摘要:

Contrast sensitivity functions were obtained from normal subjects using a spatial bandwidth equalization (SBE) technique and the more conventional display method. Static sensitivity measurements obtained with the two methods were in good agreement. However, when the patterns were counterphase flickered, sensitivity to the lower spatial frequencies was enhanced using the conventional method while sensitivity measured with the SBE technique was slightly depressed. The SBE method also was used to investigate suprathreshold contrast perception with static and flickering gratings. In general, the perception of contrast was independent of spatial frequency content of the stimulus, especially with increasing contrast levels and flicker frequencies. These studies have shown that the SBE technique is an acceptable method to assess static contrast sensitivity and suprathreshold contrast perception.

ISSN:0093-7002    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

The effect of surface protein deposits on the oxygen permeability of polyhydroxyethylmethacrylate (polyHEMA) gel contact lenses was studied using: (1) previously worn lenses with protein deposits accumulatedin vivo, and (2) new lenses with protein depositedin vitro.The oxygen permeability (Dk) of the protein-depositedin vivolenses was determined before and after cleaning, and that of the new lenses before and afterin vitroprotein deposition. For both groups of lenses, the oxygen permeability did not change significantly after either cleaning (in vivolenses) or protein deposition (in vitrolenses). It is concluded that surface protein deposits on polyHEMA lenses do not alter the oxygen permeability of the lenses.

ISSN:0093-7002    

出版商:OVID    

年代:1984

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Historically, there has been little quantitative rationale for the prescription of colored filters for color deficients. A formal prediction of the effects of any filter on dichromat luminance and chromatic discrimination is presented; these predictions were generated by using colorimetric concepts and related derived formulas to create four interactive computer-graphic tools. In addition to predicting performance of presently available commercial filters, such tools can be used to describe, classify, and even design new filters.

ISSN:0093-7002    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Using derived formulas for dichromat colorimetry and related computer graphic colorimetric tools, predictions of color discrimination performance are made for a deuteranope and protanope standard observer for each of three commercial color deficiency “treatment” filters. Five deuteranopes and five protanopes then participated in two experiments. They were asked to order the caps of the D-15 test, and in a second experiment arrange color pairs (from the D-15 test) in order of difference. Predictions and subject performance reveal that although X-Chrom aided dichromats gain both luminous and chromatic information, all dichromats used predominantly chromaticity information in discrimination tasks. The colorimetric tools correctly predicted that protanopes would derive less useful luminous information from the X-Chrom filter compared with deuteranopes, and correctly predicted an increase in discrimination of blues and purples for both classes of red-green color deficients.

ISSN:0093-7002    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

We examined the effect of luminance on low contrast visual acuity in six patients with mild reductions in vision due to senile macular degeneration (SMD) and in six normals of approximately the same age. At the highest luminance tested the SMD patients showed a reduction in acuity compared to the controls, with eccentricity and contrast effects clearly shown, The SMD patients had difficulty performing the acuity task at the lower luminances (0.26 and 0.75 cd/m2); they showed little or no increase in visual acuity with increasing contrast levels at the lower luminances. Acuity was slightly influenced by target eccentricity at these luminances. These data suggest that the adaptation mechanisms allowing the normal visual system to operate efficiently over a wide range of luminances are affected in SMD, even when clinically measured acuity is only moderately depressed.

ISSN:0093-7002    

出版商:OVID    

年代:1984

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

A 34-year-old black male presented with marked unilateral proptosis and pain in the left eye. Visual acuities were OD 6/7.5 (20/25) and OS 6/120 (20/400). His left eye was exophthalmic, had a Marcus Gunn pupil, and exposure keratitis. Sectorial pallor and a decreased Kestenbaum count were evident on the left optic nerve head. A tentative diagnosis of orbital meningioma was made and later confirmed. Optometric management of the patient, including appropriate screening tests and referrals, are discussed.

ISSN:0093-7002    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Bilateral crystalline lens opacities developed in a 39-year-old black male who had been involved in an electrical accident approximately 1 yr before our examination. The anterior subcapsular opacities had feathered edges and a slightly raised center. The typical appearance and progressive course of the opacities, as well as the history, led to the diagnosis of electric cataract.

ISSN:0093-7002    

出版商:OVID    

年代:1984

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1984

数据来源: OVID