ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

A program of research dealing with two types of sensory aids for the blind —sonar and vibrotactile —is described. Rather than immediately assessing the aids in the mobility context, which has customarily been the case, the aids' capabilities are considered in terms of the major functions of vision, that is, the exteroceptive perception of objects, surfaces, and events of the environment, and the proprioceptive perception of the self, especially the self in relation to the environment. Although sonar aids function very well for localizing objects and for providing acoustic flow specifying selfmovement, they do not provide high acuity pattern and shape information due to the long wavelength of ultrasound relative to light. This limitation is considered specifically with respect to the visual accomplishment of recovery of three-dimensional structure/motion from dynamic two-dimensional images. Vibrotactile sensory aids using optical imaging can deliver detailed pattern information to the skin and thus permit assessment of the extent to which a nonvisual system can mediate the recovery of structure problem. However, in even moderately cluttered or complicated environments the skin proves unable to resolve the amount of stimulation it receives vibrotactually. The limitations of sonar and vibrotactile sensory aids are discussed with respect to future sensory substitution efforts as well as their implications for understanding differences and similarities among the senses.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Image enhancement as an aid for the visually impaired may improve visibility of TV programs and provide portable visual aid. This paper describes the current techniques for image enhancement and their underlying models. The limitations of the various techniques and of potential methods of implementation are highlighted. Initial work in this area was based on a linear model. The finite dynamic range available in the video display and contamination of the enhanced image by high spatial frequency noise limited the model's usefulness. I propose a method to address some limitations of the original model that considers the nonlinear response of the visual system and requires enhancement of subthreshold spatial information only. This modification may increase the dynamic range available by decreasing the range previously used by the linear models to enhance visible details. However, for the modified technique to be most effective, the enhancement has to be continuously tuned, based on the patient's visual loss and the spatial frequency content of the displayed images. The implications of these limitations for the potential implementation in TV are discussed. Implementation of an image-enhancing visual aid in a head-mounted, binocular, full-field, virtual vision device may cause substantial difficulties. Patient adaptation may be difficult due to head movement and interaction of the vestibular system response with the head-mounted display. An alternate, bioptic design is proposed in which the display is positioned above or below the line of sight to be examined intermittently, possibly in a freeze-frame mode. Such implementation is also likely to be less expensive, enabling more users access to the device.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Autofocus (AF) low vision telescopes offer the potential to increase the acceptance and utilization of such low vision aids (LVA) by the visually impaired. Many patients resist conventional manual focus telescopes for a variety of reasons including appearance, field of view, weight, and utility. The elderly who comprise the significant part of the target population may also resist telescopes due to an avoidance of the technical challenge of its use. Although an AF telescope is technically advanced, it may allow for less manipulation by the wearer and hence enable its more effective application to visual tasks, especially in the near- to mid-range where depths of field narrow and the demands for focusing increase. There are many challenges involved in the application of AF technology to LVA including modification of the focusing range, signal processing for physiologically acceptable performance, and power and weight considerations. A preliminary infrared (IR) AF prototype based upon our recent work with the Ocutech Vision Enhancing System (VES) has been produced. Initial findings are presented which address the requirements of a subsequent version as well as the challenges that will be faced to optimize such a device.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The Johns Hopkins Wilmer Eye Institute and the NASA Stennis Space Center are collaborating on the development of a new high technology low vision aid called the Low Vision Enhancement System (LVES). The LVES consists of a binocular head-mounted video display system, video cameras mounted on the head-mounted display, and real-time video image processing in a system package that is battery powered and portable. Through a phased development approach, several generations of the LVES can be made available to the patient in a timely fashion. This paper describes the LVES project with major emphasis on technical problems encountered or anticipated during the development process.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Many useful applications of technology have been developed for the visually impaired. Many other devices have been developed but remain on laboratory shelves; others again have experienced problems in achieving widespread acceptability due to such problems as training, maintenance, cost, human factors considerations, difficulty in production, and other factors. The present paper examines some of these factors in order to shed light on how such problems might be avoided or solved in the future. To date, more effort in high technology has been brought to bear on problems of the blind than those of the partially sighted, so examples are drawn from the former as well as the latter to illustrate the points made here.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

This study was designed to determine optimal levels of illumination for reading for patients with age-related maculopathy. These patients comprise a large percentage of the low vision population, and illumination has a great impact on their reading ability. For many patients in this study, increased illumination levels improved their performance. Eleven of the 18 patients preferred illumination levels as high as 5920 to 7534 lux (550 to 770 ft-c). This information suggests that illumination levels higher than previously recommended will improve reading speed in most patients with age-related macular degeneration (ARMD).

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Anatomical comparisons of the horizontal visible iris diameter (HVID) and the average keratometry (Kav) measurements were made between Asians and Caucasians and also between males and females. It was found that the HVID was significantly different as a function of both culture and gender. Also found was a significant difference in the Kav between males and females but not between Asians and Caucasians.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

I measured the refractive errors of 210 eyes of 105 subjects by means of the Canon Autoref R-1 and by the Nikon autorefractometer NR7000. I also measured their dark focus of accommodation (DF) with the Canon instrument. Refractive errors had similar effects on the differences between the results produced by the two autorefractometers and on the changes in DF. The differences were statistically significant. Differences between the results produced by the two autorefractometers are thought to be mainly due to instrument myopia, which itself is strongly related to the resting state of accommodation. My results indicate a hyperopic shift in high hyperopes when they are observing through an instrument.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The effects of rigid contact lens base curve radius changes on tear pump efficiency were determined by measuring oxygen uptake on six with-the-rule corneas (with toricities between 0.37 and 1.00 D) under three conditions: (1) normal open eye, (2) after 5 min of static (without blinking) wear of polymethyl methacrylate (non-gas permeable) contact lenses, and (3) after 5 min of dynamic (with blinking once every 5 s) wear of the same lenses. The difference between the oxygen uptake rates measured under static and dynamic conditions provides an index of tear pump efficiency. Each subject wore a series of five lenses: fitted on K and 0.05 or 0.10 mm steeper and flatter than the flattest corneal meridian. The overall diameter of all lenses was 8.8 mm, the optic zone was 7.4 mm, the axial edge lift was 0.09 mm, and all other parameters were constant. The contact lens fitted on K was associated with the greatest central corneal oxygen debt under static conditions, whereas the same lens also provided for the best tear exchange with the blink. In addition, better tear exchange was found to be associated with larger palpebral aperture sizes.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID