How the Normal Features Differ from Those in an Adult

At birth the eye is large, reaching adult size at about the age of two years. One might expect that before the eye reaches its adult size, it would be long-sighted, being too small to allow parallel rays of light to be brought to a focus on the retina. In actual fact, the immature lens is more globular and thus compensates for this by its greater converging power. None the less, more than three-quarters of children aged under four years are slightly hypermetropic. The slight change of refractive error that occurs as they grow compares with the more dramatic change in axial length from 18 mm at birth to 24 mm in the adult. The slight degree of hypermetropia seen in childhood tends to disappear in adolescence. Myopia is uncommon in infancy but tends to appear between the ages of six and nine years and gradually increases over subsequent years. The rate of increase of myopia is maximal during the growing years and this can often be a cause of parental concern.

The iris of the newborn infant has a slate-grey colour because of the absence of stromal pigmentation. The normal adult colouration does not develop fully until after the first year. The pupil reacts to light at birth but the reaction can be sluggish and it might not dilate effectively in response to mydriatic drops. The fundus tends to look grey and the optic disc somewhat pale, deceiving the uninitiated into thinking that it is atrophic. The foveal light reflex, that is the spot of reflected light from the fovea, is absent or ill-defined until the infant is four to six months old. By six months the movement of the eyes should be well co-ordinated, and referral to an ophthalmologist is needed if a squint is suspected. Once children learn to identify letters, at the age of four or five years, the Snellen chart can be employed to measure visual acuity, which by this age is normally 6/9 or 6/6. The Stycar test can be used for three- to four-year olds or sometimes younger children and a similar level of visual acuity is seen as soon as the child is able to co-operate with the test conditions. Stycar results tend to be slightly better than Snellen results when measured in the same child, perhaps because the Stycar test involves seeing a single letter rather than a line.

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