Purchase this article with an account.
G. Heron, W.N. Charman; Modelling Accommodation and Ageing: The Influence of Anticipation and Voluntary Factors on Accommodation Responses . Invest. Ophthalmol. Vis. Sci. 2005;46(13):718.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Introduction: Accommodation responses can be augmented by non–visual factors like volition and anticipation of stimulus behaviour. In this study we compare accommodation responses with ageing for both step changes and sinusoidally driven changes where these non–visual features of accommodation behaviour can be expected. Methods: Accommodation responses to both step and sinusoidal changes in target vergence were measured using a Canon R1 optometer. Nineteen subjects, aged 18 to 49 years gave informed consent to participate in the study and eleven frequencies were used. Results: For step changes, response amplitude was found to decline with ageing. However there was little evidence that either reaction or response times changed with age. For sinusoidal stimuli the results were characterised by gain (the mean peak–to–peak responses divided the mean peak–to– peak stimulus) and the phase lag (the time lag between each peak or trough in the response in relation to those in the stimulus, divided by the stimulus period and multiplied by 360o). For all subjects both gain and phase were found to vary essentially linearly as a function of temporal frequency: gain fell and phase lag increased as frequency increased. Discussion: A value for gain at zero frequency was determined by extrapolation of the gain versus frequency graph for each subject, and this declined with age. For many subjects (including some older ones) gain was found to exceed the amplitude of the stimulus. Presumably these subjects were able to use volition and anticipation of the repetitive stimulus to embellish their accommodation responses. Extrapolation to the frequency axis of the gain versus frequency graph revealed the frequency at which the gain was zero and no response evident. This determines the bandwidth of the frequency response and was found to be remarkably constant for subjects less than 41 years of age. Delays associated with phase lag were found to increase with age and for older subjects this exceeded 0.6 s. Conclusions: anticipation is found to be an important factor differentiating step and sinusoidally driven responses: this imposes limitations when modelling accommodation using data derived from sinusoidal responses.
This PDF is available to Subscribers Only