01Purpose and principlesWhat the assessment is for and the core concepts behind it.
A squint is a misalignment of the visual axes. The eye may turn inwards, outwards, upwards or downwards, either continuously or intermittently. Assessment is more useful when it records this pattern than when it stops at the word squint. Establish whether the deviation is newly acquired, longstanding or only recently noticed; ask which eye turns, when it happens and whether glasses change it. Photographs or a short family video can document an intermittent appearance, but the child's clinical examination remains essential.
Alignment problems have several mechanisms. Refractive error, especially hypermetropia with excessive accommodative convergence, can contribute to esotropia. Other childhood deviations arise during binocular development. Poor vision from ocular disease can itself cause a sensory deviation, while cranial-nerve palsy or restricted movement suggests a different pathway. A family history of squint may increase the likelihood of a common developmental condition but cannot explain away new neurological symptoms or an abnormal red reflex.
Observe before touching the child. Note fixation, head posture, lid position and whether both eyes follow an interesting target. A child with a longstanding deviation may suppress the image from one eye and report no double vision. A newly acquired deviation in an older child may instead cause diplopia or closing one eye. The absence of a complaint therefore does not establish normal alignment or acuity. Use age-appropriate monocular vision testing and record how reliably the child engaged.
The corneal light-reflex test, often called the Hirschberg test, compares the positions of a light's reflections on the two corneas while the child looks at that light. Hold the target centrally at a comfortable near distance and view both eyes from the front. Similar reflection positions support approximate alignment at that moment. A temporal displacement of the reflection relative to the pupil can accompany an inward-turning eye; a nasal displacement can accompany an outward-turning eye. Interpret symmetry and observed fixation together rather than demanding an exactly central reflection in every normal eye.
This test is particularly useful when a young child cannot cooperate with more formal measurement, but it is an estimate. Anatomical differences between the visual and pupillary axes, an eccentric fixation point or a moving target can complicate interpretation. Small-angle and intermittent deviations may be missed. A prism-assisted reflex test can quantify an apparent deviation in specialist hands, but a rough millimetre estimate in primary care should not be presented as a precise surgical measurement.
Cover testing is more discriminating when the child can maintain fixation. In the cover phase, cover one eye and watch the other, uncovered eye. If that uncovered eye moves to take up fixation, it had not been aligned with the target and a manifest deviation is present. Repeat on the other side, allowing binocular viewing between attempts. When the cover is removed, movement of the previously covered eye can reveal recovery from a latent deviation. The examiner must state which eye moved and at which part of the test.
The alternate cover test repeatedly transfers the occluder between the eyes without restoring binocular fusion. It reveals the total dissociated deviation, including a latent component, and can be combined with prisms for measurement. It should not be confused with simply establishing whether a tropia is present in ordinary binocular viewing. Near and distance findings may differ, as may results with and without the prescribed spectacles. Use an appropriate fixation target and record those conditions so another examiner can interpret the result.
Pseudostrabismus describes the appearance of a turn in eyes that are aligned. Epicanthal folds or a broad nasal bridge can obscure nasal sclera, especially in photographs. Symmetric reflexes and no refixation movement on a reliable cover test support this explanation, but they are meaningful only when the examination is adequate. A child diagnosed with pseudostrabismus can later develop true strabismus. Persistent or changing parental observations deserve reassessment rather than indefinite reassurance based on a previous visit.
Key points
- Describe the direction, constancy and onset of the deviation.
- Measure vision in each eye before assuming equal function.
- Corneal reflections provide a rapid estimate of alignment.
- A symmetric light reflex cannot exclude every small or intermittent squint.
- Cover testing distinguishes manifest deviation from latent misalignment.
- Check movement and red reflex as part of assessment.
- Referral urgency depends on associated ocular and neurological findings.
02Indications, selection and cautionsWhen it is useful, when urgency changes and important limitations.
Describe esotropia, exotropia or a vertical deviation and whether fixation alternates. These observations help characterise the problem without proving normal vision in either eye.
Movement of the uncovered eye during covering identifies a tropia. A deviation seen only after binocular fusion is interrupted may represent a phoria, requiring interpretation of the full test sequence.
Compare alignment across gaze positions and check ductions. A substantial limitation or varying angle can suggest palsy or mechanical restriction, although specialist assessment is needed to identify the cause.
A head turn, tilt or closing one eye may be an adaptation to misalignment. Ask whether it is new and whether it improves the child's visual comfort.
Facial anatomy can create apparent esotropia without a manifest deviation. Confidence requires a suitable alignment examination and attention to visual function rather than inspection of a single photograph.
03Method and interpretationA systematic approach to the test and its findings.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Corneal light-reflex comparisonFirst step - Why
- Obtain an initial alignment estimate when fixation is possible.
- Interpretation and limitations
- Asymmetric reflections raise suspicion, but normal-looking reflections do not exclude a small or intermittent deviation and an offset reflection can also result from ocular anatomy.
- 02
Cover and uncover testing - Why
- Determine whether a manifest deviation is present during binocular viewing.
- Interpretation and limitations
- Watch the uncovered eye as the fellow eye is covered; an outward refixation movement means the eye had been turned inwards, while an inward movement means it had been turned outwards.
- 03
Alternate cover and prism measurement - Why
- Assess the total deviation after interrupting binocular fusion.
- Interpretation and limitations
- This may reveal a larger angle than the manifest deviation alone; record target distance and spectacle correction, and obtain orthoptic measurements when treatment planning requires precision.
- 04
Cycloplegic refraction and monocular acuity - Why
- Identify refractive contribution and an associated amblyopic deficit.
- Interpretation and limitations
- Accommodation can hide hypermetropia, while good binocular behaviour can hide unequal vision; both optical assessment and separate eye measurements are needed.
- 05
Red reflex, ocular health and neurological examination - Why
- Look for serious ocular or neurological causes of misalignment.
- Interpretation and limitations
- Abnormal reflexes, structural findings, restricted movements or associated neurological symptoms change referral urgency and may prompt specialist imaging rather than routine squint management.
04Clinical next stepsHow the result changes management or prompts escalation.
01Initial assessmentBuild a reliable descriptionFirst stepA child presents with a suspected or intermittently observed squint.+
- 1Ask about onset, frequency, direction, visual symptoms and relevant family or developmental history.
- 2Measure each eye's vision using an appropriate test and observe fixation and posture.
- 3Compare corneal reflections and perform cover testing where the child can cooperate.
- 4Check red reflexes, pupils and movements before choosing the referral pathway.
02Stable non-paralytic squintArrange ophthalmic and orthoptic careMisalignment is present without an emergency feature or movement palsy.+
- 1Refer to ophthalmology for assessment of refraction, amblyopia and binocular function.
- 2Explain that glasses may improve an accommodative component without predicting the full eventual result.
- 3Treat associated amblyopia under the specialist plan before or alongside alignment decisions.
- 4Keep a clear review route if the deviation becomes constant, vision changes or new symptoms develop.
03New concerning squintEscalate according to the associated findingsEscalationRecent misalignment is accompanied by an abnormal reflex or neurological concern.+
- 1Refer immediately to ophthalmology when a new squint accompanies loss of the red reflex.
- 2Refer immediately to acute paediatrics when a new squint accompanies headache, vomiting or ataxia.
- 3Arrange urgent neurological assessment for a paralytic squint even without other raised-pressure symptoms.
- 4Communicate onset, vision, pupils, movement limitation and associated symptoms directly to the receiving team.
05Risks, monitoring and follow-upComplications, safety checks and further assessment.
- Document which eye moved, the direction of movement and whether this occurred during covering or uncovering; an ambiguous entry such as 'cover test positive' loses clinically important information.
- At follow-up, compare acuity and alignment under similar test conditions, including near or distance target and glasses worn, so measurement differences are not mistaken for genuine progression.
- Keep families informed about the distinct aims of correcting refractive error, treating amblyopia and improving alignment, with realistic expectations for each component.
- When an examination is incomplete, record its limitations and arrange a suitably experienced assessment; do not convert inability to demonstrate a deviation into a normal result.
- Provide specific advice to seek urgent care for a new white reflex, headache with vomiting, unsteadiness, double vision or a clear deterioration in the child's visual behaviour.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Follow the eye that is visible
During the cover phase, looking at the covered eye defeats the purpose of the test. The diagnostic movement is the uncovered eye taking up fixation when its fellow is occluded.
A movement reverses the resting error
An eye that moves outward to fixate had been turned inward. Naming the observed movement without distinguishing it from the underlying deviation is a common source of examination errors.
Intermittency needs context
A deviation may appear when the child is tired, inattentive or looking at a particular distance. A brief normal examination should be interpreted alongside a credible history and any recorded episodes.
Referral does not require a precise angle
Primary care can identify concern and communicate it without a complete prism measurement. Delaying referral until a distressed child produces a perfect cover test can obstruct timely diagnosis.
A neurological pathway can be needed first
A new deviation with headache, vomiting or ataxia is not simply a routine orthoptic problem. Acute paediatric assessment addresses the possibility of intracranial disease while eye specialists contribute to the evaluation.
07Common pitfallsFrequent interpretation and management errors.
- 01
Diagnosing pseudostrabismus from facial appearance without assessing alignment and vision.
- 02
Watching the wrong eye during the cover phase.
- 03
Calling outward refixation an exotropia instead of recognising the preceding inward position.
- 04
Assuming absent diplopia excludes significant childhood misalignment.
- 05
Using a routine orthoptic referral for new squint with neurological warning symptoms.