A self-assessment instrument designed for measuring independent mobility in RP patients: generalizability to glaucoma patients

PURPOSE: To determine whether the patient-based assessment of difficulty in mobility, developed and validated in a group of patients with retinitis pigmentosa (RP), is valid for measuring perceived visual ability for independent mobility in patients with glaucoma. METHODS: A mobility questionnaire that had previously been developed was administered to 83 patient-volunteers who had various amounts of visual impairment caused by glaucoma. Each volunteer rated the perceived difficulty of walking independently in each of 35 mobility situations. A Rasch analysis of the ordinal difficulty ratings was used to estimate interval measures of perceived visual ability for independent mobility. RESULTS: The instrument showed good construct and content validity and high reliability scores. Criterion validity of the instrument was demonstrated by its ability to discriminate mobility-related behaviors such as fear of falling, asking for accompaniment, and believing their ability to travel independently is less than that of persons with normal vision. To make the perceived mobility scale comparable for the two diagnostic groups the questionnaire was restricted to those items whose difference in item-logit distributions was within +/-3 (18 items). Using the same instrument calibration, we compared the person measures between the patients with glaucoma and those with RP. Patients with glaucoma had, on average, higher perceived visual ability for independent mobility than those with RP. CONCLUSIONS: The instrument developed for patients with RP, to determine difficulty across a range of mobility situations, is a valid measure of perceived ability for independent mobility in patients with glaucoma.     

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.     

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.     

Extended wearing trial of Trifield lens device for ‘tunnel vision’

Severe visual field constriction (tunnel vision) impairs the ability to navigate and walk safely. We evaluated Trifield glasses as a mobility rehabilitation device for tunnel vision in an extended wearing trial. Twelve patients with tunnel vision (5–22° wide) due to retinitis pigmentosa or choroideremia participated in the 5‐visit wearing trial. To expand the horizontal visual field, one spectacle lens was fitted with two apex‐to‐apex prisms that vertically bisected the pupil on primary gaze. This provides visual field expansion at the expense of visual confusion (two objects with the same visual direction). Patients were asked to wear these spectacles as much as possible for the duration of the wearing trial (median 8, range 6–60 weeks). Clinical success (continued wear, indicating perceived overall benefit), visual field expansion, perceived direction and perceived visual ability were measured. Of 12 patients, nine chose to continue wearing the Trifield glasses at the end of the wearing trial. Of those nine patients, at long‐term follow‐up (35–78 weeks), three reported still wearing the Trifield glasses. Visual field expansion (median 18, range 9–38°) was demonstrated for all patients. No patient demonstrated adaptation to the change in visual direction produced by the Trifield glasses (prisms). For reported difficulty with obstacles, some differences between successful and non‐successful wearers were found. Trifield glasses provided reported benefits in obstacle avoidance to 7 of the 12 patients completing the wearing trial. Crowded environments were particularly difficult for most wearers. Possible reasons for long‐term discontinuation and lack of adaptation to perceived direction are discussed.     

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)     

Quality of life after postoperative endophthalmitis

Purpose: The aim of this study is to determine if postoperative endophthalmitis adversely affects quality of life after cataract surgery. Methods: We compared quality of life in patients who developed endophthalmitis after cataract surgery between 1 January and 31 December 2003 with those who had uncomplicated surgery. The National Eye Institute VFQ‐25 (VFQ‐25) and EuroQol EQ‐5D (EQ‐5D) questionnaires and time trade‐off utility scores were used to compare self‐perceived general health and vision‐related quality of life between groups. Linear regression was used to model differences between groups after adjusting for age, gender and visual acuity in the better eye. Results: Nineteen postoperative endophthalmitis cases were compared with 30 who had uncomplicated cataract surgery. Following surgery the mean composite VFQ‐25 score was 13.5% (95% confidence interval [CI]: 6.0–26.4, P < 0.01) lower in endophthalmitis cases. Endophthalmitis patients reported significantly lower (P < 0.05) general vision, near vision, peripheral vision, mental health and role difficulties subscales scores after adjusting for age, sex and visual acuity. No significant differences were found in other subscales. Mean time trade‐off utility and all EQ‐5D scores were similar except for mobility (95% CI: 0.04–0.68, P < 0.05). Conclusions: Endophthalmitis after cataract surgery negatively impacts on self‐perceived vision‐related quality of life, resulting in poorer psychological well‐being and ability to maintain a role in daily life.     

Referral to low vision services by ophthalmologists

Purpose: People in need of low vision rehabilitation services often experience delays in referral to services. This study investigated referral criteria of Australian ophthalmologists, the frequency of referral of their patients with low vision and their perceptions of low vision services.
Methods: A survey was sent to a representative, random sample of 200 ophthalmologists. They were asked about criteria used for the referral of their patients with low vision. The survey included questions on the frequency with which they prescribed low vision devices (LVD) and referral of their patients to low vision and rehabilitation services and peer support groups. Perceptions of the quality and availability of low vision services were also investigated.
Results: The response rate was 82%. Approximately 11% of ophthalmologists' patients have low vision. It is uncommon for ophthalmologists to prescribe LVD but 67% refer most of their patients with low vision. It is less common for them to refer to rehabilitation services (29%) or peer support services (18%). The perceived local availability of services influences the rate of referral. Ophthalmologists who used the criteria of moderate low vision (<6/21 to <6/60) are more likely to refer more of their patients than those who use the criteria of severe low vision.
Conclusions: Australian ophthalmologists refer most of their visually impaired patients to low vision services, but infrequently to rehabilitation services or peer support groups. Differences in perceived need for low vision services indicated by the criteria used for referral, and the perceived availability, influence the rate at which ophthalmologists refer their patients for services. Ophthalmologists are encouraged to refer patients with permanent visual loss to low vision services earlier.     

对比度视力检查在视感知觉学习治疗前后的临床应用研究

目的：评估屈光不正患儿视感知觉学习治疗前后的对比度视力变化,探讨视觉质量及视功能的临床意义。方法对视感知觉学习治疗的屈光不正患者50名（100眼）,随机分为两组采用电子视力测量仪检查对比度视力,评估视功能。结果所有患者视感知觉学习训练后对比度视力较国际标准视力改善明显,其中低屈光度数患者改善更明显;治疗后国际标准视力无改善的患者,对比度视力的低亮、标低仍有改善,P〈0.05。结论对比度视力能全面的反应明视力及暗视力,同时视感知觉学习训练对提高屈光不正患者对比敏感度及视力有效,值得推广。     

Difficulty in performing everyday activities in patients with juvenile macular dystrophies: comparison with patients with retinitis pigmentosa

AIMS—To ascertain the level of perceived difficulty experienced by patients with central vision loss due to juvenile macular dystrophies in the performance of everyday activities. A second objective was to compare their perceived difficulty with that of patients with retinitis pigmentosa (RP) with primarily peripheral vision loss.
METHODS—72 patients with Stargardt disease, cone dystrophy, or cone-rod dystrophy who had visual acuities worse than 20/40 and normal peripheral visual fields rated themselves on their difficulty in the performance of 33 activities encompassing a wide variety of everyday tasks. These findings were compared with the responses of 120 patients with typical RP or Usher syndrome type 2 who had visual acuities of 20/40 or better and peripheral visual field loss.
RESULTS—The juvenile macular dystrophy group reported the greatest level of overall self perceived difficulty with activities involving central vision, and lesser and variable degrees of difficulty with items within the mobility, negotiating steps, driving, and miscellaneous categories. Consistent with these findings, there were highly significant correlations between subjects' rated performances of activities involving central vision and the clinical measures of vision, including visual acuity and size of central scotoma. There were fewer significant correlations between perceived performance of activities in the other categories and the clinical measures. In general, those activities that showed significant correlations with the clinical measures of vision for the patients with juvenile macular dystrophies also showed significant differences in the patterns of responses between the juvenile macular dystrophy group and the RP group. Those items which were not correlated with the clinical measures in the juvenile macular dystrophy group tended not to show significant differences in the response patterns between the two groups.
CONCLUSION—These results provide insight into the types of perceived difficulties in performing tasks of everyday life in patients with these disorders which affect counselling of these patients.

Keywords: vision; impairment; everyday activities; juvenile macular dystrophy     

Perceived visual ability for functional vision performance among persons with low vision in the Indian state of Andhra Pradesh

PURPOSE: To determine the distribution of perceived visual ability for functional vision performance among persons with low vision in the Indian state of Andhra Pradesh. METHODS: As part of a population-based epidemiologic study, the Andhra Pradesh Eye Disease Study (APEDS), a 16-item visual function questionnaire was designed and applied to 7363 persons older than 15 years, to record the levels of difficulty perceived by the subjects. Of these, 123 persons were found to have low vision. Rasch analysis was used to convert the ordinal difficulty ratings of these 123 persons into interval measures of perceived visual ability for functional vision. RESULTS: Content validity of the questionnaire was demonstrated by good separation indices (3.17 and 5.44) and high reliability scores (0.91 and 0.97) for person and item parameters. Construct validity was shown with model fit statistics. Criterion validity of the questionnaire was shown by good discrimination among the general vision ratings. The functional situation that required the least visual ability was "reaching an object farther or closer than you thought"; the situation requiring the most visual ability was "recognizing small objects." Bivariate regression analysis determined that for every unit of logMAR visual acuity, perceived visual ability for functional vision decreased by 2.9 logit, which could explain 32% of the variability in the person measure. CONCLUSIONS: The described assessment, across a range of visual problems, is a valid way to measure perceived ability for functional vision in persons with low vision. Perceived visual ability varies with every unit of logarithm of the minimum angle of resolution (logMAR) visual acuity.     

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.     

Which factors influence patients’ maximum acceptable waiting time for cataract surgery? – a questionnaire survey

Purpose: To evaluate patients’ maximum acceptable waiting time (MAWT) and to assess the determinants of patient perceptions of MAWT. Methods: A total of 500 consecutive patients with cataract were asked to fill out a preoperative questionnaire, addressing patients’ MAWT to undergo cataract surgery. Patients’ visual impairment (VF‐14 score), education, profession and social status were evaluated, and an ophthalmologic examination was performed. Univariate analysis included Spearman’s correlation test, unpaired Student’s t‐test and the Mann–Whitney U test. Univariate and multivariate associations were calculated using unconditional logistic regression. Results: The mean MAWT was 3.17 ± 2.12 months. The mean VF‐14 score was 72.10 ± 22.54. Between VF‐14 score and MAWT, there was a significant correlation (r = 0.180, p = 0.004). Patients with higher education (high school, university) accepted significantly longer MAWT (3.92 ± 2.38 months versus 3.02 ± 2.00 months, p = 0.009). Patients who had self‐noticed visual impairment were nearly four times (OR: 3.88, 95% CI = 2.07–7.28, p < 0.001) more likely to accept only MAWT of <3 months. Conclusions: Patients with low tolerance for waiting had greater self‐reported difficulty with vision. Patients’ acceptance of waiting was not associated with clinical visual acuity measures. Education, ability to work, living independently and taking care of dependents were also strong predictors from patients’ perspective. Considering the implementation of standards for waiting lists, these facts should be taken into account.     

老年低视力和盲的病因及光学助视器在康复中的应用

目的:分析老年低视力和盲的病因及光学助视器在康复中的应用.方法:收集我院老年视力残疾患者87例,其中低视力74例,盲13例.其中男53例,女34例.先进行常规内外眼检查,必要时采用特殊检查,再进行病因分析.均屈光矫正,然后试配远用和近用光学助视器,检查配戴助视器后远、近视力,远视力≥0.05为脱盲,远视力≥0.3为脱残,近视力≥0.5为有效,<0.5为无效.结果:老年低视力患者致盲原因占首位的是高度近视,其次为黄斑变性、各类白内障、青光眼、糖尿病视网膜病变.经屈光矫正后视力提高≥2行者62例(71%),视力不矫正或矫正≤1行者25例(29%).联合远用助视器后视力≥0.3脱残者70例(80%),远视力≥0.05脱盲者10例(11%),<0.05者7例(8%),脱残率92%.配阅读眼镜及近用助视器后近视力>0.5者 60例(69%),<0.5者27例(31%).助视器经常使用者58例,不经常使用18例,基本不用或放弃者11例.结论:老年低视力及盲的病因占首位的是高度近视,其次是黄斑病变.光学助视器在其康复中的应用仍是目前可靠、经济、有效的矫治方法,应鼓励患者使用助视器,提高助视器的利用率,从而提高患者的生活质量.     

年龄相关性白内障患者的综合性视觉功能指数与跌倒影响因素之间的关系

目的：：探讨年龄相关性白内障患者的综合性视觉功能指数与跌倒影响因素之间的关系。方法：纳入96例年龄相关性白内障术前患者作为受试者,使用综合性视觉功能指数( visual-functioning index, VF-7)问卷法评估受试者的综合性视觉功能。根据其结果进行分组,比较组间的跌倒影响因素差异性,包括视力、平衡功能、移动功能、认知及抑郁状态、对跌倒的担心等。结果：其中VF-7得分较低组的受试者,其年龄通常较大,有抑郁倾向,以及更担心跌倒;得分较低组的受试者视力、平衡功能和移动功能也较差。结论：不同水平的综合性视觉功能指数的年龄相关性白内障老年患者,其跌倒影响因素,包括视力、平衡功能、移动功能之间有显著的差异。综合性视觉功能指数作为一种简单方便的自评检查方式,可以用作对年龄相关性白内障患者的跌倒风险监测。     

Visual function and subjective quality of life compared in subjects with acquired macular disease

PURPOSE: To determine the objective measures of visual function that are most relevant to subjective quality of vision and perceived reading ability in patients with acquired macular disease. METHODS: Twenty-eight patients with macular disease underwent a comprehensive assessment of visual function. The patients also completed a vision-related quality-of-life questionnaire that included a section of general questions about perceived visual performance and a section with specific questions on reading. RESULTS: Results of all tests of vision correlated highly with reported vision-related quality-of-life impairment. Low-contrast tests explained most of the variance in self-reported problems with reading. Text-reading speed correlated highly with overall concern about vision. CONCLUSIONS: Reading performance is strongly associated with vision-related quality of life. High-contrast distance acuity is not the only relevant measure of visual function in relation to the perceived visual performance of a patient with macular disease. The results suggest the importance of print contrast, even over print size, in reading performance in patients with acquired macular disease.     

Mobility and low vision: a review

Theories of mobility have been developed mainly with respect to mobility of the totally blind. How the normally sighted or the partially sighted are able to use visual information to move about in the world is not well understood. Whether the cues used by the sighted are the same as those used by the partially sighted in achieving mobility is not known. Thus the performance measures which are used have been developed on an ad hoc basis and may not be the best measures available for assessment of mobility or improvement in mobility in the partially sighted. The most important factors in mobility of the partially sighted have not been identified. They must be specified so that advice and training can be directed toward the most effective steps these patients can take in using their residual vision to achieve independent mobility.     

Is the high contrast visual acuity chart a good predictor of improvement in visual acuity with low vision aids?

Purpose:To assess whether the objective improvement seen with HCVA chart using LVAs correlates with subjective improvement in the quality of life as measured on low vision quality of life (LVQOL) questionnaire of such patients.Methods:This was a prospective, consecutive, observational study. Objective improvement in visual function was assessed using LVAs with high contrast LogMAR visual acuity chart for near and distance. Subjective improvement for distance was assessed using LVQOL score for “distance mobility and lighting”, whereas for near it was assessed using the LVQOL score for “near and fine work”. A total of 46 patients completed one follow-up after low vision trial and were included in the study.Results:Improvement in objective visual acuity was highly significant for both near and distance (P < 0.001) with LVAs. LVQOL score improved from 65.85 to 76.83 after one of using low vision aids (P < 0.001). The improvement in LVQOL score for distance and mobility was also highly significant (2.55; P < 0.001); and so was for near and fine work (5.89; P < 0.001). However, Spearman rank correlation coefficient showed no correlation between improvement in visual acuity for distance and LVQOL score improvement for distance (r_s = –.086; P = 0.57). For near also, improvement in acuity did not correlate with the LVQOL score improvement for near and fine work (r_s = 0.036; P = 0.81).Conclusion:No statistical correlation was observed between the improvements measured by objective HCVA charts and subjective improved as perceived by the patient after use of low vision devices.     

脱抑制及视功能训练治疗屈光参差性弱视的临床疗效

目的：探讨脱抑制及视功能训练治疗屈光参差性弱视患儿的临床疗效。

方法：前瞻性病例对照研究。83例屈光参差性弱视患儿纳入本研究,所有患儿均为单眼弱视,随机分为训练组(44例44眼)和对照组(39例39眼)。所有患儿常规配镜,定量遮盖,均采用家庭+诊室训练相结合的方法。对照组训练内容为：弱视训练仪(光刷、红闪、光栅等)及电脑软件精细+刺激训练。训练组除完成对照组训练项目以外,当患儿弱视眼矫正视力已经提高到0.6以上后进行单眼调节功能训练、脱抑制训练、双眼调节功能训练及双眼集合、融像功能训练。随访6mo后,对两组的视力疗效及远近立体视功能检查结果进行比较及统计学分析。

结果：训练组与对照组相比,两个组间视力改善的总有效率差异无统计学意义,但是两个组间整体的视力疗效比较差异有统计学意义(P<0.05),加入脱抑制及视功能训练后训练组远、近立体视功能改善的人数明显优于对照组,差异有统计学意义(P<0.05)。

结论：弱视治疗中加入脱抑制训练及双眼视功能训练后,能够增强弱视眼的竞争力,消除抑制,不但能提高视力,还能建立良好的视功能。     

远用光学助视器在视力残疾患者康复中的临床应用

目的:观察远用助视器在视力残疾患者的临床应用效果。方法:对32例视力残疾患者进行屈光矫正后,然后再运用单筒望远镜式助视器或眼镜式助视器提高和改善患者远用视力。结果:配用远用助视器平均视力(logMAR视力)为0.24±0.23;而在屈光矫正的基础上再应用助视器矫正的患者平均视力(logMAR视力)为0.11±0.25,即戴镜后使用远用助视器后视力好于未戴镜患者(t=4.56,P<0.05)。试戴远用助视器后25例远视力≥0.3,脱残率为78%;进行屈光矫正后,该组病例脱残率为94%(P<0.05)。结论:远用光学助视器在视力残疾患者康复有着重要作用,它可提高患者的远用视力,尤其强调在屈光矫正的基础上应用光学助视器临床疗效更为明显。