摘要:

Factors associated with edge clearance in the contact lens-corneal relationship are peripheral curve radius and width, lens diameter, and corneal shape. The effect of each parameter is quantified, permitting an examination of current design practices. Recommendations are that minor adjustments be made by changing radius, that major adjustments be made by changing width, and that the peripheral curve radius should be steepened as the diameter increases.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

A method is described for the measurement of the anterior and posterior radii of curvature and thickness of a soft (hydrogel) contact lens. The method is based on the observation of an interference pattern that is generated by two beams of light, one reflected from the surface of the lens and the other reflected from the surface of a comparison mirror. It was found that the maximum coefficient of variation for the measured values of the anterior and posterior radii of curvature was 2% and the minimum value was 0.6%. An accuracy of 1:103 for the radii of curvature and the center thickness of the lens is claimed.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Fifteen refractive astigmats were fitted with prism ballasted and truncated piano, spherical lenses and prescription toric soft lenses. The initial rotation observed with each lens type did not differ significantly, indicating that trial sets of such spherical lenses may provide an effective method of fitting toric soft lenses.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Schoolchildren (735) between the ages of 7 and 14 were examined for convergence ability. Nine percent had an objective near point of convergence of more than 1 0 cm and 1 0% had a subjective near point of convergence of more than 10 cm. The recovery point was greater than 15 cm for 9% of the subjects when measured objectively and 1 2% subjectively. The sample was analyzed with regard to age, sex, and IQ. There was no significant difference between children who showed convergence insufficiency and those who did not with regard to school results in their mother tongue and in their grade point average.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

There are conflicting reports on the effect of vergence training. In two studies using push up and prism vergence exercises the conflict is shown to result from differences in the constancy of effort. Improvement only occurs in exercises involving sustained effort in the direction being trained. The effect of alternating movements in both directions is small and inconsistent. Substantial longlasting gains in either convergence or divergence prism vergence scores can result from just 5 min of sustained effort at an angle halfway between the break and recovery points. Results for adults and children on motor-driven instruments are comparable and the scores obtained discriminate better than those from hand-turned instruments. The most likely physiological model involves potentiating processes which are specifically maximized by isometric exercise. Potentiation results in a positive feedback process, the effects of which are strong enough to precipitate strabismus and which might be deliberately manipulated in therapy of poor vergence control, if responses in the required direction can be induced.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Retinoscopy under cycloplegia with various agents can yield varied results. Additionally, cycloplegics can produce adverse local as well as central nervous system disturbances. A noncycloplegic near retinoscopy technique as promulgated by Mohindra is compared with cycloplegic retinoscopy on schoolchildren in early grades. Results obtained by a study utilizing the two techniques show that they yield similar objective measurements of refraction.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Static load tests were conducted on heat-tempered and chemtempered piano white crown glass lenses from five different optical laboratories. With both ball-on-ring and ring-on-ring loading, chemtempered lenses considerably thinner than 2.0 mm were found to be as failure resistant as 2.0-mm-thick heat-tempered lenses. A similar result was obtaind previously using the drop-ball test. It is shown that the theory of brittle fracture can be used to relate the results of different tests and provides a rational basis for comparing the relative performance of chemtempered and heat-tempered lenses.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

A versatile multi-input device based on an x-y recorder was designed for the study of the Pulfrich effect. Because the device provided constant velocity of the target, a rectangular Pulfrich effect was observed rather than the traditional elliptical effect. The instrument permits study of the response induced when the input is changed in a variety of ways.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

A method for quantifying the ERG photostimulus is presented. The units of measure are reasonably straightforward and yet consistent with laws of photochemistry and psychophysics. Application of these laws facilitates measurement with readily available photometric instrumentation.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID