A cinematographic method for the dynamic study of the image formation by the human eye. Microfluctuations of the accommodation

244

187

When a young observer attempts to accommodate steadily on a fixed stimulus, the norminally steady‐state response shows small instabilities or fluctuations (sometimes termed microfluctuations or oscillations). These fluctuations typically have an amplitude of a few tenths of a dioptre and a frequency spectrum extending up to a few Hertz. The properties of these fluctuations are described for various viewing conditions: pupil diameter, target vergence, target form, target contrast, and target luminance all influence the frequency spectra of the oscillations, as may anomalies of vision such as amblyopia. The possible roles that the fluctuations might play in the function of the accommodative system are discussed. It is suggested that the higher frequency components around 2 Hz may arise from the mechanical and elastic characteristics of the lens, zonule and ciliary body. Components at lower frequencies (<0.5 Hz) may be of more significance in the function of the accommodative control system.

Section: Dependence On Pupil Diametermentioning

confidence: 83%

Fluctuations in accommodation: a review

Charman

Heron

1988

244

187

“…Second, motor-induced factors may influence the perception of blur. Changes in position of the image of the target on the retina vary due to small rapid continuous fluctuations ( * 0.10 D; 2 Hz) in crystalline lens shape/ power even before the target begins to move (Campbell and Westheimer, 1960;Arnulf, Santamaria and Bescos, 1981). Also, small fixational eye movements may be used to help detect, interpret and process the blur (Finchman, 1951;Crane, 1966;Stark et al, 1984).…”

Section: Discussionmentioning

confidence: 99%

Dual‐mode behaviour in the human accommodation system

Hung

Ciuffreda

1988

The human accommodation system was investigated using a dynamic infra-red optometer to determine whether its feedback control process exhibited dual-mode behaviour. Ramp changes of target accommodative demand presented monocularly at various velocities (0.5-0.6 D s-1) with a fixed 2 D amplitude elicited two modes of behaviour. Smooth ramp movements were observed for low-velocity stimuli, whereas step responses predominated for high-velocity stimuli. At intermediate velocities, combined step-ramp responses were more prevalent. The characteristic of these step-ramp responses showed two important properties that suggest a pre-programming mechanism. The amplitude of the step portion of a step-ramp response approximated the value of the ramp stimulus at the time corresponding to the end of the step movement. Also, the initial step amplitude increased with increasing target ramp velocity. It appears that the amplitude of the preprogrammed accommodative movement was based on an estimate of the expected ramp target position at the end of the response. These findings are consistent with a recent unifying theory of oculomotor control in which the various oculomotor subsystems (versional and vergence eye movements and accommodation) each has fast and slow components. The fast component exhibits preprogramming, while the slow component shows continuous feedback control.

“…Since the early work of Collins (1937), the short-term fluctuations of the ocular aberrations have been studied by many investigators, who have found instabilities as large as a quarter of a diopter in steady-state accommodation (Campbell et al, 1959;Charman and Heron, 1988;Winn and Gilmartin, 1992;Hofer et al, 2001a;Zhu et al, 2004). Arnulf et al (1981) used a binocular real-time double-pass instrument (Santamarı´a et al, 1987) to demonstrate the fast temporal changes of the eyeÕs optics. Although the major fluctuations are found in defocus, almost all other low-and high-order aberrations have been shown to exhibit temporal instability, with similar spectra and frequency components (Hofer et al, 2001a;Nirmaier et al, 2003;Zhu et al, 2004Zhu et al, , 2006.…”

Section: Introductionmentioning

confidence: 99%

Temporal dynamics of ocular aberrations: monocular vs binocular vision

Mira-Agudelo

Lundström

Artal

2009

The temporal dynamics of ocular aberrations are important for the evaluation of, e.g. the accuracy of aberration estimates, the correlation to visual performance, and the requirements for real-time correction with adaptive optics. Traditionally, studies on the eye's dynamic behavior have been performed monocularly, which might have affected the results. In this study we measured aberrations and their temporal dynamics both monocularly and binocularly in the relaxed and accommodated state for six healthy subjects. Temporal frequencies up to 100 Hz were measured with a fast-acquisition Hartmann-Shack wavefront sensor having an open field-of-view configuration which allowed fixation to real targets. Wavefront aberrations were collected in temporal series of 5 s duration during binocular and monocular vision with fixation targets at 5 m and 25 cm distance. As expected, a larger temporal variability was found in the root-mean-square wavefront error when the eye accommodated, mainly for frequencies lower than 30 Hz. A statistically-significant difference in temporal behavior between monocular and binocular viewing conditions was found. However, on average it was too small to be of practical importance, although some subjects showed a notably higher variability for the monocular case during near vision. We did find differences in pupil size with mono- and binocular vision but the pupil size temporal dynamics did not behave in the same way as the aberrations' dynamics.