Visual Acuity Measurement

The accurate assessment of visual function is an important part of the neuro-ophthalmic exam. Many of the entities in subsequent chapters have decreased visual acuity as the presenting symptom. Special techniques are required to obtain an objective assessment of visual function in the young child. Table 2-1 contains a summary of the methods applicable to the various age groups.

Binocular visual acuity should be evaluated first because it is often superior to monocular function and the manipulation

TABLE 2-1. Visual Acuity Testing by Age.

Age Acuity

Test

Birth to 2 months 20/200-20/60

Observation

Blink to light

Fix and follow objects

OKN drum

2-6 months 20/50+

Observation

Blink to threat

Reach for objects

Preferential looking

OKN drum

VER

6-18 months 20/40+

Preferential looking

OKN drum

Reach for candy beads (1 cm-

-1 mm)

VER

18-36 months 20/30+

Preferential looking

OKN

Reach for candy beads (1 cm-

-1 mm)

VER

Allen cards

HOTV

3-5 years 20/30+

Reach for candy beads (1 cm-

1 mm)

Allen cards

HOTV

"E" game

Snellen chart

OKN, optokinetic nystagmus; VER, visual evoked response; HOTV, matching of Snellen characters.

OKN, optokinetic nystagmus; VER, visual evoked response; HOTV, matching of Snellen characters.

required to test the vision monocularly may result in loss of cooperation. Near visual function testing should also be attempted because in most neuro-ophthalmic disorders visual acuity will be better at near than at distance. This point is extremely important when trying to assess whether the child will be able to attend regular schools and whether large-print books or other visual aids will be necessary.

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