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

Abstract

Phone: +12269783740The final publication is available at Elsevier via http://doi.org/10.1016Elsevier via http://doi.org/10. /j.visres.2016Elsevier via http://doi.org/10. .11.001 © 2017. This manuscript version is made available under the .0/ Highlights 1. Blur accommodation but not convergence accommodation (CA/C) is reduced in myopes. 2. Myopes show a similar rate of change in the response dynamics like the emmetropes. 3. Atypical response patterns exist with blur accommodation but decrease with age. 4. Pure sensory or motor deficit doesn't predict the abnormal behavior in myopes. 5. Model simulation with altered sensory and motor gain predicts the myopic behavior.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 non-myopic 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.

Accommodation lags are higher in myopia than in emmetropia: Measurement methods and metrics matter

“…Labhishetty and Bobier 51 conducted a similar investigation to that of Jiang 50 with emmetropic and myopic children, as well as young adults for comparison. They collected data on the transient aspects of accommodation in emmetropes and myopes and used a similar control theory model to see whether their observed results could be simulated.…”

Lags and leads of accommodation in humans: Fact or fiction?

“…Accommodative responses of myopes are often different from those of emmetropes. Specifically, children, adolescents, and young adults with progressive myopia exhibit larger accommodative lags than age-matched emmetropes (Gwiazda et al, 1993;Abbott et al, 1998;He et al, 2005;Labhishetty & Bobier, 2017). In these studies, the myopic refractive error was corrected with spectacles or contact lenses and accommodation was measured objectively.…”

Is 25 Hz enough to accurately measure a dynamic change in the ocular accommodation?

“…Relationship between these parameters can be quantified using the first (velocity) and second order (acceleration) main sequence analysis. Main sequence (MS) relationship has been commonly used to describe the dynamic aspect of a motor system 1, 3, 24, 25, 26. It is the rate of change of velocity or acceleration as a function of the response amplitude.…”