Are high lags of accommodation in myopic children due to motor deficits?

The final publication is available at Elsevier via http://doi.org/10.1016/j.visres.2016.11.001 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Children with a progressing myopia exhibit an abnormal pattern of high accommodative lags coupled with high accommodative convergence (AC/A) and high accommodative adaptation. This is not predicted by the current models of accommodation and vergence. Reduced accommodative plant gain and reduced sensitivity to blur have been suggested as potential causes for this abnormal behavior. These etiologies were tested by altering parameters (sensory, controller and plant gains) in the Simulink model of accommodation. Predictions were then compared to the static and dynamic blur accommodation (BA) measures taken using a Badal optical system on 12 children (6 emmetropes and 6 myopes, 8–13 years) and 6 adults (20–35 years). Other critical parameters such as CA/C, AC/A, and accommodative adaptation were also measured. Usable BA responses were classified as either typical or atypical. Typical accommodation data confirmed the abnormal pattern of myopia along with an unchanged CA/C. Main sequence relationship remained invariant between myopic and nonmyopic children. An overall reduction was noted in the response dynamics such as peak velocity and acceleration with age. Neither a reduced plant gain nor reduced blur sensitivity could predict the abnormal accommodative behavior. A model adjustment reflecting a reduced accommodative sensory gain (ASG) coupled with an increased AC cross-link gain and reduced vergence adaptive gain does predict the empirical findings. Empirical measures also showed a greater frequency of errors in accommodative response generation (atypical responses) in both myopic and control children compared to adults.University of Waterloo, NSERC Canada, COET

Comparison of super-resolution algorithms applied to retinal images

A critical challenge in biomedical imaging is to optimally balance the trade-off among image resolution, signal-to-noise ratio, and acquisition time. Acquiring a high-resolution image is possible; however, it is either expensive or time consuming or both. Resolution is also limited by the physical properties of the imaging device, such as the nature and size of the input source radiation and the optics of the device. Super-resolution (SR), which is an off-line approach for improving the resolution of an image, is free of these trade-offs. Several methodologies, such as interpolation, frequency domain, regularization, and learning-based approaches, have been developed over the past several years for SR of natural images. We review some of these methods and demonstrate the positive impact expected from SR of retinal images and investigate the performance of various SR techniques. We use a fundus image as an example for simulations

Unmasking the linear behaviour of slow motor adaptation to prolonged convergence

This is the peer reviewed version of the following article: Erkelens, I. M., Thompson, B., & Bobier, W. R. (2016). Unmasking the linear behaviour of slow motor adaptation to prolonged convergence. European Journal of Neuroscience, 43(12), 1553–1560, which has been published in final form at https://doi.org/10.1111/ejn.13240 This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Adaptation to changing environmental demands is central to maintaining optimal motor system function. Current theories suggest that adaptation in both the skeletal-motor and oculomotor systems involves a combination of fast (reflexive) and slow (recalibration) mechanisms. Here we used the oculomotor vergence system as a model to investigate the mechanisms underlying slow motor adaptation. Unlike reaching with the upper limbs, vergence is less susceptible to changes in cognitive strategy that can affect the behaviour of motor adaptation. We tested the hypothesis that mechanisms of slow motor adaptation reflect early neural processing by assessing the linearity of adaptive responses over a large range of stimuli. Using varied disparity stimuli in conflict with accommodation, the slow adaptation of tonic vergence was found to exhibit a linear response whereby the rate (R2 = 0.85, P < 0.0001) and amplitude (R2 = 0.65, P < 0.0001) of the adaptive effects increased proportionally with stimulus amplitude. These results suggest that this slow adaptive mechanism is an early neural process, implying a fundamental physiological nature that is potentially dominated by subcortical and cerebellar substrates.University of Waterloo, NSERC, Canadian Optometric Education Trust Fund (COETF), Ontario QE II GSST Awar

The correction of static and dynamic aniseikonia with spectacles and contact lenses

This is the peer reviewed version of the following article: McNeill, S., & Bobier, W. (2017). The correction of static and dynamic aniseikonia with spectacles and contact lenses. Clinical and Experimental Optometry, 100(6), 732–734. Which has been published in final form at https://doi.org/10.1111/cxo.12516. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.We describe a case of where significant anisometropic astigmatism was accompanied with considerable asthenopic symptoms. Symptoms were not alleviated by the prescribing of a partial spectacle correction. Subsequent treatment with a contact lens and an iseikonic spectacle correction did alleviated the asthenopia We confirmed that this symptomatic relief was linked to the reduction of the static and dynamic components of aniseikonia achieved with her contact lens and iseikonic spectacle lenses compared to a standard spectacle lens design.NSERC CanadaCanadian Optometric Education Trust Fun

Effect of near adds on the variability of accommodative response in myopic children

This is the peer reviewed version of the following article: Sreenivasan, V., Irving, E. L., & Bobier, W. R. (2011). Effect of near adds on the variability of accommodative response in myopic children. Ophthalmic and Physiological Optics, 31(2), 145–154, which has been published in final form at https://doi.org/10.1111/j.1475-1313.2010.00818.x. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Purpose: Higher variability of accommodative response (VAR) has been reported in myopes and speculated to be a possible risk factor for the progression of myopia. We investigated whether near adds of +2D and −2D were capable of altering accommodative variability and also determined the influence of near phoria and viewing condition (binocular vs monocular) on the VAR in myopic and emmetropic children. Methods: Twenty-seven myopic and 25 emmetropic children between 7 and 14 years were examined. All children were classified into ‘normophores’ (0 to 4 exo), exophores (>6 exo) or esophores (>2 eso) based on their near phoria. Binocular and monocular steady-state measures of accommodation were obtained for 5 s using a PowerRefractor (Multichannel Co) while children fixated a high contrast target (33 cm) with distance correction, and then with +2D add and −2D add over the corrective lenses. The variation in accommodative responses (VAR) was defined as the standard deviation of the accommodative response during the 5 s period. Results: Myopic children showed higher VAR through their distance spectacle corrections compared to emmetropes (emmetropes = 0.23 ± 0.03D, myopes = 0.37 ± 0.07D, p 0.9). Introduction of a −2D add significantly increased the VAR in both refractive groups; however, myopes showed greater VAR compared to emmetropes (emmetropes = 0.39 ± 0.03D, myopes = 0.53 ± 0.07D, p < 0.001). Near phoria or binocular viewing did not alter the magnitude of fluctuations in either refractive group. VAR significantly correlated with the monocular accommodative error in both refractive groups (emmetropes r2 = 0.34; p < 0.0001; myopes: r2 = 0.35; p < 0.001). Pupil size, while varying with add type, did not confound the VAR. Conclusions: The near steady state accommodative response of young myopes shows greater variability than non-myopes. This difference is maintained when accommodative responses are increased beyond the vergence plane using − 2D adds. However, accommodative fluctuations were reduced to emmetropic levels when the stimulus to accommodation is reduced using a +2D add. The resulting VAR through adds appear to follow that expected from variations in accommodative demands and hence properties of the accommodative controller. Vergence postures (eso and exo phoria) do not appear to influence the VAR with and without near adds.This study was supported by grants from Canada Foundation for Innovation; NSERC Canada (WRB, ELI); CRC (ELI), COETF (VS,WRB,ELI); AOF Ezell fellowship sponsored by Bausch & Lomb (VS)

Binocular Adaptation to +2 D Lenses in Myopic and Emmetropic Children:

This is a non-final version of an article published in final form in Sreenivasan, V., Irving, E. L., & Bobier, W. R. (2009). Binocular Adaptation to +2 D Lenses in Myopic and Emmetropic Children: Optometry and Vision Science, 86(6), 731–740. https://doi.org/10.1097/OPX.0b013e3181a59d78Purpose. To compare vergence adaptation to +2 D addition lenses in myopic and emmetropic children and to evaluate the influence of the accommodative-vergence crosslink (AC/A ratio) on this adaptation. Methods. Nine myopic and 11 emmetropic children fixated a near target at a distance of 33 cm. Measures of binocular and monocular accommodation and phoria were obtained during a 20-min near task with and without +2 D lenses. Response AC/A ratios were determined from the experimental results. Vergence adaptation was quantified by the magnitude of reduction in phoria and the percentage of completeness (PC, return of adapted phoria to habitual level) after the near task. Results. Myopic children showed significantly higher AC/A ratios, which led to greater lens-induced exophoria and a greater demand for vergence adaptation. Both refractive groups showed significant vergence adaptation; however, myopes exhibited significantly reduced (p < 0.01) magnitudes compared with emmetropes (myopes = 3.95 ± 0.15 Δ; emmetropes = 4.41 ± 0.08 Δ). The mean PC was also significantly (p < 0.001) reduced in myopes (61.02 ± 1.57) compared with emmetropes (76.6 ± 2.10). There was a significant correlation between magnitude of adaptation and AC/A in both the refractive groups; however, myopes consistently showed reduced magnitudes compared to emmetropes. AC/A ratio influenced PC in emmetropic but not myopic children. In the accommodation system, +2 D lenses eliminated the accommodative lags observed in myopic children during natural viewing conditions. These lenses resulted in a small over-focus (−0.24 ± 0.27 D) at the onset of near work, which decreased during sustained viewing through the near add. Conclusions. Myopic children demonstrate reduced magnitude and completeness of vergence adaptation to +2 D lenses. The magnitude of vergence adaptation varied with AC/A in both refractive groups; however, the presence of myopia differentiated the amount of adaptation for all AC/A ratios. Conversely, the degree of completeness appears to be primarily associated with the type of refractive error.This work was supported in part by supported by grants from Canada Foundation for Innovation; Natural Sciences and Engineering Research Council of Canada; Canadian Language and Literacy Research Network; and Canadian Research Chair Award

Effect of heterophoria type and myopia on accommodative and vergence responses during sustained near activity in children

The final publication is available at Elsevier via https://doi.org/10.1016/j.visres.2012.01.011 © 2012. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The influence of phoria-type and myopia on changes to vergence and accommodation during prolonged near-task was examined in 53 children. Participants were classified into phoria and refractive categories based on near phoria and cycloplegic refraction respectively. Measures of near phoria, binocular (BA) and monocular accommodation (MA) were obtained before and during a 20 min task when children binocularly fixated a high-contrast target at 33 cm through best corrective lenses. Vergence adaptation and accommodative adaptation were quantified using changes to near phoria and tonic accommodation respectively. The direction and magnitude of vergence adaptation was modified by the phoria-type (p MA while esophores showed MA > BA in both refractive groups. Accommodative adaptation was higher in myopes (p = 0.010) but did not demonstrate a significant effect of phoria (p = 0.4). The influence of phoria-type on vergence adaptation and the pattern of BA vs. MA relates primarily to the varying fusional vergence demands created by the direction of phoria. The greater divergent (or less convergent) shift in vergence adaptation seen in myopes (compared to emmetropes) could be attributed to their higher accommodative adaptation. Nevertheless, the adaptive patterns observed in myopic children do not appear to explain their high response AV/A ratios identified as a risk factor for myopia development.This study was supported by grants from Canada Foundation for Innovation; NSERC Canada (WRB, ELI); CRC (ELI), COETF (VS, WRB, ELI); AOF Ezell fellowship sponsored by Bausch & Lomb (VS)

Can current models of accommodation and vergence predict accommodative behavior in myopic children?

The final publication is available at Elsevier via https://doi.org/10.1016/j.visres.2014.05.008 © 2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Investigations into the progression of myopia in children have long considered the role of accommodation as a cause and solution. Myopic children show high levels of accommodative adaptation, coupled with accommodative lag and high response AC/A (accommodative convergence per diopter of accommodation). This pattern differs from that predicted by current models of interaction between accommodation and vergence, where weakened reflex responses and a high AC/A would be associated with a low not high levels of accommodative adaptation. However, studies of young myopes were limited to only part of the accommodative vergence synkinesis and the reciprocal components of vergence adaptation and convergence accommodation were not studied in tandem. Accordingly, we test the hypothesis that the accommodative behavior of myopic children is not predicted by current models and whether that departure is explained by differences in the accommodative plant of the myopic child. Responses to incongruent stimuli (−2D, +2D adds, 10 prism diopter base-out prism) were investigated in 28 myopic and 25 non-myopic children aged 7–15 years. Subjects were divided into phoria groups – exo, ortho and eso based upon their near phoria. The school aged myopes showed high levels of accommodative adaptation but with reduced accommodation and high AC/A. This pattern is not explained by current adult models and could reflect a sluggish gain of the accommodative plant (ciliary muscle and lens), changes in near triad innervation or both. Further, vergence adaptation showed a predictable reciprocal relationship with the high accommodative adaptation, suggesting that departures from adult models were limited to accommodation not vergence behavior.This study was supported by grants from Canada Foundation for Innovation; NSERC Canada (WRB, ELI); CRC (ELI), COETF (VS, WRB, ELI); AOF Ezell fellowship sponsored by Bausch & Lomb (VS)

Binocular adaptation to near addition lenses in emmetropic adults

The final publication is available at Elsevier via https://doi.org/10.1016/j.visres.2008.02.015 © 2008. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Near addition lenses are prescribed to pre-presbyopic individuals for treatment of binocular motor problems such as convergence excess and to control the progression of myopia. To date, no investigation has looked at the complete sequence of binocular motor responses during a period of near work with +2 D lenses. This investigation evaluated changes to accommodation and vergence responses when young adults sustained fixation at 33 cm with +2 D addition lenses. In addition, the effect of the accommodative vergence cross-link (AV/A) on the magnitude and the completeness of binocular adaptation to these lenses were evaluated. The results showed that +2 D lenses initiate an increase in exophoria and convergence driven accommodation. The degree of the initial induced phoria was dependant upon the magnitude of the AV/A ratio. Vergence adaptation occurred after 3 min of near fixation and reduced the exophoria and convergence driven accommodation. The magnitude of vergence adaptation was dependant upon the size of the induced phoria and hence the AV/A ratio. The completeness of adaptation was seen to vary inversely with induced exophoria and thus the AV/A ratio.This study was supported by grants from Canada Foundation for Innovation; NSERC Canada (E.L.I., W.R.B.); CLLRnet (W.R.B.), CRC and PREA (E.L.I.)

Time Course of Dichoptic Masking in Normals and Suppression in Amblyopes

Purpose: To better understand the relationship between dichoptic masking in normal vision and suppression in amblyopia we address three questions: First, what is the time course of dichoptic masking in normals and amblyopes? Second, is interocular suppression low-pass or band-pass in its spatial dependence? And third, in the above two regards, is dichoptic masking in normals different from amblyopic suppression? Methods: We measured the dependence of dichoptic masking in normal controls and amblyopes on the temporal duration of presentation under three conditions; monocular (the nontested eye—i.e., dominant eye of normals or nonamblyopic eye of amblyopes, being patched), dichoptic-luminance (the nontested eye seeing a mean luminance—i.e., a DC component) and dichoptic-contrast (the nontested eye seeing high-contrast visual noise). The subject had to detect a letter in the other eye, the contrast of which was varied. Results: We found that threshold elevation relative to the patched condition occurred in both normals and amblyopes when the nontested eye saw either 1/f or band-pass filtered noise, but not just mean luminance (i.e., there was no masking from the DC component that corresponds to a channel responsive to a spatial frequency of 0 cyc/deg); longer presentation of the target (corresponding to lower temporal frequencies) produced greater threshold elevation. Conclusions: Dichoptic masking exhibits similar properties in both subject groups, being low-pass temporally and band-pass spatially, so that masking was greatest at the longest presentation durations and was not greatly affected by mean luminance in the nontested eye