Paediatric vision screening

Paediatric vision screening is a valuable prevention strategy for the early detection of potential visual disorders, which could have a negative impact on the overall development of children.¹ In fact, early childhood vision screening reduces the risk of vision loss at age 7 by more than 50%.²

According to the recommendations of the World Health Organisation (WHO), screening programmes, to be effective, should include tests that can detect the most common conditions that may be indications of serious health problems.¹

Among the most frequent causes of visual problems in childhood are refractive defectswhich affect around 12 million children under the age of 15 worldwide and are one of the main targets of vision screening programmes at a young age.¹

Another common cause of visual impairment in children is amblyopia, also known as 'lazy eye'.  It is mainly related to strabismus, refractive defects and congenital cataracts and affected individuals are more likely to have bilateral vision problems. Testing for amblyopia is one of the areas of interest in many screening programmes, because about 2-4% of children suffer from it and because effective treatments are available.¹

Strabismus, which is related to amblyopia, also requires early intervention.  early diagnosis. Other conditions included in paediatric vision screening programmes are trachoma, vitamin A deficiency, cataracts, glaucoma and retinoblastoma.¹

The main types of tests for paediatric vision screening

Red reflex test

The red reflex test is the most important screening test for infants and very young children and can be performed immediately after birth. A direct ophthalmoscope is used to visualise both eyes simultaneously. The red reflex represents the reflection of the retina through the pupillary axis. The presence of a distortion of the red reflex can be caused by an abnormality anywhere in the visual axis (e.g. in the retina in the case of retinoblastoma, in the vitreous in the case of haemorrhage, in the lens if a cataract is present, in the cornea if a scar or infection is present). An abnormality in the red reflex can also be caused by asymmetry in the refractive power of the eye, which can cause amblyopia and threaten vision.²

External examination of the eye

External examination of the eyes, eyelids and face is an important part of visual system screening. A simple examination of the eyelids can reveal ptosis and capillary haemangiomas, which are risk factors for amblyopia and other systemic diseases.

Careful inspection of eyeball size is important in screening for paediatric glaucoma, which can cause unilateral or bilateral ocular enlargement.²

Visual acuity test

Visual acuity changes with age and improves as children grow. In the first year of life, children with normal vision show an eyelid reflex, whereby they open their eyes wide when the light goes out. This reflex can be clinically useful in determining a child's perception of light.

Infants may have intermittent strabismus (both eyes turn outwards or inwards), but this normally resolves by 2-4 months of age. From the age of 6 months to 2 years, children should be able to follow an object in monocular mode and have normal alignment. Premature infants may have a delay in visual development, which should resolve by 8 weeks.²

From the age of 3 to 5, subjective vision can usually be measured using optometric tables.²

Cover test and Hirschberg test for the assessment of strabismus

A common concern among parents is strabismus (i.e. misalignment of the visual axes).² Examination techniques, such as the cover test and the Hirschberg test, are fundamental to the diagnosis of strabismus.²

The Hirschberg test is a simple, non-invasive examination in which the child has to look straight ahead while the operator shines a light into the child's eyes. In children who do not suffer from strabismus, the light reflects from the centre of the pupil if the eyes are straight. If, on the other hand, there is manifest 'exotropia' (eyes pointing outwards - divergent strabismus), the light will be reflected in the nasal position relative to the pupil, while in the case of 'exotropia' (eyes pointing inwards - convergent strabismus) the light will be reflected in the temporal direction.

The cover test requires the child to look at an object up close and at a distance, with one of the eyes covered. When the cover is removed, if squinting is present, the misaligned eye will deviate inwards or outwards.²

Ocular motility and nystagmus

In addition to alignment, ocular motility is also an important part of the eye examination of children, as it allows for the detection of disorders such as complex strabismus syndrome, congenital fourth cranial nerve palsy, Brown syndrome or Duane syndrome. In addition, the presence of nystagmus, i.e. unusual involuntary eye movements, in an infant or young child may indicate decreased vision or neurological dysfunction.²

Pupil examination

Pupils should be of equal size and responsive to light from birth. To examine pupillary response, a dark room and the use of bright light is sufficient to elicit the pupillary reflex in infants. Any evidence of anisocoria (i.e. different pupil widths) or the presence of differently shaped pupils should be referred to an ophthalmologist.²

Instrumental devices for vision screening

These are binocular instruments that can measure risk factors for vision loss (including myopia, hypermetropia, astigmatism and strabismus) by measuring refractive error, eye alignment and eyelid position. In fact, approximately 4% of children under 6 years of age suffer from myopia, from 5% to 10% suffer from astigmatism and up to 20% from hypermetropia.²

Bibliography

1. Uchenna C. Atowa, Samuel O. Wajuihian, Rekha Hansraj, A review of paediatric vision screening protocols and guidelines, Int J Ophthalmol, Vol. 12, No. 7, Jul.18, 2019
2. Allison R. Loh, Michael F. Chiang, Pediatric Vision Screening, Pediatr Rev. 2018 May;39(5):225-234. doi: 10.1542/pir.2016-0191.

Dr. Carmelo Chines
Direttore responsabile