摘要:

We describe a new glare test that uses low contrast letters and a variable surround glare source. The test is easy to administer clinically and all test targets, luminance levels, glare geometry, and viewing conditions are well controlled. We found the most useful index of disability glare to be the difference in visual acuity scores for the low contrast chart in the no-glare and high-glare conditions and refer to this as the disability glare index (DGI). We tested a group of normal subjects who were divided into younger (age 15 to 41 years) and older (age 50 to 82 years) groups. The mean DGI value for the older group (10.2 ± 4.8) was significantly higher than that for the younger group (2.3 ± 1.9). The DGI is a better discriminator between the two groups than either high or low contrast visual acuity. We attribute the significantly higher DGI values in the older group to increased intraocular light scatter. We find DGI is poorly correlated with high contrast visual acuity (r=0.33). Our findings suggest that this test of disability glare is sensitive to relatively modest changes in the ocular media. It is a potentially useful tool in detection and assessment of subtle media disturbances and in monitoring changes in the ocular media over a period of time.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

An evaluation of the reliability and relation to clinical state of a measure of low vision patient functional status was conducted. The measure included discrete tasks aggregated into three different areas: identifying objects, reading, and daily/leisure activities. Data were obtained retrospectively from case records of 247 low vision patients and 144 complete cases were used for statistical analyses. Evidence of reliability was found with coefficient alpha scores for the three areas ranging from 0.90 to 0.96. Significant relations between functional status and clinical states (acuity, contrast sensitivity, and visual field) were found with R2values ranging from 0.39 to 0.58, p<0.001.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

A limited set of illuminants and phosphor colors are commonly used in video display terminal (VDT) working environments. This study attempts to identify any combinations of such conditions that influence performance on a visually demanding counting task. Experiments were performed to test whether the phosphor color, ambient lighting spectrum, or temporal frequency characteristics of the display and ambient lighting could alter performance. Under conditions where potentially contaminating variables such as reflectance level and screen glare patterns were equalized, no significant differences in performance were produced by the particular sets of stimulus conditions tested. The results suggest that displays and illuminant types that are in common use allow substantially equivalent visual performance.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Since their rapid introduction into the workplace visual display terminals (VDT's) have been the source of a number of studies aimed at detecting effects on office workers. The published studies have been either short-term or cross-sectional, with one exception. The results have shown varying degrees of relation but by not having a comparable control group all have been limited in their value. We set out to monitor at regular intervals over a 2-year period specific visual functions that have been reported to be affected by VDT usage, and to compare VDT and non-VDT users in the same office environment. By assessing the VDT operators from the time the systems were introduced we have an accurate baseline to work from when assessing change due to the introduction of the VDT.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

We have developed a new technique for quantification of metamorphopsia using a simplified and modified Amsler grid. Furthermore, the technique used is a bisection task, a form of hyperacuity determination. This allows for very fine assessments of metamorphopsia even in the presence of cataracts.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

When a test surface or a cornea is carefully and properly positioned with respect to the Corneal Modeling System (CMS) videokeratoscope, measurements are highly repeatable, but the accuracy of the measurements is dependent on the shape of the surface. For spherical and toroidal surfaces, the CMS provides suitably accurate descriptions of the topography of the surface. For aspheric surfaces the CMS renders less accurate, but still clinically acceptable, topographic descriptions.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Confidence regions for mean dioptric power can be represented by ellipsoids in a three-dimensional space called h-space. A convenient graphical representation is provided by stereo-pair drawings that, at a glance, show the estimated accuracy with which the mean power is known. As an example, a sample of autorefractor measurements made on one eye were used to construct a 95% confidence ellipsoid for the mean objective refractive status of that eye. Key dimensions of the ellipsoid are compared with those of another eye. The analysis is of fundamental importance for scientific studies of variation and change of refractive status. Its potential clinical importance is also discussed.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Twenty-three subjects with noninsulin-dependent diabetes mellitus (NIDDM) and 23 age- and sex-matched controls were tested for sympathetic denervation of the iris dilator by comparing the mydriatic effect of the combination of 1% phenylephrine and 1% tropicamide with that of 1% tropicamide alone. Most of the diabetic subjects had no clinical signs of severe diabetic complications. Nine diabetics and two controls showed sympathetic denervation, defined as a 1 mm or greater dilation due the addition of 1% phenylephrine. One of those two controls had a recent history of vascular headache. The diabetics with pupillary neuropathy had higher glycosylated hemoglobin percentages and a history of higher fasting blood sugars (FBS's) than the diabetics with normal pupils. Our results show that pupillary neuropathy can develop in persons with diabetes, often before the other complications of diabetes become manifest.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Aphakic eyes possess considerably less oblique astigmatism than phakic eyes. The possibility that posterior iris displacement after lens extraction accounts for the observed reduction in oblique astigmatism is tested in this study. Oblique astigmatism was calculated for a phakic and an aphakic schematic eye. With no iris displacement little reduction of oblique astigmatism occurred contrary to experimental findings. However, introduction of varying levels of iris displacement reduced this aberration to values found experimentally. Posterior iris displacement (mean=1.19 mm) was confirmed in vivo by pre- and postoperative anterior chamber pachometry in eight patients.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Accurate and efficient calculation of the anterior corneal surface topography by photokeratoscopy has become important for the management or surgical treatment of refractive errors. Methods have been published that describe such calculations. The algorithms described here eliminate an assumption made in some of the earlier computational methods without an excessive increase in the computation time or increased sensitivity to measurement errors. This results in an enhanced accuracy for reconstructing corneal topographies. Computer simulation results indicate an improved accuracy in measuring the topography for nonspherical corneas. The equations given here apply to any general photokeratoscope geometry and can easily be used in computer programs. In a notable previous publication concerning the more common flat faceplate keratoscope geometry, several of the equations were presented with errors. These errors are identified as an aid to anyone who had already attempted to use those equations in a computer program.

ISSN:1040-5488    

出版商:OVID    

年代:1991

数据来源: OVID