Childhood vision development
Early visual development is in interesting area sitting on the border between ophthalmology and psychology with an element of mystery thrown in. Early development is largely marked by qualitative milestones but, from about 12 months onwards, quantitative measures can be made, the accuracy of which increase with the child's age:
- 0-1 month - baby turns to diffuse light and shows steady fixation. There are irregular horizontal pursuit and 'brightening' (the eyes widen and other movements are stopped when shown an interesting visual stimulus).
- 2-3 months - there is visually directed reaching and the baby starts to be more proficient in accommodating. By now, the most rapid visual development will have occurred and further changes are more progressive.
- 3-5 months - there is blinking to threatening stimuli and the baby starts to mimic facial expressions. Objects are examined in more detail.
- 6-12 months - the baby's vision rapidly approaches normal adult acuity and vision motivates and monitors movement towards a desired object. By a year old, near and distant acuities are good. There may be some mild hypermetropia but there is ability to focus and accommodate, and the child has depth perception. They can discriminate between simple geometric forms, scribble with a crayon and are visually interested in pictures.
- By 2 years - myelinisation of the optic nerve is completed. All optical skills are smooth and well co-ordinated and acuity is now normal.
- By 3 years - retinal tissue maturity is almost attained; there is slower ongoing development for another 4 or 5 years until complete.
The young child's retina continues to develop rapidly postnatally, until the age of two or three. Thereafter, development slows until its completion at age seven or eight. The key point about screening is to catch any problems before this development is complete in order to avoid amblyopia which occurs when the developing retina is not stimulated due to the image not reaching it or ocular misalignment (see 'Conditions' under 'Screening for ophthalmic problems', below).
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Epidemiology of childhood visual loss
Serious visual loss in childhood is uncommon; there is an incidence of 6 per 10,000 children in the UK each year developing severe visual impairment or becoming blind by their 16th birthday with ± 12 more becoming visually impaired (worse than 6/18). Therefore, there are at least 4 newly visually impaired children each day in the UK. The prevalence of visually impaired or blind children is 20 per 10,000.
Children with milder visual loss, unilateral visual problems or eye disease without visual consequences considerably outnumber those with more serious disorders. However in the long-term, they require more of the disproportionately small resources available to them than the minority with more serious problems.
Worldwide, vitamin A deficiency, trachoma, and other infections are major causes of blindness in children.
Screening for ophthalmic problems
Screening is aimed at the primary prevention of visually impairing disease (eg cicatricial retinopathy of prematurity) as well as reducing the impact of already established disease (eg early detection and treatment of congenital cataracts). The beneficial effects of early identification of vision problems are far reaching as childhood visual impairment or loss can have a significant developmental, emotional and social impact. The majority of children with severe visual impairment (6/60 or worse) have additional sensory, motor or learning impairments ± chronic disease. More 'minor' problems such as an undiagnosed refractive error can be at the root of a cascade of events defining a child's future, eg poor performance at school may contribute to the child's self-confidence and their career.
Conditions that are screened for broadly fall into one of four (overlapping) categories:
- Neonatal conditions, eg retinopathy of prematurity, retinoblastoma, cataracts - some of these conditions (eg retinoblastoma) need treatment irrespective of visual outcome whereas others need treatment primarily because of the visual outcome, eg cataract.
- Risk factors for amblyopia, eg cataract, retinoblastoma - identification of amblyopia in the preschool age is associated with good treatment prospects but, beyond seven or eight years old, a decrease in cortical plasticity limits the outcome.
- Refractive errors - anisometropia (difference in refractive error between the two eyes) is the most common cause of non-strabismic amblyopia and usually develops between two and four years old.
- Colour vision abnormalities - these are often not picked up until later but they are important in that there is evidence to suggest that this affects learning and it excludes individuals from certain jobs (eg electrician, train driver).
Overview of the screening process
Preschool screening is well-established but the role of vision screening after school entry is controversial. Some areas offer a routine test of visual acuity and colour vision in older children and teenagers. There is debate as to whether these are worthwhile screening tests, and whether they should be included in the core programme of health surveillance for all children. However:
- Always take parental concerns about vision seriously and, if in doubt, refer to the appropriate service (orthoptist, optometrist or ophthalmologist).
- A visual assessment should be included for any child being assessed for educational underachievement or learning disability including dyslexia. If they cannot see the blackboard or the book, they cannot learn. This may even present as a behavioural disorder.
- Remember, eye checks by optometrists are free to children under 16 (under 19 if in full-time education). Encourage parents of older children and teenagers to use this service, particularly if there is a family history or myopia.
- Ophthalmologist - medically qualified, generally a surgeon unless sub-specialising in medical ophthalmology (although will have had a surgical training prior to specialisation).
- Optometrist - specialist in the diagnosis and treatment of refractive errors. Depending on training, may also screen for eye disorders ± treat certain eye conditions. Works either in a hospital or community setting.
- Optician - community-based person who makes and dispenses lenses and frames. May also be a trained optometrist.
- Orthoptist - specialist in the diagnosis and treatment of ocular motility disorders, ocular misalignments and amblyopia. Works in a hospital setting.
In the UK a randomised controlled trial compared visual surveillance by health visitors and family practitioners with orthoptist assessment (measuring visual acuity, ocular alignment, stereopsis and non-cycloplegic photorefraction). The study concluded that photorefraction (detecting refractive errors) and a cover test (to detect strabismus) at age 37 months would have the best sensitivity and specificity of the methods used. Orthoptists were shown to be the most accurate screeners but the costs of this would be prohibitive in some countries. Orthoptic-led screening programmes are currently used in the UK.
The newborn examination and 6- to 8-week review
- The red reflex: use an ophthalmoscope about 30 cm from the infant's eyes. Dark spots in the red reflex can be due to cataracts, corneal abnormalities, or opacities in the vitreous. The red reflex may be absent with a dense cataract.
- Corneal light reflex to detect squint. Hold a penlight at arm's length in front of the child. When the child looks at the light, normally the light reflex is symmetrical and slightly nasal (medial) to the middle of each pupil.
- General inspection of the eyes may suggest other conditions. For example, one eye larger than the other may indicate glaucoma.
- Also at the 6- to 8-week examination, ask parents if they have any concerns about their child's vision.
A specialist examination is indicated in babies who:
- Have an abnormality detected in the above routine examinations. In particular, treat an abnormal red reflex as a medical emergency - same day referral - as vision rapidly deteriorates week on week past 6 weeks and permanent blindness in the affected eye may be averted with prompt treatment.
A note on squinting babies - intermittent squints are common in neonates, particularly when they are tired. However, with time, the eyes straighten up such that this phenomenon should have resolved by about 3 months of age. If you detect a permanent squint, refer. If you note an intermittent squint, find out more about what happens throughout the day and organise a further review in 3-4 weeks time, asking Mum to note when the child is squinting and for how long. Ask if the baby appears to be trying to focus on objects (notably, lights, faces and brightly coloured toys). If, over this time, Mum hasn't noticed the baby trying to fix its gaze on an object or if the periods of squinting are getting longer, refer.
- Have a known higher risk of visual disorders, eg low-birthweight babies at risk of retinopathy of prematurity, babies who have a close relative with an inheritable eye disorder like albinism or Usher's syndrome, and babies with known hearing impairment. Congenital rubella syndrome is currently rare but may return with a falling uptake of the measles, mumps and rubella (MMR) vaccine.
Currently, all 4-5 year olds should have a vision check prior to school entry or as part of the school entry programme (this policy is due to to be reviewed but is not expected to change). This check is carried out by the school nurse or by an orthoptist, depending on local policy. Most 4 year-olds can co-operate with a test of visual acuity; there are a number of different assessment methods appropriate for young children, varying from picture or shape tests to matching tests and, for those children able to, the Snellen chart. This said, there is increasing scepticism on the value of this test with systematic reviews showing mixed evidence to support its effectiveness.
Screening in school-aged children
There are not currently any national guidelines set out for the screening of these children. The main issue lies in detecting refractive errors. Unnoticed, these can cause a number of problems ranging from the specific problems (eg chronic headaches) to underachievement academically. This itself has a very broad impact on the child's future. However, the benefits of screening at this age are still not clear and, whilst local screening policies should not be changed, it is not recommended that new programmes be set up for this age group.
Some children are at particular risk of developing visual problems and should be subject to surveillance. These include children with:
- Sensorineural hearing impairment.
- Neurodevelopmental problems (including Down's syndrome).
- A family history of a childhood onset ophthalmic disorder, eg retinoblastoma.
The child with reading difficulties
This problem is defined as being an inability to read at an expected level despite intelligence being within the normal range. Reading difficulties can affect up to 10% of the school-age population and there may be an excess in boys. However this figure may be biased, as boys with a reading problem are more likely to be reported than girls with a reading problem. Reading difficulties an be part of a wider spectrum of problems and may be associated with refractive errors or ocular motility disorders or, as in the majority of children, due to problems unrelated to the eye. Children with dyslexia tend to have an associated writing difficulty.
Further reading & references
- NHS Evidence - screening
- Health for all Children Fourth Ed. 2002; Edited by D Hall and David Elliman; Published by OUP
- Beauchamp GR, Ellepola C, Beauchamp CL; Evidence-based medicine: the value of vision screening. Am Orthopt J. 2010;60:23-7.
- Gunaratne LA; Visual Impairment: Its Effect on Cognitive Development and Behaviour, Understanding Intellectual Disability and Health, 2002
- Positive Images - Children with a Visual Impairment, Birmingham City Council; excellent resources for families with visually impaired children.
- Willshaw H et al; A Handbook of Paediatric Ophthalmology, 2000
- Ophthalmic Services for Children, Royal College of Ophthalmologists; Scroll down the list to locate.
- Child Health Surveillance and Screening: A Critical Review of the Evidence, Centre for Community Child Health, Royal Children's Hospital Melbourne, March 2002.
- Powell C, Wedner S, Hatt S.; Vision screening for correctable visual acuity deficits in school-age children and adolescents. Cochrane Database of Systematic Reviews 2005, Issue 1. Last updated April 2006.
- Williams C, Harrad RA, Harvey I, et al; Screening for amblyopia in preschool children: results of a population-based, randomised controlled trial. ALSPAC Study Team. Avon Longitudinal Study of Pregnancy and Childhood. Ophthalmic Epidemiol. 2001 Dec;8(5):279-95.
- Congenital Cataracts, UK National Screening Committee (2006)
- The UK NSC policy on Vision defects screening in children, UK National Screening Committee (2006)
- Pre-school vision screening, Bandolier
- Powell C, Hatt S.; Screening for amblyopia in childhood. Cochrane Database of Systematic Reviews 2005, Issue 3. Last updated August 2008.
|Original Author: Dr Olivia Scott||Current Version: Dr Olivia Scott||Peer Reviewer: Dr Paul Scott|
|Last Checked: 19/04/2012||Document ID: 2923 Version: 23||© EMIS|
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