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Screening for people with mental handicap.
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How can we improve the detection of glaucoma?
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Visual acuity testing in schools: what needs to be done.
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Preventing blindness from glaucoma.
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Visual acuity in premature infants.
PURPOSE: To measure grating visual acuity in premature infants and compare it with that in full-term infants. METHODS: The visual acuity of 73 premature and 73 full-term infants was tested at 6 months of age by the Teller Acuity Card procedure. All premature infants had undergone indirect funduscopy for the detection of retinopathy of prematurity (ROP). Seven infants had developed ROP. The mean gestational age of the premature infants was 33 +/- 1.4 weeks as compared with 39.9 +/- 0.9 weeks in the full-term infants. The mean birth weights of the 2 groups were 1,906 +/- 412 and 3,244 +/- 420 g, respectively. RESULTS: Impaired binocular visual acuity was found in 53.4% of the premature infants, but in only 11% of the full-term infants (p < 0.0001). Impaired monocular visual acuity was found in 13.7% of the premature infants as compared with 2.7% of the full-term infants. Within the premature infant group, monocular visual acuity was impaired in 42.9% of those with ROP and in 10.6% of those without ROP (p = 0.0497). Pathological refraction was found in 33.3% of the prematures without ROP and in 14.3% of the prematures with ROP. This difference was not statistically significant. Visual acuity of preterm infants was not different from full-term infants when examined at 6 months of postconceptual age. CONCLUSIONS: Both monocular and binocular visual acuities as measured by the Teller Acuity Cards are worse in premature infants than in full-term infants at the same chronological age. Poor visual acuity in premature infants can be attributed mainly to immaturity of the visual system.
Colour vision testing in pre-school-aged children.
84 children aged from 2 to 6 years were tested with three different pseudo-isochromatic plates: Velhagen Pflügertrident test, Lanthony Tritan Album and Ishihara test. The Velhagen test was correctly interpreted by all of the 6- and 5-year olds, by 80% of the 4-year olds and by 20% of the 3-year olds. The Lanthony Tritan Album was well performed by all of the 6-, 5- and 4-year olds, and by 80% of the 3-year olds. The Ishihara test was acceptably performed by all of the 6- and 5-year olds, by 90% of the 4-year olds and by 40% of the 3-year olds. None of the 2-year olds could understand any of these tests. In the Ishihara test, the winding lines in the plates No. 30 and 32 were difficult for children; the incomplete interpreting of them must be accepted for a correct answer.
Anti-aliasing and dithering in the 'Freiburg Visual Acuity Test'.
Anti-aliasing is a technique for improving spatial resolution at the cost of luminance resolution. Dithering is a technique for improving luminance resolution at the cost of spatial resolution. These techniques are applied to the testing of visual function in the 'Freiburg Visual Acuity Test': by employing anti-aliasing, spatial resolution was improved. Thus, even the shape of small Landolt-Cs with oblique gaps is adequate, and visual acuities from 5/80 (0.06) up to 5/1.4 (3.6) can be tested at a distance of 5 m. By employing dithering, subthreshold contrast stimuli can be generated on a conventional display having standard 8-bit video resolution. Rapid acquisition of a semi-objective and reliable acuity estimate makes the 'Freiburg Visual Acuity Test' useful for subject screening in vision research, as well as for routine assessments in the ophthalmic practice.
The pattern of astigmatism in a Canadian preschool population.
PURPOSE: To measure magnitude, type, and central tendency of astigmatism found in a county-wide population of Canadian preschool children (mean age, 48.1 months). METHODS: Noncycloplegic autorefractive measures were taken in 1179 children attending a preschool health fair operated by their county board of health. Spherocylinder measures were transformed into three independent components. RESULTS: The equivalent sphere showed considerable variation between retinoscopy and autorefraction that was attributed to the variable overaccommodation induced by the autorefractor. Astigmatic components were not affected. Small discrepancies between the two techniques were similar to those in adults and were not of sufficient magnitude to affect validity. With-the-rule (WTR) astigmatism of at least 0.25 D was the most frequent form (45%) followed by against-the-rule (ATR; 40%) and oblique (15%). The 95th percentile for cylinder magnitude was found at 1.25 D. Astigmatisms beyond this value were predominately WTR. The mean (negative) cylinder magnitude was 0.08 Dx 015 degrees. CONCLUSIONS: When spherocylinder values are transformed into a mathematical continuum rather than WTR and ATR classifications, the true central tendency of the population is better defined and is close to zero. Astigmatisms of more than 1.25 D in the preschool child exceed the 95th percentile in this population and were more frequently WTR.
The Activities of Daily Vision Scale for cataract surgery outcomes: re-evaluating validity with Rasch analysis.
PURPOSE: The Activities of Daily Vision Scale (ADVS) has been extensively validated by traditional methodology. In the current study, Rasch analysis was used to explore further the validity of the ADVS and to determine whether improvements could be made. METHODS: Forty-three patients with cataract underwent visual acuity (VA) and contrast sensitivity (CS) testing and completed the ADVS. The data were Rasch analyzed and the value of response scale and item reduction explored. A shortened version and the original ADVS were tested for criterion validity by determining correlations with VA and CS. RESULTS: The ADVS data contained abnormally distributed items and items with ceiling effects and empty response categories. Therefore, items benefited from shortening the response scale, the optimum length being three responses. There was poor targeting of item difficulty to patient ability, because many patients with cataract were sufficiently able that they had no difficulty with many activities. Items were eliminated if the task was too easy or did not fit with the overall concept of visual disability determined by the Rasch model. A reduced ADVS version was established that had adequate precision, equivalent criterion validity, and improved targeting of item difficulty to patient ability, but this version was still not ideal. CONCLUSIONS: Despite careful traditional validation, the ADVS data contained inadequacies exposed by Rasch analysis. Through Rasch scaling, particularly with response scale reduction, the ADVS can be improved, but additional questions seem to be needed to suit the more able, including patients undergoing second eye cataract surgery. There remains a need to develop Rasch-scaled measures of visual disability for use in ophthalmic outcomes research.
Test-retest reliability of clinical Shack-Hartmann measurements.
PURPOSE: To evaluate the stability of clinical monochromatic aberrometry measurements over a wide range of time scales. METHODS: Monochromatic aberrations in four normal eyes were measured with a clinical Shack-Hartmann aberrometer. A chin rest or a supplemental bite bar attachment was used to stabilize head and eye position. Five repeated measurements were taken within one test (5 frames, t < 1 second) without realignment. With realignment between each measurement, aberration measurements were repeated five times (t < 1 hour) on each day, at the same time of day on five consecutive days, and again on 5 days at monthly intervals. A control experiment studied the effect of systematically misaligning the eye to determine whether fixation errors can account for the variation in the repeated measurements. RESULTS: Variability of wavefront root mean square (RMS) error (excluding defocus and astigmatism) was tracked across repeated measurements. Variances for different time scales were: 8.10 x 10(-5) microm2 (t < 1 second), 3.24 x 10(-4) microm2 (t < 1 hour), 4.41 x 10(-4) microm2 (t < 1 week), 9.73 x 10(-4) microm2 (t < 1 year). Bite bar and chin rest data were almost identical. Rotational fixation error up to 3 degrees accounts for only part of the variability. CONCLUSIONS: Increased variability in aberration maps between days and months indicates biological fluctuations that are large enough to prevent achievement of "perfect vision," even in the unlikely event that spherical and astigmatic refractive errors are corrected perfectly. However, lack of stability does not justify withholding treatment. A lasting benefit of aberration correction is expected despite temporal variability.
Anisometropic amblyopia: an easily overlooked cause of visual loss in children.
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Irlen lenses and reading difficulties.
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Application of the combined quality improvement ratio in the evaluation of a quality improvement activity in a managed care organization.
Assessing the impact of clinically relevant quality improvement activities (QIA) is important to managed care organizations; yet, turnover in enrollment can reduce the data available for analyses, thus decreasing the chance that a difference post-QIA will be detected. The Combined Quality Improvement Ratio (CQuIR) uses matching of patients into pairs pre- and post-QIA to systematically and validly increase the data included in the analysis for evaluation of the QIA. Using a paired cohort study design, 456 pairs of patients with diabetes were identified using the Health Plan Employer Data Information Set (HEDIS) specifications. Patients having retinal examinations were identified pre- and post-QIA. The change in retinal examination rates was analyzed and results compared using repeated pairs (RP), matched pairs (MP), and combined pairs (CP). The CQuIR methodology (which uses CP = RP + MP) resulted in an increase in sample size (n = 456 [CP] versus n = 156 [RP] and n = 300 [MP]) and consequently an increase in power (0.92 [CP] versus 0.38 [RP] and 0.82 [MP]) and a decrease in the confidence interval range (0.97 [CP] versus 2.06 [RP] and 1.14 [MP]). The CQuIR uses a statistically valid approach to increase the data available for the evaluation of QIAs.
Right to sight: accessing eye care for adults who are learning disabled.
The existing uptake of eye care services by 146 learning disabled adults was investigated using a telephone questionnaire. It was found that 39 percent were receiving less eye care than the general population; those living either with families or independently were significantly less likely to have had an examination than people living with paid support staff; 30 percent of those previously examined had been diagnosed with eye problems; and 43 percent of those previously prescribed glasses were reported as unable to tolerate them. Eye examinations were offered to all participants and were found to be possible for all who attended.The implications for service provision and development are discussed.