At 9 months, any suspected squint is clinically significant: normal binocular coordination is usually established by about 3 months, and a constant deviation requires particular attention. NICE CKS
Prepare the examination: examine the infant when alert, seated on a parent’s lap, using an engaging toy or small fixation light and allowing time and repeated attempts to maintain fixation. NICE CKS
Focused history to accompany the examination: establish age and pattern of onset, whether the deviation is constant or intermittent, sudden or gradual, and any temporal relationship to infection, illness, or head injury. NICE CKS
Ask about apparent visual difficulty, abnormal visual behaviour, parental photographs or videos, diplopia where developmentally relevant, headache, nausea, vomiting, sensory symptoms, motor symptoms, and developmental concerns. NICE CKS
Ask about prematurity, low birth weight, delivery history, neurodevelopmental, neurological and systemic disease, ocular history including refractive error, glasses, prior eye surgery or amblyopia treatment, and family history of squint or eye treatment. NICE CKS
1. Observe before touching the child: assess fixation and following behaviour, facial symmetry, and whether the eyes appear aligned in primary gaze. NICE CKS
Look for a manifest deviation and identify its apparent direction: inward, outward, upward, or downward. NICE CKS
Inspect for ptosis, pupil asymmetry, other ocular abnormalities, nystagmus, and an abnormal head posture. NICE CKS
A hypertropic eye with a head tilt to the opposite side and chin depression may suggest superior oblique weakness. NICE CKS
Consider pseudo-squint if epicanthic folds obscure nasal sclera and create an impression of esotropia despite true ocular alignment. NICE CKS
2. Corneal light reflex (Hirschberg) test: hold a pen torch approximately 50 cm in front of the infant and encourage fixation on the light. NICE CKS
Compare the corneal reflections; they should be in the same position in both corneas, whereas asymmetry suggests a squint. NICE CKS
3. Cover test for manifest strabismus (tropia): use a toy held approximately 33 cm away and ensure fixation as far as possible. NICE CKS
Cover one eye with an opaque card while watching the uncovered eye, then repeat with the other eye. NICE CKS
A movement of the previously deviated uncovered eye to take up fixation when the straight eye is covered indicates a manifest squint. NICE CKS
4. Cover–uncover and alternate cover testing for latent deviation (phoria): while the infant fixes on the toy, cover one eye for about 3 seconds, uncover it quickly, and watch the previously covered eye for a refixation movement. NICE CKS
Repeat on the other side; alternatively, move the occluder slowly between eyes without allowing binocular fusion, observing the newly uncovered eye after each switch. NICE CKS
A latent deviation is suggested by drift beneath the cover followed by corrective movement when that eye is uncovered. NICE CKS
5. Ocular motility: use a toy or light to draw gaze right, left, up, and down, assessing whether each eye moves fully in all directions. NICE CKS
Specifically assess abduction in apparent esotropia and determine whether the deviation is concomitant or incomitant. NICE CKS
In esotropia, test movements monocularly if necessary by covering one eye and encouraging the uncovered eye to follow the target, because cross-fixation can mask an abduction deficit with both eyes open. NICE CKS
6. Screen for serious ocular and systemic causes: check the red reflex and specifically exclude leukocoria. NICE CKS
An absent red reflex or white/grey pupil may indicate serious intraocular pathology, including retinoblastoma. NICE CKS
Perform an age-appropriate general and neurological assessment, looking for abnormal neurological signs, altered tone or motor findings, dysmorphic features, and craniofacial or orbital abnormalities. NICE CKS
Neurological abnormalities should prompt paediatric assessment, as squint may accompany conditions such as cerebral palsy or Möbius syndrome. NICE CKS
If feasible, assess visual behaviour or visual acuity using age-appropriate methods and perform fundoscopy. NICE CKS
Document clearly: record whether the deviation is observed or reported only, constant or intermittent, laterality, direction, fixation behaviour, corneal reflex result, cover-test findings, ocular motility including any limitation, red reflex, head posture, and neurological or dysmorphic findings. NICE CKS
Disposition: refer a child with suspected or confirmed squint to the paediatric eye service, even if the deviation is not reproduced in the consultation because it may be intermittent. NICE CKS
Arrange urgent assessment if there is leukocoria or an absent red reflex, an acquired incomitant deviation, or other evidence suggesting serious ocular or neurological disease. NICE CKS
Constant unilateral exotropia is a concerning pattern that warrants careful assessment for an underlying cause. NICE CKS