Comparison of the amplitude of accommodation determined subjectively and objectively in South African university students
Background: Historically, two clinical methods have been used for measuring the amplitude of accommodation, which are the push up and minus lens methods. However, it has been documented that the push up method overestimates amplitude of accommodation, while the minus lens method underestimates it. Aim: The purpose of this study was to compare subjective and objective procedures for determining the monocular amplitude of accommodation in young optometry students. Setting: The study was conducted in the optometry clinic at the university. Methods: Amplitude of accommodation was measured on 45 optometry students (17 males and 28 females, whose ages ranged from 21 to 27 years) using the push up, push down, minus lens, modified dynamic retinoscopy and Pascal dynamic retinoscopy methods. Data were collected by three different examiners in this study. One examiner measured all the subjective tests, while another examiner measured the modified dynamic retinoscopy. The third examiner measured the Pascal heterodynamic retinoscopy. Results: The highest amplitude of accommodation was obtained using the push up method (10.23 1.67 D) while the minus lens method gave the lowest subjective finding (8.43 1.68 D) However, the subjective methods generally produced comparable results. Both retinoscopic methods showed the lowest mean amplitude of accommodation of approximately 6.50 1.40 D. However, there was a high correlation between the various methods. Conclusion: The push up and push down methods overestimate the true amplitude of accommodation because of the relative magnification, while the minus lens method creates an abnormal viewing environment in which the target is stationary but the stimulus becomes increasingly minified. Subjective amplitude of accommodation is an inadequate measure to assess any true accommodation because it fails to differentiate between passive depth of focus and an active accommodative power change in the eye. Therefore, subjective measurement of the amplitude of accommodation may suggest that accommodation is present when it is not. Further research is needed to further validate dynamic retinoscopy as the optimal or best possible routine clinical method to assess the true amplitude of accommodation.