Velma Dobson

Visual acuity in human infants: a review and comparison of behavioral and electrophysiological studies.

Abstract Three techniques—optokinetic nystagmus (OKN), preferential looking (PL), and the visually evoked potential (VEP)—have been used to assess visual acuity in infants between birth and 6 months of age. All three techniques indicate that the visual acuity of infants increases during the first 6 months postnatal. The accumulating evidence strongly suggests that all three techniques give meaningful and reliable—if somewhat different—estimates of visual acuity in infants, and that variants of these techniques will eventually be useful for the assessment of infant vision in clinical settings.

Visual acuity development in infants and young children, as assessed by operant preferential looking

Abstract The operant preferential looking (OPL) procedure was used to obtain psychophysical estimates of visual acuity for square-wave gratings in 50 children between 5 months and 5 yr of age. Acuity developed systematically with age, from 6 min arc (5 c/deg) at 5 months to 0.75 min arc (40 c/deg) at 5 yr, a value close to adult acuity tested with the OPL stimuli. In addition, psychometric functions became steeper with age, suggesting that criterion for responding varies with age. OPL offers the possibility of using a single procedure to follow acuity development across a wide age range.

Cycloplegic Refractions in Infants and Young Children

We studied groups of normal infants and infants with amblyopia and esoropia to determine the incidence of infantile astigmatism. Under cycloplegia, 19% of normal infants had astigmatism; this was at least twice the incidence in adults, but less than one-hale that found by noncycloplegic refractions of infants. During the first three postnatal years the incidence of astigmatism and distributions of spherical equivalents and anisometropia did not distinguish normal patients from most of those with esotropia and amblyopia.

Visual acuity of human infants at scotopic, mesopic and photopic luminances.

Visual acuity of 2-month-old infants and adults was measured between -2.6 and +2.7 log10 cd/m2 using standard psychophysical techniques. The acuity-vs-luminance curve was similar for infants and adults: acuity improved with increasing luminance until 0.0 log cd/m2, and was constant above that luminance. However, the infant curve was slightly shallower than the adult curve, and infant acuity was over 3.5 octaves poorer than adult acuity at all luminances. The infant acuity-vs-luminance curve was compared with adult curves measured 21 degrees and 51 degrees from fixation, and at 21 degrees with +8, +/- 3.25 and 0.0 D of experimental refractive error. The results indicated that infants poor acuity cannot be fully explained by: refractive error, foveal immaturity, scotopic detection of stimuli, functional similarity between infant vision and adult vision in the periphery, or by an overall reduction in visual sensitivity.

Validation of the Acuity Card Procedure for Assessment of Infants with Ocular Disorders

The acuity card procedure has been shown to be a rapid method for the assessment of monocular and binocular grating acuity in normal infants from birth through 36 months of age. The current study seeks to validate the procedure further by using the acuity cards to assess 20 2- to 8-month-old infant patients with ocular disorders, including aphakia, strabismus, ptosis, and orbital hemangioma. Assessments were made with the acuity cards by two different observers, both blind to the infants diagnosis, and by a third observer using a traditional forced-choice preferential looking (FPL) procedure. One hundred percent of the infant patients completed both binocular and monocular acuity card testing in an average time of 8 minutes per test. Interobserver agreement between acuity card observers and inter-technique agreement were high, and were sustained in individual cases in which the infants acuity was not predictable from its visible signs. These results help to establish the potential clinical utility of the acuity card procedure for the assessment of infant patients.

Clinical applications of preferential looking measures of visual acuity

We have undertaken 3 lines of research aimed at the eventual transformation of the laboratory-based preferential looking (PL) acuity-testing procedures into clinically-useful techniques. (1) The first line of research involves studies of the parameters of PL testing, and the establishing of norms for various groups. The results show that acuity development is closely tied to gestational age, that infants acuity is reduced at low luminances but does not vary significantly at levels above 1 log cd/m2, and that monocular acuity is poorer than previously-published binocular acuity norms. (2) The second line involves the development of a shortened procedure (the diagnostic grating procedure) that maximizes the certainty of gaining the most critical information from an infant in a short time. In this procedure, the infant is tested with a low spatial frequency grating to screen for blindness or total lack of visual response, and another grating of a spatial frequency that is diagnostic of normal acuity for children of the patients age. Based on the results with these two gratings and the time available, the child is then tested with other gratings to refine the acuity estimate. (3) The third line of research involves using the procedure, in a laboratory setting, with individual infants and children at risk for visual acuity deficits. Longitudinal case histories of patients with strabismus, ptosis, and suspected blindness are presented.

Cycloplegic Refractions of Premature Infants

Cyclopentolate refractions of 146 premature infants disclosed higher incidences of myopia and anisometropia than those reported for full-term infants. Also, more than 70% of the premature infants had I diopter or more of astigmatism; 83% of the astigmatism was against-the-rule. Infants with shorter gestational periods had more severe myopia and astigmatism. Infants born very prematurely should undergo follow-up refractions to determine whether they retain refractive errors large enough to interfere with visual function.

Visual acuity in human infants assessed with stationary stripes and phase-alternated checkerboards

Abstract In recent studies of the development of visual acuity in infants, finer acuity has been found in studies employing visually evoked potentials (in which temporally-modulated stimuli such as alternating checkerboards are used) than in studies employing preferential looking (in which stationary gratings have typically been used). In the present experiment, phase-alternated or stationary checkerboards, and stationary square-wave gratings, were used to obtain behavioral estimates of visual acuity in 2-month-old infants. The forcedchoice preferential looking technique was used. Similar acuity values were found for all three stimuli. The results suggest that the differential acuity values found between previous visually evoked potential and preferential looking studies are not attributable to differences in the stimuli used. Other possible causes of the discrepancy are discussed.

Effect of focus on visual acuity of human infants

Recent theoretical arguments (Green et al. (1980) Vision Res. 20, 827-835) predict that young human infants should have large depths of focus compared to adults. If so, optical blur should have relatively little effect on the resolving power of infant subjects. We tested this hypothesis by measuring the influence of optical blur on acuity thresholds in 6-week old infants and adults. Using the forced-choice preferential looking (FPL) technique, we obtained acuity thresholds for each subject with five different lens powers (plano, -14 D, -3 D, + 6 D and +14 D). Acuity was differentially affected by lens power in all subjects, with the best acuity produced by high power lenses, both plus and minus, was considerably less for infants than for adults. Although the effects of negative lenses are difficult to interpret without knowing the infants exact accommodative state, the results with positive lenses support the theoretical predictions.

Photorefraction of normal and astigmatic infants during viewing of patterned stimuli

Photorefraction was used to assess the state of accommodation of 3-month old infants with and without astigmatism while they viewed stimuli in an apparatus commonly used to test infant visual acuity. The stimuli were a 1.6 c/deg vertical grating, a 1.6 c/deg horizontal grating and a cross composed of orthogonal 19 min lines, which were presented 55 cm from the infants. Most infants accommodation was appropriate for the vertical grating. Astigmatic infants did not change their focus when the orientation of the grating was changed.