Late complicationsin the vision of preterm infants
Jorge Breda
Besides retinal risks, infants who were born prematurely have also been reported to have an increased risk of other ocular complications, even if they don’t developed ROP. In addition, preterm children are at increased risk of poor motor skills, cognitive deficits and emotional or behavioral deficiencies.
Prematurity can cause effects on ocular and neurological development, as retinopathy, refractive error, strabismus, cerebral visual difficulties, color vision deficits, visual fields, contrast sensitivity and visual acuity. For those reasons, children discharged from the neonatal unit must be submitted to routine ophthalmic surveillance for the first years of life.
1-Visual acuity. It seems that a low weight birth child, may have a longer period for development of vision than a full term, which by the age of 5 years may reach the adult levels of acuity. There is evidence indicating that at the age of ten years the acuities of the low weight birth children are, on average, lower than those of the full term, with no known ocular pathology under this deficit. This condition, has been called Subnormal Visual Acuity Syndrome, and seems to be present in 1.9% of the population and reported as having a higher prevalence in the low weight born children.
2-Strabismus. There isan increased incidence of strabismus in children born prematurely and also a considerable variation on the types of strabismus encountered in this population. The higher prevalence of the divergent squint, call attention for the emergence of neurological damage, which can influence the development of binocularity. The higher incidence of refractive error and ROP are known causes as well.
3-Refraction. As it is well known, the refractive state of the eye is determined by the corneal curvature, lens thickness and overall eye length. Most of the term infants have hypermetropia, primarily axial, which is soon altered with the development of the globe and the increasing in its axial length, flattening of the lens and modification of the corneal curvature. It is a process that occurs overtime and is known as emmetropisation. In contrary, the preterm infants, despite their shorter axial lengths, are myopic. This can be originated in the arrested development of the anterior segment with flatter anterior camera, increased corneal curvature and spherical lens. It is the so called MOP (myopia of prematurity). A second group of patients are those which have myopia secondary to severe ROP, which is related with the disease process and not with the treatment.
4-Color Vision. The CRYO-ROP reported a large increase of blue-yellow color deficits in children of birth weight less than 1251 g when compared with the general adult population. However a causal link is not known.
5-Visual fields. The measurement of visual fields is not easy to do in children before the age of 5 years. Neurological anomalies like intraventricular hemorrhage can affect the visual fields as well as cryotherapy.
6-Contrast sensitivity. Due to the complexity of the task there are no reports of reduced contrast sensitivity in children before the age of 5 years. In older children, a reduction has been reported in low birth weight children when compared to those born at term. The importance of this finding is not known.