摘要:

Tear exchange due to squeezing of a soft contact lens onto the cornea by the lid is calculated from lubrication theory. The theory predicts that for a normal blink and the usual tear film thickness (8 to 10 microns) there will be a 10 to 20% tear exchange at each blink.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

The oxygen tension under hard or soft, oxygen-permeable contact lenses is calculated. The calculation recognizes delivery of oxygen to the tear fluid under the contact lens by diffusion through the lens material and by entrance of fresh, air-saturated tears at each blink. The results show that oxygen diffusion through the lens material is much more effective than tear pumping in maintaining a useful oxygen tension under the lens.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Clinical optometric findings of 633 juvenile detention youths were statistically evaluated and compared to data from the general population. The youths had a higher referral rate for refractive errors, organic problems, and muscle imbalances than the general population. Female youths exhibited a higher incidence and greater severity of myopia than males at all ages. Referral rate for astigmatism among the youths was higher than the general population although the dioptric power was in agreement with previous studies.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

American Indians show a high incidence of various ocular abnormalities. In the present study, refractive error and corneal curvature were measured in 420 Zuni school children. The mean spherical refractive error varied from +0.87 D in the lower grades to −0.62 D in the upper grades. The mean corneal astigmatism was 2.21 D and varied as a function of grade. Corneal and refractive astigmatism were highly correlated.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

A procedure has been developed for tracing a bundle of rays through an ophthalmic lens and a schematic eye with its primary line of sight pointed through various parts of the lens. A bundle of eight rays can provide data for assessing the quality of the image formed by such a system. To test the procedure and to generate data which can help in selecting a method for evaluating image quality, we selected a single lens as an example. The lens selected has a spherical back surface (-5.00 diopters) and a toric front surface (+15.00 diopters in the vertical and +10.00 diopters in the horizontal). It has a center thickness of 5 mm and glass of index 1.523. Spot diagrams were generated with the eye pointed in various directions through the ophthalmic lens. The data generated showed that peripheral bundles which fall between the principal meridians emerge as astigmatic bundles. This leads to the proposal that blur circle theory can be used for evaluating the quality of the optical image and that it suffices in the case of a spherocylindrical ophthalmic lens to base the tolerances for refractive power on measurements made in the principal meridians.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

The posterior surface curvature of eight Bausch and Lomb Soflenses™ was measured by using a Moiré interference fringe technique. This unique method was used to allow measurement of the curvature variation across the lens surface and to provide new information which may be helpful in understanding difficult fitting problems and improving fitting techniques.Central apical curvature values determined from lens measurements agreed with values published by Bausch and Lomb within 6%. Low negative power lenses became steeper, whereas higher minus power lenses became flatter away from the apex toward the lens periphery.However, none of the lenses tested was as flat in, the outer portion of the lens as predicted by hydrodynamic forced-vortex theory which i should be applicable for spun-cast fluid lenses. There was also a significant change in curvature, first flattening, then steepening across the lens as it dried out during the course of the measurement.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

This study was designed to investigate the effects of various contact lens tints on color vision. Color vision performance of eight subjects was eualuated with the Farnsworth-Mun-sell 100 Hue Test while each subject wore each of 13 differently tinted contact lenses. No signif-icant differences in color vision were found with the various lenses. However, performance on the test was affected by repetition. Regardless of the lens tints tested, color discrimination for the blue quadrant of the 100 Hue Test was the poorest. Further research is needed to determine the effect of tinted contact lenses on scotopic and mesopic vision.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

A simple water cell can be used to increase the range of an ordinary lensometer by about three times by using an application of Snell's law. This technique can be very useful in low vision applications where other methods of measuring high plus ophthalmic lenses are always cumbersome and time consuming and sometimes inaccurate or inconclusive.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Restraint of an unanesthetized rodent for biomicroscopy and photography will prove a simple task with this easily constructed rodent restrainer.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

This study in the sociology of lay knowledge seeks to conceptualize the “everyday rules” by which a patient makes choices about which practitioner should be consulted for which episode. A lay person must often choose a practitioner from among competing coteries of specialists, without having recourse to their specialized knowledge in order to classify them. The patient must develop her own typology of specialists, utilizing her own criteria. The patient becomes aware of a number of aspects of an episode, each of which requires a response of some sort. In the course of her interaction with a practitioner, the patient discovers that the practitioner is competent, in her perception to handle some aspects and inadequate to handle others, thereby presenting her with a particular constellation of competencies and inadequacies. When seeing different practitioners, the patient encounters vertical and horizontal conflict between the assessments offered her by each. She must decide which offers the competencies most needed and the inadequacies most tolerable. A practitioner's constellation may change over time or by episode. In order to secure the competencies she feels necessary, the patient may utilize a number of practitioners either sequentially or simultaneously, thereby functioning as an assembler of her own health care team.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID