Susan A. Kelly

Effect of yellow-tinted lenses on contrast sensitivity

ABSTRACT The effectiveness of yellow‐tinted lenses (Norton Visitor Wrap‐Around) on contrast thresholds for achromatic sinusoidal gratings was measured on a large sample of healthy, young adults. These measurements were compared with those obtained through luminancematched neutral goggles. Contrast sensitivity functions for stationary and drifting (2 cycles per second) gratings were measured on two groups of subjects. The results of both experiments show that those subjects demonstrating a subjective preference preferred the yellow tint to the neutral lenses by 2:1. Despite the subjective impression, however, contrast thresholds obtained with the yellow and neutral lenses were not statistically different for either the stationary or drifting gratings.

Effect of yellow-tinted lenses on brightness

Magnitude estimates of brightness were obtained for small (5-deg diameter) and large (15 deg X 20 deg) targets viewed through yellow-tinted lenses (ytls) and luminance-matched neutral lenses. The results indicate that brightness perception with ytls is up to 40% greater than that with neutral lenses when the spatial extent of the stimulus exceeds the fovea. The onset of the enhancement effect is coincident with the chromatic threshold, and its end point is coincident with psychophysical estimates of rod saturation. In a second experiment, brightness estimates were obtained for the ytls and neutral lenses during the cone plateau of the dark adaptation curve when rods, but not cones, were desensitized by bleach. The brightness-enhancement effect was negligible. These results confirm the subjective impression that brightness perception is enhanced by ytls and indicate that this effect is mediated, in large part, by the contribution of rod signals to the chromatic pathway.

Normative contrast sensitivity data for young children

Contrast sensitivity (CS) was measured in children ages 3 to 7 years using the Vistech Contrast Sensitivity distance chart (VCTS 6500). The purpose of the study was to determine how effectively the technique could be used with young children and to establish normative data for this age group. Of 286 children participating in a vision screening, the contrast sensitivity function (CSF) was measurable on 241 (84%) under binocular conditions and 229 (80%) under both binocular and monocular conditions. The 219 binocular CSFs and 208 monocular CSFs obtained from visually normal children were used to establish normative data and then compared to similar data from 50 visually normal young adults. The results indicated that there is an effect of age between 3 and 7 years, children are significantly less sensitive than adults, and adult-like levels of CS are not yet reached at 7 years of age. In addition, although the childrens mean contrast thresholds fell within the norms provided with the VCTS 6500, the variability in the childrens CSFs precludes using the Vistech data for diagnostic purposes in the young. The normative data are presented to assist the clinician in evaluating CS in young children when using the VCTS 6500.

The influence of cones on rod saturation with flashed backgrounds

The increment threshold for a middle-wavelength test flash was measured at the onset of a concentric long-wavelength background flash under conditions that have previously been shown to result in rod system saturation. The influence of the cone system on rod saturation under these conditions was assessed using the Stiles-Crawford effect in normal subjects and by measuring rod thresholds in protanopes, who are deficient in long-wavelength cones. When the background flash is made less effective for cones through the Stiles-Crawford effect, the onset of rod saturation occurs at a higher luminance of background flash than normal. Similarly, protanopes do not show the characteristics of rod saturation until a much higher-than-normal luminance of background flash. The results suggest that rod system saturation with flashed backgrounds is strongly influenced by cones.

Reliability of the CSV-1000 in adults and children.

Purpose. Test–retest reliability of the CSV-1000 (Vector Vision) has only been reported for one adult sample. We measured the reliability of this instrument in both children and adults and also investigated the effect of changing the examiner on test–retest reliability. Methods. Test–retest log contrast sensitivity (CS) measurements were obtained for 19 young adults and 15 children by the same examiner. Test–retest log CS data were obtained from 21 young adults with different examiners. Reliability was calculated using the Bland–Altman limits of agreement, the coefficient of repeatability (COR), and the intraclass correlation coefficient. Results. All three estimates of reliability for the CSV-1000 chart are low for both children and adults using the standard recommended testing protocol. If the test–retest log CS data are obtained from the same examiner then the reliability is improved, but not significantly so. Conclusions. The reliability of the CSV-1000 is low, even if the same examiner obtains test–retest data. The data indicate that this test is unlikely to be sensitive enough to provide useful information for the clinician as is, but we suggest modifications of the procedure that may significantly increase test reliability.

Orientation Anisotropy and Strabismus

Monocular contrast sensitivity (CS) measurements were obtained in the two principal meridians of eight constant unilateral strabismic subjects and four subjects diagnosed with alternating strabismus. The results indicated that: (1) the CS of both the fellow and deviating eyes of patients with a constant unilateral deviation is significantly less than that of visually normal eyes at high spatial frequencies; (2) both the fellow and deviating eyes reveal a significant reduction in CS to vertically oriented gratings. This effect is frequency-specific, occurring only at the highest spatial frequencies; (3) the magnitude of the orientation anisotropy did not vary systematically with the degree of amblyopia; and (4) a mild orientation anisotropy was observed in only three of the eight alternating strabismic eyes tested. The etiology of the vertical effect is examined with respect to the role of anomalous binocular competition, suppression and abnormal eye movements.

Automated and Manual Base Curve Assessment of Rigid Gas Permeable Contact Lenses

Abstract Verification of the base curve radius of a rigid contact lens is important because the base curve affects both the lens fit and power. This study compared the accuracy of base curve measurements obtained from the radiuscope versus the Nikon NRK-8000 autorefractor/keratometer CL attachment. Reliability coefficients were also determined for each technique. Base curve measurements for spherical, aspheric, and back toric rigid gas permeable lenses were obtained by 18 observers with the manual and automated methods in a counterbalanced order. Spherical and aspheric lens results showed the base curve estimates obtained from the radiuscope differed significantly from the automated measurements. The base curve measurements obtained from both methods were flatter than the ordered radius, but were within the conventional 0.025-mm tolerance. The reliability coefficient of the automated unit was approximately twice that of the manual unit. Toric basic curve measurements were statistically the same for both techniques, but the reliability coefficient was less than that obtained with spherical and aspheric base curves.