The visual evoked potential (VEP) is an objective tool for quantifying visual function that does not rely on a child’s verbal or motor responses. In this test, electrodes are placed over the occipital lobe to mea sure cortical electrical signals produced in response to a visual stimulus (see BCSC Section 5, Neuro- Ophthalmology). The sweep VEP is a method for estimating visual acuity in preverbal children. The child views a series of bar or grid patterns of varying spatial frequency. The amplitude of the VEP waveform decreases with increasing spatial frequency, yielding a threshold spatial frequency estimate of grating resolution acuity. VEP estimates of monocular grating resolution acuity in infants are higher than estimates based on behavioral (preferential looking) tests; based on visual cortical responses, the infant visual system can re­ solve a spatial frequency of about 5 cycles per degree at 1 month of age and well over 10 cycles per degree by 6 months of age (compare to Table 1-3 for results from preferential looking tests).

Noncycloplegic retinoscopy at near is a way to assess accommodation. In an emmetropic child with normal accommodation, the retinoscopic reflex will be close to neutralized if the child is focused appropriately on a near target located at the examiner’s working distance. Because the examiner can also assess how quickly the refractive state changes during a switch from far to near fixation, this technique is often termed dynamic retinoscopy. A poor accommodative response may indicate the need for hyperopic correction or a near- point add. Hypoaccommodation occurs more frequently in children with Down syndrome or ce re bral palsy than in the general pediatric population.

Visual fields can be assessed once visual fixation has developed (usually by 4 months of age). If the introduction of a peripheral target while the child is fixating on an in ter est­ ing central target induces a saccade toward the peripheral target, this indicates vision in the corresponding hemifield. Confrontation visual fields can be approximated in children old enough to identify or count fin gers placed in each peripheral quadrant. School- aged children can often be evaluated with manual or automated perimetry.

The pupillary light reflex is not reliably pre sent until approximately 30 weeks’ gestational age. Pupils are usually miotic in newborns and gradually increase in size until preado­ lescence. Accurate pupil testing in young children is complicated by the smaller pupil and difficulty controlling accommodation. Pupil evaluation can be facilitated by careful observation, easily accessible control of room lights to allow continued observation dur­ ing changes in room illumination, and the use of appropriate distance-fixation targets. Digital photography can also be useful for observing and documenting pupil size and symmetry.

In the Brückner test, the direct ophthalmoscope is used to obtain a red reflex si mul ta­ neously in both eyes (Fig 1-4). Foveation of the ophthalmoscope filament dims the red reflex. If strabismus is pre sent, the deviated eye will have a lighter and brighter reflex than the fixating eye; media opacities and refractive errors can also cause unequal red reflexes. The positions of the corneal light reflexes can also be assessed. This test is often used by primary care prac ti tion ers to screen for vision disorders.