Object perception by visually impaired people at different light levels

The effect of illumination on the visibility of steps and ramps for people with low vision

SIGNIFICANCE

Poor visibility of indoor features such as steps and ramps can pose mobility hazards for people with low vision. For purposes of architectural design, it is important to understand how design parameters such as the illumination level of an indoor space affect the visibility of steps and ramps.

PURPOSE

This study was aimed to examine the effect of typical variation in photopic illumination level in an indoor space on the visibility of steps and ramps for individuals with low vision.

METHODS

Steps and ramps were constructed in a large windowless room illuminated by overhead lights. Subjects with low vision completed a 5-alternative forced choice task to recognize the targets at three levels of photopic illumination, i.e., 800, 80, and 8 lux, and gave confidence ratings about their judgments on a 5-point scale. Acuities and contrast sensitivities of the subjects were also measured at each illumination level. For comparison, a group of normally sighted subjects with simulated acuity reduction also completed the step-and-ramp recognition task.

RESULTS

For both groups of subjects, recognition accuracy was not affected by illumination level. For subjects with low vision, however, there was a significant effect of illumination level on confidence rating: subjects became more confident about their judgments with increasing illumination. There was also a weak effect of illumination level on acuity and contrast sensitivity, both worsening with decreasing illumination. Recognition performance was best predicted by contrast sensitivity, whereas confidence was best predicted by visual acuity.

CONCLUSIONS

Illumination variation over a typical photopic range in an indoor space had minimal effect on the objective visibility of steps and ramps for people with low vision. However, illumination level affected subjects' confidence in hazard recognition. Design decisions on parameters such as illumination should consider the consequences on both the objective and the subjective accessibility of a space.

MNREAD Reading Vision in Adults With Glaucoma Under Mesopic and Photopic Conditions

Purpose

Despite good photopic visual acuity, glaucoma patients report difficulty performing daily activities under dim light such as reading. Here we investigated the impact of mesopic lighting conditions on reading vision of glaucoma patients.

Methods

The study design included 39 patients with glaucoma and 40 healthy controls. Reading vision was assessed with MNREAD charts under mesopic (2 cd/m2) and photopic (220 cd/m2) conditions. Four reading indexes: maximum reading speed (MRS), critical print size (CPS), reading acuity (RA), and reading accessibility index (ACC) were obtained from the MNREAD test yielding a plot of reading speed versus print size.

Results

Compared to photopic conditions, reading vision of both healthy controls and glaucoma patients significantly decreased under mesopic conditions (P < 0.05). For glaucoma patients (85% with mild or moderate glaucoma), MRS and ACC decreased by six words per minute and 0.1, respectively under mesopic conditions; CPS and RA increased by 0.25 and 0.18 logMAR, respectively. Moreover, under both photopic and mesopic conditions, reading vision of glaucoma patients was significantly worse than that of healthy controls, but the difference was greater under mesopic conditions (P < 0.05) even after controlling for age and visual acuity.

Conclusions

Mesopic conditions make reading more challenging for both healthy controls and glaucoma patients. However, reading in dim light appears to be more burdensome for glaucoma patients. Mesopic reading tests mediated by both cone and rod photoreceptor systems likely provide a more sensitive and comprehensive assessment of a patient's reading impairment than testing under photopic conditions.

Reading Vision in Adults With Early and Intermediate Age-Related Macular Degeneration Under Mesopic and Photopic Conditions

Purpose

Reading is involved in various daily activities that operate under a wide range of luminance levels. Rod- and cone-mediated mesopic visual function is known to be impaired even in early/intermediate age-related macular degeneration (AMD). It remains unclear whether and to what extent mesopic reading is impaired in early/intermediate AMD. Here, we assessed differences in reading vision between photopic and mesopic conditions in early/intermediate AMD and compared their performance to those in older adults with normal macular health.

Methods

The study included 30 patients with early/intermediate AMD and 30 healthy controls. Reading performance was tested on the MNREAD iPad app under mesopic (2 cd/m2 with a neural-density filter) and photopic (220 cd/m2) conditions. Four reading indices-maximum reading speed (MRS), critical print size (CPS), reading acuity (RA), and reading accessibility index (ACC)-were obtained from the MNREAD test, yielding a function representing reading speed versus print size.

Results

Compared to photopic conditions, patients with AMD and healthy controls both exhibited noticeable decreases in reading vision under mesopic conditions (P < 0.001) despite normal photopic visual acuity. This decrease was more pronounced in AMD even after adjusting for age (P < 0.001): Under mesopic conditions, MRS and ACC decreased by 8 words per minute and 0.1, respectively; CPS and RA were enlarged by 0.27 and 0.24 logMAR, respectively.

Conclusions

Reading vision deteriorates under mesopic conditions compared to photopic conditions in early/intermediate AMD and is accentuated compared to this difference in healthy controls.

Translational Relevance

A mesopic reading test may provide a more sensitive and comprehensive assessment of a patient's reading impairment.

Concept Mapping to Identify Content for a Performance-Based Measure of Low Luminance Vision-Related Activities of Daily Living

Purpose

The purpose of this study was to identify low luminance activities of daily living (ADL) relevant to adults with vision impairment using a concept-mapping approach.

Methods

“Group concept mapping” was utilized to identify specific ADLs that persons with vision impairment find challenging under low light conditions. In the first “brainstorming” phase, 24 adults with vision impairment from a range of eye conditions (mean age = 73 years, SD = 14 years) and 26 international low vision experts (mean experience = 22, SD = 11 years) generated statements to the focus prompt, “Thinking as broadly as possible, generate a list of statements detailing specific day-to-day activities a person with vision impairment might find challenging under low light conditions, such as in a poorly lit room or outside at dusk.” In the second phase, participants sorted activities by similarity and rated the importance of each activity. Multidimensional scaling and hierarchical cluster analysis were applied to produce concept maps showing clusters of prioritized activities.

Results

One hundred thirteen unique ideas/activities were generated, rated and sorted. Eight clusters were identified (from highest to lowest importance): hazard detection and safety outside; social interactions; navigation; near reading; selfcare and safety at home; distance spotting; searching around the home; and cooking and cleaning.

Conclusions

The conceptual framework and low luminance ADLs identified (the most important being hazard detection and safety outside, and social interactions) provide a basis for developing a performance-based measure of low luminance visual function.

Translational Relevance

A performance-based measure of low luminance vision-related ADLs is required for comprehensively and objectively assessing efficacy of eye treatments and low vision rehabilitation outcomes in adults with vision impairment.

Assessing Photoreceptor Status in Retinal Dystrophies: From High-Resolution Imaging to Functional Vision

Purpose

To describe the value of integrating phenotype/genotype data, disease staging, and evaluation of functional vision in patient-centered management of retinal dystrophies.

Methods

(1) Cross-sectional structure-function and retrospective longitudinal studies to assess the correlations between standard fundus autofluorescence (FAF), optical coherence tomography, visual acuity (VA), and perimetry (visual field [VF]) examinations to evaluate photoreceptor functional loss in a cohort of patients with rod-cone dystrophy (RCD); (2) flood-illumination adaptive optics (FIAO) imaging focusing on photoreceptor misalignment and orientation of outer segments; and (3) evaluation of the impact of visual impairment in daily life activities, based on functional (visual and mobility) vision assessment in a naturalistic environment in visually impaired subjects with RCD and subjects treated with Luxturna^Ⓡ for RPE65-related Leber congenital amaurosis before and after therapy.

Results

The results of the cross-sectional transversal study showed that (1) VA and macular sensitivity were weakly correlated with the structural variables; and (2) functional impairment (VF) was correlated with reduction of anatomical markers of photoreceptor structure and increased width of autofluorescent ring. The dimensions of the ring of increased FAF evolved faster. Other criteria that differed among groups were the lengths of the ellipsoid zone, the external limiting membrane, and the foveal thickness. FIAO revealed a variety of phenotypes: paradoxical visibility of foveal cones; heterogeneous brightness of cones; dim, inner segment–like, and RPE-like mosaic. Directional illumination by varying orientation of incident light (Stiles-Crawford effect) and the amount of side illumination (gaze-dependent imaging) affected photoreceptor visibility. Mobility assessment under different lighting conditions showed correlation with VF, VA, contrast sensitivity (CS), and dark adaptation, with different predictive values depending on mobility study paradigms and illumination level. At high illumination level (235 lux), VF was a predictor for all mobility performance models. Under low illumination (1 and 2 lux), VF was the most significant predictor of mobility performance variables, while CS best explained the number of collisions and segments. In subjects treated with Luxturna^Ⓡ, a very favorable impact on travel speed and reduction in the number of collisions, especially at low luminance, was observable 6 months following injection, in both children and adults.

Conclusions

Our results suggest the benefit of development and implementation of quantitative and reproducible tools to evaluate the status of photoreceptors and the impact of both visual impairment and novel therapies in real-life conditions. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Environmental Features Contributing to Falls in Persons With Vision Impairment: The Role of Home Lighting and Home Hazards

PURPOSE

To evaluate whether home hazards and lighting levels are associated with higher fall rates in adults with varying degrees of visual field (VF) damage from glaucoma.

METHODS

Participants with diagnosed or suspected glaucoma provided three years of prospective falls data via monthly falls diaries. A post-fall telephone questionnaire determined fall locations. Seven home areas were evaluated for hazards and lighting via an in-home assessment. Multivariate models adjusting for relevant confounders, including age, sex, comorbidity, and severity of VF damage, evaluated the influence of hazards and lighting on fall rates in each home region.

RESULTS

Mean baseline age for the 170 participants was 71.0 (7.6) years and 78 (46%) of participants were female. Fifty-nine participants experienced a total of 83 home falls, with the greatest number of falls occurring on the indoor stairs (n = 24, 29%) and bedroom (n = 17, 21%). Neither the number nor the percentage of hazardous items graded as hazardous was associated with the rate of falls (P > .26). Each 10-fold increase in room lighting was associated with 35% fewer falls in that home region (P = .02). The relation between lighting and the rate of falls did not differ with the degree of visual field damage (P > .3), and a lower fall rate was noted with better lighting even in participants with mild or no VF damage (rate ratio = 0.52/10-fold better lighting; P = 0.01).

CONCLUSIONS

Fewer home falls were found with better lighting, but not with fewer home hazards. Lighting improvements at home may reduce fall rates in older adults. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

International Paralympic Committee (IPC) and International Blind Sports Federation (IBSA) Joint Position Stand on the Sport-Specific Classification of Athletes with Vision Impairment

Classification is a defining characteristic of para-sports whereby eligible athletes are allocated a sport class to compete against others with similar activity limitations. To account for the unique characteristics of each sport, para-sports should develop their own classification system using evidence that demonstrates the impact of impairment on performance in that sport. Although the move towards sport-specific classification has progressed in sports for athletes with physical and intellectual impairments, sports for athletes with vision impairment (VI) continue to use the same three classes irrespective of the sport, with classes delineated by legal definitions of low vision and blindness. The aim of this joint International Paralympic Committee/International Blind Sports Federation (IPC/IBSA) Position Stand is to provide guidance for how evidence-based sport-specific classification should be achieved in VI sports. It does so by outlining three conceptual research models (correlation, simulation, and component analysis) that can be used to establish both the minimum impairment required to compete plus the appropriate number of sport classes and their inclusion criteria. The present evaluation of vision relies on measures of visual acuity and field, but new criteria may require a sport-specific combination of additional measures of visual function (e.g. contrast, motion, and light sensitivity) to better account for the impact of VI on sport performance. Moreover, the test procedures used during athlete evaluation (e.g. whether to evaluate both eyes individually or together) should be chosen to better represent the habitual viewing situation experienced in that sport. The development of sport-specific criteria should enhance the legitimacy of competition and encourage increased grassroots participation in VI sports.

Low vision rehabilitation: An update

This article provides information concerning issues related to the care of individuals who are visually impaired. Issues reviewed include determining who should be referred for vision rehabilitation services, Charles Bonnet syndrome, visual acuity, contrast sensitivity and visual field testing along with Useful Field of View testing. This article also discusses technology advances that can enhance the visual functioning of individuals who are visually impaired, including how these advances can help drivers with visual impairments to continue to safely operate motor vehicles, at least on a limited basis. Finally, resources that are available to both encourage and motivate patients to take advantages of vision rehabilitation services are reviewed.

Effects of Lighting on Reading Speed as a Function of Letter Size

OBJECTIVE

We sought to determine under what conditions brighter lighting improves reading performance.

METHOD

Thirteen participants with typical sight and 9 participants with age-related macular degeneration (AMD) read sentences ranging from 0.0 to 1.3 logMAR under luminance levels ranging from 3.5 to 696 cd/m².

RESULTS

At the dimmest luminance level (3.5 cd/m²), reading speeds were slowest at the smaller letter sizes and reached an asymptote for larger sizes. When luminance was increased to 30 cd/m², reading speed increased only for the smaller letter sizes. Additional lighting did not increase reading speeds for any letter size. Similar size-related effects of luminance were observed in participants with AMD.

CONCLUSION

In some instances, performance on acuity-limited tasks might be improved by brighter lighting. However, brighter lighting does not always improve reading; the magnitude of the effect depends on the text size and the relative changes in light level.

Home lighting assessment for clients with low vision

OBJECTIVE

The goal was to develop an objective, comprehensive, near-task home lighting assessment for older adults with low vision.

METHOD

A home lighting assessment was developed and tested with older adults with low vision. Interrater and test-retest reliability studies were conducted. Clinical utility was assessed by occupational therapists with expertise in low vision rehabilitation.

RESULTS

Interrater reliability was high (intraclass correlation coefficient [ICC] = .83-1.0). Test-retest reliability was moderate (ICC = .67). Responses to a Clinical Utility Feedback Form developed for this study indicated that the Home Environment Lighting Assessment (HELA) has strong clinical utility.

CONCLUSION

The HELA provides a structured tool to describe the quantitative and qualitative aspects of home lighting environments where near tasks are performed and can be used to plan lighting interventions. The HELA has the potential to affect assessment and intervention practices of rehabilitation professionals in the area of low vision and improve near-task performance of people with low vision.

Assessment of night vision problems in patients with congenital stationary night blindness

Congenital Stationary Night Blindness (CSNB) is a retinal disorder caused by a signal transmission defect between photoreceptors and bipolar cells. CSNB can be subdivided in CSNB2 (rod signal transmission reduced) and CSNB1 (rod signal transmission absent). The present study is the first in which night vision problems are assessed in CSNB patients in a systematic way, with the purpose of improving rehabilitation for these patients. We assessed the night vision problems of 13 CSNB2 patients and 9 CSNB1 patients by means of a questionnaire on low luminance situations. We furthermore investigated their dark adapted visual functions by the Goldmann Weekers dark adaptation curve, a dark adapted static visual field, and a two-dimensional version of the “Light Lab”. In the latter test, a digital image of a living room with objects was projected on a screen. While increasing the luminance of the image, we asked the patients to report on detection and recognition of objects. The questionnaire showed that the CSNB2 patients hardly experienced any night vision problems, while all CSNB1 patients experienced some problems although they generally did not describe them as severe. The three scotopic tests showed minimally to moderately decreased dark adapted visual functions in the CSNB2 patients, with differences between patients. In contrast, the dark adapted visual functions of the CSNB1 patients were more severely affected, but showed almost no differences between patients. The results from the “2D Light Lab” showed that all CSNB1 patients were blind at low intensities (equal to starlight), but quickly regained vision at higher intensities (full moonlight). Just above their dark adapted thresholds both CSNB1 and CSNB2 patients had normal visual fields. From the results we conclude that night vision problems in CSNB, in contrast to what the name suggests, are not conspicuous and generally not disabling.

Luminance affects age-related deficits in object detection: implications for computerized psychological assessments

As psychological instruments are converted for administration on computers, differences in luminance and contrast of these displays may affect performance. Specifically, high-luminance assessments may mask age-group differences that are apparent under lower luminance conditions. We examined the effects of luminance and contrast on object detection using computerized and naturalistic assessments. Younger and older adults displayed more differences in performance across differing contrast levels in conditions that were matched for luminance, despite the conditions appearing perceptually different. These findings indicate that computerized assessments should be created with luminance levels that are similar to those of the tasks they purport to simulate in order to enhance their validity.

Theoretical Comparison of Aberration-correcting Customized and Aspheric Intraocular Lenses

PURPOSE

To assess the performance and optical limitations of standard, aspheric, and wavefront-customized intraocular lenses (IOLs) using clinically verified pseudophakic eye models.

METHODS

White light pseudophakic eye models were constructed from physical measurements performed on 46 individual cataract patients and subsequently verified using the clinically measured contrast sensitivity function (CSF) and wavefront aberration of pseudophakic patients implanted with two different types of IOLs. These models are then used to design IOLs that correct the astigmatism and higher order aberrations of each individual eye model's cornea and to investigate how this correction would affect visual benefit, subjective tolerance to lens misalignment (tilt, decentration, and rotation), and depth of field.

RESULTS

Physiological eye models and clinical outcomes show similar levels of higher order aberration and contrast improvement. Customized correction of ocular wavefront aberrations with an IOL results in contrast improvements on the order of 200% over the control and the Tecnis IOLs. The customized lenses can be, on average, decentered by as much as 0.8 mm, tilted > 10 degrees , and rotated as much as 15 degrees before their polychromatic modulation transfer function at 8 cycles/degree is less than that of the Tecnis or spherical control lens. Correction of wavefront aberration results in a narrower through focus curve but better out of focus performance for +/- 0.50 diopters.

CONCLUSIONS

The use of realistic eye models that include higher order aberrations and chromatic aberrations are important when determining the impact of new IOL designs. Customized IOLs show the potential to improve visual performance.

Quality of light and quality of life--the effect of lighting adaptation among people with low vision

PURPOSE

The study has investigated the effect of lighting on the daily activities (ADL) of the visually impaired in their homes by comparison before and after light adjustments were made in the kitchen, hall and bathroom. It has also investigated the additional effects on the quality of life after providing task lighting in the living room.

METHOD

A total of 56 people were consecutively recruited from those receiving lighting adaptation help by the Low Vision Clinic in Göteborg. Ten persons did not complete the study. After medical examinations, lighting standards and psychosocial factors were charted. After lighting improvements were carried out in the kitchen, hall and bathroom, the subjects were randomly divided into two groups, an intervention and a comparison group. The task lighting in the living room was also improved for those included in the intervention group. Follow-up interviews to determine ADL and quality of life were performed 6 months after lighting adaptation.

RESULTS

A marked effect on quality of life of the lighting in the living room was found for the intervention group. The effect on ADL of the basic lighting adaptation in kitchen, hall and bathroom for both groups was significant for tasks carried out on the working surface in the kitchen. Other activities in the kitchen and in the bathroom tended to improve but changes were not significant.

CONCLUSION

The results confirm that it is possible to increase quality of life by improving the lighting conditions.

Predicting practical fitness to drive in drivers with visual field defects caused by ocular pathology

Vision, viewing efficiency, visual attention, and on-road driving performance were assessed in 100 participants with central and/or peripheral visual field defects caused by ocular pathology. Driving was evaluated by the Dutch driving license authority making use of the protocol for investigating practical fitness to drive. A smaller percentage of participants with central visual field defects passed the on-road driving test, in comparison with participants with peripheral or mild field defects. The predictive power of a model based on the current vision requirements for driving significantly increased when taking compensatory viewing efficiency into account. The results of the latter model were comparable to those of a model based on tests of visual attention and contrast sensitivity. Despite the increased explained variance of practical fitness to drive when taking higher-order visual functions into account, sensitivity and specificity remained quite low, limiting the use of these tests in identifying unfit drivers. Actual or potential applications of this research include the development of training programs to improve practical fitness to drive in drivers with visual field defects.

Binocular contrast inhibition in subjects with age-related macular degeneration

In subjects with normal vision, binocular contrast sensitivity is generally higher than monocular sensitivity, indicating summation of contrast in the two eyes. We have compared monocular and binocular contrast sensitivity and acuity for a group of 13 subjects with age-related macular degeneration (AMD). Relative to a normal control group, many of the AMD subjects showed reduced binocular contrast summation, and binocular inhibition was found for eight subjects for a narrow or an extended frequency band. A better monocular than binocular function may have practical implications for reading and orientation in AMD.

Assessing spatial vision - automated measurement of the contrast-sensitivity function in the hooded rat

The contrast-sensitivity function (CSF) provides a concise and thorough description of an organism's spatial vision; it is widely used to describe vision in animals and humans, to track developmental changes in vision, and to compare vision among different species. Despite the predominance of rats in neuroscience research, their vision is not thoroughly studied due to the complexity of psychophysical measurement and a generally held notion that rat vision is poor. We therefore designed an economical and rapid method to assess the hooded rat's CSF, using a computer monitor to display stimuli and an infrared touch screen to record responses. A six-alternative forced-choice task presented trials in which a sine-wave grating (S+), varying in spatial frequency and contrast, was displayed at different locations along with five gray stimuli (S-). Nose pokes to the S+ but not the S- produced water reinforcers. Contrasts were tested at each spatial frequency with a simple adaptive procedure until stimulus detection fell below chance. Psychometric functions were obtained by maximum-likelihood fitting of a logistic function to the raw data, obtaining the threshold as the function's point of inflection. As in previous studies with rats, CSFs showed an inverse-U shape with peak sensitivity at 0.12 cyc/deg and acuity just under 1 cyc/deg. The results indicate the present computer-controlled behavioral testing device is a precise and efficient instrument to assess spatial visual function in rats.