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Long-term ocular complications in children born preterm

Preterm babies are at increased risk of developing ROP and other long-term ocular complications.
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Preterm babies spend a shorter time in utero, as a result they experience delayed development of their visual sensory system. This puts preterm babies at an increased risk of developing retinopathy of prematurity and other long-term ocular complications including various kinds of refractive error and strabismus (squint). There can also be significant impact from cerebral visual impairment which is associated with delayed visual maturation and cerebral palsy. In delayed visual maturation, a preterm baby’s visual pathways (especially the magnocellular pathway and the dorsal stream of visual processing) experience delays in development during the first three to six months of life. These conditions have all been found to be more severe with increasing prematurity.
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Deficits in visual acuity, contrast sensitivity, colour vision (commonly a blue-yellow) and visual field are also associated with preterm birth. For the child, the consequences of all these conditions impact their psychological and educational development. Refractive errors Refractive errors are more common in children born preterm than in those born at term. In particular, preterm babies are more likely to develop myopia. Myopia is caused by a long axial length of the eye, a flat anterior chamber and a thick lens. In preterm babies with no ROP, myopia is usually mild and develops at around four to five years of age. It can also sometimes progress during the teenage years.
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Babies who have developed any degree of ROP are at a higher risk than those who did not, and the myopia may be more severe and have an earlier onset. Babies who have been treated for sight-threatening ROP are at the greatest risk of developing high myopia (more than 5 dioptres) during their first six to nine months. This becomes relatively stable by 36 months.
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Other refractive errors such as astigmatism (distortion of vision) and anisometropia (a different refractive error in each eye) are also more common amongst children born preterm.
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Strabismus occurs in children born preterm alongside and without refractive errors. Strabismus is a misalignment of the eyes and can be caused by vision loss in one or both eyes, cranial nerve paralysis or a problem within the visual pathway. In children born preterm, the prevalence of strabismus at six years of age can be up to 26%.
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Visual impairment after ROP treatment: ROP treatment can lead to some visual impairment from visual field constrictions and defects. And there is evidence that myopia is associated with ROP treatment as well as severity of ROP disease. Following ROP treatment it is important to also look out for the development of cataract and glaucoma. These are rare complications of laser treatment.
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Cerebral visual impairment: Cerebral visual impairment (or CVI) is a deficiency in the visual processing function due to malfunction or damage to the visual pathways and visual centres in the brain. In preterm babies one of the commonest causes of CVI is a periventricular leukomalacia caused by reduced blood flow in the white brain tissue involved in processing vision. This affects visual pathways in different lobes of the brain. In children with CVI, findings from comprehensive ocular examination do not explain the wide range of visual difficulties experienced by the child and observed by parents. These can include visual field defects, colour defects or colour washout, difficulty with recognising facial expressions, shapes, sizes or direction.
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The child may find crowded places frightening or have limited capacity to pay attention. Unlike ROP, CVI has not received much attention. And there are no guidelines about regular long-term follow-up of these children if they did not also develop ROP.
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The evidence strongly indicates that every premature baby requires long term ophthalmic follow-up. The appointments should be scheduled based on whether the child has received ROP treatment, or has not had ROP or not required ROP treatment Preterm babies who received treatment for ROP should be seen every three months till the age of one year. After that they should be seen every six months till the age of four to five years. Babies who did not develop ROP or did not require treatment for ROP need to be seen at two months of age. If they have developed central, steady and stable fixation and insignificant refractive errors, they can be seen every six months till the age of one year.
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If they are fine at one year, then they should be seen again at three to four years old, unless there’s any specific concern in between. At each visit, tests should be done by a transdisciplinary team that involves a paediatrician, neurologist and ophthalmologist. At the first check-up at 2 months of age, if the baby does not have normal fixation, a detailed visual acuity test and ocular examination needs to take place. Refractive errors must be assessed and other ocular complications such as cataract or retinal complications due to ROP must also be considered. If ocular examination does not explain vision, CVI or delayed visual maturation should be thought of.
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In these cases, vision intervention activities to promote visual awareness and fixation should be started. If no significant improvement in vision is seen after this, then CVI is likely. A detailed functional vision assessment must be done and interventions planned which consider the baby’s daily routines.
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Sometimes preterm children do not have any vision related problems in their early childhood but start manifesting difficulties around the age of four to five years which are not explained by an eye examination. In these cases, a detailed profile of the different aspects of the child’s visual function should be created using an inventory. This is then used to develop suitable interventions. Some visual dysfunctions can be quite disabling for the child.
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For example: Poor eye contact and difficulty in understanding facial expressions mean the child may get labelled as autistic. Inaccurate movements while approaching things or frequent falls while walking can lead to the child being labelled as clumsy. Difficulty in remembering numbers, shapes, letters, and difficulties with fine motor movements of fingers can lead to the child being labelled as dyslexic. Difficulties in sustained visual attention and crowded environments can lead to the child being labelled as having as attention deficit activity disorder. And difficulty in remembering routes mean the child can get labelled as stupid.
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For each of these difficulties, intervention strategies can be suggested which can be life changing for the child, for example, decluttering the child’s environment by removing competing visual stimuli, or ensuring there is no low height furniture at home, focusing on one thing at a time whilst learning, and giving non-visual breaks while learning.
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In summary: Every prematurely born child needs regular ophthalmological examination till the age of four to five years, irrespective of whether they have had ROP. At age two months, they should have a comprehensive eye examination to check the development of the vision system and identify any treatable problems. Thereafter, they should be seen every 3 or 6 months (depending on whether they have had ROP) till the age of one year. They should then be seen once a year until four or five years old, unless there is any particular concern.

The development of the eye is complex and closely linked with the development of the brain. The following three factors influence visual outcomes for infants and children born preterm:

  • The degree of prematurity and how sick the baby was
  • Whether retinopathy of prematurity developed and how severe it was
  • Whether neurological lesions developed in utero, during delivery or after birth.

Refractive errors, where light entering the eye is not focused properly on the retina, are more common in children born preterm than at term. The risk is higher if ROP developed, and far higher if treatment was given.

In refractive errors there is a mismatch between the focusing ability of the structures at the front of the eye (the cornea and lens) and the length of the eye.

‘Emmetropisation’ is the process of refractive development whereby the ocular components grow in a coordinated fashion to create an eye without refractive error. This process, which is fine-tuned by vision, is jeopardised in the preterm baby for two reasons: first, the effect of being born preterm and second, as a consequence of ROP. Early exteriorisation due to preterm birth shortens the intrauterine period and removes the fetus from a protective environment ideally suited to promote growth and provides the optimal level of stimulation. Unsurprisingly, the visual system of the preterm baby can be affected by removal from this milieu as well as by exposure to a very different biological and physical environment. Fledelius demonstrated over 30 years ago that the eyes of children born prematurely but who did not have ROP did not grow normally. He showed that structures at the front of the eye, namely the cornea and lens, both of which play a vital role in focusing light onto the retina, were different: corneas of children born preterm are more curved, and the lens is thicker, both of which increase the focusing power of the eye, leading to short-sightedness (myopia). This myopia, which is not due to ROP, is of low degree and is referred to as ‘myopia of prematurity’.’

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Retinopathy of Prematurity: Practical Approaches to Prevent Blindness

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Excerpted from Fielder, A. et al. Impact of retinopathy of prematurity on ocular structures and visual functions. Archives of Disease in Childhood – Fetal and Neonatal Edition 2015;100:F179-F184.

As you watch this video consider the different teams and services which are needed to support follow-up care for preterm babies.

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