Karen D. Fern

Visual acuity of the preschool child: a review

ABSTRACT The need for visual acuity assessment in preschool children has long been recognized, yet there are no standardized visual acuity norms or screening criteria. This report reviews the literature on distance visual acuity in the preschool child. The areas of review include: (1) methods of assessment of visual acuity; (2) visual acuity norms obtained with these tests; (3) reasons for the variations in reported visual acuity norms; (4) variations in referral criteria for vision screenings; (5) testability reported for various visual acuity tests; and (6) important design principles and recommendations for preschool visual acuity tests. It is concluded that a well designed preschool visual acuity test should consist of high contrast Snellen optotypes without directional components that progress in 0.1 log steps down to a level of 6/3. To improve testability, a matching or forced choice response should be used. Of the tests that have been standardized, STYCAR (Sheridan‐Gardiner) comes closest to meeting these criteria.

1% Cyclopentolate hydrochloride : another look at the time course of cycloplegia using an objective measure of the accommodative response

The time course of cycloplegia was measured by monitoring residual accommodation after the application of 1 drop (29.3/*l) of 1% cyclopentolate hydrochloride. Three different measures of residual accommodation were made, one objective assessment with an optometer, and two subjective assessments similar to those used by previous investigators. Pupil diameter was also measured in a subgroup of individuals to compare the time course of the induced mydriasis to that of the cycloplegia. When residual accommodation is measured objectively, maximum cycloplegia occurs 10 min after the application of 1% cyclopentolate hydrochloride in individuals with light irides. This result suggests that the standard clinical protocol of delaying refraction 30 to 60 min after the application of cyclopentolate hydrochloride may be too conservative for individuals with light irides. For individuals with dark irides, 30 to 40 min is required for maximum cycloplegia, and the magnitude of residual accommodation in these individuals is similar to that found in light iris individuals at 10 min. When subjective measures are used to estimate residual accommodation, more accommodation is present and the time at which maximum cycloplegia occurs is delayed for individuals with light irides. These results are in agreement with previous studies using subjective techniques. Regardless of iris color or measurement method, the time course for pupil dilation is not the same as the time course for cycloplegia.

Visual acuity outcome in isometropic hyperopia.

Refractive amblyopia may occur as a unilateral or bilateral condition. Although bilateral refractive amblyopia may account for 1 to 2% of all refractive amblyopia, there is little consistent information in the literature regarding isoametropic amblyopia resulting from bilateral hyperopia. Hence, this retrospective study investigated the prevalence of reduced aided acuity in patients aged 10 years and younger (mean age 3.97 years) with 5 D or more of isometropic hyperopia and considered the following factors that may influence visual acuity: (1) age at first correction; (2) magnitude of hyperopia; and (3) duration of refractive correction of the hyperopia. The results indicate that the majority of patients (87%) have aided acuity poorer than 6/6 at initial correction of refractive error. However, if the full hyperopic correction was worn for 1 year or longer, only 43% of these patients demonstrated acuity poorer than 6/6 and none showed acuity poorer than 6/12. The magnitude of the hyperopia appeared to have the greatest influence on the visual acuity outcome both at initial correction of refractive error and 1 year or longer after correction. Duration of correction also influenced the visual acuity outcome, but to a lesser extent than the magnitude of refractive error. In contrast, the age of first correction showed little correlation with visual acuity either at the time of first refractive correction or after a minimum of 1 year of correction.

Contour Interaction in the Preschool Child

ABSTRACT Preschool children show poorer visual acuity when tested with multiple optotypes than when tested with isolated optotypes. This difference in performance could be the result of contour interaction or the greater distractions imposed by a multiple optotype display, which may be beyond a young childs ability. To differentiate between these alternatives, isolated and surrounded visual acuity were measured in children aged 2 to 7 years by pairing a Landolt C with an O. The surrounded optotypes were identical to the isolated optotypes with the exception of the flanking bars located at 2.5 times the minimum angle of resolution (MAR) of the optotype. A two‐alternative forced choice interleaved paradigm was used to measure surrounded and isolated visual acuity defined as 75% correct. When the test demands were equated by measuring isolated and surrounded acuity using a single optotype, poorer visual acuity was obtained with surrounded optotypes. This suggests that preschool children, like adults, show contour interaction.

Motion coherence in infants.

Two perpendicular square-wave gratings (i.e. plaids) were used to investigate motion coherence in 1-, 2- and 3-month-old infants. The direction of motion of the stimulus was judged by an adult observer, on the basis of the induced optokinetic nystagmus (OKN) in an eight-alternative eye movement voting paradigm. Infants as young as 1 month of age demonstrated OKN in the direction consistent with motion coherence. There was no significant difference among the performances of 1-, 2- or 3-month-old infants. However, the percentage of trials on which infants demonstrated OKN in the coherence direction was less than that obtained from adults tested with the same paradigm. Movshon, Adelson, Gizzi and Newsome (1985) have suggested that the cohered motion of a complex pattern may be processed after the orientation of the components of the pattern, perhaps in the middle temporal area of the visual cortex (MT). The present results suggest that either young infants and adults process the motion of complex patterns similarly or that the OKN consistent with the direction of motion coherence observed in infants involves subcortical nonoriented visual centers rather than the higher level process which is presumed to occur in adults.

Contour interaction function in the preschool child

Contour interaction was investigated in 12 preschool children 3 to 4 years of age, and compared to the results obtained from 5 normal adults tested under an identical paradigm. Observers viewed the display from a distance at which they could identify the location of a gap (up or down) in an isolated C correctly on 90 to 95% of the trials. The isolated C and Cs with bars tangentially located at various positions above and below the test optotype were intermixed randomly. Percent correct was plotted as a function of the angular subtense of the gap width of the test optotype. A significant decrease in performance was found when the bars were positioned at 0.71 to 1.42 times the angular subtense of the gap for both the preschool children and the adults. The results suggest that preschool children demonstrate contour interaction that is quantitatively similar to adults. Because the spacing of letters on standard acuity charts is typically larger than the range over which contour interaction occurs, the poorer acuity often measured with charts compared to isolated letter presentation in preschool children suggests that factors other than contour interaction (perhaps attentional factors) are involved.

Testing Stereopsis in the Preschool Child: Is It Clinically Useful?

The evaluation of stereoacuity should provide an unambiguous assessment of binocular function in infants and young children. Unfortunately, clinical measures of stereopsis in these young patients often result in stereotheresholds poorer than the criteria suggested to differentiate normal from anomalous binocular vision. Thus, two experiments were conducted to determine whether the large stereothresholds frequently demonstrated on tests designed for young children are diagnostic of normal binocular function in preschool children. The first experiment investigated the salience of the monocular cues in the Lang and Frisby stereotests in normal preschool children (2 to 5 years old). None of the children who passed either the Frisby or the Lang stereotest under binocular conditions were able to pass either test monocularly, even after passing the test binocularly. In the second experiment, preschool children with abnormal binocular vision were tested with the Lang and Frisby stereotests to determine if large disparities (730 to 800 seconds of arc [arcsec]) could be passed without normal binocular vision. None of the children with strabismus passed either stereotest. However, two children with anisometropia passed the Frisby test and one of these children also passed the Lang test. These results suggest that in the absence of other clinical findings to the contrary, the demonstration of gross stereopsis with either the Frisby (730 arcsec) or Lang (733 or 800 arcsec) test in the preschool child implies normal binocular function. Thus, clinical tests of stereopsis for infants and preschool children, like those used routinely for adults, can provide evidence of binocular function without approaching stereothreshold.

Myopia Progression in Children Wearing Spectacles vs. Switching to Contact Lenses.

Purpose. To investigate myopia progression in Correction of Myopia Evaluation Trial (COMET) participants who switched to soft contact lenses (CLs) vs. remained in spectacles after the clinical trial ended. Methods. Four hundred sixty-nine ethnically diverse, 6- to 11-year-old myopic children were randomly assigned to wear single vision lenses (SVLs) or progressive addition spectacle lenses (PALs) for 5 years as part of COMET. Afterwards they could choose another lens type, including CLs. Data in this article are from 286 participants who wore their original spectacle lenses for 6 years (n = 199) or wore CLs most or all the time between the 5- and 6-year visits (n = 87). Refractive error and axial length (AL) were measured after cycloplegia with 1% Tropicamide. The primary outcome was myopia progression between the 5- and 6-year visits. Two-year myopia progression was evaluated in a subset of 183 participants who wore the same lens type for an additional year. Myopia progression and AL were compared between the two lens groups using multiple linear regression. Results. Participants in the two groups were similar with respect to age, ethnicity, myopia at 5-years, accommodation and phoria, but more girls switched to CLs than remained in spectacles (p < 0.0001). Mean (±SD) myopia progression was higher (p = 0.003) after 1 year in the CL group [−0.28 ± 0.33 diopter (D)] than the spectacle group (−0.14 ± 0.36 D), and remained higher after 2 years in the 2-year subset (−0.52 ± 0.46 D vs. −0.25 ± 0.39 D, p < 0.0001). Results were similar after adjustment for related factors. No significant differences in AL were found between groups after adjustment. Corneal curvature remained unchanged in both groups. Conclusions. COMET children switching from glasses to CLs experienced a small, statistically significant but clinically inconsequential increase in myopia progression.

The effect of strabismus on a young child's selection of a playmate

Purpose:  This study investigated the effect of strabismus on a childs playmate selection.

Ten-year changes in fusional vergence, phoria, and nearpoint of convergence in myopic children.

Purpose. To identify longitudinal changes in fusional vergence ranges and their relationship to other clinical measures in young myopic subjects. Methods. Measurements were collected annually for 10 years on 114 subjects from the University of Houston Correction of Myopia Evaluation Trial cohort. Subject age was 7 to 13 years at year 1 of follow-up. Measurements included refractive error, distance and near phoria, interpupillary distance (IPD), prism bar fusional vergence ranges, and nearpoint of convergence (NPC). Multilevel modeling was used to determine baseline and rate of change for fusional vergence ranges and the impact of phoria, IPD, and NPC on these measures. Results. Year 1 mean distance base-out (BO) break was 20 prism diopters (pd) and decreased 5.6 pd over 10 years (p < 0.001). Mean near BO break was 30 pd at year 1 and decreased 9.4 pd over 10 years (p < 0.001). Greater esophoria was significantly related to greater BO break (p < 0.02) and receded NPC was significantly related to lower magnitude BO break at near (p < 0.001). Distance IPD increased 3 mm over 10 years (p < 0.001) but was unrelated to the magnitude of the BO ranges (p > 0.2). Mean distance base-in (BI) break was 7 pd at year 1 and increased 0.5 pd in 10 years (p = 0.04). Mean near BI break was 13 pd at year 1 and did not significantly change. Mean distance phoria was 0.1 pd exophoria at year 1 and did not change, whereas near phoria was 2.4 pd esophoria at year 1 and became more exophoric (4 pd in 10 years, p < 0.001). Conclusions. These results suggest that for myopic children convergence ranges decrease for both distance and near viewing during the school years as near phoria becomes more exophoric. These findings could have clinical implications given that compensating convergence ranges decrease as near phoria becomes more divergent.