[Show abstract][Hide abstract] ABSTRACT: Using visual feedback to modify sensorimotor output in response to changes in the external environment is essential for daily function. Prism adaptation is a well-established experimental paradigm to quantify sensorimotor adaptation; that is, how the sensorimotor system adapts to an optically-altered visuospatial environment. Amblyopia is a neurodevelopmental disorder characterized by spatiotemporal deficits in vision that impacts manual and oculomotor function. This study explored the effects of anisometropic amblyopia on prism adaptation.
Eight participants with anisometropic amblyopia and 11 visually-normal adults, all right-handed, were tested. Participants pointed to visual targets and were presented with feedback of hand position near the terminus of limb movement in three blocks: baseline, adaptation, and deadaptation. Adaptation was induced by viewing with binocular 11.4° (20 prism diopter [PD]) left-shifting prisms. All tasks were performed during binocular viewing.
Participants with anisometropic amblyopia required significantly more trials (i.e., increased time constant) to adapt to prismatic optical displacement than visually-normal controls. During the rapid error correction phase of adaptation, people with anisometropic amblyopia also exhibited greater variance in motor output than visually-normal controls.
Amblyopia impacts on the ability to adapt the sensorimotor system to an optically-displaced visual environment. The increased time constant and greater variance in motor output during the rapid error correction phase of adaptation may indicate deficits in processing of visual information as a result of degraded spatiotemporal vision in amblyopia.
[Show abstract][Hide abstract] ABSTRACT: New behavioral treatment methods, including dichoptic training, perceptual learning, and video gaming, have been proposed to improve visual function in adult amblyopia. Here, we conducted a meta-analysis of these methods to investigate the factors involved in amblyopia recovery and their clinical significance.
Mean and individual participant data meta-analyses were performed on 24 studies using the new behavioral methods in adults. Studies were identified using PubMed, Google Scholar, and published reviews.
The new methods yielded a mean improvement in visual acuity of 0.17 logMAR with 32% participants achieving gains ≥ 0.2 logMAR, and a mean improvement in stereo sensitivity of 0.01 arcsec-1 with 42% of participants improving ≥2 octaves. The most significant predictor of treatment outcome was visual acuity at the onset of treatment. Participants with more severe amblyopia improved more on visual acuity and less on stereo sensitivity than those with milder amblyopia. Better initial stereo sensitivity was a predictor of greater gains in stereo sensitivity following treatment. Treatment type, amblyopia type, age, and training duration did not have any significant influence on visual and stereo acuity outcomes.
Our analyses showed that some participants may benefit from the new treatments; however, clinical trials are required to confirm these findings. Despite the diverse nature of the new behavioral methods, the lack of significant differences in visual and stereo sensitivity outcomes among them suggests that visual attention-a common element among the varied treatment methods-may play an important role in amblyopia recovery.
[Show abstract][Hide abstract] ABSTRACT: Purpose:To examine the effects of strabismic amblyopia and strabismus only without amblyopia on the temporal pattern of eye-hand coordination during both the planning and execution stages of visually-guided reaching. Methods:Forty-six adults (16 with strabismic amblyopia, 14 with strabismus only, and 16 visually-normal) executed reach-to-touch movements toward targets presented to the left or right of central fixation. Viewing conditions were binocular, monocular viewing with the amblyopic and with the fellow eye. Results:The temporal pattern of eye-hand coordination prior to reach initiation was comparable in the three groups tested. However, participants with strabismic amblyopia and strabismus only had a longer duration of the reach acceleration phase following target fixation in all viewing conditions in comparison to visually-normal participants (p<0.05). No significant differences were found among participants with amblyopia with different levels of acuity and stereoacuity loss. Participants with strabismic amblyopia and strabismus only initiated reach-related secondary saccades significantly more frequently in comparison to visually-normal participants. The amplitude and peak velocity of these saccades were significantly greater during amblyopic eye viewing in participants with amblyopia who also had negative stereopsis. Conclusions:Adults with strabismic amblyopia and strabismus only showed an altered pattern of temporal eye-hand coordination during the reach acceleration phase, which might affect their ability to modify reach trajectory using early online control. Secondary reach-related saccades may provide a compensatory mechanism to facilitate the late online control process in order to ensure relatively good reaching performance during binocular and fellow eye viewing.
[Show abstract][Hide abstract] ABSTRACT: The prevalence of strabismus varies according to the population studied, ethnicity, and geographic region. Previous studies of Asian populations have found that, unlike Western populations, esotropia is 2.5 times less common than exotropia. Because of the homogeneous nature of the local populations studied, however, it is difficult to ascertain the real difference in the epidemiology among ethnic groups. The aim of this study was to determine the positive predictive value of referrals for infantile esotropia in otherwise healthy children referred to a tertiary eye care center in a large center in North America that serves a ethnically diverse population of over 8 million. We found a very low positive predictive value (5.9%) and a very high false referral rate (94.1%) among Chinese children referred for early-onset esotropia.
Journal of American Association for Pediatric Ophthalmology and Strabismus 09/2014; 18(5). DOI:10.1016/j.jaapos.2014.06.004 · 1.14 Impact Factor
[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: 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 08/2013; 8(8):e68613. DOI:10.1371/journal.pone.0068613 · 3.53 Impact Factor
[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. DOI:10.1016/j.jcjo.2012.10.001 · 1.30 Impact Factor