ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1988.tb01074.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The Snellen test has been the most popular clinical measurement of spatial vision for over a century, but it does not fully express the visual ability of an individual. For more analytical purposes the information capacity of the visual system may be assessed by tests of contrast sensitivity and peripheral vision. The visual system selectively reduces the spatial information content of the visual field to avoid overloading the limited capacity for perception and decision making in the brain. The ways in which this reduction occurs and the processing of spatial information is of interest in many disciplines, and theoretical knowledge has been accelerated by the study of artifical intelligence. These processes may be investigated in human subjects by psychophysical and electrophysiological techniques. This provides additional information for diagnostic purposes and will form the basis of new systems of clinical investigation.

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1988.tb01075.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A high‐frequency eye test chart using letters or figures of alternating black and white stripes (or dots) on a grey background was developed. Any cross‐section of the letters has a Fourier transform with a zero frequency component equal to the luminance of the grey background. When the letters are out of focus, their image on the retina fades rapidly into the grey background, rendering them invisible rather than merely blurred as in a standard chart. The chart was calibrated by simulating refractive errors with defocusing lenses applied to a photographic camera and to subjects' eyes. No constant ratio was found between the size of the Snellen letters and the size of the high‐frequency letters for equal visibility. The new chart requires letters for 20/200 acuity to be only 3.6 times larger than those for 20/20 vision. Results confirm the arbitrary nature of the Snellen fraction and warn about the accuracy of visual acuity determined by using charts of different letter types, calibrated by Snellen's s

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1988.tb01076.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The Mallett test for near vision and the Sheedy Disparometer are compared in terms of their ability to measure associated heterophoria. Twenty‐two asymptopmatic subjects were used. With the Disparometer, ten of these subjects, familiar with making prism vergence measurements, exhibited stable forced vergence fixation disparity curves, and the associated heterophoria values using both instruments were not significantly different. However, the twelve subjects not familiar with making such measurements generated fluctuating, unstable fixation disparity curves, and the associated heterophoria values were significantly different. Repeated trials with the randomly selected naäve subjects led to flatter, more stable fixation disparity curves and lower values for the x‐and y‐intercepts when using the Disparometer. The Mallett test, however, produced identical values for associated heterophoria in each successive trial. Therefore, the validity of measurements using the Disparometer in a clinical setting is ques

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1988.tb01077.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The relationship between pupil size and perimetric sensitivity was investigated in group of clinically normal emmetropic subjects using the Dicon AP3000 computer‐assisted perimeter at bowl luminances of 10 asb and 45 asb. Pupil size was modified with the motic thymoxamine 0.5% and the mydriatic phenylephrine 10%; saline was used as the control. Perimetric sensitivity increased with an increase in pupil size. The effect was greatest for peripheral locations for both bowl luminances. The fluctuations in perimetric sensitivity increased with peripheral angle and with decrease in pupil size for both bowl luminance

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1988.tb01078.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The relationship between accommodative fluctuations and perimetric sensitivity was investigated in a group of 10 clinically normal emmetropic subjects using the Dicon AP3000 computer‐assisted perimeter at a bowl luminance of 10 asb. Accommodative microfluctuations were attenuated with the antimuscarinic drug cyclopentolate HCL 1% and the concomitant mydriasis was matched on a separate trial using the sympathomimetic phenylephrine HCI 10%. Saline 0.9% was used as the control. Accommodative microfluctuations were found to play a minor role in determining the magnitude of sensitivity out to an eccentricity of 50; between 50and 27.50, the effect of microfluctuations was masked by the mydriasis produced by the drugs used in the study. The range of sensitivity values at a given location were reduced when accommodative fluctuations were minimize

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1988.tb01079.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Changes in the axis of astigmatism have been followed up in the same individuals over several decades. Only a proportion of subjects with direct astigmastism in their youth change to inverse astigmatism by way of oblique astigmatism.

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1988.tb01080.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Experiments are described in which the steady‐state accommodation response to binocularly viewed targets at various distances in the range 0.2–5 m was measured by laser optometry in normal, near‐emmetropic subjects. Responses were determined with naked‐eye viewing and when equal pairs of either spherical lenses or base‐in or base‐out prisms were placed before the eyes. Snellen acuity was also measured under the same range of conditions. The results show that, although the most accurate accommodation responses were found under natural viewing, the response accuracy was remarkably robust against both lenses and prisms. There was, however, always some change in response level to any increment in lens or prism power. The results are discussed in terms of earlier theories and data on the general relationship between accommodation and

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1988.tb01081.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

If the positions of the principal points of the crystalline lens are conjectured, its equivalent power and that of the eye can be calculated as described from ocular dioptrics. The only data required are the subject's refractive error and the results of keratometry adn A‐scan ultrasonography. The method assumes the profile of the lens of conform to and arbitrary norm. If the unkown lesn profile of given eye differs from this norm, errors will arise. These are shown to be realatively small, and even in extreme cases unlikely to exceed ±1.0 D for the lesn and + 0.5 D for the e

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1988.tb01082.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The reaction‐time for movement was found to be around 150 ms and was compared with the time required to take action while two moving lines are on a collision course. Subjects were trained to either avoid or maximize collision. They did so accurately. The action‐time was about one‐third the reaction

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1988.tb01083.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY