摘要:

The purpose of this study was to assess the effects of horizontal and vertical vergence training on fusional vergences and the fixation disparity (FD) curve. Thirty-four subjects were divided into three groups. One-third served as controls and the other two-thirds underwent 5 h of supervised horizontal and vertical vergence training, respectively. Before and after the 4 week training period, vergences and FD curves were measured by a single individual who was intentionally uninformed of each subject's group. We hypothesized that the subjects in the horizontal training group would have increased vergence amplitudes and flatter FD slopes. Our analysis revealed that the positive vergences increased significantly for those in the horizontal group. No evidence was found to suggest changes in any variables related to the FD curve. Because type II errors were likely to be unacceptably large, further work is necessary to determine the relation between fusional vergence training and variables derived from the FD curve.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

The purpose of this study was to assess the effects of horizontal and vertical vergence training on vertical fusional amplitudes, the vertical fixation disparity (VFD) curve, and prism adaptation. Thirty-four subjects were divided into three groups. One-third served as controls and the other two-thirds underwent 5 h of supervised horizontal and vertical vergence training, respectively. We hypothesized that subjects in the vertical group would manifest increased vertical vergence amplitude and coefficients of adaptation in concert with flatter VFD slopes. Before and after the 4-week training period, vertical vergences, fixation disparity (FD) curves, and coefficients of vertical prism adaptation were measured by a single individual who was intentionally uninformed of each subject's group. Analysis of the data suggests that changes in the vertical fusional amplitudes increased slightly. Although changes in the VFD slope and coefficient of prism adaptation were not statistically significant, the changes were much greater in the vertical group and in the hypothesized direction. We suggest that the results offer preliminary support for our hypothesis.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

The effects of monovision (MV) contact lens wear on the performance of occupational-type nearpoint tasks was evaluated on 18 presbyopic subjects (ages 44 to 67 years) by comparing MV performance (MV condition) to that with distance contact lenses with reading glasses (BV condition). Each subject had correctable distance visual acuity of 6/6 (20/20) in each eye, at least 60 sec arc of near stereopsis, good ocular health, and no previous MV experience. Time performance and error performance for 3 nearpoint occupational tasks (pointers and straws, card filing, and letter editing) were measured with the MV correction and BV correction. Measurements were taken at dispensing and at 2 weeks and 8 weeks after dispensing. Subjects were instructed to wear the MV soft spherical contact lenses at least 8 h per day. We measured BV time performance to be better than MV time performance by 2.8 to 5.7% and also measured an increased number of errors with MV.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Three distinct methodologies have been used to assess corneal oxygen supply during contact lens wear–oxygen transmissibility (Dk/L), equivalent oxygen percentage (EOP), and corneal swelling. To examine the interrelation among these methodologies, we measured the EOP and the amount of corneal swelling in response to a set of contact lenses of a range of Dk/L values on 10 subjects. We also measured the corneal swelling response after exposure to gas mixtures of 0.00, 1.01, 2.65, 5.13, and 10.3% oxygen concentration (balance nitrogen). Analysis of covariance showed that the relation between corneal swelling and EOP during lens wear was significantly different from the relation between corneal swelling and oxygen concentration after exposure to the gas mixtures, leading to different estimates of the minimum oxygen tension required to avoid corneal swelling (18.0% for the EOP technique vs. 10.9% for the gas mixtures). This discrepancy may be explained in terms of the underlying assumptions of the various techniques and by consideration of the mechanisms of corneal swelling during contact lens wear. The clinical implication of this result is that an EOP of 18% should be used as the basis for the development of a daily wear contact lens that provides an “edema-free” response.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Materials with a high refractive index have a considerable level of chromatic dispersion which, around the periphery of corrective lenses, may affect the wearer's visual acuity. By measuring visual acuity through prisms of increasing chromatic power we have established the relation between chromatic power and visual acuity. The maximum chromatic dispersion of materials useable in ophthalmic optics can be deduced from these results.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Ellipses were fitted to 129 nerve heads and corresponding blind spots in an attempt to determine how faithfully the elliptical nature of the nerve head is reflected in the blind spot. The blind spots are found to be 2 to 3 times more elliptical (based on the ratio of the long axis to the short axis) than the nerve heads. The correlation between the ratios mentioned above is found to be negligible (Pearson r = 0.07 for Goldmann 1–2 blind spots and 0.18 for Goldmann 1–4 blind spots).

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

In four studies, the comparability of several measures of contrast sensitivity functions (CSF's) as well as their individual test-retest reliabilities were determined with observers drawn from a college population. The relation between CSF scores obtained by different tests or by different psychophysical procedures with the same test was consistently low and frequently nonexistent. These low inter-test reliabilities were found to be due to the lack of reliability of some of the individual tests. In particular, with both stationary and flickering gratings, the von Bekesy tracking procedure produced unacceptable variations in contrast estimates. Fortunately, the reliabilities of other procedures, particularly the simple adjustment method, were much higher (>0.70). CSF scores obtained from the wall-chart method exhibited insufficient variability among observers in the college sample to permit similar reliability estimates to be determined. Implications of the test characteristics are discussed for users of the CSF.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

The purpose of the study was to determine to what extent induced aniseikonia affects fixation performance. Aniseikonia was induced in the vertical meridian only, whereas fixation alignment was monitored in the horizontal meridian. A previously developed technique based on the dependency of border enhancement bandwidth on fixation eccentricity was used to monitor deviations from central fixation during fusion. Stress on the fusion mechanism was supplied by controlled increments of forced horizontal vergence. It was found that deviation from central fixation in the horizontal meridian generally increases with increasing amounts of vertical aniseikonia. The effect is particularly pronounced for small amounts of aniseikonia.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID