Eye movements and reading in macular disease: Further support for the shrinking perceptual span hypothesis

Enhancing the Functional Performance of Patients with Late-Stage Age-Related Macular Degeneration Implanted with a Miniature Telescope using Rehabilitation Training

INTRODUCTION

In this work, our aim is to report the functional outcomes of cataract surgery with smaller-incision new-generation miniature telescope (SING IMT) implantation followed by rehabilitation training in patients with central visual loss due to late-stage age-related macular degeneration (AMD).

METHODS

This retrospective study included patients who were monocularly implanted with SING IMT and then followed a rehabilitation program based on 6 biweekly sessions focused on visual abilities, reading, writing, visual motor integration and mobility. A total of 11 participants were included in this study. Reading acuity (RA), reading speed (RS), and fixation stability (FS) were assessed biweekly at 6-, 8-, 10-, 12-, 14-, and 16-week follow-up visits after SING IMT implantation and at a final assessment at 24 weeks. Best-corrected distance visual acuity (BCDVA) was also measured at baseline and at the same postoperative timepoints.

RESULTS

Mean baseline BCDVA was 12.5 ± 8.6 letter score. Both RA and RS were found to be significantly improved from the first rehabilitation session (6 weeks after surgery) to the last session (24 weeks after surgery). At the end of the rehabilitation program, mean RA was 0.45 ± 0.19 LogMAR and mean RS was 30.9 ± 17.6 words per minute. Moreover, all patients achieved a FS of 15 s or more after the last rehabilitation session. Most patients (55%) achieved an improvement of 15 letters in BCDVA at the end of the study.

CONCLUSIONS

This study suggests that rehabilitation training can improve visual functions of patients with late-stage AMD implanted with SING IMT in real-world tasks such as reading skills.

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.

Efficacy οf Wet Age-related Macular Degeneration Treatment οn Reading: A Pilot Study Using Eye-movement Analysis

SIGNIFICANCE

Functional vision, as evaluated with silent passage reading speed, improves after anti-vascular endothelial growth factor (anti-VEGF) treatment in patients with wet age-related macular antidegeneration (wAMD), reflecting primarily a concomitant reduction in the number of fixations. Implementing eye movement analysis when reading may better characterize the effectiveness of therapeutic approaches in wAMD.

PURPOSE

This study aimed to evaluate silent reading performance by means of eye fixation analysis before and after anti-VEGF treatment in wAMD patients.

METHODS

Sixteen wAMD patients who underwent anti-VEGF treatment in one eye and visual acuity (VA) better than 0.5 logMAR served as the AMD group. Twenty adults without ocular pathology served as the control group. Central retinal thickness and near VA were assessed at baseline and 3 to 4 months after their first visit. Reading performance was evaluated using short passages of 0.4-logMAR print size. Eye movements were recorded using EyeLink II video eye tracker. Data analysis included computation of reading speed, fixation duration, number of fixations, and percentage of regressions. Frequency distributions of fixation durations were analyzed with ex-Gaussian fittings.

RESULTS

In the AMD group, silent reading speed in the treated eye correlated well with central retinal thickness reduction and improved significantly by an average of 15.9 ± 28.5 words per minute (P = .04). This improvement was accompanied by an average reduction of 0.24 ± 0.38 in fixations per word (P = .03). The corresponding improvement in monocular VA was not statistically significant. Other eye fixation parameters did not change significantly after treatment. No statistically significant differences were found in the control group.

CONCLUSIONS

Visual acuity tests may underestimate the potential therapeutic effects after anti-VEGF treatment in patients with relatively good acuity who are being treated for wAMD. Evaluating silent reading performance and eye fixation parameters may better characterize the effectiveness of therapeutic approaches in wAMD patients.

Reconciling print-size and display-size constraints on reading

Two fundamental constraints limit the number of characters in text that can be displayed at one time-print size and display size. These dual constraints conflict in two important situations-when people with normal vision read text on small digital displays, and when people with low vision read magnified text. Here, we describe a unified framework for evaluating the joint impact of these constraints on reading performance. We measured reading speed as a function of print size for three digital formats (laptop, tablet, and cellphone) for 30 normally sighted and 10 low-vision participants. Our results showed that a minimum number of characters per line is required to achieve a criterion of 80% of maximum reading speed: 13 characters for normally sighted and eight characters for low-vision readers. This critical number of characters is nearly constant across font and display format. Possible reasons for this required number of characters are discussed. Combining these character count constraints with the requirements for adequate print size reveals that an individual's use of a small digital display or the need for magnified print can shrink or entirely eliminate the range of print size necessary for achieving maximum reading speed.

Reading with central vision loss: binocular summation and inhibition

Purpose

There are conflicting reports as to whether there is a binocular advantage or disadvantage when reading with central vision loss. This study examined binocular reading summation in patients with macular degeneration.

Methods

Seventy‐one patients with bilateral central vision loss [mean age: 63 (S.D. = 21) years] participated. Reading performances during binocular and monocular viewing with the better eye (i.e., the eye with the best monocular visual acuity) were evaluated using different versions of the Italian MNREAD reading chart (www.precision‐vision.com). Fixation stability and preferred retinal loci (PRLs) were recorded monocularly for each eye. The overall sample was split into inhibition, equality, and summation groups based on the binocular ratio (i.e., binocular/monocular) of the maximum reading speed.

Results

41% of patients experienced binocular inhibition, 42% summation, and 17% equality. Binocular reading speed of the inhibition group was approximately 30 words per minute slower than those of the equality and summation groups, although the inhibition group had the best visual acuity. These patients generally had monocular PRLs in non‐corresponding locations temporal or nasal to the scotoma, had the largest interocular acuity difference and lacked residual stereopsis. The three groups did not differ in fixational control, contrast sensitivity or critical print size.

Conclusions

Equal proportions of patients with central vision loss show binocular reading summation and inhibition. Patients with binocular reading inhibition have poorer reading performance and different clinical characteristics than those with binocular reading summation and equality.

Validation of the International Reading Speed Texts in a Canadian Sample

SIGNIFICANCE

The International Reading Speed Texts (IReST) is a valid measure of reading speed in a Canadian sample. However, if clinicians desire to assess reading comprehension using the IReST, this will significantly reduce reading speeds of individuals with normal vision or reduced visual acuity and therefore should use the values presented here.

PURPOSE

The purposes of this study are (1) to validate the IReST in an English-speaking Canadian sample and (2) to examine how reading comprehension questions and reduced visual acuity affect reading speed on the IReST.

METHODS

For study 1, Canadian English speakers (n = 25) read all 10 IReST following the procedures used in the original IReST validation. For study 2, Canadian English speakers (n = 50) read all 10 IReST, half with normal/corrected-to-normal vision and half with reduced visual acuity, and were asked reading comprehension questions.

RESULTS

No significant differences were found between Canadian sample and the published IReST values (in all cases, P > .05; mean difference [Mdiff] = -5.30 to +11.43; Cohen d = -0.15 to +0.27; Bayes factors = 0.41, 0.09). Assessing reading comprehension with multiple-choice questions on the IReST significantly reduced reading speeds in the normal vision condition (Mdiff = 25.3; 95% confidence interval, -16.7 to -34.1) and in the simulated impairment condition (Mdiff = 59.3; 95% confidence interval, -47.7 to -71).

CONCLUSIONS

The IReST is a valid measure that can be used to assess reading speed in a Canadian English-speaking sample. If researchers/clinicians wish to assess both reading speed and comprehension, using multiple-choice reading comprehension questions, then the values provided by the IReST will likely underestimate an individual's true reading speed in individuals with normal/corrected-to-normal vision or reduced visual acuity.

Comparing Reading Speeds for Reading Standardized Single Sentences and Paragraphs in Patients with Maculopathy

INTRODUCTION

The purpose of this study was to compare reading speeds (RS) of either paragraphs of text or single sentences in patients with maculopathy by investigating the repeatability of RS to decide which text type to use in studies on patients with maculopathy.

METHODS

RS was measured for standardized texts in 25 participants with a central scotoma due to maculopathy (mean age 77.8 years ± 9.9 SD, mean binocular visual acuity 0.65 logMAR (±0.85 SD), median magnification requirement 3-fold). Reading 3 single sentences taken from the Radner reading charts (sample #1, #2, and #3) of 14 words and reading 3 paragraphs of International Reading Speed Texts (IReST, sample # 3, #6, and #10) with a mean of 132 (±3.2 SD) words, each in German, were compared. The 6 texts were read aloud in random order from a closed-circuit TV system, with size adjusted according to the individual magnification requirement. Reading time was measured by stopwatch, and speed was calculated in correctly read words per minute (wpm). Differences in RS depending on text length (single sentence vs. paragraph) and text sample were calculated by the Bland-Altman analysis.

RESULTS

The mean RS showed no significant difference between 2 charts of the same kind (sentences: 93 wpm ± 37 SD; paragraphs: 95 wpm ± 38 SD). RS differences between 2 charts were lower in paragraphs than in single sentences. Highest correlations of RS between all 6 texts existed between the 3 IReST text samples (r = 0.98, 0.98, and 0.98) compared with the 3 Radner sentences (r = 0.89, 0.81, and 0.90). The inter-chart reliability (coefficient of repeatability) was smaller for the paragraphs (12.9 wpm) than for the single sentences (36.4 wpm).

CONCLUSION

In patients with maculopathy, single sentences are well suited for single measurement of RS. For repeated measurements (e.g., monitoring the course of a reading disorder or assessing effects of interventions), paragraphs are preferable because of their lower variability of RS between the paragraphs.

Visual searching capabilities in Age-Related Macular Degeneration (AMD) subjects

A decrease in visual perception with age was observed due to a decline in neurocognitive and visual functions. Previous studies showed that aging affects visual processes and contextual perceptual phenomena. The aim of our study was to explore the effect of age as well as the effect of Age-Related Macular Degeneration (AMD) on the visual searching task. Three groups of twenty-one subjects were recruited: AMD subjects (mean age 72.29 ± 4.83 years); healthy elderly (72.55 ± 4.95); and young healthy volunteers (28.38 ± 2.77). Visual perception functions were evaluated with a modified barrage test developed by Metrisquare. Our results showed that AMD patients and elderly do not differ in terms of time, omissions and errors. However both were slower to perform the visual perception tests when compared with young adults. Regarding the number of errors and omissions, we only found significant differences between the young and the AMD subjects, the later making more omissions and errors respect to young healthy volunteers. Despite AMD patients made more errors likely because to their poor fixation capability, we could conclude that AMD patients, as well as healthy elderly subjects, could compensate their altered visual strategies by taking more time to perform the visual searching tasks, probably due to cortical plasticity.HighlightsAMD patients and healthy elderly subjects do not differ in terms of time, omissions and errors.AMD patients, as well as healthy elderly subjects could compensate their visual difficulties by taking more time to perform the visual searching tasks when compared to young healthy volunteers. It is probably due to cortical plasticity.Note, however that AMD patients could make more errors when compared to young healthy volunteers, probably due to their poor fixation capability.The number of omissions and errors not different in healthy young and in elderly subjects.

Perceptual Learning of Visual Span Improves Chinese Reading Speed

Purpose

Evidence has indicated that the size of the visual span (the number of identifiable letters without movement of the eyes) and reading speed can be boosted through perceptual learning in alphabetic scripts. In this study, we investigated whether benefits of perceptual learning could be extended to visual-span size and sentence reading (all characters are presented at the same time) for Chinese characters and explored changes in sensory factors contributing to changes in visual-span size following training.

Methods

We randomly assigned 26 normally sighted subjects to either a control group (n = 13) or a training group (n = 13). Pre- and posttests were administered to evaluate visual-span profiles (VSPs) and reading speed. Training consisted of trigram (sequences of three characters) character-recognition trials over 4 consecutive days. VSPs are plots of recognition accuracy as a function of character position. Visual-span size was quantified as the area under VSPs in bits of information transmitted. A decomposition analysis of VSPs was used to quantify the effects of sensory factors (crowding and mislocation). We compared the size and sensory factors of visual span and reading speed following training.

Results

Following training, the visual-span size significantly increased by 11.7 bits, and reading speed increased by 50.8%. The decomposition analysis showed a significant reduction for crowding (-13.1 bits) but a minor increase in the magnitude of mislocation errors (1.46 bits) following training.

Conclusions

These results suggest that perceptual learning expands the visual-span size and further improves Chinese text sentence-reading speed, indicating that visual span may be a common sensory limitation on reading that can be overcome with practice.

Training peripheral vision to read: Boosting the speed of letter processing

Central-field loss necessitates the use of peripheral vision which makes reading slow and difficult. Slower temporal processing of letter recognition has been shown to be a limiting factor in peripheral letter recognition and reading. Previous studies showed that perceptual learning can increase the number of letters recognized on each fixation and is accompanied by an increase in reading speed. We hypothesized that improvement in temporal processing speed underlies the observed training effects. Here, we proposed an adaptive training procedure to focus on boosting the speed of letter recognition, and investigated whether peripheral reading would be enhanced by this training method. Seven normally-sighted subjects were trained with four daily one-hour sessions of a letter recognition task at 10° in the lower visual field in a pre/post design. During training, we adjusted stimulus duration on a block by block basis to maintain task difficulty near a pre-defined level of 80% performance accuracy. Stimulus duration progressively decreased with training, indicative of faster letter recognition at the 80% criterion. Following training, reading speed measured using a rapid serial visual presentation showed a substantial improvement in the trained (lower) field (41%) and the untrained (upper) field (27%), similar to the improvements observed from the training with a fixed stimulus duration. Despite being no more effective than the previous training, the adaptive temporal training method may allow individualized training, and may have advantages for clinical populations.

Slow Reading in Glaucoma: Is it due to the Shrinking Visual Span in Central Vision?

Purpose

Glaucoma is a leading cause of blindness worldwide, characterized by progressive loss of retinal ganglion cells. Patients with bilateral glaucoma read slower than normal cohorts. Here we examined the factors that may underlie slow reading in glaucoma and determined the best predictor of reading speed in glaucoma.

Methods

A total of 38 subjects participated in this study: 17 patients with primary open-angle glaucoma (mean age = 64.71 years) and 21 age-similar normal controls (58.24 years). For each subject, we measured binocular visual acuity (BVA); binocular contrast sensitivity (BCS); stereoacuity; visual field mean deviation (MD); and the visual span (i.e., the number of letters recognizable at one glance) known to limit reading speed. The visual span was measured with a trigram letter-recognition task in which subjects identify trigrams flashed at varying letter positions left and right of the fixation. Oral reading speed was measured with short blocks of text.

Results

Even after controlling for age, glaucoma patients showed significantly slower reading speed (by 19%, P < 0.05) and smaller visual span (by 11 bits, P < 0.001) compared to normal controls. While their BVA was relatively normal (20/20 Snellen equivalent), their BCS (P < 0.001); stereoacuity (P < 0.001); and visual field MD (P < 0.001) showed pronounced deficits. Multiple regression analysis further revealed that reading speed in glaucoma was best predicted by the visual span.

Conclusions

Our results showed that slower reading speed in glaucoma was closely related to the shrinkage of the visual span. Our findings further support the view that the visual span plays a limiting role in reading speed.

Evaluation of a gaze-controlled vision enhancement system for reading in visually impaired people

People with low vision, especially those with Central Field Loss (CFL), need magnification to read. The flexibility of Electronic Vision Enhancement Systems (EVES) offers several ways of magnifying text. Due to the restricted field of view of EVES, the need for magnification is conflicting with the need to navigate through text (panning). We have developed and implemented a real-time gaze-controlled system whose goal is to optimize the possibility of magnifying a portion of text while maintaining global viewing of the other portions of the text (condition 1). Two other conditions were implemented that mimicked commercially available advanced systems known as CCTV (closed-circuit television systems)—conditions 2 and 3. In these two conditions, magnification was uniformly applied to the whole text without any possibility to specifically select a region of interest. The three conditions were implemented on the same computer to remove differences that might have been induced by dissimilar equipment. A gaze-contingent artificial 10° scotoma (a mask continuously displayed in real time on the screen at the gaze location) was used in the three conditions in order to simulate macular degeneration. Ten healthy subjects with a gaze-contingent scotoma read aloud sentences from a French newspaper in nine experimental one-hour sessions. Reading speed was measured and constituted the main dependent variable to compare the three conditions. All subjects were able to use condition 1 and they found it slightly more comfortable to use than condition 2 (and similar to condition 3). Importantly, reading speed results did not show any significant difference between the three systems. In addition, learning curves were similar in the three conditions. This proof of concept study suggests that the principles underlying the gaze-controlled enhanced system might be further developed and fruitfully incorporated in different kinds of EVES for low vision reading.

Effects of Temporal Modulation on Crowding, Visual Span, and Reading

PURPOSE

Crowding, the increased difficulty in recognizing a target due to the proximity of adjacent objects, is identified as the main sensory constraint for the size of the visual span (the number of letters recognized without moving the eyes) and reading speed in peripheral vision. The goal of the present study is to assess the impact of temporal modulation on crowding, visual span, and reading in the periphery.

METHODS

Six normally sighted young adults participated in the study. Four temporal modulation patterns were examined: (1) moving scotoma (sequentially masking the component letters in a letter string or word), (2) moving window (sequentially presenting the component letters), (3) flashing (repeatedly masking and presenting all letters simultaneously), and (4) static (the control condition; no temporal changes during the presentation). For each condition, we obtained the spatial extent of crowding, the size of the visual span, and reading speeds measured by the rapid serial visual presentation method.

RESULTS

Compared with the static condition, the spatial extent of crowding was reduced in the moving window condition. Both the moving window and moving scotoma conditions led to a faster reading speed for print sizes smaller than critical print size (the smallest print size that allows maximum reading speed). However, none of the temporal modulations increased the size of the visual span and reading speed for print sizes larger than critical print size.

CONCLUSIONS

The results suggest that the temporal modulation patterns are of limited benefit for peripheral reading despite the substantial improvement for slow reading when print size is close to acuity threshold.

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.

Using eye tracking to assess reading performance in patients with glaucoma: a within-person study

Reading is often cited as a demanding task for patients with glaucomatous visual field (VF) loss, yet reading speed varies widely between patients and does not appear to be predicted by standard visual function measures. This within-person study aimed to investigate reading duration and eye movements when reading short passages of text in a patient's worse eye (most VF damage) when compared to their better eye (least VF damage). Reading duration and saccade rate were significantly different on average in the worse eye when compared to the better eye (P < 0.001) in 14 patients with glaucoma that had median (interquartile range) between-eye difference in mean deviation (MD; a standard clinical measure for VF loss) of 9.8 (8.3 to 14.8) dB; differences were not related to the size of the difference in MD between eyes. Patients with a more pronounced effect of longer reading duration on their worse eye made a larger proportion of "regressions" (backward saccades) and "unknown" EMs (not adhering to expected reading patterns) when reading with the worse eye when compared to the better eye. A between-eye study in patients with asymmetric disease, coupled with eye tracking, provides a useful experimental design for exploring reading performance in glaucoma.

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.

Patient-reported outcomes in Spanish patients diagnosed with bilateral age-related macular degeneration

PURPOSE

To evaluate the patient-reported outcomes (PRO) in age-related macular degeneration (AMD) patients by using instruments for eliciting health status and vision specific issues.

METHODS

PRO were assessed using the 25-item National Eye Institute Visual Function Questionnaire (NEIVFQ-25) and the Short-Form General Health Survey (SF-12).

RESULTS

The mean age and corrected distance visual acuity (CDVA) in the better eye of the AMD patients were 82.53 ± 5.17 years and 0.82 ± 0.43 logMAR, respectively. The overall NEIVFQ-25 composite score was 57.89. SF-12 physical and mental component summary scores were 37.28 and 57.25, respectively. There were significant correlations (p ≤ 0.05) between CDVA and the following NEIVFQ-25 subscales: general (r = -0.73), near (r = -0.40) and distance vision (r = -0.60), role limitations (r = -0.40), social function (r = -0.48) and mental health (r = -0.38).

CONCLUSIONS

Visual function is severely affected in AMD patients. It hampers their daily living without, however, deeply disturbing their social function. This may help them retain adequate mental health despite their poor physical status.

Eye movements during visual search in patients with glaucoma

Background

Glaucoma has been shown to lead to disability in many daily tasks including visual search. This study aims to determine whether the saccadic eye movements of people with glaucoma differ from those of people with normal vision, and to investigate the association between eye movements and impaired visual search.

Methods

Forty patients (mean age: 67 [SD: 9] years) with a range of glaucomatous visual field (VF) defects in both eyes (mean best eye mean deviation [MD]: –5.9 (SD: 5.4) dB) and 40 age-related people with normal vision (mean age: 66 [SD: 10] years) were timed as they searched for a series of target objects in computer displayed photographs of real world scenes. Eye movements were simultaneously recorded using an eye tracker. Average number of saccades per second, average saccade amplitude and average search duration across trials were recorded. These response variables were compared with measurements of VF and contrast sensitivity.

Results

The average rate of saccades made by the patient group was significantly smaller than the number made by controls during the visual search task (P = 0.02; mean reduction of 5.6% (95% CI: 0.1 to 10.4%). There was no difference in average saccade amplitude between the patients and the controls (P = 0.09). Average number of saccades was weakly correlated with aspects of visual function, with patients with worse contrast sensitivity (PR logCS; Spearman’s rho: 0.42; P = 0.006) and more severe VF defects (best eye MD; Spearman’s rho: 0.34; P = 0.037) tending to make less eye movements during the task. Average detection time in the search task was associated with the average rate of saccades in the patient group (Spearman’s rho = −0.65; P < 0.001) but this was not apparent in the controls.

Conclusions

The average rate of saccades made during visual search by this group of patients was fewer than those made by people with normal vision of a similar average age. There was wide variability in saccade rate in the patients but there was an association between an increase in this measure and better performance in the search task. Assessment of eye movements in individuals with glaucoma might provide insight into the functional deficits of the disease.

Audiovisual integration in low vision individuals

Behavioral and neurophysiological studies have shown an enhancement of visual perception in crossmodal audiovisual stimulation conditions, both for sensitivity and reaction times, when the stimulation in the two sensory modalities occurs in condition of space and time congruency. The purpose of the present work is to verify whether congruent visual and acoustic stimulations can improve the detection of visual stimuli in people affected by low vision. Participants were asked to detect the presence of a visual stimulus (yes/no task) either presented in isolation (i.e., unimodal visual stimulation) or simultaneously with auditory stimuli, which could be placed in the same spatial position (i.e., crossmodal congruent conditions) or in different spatial positions (i.e., crossmodal incongruent conditions). The results show for the first time audiovisual integration effects in low vision individuals. In particular, it has been observed a significant visual detection benefit in the crossmodal congruent as compared to the unimodal visual condition. This effect is selective for visual stimulation that occurs in the portion of visual field that is impaired, and disappears in the region of space in which vision is spared. Surprisingly, there is a marginal crossmodal benefit when the sound is presented at 16 degrees far from the visual stimulus. The observed crossmodal effect seems to be determined by the contribution of both senses to a model of optimal combination, in which the most reliable provides the highest contribution. These results, indicating a significant beneficial effect of synchronous and spatially congruent sounds in a visual detection task, seem very promising for the development of a rehabilitation approach of low vision diseases based on the principles of multisensory integration.

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.

Exploring eye movements in patients with glaucoma when viewing a driving scene

Background

Glaucoma is a progressive eye disease and a leading cause of visual disability. Automated assessment of the visual field determines the different stages in the disease process: it would be desirable to link these measurements taken in the clinic with patient's actual function, or establish if patients compensate for their restricted field of view when performing everyday tasks. Hence, this study investigated eye movements in glaucomatous patients when viewing driving scenes in a hazard perception test (HPT).

Methodology/Principal Findings

The HPT is a component of the UK driving licence test consisting of a series of short film clips of various traffic scenes viewed from the driver's perspective each containing hazardous situations that require the camera car to change direction or slow down. Data from nine glaucomatous patients with binocular visual field defects and ten age-matched control subjects were considered (all experienced drivers). Each subject viewed 26 different films with eye movements simultaneously monitored by an eye tracker. Computer software was purpose written to pre-process the data, co-register it to the film clips and to quantify eye movements and point-of-regard (using a dynamic bivariate contour ellipse analysis). On average, and across all HPT films, patients exhibited different eye movement characteristics to controls making, for example, significantly more saccades (P<0.001; 95% confidence interval for mean increase: 9.2 to 22.4%). Whilst the average region of ‘point-of-regard’ of the patients did not differ significantly from the controls, there were revealing cases where patients failed to see a hazard in relation to their binocular visual field defect.

Conclusions/Significance

Characteristics of eye movement patterns in patients with bilateral glaucoma can differ significantly from age-matched controls when viewing a traffic scene. Further studies of eye movements made by glaucomatous patients could provide useful information about the definition of the visual field component required for fitness to drive.

Page mode reading with simulated scotomas: oculo-motor patterns

This study investigated the relationship between reading speed and oculo-motor parameters when normally sighted observers had to read single sentences with an artificial macular scotoma. Using multiple regression analysis, our main result shows that two significant predictors, number of saccades per sentence followed by average fixation duration, account for 94% of reading speed variance: reading speed decreases when number of saccades and fixation duration increase. The number of letters per forward saccade (L/FS), which was measured directly in contrast to previous studies, is not a significant predictor. The results suggest that, independently of the size of saccades, some or all portions of a sentence are temporally integrated across an increasing number of fixations as reading speed is reduced.

Page mode reading with simulated scotomas: a modest effect of interline spacing on reading speed

Crowding is thought to be one potent limiting factor of reading in peripheral vision. While several studies investigated how crowding between horizontally adjacent letters or words can influence eccentric reading, little attention has been paid to the influence of vertically adjacent lines of text. The goal of this study was to examine the dependence of page mode reading performance (speed and accuracy) on interline spacing. A gaze-contingent visual display was used to simulate a visual central scotoma while normally sighted observers read meaningful French sentences following MNREAD principles. The sensitivity of this new material to low-level factors was confirmed by showing strong effects of perceptual learning, print size and scotoma size on reading performance. In contrast, reading speed was only slightly modulated by interline spacing even for the largest range tested: a 26% gain for a 178% increase in spacing. This modest effect sharply contrasts with the dramatic influence of vertical word spacing found in a recent RSVP study. This discrepancy suggests either that vertical crowding is minimized when reading meaningful sentences, or that the interaction between crowding and other factors such as attention and/or visuo-motor control is dependent on the paradigm used to assess reading speed (page vs. RSVP mode).

Relationship between visual span and reading performance in age-related macular degeneration

PURPOSE

Visual-span profiles are plots of letter-recognition accuracy as a function of letter position left and right of the point of fixation. Legge, Mansfield, and Chung [Legge, G. E., Mansfield, J. S., & Chung, S. T. L. (2001). Psychophysics of reading-XX. Linking letter recognition to reading speed in central and peripheral vision. Vision Research, 41(6), 725-743] proposed that reduced size of the visual span is a spatial factor limiting reading speed in patients with age-related macular degeneration (AMD). We have recently shown that a temporal property of letter recognition--the exposure time required for a high level of accuracy--is also a factor limiting reading speed in AMD [Cheong, A. M. Y., Legge, G. E., Lawrence, M. G., Cheung, S. H., & Ruff, M. (2007). Relationship between slow visual processing and reading speed in people with macular degeneration. Vision Research, 47, 2943-2965]. We measured the visual-span profiles of AMD subjects and assessed the relationship of the spatial and temporal properties of these profiles to reading speed.

METHODS

Thirteen AMD subjects and 11 age-matched normals were tested. Visual-span profiles were measured by using the trigram letter-recognition method described by Legge et al. (2001). Each individual's temporal threshold for letter recognition (80% accuracy criterion) was used as the exposure time for measuring the visual-span profile. Size of the visual span was computed as the area under the profile in bits of information transmitted. The information transfer rate in bits per second was defined as the visual-span size in bits divided by the exposure time in sec.

RESULTS

AMD visual-span sizes were substantially smaller (median of 23.9 bits) than normal visual-span sizes in central vision (median of 40.8 bits, p<.01). For the nine AMD subjects with eccentric fixation, the visual-span sizes (median of 20.6 bits) were also significantly smaller than visual spans of normal controls at 10 degrees below fixation in peripheral vision (median of 29.0 bits, p=.01). Information transfer rate for the AMD subjects (median of 29.5 bits/s) was significantly slower than that for the age-matched normals at both central and peripheral vision (median of 411.7 and 290.5 bits/s respectively, ps<.01). Information transfer rates were more strongly correlated with reading speed than the size of the visual span, and explained 36% of the variance in AMD reading speed.

CONCLUSION

Both visual-span size and information transfer rate were significantly impaired in the AMD subjects compared with age-matched normals. Information transfer rate, representing the combined effects of a reduced visual span and slower temporal processing of letters, was a better predictor of reading speed in AMD subjects than was the size of the visual span.

Relationship between slow visual processing and reading speed in people with macular degeneration

PURPOSE

People with macular degeneration (MD) often read slowly even with adequate magnification to compensate for acuity loss. Oculomotor deficits may affect reading in MD, but cannot fully explain the substantial reduction in reading speed. Central-field loss (CFL) is often a consequence of macular degeneration, necessitating the use of peripheral vision for reading. We hypothesized that slower temporal processing of visual patterns in peripheral vision is a factor contributing to slow reading performance in MD patients.

METHODS

Fifteen subjects with MD, including 12 with CFL, and five age-matched control subjects were recruited. Maximum reading speed and critical print size were measured with rapid serial visual presentation (RSVP). Temporal processing speed was studied by measuring letter-recognition accuracy for strings of three randomly selected letters centered at fixation for a range of exposure times. Temporal threshold was defined as the exposure time yielding 80% recognition accuracy for the central letter.

RESULTS

Temporal thresholds for the MD subjects ranged from 159 to 5881 ms, much longer than values for age-matched controls in central vision (13 ms, p<0.01). The mean temporal threshold for the 11 MD subjects who used eccentric fixation (1555.8 +/- 1708.4 ms) was much longer than the mean temporal threshold (97.0 +/- 34.2 ms, p<0.01) for the age-matched controls at 10 degrees in the lower visual field. Individual temporal thresholds accounted for 30% of the variance in reading speed (p<0.05).

CONCLUSION

The significant association between increased temporal threshold for letter recognition and reduced reading speed is consistent with the hypothesis that slower visual processing of letter recognition is one of the factors limiting reading speed in MD subjects.

What is the minimum field of view required for efficient navigation?

Critical points were computed to determine the minimum field of view (FOV) size required for efficient navigation. Navigation performance in 20 normally sighted subjects was assessed using an immersive virtual environment. Subjects were instructed to walk through a virtual forest to a target tree as quickly as possible without hitting any obstacles (trees, boulders, and holes). The navigation task was performed in three FOV and image contrast conditions under binocular, monocular, chromatic and achromatic viewing conditions. FOV was constricted to 10 degrees , 20 degrees and 40 degrees diameter and average image contrast was nominally high (11%), medium (6%) and low (3%). Navigation performance was scored as latency in walk initiation, walk time to reach goal and the number of obstacle contacts. The results revealed a linear relationship between log FOV and the two time measures, log latency and log walk time. The slopes of the linear regressions for log latency and log walk time ranged between -0.11 and -0.41. Critical points were computed from the non-linear relationships found between the number of obstacle contacts and FOV. The critical points for efficient navigation were FOVs of 32.1 degrees , 18.4 degrees and 10.9 degrees (diam.) for low, medium and high image contrast levels, respectively, highlighting the importance of contrast on the size of the FOV required for efficient navigation. Neither binocularity nor image chromaticity significantly affected navigation performance. The findings of this study have important implications in the design and prescription of head mounted displays intended to augment navigation performance.