University of Edinburgh

Course: Visual Assessment of Children: The Orthoptist Role

Presented on Wednesday 9 February 2005

Abnormal Development - Anisometropia, strabismus, nystagmus, etc

Joan Ballantyne
Head Orthoptist
North Glasgow University Hospitals
Stobhill Hospital

Crofts et al (1998)

1.25/1000 had visual impairment; 72% of <1500g had associated impairments


  • Prenatal 60%
  • Perinatal 24%
  • Postnatal 10%
  • Rest unclassifiable
  • 84% originate before or at birth
  • 36% due to cortical visual impairment
  • 13% to optic atrophy
  • 10% to cataract
  • 6% each to nystagmus, retinal dystrophy and retinopathy of prematurity.

Unilateral conditions have a more profound effect on the visual development of the affected eye. Bilateral conditions have a more profound effect on the child?s general development.

Conditions affecting the eye and lids

  • Unilateral
  • Bilateral

The earlier the onset the more effect there is on the visual system.

Prenatal conditions

  • Rubella (CRS)
  • Cataracts (75% are bilateral)
  • Retinal pigment changes, glaucoma, microphthalmos, corneal problems and oedema.
  • Toxoplasmosis
  • Cytomegalovirus
  • Congenital conditions such as these if unilateral or asymmetrical often present as a squint or with leukocoria.

Lid anomalies

Congenital ptosis (drooping of the upper eyelid). Interferes with normal visual development if the lid obscures the pupil by reducing the visual stimulus. Usually unilateral which will lead to amblyopia if untreated.

Conditions affecting the iris and choroid

  • Albinism: Lack of pigment in the iris and choroid. The defect may affect the eyes only.
  • Ocular albinism
  • Oculocutaneous albinism affects both the eyes and the skin.

Reduced vision and contrast sensitivity.

  • Central retinal (foveal) underdevelopment
  • Iris translucency
  • Refractive errors
  • Amblyopia
  • nystagmus and squint
  • Photophobia.


  • Complete or partial absence of the iris.
  • Nystagmus
  • Photophobia
  • Associated conditions include cataract and glaucoma.


  • Congenital Cataract
  • No known aetiology
  • Inherited
  • Intrauterine infection (rubella)
  • Chromosomal abnormalities

The degree of visual impairment will depend on the

  • density
  • extent
  • position
  • of the cataract

Congenital cataract causes stimulus deprivation of the visual system. This is greatest if the cataract completely obscures the pupil.

Bilateral congenital cataract: early surgery is indicated to achieve the best visual outcome. Bilateral central cataract will cause bilateral stimulus deprivation but as the loss is symmetrical, both sides of the visual cortex will receive input and whilst the initial effect on the child is profound, the eyes might remain straight.

Unilateral cataract: Severe inequality of visual stimulus resulting in loss of cortical development. Unilateral cataract has a poorer visual prognosis for the affected eye; Stimulus deprivation amblyopia; Squint amblyopia.

When the opaque lens is removed, the eye becomes very long sighted and the resulting anisometropia (difference in spectacle correction) also worsens the prognosis.

Accurate correction of both unilateral and bilateral aphakia is vital and this can be achieved using contact lenses spectacle lenses.

Use of intra-ocular lens implants is controversial but not normally advised as the primary treatment. These may be considered when the child is older.

Strabismus (Squint)

  • Amblyopia
  • Functional loss of vision
  • Loss is greatest
    • if the squint is of early onset
    • if it always occurs in one eye
    • more than one factor causing amblyopia is present.


  • Stimulus deprivation (the retina is deprived of light/form by cataract, ptosis or occlusion)
  • Squint (strabismus)
  • Refractive error especially unequal.


Rhythmic movements of the eyes which can be fine or coarse, pendular or jerky, fast or slow. Sensory defect where there is visual loss, eg: cataract, albinism, ON hypoplasia, ROP, etc.

Nystagmus can also be found following an infantile convergent squint.

Congenital idiopathic nystagmus where vision can be good and there is no neurological deficit or pathology.

Neurological in conditions such as tumour, metabolic disease, malformations and trauma.


Leukocoria (white pupil)

Raised intra-ocular pressure in childhood (glaucoma or buphthalmos)

  • Infantile glaucoma
  • isolated
  • in conjunction with syndromes, eg: Sturge-Weber, neurofibromatosis
  • secondary to, eg: aphakia, ROP, etc.

Retinopathy of Prematurity

  • Related to:
    • Gestational age
    • birth weight
    • oxygen intake
  • Other factors:
    • twins
    • intraventricular haemorrhage
    • recurrent apnoea, etc

ROP is divided into 5 stages

Stage 1 and 2 frequently resolve completely but can be associated with myopia.

Others progress through stage 3 especially those with shorter GA, lower birth weight and oxygen.

?Normal? eyes with nystagmus and suspected loss of vision. Causes include

  • Nystagmus
  • Leber?s amaurosis
  • CSNB Nystagmus
  • photophobia
  • achromatopsia

Leber?s Amaurosis

Inherited congenital blindness associated with roving eye movements and eye poking. High hypermetropia and pseudo papilloedema.

No learning difficulties in the majority.

Congenital stationary night blindness (CSNB)

  • Reduced vision but not usually <6/60
  • nystagmus
  • normal fundus
  • may have high myopia
  • static condition
  • pupils constrict in the dark

Rod monochromatism (achromatopsia)

  • Complete colour blindness photophobia from infancy
  • nystagmus
  • reduced vision but good night vision
  • high hypermetropia
  • asymmetrical OKN

Inherited neurometabolic conditions

Mucopolysaccharidoses ? 7 types.

Longer lifespan may mean that visual involvement interferes with learning.

Ocular problems

  • Corneal clouding
  • glaucoma due to blockage of normal drainage
  • retinal degeneration (not MPS IVA)
  • optic neuropathy (not MPS IV;MPSIII)

Anomalies of the anterior visual pathways

  • Developmental anomalies
  • optic nerve hypoplasia
  • optic nerve coloboma


Failure of foetal cleft to close

Effect on vision is variable dependent on how much the retina is involved. Usually unilateral so effect on general development is reduced.

Optic nerve hypoplasia

Visual loss depends on degree of involvement bilaterality symmetry/asymmetry of the defect.

Optic disc hypoplasia can be associated with aniridia developmental anomalies of the CNS such as septo-optic dysplasia, holoprosencephaly, anencephaly, etc.

Septo-optic dysplasia

Absence of septum pellucidum between the lateral ventricles of the brain. Visual impairment due to: optic nerve hypoplasia; nystagmus.

They may have insufficient growth hormone = short stature Intellectually they may be normal or have learning difficulties.

Cortical visual defects

Diagnosis of DVI is indicated where there is abnormal visual performance that cannot be attributed to the eyes. CVI may be developmental acquired

Cortical visual defects co-exist with many other medical and learning problems. The visual involvement will add to educational difficulties; parenting worries; cognitive problems.

Ocular abnormalities include:

  • optic nerve hypoplasia and atrophy
  • poor vision and poor fixation
  • visual field loss squint and high refractive error
  • nystagmus

Developmental anomalies of the posterior visual pathways and cortex

  • Lyssencephaly
  • Neurones fail to migrate causing absence of the normal cortical gyrae.
  • Holoprosencephaly
  • Mild septo-optic dysplasia?
  • single cerebral ventricle with other abnormalities eg: microcephaly, optic nerve hypoplasia, coloboma, etc

Lissencephaly (Agyria)

Failure of neurones to migrate causing absence of the normal gyri.

Widespread developmental defects and seizures.

Acquired disorders of the pathways and cortex

Common in preterm, low birth weight or sick babies.

Cortical visual impairment

  • Hypoxic/ischaemic episodes
  • perinatal anoxia/hypoxia
  • cardio-respiratory arrest
  • near cot death
  • trauma including NAI

Cortical visual impairment

Infections, eg: meningitis

  • hydrocephalus
  • shunt failure
  • antenatal drug use
  • associated conditions include:
  • cerebral palsy and developmental delay.

Periventricular leukomalacia

Lack of oxygen or blood to the Periventricular area of the brain causing loss or death of tissue.

  • Ischaemic damage followed by haemorrhage ? severe damage to the posterior visual pathways, leading to
  • cortical visual loss
  • eyes rotated down
  • convergent squint


Visual field defects are normally present and may involve one halls of the field (hemianopia)

Inferior field defects are common in children with hypoxic/ischaemic damage and PVL and also occur in children who also have CP.


  • Developmental defects
  • acquired (infections)
  • IVth ventricle and aqueduct anomalies
  • secondary to a space occupying lesion

Ocular manifestations of hydrocephalus include:

  • inability to look up
  • convergent squint
  • papilloedema (childhood onset)
  • nystagmus
  • optic atrophy following papilloedema