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.     

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.     

Prevalence and causes of vision loss in central Tanzania

A population-based survey of the prevalence of major blinding disorders was conducted in three villages in central Tanzania. Overall, 1827 people overthe age of seven years old were examined. In those age seven and older, the prevalence of bilateral blindness (visual acuity in the better eye of <3/60) was 1.26% and monocular blindness (visual acuity of <3/60 in one eye) was 4.32% and the prevalence of visual impairment (visual acuity <6/18 but 3/60 in both eyes was 1.04% and in one eye was 1.75%. Corneal opacities were responsible for 44% of bilateral and 39% of monocular blindness and resulted from trachoma, measles often in association with Vitamin A deficiency, keratoconjunctivitis, and the use of traditional eye medicines. Cataracts accounted for 22% of bilateral and 6% of monocular blindness. Readily preventable or reversible causes of blindness were responsible for 65% of cases of bilateral and 46% of monocular blindness.Abbreviations TEM traditional eye medicines     

Functional changes at the preferred retinal locus in subjects with bilateral central vision loss

Graefe's Archive for Clinical and Experimental Ophthalmology - Subjects with bilateral central vision loss (CVL) use a retinal region called the preferred retinal locus (PRL) for performing...     

Visual function and biofeedback training of patients with central vision loss: a review

Older individuals with macular diseases, such as age-related macular degeneration, experience central vision loss (CVL) due to degeneration of their photoreceptors and retinal cells. Patients with CVL may experience various vision impairments, including of visual acuity, fixation stability, contrast sensitivity, and stereoacuity. After CVL, most patients develop a preferred retinal locus outside the affected macular region, which serves as a new visual reference. In this review, we provide an overview of the visual function and impairment in individuals with CVL. In addition, the important role of biofeedback training on the visual function and activity of individuals with CVL is also reviewed. Accordingly, the location and development of the preferred retinal loci are discussed. Finally, this review discusses how to conduct biofeedback training to treat individuals with CVL.     

Effect of low luminance on face recognition in adults with central and peripheral vision loss

Purpose

To investigate the effect of low luminance on face recognition, specifically facial identity discrimination (FID) and facial expression recognition (FER), in adults with central vision loss (CVL) and peripheral vision loss (PVL) and to explore the association between clinical vision measures and low luminance FID and FER.

Methods

Participants included 33 adults with CVL, 17 with PVL and 20 controls. FID and FER were assessed under photopic and low luminance conditions. For the FID task, 12 sets of three faces with neutral expressions were presented and participants asked to indicate the odd-face-out. For FER, 12 single faces were presented and participants asked to name the expression (neutral, happy or angry). Photopic and low luminance visual acuity (VA) and contrast sensitivity (CS) were recorded for all participants and for the PVL group, Humphrey Field Analyzer (HFA) 24-2 mean deviation (MD).

Results

FID accuracy in CVL, and to a lesser extent PVL, was reduced under low compared with photopic luminance (mean reduction 20% and 8% respectively; p < 0.001). FER accuracy was reduced only in CVL (mean reduction 25%; p < 0.001). For both CVL and PVL, low luminance and photopic VA and CS were moderately to strongly correlated with low luminance FID (ρ = 0.61–0.77, p < 0.05). For PVL, better eye HFA 24-2 MD was moderately correlated with low luminance FID (ρ = 0.54, p = 0.02). Results were similar for low luminance FER. Together, photopic VA and CS explained 75% of the variance in low luminance FID, and photopic VA explained 61% of the variance in low luminance FER. Low luminance vision measures explained little additional variance.

Conclusion

Low luminance significantly reduced face recognition, particularly for adults with CVL. Worse VA and CS were associated with reduced face recognition. Clinically, photopic VA is a good predictor of face recognition under low luminance conditions.     

Maximum reading speed and binocular summation in patients with central vision loss

Objective

Visual acuity is a poor predictor of the maximum reading speed of patients with central vision loss. This study examines the effects of binocular summation of acuity on the maximum reading speed of these patients.

Design

Prospective, observational case series.

Participants

Twenty patients with central vision loss participated.

Methods

Maximum reading speed was measured binocularly using the MNREAD acuity charts. Monocular and binocular acuities were measured with the Early Treatment Diabetic Retinopathy Study (ETDRS) chart. Binocular summation was evaluated with a binocular ratio (BR) calculated as the ratio between the acuity of the better eye to binocular acuity. Fixation stability and preferred retinal locus (PRL) distance from the former fovea were evaluated with the MP-1 microperimetre.

Results

Six patients experienced acuity summation (BR > 1.05), 5 experienced acuity inhibition (BR < 0.95), and 9 showed equality (BR = 1 ± 0.05). There were no differences in the mean acuity of the better eye, fixation stability, or PRL distance from the fovea of the 3 groups. Maximum reading speed was significantly slower (p < 0.05) for patients who experienced binocular inhibition (mean 42 ± 27 words/min [wpm], median 40 wpm) than for those who experienced binocular summation (mean 107 ± 39 wpm, median 108 wpm) or equality (mean 111 ± 62 wpm, median 90 wpm). BR correlated with the maximum reading speed for the overall sample (r[18] = 0.49, p = 0.03). BR together with PRL distance from the former fovea in the better eye explained 45% of the variance in maximum reading speed.

Conclusions

Binocular summation of acuity rather than visual acuity alone affects maximum reading speed of patients with central vision loss. Patients with binocular inhibition read significantly slower than those with binocular summation or equality. Assessment of binocular summation is important when devising reading rehabilitation techniques.     

The effect of letter-stroke boldness on reading speed in central and peripheral vision

People with central vision loss often prefer boldface print over normal print for reading. However, little is known about how reading speed is influenced by the letter-stroke boldness of font. In this study, we examined the reliance of reading speed on stroke boldness, and determined whether this reliance differs between the normal central and peripheral vision. Reading speed was measured using the rapid serial visual presentation paradigm, where observers with normal vision read aloud short single sentences presented on a computer monitor, one word at a time. Text was rendered in Courier at six levels of boldness, defined as the stroke-width normalized to that of the standard Courier font: 0.27, 0.72, 1, 1.48, 1.89 and 3.04× the standard. Testings were conducted at the fovea and 10° in the inferior visual field. Print sizes used were 0.8× and 1.4× the critical print size (smallest print size that can be read at the maximum reading speed). At the fovea, reading speed was invariant for the middle four levels of boldness, but dropped by 23.3% for the least and the most bold text. At 10° eccentricity, reading speed was virtually the same for all boldness <1, but showed a poorer tolerance to bolder text, dropping by 21.5% for 1.89× boldness and 51% for the most bold (3.04×) text. These results could not be accounted for by the changes in print size or the RMS contrast of text associated with changes in stroke boldness. Our results suggest that contrary to the popular belief, reading speed does not benefit from bold text in the normal fovea and periphery. Excessive increase in stroke boldness may even impair reading speed, especially in the periphery.     

The effect of letter spacing on reading speed in central and peripheral vision

PURPOSE: Crowding, the adverse spatial interaction due to proximity of adjacent letters, has been suggested as an explanation for slow reading in peripheral vision. The purpose of this study was to examine whether reading speed can be improved in normal peripheral vision by increasing the letter spacing. Also tested was whether letter spacing imposes a different limit on reading speed of small versus large print. METHODS: Six normal observers read aloud single, short sentences presented on a computer monitor, one word at a time, by rapid serial visual presentation (RSVP). Reading speeds were calculated based on the RSVP exposure durations yielding 80% correctly read words. Letters were rendered in Courier, a fixed-width font. Testing was conducted at the fovea, 5 degrees and 10 degrees in the inferior visual field. The critical print size (CPS) was first determined for each observer by measuring reading speeds for four print sizes, using the standard letter spacing (center-to-center separation of adjacent letters; standard Courier spacing: 1.16 times the width of the lowercase x). Text was then presented at 0.8 x or 1.5x CPS, and reading speed was measured for five letter spacings, ranging from 0.5 times to 2 times the standard spacing. RESULTS: As expected, reading speed was highest at the fovea, decreased with eccentricity, and was faster for the larger print size. At all eccentricities and for both print sizes, reading speed increased with letter spacing, up to a critical letter spacing, and then either remained constant at the same reading speed or decreased slightly for larger letter spacings. The value of the critical letter spacing was very close to the standard letter spacing and did not depend on eccentricity or print size. CONCLUSIONS: Increased letter spacing beyond the standard size, which presumably decreases the adverse effect of crowding, does not lead to an increase in reading speed in central or peripheral vision.     

重视老年人视力损害与跌倒关系的研究

老年人跌倒是一重要的公共卫生问题,在我国65岁以上者每年有30％～40％发生跌倒,其中20％～30％可造成严重的身体损伤（如髋部骨折及颅脑外伤）,同时约60％的老年人在跌倒后会出现心理障碍、活动受限及生存质量明显下降,在意外事故死亡中,近1／2是由跌倒所致。视力损害是老年人跌倒最重要的危险因素。本文介绍了视力损害老年人跌倒后的严重后果及干预措施,目的是唤起大家对视力损害老年人跌倒防范的紧迫性及严重性给予更多的关注。     

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.     

Association between vision impairment and driving exposure in older adults aged 70 years and over: a population‐based examination

Purpose: To examine the relationship between vision impairment and driving exposure (amount of driving one does) in a population‐based sample of older drivers and to examine to what extent cognitive status impacts this relationship. Methods: Enrollees consisted of a population‐based sample of older adults from Alabama who were ≥70 years old, held a current driver’s license, and had driven within the last 3 months. Three aspects of visual function were measured under binocular conditions – habitual distance visual acuity, contrast sensitivity and visual processing speed. General cognitive status was assessed with the mini‐mental status examination. Driving exposure was estimated by the Driving Habits Questionnaire that asked about the number of miles, places, trips and days driven per week. Results: Drivers with impaired contrast sensitivity exhibited reduced annual mileage, and a decreased number of places and trips driven per week compared to those with normal contrast sensitivity, even after adjustment for other factors. Slowed visual processing speed was associated with reduced number of days driven per week after adjustment. Visual acuity deficit was not associated with changes in driving exposure. Cognitive status did not impact any of the associations between vision impairment and driving exposure. Conclusion: Older drivers with contrast sensitivity impairment exhibit reduced driving exposure in terms of number of trips and places they drive per week, as well as decreased annual mileage. These apparent self‐regulatory practices should be viewed as adaptive because contrast sensitivity impairment elevates motor vehicle collision (MVC) risk and reduction in driving exposure can reduce MVC risk.     

Significant improvements in near vision,reading speed,central visual field and related quality of life after ranibizumab treatment of wet age‐related macular degeneration

Purpose: To investigate the effects on near visual acuity, reading speed, central visual field and related quality of life of ranibizumab treatment of wet age‐related macular degeneration (AMD). Methods: The study was a prospective, non‐comparative consecutive case series, followed for 3 months and investigator‐driven. Thirty eyes of 30 patients with wet AMD were included, mean age 75 years (range 69–95 years). In addition to a full ophthalmological examination – including best‐corrected visual acuity (BCVA; Early Treatment Diabetic Research Study chart), fundus biomicroscopy, fundus photography, fluorescein angiography, indocyanine green angiography (occult cases) and ocular coherence tomography – near visual acuity, reading speed, central visual field and quality of life for related activities were also investigated at baseline and at 3 months after ranibizumab treatment. Results: Mean BCVA increased from 62 ± 11 to 66 ± 14 letters at 3 months (7%; p = 0.018). Near vision improved from 9 ± 5 to 6 ± 3 points (33%; p = 0.0006) and reading speed increased from 59 ± 40 to 85 ± 50 words/min (44%; p < 0.0001). The mean deviation from normal of the visual field improved from ?9 ± 7 to ?6 ± 5 dB (33%; p < 0.0001). Quality of life improved for distance activities from 54 ± 28 to 63 ± 28 points (17%; p < 0.0001) but significantly (p = 0.024) more for near activities, from 49 ± 26 to 63 ± 26 points (29%; p < 0.0001). Reading newspaper text in the group in which the better eye was treated showed the highest increase in quality of life score of all: 116%. Conclusion: The increase in BCVA after ranibizumab treatment is well established. The present study also showed significant improvements in other important visual qualities, such as near visual acuity, reading speed, central visual field and several activities influencing quality of life. The improvement was greater for near activities than for distance activities. Therefore, the beneficial effects of ranibizumab treatment shown here are more extensive than those reported previously.     

Training to improve temporal processing of letters benefits reading speed for people with central vision loss

Reading is slow and difficult for many people with central vision loss. A previous study showed that the temporal threshold for letter recognition is a major factor limiting reading speed for people with central vision loss. Here, we asked whether the temporal threshold for letter recognition for people with central vision loss could be improved through training and, if so, whether that would benefit reading. Training consisted of six sessions (3000 trials) of recognizing letter trigrams presented at fixation. Trigrams were initially presented at a baseline temporal threshold that was decreased by 0.1 log step when observers’ letter recognition accuracies reached 80% or higher for four consecutive blocks. Before and after training, we measured observers’ visual acuity, preferred retinal locus for fixation, fixation stability, reading speeds using the rapid serial visual presentation (RSVP) paradigm, the MNREAD Acuity Chart and 100-word passages, the baseline temporal threshold for letter recognition at 80% accuracy, and a visual-span profile. After training, the temporal threshold was decreased by 68%. This improvement was accompanied by a higher RSVP maximum reading speed (but no change in MNREAD and passage reading speeds) and a larger visual span. A mediation analysis showed that the relationship between the temporal threshold and RSVP maximum reading speed was mainly mediated by the information transfer rate (size of visual span/temporal duration). Our results showed that the temporal threshold for letter recognition is amenable to training and can improve RSVP reading speeds, offering a practical means to improve reading speed for people with central vision loss.     

Fulminant orbital cellulitis with complete loss of vision

Bacterial orbital cellulitis is a condition that rarely presents with complete loss of vision. A case is reported of a 69‐year‐old man who presented with fulminant onset of proptosis, significant ophthalmoplegia and no perception of light. Computed tomography showed no evidence of paranasal sinus disease. Despite treatment with intravenous flucloxacillin, ceftriaxone and metronidazole, and later, penicillin after Streptococcus pyogenes was grown from tissue culture, there was no improvement in vision; however, ocular motility returned to normal.     

Central and peripheral vision loss associated with nefazodone usage

A 35-year-old woman who reported persistent significant vision loss for 3 years after taking the antidepressant nefazodone was referred for electrophysiological assessment of vision. The vision changes included reduced acuities, reduced colour vision and visual field constriction in both eyes and were thought to be associated with the use of nefazodone for 6 – 8 weeks, 3 years earlier. Multifocal electroretinograms and visual evoked potentials were recorded using the Visual Evoked Response Imaging System (VERIS) to investigate the nature and site of the neural deficit. The summed retinal response showed a normal a- and b-wave latency and amplitude, however, the retinal topographic mfERGs showed a severe depression of the macular response in both eyes. The cortical topographic multifocal VEP mapping also showed a central depression in the right eye compared with the left. Two-frame motion and pattern custom mfVEP were also measured to assess different forms of cortical processing and especially of motion as nefazodone has previously been associated with image persistence with moving stimuli. The responses to two frame-motion showed signs of abnormality. Thus these results suggest that the primary locus of neural damage is retinal and is likely to have resulted from neurotoxicity. Other competing hypotheses such as hysterical blindness must be ruled out.