An intermittent exotropia in a six-year-old whose mother wants 'the patch'
Tomas, 6 years 2 months, attends for his first full eye examination. His mother has noticed his left eye drifting out when he is tired, and his Grade 1 teacher says he loses his place when reading. Entering acuities are 6/7.5 OD and 6/9 OS on a crowded Sheridan–Gardiner chart. Cover test shows an intermittent exotropia of about 18Δ at distance and 12Δ at near that he recovers with a blink; near stereoacuity is 100 seconds of arc; near point of convergence is 8 cm. Cycloplegic retinoscopy with cyclopentolate 1% gives +1.25/−0.50×180 OD and +1.50/−0.75×10 OS. Anterior segment and dilated fundus examination are normal. He is well, takes no medication, and his mother asks whether he needs 'exercises or the patch'.
1. Is this amblyopia? Set out the reasoning that leads you to yes or no, and name the additional tests that would most change your conclusion.
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On these data, no - and the reasoning matters more than the label.
- 6/9 in a crowded test at 6 years sits at the lower edge of normal, and a one-line interocular difference is within test–retest variability in this age group.
- There is no amblyogenic refractive error: the two eyes are within about 0.50 D spherical equivalent of each other, and the hyperopia is far below any treatment threshold. Anisometropic amblyopia is not plausible here.
- The strabismus is intermittent and he alternates or recovers spontaneously, so there is no constant suppression scotoma driving amblyopia.
- Normal stereoacuity (100″) argues against established suppression.
Tests that would most change my view:
- Fixation preference (10Δ induced tropia or a graded blur test) to confirm he alternates freely.
- Repeat acuity with single-surround and matching optotypes, watching attention - the 6/9 may be an attention artefact.
- Post-cycloplegic cover test at distance and near, with a formal control score (e.g. Newcastle) measured at home and in clinic.
- Versions and ductions for oblique overaction and a V pattern; a full dilated fundus with disc and macula check.
- History: prematurity, neurological or developmental concerns, family history of strabismus.
2. Do you prescribe? Weigh the realistic options - no prescription, full plus, over-minus lenses, patching, exercises - and justify what you would actually do for this child.
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Patching is not indicated: there is no amblyopia to treat, and patching an intermittent exotrope risks disrupting a fragile binocular balance.
Full plus is counterproductive here: at +1.50 D the hyperopia is normal for age, and plus lenses relax accommodation and therefore accommodative convergence - in an exotrope that can unmask or worsen the deviation. There is no high AC/A pattern to justify it.
Over-minus lenses are a real option but not my first move. Minus lenses stimulate accommodation, drive convergence and can improve control in intermittent exotropia. Against them: they add accommodative demand, may accelerate myopia progression in a child already showing with-the-rule astigmatism and low hyperopia, and the evidence for long-term benefit is modest. With good control, 100″ stereo and a low control score, observation is defensible.
Office-based vision therapy has weak evidence in intermittent exotropia and should not be sold to this mother as a cure.
My plan: no prescription today; explain the natural history; review in three months with control scoring, stereoacuity and acuity. Refer to paediatric ophthalmology or orthoptics if control deteriorates (persistent manifest deviation, high clinic score), if stereoacuity falls, if acuity fails to equalise, or if the deviation becomes constant. Revisit over-minus if control worsens but stereo remains good.
3. His mother came expecting 'exercises or the patch'. Script how you explain the findings, and state what you tell her to watch for and when to return.
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Name it, normalise it, then set the plan.
'I want to be clear about what this is and what it isn't. Tomas has an intermittent exotropia - when he's tired or daydreaming, the left eye drifts out and then comes back. His eyes are healthy, his vision is normal for his age in both eyes, and his 3D vision is good. This is not a lazy eye, so the patch would not help him, and glasses would not fix it either. Many children stay exactly like this for years.'
Address the reading concern honestly: losing his place is common in Grade 1 and isn't explained by his vision, which is normal. Suggest the teacher note when it happens and check again at review; don't let the eye finding become the explanation for every classroom difficulty.
What to watch for: the eye staying out for longer or no longer coming back; him closing or covering one eye in bright light; new complaints of double vision; a noticeable drop in his 3D vision or in how well he uses the left eye.
Return sooner than three months if any of those appear. Give written information, and ask what questions she has before she leaves - she came for a treatment and is leaving with a plan, which needs to be said out loud.