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

TitleIs 25 Hz enough to accurately measure a dynamic change in the ocular accommodation?
Publication TypeJournal Article
Year of Publication2019
AuthorsLabhishetty, V., W. Bobier, and V. Lakshminarayanan
JournalJournal of Optometry
Keywordsaccommodation, adolescent, adult, child, devices, eye refraction, Fast Fourier transformation, female, Fourier analysis, human, Humans, Main sequence, male, Ocular, optometry, physiology, procedures, Refraction, refractometry, Sampling rate, young adult

Background: Accommodation is often recorded at a low sampling rate using devices such as autorefractors that are designed to measure the static refractive error. It is therefore important to determine if that resolution is sufficient to accurately measure the dynamic properties of accommodation. The current study provides both theoretical and empirical evidence on the ideal sampling rate necessary to measure a dynamic response. Methods: Accommodative and disaccommodative step stimuli ranging from 1–3D (1D steps) were presented using a Badal optical system. Responses from 12 children (8–13 years) and 6 adults (20–35 years) were recorded using a dynamic photorefractor (DPR). Fast Fourier transformation was applied to the unsmoothed dynamic responses including position, velocity and acceleration. Also, velocity and acceleration main sequence (MS) characteristics were compared between three photorefractor conditions on 3 subjects. Results: The Nyquist sampling limit necessary to accurately estimate position, velocity and acceleration was at least 5, 10 and 70 Hz, respectively. Peak velocity and acceleration were significantly underestimated at a lower rate (p 0.5). Conclusion: Contrary to the previous findings, a dynamic accommodative response exhibited frequencies larger than 10 Hz. Stimulus direction and amplitude had no influence on the frequencies present in the dynamic response. Peak velocity and acceleration can be significantly underestimated when sampled at a lower rate. Taken as a whole, low sampling rate instruments can accurately estimate static accommodation, however, caution needs to be exercised when using them for dynamic accommodation. © 2018 Spanish General Council of Optometry