In the early years, visual acuity should be assessed as part of each general “well child” examination. It is best not to wait until the child is old enough to respond to visual charts, since these may not furnish accurate information until school age.
During the first 3–4 years, estimations of vision rely greatly on observation and reports about the child's behavior both at play and during interactions with parents and with other children. Unfortunately, at this age, seemingly normal visual performance is possible with relatively poor vision, and obviously abnormal performance probably reflects extremely poor acuity. The influence of visual impairment on motor and social development must always be borne in mind. The pupillary responses to light are a gross test of visual function and are reliable only for ruling out complete dysfunction of the anterior visual or efferent pupillary pathways. The ability to fixate and follow a target is much more informative. The target must be appropriate to the age of the child. Binocular following and converging reflexes are best examined first to establish the child's cooperation. Each eye should then be tested separately, preferably with occlusion of the fellow eye by an adhesive patch. Comparison of the performance of the two eyes will give useful information about their relative acuities. Resistance to occlusion of one eye strongly suggests it is the preferred eye, and therefore that the fellow eye must have comparatively poor vision. In cases of latent nystagmus—nystagmus increasing with occlusion of one eye—the child is likely to resent occlusion of each eye because of the effect such nystagmus has on visual acuity. Manifest nystagmus may be indicative of an anterior visual pathway disorder or other central nervous system disease until these have been excluded. (Further discussion of the assessment of nystagmus is given in Chapter 14.)
After 3 months of age, the presence of strabismus, detected by examining the relative position of the corneal light reflections, must also be regarded as indicative of poor vision in the deviated eye, particularly if this eye does not take up or is slow to take up fixation of a light upon occlusion of the fellow eye. (Further discussion of the assessment of strabismus is given in Chapter 12.)
These inferences about the status of the developing sensory systems can now be augmented by the quantitative techniques of optokinetic nystagmus, forced-choice preferential looking methods, and visually evoked responses (see Chapter 2). Although visually evoked potentials have suggested that normal adult visual acuity is attained before 2 years of age, this is probably an overestimate and it is likely that 3–4 years of age is a more accurate estimate (Table 17–2). Forced-choice preferential looking methods have gained increasing popularity as a reliable and relatively easy assessment of visual acuity in preverbal children, even in the very young. This technique does, however, have a tendency to overestimate visual acuity in amblyopes.
Table 17–2. Development of Visual Acuity (Approximate) ||Download (.pdf)
Table 17–2. Development of Visual Acuity (Approximate)
From about age 4 on, it becomes possible to elicit subjective responses by use of the illiterate “E” chart, child recognition figures, Lea figures, or HOTV cards. Usually, at the first- or second-grade level, the regular Snellen chart may be employed. Stereoacuity can be shown to develop in most infants beginning at 3 months of age, but clinical testing is not generally possible until 3–4 years of age. Absence of stereopsis, as judged with the Random Dot “E” test or the Titmus stereo test, is suggestive of strabismus or amblyopia and should prompt further investigation.
Objective refraction is an important part of the pediatric ophthalmic examination, especially if there is any suggestion of poor vision or strabismus. In young children, this should be performed under cycloplegia in order to overcome the child's tendency to accommodate. In most circumstances, cyclopentolate 1% drops applied twice—separated by an interval of 5 minutes—30 minutes prior to examination will provide sufficient cycloplegia, but atropine cycloplegia may be required if convergent strabismus is present or the eyes are heavily pigmented. Because atropine drops can be associated with systemic side effects, atropine 1% ophthalmic ointment applied once daily for 2 or 3 days prior to examination is the recommended regimen. The parents should be warned of the symptoms of atropine toxicity—fever, flushed face, and rapid pulse—and the necessity for discontinuing treatment, cooling the child with sponge bathing, and, in severe cases, seeking urgent medical assistance. Cycloplegic refraction provides the additional advantage of good mydriasis to facilitate examination of the fundus.
About 80% of children between the ages of 2 and 6 years are hyperopic, 5% are myopic, and 15% are emmetropic. About 10% have refractive errors that require correction before age 7 or 8. Myopia often develops between ages 6 and 9 and increases throughout adolescence, with the greatest change at the time of puberty. Astigmatism is relatively common in babies but decreases in prevalence during the first few years of life. Thereafter, it remains relatively constant in prevalence and degree throughout life. Asymmetric refractive error can lead to (anisometropic) amblyopia, which is detected only by assessing visual acuity.
Anterior & Posterior Segment Examination
Further examination needs to be tailored to each child's age and ability to cooperate. Anterior segment examination in the young child relies mainly on the use of a hand light and magnifying loupe, but slitlamp examination is often possible in babies with the cooperation of the mother and in young children with appropriate encouragement. Measurement of intraocular pressure and gonioscopy are more of a problem and frequently necessitate examination under anesthesia. Fundus examination relies on good mydriasis. It is generally easier in neonates and babies than in young children because they can be restrained easily by being wrapped in a blanket and examination is often easily accomplished by allowing the infant to feed or nurse during the examination, at which time it is often possible to obtain intraocular pressure measurements as well as examine the eye thoroughly.
The foveal light reflection is absent in infants. Instead, the macula has a bright “mother-of-pearl” appearance with a suggestion of elevation. This is more pronounced in heavily pigmented infants. At 3–4 months of age, the macula becomes slightly concave and the foveal light reflection appears.
The peripheral fundus in the infant is gray, in contrast to the orange-red fundus of the adult. In white infants, the pigmentation is more pronounced near the posterior pole and gradually fades to almost white at the periphery. In more heavily pigmented infants, there is more pigment in the fundus, and a gray-blue sheen is seen throughout the periphery. In white infants, a white periphery is normal and should not be confused with retinoblastoma. During the next several months, pigment continues to be deposited in the retina, and usually at about 2 years of age, the adult color is evident.