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The eye sits within the skull and is surrounded by six muscles that move the eye.
The human eye has three layers.
The cornea and lens bend the light that enters the eye. The light passes through the vitreous gel to the retina where it forms an inverted image of the visual world.
The macular is the central part of the retina, with the fovea at its centre. The fovea has many cones, which enable detailed vision; the fovea is used for looking directly at an object. The rods increase in number moving away from the macular area.
The rods are important for seeing in the dark and for being aware of objects in the peripheral field of view.
The cones and rods convert the light energy into a ‘neural’ signal. The signal leaves the eye at the optic nerve and passes back to the brain - the occipital cortex. The occipital cortex processes the signal and passes it on to specific areas of the brain. This onward passage of attributes of the signal and the function of the brain areas enable the perception of fine detail, 3D, colour and motion and the coordination of the movement of the two eyes.
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Research has shown that vision is poor at birth and there is a ‘critical period’ in childhood in which anatomical and physiological changes in the eye and brain pathways enable a normal level of vision to develop.
The level of vision (visual acuity) improves rapidly during the first year of life and then continues to develop more slowly. The normal ‘adult’ level of vision is reached between 3 to 5 years of age. However, the development of vision remains vulnerable to disruption up to 7 - 8 years of age.
An infant’s eyes are poorly coordinated during the first 2 months of life and can ‘wander’ and an eye appear to ‘turn’ in or out some of the time. This reduces with the eyes being aligned (straight) with coordinated eye movement and working together (binocular vision and seeing in 3D) by 4 to 6 months of age.
To develop a normal level of vision each eye must be able to send clear and similar ‘images’ to the ‘eye’ brain areas during the developmental period. Anything that prevents light entering the eye (structural abnormality), or causes abnormal eye movement / coordination (squint) or blurred images (refractive error) will disrupt the normal pattern of visual development. Disruption of development during this critical period can cause a permanent visual defect if not detected and treated.
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Due to the development of vision from birth to 7 - 8 years of age the priority in children’s eye care is early detection of a condition that interrupts or hinders the normal development (i.e. squint, refractive error and structural abnormality).
Vision surveillance systems are in place for the pre-school child to detect early or evolving signs of a visual condition in those at high risk or suspected of having a problem.
This includes national screening programmes for prematurely born infants at risk of retinopathy of prematurity and children diagnosed with neuro-sensorial hearing loss.
Children with a learning disability, neurological syndrome/condition or systemic disease associated with visual conditions, are routinely referred for visual assessment within the hospital eye service as they have an increased risk of a visual problem.
Parents or a health professional may suspect a visual problem or squint and the child can be referred to an eye health care professional.
A child with reduced vision may not show any outward signs of a visual problem. The school vision screening at age 4 - 5 years is the only vision test offered to all children during the critical period of vision development. It enables those children with reduced vision to be identified so they can be referred for further eye tests, diagnosis and treatment, as well as to reliably exclude children with normal vision.
It is generally the non-obvious small squints and reduced vision due to refractive error that are detected through the school vision screening. This is because children with these conditions rarely present to an eye health care professional, as no problem is apparent.
School vision screening is carried out at an age when the critical period of vision development is nearing completion. This means it is essential that the screening takes place and the vision test is conducted correctly. Failure to detect reduced vision and refer the child for diagnosis and treatment may lead to the child having a permanent, untreatable, vision defect.
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To develop normal vision each eye must be able to send clear and similar images to the ‘eye’ brain areas. Any defect that prevents this during early childhood will disrupt the development, and if left undetected this damage may be permanent.
Conditions that disrupt development are those that prevent light entering the eye (structural abnormality), cause abnormal eye movement/coordination (squint) or blurred images (refractive error):
An uncorrected refractive error, a squint, or abnormality of the eye will cause a permanent reduction in vision, termed Amblyopia, if not detected and treated during the critical period of vision development. Amblyopia is known colloquially as a ‘lazy eye’.
If the condition disrupting the visual development is detected promptly glasses and / or patching may be recommended as part of the treatment.
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Although systems are in place for visual surveillance of children of pre-school age, vision defects can develop during the first years of life and may not be apparent.
The vision assessment at school entry is important as it can be the only way a visual problem is discovered. Children can appear to function normally with no suggestion of reduced vision. This can be because one eye is ‘doing all the work’, or both eyes have reduced vision but the child manages with daily tasks. A child does not know they should be able to ‘see better’. Children with visual loss, even severe loss, can function well because that is what they are used to. Parents/carers of children referred from school vision screening are often shocked to discover that their child had a vision problem.
In school a visual problem may become apparent because the child does not progress with learning to read and write. Difficulties with learning can lead to behavioural problems and / or frustration in school. At age 4 to 5 years a child is still within the critical period of visual development, so reduced vision can be identified and treated preventing a lifelong visual problem and lasting impact on educational development.
It is not uncommon for a teacher and/or parents to notice an improvement in a child’s reading and school work or behaviour/attitude to school once treatment is given.
A child with special educational needs/learning disabilities is more likely to have visual problems and it is essential that they receive the vision screening if not already under the care of an eye professional. The Orthoptist lead in your area will advise you of the local arrangements to ensure these children are seen.
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Vision is measured as Visual acuity. Visual acuity is a measure of our ability to detect fine detail.
The Keeler crowded LogMAR test is used to measure visual acuity for the school vision screening. The test was designed for use with children aged 3½ to 5 years but children vary in their ability and cooperation to do the test.
The test requires a 3 metre test distance and consists of 2 ‘flip over’ books. It has pages of 4 letters in a line, within a box. The box ensures that the letters at the beginning and the end of the row are as difficult to see as the two letters in the middle of the row. The letters X V O H U Y are used with a matching key card.
Each letter has a value of 0.025. This means that every letter that has been seen correctly contributes to the vision ‘scored’.
The books contain a series of screening cards that are used to identify a starting point for the measurement of row acuity. The observer shows the first letter on the screening card row and asks the child to match the letter with the corresponding letter on the key card. The letter size is decreased until the child is no longer able to name or match the letter on the screening card. The smallest size letter seen on the screening card is then shown as a row of letters. Letter size can be decreased until the child is no longer able to match any letter, i.e. the limit of visual acuity is reached. As each letter has a score the acuity is recorded to the last letter seen, as a logMAR value.
Ideally two vision screeners should be available for each screening session. One to undertake the test and the other to sit by the child to offer encouragement, confirm results on the key card if used, and to supervise the child i.e. ensure the child does not lean forward, keeps head straight, and does not peep.
A child should achieve 0.200 or better for each eye in order to pass the vision screening.
The Orthoptist lead in your area will:
You will be required to produce a reflective account of undertaking the vision screening processes which will be reviewed and signed by the Orthoptist.
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Multi-agency team members include eye health care professionals, Qualified Teacher for the Visually Impaired and Eye Care Liaison Officer.
Orthoptist – An eye health care professional trained in the diagnosis and management of eye disorders, squint and amblyopia. Orthoptists are also involved in screening for eye disorders. Orthoptists work within the hospital eye service in hospitals and community clinics.
Optometrist (formerly known as Optician) – An eye health care professional trained to test for and prescribe glasses, to screen for eye disorders and to check the health of the eyes. Optometrists usually work in High Street practices.
Ophthalmologist - A doctor trained in the diagnosis and management of eye conditions, including surgery. Ophthalmologists work within the hospital eye service.
Qualified Teacher for the Visually Impaired (QTVI) - A specially trained teacher who works in mainstream and special schools liaising with staff and families/carers to support a child with visual impairment to fulfil their educational potential.
Eye Care Liaison Officer (ECLO) – Works within the hospital eye service to provide advice and support for those who have visual impairment at a level that requires sight loss registration. ECLOs will direct a child’s family/carers to resources, activities and financial benefits and act as a link with community support services i.e. social services and third sector charitable organisations.
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A child referred from the school vision screening will have a full eye examination to enable diagnosis of the condition and treatment. Treatment may include glasses and/or patching. A child will be reviewed regularly by their eye health care professional to ensure he/she achieves their visual potential. The majority of children referred from the school screening who receive and undertake the necessary treatment will achieve a level of vision that does not impact on their education or work life opportunities.
A child with severe visual loss in both eyes may require registration by an Ophthalmologist, as visually impaired and receive support from the QTVI and ECLO.
A child with severe loss in both eyes will require a statement of educational needs. The purpose is to ensure the child’s visual and general ability are given consideration in the delivery of his/her education to ensure progress in school. The statement is usually prepared through input from the multi-agency workers. It details a child’s identified needs and any additional help the child should receive in school. Most children should have their needs met within a mainstream school.
As a visually impaired child gets older he/she may benefit from the provision of Low Vision Aids which in Wales are provided by Optometrists registered with the Welsh Low Vision Scheme.
Depending on the degree of visual impairment, the QTVI may teach the child Braille, and a Habilitation Officer may work with the child for mobility training and using a cane.
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Optometrists, hospital eye services, eye health care professional bodies and 3rd sector charitable organisation provide details for those with vision defects.
https://www.nhs.uk/childrens-eyes
https://www.orthoptics.org.uk/patients-and-public/
https://www.rcophth.ac.uk/patients/
https://www.rcophth.ac.uk/patients/links-to-charities/
https://www.moorfields.nhs.uk/listing/conditions
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Failure to detect and treat a visual defect within the critical period of a child’s visual development may lead to a lifelong, permanent visual loss which could adversely affect their educational attainment, employment opportunities and have psycho- social implications.
A child with severe bilateral visual impairment requires early diagnosis and support from the multi-agency team to ensure they have access to the appropriate resources, activities, financial benefits and educational support so he/she can achieve their potential.
A child with special educational needs is more likely to have visual problems. It is essential he/she receives eye examinations appropriate to their ability from an early age to ensure any visual defect is detected and treated and does not hinder their general development and potential.
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The Orthoptist providing the practical training and assessment of competence to undertake the vision testing will provide you with details of the local referral routes and polices/procedures for children who fail the vision screening. The Orthoptist will ensure you understand:
The Orthoptist will be available to provide advice and support you require.