• Strabismus is a disturbance of conjugate eye movement where the eyes cannot look simultaneously at the same point.
• In manifest strabismus (heterotropia), the eyes constantly look in different directions (which may be clearly visible from outside). Severe manifest strabismus often causes diplopia.
• Latent strabismus (heterophoria) can only be detected by a test, such as the cover test. It may cause difficulty reading and headaches.
• Sudden strabismus and diplopia warrant urgent ophthalmological examination.
  • Emergency referral to an ophthalmologist or a neurologist is necessary (after consultation by phone) if sudden diplopia is associated with anisocoria.
• Symptoms often begin gradually and urgent referral is unnecessary unless there are also neurological disturbances.

• Diplopia
• Eye deviation
• Difficulty fixating
• Difficulty reading
• Reduced visual acuity
• Headache

• See (Eye examination)
• Best corrected visual acuity
• Eye movements
• Cover test
  • The most important examination in patients with strabismus
  • Consists of covering and uncovering tests. Both can be done easily by a general practitioner.
  • For the performance of the cover test, see (Eye examination)
• Inspection of the pupils
• Measurement of intraocular pressure

Hirschberg test

• Shine a penlight or equivalent into the eyes.
• Inspect the position of the pin-point reflections of light off the cornea.
  • If the eyes are normally aligned, the light reflexes are symmetrically positioned.
  • If there is inward strabismus (i.e. esotropia, convergent strabismus), the light reflex will appear outwardly (i.e. temporally, laterally) displaced from the centre of the cornea.
  • If there is outward strabismus (i.e. exotropia, divergent strabismus), the light reflex will appear inwardly (i.e. nasally, medially) displaced from the centre of the cornea.

Abnormal red reflex (Bruckner test or Brückner test)

• Ask the patient to look directly at the light to obtain a red reflex simultaneously in both eyes.
• An abnormal red reflex in one eye may suggest strabismus.
• Make sure that the red reflexes are normal when testing each eye separately.

Observation of an abnormal head position

• An abnormal head position can, in association with other factors, suggest strabismus.
  • Turning or tilting the head may compensate for the functional visual handicap due to strabismus.

Bielschowsky head tilt test

• Useful for assessing vertical strabismus
• Tilt the patient’s head alternately towards the right and left shoulders.
• Follow vertical eye movement to detect any abnormality, such as the patient’s right eye deviating more upwards or downwards when the head is tilted to the right.

Examination of eye movements and pupillary reactions

• See article Eye examination(Eye examination)

Inspection of the eyelids

• Are both eyelids in the normal position or is there a difference, such as one eyelid drooping clearly more than the other?

• Paralysis of one of the extraocular muscles controlling eye movements (Neurological eye symptoms)
  • A common cause of acute-onset diplopia in adults
  • Examine immediately whether the patient has diplopia when looking simultaneously with both eyes (binocular diplopia) or when one eye is covered (monocular diplopia).
• Brain tumour, aneurysm or temporal arteritis
  • If the patient has diplopia and a dilated, fixed pupil, and the eye is turned down- and outward, there may be a brain tumour or aneurysm pressing on the parasympathetic, superficial fibres of the 3rd cranial nerve.
  • The possibility of a life-threatening situation or one threatening the patient’s vision must be excluded.

• Strabismus can be treated by prism glasses or surgery, as necessary.