Normative Distribution of Visual Acuity in 3- to 6-Year-Old Chinese Preschoolers: the Shenzhen Kindergarten Eye Study
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Clinical and Epidemiologic Research Normative Distribution of Visual Acuity in 3- to 6-Year-Old Chinese Preschoolers: The Shenzhen Kindergarten Eye Study Xinxing Guo,1 Min Fu,2 Juan Lu,¨ 2 Qixia Chen,2 Yangfa Zeng,1 Xiaohu Ding,1 Ian G. Morgan,3 and Mingguang He1,4 1State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China 2Department of Ophthalmology, Shenzhen Maternity and Child Healthcare Hospital, Southern Medical University, Shenzhen, China 3Research School of Biological Science, Australian National University, Canberra, Australian Capital Territory, Australia 4Centre for Eye Research Australia, University of Melbourne, Melbourne, Australia Correspondence: Mingguang He, PURPOSE. To document the distribution of uncorrected visual acuity (UCVA) in a defined Department of Preventive Ophthal- population of Chinese preschoolers and to discuss its implications for vision referral. mology, Zhongshan Ophthalmic Center, Guangzhou 510060, People’s METHODS. Preschoolers aged 3 to 6 years old were recruited from kindergartens in Shenzen. Republic of China; Uncorrected visual acuity was estimated by using Early Treatment Diabetic Retinopathy Study [email protected]. Tumbling E charts, followed by cycloplegic refraction and ocular examination. The reference XG and MF contributed equally to the population was defined as children without clinically significant ocular abnormalities, with work presented here and should spherical equivalent refraction greater than À0.50 to less than þ2.00 diopters (D), therefore be regarded as equivalent astigmatism less than 0.75 D, and anisometropia less than 2.00 D. The age-specific UCVA authors. cutoffs were defined by the line where the single-sided 95th percentile of the reference Submitted: August 8, 2014 population fell. Accepted: January 28, 2015 RESULTS. A total of 483 of the 1255 children enrolled were considered the reference Citation: Guo X, Fu M, Lu¨ J, et al. population. The monocular UCVA cutoff fell on the line of 20/63 at age 3, 20/50 at age 4, and Normative distribution of visual acuity 20/40 at ages 5 and 6. Using no better than these lines as criteria generated referral rates of in 3- to 6-year-old Chinese preschool- 9.4% to 27.8% in the general population at different ages, and detected 83.3% and more than ers: the Shenzhen Kindergarten Eye 90.0% of those with myopia and amblyopia, respectively. Using uncorrected interocular Study. Invest Ophthalmol Vis Sci. difference of two or more lines referred 3.6% to 4.3% of the population but identified only 2015;56:1985–1992. DOI:10.1167/ approximately 20.0% of those with amblyopia. iovs.14-15422 CONCLUSIONS. Visual acuity is still developing in preschoolers even at age 6. Most children with myopia and amblyopia can be identified with age-specific, monocular UCVA cutoffs in vision screening using Tumbling E charts, with tolerable false-positive rates. Further studies are needed to define the age at which children without significant refractive errors reach 20/20 UCVA. Keywords: visual acuity, vision screening, normative distribution etermination of visual acuity (VA), especially uncorrected therefore ideally needs to detect both amblyopia itself, and D VA (UCVA), is generally the first clinical step in identifying amblyopia risk factors, including refractive errors. abnormal vision.1 Unfortunately, when screening children, VA Age-specific and chart-specific referral cutoffs can be criteria for referral of cases of suspected amblyopia and established only on the basis of normative data, obtained by refractive error are not uniform internationally, particularly studying reference populations of children who do not have 2–4 for children of preschool age. This is, in part, because of ocular abnormalities that would lower VA, and who do not have the different charts used in different countries, but also refractive errors that would be expected to reduce VA. because the visual system and cognitive capacities are still Normative data of this kind have been reported in samples of developing in children of preschool age, requiring the children of African American, Hispanic, and European Cauca- development of age-specific, and chart-specific cutoffs for sian ethnicity, and age-specific and chart-specific VA cutoffs referral. 13,14 Amblyopia, one of the major causes of vision impairment in have been proposed. children, with a reported prevalence of 1% to 5% in population- Detailed normative data on VA are not yet available for based surveys,5–9 needs to be treated by the age of 5 to 7 for Chinese preschool children aged 3 to 6 years. In China, and in maximum effectiveness.10,11 Diagnosis of amblyopia depends many other countries, Tumbling E charts are commonly used to a significant extent on associations with amblyopia risk for VA screening. We have therefore carried out a cross- factors, which include strabismus and refractive errors, such as sectional study to estimate the normative distribution of UCVA more severe myopia, hyperopia, astigmatism, and anisometro- in Chinese children 3 to 6 years old by using Tumbling E charts, pia.4,12 A valid referral VA criterion for preschool children exploring appropriate VA cutoffs for referral and their Copyright 2015 The Association for Research in Vision and Ophthalmology, Inc. www.iovs.org j ISSN: 1552-5783 1985 Downloaded from tvst.arvojournals.org on 09/24/2021 Normative Distribution of VA in Preschoolers IOVS j March 2015 j Vol. 56 j No. 3 j 1986 implications for vision screening in Chinese children of removed), exotropia (inward movement), or vertical tropia preschool age. (downward or upward movement). Tropias were distinguished from phorias, which were identified from movement of the covered eye after the cover was removed. The degree of tropia METHODS was measured using Hirschberg’s method for observation of the corneal light reflex. Study Population Cycloplegia was then induced with 2 drops 1% cyclopen- The Shenzhen Kindergarten Eye Study was conducted in 2012, tolate, administered 5 minutes apart, with a third drop with the aims of investigating VA, refraction, and ocular administered 20 minutes later. Cycloplegia and pupil dilation biometry in children of preschool age, and identifying the risk were evaluated after an additional 15 minutes. Cycloplegia was considered complete if a pupillary light reflex was absent, with factors for refractive errors and amblyopia. pupils dilated to 6 mm or larger. Refraction was performed The project conformed to the tenets of the Declaration of with a desktop auto-refractor (KR8800; Topcon Corp., Tokyo, Helsinki and ethical approval was given by the institutional Japan). The data on spherical and cylindrical power and axis, review board of Zhongshan Ophthalmic Center. Written and the barcode ID were automatically extracted from the informed consent was obtained from parents or guardians, device. Only the children with successful cycloplegia were after the study purposes and contents were explained in detail included in the analysis. Subjective refraction was then in a school seminar for them. assessed monocularly, using the autorefraction values as a A total of 1255 children aged 3 to 6 years whose parents or starting reference. Lenses of different spherical and cylindrical guardians provided written consent were recruited of 1764 diopters were inserted into the trial frame and the aided VA children from eight participating kindergartens in different was measured at the same time. The principle of maximum administrative regions of Shenzhen, China, with a participation plus to maximum VA was followed to determine the endpoint rate of 71.1%. The eight kindergartens were drawn from the of subjective refraction. The best-corrected VA (BCVA) also was first-class public kindergartens from either Shenzhen City or recorded based on the monocular subjective refraction, using the adjoining Guangdong Province, with high standards of the same protocol and VA chart. facilities and teaching staff. The anterior segment, including eyelid, conjunctiva, cor- nea, iris, and pupil, and the posterior segment, including Ocular/Physical Examinations fundus, optic disc, and macula, were then evaluated by slit lamp examination and indirect ophthalmoscopy, performed by Field examinations were performed from June to July 2012 by a an ophthalmologist. A principal cause of visual impairment for group of optometrists, ophthalmic nurses, and ophthalmolo- eyes with UCVA less than or equal to 20/40 was assigned by gists. Examinations were conducted in each kindergarten that ophthalmologist. during the weekdays while the classes were in session. Data were collected either manually (i.e., VA data) or automatically by the measuring devices (i.e., refraction data by the auto- Definitions refractor). A barcode system was used to record participant Spherical equivalent refraction was calculated as spherical identity as a unique code, enabling marked reduction in errors diopters þ 1/2 cylindrical diopters. Interocular difference in combining data obtained manually and automatically. (IOD) was defined as the absolute difference in VA between Uncorrected visual acuity was tested by a trained ophthal- the two eyes. Myopia was defined as SER less than or equal to mic nurse, first in the right eye, and then in the left, at 4 m by À0.50 D in either eye; hyperopia was defined as SER greater using a retro-illuminated logMAR chart with Tumbling E than or equal to þ2.00 D in either eye. Astigmatism was defined optotypes (Precision Vision, La Salle, IL, USA). The standard as a cylindrical refractive error greater than or equal to 0.75 D, operating protocol from the Refractive Error Study in Children and anisometropia was defined as an SER difference greater 15 was followed. In brief, the VA measurements began at a than or equal to 2.00 D interocularly. distance of 4 m with the top line (20/200). If the orientation of Different definitions of amblyopia were adopted in the at least four of the five optotypes was correctly identified, the current analysis. The American Academy of Ophthalmology child was then tested by dropping down to line 4 (20/100).