摘要:

Surface damage incurred as a result of removing poly methyl methacrylate (PMMA) contact lenses from various contact lens carrying cases was monitored by photographic techniques. As compared to the controls, the experimental lenses showed consistent increases in surface damage, particularly if they were removed by a sliding (dragging) motion along the contours of the case.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Strain distirubtions on impacted ophthalmic lenses were measured with strain gages. The strain distributions, which resulted from impacts produced with a special apparatus, were shown to be comparable to those which arise in the FDA drop-ball test. The measured strain drops off very rapidly away from the impact point, implying that only a small part of the lens is really being tested. The results are in good agreement with the quasi-static predictions. The effect of differences in lens power, of input kinetic energy, and of inserting the lens in a polyethylene bag are also investigated.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

The visual evoked response (VER) has been considered an objective indicator of visual and perceptual processing, although as yet there is no clear evidence of a relationship between visual recognition and electrophysiological activity. The present study was performed to determine whether VER's can provide indications of differences in responses to word stimuli presented in different parts of the visual field. Additionally, evidence was sought as to whether the left and right hemispheres process visual information symmetrically. In 20 adult subjects with normal binocular vision, VER's were recorded simultaneously from left and right hemispheres in response to the repeated presentation of a three-letter word in each of 7 visual field locations. VER's of any subject in response to one stimulus site were consistent and repeatable; inter subject variation was large. For subject comparison, amplitude of VER was the measured response. No significant or consistent amplitude characteristics were identified that related to recognition of the stimulus. From comparison of responses to the different field locations, central stimulation (at 0°) evoked the largest peak-to-trough amplitude (&OV0398; = 8.21 μV, ± 2.56). Amplitudes tended to be larger at 4“ than at 2° from center; left field stimulation tended to give larger amplitudes than right field; however, these trends were statistically insignificant. Although overall mean responses from the right hemisphere were larger than from the left, this difference was not valid since 11 subjects had larger right hemisphere responses, whereas 9 had larger amplitudes from the left hemisphere. Thus, the study suggests that the VER reflects some net electrical activity from the recording sites that may be traced to an external sensory stimulus and shows that this activity is symmetrical for each hemisphere.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

The calculation of magnification differences is treated well in a number of texts,1, 3, 4, 5, 7but the formulas are not always presented in their most convenient form. Because of this, many complex schemes have been illustrated2and many different versions have been published.3, 4, 5The purpose of this paper is to present the pertinent equations in a simplified manner and to illustrate them by a specific example, namely, the case of monocular aphakia.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Two formulas are presented which permit rapid determination of accommodative and convergence demands in a Brewster stereoscope. The formulas are easily applied and are valid for any circumstances. The formula for convergence is unique in that it is independent of the patient's interpupillary setting for all instrument settings and yields results directly comparable to standard clinicat measurements. The formula for accommodation is:A = 1/TD - PThe formula for convergence is:C = (P × LS) - TS/ TDThest formulas hold where A is accommodation in diopters, C is convergence in prism diopters, TD is distance of stereogram from stereoscope lenses in meters, P is power of stereoscope lenses in diopters, LS is separation of optical centers of stereoscope lenses in centimeters, and TS is he separation of corresponding points of the stereogram half-views in centimeters.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

The manufacturers of telescopic instruments typically describe their products in terms of the magnification produced. Most include some reference to the “object field” or the “acceptance angle,” i.e., the angle subtended by the entrance port at the center of the entrance pupil. This paper considers varied factors utilized for calculating magnification and object field and proposes expressing the object field in terms of prism diopters rather than degrees.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Confusion and misconceptions characterize the designation of near visual acuities because of the numerous systems in use. Most of these systems do not lend themselves to accurate or easy usage or to comparison with other test distances. Use of the M system, with the actual test distances recorded in meters, is suggested as a simplified system for standardization.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

The present paper reviews recent studies of retinal pathology from the American and British Journals of Ophthalmology during a one-year period (1973–1974). Selection is on the basis of potential value to clinical optometrists. Certain underlying factors in several types of retinal degeneration are first discussed, followed by characteristics of diabetic maculopathy and of other types of macular degeneration including that due to aging. Some material is presented on retinopathies related to sickle cell traits, to viral and worm infections, and to injury. Following a review of certain recent studies of retinoschisis, retinoblastoma, and retrolental fibroplasia, a concluding section deals with retinal detachments and breaks.

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1976

数据来源: OVID