Mobility performance with retinitis pigmentosa

Purpose : Reduced mobility can have a serious impact on quality of life. Though previous studies have demonstrated that some vision measures relate to the mobility of subjects with simulated and true low vision, the relationship between residual vision and mobility is not clear. We investigated the relationship between clinical vision measures and mobility performance under different illumination levels for subjects with retinitis pigmentosa (RP). Methods : Binocular visual acuities, letter contrast sensitivities and static central threshold visual fields were measured on 10 subjects with RP and nine age-matched control subjects. Mobility performance was measured on an indoor mobility course at high and low illuminances and was assessed by percentage preferred walking speed (PPWS) and number of errors. Results : The RP group showed significantly reduced PPWS and greater numbers of errors than the control group. The reduction in illumination resulted in significantly worse error and PPWS scores. Unlike the control group, the presence of a glare source did not reduce the PPWS of the RP group under high illumination. Multiple regression analyses showed that the average visual field extent was the most significant predictor of mobility; letter contrast sensitivity and visual acuity added to the regression models for the low illumination measures to account for up to 75 per cent of the variation in mobility performance. Conclusions : People with RP have worse mobility than people with normal vision, more so under reduced illumination levels. Visual field extent was the strongest predictor of mobility performance. (Clin Exp Optom 1996; 80: 1: 1–12)     

Mobility performance of low‐vision adults using an electronic mobility aid

Visually impaired people rank obstacle location and identification as two of the most important mobility problems faced. Traditional mobility aids (the long cane) provide information about where an object is located but only within their limited (one metre) range. Although objects are located when traditional aids are used, it is unlikely that they are identified. The Bristol Mobility Aid (BMA) is an electronic travel aid that presents scene images to remaining residual vision in a number of view formats. Previous work has suggested visually impaired observers have better static object recognition using this aid. We investigated the mobility performance of subjects with retinitis pigmentosa using the BMA by determining the percentage preferred walking speed (PPWS), and the number of errors made with three different BMA headset views on an indoor mobility course. We found low‐vision subjects had significantly reduced PPWS in two of the three headset views and interestingly, sighted subjects had significantly reduced PPWS when using the BMA in all three views. The numbers of errors made were significantly higher across all vision groups when the BMA was worn. We found that the BMA does not currently increase mobility in the visually impaired. Results are discussed in terms of modifications that could be made to the aid and methodological limitations.     

Computer hardware and software to assist the visually impaired and blind

Modern developments in computer hardware and software for the business world have been adapted to allow the partially sighted and blind to participate successfully in computer usage in education, employment and recreation. Adaptations such as the enlargement of the whole screen display, production of enlarged print and voice output of screen contents can assist the partially sighted. Conversion of computer screen information into speech or braille can be used in conjunction with sound boards and touch pads to allow the totally blind access to the exact spatial layout of screen contents
Optical character recognition devices whereby the printed page can be accessed by computer, and recent voice recognition techniques which allow a computer to interpret voiced commands, can also be used to assist the totally blind. Developments in these areas are discussed together with specific examples of equipment now available which make use of the various methods described     

Orientation and mobility outcome measures

Despite orientation and mobility (O&M) being a significant factor determining quality of life of people with low vision or blindness, there are no gold standard measures or agreement on how to measure O&M performance. In the first part of this systematic review, an inventory of O&M outcome measures used by recent studies to assess the performance of orientation and/or mobility of adults with vision impairment (low vision and blindness) is presented. A wide variety of O&M outcome measures have been implemented in different fields of study, such as epidemiologic research and interventional studies evaluating training, assistive technology, vision rehabilitation and vision restoration. The most frequent aspect of outcome measures is efficiency such as time, distance, speed and percentage of preferred walking speed, followed by obstacle contacts and avoidance, and dis/orientation and veering. Other less commonly used aspects are target identification, safety and social interaction and self-reported outcome measures. Some studies employ sophisticated equipment to capture and analyse O&M performance in a laboratory setting, while others carry out their assessment in real-world indoor or outdoor environments. In the second part of this review, the appropriateness of implementing the identified outcome measures to assess O&M performance in clinical and functional O&M practice is evaluated. Nearly a half of these outcome measures meet all four criteria of face validity (either clinical or functional), responsiveness, reliability and feasibility and have the potential to be implemented in clinical or functional O&M practice. The findings of this review confirm the complicated and dynamic nature of O&M. Multiple measures are required in any evaluation of O&M performance to facilitate holistic assessment of O&M abilities and limitations of each individual.     

Preferred walking speed for assessment of mobility performance: sighted guide versus non‐sighted guide techniques

Background: If visually impaired people had their sight fully restored, it is assumed that they would walk at their optimal speeds. Previous mobility studies have used preferred walking speed (PWS) to measure walking efficiency of visually impaired adults. Therefore, the actual speeds that visually impaired people adopt on a route can be expressed as a percentage of their preferred walking speed (PPWS). There have been two approaches used in previous studies for determining preferred walking speed.

• 1 the sighted guide technique (SG), which requires a subject to walk with a sighted guide and regard the latter as a perfect mobility aid, with the subject setting the preferred (optimal) walking pace.
• 2 the non‐sighted guide technique (NonSG), which requires a subject to walk alone along an unobstructed straight path for a certain distance, adopting the preferred (optimal) walking speed.

There is some debate on which technique is the better. This study was conducted to determine if there is any difference between the two techniques for determining visually impaired subjects' preferred walking speeds. Methods: Fourteen visually impaired adult subjects were recruited. PWS was determined by recording the time taken for a subject to walk an unobstructed, straight 20‐metre corridor path using each technique. Results: There was no significant difference in PWS using the sighted guide and non‐guided techniques. Conclusions: Either the SG or NonSG techniques can be used to determine PWS for a heterogeneous group of visually impaired subjects.     

Visual performance and reading capacity of partially sighted persons in a rehabilitation center

Visual acuity and reading performance of 178 partially sighted patients from a rehabilitation center were measured using a TV text display device. A linear relation was demonstrated between visual acuity and reading speed for patients with visual acuity values below 15% of the normal value. With respect to reading performance, three groups of partially sighted patients could be distinguished: (1) 25% of the patients are unable to read visually and require tactile reading aids; (2) 50% are partially sighted and require high-magnification electronic reading aids; (3) 25% can read normal text by using optical magnifying devices. There is evidence that reading performance is related to the nature of the underlying ocular problem, such as refractive anomalies, macular degeneration, or other diseases.     

Measurements of preferred walking speed in subjects with central and peripheral vision loss

BACKGROUND: Previous mobility studies have used Preferred Walking Speed (PWS) in order to determine the walking efficiency in terms of the Percent Preferred Walking Speed (PPWS) of visually impaired adults. PWS has been measured in previous studies using the sighted guide (SG) and non-sighted guide (NSG) techniques. This study compared the NSG, SG and string (ST) (subjects walked by holding on lightly to a cardboard tube attached to a piece of string) techniques of measuring PWS in visually impaired subjects. METHODS: Forty visually impaired subjects with central and peripheral vision loss were recruited. PWS was measured using the NSG, SG and ST techniques. For each technique, PWS was determined by recording the time taken for a subject to walk an unobstructed, straight 20-m corridor. RESULTS: There were no significant differences in PWS using the SG, NSG and ST techniques. CONCLUSION: For assessing walking efficiency, either the SG, NSG or ST technique could be employed when measuring PWS in visually impaired subjects.     

Problems to be overcome in high-tech devices for the visually impaired.

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.     

Vision and mobility performance of subjects with age-related macular degeneration.

PURPOSE: To investigate the effects of age-related macular degeneration (ARMD) on mobility performance and to identify the vision determinants of mobility in subjects with ARMD. METHODS: Walking speed and the number of obstacle contacts made on a 79-m indoor mobility course were measured in 21 subjects with ARMD and 11 age-matched subjects with normal vision. The mobility measures were transformed to percentage preferred walking speed and contacts score. The vision functions assessed included binocular visual acuity, contrast sensitivity, and visual field. RESULTS: In this study, subjects with ARMD did not walk significantly slower or make significantly more obstacle contacts on the mobility course than the normally sighted subjects of similar age. Between 29% and 35% of the variance in the ARMD mobility performance was accounted for by visual field and contrast sensitivity measures. The most significant predictor of mobility performance scored as percentage preferred walking speed was the size of a binocular central scotoma. CONCLUSION: As the size of a binocular central scotoma increases, mobility performance decreases.     

Contrast enhancement in the public environment--improvement in orienting capacity of visually handicapped patients]

BACKGROUND: Partially sighted often experience problems in orientation in public areas. Individual visual aids can only be used with limitations. Improving light intensity and colour contrasts of timetables, information signs, direction symbols, etc. can provide remedies. Experimentally substantiated directives do not yet exist. PATIENTS AND METHODS: Experiments were conducted in 231 partially sighted subjects (binocular vision < 0.3) diagnosed as experiencing dullness when watching the media, having maculopathies, glaucomas, or dystrophic alterations of the retina or choroid, and in 43 normal subjects to determine the subjective assessment of colour and light-intensity contrasts. The presented contrast patterns were Hartmann-characters as infield (3.3 degrees) with a rectangular surround (19.5 degrees x 14.3 degrees). Three experimental series were carried out in which subjects assigned 14 non-coloured/non-coloured contrasts, 35 non-coloured/colour contrasts and 30 colour/colour contrasts to any of the five assessment classes of extremely poor, poor, optimal, sharp, extremely sharp. The colour contrasts consisted of combinations of yellow, green, red, purple, blue, and non-coloured. RESULTS: For non-coloured/non-coloured, the subjects preferred positive contrasts (bright infield, dark surround). Preferred contrast levels were 0.91 to 0.99 for positive contrasts and -0.96 to -0.99 for negative contrasts. For colour/non-coloured contrasts, 90% of the partially sighted preferred yellow as the foreground colour with a contrast level above 0.89. For colour/colour contrasts, optimal assessments of 90% of all partially sighted were yellow/purple and yellow/blue with contrast levels above 0.90. The determined results are applicable for the exact experimental contrast settings only. A field manual was prepared for planning and design of contrasts suited for the partially sighted in public areas. CONCLUSIONS: Partially sighted, in subjective contrasts assessment, prefer bright characters of signs on a dark background for both non-coloured and colour contrasts with contrast levels above 0.9. Yellow was the preferred infield colour.     

Features of the development of a welfare system for visually disabled people in Denmark

PURPOSE: To describe the development of a formal system of welfare for blind and partially sighted people in Denmark. METHODS: The principal laws in Denmark relating to a formal system of welfare for blind and partially sighted people are noted and commented on. No such collection of laws has been found in the literature. The history of aid to visually disabled people in Denmark is described, as are the Danish classifications of visual impairment. DEVELOPMENT: Formalized welfare for blind and partially sighted people was started in Denmark in 1811, as a private initiative by the Kjaede Order. Later, the Danish state took over responsibility, and in 1858 the Royal Danish Institute for the Blind was established. Since then a series of laws concerning welfare for blind and partially sighted people have been issued in accordance with economic and social development in Denmark. In 1858 the Braille writing system for blind people was introduced. The Danish Association of the Blind was founded in 1911 and has profoundly influenced subsequent legislation. During the last 10 years, several visual centres have been established. Since 1968 prevention of blindness has also played a prominent role in Denmark. CONCLUSION: Great steps have been taken towards improving the welfare of blind and partially sighted people. However, being blind is still very difficult. Modern technologies and hectic lifestyles have created new problems for blind people. The obligations of the Danish state towards visually disabled people have, therefore, increased in recent years.     

The incidence of visual impairment due to diabetic retinopathy in Leeds

AIM: A key aim of the photographic screening model for diabetic retinopathy advocated by the National Screening Committee is a reduction in new blindness due to diabetic retinopathy within 5 years. This study determines the incidence of visual impairment due to diabetic retinopathy in Leeds in 2002 and provides a benchmark against which the success of the retinopathy screening programme in Leeds will be judged. METHODS: A retrospective review of all blind and partially sighted registrations for 2002 was conducted. The 2001 Census data and the diabetes prevalence model developed by the Yorkshire and Humber Public Health Observatory were used to determine the total and diabetic populations of Leeds. RESULTS: Diabetic retinopathy was the primary cause of registration in 24 of the 398 completed records obtained; seven patients were registered blind and 17 partially sighted. For the total population in 2002, the incidence of blind and partially sighted registration due to diabetic retinopathy was 10 per million and 24 per million per year, respectively. For the diabetic population of Leeds in 2002, the incidence of blind and partial sighted registration due to diabetic retinopathy was 337 and 817 per million per year, respectively. CONCLUSIONS: The incidence of blind registration due to diabetic retinopathy in Leeds in 2002 is similar to the estimate provided by the National Screening Committee but higher than the figure from other UK centres.     

Social costs of visual handicap and blindness. Rehabilitation resources for blind patients]

The number of blind and partially sighted persons in Germany is growing. Increasing social cost and human suffering are related. Measures to counteract this development (e.g. prevention, rehabilitation) are needed. This work gives an overview of the social cost of visual impairment; rehabilitation efforts and needs for eye diseases are considered. MATERIALS AND METHODS: Data from several sources have been analysed in regard to social cost of blindness and rehabilitation efforts for eye diseases: e.g. from the Bavarian and Federal statistical agencies (number of blind and partially sighted), form the German veterans administrations (number of early retired) etc. The results relate to the former Federal Republic of Germany before unification; data from the five new states are not yet available. RESULTS: 1. social cost: The funds needed for blindness compensation payments increased steadily; new figures from Bavaria indicate that in Germany a total of 1,000,000 DM is needed. As a trend the yearly rise over the last 10 years was 6% in Bavaria. Indirect social cost ist caused by early retirement of blind or visually handicapped people; yearly 1% (2000 cases) of all early retirement is due to eye diseases. 2. rehabilitation efforts: For the annual incidence of blind and partially sighted--an estimated 17,000 blind and 50,000 partially sighted--only 12,000 rehabilitation measures are provided in Germany. For the age group over 65 years (which makes up to 60% of all visually impaired) only 800 rehabilitation measures are being completed yearly. In the ophthalmology sector the provision of low vision aids to visually handicapped people is incomplete. A maximum of 60% of all practising ophthalmologists in Bavaria provide this service. On the basis of own data (and from the medical service of medical assistance insurances) it is obvious that 20-50% of the prescribed low vision aids do not fit the requirements of the visually handicapped. In general too high a magnification is prescribed. CONCLUSIONS: More visual rehabilitation services are needed to cope with the growing demand, especially for low vision aids. A prerequisit for a higher coverage with low vision aids is a better reimbursement of the prescribing ophthalmologist by medical assistance insurances.     

Use of Cataract Services in Eastern Africa—A Study from Tanzania

Purpose: To establish the proportion of patients who are blind or have low vision prior to undergoing cataract surgery at tertiary referral centers in Tanzania. To assess which patient groups presenting for cataract surgery are more likely to be blind or visually impaired. Methods: Using pre-existing computerized audit systems we gathered data on pre-operative visual status, age, gender and presentation mode (walk-in or outreach) for 3765 patients undergoing 4258 cataract operations at 2 hospitals in Tanzania. Visual status was defined based on vision in the better eye. Results: 32% of operations were performed on blind patients, 37% on patients with low vision and 31% on normally sighted patients. Predictors of blindness at presentation were: female sex (OR 1.15; 95% CI 1.00–1.32); referral from a rural outreach program (OR 1.75; 95% CI 1.51–2.02) and older age (OR 1.02; 95% CI 1.01–1.02). Conclusions: It is not only the blind who present to cataract services in Tanzania. The demand for surgery amongst patients who or are normally sighted represents a positive move towards prevention, and not only cure of cataract blindness in Tanzania. However, it also highlights the need to target those left blind from cataract in order to deliver services to those most in need. Cataract programs targeting patients in rural areas and older patients are likely to increase the number of blind patients benefiting from cataract services.     

Vision and self‐reported mobility performance in patients with low vision

Background: As vision plays a significant role in mobility performance, it is usual to refer low vision patients, particularly those who complain of mobility difficulties, for orientation and mobility (O&M) training to help them maintain safe independent travel. Our study aimed to determine whether there was a relationship between measures of vision and self‐reported mobility, and the applicability of a patient‐based mobility assessment in patients with heterogeneous causes of visual loss. Method: We assessed the high and low contrast visual acuity, visual field and scanning ability of 30 patients with low vision. A validated mobility questionnaire was used to assess the participants’ perceived visual ability for independent mobility. Results: Vision was significantly correlated with self‐reported mobility performance, however, visual field was a significant predictor accounting for 56.5 per cent of the variance. The instrument was well constructed with valid content and high reliability scores. Conclusions: Self‐reported mobility performance together with measures of vision could be used as a guide to refer patients for O&M training. The patient‐based assessment instrument was valid to measure perceived visual ability for independent mobility in patients with heterogeneous causes of visual loss.     

Real-world indoor mobility with simulated prosthetic vision: The benefits and feasibility of contour-based scene simplification at different phosphene resolutions

Neuroprosthetic implants are a promising technology for restoring some form of vision in people with visual impairments via electrical neurostimulation in the visual pathway. Although an artificially generated prosthetic percept is relatively limited compared with normal vision, it may provide some elementary perception of the surroundings, re-enabling daily living functionality. For mobility in particular, various studies have investigated the benefits of visual neuroprosthetics in a simulated prosthetic vision paradigm with varying outcomes. The previous literature suggests that scene simplification via image processing, and particularly contour extraction, may potentially improve the mobility performance in a virtual environment. In the current simulation study with sighted participants, we explore both the theoretically attainable benefits of strict scene simplification in an indoor environment by controlling the environmental complexity, as well as the practically achieved improvement with a deep learning-based surface boundary detection implementation compared with traditional edge detection. A simulated electrode resolution of 26 × 26 was found to provide sufficient information for mobility in a simple environment. Our results suggest that, for a lower number of implanted electrodes, the removal of background textures and within-surface gradients may be beneficial in theory. However, the deep learning-based implementation for surface boundary detection did not improve mobility performance in the current study. Furthermore, our findings indicate that, for a greater number of electrodes, the removal of within-surface gradients and background textures may deteriorate, rather than improve, mobility. Therefore, finding a balanced amount of scene simplification requires a careful tradeoff between informativity and interpretability that may depend on the number of implanted electrodes.     

Measuring mobility performance: experience gained in designing a mobility course

Background: This paper reviews the most common methods of measuring and scoring orientation and mobility (O and M) and the effects of visual impairment on O and M. We discuss the difficulties inherent in designing a ‘real‐world’ course to measure O and M and we describe the course that we finally used. Methods: Thirty‐five participants in two age groups, with low vision due to a variety of disorders, took part in mobility trials on the final version of the course. Aspects of visual function were measured. Results: Factor analysis indicated that mobility errors, visual detection distance and visual identification distance were grouped with measures of visual acuity, contrast sensitivity and Humphrey visual field mean deviation, while preferred walking speed and walking speed were separately grouped. Humphrey pattern standard deviation did not group with any other measure and neither did percentage preferred walking speed. This study is in agreement with other studies that visual field and contrast sensitivity, sometimes with low contrast visual acuity, were the best clinical visual predictors of mobility performance. Based on our experiences we present a number of recommendations for designing courses for assessing mobility. Conclusions: For future studies, it would behove researchers to include a range of mobility measures, until further understanding is gained about how they are interrelated and contribute information on the relationship among mobility, vision and other individual factors.     

An evaluation of night vision mobility aids

Two night vision aids are commercially available to help individuals who have diseases that cause night blindness. The ITT Night Vision Aid (NVA) is a light amplification device; the Wide Angle Mobility Light (WAML) is a wide beam flashlight. The effectiveness of both instruments in helping night-blind, field-restricted subjects to walk a course of residential streets at night was tested. WAML users were also surveyed to determine the usage, applications, and reliability of the device. We found that the WAML significantly reduced error rates and was preferred by most subjects; it was reported to be used regularly by individuals who owned it. The NVA did not significantly improve error scores, and was not effective as an ambulatory night mobility aid for most patients.     

Illumination research as part of a visual assessment of visually impaired individuals

In this paper we describe a method for the preliminary assessment of the illumination needs of partially sighted individuals. The method is based on determining the smallest readable lettersize under different levels of illumination. Half of the partially sighted in our population had a performance that was dependent upon the level of illumination. At the same time, most of those for whom no improvement in performance was found, did express a preference for a certain level of illumination. Therefore, there remain discrepancies between the objectively determined optimal level and the preference for a certain level. We conclude that the current method is a useful but insufficient method of determining the illumination needs of partially sighted individuals.     

Visual–tactile shape perception in the visually restored with artificial vision

Retinal prostheses partially restore vision to late blind patients with retinitis pigmentosa through electrical stimulation of still-viable retinal ganglion cells. We investigated whether the late blind can perform visual–tactile shape matching following the partial restoration of vision via retinal prostheses after decades of blindness.We tested for visual–visual, tactile–tactile, and visual–tactile two-dimensional shape matching with six Argus II retinal prosthesis patients, ten sighted controls, and eight sighted controls with simulated ultra-low vision. In the Argus II patients, the visual–visual shape matching performance was significantly greater than chance. Although the visual–tactile shape matching performance of the Argus II patients was not significantly greater than chance, it was significantly higher with longer duration of prosthesis use. The sighted controls using natural vision and the sighted controls with simulated ultra-low vision both performed the visual–visual and visual–tactile shape matching tasks significantly more accurately than the Argus II patients. The tactile–tactile matching was not significantly different between the Argus II patients and sighted controls with or without simulated ultra-low vision.These results show that experienced retinal prosthesis patients can match shapes across the senses and integrate artificial vision with somatosensation. The correlation of retinal prosthesis patients’ crossmodal shape matching performance with the duration of device use supports the value of experience to crossmodal shape learning. These crossmodal shape matching results in Argus II patients are the first step toward understanding crossmodal perception after artificial visual restoration.