Interobserver Reliability of the Teller Acuity Card

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To compare interobserver agreement for Teller Acuity Card estimates of grating ... Teller Acuity Card testing conducted by experienced testers is as reliable in.
Interobserver Reliability of the Teller Acuity Card Procedure in Pediatric Patients Lisa M. Getz,* Velma Dobson,*-\- Beatriz Luna,^ and Clay Mashj

Purpose. To compare interobserver agreement for Teller Acuity Card estimates of grating acuity between children with ocular or neurologic abnormalities, or both, and age-matched healthy preterm children. Methods. Subjects were 57 children, 3 to 38 months of age, who were referred for visual assessment because of diagnosed or suspected visual impairment (clinical group), and 57 healthy preterm children with no known visual or neurologic abnormalities (control group), each of whom was matched to a clinical subject, based on corrected age at the time of testing, and type of testing (monocular or binocular). Each child's grating acuity was tested by two independent observers. Results. Interobserver agreement of 1 octave or better was found in 91% of the monocular and 96% of the binocular clinical test-retest comparisons and in 95% of the monocular and 96% of the binocular control comparisons. For estimates of interocular acuity difference, interobserver agreement of 1 octave or better was found in 88% of clinical subjects and 88% of control subjects. Average test time was significantly longer in the clinical group (4.1 minutes [SD = 1.9] for monocular and 3.6 minutes [SD = 1.9] for binocular tests) than in the control group (2.5 minutes [SD = 0.9] for monocular and 2.4 minutes [SD = 0.6] for binocular tests), suggesting that children in the clinical group were more difficult to test. Conclusions. Teller Acuity Card testing conducted by experienced testers is as reliable in children with mild to severe ocular or neurologic abnormalities as it is in healthy children, even though children with abnormalities may be more difficult to test. Invest Ophthalmol VisSci. 1996;37:180-187.

L he acuity card procedure was developed to allow rapid assessment of grating acuity of infants and young children in clinical settings.1 In the procedure, the patient is shown a series of gratings composed of blackand-white stripes on a gray background. A trained tester observes the patient's eye and head movement responses to the gratings and, based on these responses, makes a judgment as to the finest grating (smallest stripes) the patient can distinguish from the gray background. Because acuity estimates obtained with the acuity From tlie Departments of * Psychiatry and •f Psychology, University of Pittslrurgh, Pennsylvania. Presented in part at the AliVO Annual Meeting, May 1994, Sarasota, Florida. Suppoited by National Institutes of Health grant EY05804. Submitted for publication February 27, 1995; revised July 19, 1995; accepted September 1, 1995. Proprietary interest category: C. Refmnl requests: Velma Dobson, Department of Ophthalmology, University of Arizona School of Medicine, 1801 N. Campbell, Tucson, AZ 85719-3758.

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card procedure are dependent on the subjective judgment of the tester and because previous studies have shown small but reliable differences among testers in their tendency to obtain higher or lower acuity values, 2 " 5 it is important to document the interobserver test-retest reliability of the acuity card procedure. Previous reports'~4>6~14 have indicated that the interobserver reliability of acuity card testing is similar to that of more scientifically rigorous, laboratory-based, forced-choice preferential looking procedures. 15 " 18 However, studies in which the Teller Acuity Card (TAC) procedure was used to test children with ocular or neurologic abnormalities 9 " l2cl8 generally showed poorer interobserver agreement than was found in studies of the TAC procedure in which subjects were healthy, normal infants and children.1'4'11'7 The purpose of the current research was to examine, within a single study, interobserver test-retest reliability of healthy children and children with ocular

Investigative Ophthalmology & Visual Science, January 1996, Vol. 37, No. 1 Copyright © Association for Research in Vision and Ophthalmology

Reliability of Teller Acuity Card in Patients

or neurologic abnormalities. The goal was to determine whether the lower interobserver reliability seen in studies in which abnormal subjects were tested was caused by differences in the reliability of testers in working with normal versus abnormal children or to procedural differences across studies. METHODS Subjects Subjects were 114 children between 3 and 38 months of age (mean = 13.8 months, SD = 9.2). Half of these children (the clinical group) were referred for visual acuity assessment because of diagnosed or suspected visual impairment. Included in the clinical group were children with unilateral or bilateral cataract or aphakia (n = 18), cortical visual impairment and/or brain abnormalities, including encephalopathy, seizures, hydrocephalus, and brain trauma (n = 18), optic nerve abnormality (n = 4), chromosomal abnormality (n = 4), albinism (n = 2), nystagmus (n - 2), strabismus (n = 2), coloboma (n = 2), and other abnormalities (n = 5), including macular scar, hemangioma, glaucoma, iridectomy, retinal reattachment (one case of each). Forty-six children in the clinical group were full-term, and 11 were preterm (gestational age ^36 weeks). The remaining 57 children (the control group) were healthy children whose gestational ages were ^36 weeks and who were participants in a follow-up study of infants treated in a neonatal intensive care unit. Healthy preterm children were used as control subjects because of their availability and because of difficulties in recruiting full-term subjects in our research setting. Previous research has indicated that interobserver reliability in healthy preterm children is similar to that in full-term children.23 Children in the control group had no perinatal complications known to affect visual development, e.g., retinopathy of prematurity, periventricular leukomalacia, severe intraventricular hemorrhage (grade HI or IV), encephalopathy, or seizures, and no known visual abnormalities, e.g. strabismus or nystagmus, as determined by an eye examination by a pediatric ophthalmologist (26 subjects) or parental report (31 subjects). Each child in the control group was matched to a clinical subject, based on type of testing (monocular or binocular), and corrected age at the time of testing (±3 weeks for children younger than 6 months, ±4 weeks for children 6 to 12 months of age, and ±8 weeks for children older than 1 year of age). Apparatus and Procedure The tenets of the Declaration of Helsinki were followed, and the study was approved by the human sub-

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jects committees of the University of Pittsburgh and Magee-Women's Hospital. Informed written consent was obtained from the child's parent before testing. The apparatus consisted of a set of 17 TACs and a TAC stage through which the cards are presented (Vistech, Dayton, OH). Fifteen cards contained a 12.5 X 12.5-cm patch of black-and-white grating, one was a blank gray card, and one, the Low Vision card, contained a 25 X 23-cm patch of 2.2-cm wide stripes. In 98% of the tests, subjects were tested by one of three observers who had more than three years of experience using the TAC procedure. Two percent of tests were conducted by two additional observers, each of whom had more than one year of experience with TAC testing. In 21 (36.8%) of the 57 matched pairs, the same two observers tested both the clinical and the control member of the pair. This was not possible for the remaining pairs because of scheduling constraints. After informed consent was obtained from the parent, the child was seated on the parent's lap or alone in front of the stage. Initially, testing was attempted at 38 cm for children younger than 7 months of age and at 55 cm for those between 7 months and 3 years. Children with low vision often were tested without the stage, at a nearer test distance (19 or 9.5 cm). Children with nystagmus that interfered with the observer's ability to judge whether the child was looking to the left or to the right side of the card were tested outside the stage, using vertical presentation of the cards.19 Vertical presentation of the cards allowed the observer to use up-down eye and head movements, rather than horizontal eye and head movements, as an indicator of whether the child could see the gratings on each acuity card.19 ' For each child in the clinical group, grating acuity was assessed monocularly or binocularly, according to the request of the referring physician and the level of cooperation of the child for monocular testing. The matched control subject was tested in the same manner as the clinical subject to whom he or she was matched. When monocular testing was conducted, the first observer tested one eye. This was followed by the second observer's test of that same eye. The second observer then tested the other eye, after which the first observer tested that eye. Observers were masked to each other's acuity results until all testing had been completed. The testing procedure used was that recommended in the TAC manual.20 Testing begins with a specific "start card," based on a child's age, which is followed by presentation of cards containing gratings that increase in spatial frequency in approximately half-octave steps. The observer is masked to the location, but not the spatial frequency, of the grating on

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Investigative Ophthalmology 8c Visual Science, January 1996, Vol. 37, No. 1

each card. Acuity is estimated as the finest grating that the observer judges the child can see, based on the child's looking behavior in response to several presentations of each card. Test time was measured from the time the the first card was presented until the time that observer arrived at an acuity estimate. Data Analysis Acuity scores were converted to log values. Interobserver differences for the eye tested first, the eye tested second, and for binocular acuity results were calculated to the nearest 0.5 octave (the approximate difference in spatial frequency between adjacent acuity cards). For children tested monocularly, interocular acuity difference (IAD) was calculated as the signed difference, to the nearest 0.5 octave, between the acuity of the right eye and the acuity of the left eye, converted to octaves. Interobserver difference in IAD was calculated as the difference, in octaves, between the IADs obtained by the two observers, with the sign of the difference maintained in the calculation (— if the acuity of the right eye was better than the acuity of the left eye; -I- if the left eye had the better acuity). For example, if the first observer found 0.5 octave better acuity in the right eye than the left eye, and the second observer found 0.5 octave better acuity in the left eye than the right eye, then the interobserver difference in IAD was 1 octave. RESULTS Figure 1 compares interobserver agreement for each matched pair of clinical and control subjects. Separate plots show results for subjects tested monocularly (the eye tested first, the eye tested second, and interocular acuity difference) and for subjects tested binocularly. Interocular acuity difference data are not available for all subjects tested monocularly because not all subjects tested monocularly completed testing of both eyes. Across all four plots, 38 points lie on the unity line, indicating equal interobserver agreement for the clinical and control member of a pair. In 37 pairs (points above the line), a smaller interobserver difference was found for the control than for the clinical member of the pair, and in 32 pairs (points below the line), a smaller interobserver difference was found for the clinical member of the pair. Chi-square analysis indicated no difference in the proportion of points lying above the unity line and the proportion of points lying below the unity line, across the four test conditions. Chi-square analysis also indicated that there was no difference in the proportion of data points lying above versus lying below the line, for pairs in which the clinical member had an average acuity score more than 1 octave below that of the matched control subject

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