I’ision Res. Vol. 23, No. IO, pp. 1019-1024. 1983 0042s6989/83 $3.00 + 0.00 Printed in Great Britain. All rights reserved Copyright c 1983 Pergamon Press Ltd VISUAL ACUITY AND ITS MERIDIONAL VARIATIONS IN CHILDREN AGED 7-60 MONTHS E. E. BIRCH*, J. GWIAZDA, J. A. BAUER JR, J. NAEGELE and R. HELD Massachusetts Institute of Technology, Bldg EIO-138, Cambridge, MA 02139, U.S.A. (Recked 25 May 1982; in recisedforrn I5 October 1982; in re-revisedform 25 January 1983) Abstract-A new operant procedure was used to assess grating acuity in children aged 7-60 months. The procedure was successful for 95% of the children sampled and had high test-retest reliability. Visual acuity for main axis (horizontal and vertical) gratings improved from 6/15 at 12 months to 6/6 at 60 months. For the 7-16 month age group, preferential-looking estimates of acuity agreed well with operant estimates. Acuity tbr obhque gratmgs was approximately l/4 octave lower than main axis acuity throughout the age range. The results suggest that the human visual system continues to develop throughout the first 5 years of life. Acuity children development oblique effect INTRODUCTION Early assessment of visual acuity is highly desirable since many congenital and childhood visual anoma- lies may lead to permanent visual loss if not detected and effectively treated during the first 5 years of life. While there exist a wide variety of test objects for measuring visual acuity (e.g. Snellen letters, Landolt rings, Allen figures), most standard tests cannot be performed reliably by children under 3 years of age because of lack of cooperation and/or comprehen- sion. In recent years, preferential-looking at gratings has been utilized as a technique for testing the acuity of infants up to 1 year of age (Dobson and Teller, 1978; Gwiazda et al., 1978). Beyond 1 year of age, toddlers become too active and the usefulness of the procedure diminishes. As a consequence, there are few normative acuity data for toddlers aged 12-30 *Present address: Vision Research Center, Retina Founda- tion of the Southwest 8220 Walnut Hill Lane, Suite 012, Dallas. TX 75231. U.S.A. tin order’ to measuie the contrast of the gratings, a photometer (United Detector Technologv) was used in conjunction with a slit aperture whicx’was inserted directly in front of the grating. The slit width was very narrow relative to the stripe width and was positioned parallel to the stripes. The slit was sequentially posi- tioned so that the luminances (L) of the maxima and minima of the square-wave gratings were measured and contrast was calculated as C = (L,,, - L,,,) + (L,,, + L,;,). The space-averaged luminance of the gratings was calculated by measuring the overall neutral density of each transparency in a densitometer. The intensity of the projector lamp with a blank slide frame in the projector was measured at the screen with photometer and the neutral density for each stimulus as measured above was subtracted. The range of space- averaged luminances was + 1.25% of the mean value (205 cd/m’). months, a period when children are notoriously difficult to test. The present paper presents data describing the course of development of visual acuity for children aged 7 months to 5 years without refrac- tive or other visual problems. These data were ob- tained by an operant technique that can be used successfully and reliably in this age range. METHODS Subjects Children aged 7-60 months were refracted with non-cycloplegic near-retinoscopy (Mohindra, 1977) and any child with one or more of the following conditions was excluded: one or more diopters of astigmatism, more than three diopters of hyperopia, more than one diopter of myopia, one or more diopters of anisometropia, phoria, tropia, or observ- able ocular disease. Two hundred and ninety-seven children who fit these refractive criteria participated and were categorized into 6-month gestational age groups. All repeated measures for an individual child within age group were combined for a single acuity estimate. Nine adults, aged 20-50 yr, wearing their normal optical corrections, were also tested. Stimuli Stimuli were black and white, high contrast (>80%) square-wave gratings paired with equal lu- minance greys (72c/deg gratings)?. The space aver- aged luminance of each stimulus pair was 205 cd/m2. Three spatial frequencies were employed in training: 0.38, 0.75 and 1.5 c/deg. Eight spatial frequencies were employed in testing: 2.25, 4.5, 6.0, 9.0, 12.0, 18.0, 24.0 and 36.0c/deg. Four grating orientations were possible: horizontal, vertical, right oblique (45 deg), and left oblique (135 deg). Two Kodak 1019