Biomedical subjects

G Lynn Mitchell

Publications and source records attributed to G Lynn Mitchell.

60 records · Page 4Linked to original sources

PubMed2002

Evaluation of tear film interference patterns and measures of tear break-up time.

PURPOSE: The purpose of this study was to compare the agreement within and between examiners when evaluating real-time and digital photographs of TearScope Plus tear film interference patterns. We also evaluated between-examiner agreement of noninvasive digital tear break-up time (NITBUT) using the TearScope, the relation between NITBUT and tear film interference patterns, and the relation between NITBUT and tear break-up time (TBUT). METHODS: Forty nondry eye patients were seen for digital imaging of the tear film using the TearScope Plus mounted on a slit-lamp with the EyeCap Ophthalmic Image Capture System. Two independent examiners first assessed the tear interference pattern in real-time and then captured the patterns and NITBUT digitally for a period of approximately 60 s. Each image series was later graded for interference pattern and NITBUT by the two independent, masked examiners. RESULTS: Within-examiner comparisons of real-time and digital tear pattern photograph grading showed moderate to substantial agreement for experienced examiners (kappa for examiner 1 = 0.76 and kappa for examiner 2 = 0.55). Between-examiner agreement when grading tear patterns was also substantial in real-time (kappa = 0.72) and moderate when using digital photography (kappa = 0.59). The between-examiner mean NITBUT was 11.2+/-6.8 s and the 95% limits of agreement between examiners were -19.2 to +9.2 s. The mean TBUT was 7.6+/-10.4 s, and it was on average 3.7+/-12.0 s shorter than NITBUT (p = 0.06). Thicker tear film interference patterns graded photographically were associated with longer NITBUTs for both examiners (p = 0.001). CONCLUSIONS: There is moderate to substantial within- and between-examiner agreement when comparing real-time and digital tear interference patterns photographs when using the TearScope. Although there is considerable between-examiner variability with the NITBUT test, the thicker lipid layer tear patterns tend to be associated with longer NITBUTs.

Adult↗

PubMed2002

Is visual memory predictive of below-average academic achievement in second through fourth graders?

PURPOSE: Controversy exists regarding the relation between visual memory and academic achievement. METHODS: A masked investigation of the relation between visual memory and academics was performed in 155 second-through fourth-grade children (mean age = 8.83 years). Visual memory ability was assessed with the Test of Visual Perceptual Skills visual memory subtest. The school administered the Otis-Lennon School Ability Test and Stanford Achievement Test. Age and verbal ability were controlled in all regression analyses. RESULTS: Visual memory score was significantly predictive of below-average word decoding (p = 0.027), total math score (p = 0.031), and Stanford complete battery score (p = 0.018). Visual memory score showed a positive trend in predicting reading comprehension (p = 0.093). CONCLUSIONS: Poor visual memory ability (as measured by the Test of Visual Perceptual Skills) is significantly related to below-average reading decoding, math, and overall academic achievement (as measured by the Stanford Achievement Test) in second- through fourth-grade children, while controlling for age and verbal ability.

Achievement↗

PubMed2002

Visual performance and comfort with the Rose K lens for keratoconus.

PURPOSE: The "Rose K Lens for Keratoconus" is a proprietary rigid contact lens design that has been reported and marketed as a lens that provides better visual acuity and comfort than other rigid contact lens designs for keratoconus. METHODS: Twenty patients with keratoconus who were wearing rigid contact lenses were refitted into the Rose K lenses. Visual acuity measurements were taken with habitual lenses at the baseline visit and with the Rose K lenses at the completion of the study. Questionnaires were used to assess vision-specific quality of life, contact lens comfort, and self-reported assessment of vision. RESULTS: There were no statistically significant changes in high- or low-contrast visual acuity with the Rose K lenses. There was statistically significant improvement in self-reported assessment of vision and self-reported assessment of comfort in the eyes with more advanced keratoconus. At the conclusion of the study, 72% of patients preferred the Rose K lenses over their habitual lenses, and 87% reported that they would continue wearing the Rose K lenses. CONCLUSIONS: There was no difference in the visual acuity with the Rose K lenses compared with the patients' habitual lenses. Subjective assessment of vision and comfort indicate a statistical improvement for more advanced keratoconus with the Rose K lens. We could not rule out a placebo effect as a source of subjective improvement in vision and comfort. Nevertheless, the successful fit rate and patient preference demonstrate the usefulness of the Rose K lens in clinical practice.

Adult↗

PubMed2002

Enhancing RGP contact lens performance: comparing back surface options.

BACKGROUND: In some cases, rigid gas-permeable (RGP) contact lenses may be the best--or only--means of refractive correction. High Dk RGP materials have markedly reduced hypoxia under those lenses. With aspheric lens back surface designs, post-lens circulation may be enhanced as well by maximizing the provision of nutrients and the clearance of metabolic by-products, toxins, and debris, while minimizing the risk of lens binding. METHODS: Performances of four aspheric back surface RGP designs were compared with a spherical optic zone and peripheral curve back surface reference design. Oxygen uptake rates were measured for each of 40 wearing combinations (five lens designs fitted to each of eight eyes) under non-blink and blink conditions for their effectiveness in reduction of post-lens hypoxia. Hypoxic reductions with blinking were scaled in exchange efficiency (EE) units, and used as relative indicators of post-lens tear exchange. RESULTS: Combined exchange efficiency index (EE) scores (averaged responses across all eight eyes) for each of the five lens back surface designs ranged from a best overall performance of +13.9 EE units down to only +2.5 EE units, with the spherical reference design averaging +8.9 EE units. Tear pump efficiency of each of the eight eyes (averaged responses across all five lens designs) ranged from a high of +12.3 EE units down to -9.8 EE units (i.e., worse than the non-blink condition of 0 EE units). Among the 40 eye-lens back surface design combinations studied here, the highest exchange efficiency score registered was +28.4 EE units, the lowest being -13.8 EE units. CONCLUSIONS: Aspheric lens back surface and/or peripheral curve designs were found to vary significantly in their post-lens exchange efficiency performances, but no "universal problem-solver" design was found among the five we investigated.

Adult↗

PubMed2002

Parental myopia, near work, school achievement, and children's refractive error.

PURPOSE: To quantify the degree of association between juvenile myopia and parental myopia, near work, and school achievement. METHODS: Refractive error, parental refractive status, current level of near activities (assumed working distance-weighted hours per week spent studying, reading for pleasure, watching television, playing video games or working on the computer), hours per week spent playing sports, and level of school achievement (scores on the Iowa Tests of Basic Skills [ITBS]) were assessed in 366 eighth grade children who participated in the Orinda Longitudinal Study of Myopia in 1991 to 1996. RESULTS: Children with myopia were more likely to have parents with myopia; to spend significantly more time studying, more time reading, and less time playing sports; and to score higher on the ITBS Reading and Total Language subtests than emmetropic children (chi(2) and Wilcoxon rank-sum tests; P < 0.024). Multivariate logistic regression models showed no substantial confounding effects between parental myopia, near work, sports activity, and school achievement, suggesting that each factor has an independent association with myopia. The multivariate odds ratio (95% confidence interval) for two compared with no parents with myopia was 6.40 (2.17-18.87) and was 1.020 (1.008-1.032) for each diopter-hour per week of near work. Interactions between parental myopia and near work were not significant (P = 0.67), indicating no increase in the risk associated with near work with an increasing number of parents with myopia. CONCLUSIONS: Heredity was the most important factor associated with juvenile myopia, with smaller independent contributions from more near work, higher school achievement, and less time in sports activity. There was no evidence that children inherit a myopigenic environment or a susceptibility to the effects of near work from their parents.

Adolescent↗

PubMedDate not supplied

Randot stereoacuity testing in young children.

OBJECTIVE: The Randot test is a commonly used stereoacuity test with child-friendly targets; however, little has been published about its use for young children. We sought to determine the completion rate of the Randot test among young children with normal vision and to calculate normative values. SUBJECTS AND METHODS: The Randot stereoacuity test was administered to 264 children whose ages ranged from 3 to 7 years. Because this was an investigation to determine the percentage of children who could complete the Randot test, children who failed a vision screening modified from the Modified Clinical Technique were excluded to minimize confounding factors (ie, a lack of measurable stereopsis due to vision problems rather than inability to understand the test). Completion rates and cumulative percentages were calculated by age. RESULTS: A completion rate of 98.5% was found. Median Randot stereoacuities were 100 seconds of arc for the 3-year-old children, 70 seconds of arc for the 4-year-old children, 50 seconds of arc for the 5-year-old children, 40 seconds of arc for the 6-year-old children, and 45 seconds of arc for the 7-year-old children. Kruskal-Wallis testing revealed a significant change in stereoacuity with age (chi-square, 35.55; df = 4; P < .001), and pairwise comparisons (alpha = 0.05) revealed that the 3- and 4-year-old children were significantly different from the 5-, 6-, and 7-year-old children. CONCLUSIONS: Randot stereoacuity can be assessed for most preschool children and all young school-aged children. In the absence of significant refractive error, strabismus, or reduced or unequal acuity, most 4-year-old children should have a Randot stereoacuity of 70 seconds of arc or better and most young school-aged children should have a Randot stereoacuity of 50 seconds of arc.

Child↗