabismus is when the orbits are not aligned properly. It is defined as misalignment of the eyes affecting the ability to attain stereopsis.
| Name | Action | Controlling cranial nerve |
|---|---|---|
| Lateral Rectus | Moves eye laterally | VI (abducens) |
| Medial Rectus | Moves eye medially | III (oculomotor) |
| Superior Rectus | Elevates eye and turns it medially | III (oculomotor) |
| Inferior Rectus | Depresses eye and turns it medially | III (oculomotor) |
| Inferior Oblique | Elevates eye and turns it laterally | III (oculomotor) |
| Superior Oblique | Depresses eye and turns it laterally | IV (trochlear) |
Typically diagnosed by 4 years of age.
- Risk factors
- Myopia and Hyperopia
- FHx of strabismus
- Neuromuscular disorders affecting Extraocular muscles (e.g. Cerebral palsy)
- Developmental disorders (e.g. Down syndrome)
- Cataracts
- Traumatic brain injury
- Tumor of the brain or eye
- Hx of CNS infection
- Drugs/toxins (especiallyLead intoxication)
- Graves’disease
- Causes
- Refractive errors
- Orbital size discrepancy
- Hypertelorism or hypotelorism
- Weakness of Extraocular Muscles
- Abnormal insertion of Extraocular Muscles
- Abnormal tone/tonic innervation of an Extraocular Muscle
- Signs and symptoms
- Diplopia
- Eye strain
- Headache
- Blurry vision
- Poor depth perception
- Difficulty reading or learning to read
- Misalignment may be obvious in severe cases
- Physical examination
- Cardinal eye motions: Examine for proper eye movement through all fields of vision (cross and box method)
- Cover-uncover test: to reveal manifest deviation (”tropia”). Cover one eye and observe the other eye. If it moves outwards it demonstrates esotropia (the eye is moving into an appropriate position IE. it was too far inward to begin with), and vice versa.
- Cross-cover test: to reveal latent deviation (”phoria”). Cover the eyes alternatively. If the eye has phoria it will be seen moving back into normal position after being uncovered (covering it causes it to go into a deviated position)
Esophoria/esotropia
Esophoria and esotropia are seen more commonly in young people.
Types
| Type | When it is pronounced | Nota bene |
|---|---|---|
| Convergence excess | Esophoria is pronounced when focusing on near objects | Most common congenital type and is associated with farsightedness |
| Divergence weakness | Esophoria is pronounced when focusing on distant object | |
| Non-specific |
- Treatment Treatment depends on cause
- Refer to optometrist and ophthalmologist for correction
- Treat refractory abnormalities with glasses or bifocals
- Recession/Resection Surgery (optimal between 6 months and 2 years of age)
Exophoria/exotropia
Exophoria and exotropia are more common in older adults with presbycusis. The stop using their convergence muscles and they become weak. It usually begins in children after 2 years older.
Types
| Type | When it is pronounced |
|---|---|
| Convergence weakness | Exophoria is more pronounced when focusing on a near object |
| Divergence excess | Exophoria is more pronounced when focusing on a distant object |
| Non-specific |
- Treatment
- Refer to optometris and ophtalmologist for correction
- Treat refractory abnormalities with glasses or bifocals
- Orthopic exercises
- Surgery (particularly in children to prevent permanent damage)
Acute Strabismus
Strabismus developing acutely after age 5 is suspicious and should be considered for neurologic secondary causes.
- Causes
- CNS tumor
- Head trauma
- Multiple sclerosis
- Chiari malformation
- Opthalmoplegic migraine
- Meningitis/encephalitis
- Neurovascular disease
Pseudostrabismus
Pseudostrabismus is a false appearance of strabismus due to factors that affect the eye appearance or that displace the eyeball. It is more common in infants and Asian children (the epicanthal fold may make it look like the patient has and esotropia). Ptosis can also cause a pseudohypertropia.
Complications of Strabismus
- Complications
- Amblyopia
- Interference with interpersonal relationships (difficulty maintaining perceived eye contact)
- Increased risk of developing mental health illness
- Employment problems – airline pilots, mechanics and any other jobs that require good depth perception
