[Show abstract][Hide abstract] ABSTRACT: Purpose. The post-illumination pupil response (PIPR) is produced by intrinsically photosensitive retinal ganglion cells (ipRGCs). We aimed to refine the testing conditions for PIPR by investigating whether a greater PIPR can be induced using full-field light stimuli of shorter duration and lower intensity than that produced by existing protocols that use central-field stimuli. Methods. Pupil response was recorded with an eye tracker in 10 visually-normal subjects. Red and blue light stimuli were presented using a Ganzfeld system. In Experiment 1 (intensity trials), PIPR was induced using 1 s full-field stimuli of increasing intensities from 0.1 to 400 cd/m2 (11 steps). For comparison, PIPR was also induced using a 60°×90° central-field blue stimulus of 400 cd/m2. In Experiment 2 (duration trials), PIPR was induced using 100 and 400 cd/m2 full-field stimulus of increasing duration from 4 to 1000 ms (10 steps). Results. PIPR increased monotonically with increasing stimulus intensity. Full-field stimulation using blue light at 400 cd/m2 intensity induced significantly more sustained PIPR than central-field stimulation (p=0.001). In addition, PIPR increased as the stimulus duration increased from 4-200 ms; however, no further increase in PIPR was observed when the duration increased from 400-1000 ms. Conclusions. Compared to existing central-field protocols, larger PIPR can be induced with a full-field stimulus with lower intensity and shorter duration, indicating that PIPR is a function of stimulus intensity, stimulus duration, and retinal area stimulated. The testing protocol can be refined with this new knowledge to target particular clinical populations.
[Show abstract][Hide abstract] ABSTRACT: Purpose. To examine the effects of impaired spatiotemporal vision on reaching movements in participants with strabismic amblyopia and to compare their performance to those with strabismus only without amblyopia and to visually-normal participants. Methods. Sixteen adults with strabismic amblyopia, 14 adults with strabismus only, and 16 visually-normal adults were recruited. Participants executed reach-to-touch movements toward visual targets in 3 viewing conditions: both eyes, monocular amblyopic eye (non-dominant eye), and monocular fellow eye (dominant eye). Results. Both groups with abnormal binocular vision had reach latency, accuracy, and precision comparable to visually-normal participants when viewing with both eyes and fellow (dominant) eye. Latencies were significantly delayed by >30 ms in all participants with reduced binocularity during amblyopic eye or non-dominant eye viewing (p<0.0001). Participants with strabismic amblyopia and negative stereopsis also had reduced reach precision (i.e., increased variability) during amblyopic eye viewing. Participants with strabismus only and those with strabismic amblyopia used a similar motor strategy-regardless of viewing condition, reach peak acceleration was significantly reduced (p<0.05) and the duration of acceleration phase was extended in comparison to visually-normal participants. There were no significant differences for the deceleration phase. Conclusion. Participants with strabismic amblyopia and those with strabismus only attain relatively normal reach accuracy and precision. However, they employ a different reach strategy that involves changing the motor plan. Our results provide further support that normal binocular vision during development provides important input for the development of visually-guided reaching movements.
[Show abstract][Hide abstract] ABSTRACT: Purpose: The effects on multisensory integration have rarely been examined in amblyopia. The McGurk effect is a well-established audiovisual illusion that is manifested when an auditory phoneme is presented concurrently with an incongruent visual phoneme. Visually normal viewers will hear a phoneme that does not match the actual auditory stimulus, having been perceptually influenced by the visual phoneme. This study examines audiovisual integration in adults with amblyopia. Methods: Twenty-two patients with amblyopia and 25 visually normal controls participated. Participants viewed videos of combinations of visual and auditory phonemes, and were asked to report what they heard. Some videos had congruent video and audio (control), while others had incongruent video and audio (McGurk). The McGurk effect is strongest when the visual phoneme dominates over the audio phoneme, resulting in low auditory accuracy on the task. Results: Adults with amblyopia demonstrated a weaker McGurk effect than visually normal controls (p=0.01). The difference was greatest when viewing monocularly with the amblyopic eye, and it was also evident when viewing binocularly or monocularly with the fellow eye. No correlations were found between the strength of the McGurk effect and either visual acuity or stereoacuity in patients. Patients and controls showed a similar response pattern to different speakers and syllables, and patients consistently demonstrated a weaker effect than controls. Conclusions: Abnormal visual experience early in life can have negative consequences for audiovisual integration that persists into adulthood in people with amblyopia.
[Show abstract][Hide abstract] ABSTRACT: PURPOSE. Amblyopia is a developmental disorder characterized by impairment of spatiotemporal visual processing that also affects oculomotor and manual motor function. We investigated the effects of amblyopia on short-term visuomotor adaptation using a saccadic adaptation paradigm. METHODS. Eight patients with anisometropic amblyopia and 11 visually-normal controls participated. Saccadic adaptation was induced using a double-step paradigm that displaced a saccadic visual target (at ±19º) back toward central fixation by 4.2º during ongoing saccade. Three test blocks-preadaptation, adaptation, and postadaptation-were performed sequentially while participants viewed binocularly and monocularly with the amblyopic and fellow eye (nondominant and dominant eye in controls) in three separate sessions. The spatial and temporal characteristics of saccadic adaptation were measured. RESULTS. Patients exhibited diminished saccadic gain adaptation. The percentage change in saccadic gain was lower in patients during amblyopic eye and binocular viewing as compared to controls. Saccadic latencies were longer, and saccadic gains and latencies were more variable in patients during amblyopic eye viewing. The time constants of adaptation were comparable between controls and patients under all viewing conditions. CONCLUSIONS. The short-term adaptation of saccadic gain was weaker and more variable in patients during amblyopic eye and binocular viewing. Our findings suggest that visual error information necessary for adaptation is imprecise in amblyopia, leading to reduced modulation of saccadic gain, and support the proposal that the error signal driving saccadic adaptation is visual.
[Show abstract][Hide abstract] ABSTRACT: PURPOSE: To investigate whether the evidence-based recommendations by the Pediatric Eye Disease Investigator Group (PEDIG) as initial treatment of amblyopia have been implemented into clinical practice and to discuss the necessary steps in translating evidence-based knowledge to inform clinical decision making. DESIGN: Retrospective cohort study. PARTICIPANTS: Children with amblyopia seen from 2007 through 2009 by academic and community ophthalmologists in a large urban center in North America that serves a population of more than 8 million. Using PEDIG criteria, moderate amblyopia was defined as visual acuity between 20/40 and 20/80 and severe amblyopia was defined as visual acuity between 20/100 and 20/400. INTERVENTION: Patching of the sound eye. MAIN OUTCOME MEASURES: The number of prescribed patching hours daily and the amblyopic eye visual acuity expressed as logarithm of the minimum angle of resolution (logMAR). RESULTS: For moderate amblyopia, the cohort (n = 71) was prescribed a mean of 3.2 hours of daily patching (95% confidence interval [CI]: 2.8-3.6 hours), which is significantly greater than the recommended 2 hours of daily patching for initial treatment. Only 24% (95% CI, 16%-35%) of them were prescribed the recommended initial patching hours. The amblyopic eye acuity on the 3- to 6-month visit in the cohort (0.23 logMAR) was similar to that of the 4-month visit in the PEDIG cohort (0.24 logMAR; P = 0.74). For severe amblyopia, the cohort (n = 52) was prescribed a mean of 3.9 hours of daily patching (95% CI, 3.5-4.3 hours), which is significantly lower than the recommended 6 hours of daily patching for initial treatment. Only 12% (95% CI, 5%-23%) of them were prescribed the recommended initial patching hours. The amblyopic eye acuity at the 7- to 12-month visit in the cohort (0.44 logMAR) was comparable with that of the 4-month visit in the PEDIG cohort (0.40 logMAR; P = 0.35). CONCLUSIONS: The evidence-based recommendations for amblyopia management have not been translated widely into changes in clinical practice in a large urban center in North America, although there is a general move from full-time to part-time patching since the PEDIG results were published. Using a well-established framework for knowledge translation, the Knowledge-to-Action Cycle, the necessary steps required to implement new knowledge into actual clinical practice are discussed. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.
[Show abstract][Hide abstract] ABSTRACT: To evaluate the research productivity of Canadian ophthalmology departments in terms of research volume, impact, funding, and cost-efficiency, and compare these measures with the top 6 U.S. departments.
Using the Web of Science, we obtained the number of peer-reviewed research articles and citations in which an author listed an ophthalmology department (or affiliated university or hospital) from 2001 to 2010 in the top 10 ophthalmology and vision sciences journals, as well as the Canadian Journal of Ophthalmology. Federal research funding received from the Canadian Institutes of Health Research and National Institutes of Health was also obtained.
The 3 universities that produced the highest number of articles were the University of Toronto (UofT), McGill University, and the University of British Columbia (UBC). UofT also produced the largest number of citations, followed by UBC and Dalhousie University. For the number of citations per article, the top 3 were the University of Ottawa, Dalhousie University, and the University of Calgary. McGill University, the University of Montreal, and UofT received the most federal funding. The 3 Canadian universities with the lowest funding (cost) per article were UofT, UBC, and McMaster University. The top contributors to the Canadian Journal of Ophthalmology from 2001 to 2010 were UofT, the University of Ottawa, and McGill University.
Larger Canadian departments tended to generate higher research volume and obtained more federal funding, but smaller departments also contributed significantly, and sometimes surpassed larger departments, in terms of research impact and cost-efficiency. The top 6 U.S. departments generated higher research volume and received more federal research funding than their Canadian counterparts. However, when research impact and cost-efficiency were examined, Canadian departments performed similar to the top U.S. departments.
Canadian Journal of Ophthalmology 02/2013; 48(1):46-55. · 1.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Errors in eye movements can be corrected during the ongoing saccade through in-flight modifications (i.e., online control), or by programming a secondary eye movement (i.e., offline control). In a reflexive saccade task, the oculomotor system can use extraretinal information (i.e., efference copy) online to correct errors in the primary saccade, and offline retinal information to generate a secondary corrective saccade. The purpose of this study was to examine the error correction mechanisms in the antisaccade task. The roles of extraretinal and retinal feedback in maintaining eye movement accuracy were investigated by presenting visual feedback at the spatial goal of the antisaccade. We found that online control for antisaccade is not affected by the presence of visual feedback; that is whether visual feedback is present or not, the duration of the deceleration interval was extended and significantly correlated with reduced antisaccade endpoint error. We postulate that the extended duration of deceleration is a feature of online control during volitional saccades to improve their endpoint accuracy. We found that secondary saccades were generated more frequently in the antisaccade task compared to the reflexive saccade task. Furthermore, we found evidence for a greater contribution from extraretinal sources of feedback in programming the secondary "corrective" saccades in the antisaccade task. Nonetheless, secondary saccades were more corrective for the remaining antisaccade amplitude error in the presence of visual feedback of the target. Taken together, our results reveal a distinctive online error control strategy through an extension of the deceleration interval in the antisaccade task. Target feedback does not improve online control, rather it improves the accuracy of secondary saccades in the antisaccade task.
PLoS ONE 01/2013; 8(8):e68613. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background: We have shown previously that anisometropic amblyopia affects the programming and execution of saccades. The aim of the current paper is to investigate the impact of strabismic amblyopia on saccade performance. Methods: Fourteen adults with strabismic amblyopia, 13 adults with strabismus without amblyopia, and 14 visually-normal adults performed saccades and reach-to-touch movements to targets presented at ±5º and ±10º eccentricity during binocular and monocular viewing. Latency, amplitude and peak velocity of primary and secondary saccades were measured. Results: In contrast to visually-normal participants who had shorter primary saccade latency during binocular viewing, no binocular advantage was found in patients with strabismus with or without amblyopia. Patients with amblyopia had longer saccade latency during amblyopic eye viewing (p<0.0001); however, there were no significant differences in saccade amplitude precision among the 3 groups across viewing conditions. Further analysis showed that only patients with severe amblyopia and no stereopsis (n=4) exhibited longer latency (which was more pronounced for more central targets; p<0.0001), and they also had reduced amplitude precision during amblyopic eye viewing. In contrast, patients with mild amblyopia (n=5) and no stereopsis had normal latency and reduced precision during amblyopic eye viewing (p<0.001), while those with gross stereopsis (n=5) had normal latency and precision. There were no differences in peak velocity among the groups. Conclusions: We found distinct patterns of saccade performance according to different levels of visual acuity and stereoscopic losses in strabismic amblyopia. These findings are in contrast to those in anisometropic amblyopia in which the altered saccade performance was independent of the extent of visual acuity or stereoscopic deficits. These results are most likely due to different long-term sensory suppression mechanisms in strabismic vs. anisometropic amblyopia.
[Show abstract][Hide abstract] ABSTRACT: Amblyopia is a visual impairment secondary to abnormal visual experience (e.g., strabismus, anisometropia, form deprivation) during early childhood that cannot be corrected immediately by glasses alone. It is the most common cause of monocular blindness globally. Patching remains the mainstay of treatment, but it is not always successful and there are also compliance and recurrence issues. Because amblyopia is a neural disorder that results from abnormal stimulation of the brain during the critical periods of visual development, it is essential to understand the neural mechanisms of amblyopia in order to devise better treatment strategies. In this review, I examine our current understanding of the neural mechanisms that underlie the characteristic deficits associated with amblyopia. I then examine modern neuroimaging findings that show how amblyopia affects various brain regions and how it disrupts the interactions among these brain regions. Following this, I review current concepts of brain plasticity and their implications for novel therapeutic strategies, including perceptual learning and binocular therapy, that may be beneficial for both children and adults with amblyopia.
Canadian Journal of Ophthalmology 10/2012; 47(5):399-409. · 1.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated whether the sensory impairments of amblyopia are associated with a decrease in eye position stability (PS).
The positions of both eyes were recorded simultaneously in three viewing conditions: binocular, monocular fellow eye viewing (right eye for controls), and monocular amblyopic eye viewing (left eye for controls). For monocular conditions, movements of the covered eye were also recorded (open-loop testing). Bivariate contour ellipses (BCEAs), representing the region over which eye positions were found 68.2% of the time, were calculated and normalized by log transformation.
For controls, there were no differences between eyes. Binocular PS (log(10)BCEA = -0.88) was better than monocular PS (log(10)BCEA = -0.59) indicating binocular summation, and the PS of the viewing eye was better than that of the covered eye (log(10)BCEA = -0.33). For patients, the amblyopic eye exhibited a significant decrease in PS during amblyopic eye (log(10)BCEA = -0.20), fellow eye (log(10)BCEA = 0.0004), and binocular (log(10)BCEA = -0.44) viewing. The PS of the fellow eye depended on viewing condition: it was comparable to controls during binocular (log(10)BCEA = -0.77) and fellow eye viewing (log(10)BCEA = -0.52), but it decreased during amblyopic eye viewing (log(10)BCEA = 0.08). Patients exhibited binocular summation during fellow eye viewing, but not during amblyopic eye viewing. Decrease in PS in patients was mainly due to slow eye drifts.
Deficits in spatiotemporal vision in amblyopia are associated with poor PS. PS of amblyopic and fellow eyes is differentially affected depending on viewing condition.
[Show abstract][Hide abstract] ABSTRACT: We previously showed that anisometropic amblyopia affects the programming and execution of saccades and reaching movements. In our current study, we investigated whether these amblyopia-related changes simply are due to a reduction in visual acuity alone by inducing artificial blur in one eye in visually-normal participants.
Twelve visually-normal participants performed saccades and reach-to-touch movements to targets presented on a computer screen during binocular and monocular viewing. A contact lens was used to blur the vision of one eye to a mean acuity level of 20/50. Saccades and reaching kinematics were compared before blur, immediately after blur, and 5 hours after blur was induced. The 5 hours after blur kinematic data from visually-normal participants also were compared to those from 12 patients with anisometropic amblyopia who had comparable acuity in the amblyopic eye.
Primary saccades (latency, amplitude, peak velocity), reaching movements (reaction time, movement time, peak acceleration, duration of the acceleration phase), and eye-hand coordination (saccade-to-reach planning interval, saccade-to-reach peak velocity interval) were not affected by induced monocular blur in visually-normal participants, either immediately or 5 hours after blur. Compared to visually-normal participants after 5 hours of blur, patients with anisometropic amblyopia had significantly longer and more variable saccade latency during amblyopic eye viewing, lower peak acceleration, and a longer acceleration phase during reaching, and a different temporal pattern of eye-hand coordination.
Artificially-induced monocular blur in visually-normal participants did not affect saccades, reaching movements, and eye-hand coordination during a simple reach-to-touch task even after a period of blur exposure. In contrast, patients with anisometropic amblyopia demonstrated significantly different kinematics while performing the same task. These results indicate that loss of visual acuity alone cannot explain the kinematic changes seen in patients with mild anisometropic amblyopia.
[Show abstract][Hide abstract] ABSTRACT: Impairment of spatiotemporal visual processing in amblyopia has been studied extensively, but its effects on visuomotor tasks have rarely been examined. Here, we investigate how visual deficits in amblyopia affect motor planning and online control of visually-guided, unconstrained reaching movements.
Thirteen patients with mild amblyopia, 13 with severe amblyopia and 13 visually-normal participants were recruited. Participants reached and touched a visual target during binocular and monocular viewing. Motor planning was assessed by examining spatial variability of the trajectory at 50-100 ms after movement onset. Online control was assessed by examining the endpoint variability and by calculating the coefficient of determination (R(2)) which correlates the spatial position of the limb during the movement to endpoint position.
Patients with amblyopia had reduced precision of the motor plan in all viewing conditions as evidenced by increased variability of the reach early in the trajectory. Endpoint precision was comparable between patients with mild amblyopia and control participants. Patients with severe amblyopia had reduced endpoint precision along azimuth and elevation during amblyopic eye viewing only, and along the depth axis in all viewing conditions. In addition, they had significantly higher R(2) values at 70% of movement time along the elevation and depth axes during amblyopic eye viewing.
Sensory uncertainty due to amblyopia leads to reduced precision of the motor plan. The ability to implement online corrections depends on the severity of the visual deficit, viewing condition, and the axis of the reaching movement. Patients with mild amblyopia used online control effectively to compensate for the reduced precision of the motor plan. In contrast, patients with severe amblyopia were not able to use online control as effectively to amend the limb trajectory especially along the depth axis, which could be due to their abnormal stereopsis.
PLoS ONE 01/2012; 7(2):e31075. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To determine the sensitivity and specificity of a new upright-supine test to differentiate skew deviation from trochlear nerve palsy and other causes of vertical strabismus in a large number of patients.
The study consisted of 125 consecutive patients who sought treatment from January 1, 2008, through December 31, 2010, for vertical strabismus of various causes: skew deviation (25 patients), trochlear nerve palsy (58 patients), restrictive causes (14 patients), and other causes (eg, myasthenia gravis and childhood strabismus) (28 patients). Twenty healthy participants served as controls. The deviation was measured by the prism and alternate cover test using a near target at ⅓ m in both the upright and supine positions. A vertical strabismus that decreased by 50% or more from the upright to supine position constituted a positive test result.
The upright-supine test result was positive in 20 of 25 patients with skew deviation (sensitivity, 80%) but negative in all patients with trochlear nerve palsy, restrictive, or other causes (specificity, 100%).
The upright-supine test is highly specific for differentiating skew deviation from other causes of vertical strabismus. This test could be added as a fourth step after the 3-step test, and if the result is positive, neuroimaging should be considered if indicated clinically.
Archives of ophthalmology 12/2011; 129(12):1570-5. · 3.86 Impact Factor