Matching cards allow testing in children who can’t or won’t name optotypes. Handouts with test optotypes may be given to families to practice at home ahead of time.

Because results may vary with dif fer ent methods, test details (optotype; linear vs single crowded pre sen ta tion) should always be recorded. When transitioning to a new method dur­ ing ongoing amblyopia treatment, retesting with the method used at the previous visit helps assess for interval change. Table 1-1 shows normative data for HOTV recognition visual acu­ ity for children at dif fer ent ages, as mea sured by an eye care professional ( these are not the same as referral thresholds in the context of primary care vision screening). Further tips for checking visual recognition acuity can be found in BCSC Section 3, Clinical Optics and Vision Rehabilitation, in the “Quick- Start Guide to Optics and How to Refract.”

T able 1-1 Monocular HOTV Optotype Recognition Acuity Test Results in Preschool Children

^a Over 95% of children with normal vision are expected to achieve this level of visual acuity or better. Information from Pan Y, Tarczy- Hornoch K, Cotter SA, et al; Multi- Ethnic Pediatric Eye Disease Study Group. Visual acuity norms in preschool children: The Multi- Ethnic Pediatric Eye Disease Study. Optom Vis Sci. 2009;86(6):607–612.

While checking vision, the practitioner can make the child feel successful by initially presenting optotypes that can be readily discerned and then saying, “That’s too easy— let’s try this one.”

In infants and toddlers who are too young to undergo optotype testing, fixation and fol­ lowing (tracking) be hav ior is tested. Each eye is tested while the fellow eye is occluded. Consistent objection to occlusion of 1 eye but not the other suggests a clinically significant difference in visual acuity between the eyes. The size of the smallest target tracked at a given viewing distance (eg, face vs 2-in toy) may be noted for each eye. Normal develop­ ment of fixation and following be hav ior is described in Chapter 15.

Children can tire quickly of the same toy; have several accommodative near targets available and apply the “1 toy, 1 look” rule. Photos or videos on a phone can also be used as near - fixation targets.

Fixation preference testing may also be performed; this is assessed under binocular viewing conditions. This is not a mea sure of monocular visual acuity, but it does provide information about how strongly the nondominant eye is suppressed with both eyes open. For a patient with strabismus, the first step in fixation preference testing is determining the preferred, or dominant, eye. The second step is to determine how well the child holds or maintains fixation with the nonpreferred eye. Starting from fixation with the nonpre­ ferred eye, with the preferred eye occluded, the occluder is removed; the examiner notes whether fixation is maintained with the nondominant eye or reverts to the dominant eye (and, if the latter, how quickly) (Video 1-1). The patient’s ability to maintain fixation through a blink or smooth pursuit is also noted.

VIDEO 1-1 Fixation preference testing.

Animation developed by Steven M. Archer, MD, and Kristina

For children with microstrabismus or no strabismus, the induced tropia test is used to determine the preferred eye (see the Appendix at the back of this volume for strabismus terminology). When a 10 prism diopter ( Δ) to 20 Δ base-down prism is introduced over the right eye, the child may

The test is repeated with the prism over the left eye. If the child prefers the same eye on both tests, a fixation preference is pre sent. A child who has no fixation preference either alternates fixation or consistently prefers the eye with prism or the eye without prism re­ gardless of which eye has the prism.

To determine how well the child holds or maintains fixation with the nonpreferred eye, the examiner occludes the preferred eye, holding a base- down prism under the oc­ cluder, so that the child is initially fixating with the nonpreferred eye; when the occluder is removed, with the prism still in place, the examiner notes whether fixation is maintained with the nondominant eye, or if it reverts to the dominant eye (as described above for strabismic patients; see Video 1-1).