摘要:

An array of stimulus characteristics, such as spatial frequency content, contrast, color, and size, as well as higher-level control aspects, such as cognitive demand, instruction set, and volitional effort, may influence the steady-state accommodative response. Several experiments are reviewed which demonstrate clearly the remarkable robustness of accommodation to marked variations in these parameters. The retinal luminance gradient appears to be the primary determinant of overall response accuracy. These findings are of theoretical interest in understanding basic aspects of accommodative control, as well as being of practical importance. They suggest that the accommodative response remains relatively stable and accurate despite dynamic changes in retinal-image quality which occur under experimental and clinical, as well as more naturalistic, viewing conditions

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Occasionally in patients who have symptoms suggestive of a vertical heterophoria no deviation is found, even on careful examination. Six days of occlusion have been recommended for uncovering such “latent” vertical deviations. We investigated prolonged monocular occlusion (Part I) and found that vertical deviations of varying amounts manifested on symptomatic and asymptomatic subjects. Thus, results of prolonged occlusion can be difficult to interpret. Nonadaptive vertical vergence systems have been implicated in development of symptoms. Therefore, it may be that diagnostic monocular occlusion is not appropriate unless patients have symptoms of vertical imbalance. We used (24 h) occlusion and associated phoria measurements (Part II) to determine vertical prism prescriptions which eliminated symptoms of seven symptomatic patients who did not show significant vertical heterophoria on routine clinical testing. We present data and case reports which elucidate the efficacy of this procedure

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

To assess the reliability of the Vis tech Contrast Test System (VCTS), contrast sensitivity functions (CSF's) were estimated using all forms of the VCTS in 92 subjects aged 20 to 73 years, who were refracted for the test distance. Over a 3-month period, nine estimates at each spatial frequency and an equivalent number of acuity measures were obtained. The contrast sensitivity of older adults was lower than that of the younger adults, particularly at higher spatial frequencies. Practice effects which varied as a function of spatial frequency were also observed. Reliabilities for single-form estimates of contrast sensitivity (CS) were frequency-dependent, and ranged from 0.41 to 0.65. Three-form average estimates of CS yielded reliabilities ranging from 0.62 to 0.77. Consistent with the assertion that low VCTS reliabilities are due, in part, to measurement error, the reliabilities for acuity were uniformly higher than for the VCTS. Results are discussed in relation to clinical use of the VCTS across the life span

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Optometrists see many patients who complain of reading difficulty. The Dyslexia Screener (TDS) is an instrument which has been developed to determine, within 5 min, whether or not a patient shows evidence of having one of the three basic types of dyslexia (a coding problem in reading and spelling). Results using TDS were compared with the Dyslexia Determination Test (DDT). TDS rating scores were shown to contain much of the same clinical information as the DDT rating scores

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

The Illuminating Engineering Society of North America (IES) has adopted recommendations for the luminance transition in a tunnel that deviate greatly from the curves proposed by the International Commission on Illumination (CIE) and contained in the DIN Standards (German Standards). The IES has based its guidelines on practical considerations but they have neither scientific nor experimental foundation. In order to clarify the discrepancy, the physiological processes of adaptation of the eye during a change in luminance have been modeled, and their impact on the required luminance in the transition necessary to ensure visibility have been derived. Using Fry's model for the kinetics of the eye's response, and Adrian's AL model, the course of the luminance transition has been calculated. The results are compared with the IES and the CIE standards. A comparison of the resulting curve with that suggested by the CIE reveals small differences only. In general the comparison indicates that the experimentally determined CIE curve agrees with results derived from the fundamentals of dark adaptation. However, the IES suggestion falls short. An eye requires about twice as long to adapt to the luminance transition as is considered in the IES proposal

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

The acuities of three subjects with good visual acuity and stereo acuity were reduced by the addition of diffusing filters placed before one or both eyes; these subjects then underwent automated stereo acuity and visual acuity tests. Results were idiosyncratic and differed from subject to subject to such an extent that no general rule sufficed to describe the effect of different degrees of blur on visual acuity and stereo acuity. It had been thought that blur degraded stereo acuity more than visual acuity but most of the results from one subject indicated the opposite effect. The effects of monocular vs. binocular blur are discussed

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

3 D). However, it provides accurate values of the variation in off-axis surface power for low powered lenses with aspheric front surfaces. There were considerable systematic errors associated with the measurement of prism. A simple raytracing method was developed to predict the results of measurements with the Humphrey Lens Analyzer. Predictions of off-axis power were good when lenses were rotated about a position corresponding to the center-of-rotation of an eye, but were poorer when lenses were rotated about the center of curvature of their back surfaces. Predictions of primatic efforts were good in both situations. A method by which the Humphrey Lens Analyzer should provide an accurate measurement of off-axis powers corresponding to eye rotation behind a spectacle lens is described, but has not been tested.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

The effect of changes in rigid contact lens overall and optic zone diameters on tear pump efficiency were studied using a polarographic technique. Six overall diameters ranged from 7.6 to 10.6 mm in 0.6-mm steps, with the optic zone diameter always being 1.4 mm smaller. Base curve radii were made flatter as lens overall/optic zone diameters increased in order to maintain a constant tear layer thickness. All other parameters were held constant. Oxygen uptake rates were measured for the normal, open eye, as well as after 5 m in of static (without blinking) and dynamic (with blinking once every 5 s) wear of each lens design. Under both static and dynamic conditions, oxygen uptake rates increased with increase in lens overall/optic zone diameter. The differences between the static and dynamic condition data served as an index of tear pump efficiency for each lens. These differences decreased with increase in lens overall/optic zone diameter

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Altitudinal hemianopsia is a relatively rare visual field defect. A case report is presented describing a patinet suffering from sudden-onset traumatic altitudinal hemianopsia. Other conditions which may produce sudden or gradual onset altitudinal hemianopsias are discussed. The importance of the optometrist being aware of the possiblility of an altitudinal visual field defect in conditions of trauma to the face after motor vehicle accidents is stressed.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Spectrophotometric measurements were obtained on 40 pairs of children's sunglasses. Some of these sunglasses provide excellent protection from the potentially damaging effects of ultraviolet radiation (UVR), whereas others fail to provide adequate protection for the crystalline lens and retina. Some labels were ambiguous and misleading with respect to whether the sunglass provided adequate absorption of UVR

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID