Low vision reading with sequential word presentation

Altered Eye Movements During Reading With Simulated Central and Peripheral Visual Field Defects

Purpose

Although foveal vision provides fine spatial information, parafoveal and peripheral vision are also known to be important for efficient reading behaviors. Here we systematically investigate how different types and sizes of visual field defects affect the way visual information is acquired via eye movements during reading.

Methods

Using gaze-contingent displays, simulated scotomas were induced in 24 adults with normal or corrected-to-normal vision during a reading task. The study design included peripheral and central scotomas of varying sizes (aperture or scotoma size of 2°, 4°, 6°, 8°, and 10°) and no-scotoma conditions. Eye movements (e.g., forward/backward saccades, fixations, microsaccades) were plotted as a function of either the aperture or scotoma size, and their relationships were characterized by the best fitting model.

Results

When the aperture size of the peripheral scotoma decreased below 6° (11 visible letters), there were significant decreases in saccade amplitude and velocity, as well as substantial increases in fixation duration and the number of fixations. Its dependency on the aperture size is best characterized by an exponential decay or growth function in log-linear coordinates. However, saccade amplitude and velocity, fixation duration, and forward/regressive saccades increased more or less linearly with increasing central scotoma size in log-linear coordinates.

Conclusions

Our results showed differential impacts of central and peripheral vision loss on reading behaviors while lending further support for the importance of foveal and parafoveal vision in reading. These apparently deviated oculomotor behaviors may in part reflect optimal reading strategies to compensate for the loss of visual information.

Altered eye movements during reading under degraded viewing conditions: Background luminance, text blur, and text contrast

Degraded viewing conditions caused by either natural environments or visual disorders lead to slow reading. Here, we systematically investigated how eye movement patterns during reading are affected by degraded viewing conditions in terms of spatial resolution, contrast, and background luminance. Using a high-speed eye tracker, binocular eye movements were obtained from 14 young normally sighted adults. Images of text passages were manipulated with varying degrees of background luminance (1.3-265 cd/m2), text blur (severe blur to no blur), or text contrast (2.6%-100%). We analyzed changes in key eye movement features, such as saccades, microsaccades, regressive saccades, fixations, and return-sweeps across different viewing conditions. No significant changes were observed for the range of tested background luminance values. However, with increasing text blur and decreasing text contrast, we observed a significant decrease in saccade amplitude and velocity, as well as a significant increase in fixation duration, number of fixations, proportion of regressive saccades, microsaccade rate, and duration of return-sweeps. Among all, saccade amplitude, fixation duration, and proportion of regressive saccades turned out to be the most significant contributors to reading speed, together accounting for 90% of variance in reading speed. Our results together showed that, when presented with degraded viewing conditions, the patterns of eye movements during reading were altered accordingly. These findings may suggest that the seemingly deviated eye movements observed in individuals with visual impairments may be in part resulting from active and optimal information acquisition strategies operated when visual sensory input becomes substantially deprived.

Digital Reading with Low Vision: Principles for Selecting Display Size

SIGNIFICANCE

Digital reading devices have become increasingly popular among people with low vision. Because displays come in many sizes ranging from smart watches to large desktop computer displays, it is important to have principles to guide people with low vision in selecting suitable displays for reading.

PURPOSE

The selection of effective digital displays for reading by people with low vision focuses attention on the interacting effects of print size, display size, font, visual acuity, and reading distance. This technical report aims to provide principles for identifying the minimum size of digital displays required for fluent reading by people with low vision.

METHODS

We emphasize two critical factors in selecting an appropriate reading display: angular print size, which should exceed the individual's critical print size, and display size, which should allow at least 13 characters to be presented on each line. Our approach considers a low-vision individual's acuity and preferences for viewing distance and fonts.

RESULTS

Through an illustrative example, we demonstrate how our approach can be used to determine display size for a low-vision individual with 20/200 acuity and central field loss who wants to read at 30-cm viewing distance with the Times Roman font. We have developed a web application based on our recommended approach to provide easy access to our algorithm.

CONCLUSIONS

We provide a procedure to guide the selection of appropriate displays for a wide range of acuities. Our approach can help clinicians in making recommendations for their patients, digital product designers in developing more accessible devices, and low-vision individuals in selecting digital displays for reading.

A comparison of reading, in people with simulated and actual central vision loss, with static text, horizontally scrolling text, and rapid serial visual presentation

Reading with central vision loss (CVL), as caused by macular disease, may be enhanced by presenting text using dynamic formats such as horizontally scrolling text or rapid serial visual presentation (RSVP). The rationale for these dynamic text formats is that they can be read while holding gaze away from the text, potentially supporting reading while using the eccentric viewing strategy. This study was designed to evaluate the practice of reading with CVL, with passages of text presented as static sentences, with horizontal scrolling sentences, or as single-word RSVP. In separate studies, normally sighted participants with a simulated (artificial) central scotoma, controlled by an eye-tracker, or participants with CVL resulting from macular degeneration read passages of text using the eccentric viewing technique. Comprehension was better overall with scrolling text when reading with a simulated CVL, whereas RSVP produced lower overall comprehension and high error rates. Analysis of eye movement behavior showed that participants consistently adopted a strategy of making multiple horizontal saccades on the text itself. Adherence to using eccentric viewing was better with RSVP, but this did not translate into better reading performance. Participants with macular degeneration and an actual CVL also showed the highest comprehension and lowest error rates with scrolling text and the lowest comprehension and highest errors with RSVP. We conclude that scrolling text can support effective reading in people with CVL and has potential as a reading aid.

Test-retest Reliability of the qReading Method in Normally Sighted Young Adults

SIGNIFICANCE

We recently developed a novel Bayesian adaptive method, qReading, to measure reading function. The qReading method has both the efficiency and excellent test-retest reliability in normally sighted young adults to make it an excellent candidate for future studies of its value in diagnosis and longitudinal evaluation of treatment and/or rehabilitation outcomes.

PURPOSE

A novel Bayesian adaptive method, qReading, was recently developed to measure reading function. Here we performed a systematic assessment of the test-retest reliability of the qReading method.

METHODS

The variability of five repeated measurements of the reading curve was examined in two settings: within session and between sessions. For the within-session design, we considered two subpopulations: naive observers and experienced observers. All observers were normally sighted young adults. For each set of data, in addition to examining the intrinsic precision of the qReading method (the half width of the credible interval of the posterior distribution of the estimated performance), we computed four metrics to assess repeatability: standard deviation, Bland-Altman coefficient of repeatability, correlation coefficient, and Fractional Rank Precision.

RESULTS

Extrinsic factors such as observer, time interval between repeated measures, and observer experience all contribute to the variation across measurements. Nevertheless, the four metrics consistently show that the variability across five repeated measurements is small for each set of data. This is true even without taking learning effects into account (standard deviations, ≤0.092 log10 units; Bland-Altman coefficient of repeatability, ≤0.15 (log10)2 units; correlation coefficient, ≥0.91; and Fractional Rank Precision, ≥0.81).

CONCLUSIONS

The qReading method has excellent test-retest reliability in normally sighted young adults.

Eye Movements in Macular Degeneration

In healthy vision, the fovea provides high acuity and serves as the locus for fixation achieved through saccadic eye movements. Bilateral loss of the foveal regions in both eyes causes individuals to adopt an eccentric locus for fixation. This review deals with the eye movement consequences of the loss of the foveal oculomotor reference and the ability of individuals to use an eccentric fixation locus as the new oculomotor reference. Eye movements are an integral part of everyday activities, such as reading, searching for an item of interest, eye-hand coordination, navigation, or tracking an approaching car. We consider how these tasks are impacted by the need to use an eccentric locus for fixation and as a reference for eye movements, specifically saccadic and smooth pursuit eye movements. Expected final online publication date for the Annual Review of Vision Science, Volume 7 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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.

Effects of Task on Reading Performance Estimates

Reading is a primary problem for low vision patients and a common functional endpoint for eye disease. However, there is limited agreement on reading assessment methods for clinical outcomes. Many clinical reading tests lack standardized materials for repeated testing and cannot be self-administered, which limit their use for vision rehabilitation monitoring and remote assessment. We compared three different reading assessment methods to address these limitations. Normally sighted participants (N = 12) completed MNREAD, and two forced-choice reading tests at multiple font sizes in counterbalanced order. In a word identification task, participants indicated whether 5-letter pentagrams, syntactically matched to English, were words or non-words. In a true/false reading task, participants indicated whether four-word sentences presented in RSVP were logically true or false. The reading speed vs. print size data from each experiment were fit by an exponential function with parameters for reading acuity, critical print size and maximum reading speed. In all cases, reading speed increased quickly as an exponential function of text size. Reading speed and critical print size significantly differed across tasks, but not reading acuity. Reading speeds were faster for word/non-word and true/false reading tasks, consistent with the elimination of eye movement load in RSVP but required larger text sizes to achieve those faster reading speeds. These different reading tasks quantify distinct aspects of reading behavior and the preferred assessment method may depend on the goal of intervention. Reading performance is an important clinical endpoint and a key quality of life indicator, however, differences across methods complicate direct comparisons across studies.

Asymmetries of reading eye movements in simulated central vision loss

Patients with central vision loss are forced to use an eccentric retinal location as a substitute for the fovea, called a preferred retinal locus, or PRL. Clinical studies have shown that patients habitually choose a PRL located either to the left, and/or below the scotoma in the visual field. The position to the right of the scotoma is almost never chosen, even though this would be theoretically more suitable for reading, since the scotoma no longer blocks the upcoming text. In the current study, we tested whether this asymmetry may have an oculomotor basis. Six normally sighted subjects viewed page-like text with a simulated scotoma, identifying embedded numbers in "words" comprising random letters. Subjects trained and tested with three different artificial PRL ("pseudo-PRL," or pPRL) locations: inferior, to the right, or to the left of the scotoma. After several training blocks for each pPRL position, subjects were found to produce reliable oculomotor control. Both reading speed and eye movement characteristics reproduced observations from traditional paradigms such as page-mode reading and RSVP for an advantage for an inferior pPRL. While left and right positions resulted in similar reading speeds, we observed that a right pPRL caused excessively large saccades and more direction switches, exhibiting a zig-zag pattern that developed spontaneously. Thus, we propose that patients' typical avoidance of pPRL positions to the right of their scotoma could have an oculomotor component: the erratic eye motion might potentially negate the perceptual benefit that this pPRL would offer.

Reading in the presence of macular disease: a mini-review

Purpose

Reading is vital to full participation in modern society. To millions of people suffering from macular disease that results in a central scotoma, reading is difficult and inefficient, rendering reading as the primary goal for most patients seeking low vision rehabilitation. The goals of this review paper are to summarize the dependence of reading speed on several key visual and typographical factors and the current methods or technologies for improving reading performance for people with macular disease.

Important findings

In general, reading speed for people with macular disease depends on print size, text contrast, size of the visual span, temporal processing of letters and oculomotor control. Attempts at improving reading speed by reducing the crowding effect between letters, words or lines; or optimizing properties of typeface such as the presence of serifs or stroke‐width thickness proved to be futile, with any improvement being modest at best. Currently, the most promising method to improve reading speed for people with macular disease is training, including perceptual learning or oculomotor training.

Summary

The limitation on reading speed for people with macular disease is likely to be multi‐factorial. Future studies should try to understand how different factors interact to limit reading speed, and whether different methods could be combined to produce a much greater benefit.

Reading by Children with Low Vision

This study of the reading of text found that despite their lower reading speed on a reading-comprehension task, the children with low vision comprehended texts at least as well as did the sighted children. Children with low vision need more time to read and comprehend a text, but they seem to use this time with enough efficiency to process the semantic, as well as the syntactic, information.

Relative-size Magnification versus Relative-distance Magnification: Effect on the Reading Performance of Adults with Normal and Low Vision

In the study reported here, the effect of character size on the reading rates of adults with normal and low vision was measured using both relative-size magnification (by which the print size is increased) and relative-distance magnification (by which the reading distance is decreased with appropriate optical correction). With relative-distance magnification, the reading rates of the subjects with normal vision were slower at close distances, but the results were small and inconsistent. For the subjects with low vision, the magnification method did not affect their reading rates.

Assessing reading performance in the periphery with a Bayesian adaptive approach: The qReading method

Reading is a crucial visual activity and a fundamental skill in daily life. Rapid Serial Visual Presentation (RSVP) is a text-presentation paradigm that has been extensively used in the laboratory to study basic characteristics of reading performance. However, measuring reading function (reading speed vs. print size) is time-consuming for RSVP reading using conventional testing procedures. In this study, we develop a novel method, qReading, utilizing the Bayesian adaptive testing framework to measure reading function in the periphery. We perform both a psychophysical experiment and computer simulations to validate the qReading method. In the experiment, words are presented using an RSVP paradigm at 10° in the lower visual field. The reading function obtained from the qReading method with 50 trials exhibits good agreement (i.e., high accuracy) with the reading function obtained from a conventional method (method of constant stimuli [MCS]) with 186 trials (mean root mean square error: 0.12 log10 units). Simulations further confirm that the qReading method provides an unbiased measure. The qReading procedure also demonstrates excellent precision (half width of 68.2% credible interval: 0.02 log10 units with 50 trials) compared to the MCS method (0.03 log10 units with 186 trials). This investigation establishes that the qReading method can adequately measure the reading function in the normal periphery with high accuracy, precision, and efficiency, and is a potentially valuable tool for both research and clinical assessments.

Reading with letter transpositions in central and peripheral vision

We used a letter transposition (LT) technique to investigate letter position coding during reading in central and peripheral vision. Eighteen subjects read aloud sentences in a rapid serial visual presentation task. The tests contained a baseline and three LT conditions with initial, internal, and final transpositions (e.g., “reading” to “erading”, “raeding”, and “readign”). The four reading conditions were tested in separate blocks. We found that LT had a smaller cost on peripheral (10° lower field) than on central reading speed, possibly due to the higher intrinsic position uncertainty of letters in the periphery. The pattern of cost (initial > final > internal) was the same for central and peripheral vision, indicating a similar lexical route for both. In the periphery, LT only affected transposed words, while in central vision it also affected untransposed words. This spread of the LT effect in central vision could not be accounted for by increased attention or memory load, or by decreased sentence context.

The influence of word frequency on word reading speed when individuals with macular diseases read text

People with central field loss (CFL) use peripheral vision to identify words. Eccentric vision provides ambiguous visual inputs to the processes leading to lexical access. Our purpose was to explore the hypothesis that this ambiguity leads to strong influences of inferential processes, our prediction being that increasing word frequency would decrease word reading time. Individuals with bilateral CFL induced by macular diseases read French sentences displayed with a self-paced reading method. Reading time of the last word of each sentence (target word) was recorded. Each target word (in sentence n) was matched with a synonym word (in sentence n+1) of the same length. When using absolute frequency value (Analysis 1), we found that reading time of target words decreased when word frequency increases, even when controlling for word length. The amplitude of this effect is larger than reported in previous investigations of reading with normal subjects. When comparing the effect of relative frequency (low vs. high) within each pair of synonyms (Analysis 2), results show the same pattern as the one observed in Analysis 1. Our results demonstrate clear-cut frequency effects on word reading time and suggest that inferential processes are stronger in CFL readers than in normally sighted observers. These results might also help design text simplification tools tailored for low-vision patients.

Bolder print does not increase reading speed in people with central vision loss

Patients with central vision loss are often advised by low vision rehabilitation professionals to read bolder print to ameliorate their reading difficulties. Is boldface print really effective in improving reading performance for people with central vision loss? In this study, we evaluated how reading speed depends on the stroke-width of text in people with central vision loss. Ten participants with long-standing central vision loss read aloud single, short sentences presented on a computer monitor, one word at a time, using rapid serial visual presentation (RSVP). Reading speed was calculated based on the RSVP word exposure duration that yielded 80% of words read correctly. Text was rendered in Courier and at six boldness levels, defined as the width of the letter-strokes normalized to that of the standard Courier font: 0.27, 0.72, 1, 1.48, 1.89 and 3.04× the standard. Reading speed was measured for two print sizes - 0.8× and 1.4× the critical print size (the smallest print size that can be read at the maximum reading speed). For all participants and both print sizes, reading speeds were essentially the same for text with stroke-width boldness ranging from 0.72 to 1.89× the standard, and were significantly lower for the thinnest and the boldest print. Most importantly, reading speed was not higher for bolder print than for the standard one. Despite the clinical wisdom that patients with central vision loss might benefit from bolder print, print with stroke-widths larger than the standard does not significantly improve reading speed for participants with central vision loss.

Determinants of Reading Performance in Eyes with Foveal-Sparing Geographic Atrophy

PURPOSE

To identify anatomic determinants of reading performance in eyes with foveal-sparing geographic atrophy (GA).

DESIGN

Prospectively recruited, cross-sectional study, SIGHT (clinicaltrials.gov identifier, NCT02332343).

PARTICIPANTS

Patients with foveal-sparing GA secondary to age-related macular degeneration (AMD).

METHODS

Monocular best-corrected visual acuity and reading acuity together with reading speed were assessed using Radner charts. Fundus autofluorescence, near-infrared reflectance, and spectral-domain OCT images were acquired using a Spectralis device. The minimal required reading rectangle (M3R), 19 letters × 2.4 lines in the smallest readable print size of an individual eye, was computed. The status of the M3R was determined as either free of atrophy or involved in the atrophic process, and the impact on reading was assessed.

MAIN OUTCOME MEASURES

Radner reading score (logRAD) and reading speed (words per minute [wpm]).

RESULTS

A total of 45 eyes of 31 patients (30 women; mean age, 76.14 years [range, 64.17-89.22 years]) were included. Median best-corrected visual acuity was 0.20 logarithm of the minimum angle of resolution (logMAR; Snellen equivalent, 20/32). Reading score was 0.52 logRAD (IQR, 0.30-1.4 logRAD) and maximum reading speed was 141.19 wpm (IQR, 105.52-164.62 wpm). In 27 eyes, the M3R was involved in the atrophic process. This was associated with a significant worsening in Radner score (1.21 logRAD [IQR, 0.46-1.40 logRAD] vs. 0.31 logRAD [IQR, 0.20-0.51 logRAD]; P < 0.001) and reading speed (110.84 wpm [IQR, 90.0-131.92 wpm] vs. 162.34 wpm [IQR, 137.51-176.66 wpm]; P = 0.002). Eyes in which the M3R was nonatrophic additionally showed an increase in reading speed with decreasing print size (peak increase, +73.08 wpm [IQR, 27.43-86.64 wpm] compared with the largest test sentence).

CONCLUSIONS

The results indicate that a defined area on the retina that can be assessed by retinal imaging is required for unhindered reading in patients with foveal-sparing GA. The findings highlight that smaller test sentences can be read faster by patients with this AMD subphenotype. Our results allow prediction of reading impairment based on imaging parameters in clinical routine and may support establishing anatomic surrogate end points in clinical trials. Furthermore, the findings could be used to facilitate the adjustment of magnifying reading aids.

Bayesian adaptive assessment of the reading function for vision: The qReading method

Reading is a fundamental skill that can be significantly affected by visual disabilities. Reading performance, which typically is measured as reading speed with a reading chart, is a key endpoint for quantifying normal or abnormal vision. Despite its importance for clinical vision, existing reading tests for vision are time consuming and difficult to administer. Here, we propose a Bayesian adaptive method, the qReading method, for automated assessment of the reading speed versus print size function. We implemented the qReading method with a word/nonword lexical decision task and validated the method with computer simulations and a psychophysical experiment. Computer simulations showed that both the interrun standard deviation and intrarun half width of the 68.2% credible interval of the estimated reading speeds from the qReading method were less than 0.1 log10 units after 150 trials, with a bias of 0.05 log10 units. In the psychophysical experiment, reading functions measured by the qReading and Psi methods (Kontsevich & Tyler, 1999) in a word/nonword lexical decision task were compared. The estimated reading functions obtained with the qReading and Psi methods were highly correlated (r = 0.966 ± 0.004, p < 0.01). The precision of the qReading method with 225 trials was comparable to that of the Psi method with 450 trials. We conclude that the qReading method can precisely and accurately assess the reading function in much reduced time, with great promise in both basic research and clinical applications.

Impact of simulated micro-scotomas on reading performance in central and peripheral retina

Observers with central field loss typically fixate within a non-foveal region called the preferred retinal locus, which can include localized sensitivity losses, or micro-scotomas (Krishnan and Bedell, 2018). In this study, we simulated micro-scotomas at the fovea and in the peripheral retina to assess their impact on reading speed. Ten younger (<36 years old) and 8 older (>50 years old) naïve observers with normal vision monocularly read high and/or low contrast sentences, presented at or above the critical print size for young observers at the fovea and at 5 and 10 deg in the inferior visual field. Reading material comprised MNREAD sentences and sentences taken from novels that were presented in rapid serial visual presentation (RSVP) format. Randomly distributed 13 × 13 arc min blocks corresponding to 0-78% of the text area (corresponding to ∼0-17 micro-scotomas/deg²) were set to the background luminance to simulate micro-scotomas. A staircase algorithm estimated maximum reading speed from the threshold exposure duration for each combination of retinal eccentricity, contrast and micro-scotoma density in both age groups. Log₁₀(RSVP reading speed) decreased significantly with simulated micro-scotoma density and eccentricity. Across conditions, reading speed was slower with low-compared to high-contrast text and was faster in younger than older normal observers. For a given eccentricity and contrast, a higher density of random element losses maximally affected older observers with normal vision. These outcomes may explain some of the reading deficits observed in older observers with central field loss.

Word Mode: a crowding-free reading protocol for individuals with macular disease

Central retinal loss through macular disease markedly reduces the ability to read largely because identification of a word using peripheral vision is negatively influenced by nearby text, a phenomenon termed visual crowding. Here, we present a novel peripheral reading protocol, termed Word Mode, that eliminates crowding by presenting each word in isolation but in a position that mimics its natural position in the line of text being read, with each new word elicited using a self-paced button press. We used a gaze-contingent paradigm to simulate a central scotoma in four normally-sighted observers, and measured oral reading speed for text positioned 7.5° in the inferior field. Compared with reading whole sentences, our crowding-free protocol increased peripheral reading speeds by up to a factor of seven, resulted in significantly fewer reading errors and fixations per sentence, and reduced both the critical print size and the text size required for spot reading by 0.2-0.3 logMAR. We conclude that the level of reading efficiency afforded by the crowding-free reading protocol Word Mode may return reading as a viable activity to many individuals with macular disease.

Rehabilitation Approaches in Macular Degeneration Patients

Age related macular degeneration (AMD) is a visual disease that affects elderly population. It entails a progressive loss of central vision whose consequences are dramatic for the patient's quality of life. Current rehabilitation programs are restricted to technical aids based on visual devices. They only temporarily improve specific visual functions such as reading skills. Considering the rapid increase of the aging population worldwide, it is crucial to intensify clinical research on AMD in order to develop simple and efficient methods that improve the patient's visual performances in many different contexts. One very promising approach to face this challenge is based on perceptual learning (PL). Through intensive practice, PL can induce neural plasticity in sensory cortices and result in long-lasting enhancements for various perceptual tasks in both normal and visually impaired populations. A growing number of studies showed how appropriate PL protocols improve visual functions in visual disorders, namely amblyopia, presbyopia or myopia. In order to successfully apply these approaches to more severe conditions such as AMD, numerous challenges have to be overcome. Indeed, the overall elderly age of patients and the reduced cortical surface that is devoted to peripheral vision potentially limit neural plasticity in this population. In addition, ocular fixation becomes much less stable because patients have to rely on peripheral fixation spots outside the scotoma whose size keeps on evolving. The aim of this review article is to discuss the recent literature on this topic and to offer a unified approach for developing new rehabilitation programs of AMD using PL. We argue that with an appropriate experimental and training protocol that is adapted to each patient needs, PL can offer fascinating opportunities for the development of simple, non-expensive rehabilitation approaches a large spectrum of visual functions in AMD patients.

The Evaluation of Reading Performance with Minnesota Low Vision Reading Charts in Patients with Age-related Macular Degeneration

PURPOSE:

To evaluate the reading performance using the Minnesota low vision reading (MNREAD) charts, of patients with age-related macular degeneration (AMD) who use low vision aid (LVA) devices.

MATERIALS AND METHODS:

This prospective study enrolled 27 patients with AMD. Distance visual acuity (VA) was evaluated with a distance chart designed for patients with low vision. Near vision and reading performance were evaluated with the Turkish version of the MNREAD charts. Unaided vision and vision with LVA devices and high spherical add near glasses was measured. P <0.05 was considered statistically significant.

RESULTS:

The mean unaided near VA was 1.05 ± 0.27 log of the minimum angle of resolution (LogMAR). The mean VA with the LVA devices was 0.71 ± 0.41 LogMAR. Reading acuity ranged between 1.15 and 0.21 LogMAR, critical print size was between − 1.2 and 0.2 LogMAR. Maximum reading speeds were between 0 and 103 words/min. The cases are divided into groups in terms of reading speed according to age, gender, diagnosis, and education. Reading speed was negatively correlated to increasing age.

CONCLUSION:

MNREAD reading charts can be used to evaluate reading performance in patients with AMD with low vision. The outcomes of the present study indicate that optical correction is adequate for near VA requirements in this patient population. However, optical correction was inadequate for improving reading performance. Appropriate rehabilitation programs can be used to increase reading speed.

Eye Movement Training and Suggested Gaze Strategies in Tunnel Vision - A Randomized and Controlled Pilot Study

PURPOSE

Degenerative retinal diseases, especially retinitis pigmentosa (RP), lead to severe peripheral visual field loss (tunnel vision), which impairs mobility. The lack of peripheral information leads to fewer horizontal eye movements and, thus, diminished scanning in RP patients in a natural environment walking task. This randomized controlled study aimed to improve mobility and the dynamic visual field by applying a compensatory Exploratory Saccadic Training (EST).

METHODS

Oculomotor responses during walking and avoiding obstacles in a controlled environment were studied before and after saccade or reading training in 25 RP patients. Eye movements were recorded using a mobile infrared eye tracker (Tobii glasses) that measured a range of spatial and temporal variables. Patients were randomly assigned to two training conditions: Saccade (experimental) and reading (control) training. All subjects who first performed reading training underwent experimental training later (waiting list control group). To assess the effect of training on subjects, we measured performance in the training task and the following outcome variables related to daily life: Response Time (RT) during exploratory saccade training, Percent Preferred Walking Speed (PPWS), the number of collisions with obstacles, eye position variability, fixation duration, and the total number of fixations including the ones in the subjects' blind area of the visual field.

RESULTS

In the saccade training group, RTs on average decreased, while the PPWS significantly increased. The improvement persisted, as tested 6 weeks after the end of the training. On average, the eye movement range of RP patients before and after training was similar to that of healthy observers. In both, the experimental and reading training groups, we found many fixations outside the subjects' seeing visual field before and after training. The average fixation duration was significantly shorter after the training, but only in the experimental training condition.

CONCLUSIONS

We conclude that the exploratory saccade training was beneficial for RP patients and resulted in shorter fixation durations after the training. We also found a significant improvement in relative walking speed during navigation in a real-world like controlled environment.

The value of Tablets as reading aids for individuals with central visual field loss: an evaluation of eccentric reading with static and scrolling text

Purpose

Technological devices such as smartphones and tablets are widely available and increasingly used as visual aids. This study evaluated the use of a novel app for tablets (MD_evReader) developed as a reading aid for individuals with a central field loss resulting from macular degeneration. The MD_evReader app scrolls text as single lines (similar to a news ticker) and is intended to enhance reading performance using the eccentric viewing technique by both reducing the demands on the eye movement system and minimising the deleterious effects of perceptual crowding. Reading performance with scrolling text was compared with reading static sentences, also presented on a tablet computer.

Methods

Twenty‐six people with low vision (diagnosis of macular degeneration) read static or dynamic text (scrolled from right to left), presented as a single line at high contrast on a tablet device. Reading error rates and comprehension were recorded for both text formats, and the participant's subjective experience of reading with the app was assessed using a simple questionnaire.

Results

The average reading speed for static and dynamic text was not significantly different and equal to or greater than 85 words per minute. The comprehension scores for both text formats were also similar, equal to approximately 95% correct. However, reading error rates were significantly (p = 0.02) less for dynamic text than for static text. The participants’ questionnaire ratings of their reading experience with the MD_evReader were highly positive and indicated a preference for reading with this app compared with their usual method.

Conclusions

Our data show that reading performance with scrolling text is at least equal to that achieved with static text and in some respects (reading error rate) is better than static text. Bespoke apps informed by an understanding of the underlying sensorimotor processes involved in a cognitive task such as reading have excellent potential as aids for people with visual impairments.

Measurement properties of continuous text reading performance tests

PURPOSE

Measurement properties of tests to assess reading acuity or reading performance have not been extensively evaluated. This study aims to provide an overview of the literature on available continuous text reading tests and their measurement properties.

METHODS

A literature search was performed in PubMed, Embase and PsycInfo. Subsequently, information on design and content of reading tests, study design and measurement properties were extracted using consensus-based standards for selection of health measurement instruments. Quality of studies, reading tests and measurement properties were systematically assessed using pre-specified criteria.

RESULTS

From 2334 identified articles, 20 relevant articles were found on measurement properties of three reading tests in various languages: IReST, MNread Reading Test and Radner Reading Charts. All three reading tests scored high on content validity. Reproducibility studies (repeated measurements between different testing sessions) of the IReST and MNread of commercially available reading tests in different languages were missing. The IReST scored best on inter-language comparison, the MNread scored well in repeatability studies (repeated measurements under the same conditions) and the Radner showed good reproducibility in studies.

CONCLUSIONS

Although in daily practice there are other continuous text reading tests available meeting the criteria of this review, measurement properties were described in scientific studies for only three of them. Of the few available studies, the quality and content of study design and methodology used varied. For testing existing reading tests and the development of new ones, for example in other languages, we make several recommendations, including careful description of patient characteristics, use of objective and subjective lighting levels, good control of working distance, documentation of the number of raters and their training, careful documentation of scoring rules and the use of Bland-Altman analyses or similar for reproducibility and repeatability studies.

Severity of vision loss interacts with word-specific features to impact out-loud reading in glaucoma

PURPOSE

To assess the impact of glaucoma-related vision loss on measures of out-loud reading, including time to say individual words, interval time between consecutive words, lexical errors, skipped words, and repetitions.

METHODS

Glaucoma subjects (n = 63) with bilateral visual field loss and glaucoma suspect controls (n = 57) were recorded while reading a standardized passage out loud. A masked evaluator determined the start and end of each recorded word and identified reading errors.

RESULTS

Glaucoma subjects demonstrated longer durations to recite individual words (265 vs. 243 ms, P < 0.001), longer intervals between words (154 vs. 124 ms, P < 0.001), and longer word/post-word interval complexes (the time spanned by the word and the interval following the word; 419 vs. 367 ms, P < 0.001) than controls. In multivariable analyses, each 0.1 decrement in log contrast sensitivity (logCS) was associated with a 15.0 ms longer word/post-interval complex (95% confidence interval [CI] = 9.6-20.4; P < 0.001). Contrast sensitivity was found to significantly interact with word length, word frequency, and word location at the end of a line with regards to word/post-word interval complex duration (P < 0.05 for all). Glaucoma severity was also associated with more lexical errors (Odds ratio = 1.20 for every 0.1 logCS decrement; 95% CI = 1.02-1.39, P < 0.05), but not with more skipped or repeated words.

CONCLUSIONS

Glaucoma patients with greater vision loss make more lexical errors, are slower in reciting longer and less frequently used words, and more slowly transition to new lines of text. These problem areas may require special attention when designing methods to rehabilitate reading in patients with glaucoma.

Changes across the psychometric function following perceptual learning of an RSVP reading task

Several recent studies have shown that perceptual learning can result in improvements in reading speed for people with macular disease (e.g., Chung, 2011; Tarita-Nistor et al., 2014). The improvements were reported as an increase in reading speed defined by specific criteria; however, little is known about how other properties of the reading performance or the participants' perceptual responses change as a consequence of learning. In this paper, we performed detailed analyses of data following perceptual learning using an RSVP (rapid serial visual presentation) reading task, looking beyond the change in reading speed defined by the threshold at a given accuracy on a psychometric function relating response accuracy with word exposure duration. Specifically, we explored the statistical characteristics of the response data to address two specific questions: was there a change in the slope of the psychometric function and did the improvements in performance occur consistently across different word exposure durations? Our results show that there is a general steepening of the slope of the psychometric function, leading to non-uniform improvements across stimulus levels.

Areas of the visual field important during reading in patients with glaucoma

PURPOSE

To determine the areas of the binocular visual field (VF) associated with reading speed in glaucomatous patients with preserved visual acuity (VA).

MATERIALS AND METHODS

Fifty-four patients with glaucoma (mean age ± standard deviation 70 ± 8 years) and 38 visually healthy controls (mean age 66 ± 9 years) had silent reading speeds measured using non-scrolling text on a computer setup. Participants completed three cognitive tests and tests of visual function, including the Humphrey 24-2 threshold VF test in each eye; the results were combined to produce binocular integrated VFs (IVFs). Regression analyses using the control group to correct for cognitive test scores, age and VA were conducted to obtain the IVF mean deviation (MD) and total deviation (TD) value from each IVF test location. Concordance between reading speed and TD, assessed using R (2) statistics, was ranked in order of importance to explore the parts of the IVF most likely to be linked with reading speed.

RESULTS

No significant association between IVF MD value and reading speed was observed (p = 0.38). Ranking individual thresholds indicated that the inferior left section of the IVF was most likely to be associated with reading speed.

CONCLUSIONS

Certain regions of the binocular VF impairment may be associated with reading performance even in patients with preserved VA. The inferior left region of patient IVFs may be important for changing lines during reading.

Eye movements and reading in glaucoma: observations on patients with advanced visual field loss

PURPOSE

To investigate the relationship between reading speed and eye movements in patients with advanced glaucomatous visual field (VF) defects and age-similar visually healthy people.

METHODS

Eighteen patients with advanced bilateral VF defects (mean age: 71, standard deviation [SD]: 7 years) and 39 controls (mean age: 67, SD: 8 years) had reading speed measured using short passages of text on a computer set-up incorporating eye tracking. Scanpaths were plotted and analysed from these experiments to derive measures of 'perceptual span' (total number of letters read per number of saccades) and 'text saturation' (the distance between the first and last fixation on lines of text). Another eye movement measure, termed 'saccadic frequency' (total number of saccades made to read a single word), was derived from a separate lexical decision task, where words were presented in isolation.

RESULTS

Significant linear association was demonstrated between perceptual span and reading speed in patients (R (2) = 0.42) and controls (R (2) = 0.56). Linear association between saccadic frequency during the LDT and reading speed was also found in patients (R (2) = 0.42), but not in controls (R (2) = 0.02). Patients also exhibited greater average text saturation than controls (P = 0.004).

CONCLUSION

Some, but not all, patients with advanced VF defects read slower than controls using short text passages. Differences in eye movement behaviour may partly account for this variability in patients. These patients were shown to saturate lines of text more during reading, which may explain previously-reported difficulties with sustained reading.

How effective is eccentric viewing training? A systematic literature review

PURPOSE

The global prevalence of age-related macular degeneration and associated central vision loss is rising. Central vision loss hinders the performance of many activities of daily living. Adaptive strategies such as eccentric viewing and steady eye strategy may be used to compensate for central vision loss. In order to establish the potential of these rehabilitation strategies, this systematic review evaluates current literature regarding the effectiveness of eccentric viewing and steady eye strategy training in people with central vision loss.

RESULTS

The search strategies identified 2605 publications, 36 of which met the inclusion criteria for the review, but only three of which were randomised controlled trials. This literature shows that eccentric viewing and steady eye strategy training can improve near visual acuity, reading speed, and performance of activities of daily living in people with central vision loss. However, there was insufficient literature to establish a relationship between training and distance visual acuity or quality of life. There is no conclusive evidence to show that a particular model of eccentric viewing training is superior to another, little clear evidence of a relationship between participant characteristics and training outcomes and no data regarding the cost effectiveness of training.

CONCLUSION

This report highlights the need for further robust research to establish the true potential and cost effectiveness of eccentric viewing and steady eye strategy training as a rehabilitation strategy for individuals with central vision loss.

The Glenn A. Fry Award Lecture 2012: Plasticity of the visual system following central vision loss

Following the onset of central vision loss, most patients develop an eccentric retinal location outside the affected macular region, the preferred retinal locus (PRL), as their new reference for visual tasks. The first goal of this article is to present behavioral evidence showing the presence of experience-dependent plasticity in people with central vision loss. The evidence includes the presence of oculomotor re-referencing of fixational saccades to the PRL; the characteristics of the shape of the crowding zone (spatial region within which the presence of other objects affects the recognition of a target) at the PRL are more "foveal-like" instead of resembling those of the normal periphery; and the change in the shape of the crowding zone at a para-PRL location that includes a component referenced to the PRL. These findings suggest that there is a shift in the referencing locus of the oculomotor and the sensory visual system from the fovea to the PRL for people with central vision loss, implying that the visual system for these individuals is still plastic and can be modified through experiences. The second goal of the article is to demonstrate the feasibility of applying perceptual learning, which capitalizes on the presence of plasticity, as a tool to improve functional vision for people with central vision loss. Our finding that visual function could improve with perceptual learning presents an exciting possibility for the development of an alternative rehabilitative strategy for people with central vision loss.

Enhanced text spacing improves reading performance in individuals with macular disease

The search by many investigators for a solution to the reading problems encountered by individuals with no central vision has been long and, to date, not very fruitful. Most textual manipulations, including font size, have led to only modest gains in reading speed. Previous work on spatial integrative properties of peripheral retina suggests that ‘visual crowding’ may be a major factor contributing to inefficient reading. Crowding refers to the fact that juxtaposed targets viewed eccentrically may be difficult to identify. The purpose of this study was to assess the combined effects of line spacing and word spacing on the ability of individuals with age-related macular degeneration (ARMD) to read short passages of text that were printed with either high (87.5%) or low contrast (17.5%) letters. Low contrast text was used to avoid potential ceiling effects and to mimic a possible reduction in letter contrast with light scatter from media opacities. For both low and high contrast text, the fastest reading speeds we measured were for passages of text with double line and double word spacing. In comparison with standard single spacing, double word/line spacing increased reading speed by approximately 26% with high contrast text (p < 0.001), and by 46% with low contrast text (p < 0.001). In addition, double line/word spacing more than halved the number of reading errors obtained with single spaced text. We compare our results with previous reading studies on ARMD patients, and conclude that crowding is detrimental to reading and that its effects can be reduced with enhanced text spacing. Spacing is particularly important when the contrast of the text is reduced, as may occur with intraocular light scatter or poor viewing conditions. We recommend that macular disease patients should employ double line spacing and double-character word spacing to maximize their reading efficiency.

Repeatability of visual function measures in age-related macular degeneration

PURPOSE

To assess repeatability of visual function measures in patients with early, intermediate or late age-related macular degeneration (AMD) without active neovascular disease in the study eye, but active neovascular AMD in the fellow eye.

METHODS

One hundred subjects from an ongoing trial were screened for this study in which their LogMAR acuity, contrast sensitivity and reading performance were assessed using standardised protocols by trained optometrists. The same measures were repeated one month later and repeatability of the visual functions assessed.

RESULTS

Data from 83 subjects satisfied inclusion criteria for analysis. Coefficient of repeatability was 14.9 letters for LogMAR visual acuity , 7.2 letters for Pelli Robson contrast sensitivity, 0.72 for LogMAR reading acuity, 110.4 words/ min for reading speed and 0.67 for LogMAR critical print size. Intraclass correlation coefficients allowed comparison between measures and were found to be 0.96 for LogMAR visual acuity, 0.93 for contrast sensitivity, 0.75 for LogMAR reading acuity, 0.79 for reading speed and 0.74 for LogMAR critical print size. Coefficients of variation were 9.4 %, 10.7 %, 48.4 %, 28.4 % and 31.8 % respectively.

CONCLUSIONS

We found coefficients of repeatability that concurred with previous studies demonstrating variability of visual functions in patients with AMD. In addition, we found intraclass correlation coefficients to be better with visual acuity and contrast sensitivity than with measures of reading performance.

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.

Measuring reading performance

Despite significant changes in the treatment of common eye conditions like cataract and age-related macular degeneration, reading difficulty remains the most common complaint of patients referred for low vision services. Clinical reading tests have been widely used since Jaeger introduced his test types in 1854. A brief review of the major developments in clinical reading tests is provided, followed by a discussion of some of the main controversies in clinical reading assessment. Data for the Salisbury Eye Evaluation (SEE) study demonstrate that standardised clinical reading tests are highly predictive of reading performance under natural, real world conditions, and that discrepancies between self-reported reading ability and measured reading performance may be indicative of people who are at a pre-clinical stage of disability, but are at risk for progression to clinical disability. If measured reading performance is to continue to increase in importance as a clinical outcome measure, there must be agreement on what should be measured (e.g. speed or comprehension) and how it should be measured (e.g. reading silently or aloud). Perhaps most important, the methods for assessing reading performance and the algorithms for scoring reading tests need to be optimised so that the reliability and responsiveness of reading tests can be improved.

Contour enhancement benefits older adults with simulated central field loss

PURPOSE

Age-related macular degeneration is the leading cause of vision loss among Americans aged >65 years. Currently, no effective treatment can reverse the central vision loss associated with most age-related macular degeneration. Digital image-processing techniques have been developed to improve image visibility for peripheral vision; however, both the selection and efficacy of such methods are limited. Progress has been difficult for two reasons: the exact nature of image enhancement that might benefit peripheral vision is not well understood, and efficient methods for testing such techniques have been elusive. The current study aims to develop both an effective image enhancement technique for peripheral vision and an efficient means for validating the technique.

METHODS

We used a novel contour-detection algorithm to locate shape-defining edges in images based on natural-image statistics. We then enhanced the scene by locally boosting the luminance contrast along such contours. Using a gaze-contingent display, we simulated central visual field loss in normally sighted young (aged 18-30 years) and older adults (aged 58-88 years). Visual search performance was measured as a function of contour enhancement strength ["original" (unenhanced), "medium," and "high"]. For preference task, a separate group of subjects judged which image in a pair "would lead to better search performance."

RESULTS

We found that although contour enhancement had no significant effect on search time and accuracy in young adults, Medium enhancement resulted in significantly shorter search time in older adults (about 13% reduction relative to original). Both age-groups preferred images with Medium enhancement over original (2-7 times). Furthermore, across age-groups, image content types, and enhancement strengths, there was a robust correlation between preference and performance.

CONCLUSIONS

Our findings demonstrate a beneficial role of contour enhancement in peripheral vision for older adults. Our findings further suggest that task-specific preference judgments can be an efficient surrogate for performance testing.

Dependence of reading speed on letter spacing in central vision loss

PURPOSE

Crowding, the difficulty in recognizing a letter in close proximity with other letters, has been suggested as an explanation for slow reading in people with central vision loss. The goals of this study were (1) to examine whether increased letter spacing in words, which presumably reduces crowding among letters, would benefit reading for people with central vision loss and (2) to relate our finding to the current account of faulty feature integration of crowding.

METHODS

Fourteen observers with central vision loss read aloud single sentences, one word at a time, using rapid serial visual presentation. Reading speeds were calculated based on the rapid serial visual presentation exposure durations yielding 80% accuracy. Letters were rendered in Courier, a fixed-width font. Observers were tested at 1.4× the critical print size (CPS), three were also tested at 0.8× CPS. Reading speed was measured for five center-to-center letter spacings (range: 0.5-2× the standard spacing). The preferred retinal locus for fixation was determined for nine of the observers, from which we calculated the horizontal dimension of the integration field for crowding.

RESULTS

All observers showed increased reading speed with letter spacing for small spacings, until an optimal spacing, beyond which reading speed either showed a plateau, or dropped as letter spacing further increased. The optimal spacing averaged 0.95 ± 0.06× [±95% confidence interval] the standard spacing for 1.4× CPS (similar for 0.8× CPS), which was not different from the standard. When converted to angular size, the measured values of the optimal letter spacing for reading show a good relationship with the calculated horizontal dimension of the integration field.

CONCLUSIONS

Increased letter spacing beyond the standard size, which presumably reduces crowding among letters in text, does not improve reading speed for people with central vision loss. The optimal letter spacing for reading can be predicted based on the preferred retinal locus.

Can reading-specific training stimuli improve the effect of perceptual learning on peripheral reading speed?

In a previous study, Chung, Legge, and Cheung (2004) showed that training using repeated presentation of trigrams (sequences of three random letters) resulted in an increase in the size of the visual span (number of letters recognized in a glance) and reading speed in the normal periphery. In this study, we asked whether we could optimize the benefit of trigram training on reading speed by using trigrams more specific to the reading task (i.e., trigrams frequently used in the English language) and presenting them according to their frequencies of occurrence in normal English usage and observers' performance. Averaged across seven observers, our training paradigm (4 days of training) increased the size of the visual span by 6.44 bits, with an accompanied 63.6% increase in the maximum reading speed, compared with the values before training. However, these benefits were not statistically different from those of Chung, Legge, and Cheung (2004) using a random-trigram training paradigm. Our findings confirm the possibility of increasing the size of the visual span and reading speed in the normal periphery with perceptual learning, and suggest that the benefits of training on letter recognition and maximum reading speed may not be linked to the types of letter strings presented during training.

Spatial-frequency cutoff requirements for pattern recognition in central and peripheral vision

It is well known that object recognition requires spatial frequencies exceeding some critical cutoff value. People with central scotomas who rely on peripheral vision have substantial difficulty with reading and face recognition. Deficiencies of pattern recognition in peripheral vision, might result in higher cutoff requirements, and may contribute to the functional problems of people with central-field loss. Here we asked about differences in spatial-cutoff requirements in central and peripheral vision for letter and face recognition. The stimuli were the 26 letters of the English alphabet and 26 celebrity faces. Each image was blurred using a low-pass filter in the spatial frequency domain. Critical cutoffs (defined as the minimum low-pass filter cutoff yielding 80% accuracy) were obtained by measuring recognition accuracy as a function of cutoff frequency (in cycles per object). Our data showed that critical cutoffs increased from central to peripheral vision by 20% for letter recognition and by 50% for face recognition. We asked whether these differences could be accounted for by central/peripheral differences in the contrast sensitivity function (CSF). We addressed this question by implementing an ideal-observer model which incorporates empirical CSF measurements and tested the model on letter and face recognition. The success of the model indicates that central/peripheral differences in the cutoff requirements for letter and face recognition can be accounted for by the information content of the stimulus limited by the shape of the human CSF, combined with a source of internal noise and followed by an optimal decision rule.

Influence of background on image recognition in normal vision and age-related macular degeneration

PURPOSE

The influence of background attenuation on the spatial frequency bandwidth requirements for image recognition was assessed in normal young and older groups and in a group with age-related macular degeneration (AMD). Bandwidth requirements were also assessed in the visual periphery of young normal observers.

METHODS

In Experiment 1, each observer was presented with 20 series of images. Each series consisted of a sequence of progressively low-pass filtered images, presented in an order of increasing bandwidth, i.e., according to an ascending method of limits. For half of the series, the background of the base image was selectively darkened by 80% of its original luminance. Three measures were analyzed: (1) the critical bandwidth defined as the bandwidth in cycles/image (cpi) at which 50% of the images were recognized, (2) the minimal bandwidth, defined as the minimal bandwidth at which images were recognized and (3) the proportion of images recognized at full bandwidth. In Experiment 2, young normal observers were similarly tested in central vision and at 5.5° eccentricity (superior or inferior visual field). A third background attenuation condition was included, as well, in which the background was low-pass filtered.

RESULTS

The critical bandwidth for image recognition was significantly reduced by darkening the image background for normal young and old and the AMD groups. This improvement was found to be contrast dependent for the darkened background. In addition, AMD observers tended to recognize more images at full bandwidth if the background was darkened. For normal young observers, making the background low-pass was ineffective in lowering the critical bandwidth in the fovea. Fewer images were recognized at full bandwidth at 5.5° eccentricity for a low-pass background and marginally fewer for a darkened background.

CONCLUSIONS

Selective attenuation of the image background can lead to reductions in the bandwidth requirements for image recognition in AMD. However, performance of young normal observers for images presented in the periphery was unlike AMD performance under the conditions investigated. These results have interesting implications for the design of image enhancement algorithms to aid low vision observers.

Improving reading speed for people with central vision loss through perceptual learning

PURPOSE

Perceptual learning has been shown to be effective in improving visual functions in the normal adult visual system, as well as in adults with amblyopia. In this study, the feasibility of applying perceptual learning to enhance reading speed in people with long-standing central vision loss was evaluated.

METHODS

Six observers (mean age, 73.8) with long-standing central vision loss practiced an oral sentence-reading task, with words presented sequentially using rapid serial visual presentation (RSVP). A pre-test consisted of measurements of visual acuities, RSVP reading speeds for six print sizes, the location of the preferred retinal locus for fixation (fPRL), and fixation stability. Training consisted of six weekly sessions of RSVP reading, with 300 sentences presented per session. A post-test, identical with the pre-test, followed the training.

RESULTS

All observers showed improved RSVP reading speed after training. The improvement averaged 53% (range, 34-70%). Comparisons of pre- and post-test measurements revealed little changes in visual acuity, critical print size, location of the fPRL, and fixation stability.

CONCLUSIONS

The specificity of the learning effect, and the lack of changes to the fPRL location and fixation stability suggest that the improvements are not due to observers adopting a retinal location with better visual capability, or an improvement in fixation. Rather, the improvements are likely to represent genuine plasticity of the visual system despite the older ages of the observers, coupled with long-standing sensory deficits. Perceptual learning might be an effective way of enhancing visual performance for people with central vision loss.

Training to improve reading speed in patients with juvenile macular dystrophy: a randomized study comparing two training methods

PURPOSE

In this study, we examined the clinical application of two training methods for optimizing reading ability in patients with juvenile macular dystrophy with established eccentric preferred retinal locus and optimal use of low-vision aids.

METHOD

This randomized study included 36 patients with juvenile macular dystrophy (35 with Stargardt's disease and one with Best's disease). All patients have been using individually optimized low-vision aids. After careful ophthalmological examination, patients were randomized into two groups: Group 1: Training to read during rapid serial visual presentation (RSVP) with elimination of eye movements as far as possible (n = 20); Group 2: Training to optimize reading eye movements (SM, sensomotoric training) (n = 16). Only patients with magnification requirement up to sixfold were included in the study. Training was performed for 4 weeks with an intensity of ½ hr per day and 5 days a week. Reading speed during page reading was measured before and after training. Eye movements during silent reading were recorded before and after training using a video eye tracker in 11 patients (five patients of SM and six of RSVP training group) and using an infrared reflection system in five patients (three patients from the SM and two patients of RSVP training group).

RESULTS

Age, visual acuity and magnification requirement did not differ significantly between the two groups. The median reading speed was 83 words per minute (wpm) (interquartile range 74-105 wpm) in the RSVP training group and 102 (interquartile range 63-126 wpm) in the SM group before training and increased significantly to 104 (interquartile range 81-124 wpm) and 122, respectively (interquartile range 102-137 wpm; p = 0.01 and 0.006) after training, i.e. patients with RSVP training increased their reading speed by a median of 21 wpm, while it was 20 wpm in the SM group. There were individual patients, who benefited strongly from the training. Eye movement recordings before and after training showed that in the RSVP group, increasing reading speed correlated with decreasing fixation duration (r = -0.75, p = 0.03), whereas in the SM group, increasing reading speed correlated with a decreasing number of forward saccades (r = -0.9, p = 0.01).

CONCLUSION

Although the median effect of both training methods was limited, individual patients benefited well. Our results may indicate a difference in the training effect between both methods on the reading strategy: the RSVP method reduces fixation duration, the SM method decreases the number of forward saccades. Patients can apply their newly learned reading strategy in the natural reading situation, e.g. in page reading without special presentation of the text. These results can be used as a basis for further improvement in training methods for optimizing reading performance in patients with a central scotoma.

Enhancing visual performance for people with central vision loss

People with central vision loss must use peripheral vision for visual tasks. It is well known that performance for almost all spatial tasks is worse in the normal periphery than in the normal fovea. The primary goal of my ongoing research is to understand the limiting factors and the potential for enhancing vision for people with central vision loss. Here I review my previous work related to understanding the limiting factors on reading, a task that is the primary complaint of many patients with age-related macular degeneration, the leading cause of visual impairment in the elderly. I also review my work related to enhancing visual functions in the normal periphery and how it may be applied to people with central vision loss.

Contrast polarity differences reduce crowding but do not benefit reading performance in peripheral vision

Previous studies have shown that the spatial extent of crowding in peripheral vision is reduced when a target letter and its flanking letters have opposite contrast polarity. We have examined if this reduction in crowding leads to improved reading performance. We compared the spatial extent of crowding, visual-span profiles (plots of letter-recognition accuracy versus letter position), and reading speed at 10 degrees inferior visual field, using white letters, black letters, or mixtures of white and black letters, presented on a mid-gray background. Consistent with previous studies, the spatial extent of crowding was reduced when the target and flanking letters had opposite contrast polarity. However, using mixed contrast polarity did not lead to improvements in visual-span profiles or reading speed.