Among newborns the distinction between essential anisocoria and Horner's syndrome is particularly important. Absence of sympathetic supply to the iris is frequently associated with mediastinal disease, such as in infants with neuroblastomas. Thus, Horner's syndrome requires an identification of the cause of the sympathetic deficit before it is dismissed as unimportant.

Nevertheless, even with thorough study, in only about 20% of cases of infantile Horner's syndrome will the exact cause be found. When a Horner's syndrome appears in the first few months of life, a typical heterochromia iridis will eventually appear. Initially, the irides will have identical color. But, since the development of iris stromal pigmentation requires the presence of an intact sympathetic supply, an easily apparent difference in iris color will appear by age 2 (■ Fig. 19.2).

Bilaterally absent or very poor pupillary light responses in an otherwise seemingly healthy infant most frequently indicate Leber's congenital amaurosis. This should be distinguished from delayed maturation of the pupillomotor pathways in which the pupillary light responses may be slow but are preserved.

Fig. 19.2. Early childhood Horner's syndrome in the left eye with evident heterochromia iridis and miosis. Heterochromia is a reliable sign of an infantile onset

Color Vision Testing

For testing color vision in preschool children, the Matsub-ara Color Vision Test (Handaya Co., Ltd., Tokyo) and the Color Vision Made Easy test by T.L. Waggoner (1994) have proved to be useful. In a modification analogous to the form comparison method (Lea test), black-and-white copies can be used for comparison.

Oculomotor Testing

When testing oculomotor function in small children, including pursuit and saccadic movements (see Chap. 11), the use of attractive toys, such as finger puppets, blinking colored lights, or small sound makers, has proved helpful.

Visual Field Testing

A precise measure of visual field function in infants and toddlers is not possible. However, neuro-ophthalmically relevant defects are homonymous or bitemporal hemiano-pias, marked altitudinal deficits, or sector defects. Profound defects of this sort can usually be detected with a modified type of confrontational visual field testing. A summary is provided in ■ Table 19.5. ■ Figure 19.3 illustrates the preferred method for use with infants and also the procedure intended for use with somewhat older children.

Table 19.5. Visual field testing of children

Vestibuloocular Reflexes

When testing vestibuloocular reflexes (VOR) and their suppression in infants, it is best to hold the child in both hands with the arms extended, and then to turn to the right or left, while observing the child's eye movements (■ Fig. 19.4 a).

When testing the so-called doll's eye phenomenon, the child's head is moved while the body is held in a fixed position. This is easily done for horizontal movements, but is difficult for vertical movements. Vertical manipulation of the head often results in a loss of the child's cooperation (■ Fig. 19.4 b).

A detailed discussion of the testing of optokinetic nystagmus and the differential diagnosis of ocular motility disorders can be found in Chaps. 10 and 11.

Table 19.5. Visual field testing of children

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