engaging during the examination helps create a “safe” environment. Gaining the child’s confidence makes for a faster and better examination, easier follow-up visits, and greater parental support.
It is helpful to begin by asking easy questions with simple answers. For example, children enjoy being regarded as “big” and correcting adults when they are wrong. The practitioner can tell them they look “so grown up”; grossly overestimate their age or grade level and then ask, “Is that right?” A simple joke can relax both child and parent.
To initiate physical contact with a child, the practitioner can say “give me five” or admire the patient’s clothing or shoes. Pushing the “magic button” on the nose of a child as a video presentation or mechanical animals are surreptitiously activated with the foot pedal allows work to be done close to the child’s face while he or she is distracted.
As there may be only a few moments of cooperation, the most important features should be checked at the beginning of the examination. If fusion is in doubt, it should be checked first before being disrupted with other tests, including those for vision. While checking vision, the practitioner can make children feel successful by initially giving them objects they can readily discern, then saying, “That’s too easy—let’s try this one.”
A different vocabulary should be developed for working with children, such as “I want to show you something special” instead of “I want to examine you.” Use “magic sunglasses” for the stereo glasses, “special flashlight” for the retinoscope, “funny hat” for the indirect ophthalmoscope, and “magnifying glass” for the indirect lens. Confrontation visual field testing can be performed as a counting-fingers game or Simon Says. Children might be talked into a slit-lamp examination if the practitioner says that they can “drive the motorcycle” by grabbing the handles of the slit lamp. Using the imagination to “play” with children as the examination proceeds can be beneficial. Children will be more cooperative if the practitioner is sharing an experience with them instead of doing something to them.
The most threatening or most unpleasant part of the examination should be reserved for the end. The least expensive test that can be ordered is a return office visit. Children who become totally uncooperative can return later to finish the examination.
For the follow-up examination of an infant who is fussy during the first visit, ask the parent to bring the child in hungry and then feed him or her during the examination.
When dealing with a vision-threatening or life-threatening problem, the practitioner must persist with the examination and even use sedation or anesthesia when necessary.
Examination: Specific Elements
Visual Acuity Assessment
Visual acuity assessment requires different approaches depending on the age and cooperativeness of the child. Ideally, measurements at distance with crowded Snellen or Sloan letter optotypes guide amblyopia diagnosis and management. Commonly, however, the child suspected of having amblyopia is preverbal, preliterate, or not fully cooperative. In such cases, clinical options include assessing fixation behavior and using preliterate eye charts. Table 1-1 lists the expected acuity for various tests at different ages. Copies of whatever optotypes are appropriate for the child (eg, Allen cards, LEA symbols) can be given to the parent for at-home rehearsal to help distinguish not seeing the test object from not understanding the test.
Table 1-1
In infants and toddlers, fixation behavior is observed to qualitatively assess vision. Fixation and following (tracking) behavior is observed as the child’s attention is directed to the examiner’s face or a small toy in the examiner’s hand. Fixation preference is determined by observing a child’s response to covering 1 eye compared with covering the other. Children typically resist occlusion of the eye with better vision. It is also important to determine whether each eye can maintain fixation through smooth pursuit or a blink; strong fixation preference for 1 eye indicates decreased vision in the nonpreferred eye.
Fixation behavior may be characterized by the CSM (Central, Steady, and Maintained) method. Central refers to foveal fixation with a centrally located corneal light reflex, tested monocularly. If the fixation target is viewed eccentrically, fixation is termed uncentral (UC). Steady refers to the absence of nystagmus and other motor disruptions of fixation. The S assessment is also performed monocularly. Maintained refers to fixation that is held after the opposite eye is uncovered. An eye that does not maintain fixation under binocular conditions may be presumed to have lower visual acuity than the opposite eye. Maintained fixation is easier to identify in a strabismic patient. For children with small-angle strabismus or no strabismus, the induced tropia test may be performed. First, the examiner directs the child’s attention to a target. Then a 10–15 prism diopter base-down prism is placed in front of 1 eye, and the eyes are observed. If the eyes move up, the child is using the eye under the prism, and vice versa. The test should be repeated a few times on each eye. If the child consistently chooses the eye with the prism or the eye without the prism regardless of which eye has the prism, or if fixation spontaneously alternates between the eyes while the prism is in place, no preference is present. If the child consistently fixates with the same eye, the opposite eye likely has decreased vision. The visual acuity of an eye that has eccentric fixation and nystagmoid movements when attempting fixation would be designated uncentral, unsteady, and unmaintained (UC, US, UM).
Monocular recognition testing—which involves having the patient identify letters, numbers, or symbols, all generically referred to as optotypes—is the preferred method of assessing visual acuity. The optotypes may be presented on a wall chart, computer monitor, or handheld card. The acuity test should be calibrated for the test distance used. Because of the potential for variable or inaccurate viewing distances when testing at near, measurement at distance is preferred for managing amblyopia.
Various optotypes are available for testing preliterate children. LEA symbols and the HOTV test are reliable for preschool-aged children. Testability may be improved by having a shy child point and match rather than verbalize the optotypes. Other optotypes such as the Allen figures do not conform to accepted parameters of optotype design and therefore provide less accurate results. Most pediatric ophthalmologists consider letter (Sloan or Snellen) acuity optotypes the most accurate, followed in decreasing order of accuracy by HOTV and LEA symbols, the tumbling E, Allen figures, and fixation behavior. The examiner should use the most sophisticated test that the child can perform.
For patients with amblyopia, a line of optotypes (linear acuity) or single optotypes surrounded by contour interaction bars (“crowding bars”; Fig 1-2) should be used, because acuity is overestimated if vision is measured with isolated optotypes. The lines should be spaced such that the distance between optotypes is no greater than the width of the optotypes on a given line. The Bailey-Lovie and ETDRS (Early Treatment of Diabetic Retinopathy Study) chart designs incorporate appropriate linear optotype spacing, a consistent number of optotypes on each line, and a logarithmic (logMAR) change
in letter size between chart lines (Fig 1-3). See also BCSC Section 3, Clinical Optics.
Figure 1-2 Crowded optotypes. (Courtesy of the Good-Lite Company and Robert W. Hered, MD.)
Figure 1-3 LogMAR visual acuity chart with LEA symbols. (Courtesy of the Good-Lite Company and Robert W. Hered, MD.)
By convention, visual acuity is determined first for the right eye and then for the left. A patch or
other occluder is used in front of the left eye as the acuity of the right eye is checked, then vice versa. An adhesive patch is the most effective occluder because it reduces the possibility that the child will “peek” with the fellow eye. Computerized visual acuity test systems allow for more variety in optotype presentation, reducing errors due to memorization of letters. Patients with nystagmus may show better binocular visual acuity than monocular visual acuity with either eye occluded. To assess distance monocular visual acuity in this situation, the fellow eye should be fogged with a translucent occluder or a lens +5 diopters (D) greater than the refractive error in that eye. Patients with poor vision may need to move closer to the chart until they can see the 20/400 line. In such cases, visual acuity is recorded as the distance in feet (numerator) over the size of the letter (denominator); for example, if the patient is able to read 20/400 optotypes at 5 ft, the acuity is recorded as 5/400. See the visual acuity conversion chart on the inside front cover of the book, which provides conversions of visual acuity measurements for the various methods in use—the Snellen fraction, decimal notation (Visus), visual angle minute of arc, and base-10 logarithm of the minimum angle of resolution (logMAR).
The line with the smallest figures in which the majority of letters can be read accurately is recorded; if the patient misses a few of the figures on a line, a notation is made. In addition to recording the results, the clinician should identify the type of test used, including the optotype and whether crowding was used, to facilitate comparison with measurements taken at other times.
Uncorrected and corrected near visual acuity is determined, again using age-appropriate optotypes. Because of the potential for inaccuracy related to viewing distance, near visual acuities should not be compared with distance acuities in children. Measuring near visual acuity in children with reduced vision is helpful in determining how they will function at school.
Alternative Methods of Visual Acuity Assessment in Preverbal Children
Two major methods are used to quantitate visual acuity in preverbal infants and toddlers: preferential looking (PL) and visually evoked potential (VEP).
Preferential looking tests
These tests assess visual acuity by observing the child’s response to a visual stimulus. Teller Acuity Cards II (Stereo Optical Co, Chicago, IL) are a series of rectangular cards on which alternating black and white stripes are printed on a gray background. The stripes are printed on one side of the card only (Fig 1-4). Movement of the eyes toward the side with the stripes indicates that the child is able to see them. Stripe width decreases on successive cards. Seeing narrower stripes denotes better vision. The Cardiff Acuity Test, which is popular in Europe, uses vanishing optotypes.