摘要:

Two methods of clinically inspecting and verifying rigid back surface aspheric contact lenses were investigated. A modification of the Radiuscope was found to be an accurate method for making such measurements. Measurement data of a number of aspheric lenses obtained by using this procedure are presented.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Visual evoked responses (VERs) were obtained from seven normal eyes, using high contrast square-wave gratings of varying bar size on an 8° or 24° stimulus field. VER amplitude was plotted as a function of bar size. These plots, called square wave transfer functions (SWTFs), have one or more peaks when generated by a 24° field. In some individuals, the small bar size extreme of the function can be fitted well with a straight line for purposes of extrapolation to the visual acuity bar size. However, interindividual differences in the shape of the 24° field SWTF invalidates any a priori assumption of what bar sizes may be included in the extrapolation. Results from three subjects, using an 8° field, suggest that a more uniform single-peaked triangular SWTF with a peak near 5 min arc may be assumed for extrapolation purposes. The interindividual SWTF differences obtained with the 24° field were not random, the subjects falling into one of two groups on the basis of SWTF shape. This SWTF shape dichotomy may be correlated with the presence or absence of strabismus.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Using an infra-red dynamic optometer, a qualitative comparison of the accommodation responses of two observers to step changes in target position showed marked differences in their ability to accommodate correctly. Measurement of reaction time (or latency) gave results comparable with those of other workers and independent of target position. Measurements of response time showed for one observer that the response time was dependent on the extent of the accommodative change required; this was not true of the other observer. Possible reasons for the intersubject differences and the role of the instructions given to the observer are discussed.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

By noting the direction of gaze in which the vertical phoria is largest, one can determine where binocular discomfort is likely to be greatest. Treatment of the discomfort is then based upon prescribing horizontal prism for the horizontal phoria. The recommended amount of horizontal prism is that amount which reduces the vertical fixation disparity to zero. Although the fixation disparity can change in different directions of gaze, in most instances, the prescribed amount of horizontal prism is determined in the primary position of gaze.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Ocular fundus photographs of 100 eyes were obtained from an institutionalized population of patients with Down's Syndrome (66 males, 34 females). The vascularity of the optic nerve head was assessed in each photograph by counting the number of arterioles, venules, and fine vessels crossing the disc margin. The results of this analysis were compared to similar data obtained from 100 ocular fundus photographs of normal patients and show that there are more large vessels crossing the disc margin in those with Down's Syndrome.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Measured values for ametropia-correcting powers and front surface radii of lenses on the eye are compared to values which would be expected, using the Equal Change Hypothesis and the Invariant Normals-Constant Arc Hypothesis. Photographs of various lenses on the eye, with large molecule fluorescein instilled, are presented and show no noticeable tear lens of a finite power. These photographs and our data indicate that the Equal Change Hypothesis is not valid for predicting lens power changes due to flexure. In contrast, the Invariant Normals-Constant Arc Hypothesis appears to closely predict lens flexure effects. A clinical application of this study would be to note that thin minus hydrogels correct slightly more ametropia in their flexed state than in their unflexed state. Thin plus hydrogels correct slightly less ametropia in the flexed state than in the unflexed state.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Eye movements in a subject with jerk nystagmus were recorded during a variety of tracking tasks using a photoelectric method. New findings included ability to reduce nystagmus amplitude and frequency when instructed “to hold the eye steady” rather than “to fixate” in the presence of a visible target, changes in nystagmus characteristics and visual acuity as a function of head position which related to overall retinal-image motion, marked variability of nystagmus especially during reading, and necessity of a prolonged period of visual feedback for generation of nystagmus to approach a “steady-state” level. Clinical implications of these findings are discussed, including use of the “hold” command during ophthalmoscopy in patients with nystagmus.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

The luminance of the background and of the target (visual acuity letter) was measured for five commonly used visual acuity screen materials. Most materials were found to be highly nonlambertian. A greater than threefold difference in reflectance normal to the surface was found for the respective screens tested. The percent polarization maintained by each screen material, using American Optical Vectograph systems, was measured. The relative illuminations generated by eight projector systems were compared. A discussion of the factors and recommendations for improvements related to projected chart visibility are made.

ISSN:0093-7002    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

During ocular examinations, it often is necessary for the doctor to both inspect and treat the eye simultaneously. An instrument has been developed which makes this process considerably simpler.

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