This lecture, delivered by Dr. Kendrick Shih for the MBBS V Senior Clerkship, walks through the five most common paediatric ophthalmic presentations in a scenario-based format ^[1]. The underlying thread is: the paediatric visual system is immature and developing — so any obstruction to clear, focused images reaching the visual cortex during the critical period can cause permanent visual loss (amblyopia) if not detected and treated early. That's why this matters.

1. Understand how the visual system develops in children and why that development creates a unique vulnerability window.
2. Assess visual acuity in pre-verbal and verbal children using age-appropriate methods.
3. Recognize, classify, and manage refractive errors, amblyopia, strabismus, epiphora (tearing), and leukocoria in children.
4. Know when to refer urgently (e.g., leukocoria → retinoblastoma) versus manage conservatively (e.g., nasolacrimal duct obstruction).
5. Understand the Hong Kong public-health context: Pre-School Vision Screening by the Department of Health at age 4–5 years at MCHCs.

• Birth: Very poor; the lecture's visual-evoked-potential example is approximately 20/600 (6/180). A light response alone is not a numerical acuity test.
• 6 weeks: Fixation develops.
• 3 months: Central, steady, maintained (CSM) fixation.
• 6 months: ~6/18–6/36.
• 1 year: ~6/12–6/9.
• Preschool years: Recognition acuity approaches adult levels, but the measured value depends strongly on the test and cooperation.

The graph on slide 9 is schematic: it conveys rapid improvement in the first months and slower maturation thereafter, not a set of pass/fail acuity thresholds for each age.

Fixation reflex — ability to fixate and follow (maintain fixation) a target (e.g., light, small toy) — NOT present at birth. ^[1]

Clinical pearl: If a child cannot fix and follow by 3 months, this is a red flag for significant visual impairment and warrants urgent ophthalmology referral.

Stereoacuity: Starts at 4 months, peaks at 2 years and well developed by 4 years, slow beyond 4 years and complete by 9 years. ^[1]

• Tested using Frisby Stereo Tests (graded circles and animals) or Titmus Fly ^[1].
• Good stereoacuity requires two aligned eyes each with reasonable acuity — it is destroyed by strabismus or amblyopia.
• Clinical relevance: If stereoacuity is poor, suspect strabismus or amblyopia even if monocular VA seems acceptable.

The history should include:

• Birth history
• Ocular history
• Previous ocular surgery
• Use of corrective lenses
• Family history ^[1]

In children, cycloplegic refraction is essential. ^[2]

Why: Children have strong accommodation. Without cycloplegia, accommodation can mask hyperopia and produce a falsely myopic result. Cyclopentolate is commonly used; atropine may be selected for particular children or when stronger/prolonged cycloplegia is required. Agent, concentration and safety screening are determined by the eye clinician.

Treatment: Improve vision AND prevent amblyopia ^[1]

• Prescription glasses / contact lens — correct the refractive error so a clear image reaches the retina.
• Prevent myopic progression — this is a major public health issue in East Asia:

In Hong Kong, the Department of Health Family Health Service provides Pre-School Vision Screening for children aged 4–5 years at MCHCs. ^[1][11]

Amblyopia = reduced visual acuity in one (or both) eyes that cannot be fully corrected with lenses and for which no structural or pathological cause is found on examination. It results from abnormal visual experience during the critical period of visual development.

Why does it happen from first principles? The visual cortex receives inputs from both eyes during development. If one eye consistently sends a blurrier image (due to refractive error, occlusion, or misalignment), the cortex preferentially processes the clearer input and actively suppresses the blurry one. Over time, the cortical connections from the affected eye are pruned → permanent reduction in that eye's visual capacity.

The slide's paired lighthouse diagrams encode this distinction: anisometropia gives poor focus in one eye, whereas high bilateral ametropia gives poor focus in both. Amblyopia may therefore be unilateral or bilateral.

Correct underlying cause → Correct any refractive error → Occlusion therapy (patching) ^[1]

• Patching dose is prescribed according to age, acuity, cause and response; more is not automatically better. Follow-up is needed to measure improvement, adherence and the rare risk of reverse amblyopia in the patched eye.
• Alternatives to patching: atropine penalization (blur the good eye pharmacologically with atropine drops — dilates pupil + paralyzes accommodation → blurs near vision in the good eye).
• Critical: Earlier treatment gives the best average response, but children and younger teenagers can still improve; AAPOS notes benefit from starting treatment up to about age 14 in NIH-supported studies. Treatment should be individualised rather than denied solely because the child is older than 9. ^[6]

When the eyes are misaligned, the brain receives two different images. In adults, this causes diplopia (double vision). In children, the brain has a powerful adaptive mechanism: it suppresses the image from the deviating eye to avoid confusion. This is good for comfort but terrible for development — it leads to strabismic amblyopia in the suppressed eye.

Visual suppression of deviating eye → Because of visual suppression [children don't get diplopia, but they get amblyopia instead] ^[1]

• The foveae have a common visual direction, and corresponding retinal elements of the two eyes support single binocular vision.
• Bifoveal fixation is the basic requirement for stereopsis (3D).
• In abnormal retinal correspondence, the fovea of one eye corresponds with an extrafoveal retinal area in the other eye; visual suppression of the deviating eye may occur. This is part of the basis of the cover test ^[1].

Corneal light reflex (Hirschberg test), Cover test (heterotropia), Uncover test (heterophoria), All stereoacuity tests ^[1]

How to read the alignment diagrams (slides 33–36): compare the corneal reflexes rather than the apparent amount of nasal sclera. The reflex is displaced opposite the deviation (temporal in esotropia, nasal in exotropia, inferior in hypertropia). Hirschberg is a screening estimate, not a substitute for prism measurement. In the cover-test sequence, movement of the uncovered deviating eye to take fixation proves a tropia; in the uncover sequence, refixation of the previously covered eye reveals a phoria.

Fully Accommodative Esotropia: Full correction of hypermetropia with glasses eliminates the accommodative drive, which is linked with convergence (accommodation-convergence reflex). ^[1]

From first principles:

• The child is hyperopic → to see clearly, the child must accommodate (increase lens power).
• Accommodation is neurally linked to convergence (the eyes turn inward together) — this is the accommodation-convergence reflex.
• Excessive accommodation (as in uncorrected hyperopia) → excessive convergence → esotropia.
• Fix: Prescribe full hyperopic correction → less accommodation needed → less convergence → eyes straighten.

The scenario photographs make the mechanism visible: without spectacles the right eye turns inward, while full hyperopic correction restores much better alignment. That before/after comparison is the visual clue for a fully accommodative component; any residual deviation with the full prescription suggests a partially accommodative esotropia.

Right eye refractive (anisometropic) / strabismic amblyopia ^[1] — In this scenario the right eye has both mechanisms causing amblyopia: it is more hyperopic AND it is the deviating eye.

Management: Occlusion therapy (patching of normal eye → left eye). Consider squint surgery if develops Partially Accommodative Esotropia. ^[1]

Epiphora reflects either increased tear production or decreased drainage. The epiblepharon photographs show a lower-lid skin fold rotating the lashes vertically against the globe: corneal irritation drives reflex tearing. Many cases improve as the face grows, but corneal staining or persistent symptoms need ophthalmic review; surgery is reserved for significant cases ^[1]. Decreased drainage may result from failure of canalisation of the nasolacrimal duct, as in CNLDO.

Mechanism: The nasolacrimal duct (NLD) drains tears from the eye into the nose. Persistence of a thin membrane at its distal end (the valve of Hasner) is the commonest mechanism. More than 5% of infants have symptomatic obstruction; the presence of an uncanalised membrane at birth is much more common than symptomatic disease. Tear overflow, mucous discharge and crusting result because tears and debris are not draining normally. ^[7]

Why it usually resolves: About 90% of symptomatic cases clear spontaneously during the first 12 months as the duct canalises. ^[7]

What the slide images add: the scenario photograph shows tears and yellow crusting at the medial canthi with relatively quiet conjunctiva, favouring obstruction over primary conjunctivitis. The lacrimal diagram traces the route punctum → canaliculus → lacrimal sac → nasolacrimal duct → nose. A bluish medial-canthal swelling suggests a dacryocystocele; bilateral lesions can extend into the nose and obstruct an infant's airway, so early specialist assessment is needed. ^[7]

The lecture specifically asks: "What are important differential diagnoses?" ^[1]

Painful erythematous swelling over the sac with fever or systemic illness suggests dacryocystitis, not uncomplicated obstruction, and requires urgent systemic antibiotics; hospital treatment may be needed. ^[7]

Differential diagnoses: ^[1]

Severe corneal pathologies that obscure any view of the iris and pupil, by definition, cannot give rise to leukocoria. ^[1]

Why it's the #1 concern: Retinoblastoma is the most common primary intraocular malignancy in children. Survival is very high in well-resourced settings when disease is detected and treated before extraocular spread, but untreated or metastatic disease can be fatal. Early diagnosis protects life first, then the globe and useful vision where feasible. ^[9]

MRI of the brain and orbits helps assess extraocular/optic-nerve disease and screens for pineoblastoma (trilateral retinoblastoma) in the appropriate risk group. Ocular ultrasound helps define an intraocular mass and calcification. The “?CT” on the older diagnosis slide should be read historically: current NCI guidance generally avoids routine CT screening because of radiation exposure. ^[9]

How to read the tumour images and flow (slides 51–55): the fundus photograph shows a pale retinal mass; the bisected globe shows how a large tumour can fill the vitreous cavity. Spread can occur through the optic nerve into the CNS, through choroidal vessels haematogenously (including bone/bone marrow), or directly through sclera into the orbit. Treatment priorities are ordered save life → save globe → save useful vision, balancing ocular salvage against metastatic and late-treatment risks. ^[1][9]

Paediatric cataract has an estimated incidence of 1–6 per 10,000 births. The lecture groups cases broadly into approximately one-third idiopathic, one-third hereditary (AD > AR > X-linked), and one-third associated with systemic disease; examples include Down syndrome, Lowe syndrome, galactosaemia, hypoglycaemia, hypocalcaemia, TORCH infection, and anterior-segment dysgenesis ^[1].

The cataract montage illustrates that opacity is not a single morphology: dense central, lamellar/speckled and polar/localised lens opacities can all alter the red reflex differently. Clinical urgency depends on visual-axis obstruction, density, laterality, age and visual behaviour, not the mere presence of any small lens opacity. ^[12]

From congenital rubella syndrome ^[4]: Permanent manifestations include congenital cataracts, pigmented retinopathy, congenital glaucoma, microphthalmos — all testable ophthalmological findings.

The strabismus section links directly to GC 124 content on CN III/IV/VI palsies. In children, cranial nerve palsies present as incomitant strabismus (angle changes with direction of gaze). In adults, the same palsies present with diplopia (because the adult brain cannot suppress one image).

Cataracts and retinopathy from rubella are important for the leukocoria differential and for prenatal counselling lectures. CRS ocular features: congenital cataracts, pigmented retinopathy, congenital glaucoma, microphthalmos.

Pre-school vision screening at MCHCs fits into the ICHDP framework. Know that vision screening is one of several surveillance components alongside growth monitoring, developmental surveillance, and hearing screening.