Microfluctuations in accommodation: an update on their characteristics and possible role

Charman, W. N.; Heron, Gordon

doi:10.1111/opo.12234

Cited by 86 publications

(126 citation statements)

References 175 publications

(284 reference statements)

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“…Aside from the impact of heart rate variability and respiration on the LFC, part of the LFC is considered to be part of the accommodation control system owing to changes with depth of focus (Charman and Heron 1988, 2015; Winn 2000). Hence, this may be the mechanism which also imparts chaos in the microfluctuations in accommodation.…”

Section: Discussionmentioning

confidence: 99%

“…It is well known that even when fixating on a stationary object of interest, the eye exhibits microfluctuations in accommodation. These fluctuations are a few tenths of a dioptre in magnitude and change at a rate of several Hertz (Charman and Heron 1988, 2015). Since their first observation by Collins (1937), many investigations have been carried out to determine what role, if any, they play in accommodation control.…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity of Chaos Measures in Detecting Stress in the Focusing Control Mechanism of the Short-Sighted Eye

2017

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When fixating on a stationary object, the power of the eye’s lens fluctuates. Studies have suggested that changes in these so-called microfluctuations in accommodation may be a factor in the onset and progression of short-sightedness. Like many physiological signals, the fluctuations in the power of the lens exhibit chaotic behaviour. A breakdown or reduction in chaos in physiological systems indicates stress to the system or pathology. The purpose of this study was to determine whether the chaos in fluctuations of the power of the lens changes with refractive error, i.e. how short-sighted a subject is, and/or accommodative demand, i.e. the effective distance of the object that is being viewed. Six emmetropes (EMMs, non-short-sighted), six early-onset myopes (EOMs, onset of short-sightedness before the age of 15), and six late-onset myopes (LOMs, onset of short-sightedness after the age of 15) took part in the study. Accommodative microfluctuations were measured at 22 Hz using an SRW-5000 autorefractor at accommodative demands of 1 D (dioptres), 2 D, and 3 D. Chaos theory analysis was used to determine the embedding lag, embedding dimension, limit of predictability, and Lyapunov exponent. Topological transitivity was also tested for. For comparison, the power spectrum and standard deviation were calculated for each time record. The EMMs had a statistically significant higher Lyapunov exponent than the LOMs ( vs. ) and a lower embedding dimension than the LOMs ( vs. ). There was insufficient evidence (non-significant p value) of a difference between EOMs and EMMs or EOMs and LOMs. The majority of time records were topologically transitive. There was insufficient evidence of accommodative demand having an effect. Power spectrum analysis and assessment of the standard deviation of the fluctuations failed to discern differences based on refractive error. Chaos differences in accommodation microfluctuations indicate that the control system for LOMs is under stress in comparison to EMMs. Chaos theory analysis is a more sensitive marker of changes in accommodation microfluctuations than traditional analysis methods.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sensitivity of Chaos Measures in Detecting Stress in the Focusing Control Mechanism of the Short-Sighted Eye

2017

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“…During monocular viewing, many factors can serve as directional cues for the visual system, such as apparent distance and size,3 chromatic aberration of the eye1, 4, 5 and microfluctuations of accommodation 6, 7, 8. Monochromatic aberrations also may be used to determine the direction of defocus, since even‐order aberrations such as astigmatism and spherical aberration form a different point spread function (PSF) depending on the sign of defocus (whether images are formed behind or in front of the photoreceptors layer) 9…”

Section: Introductionmentioning

confidence: 99%

Human eyes do not need monochromatic aberrations for dynamic accommodation

Bernal-Molina

Marín-Franch

Águila-Carrasco

et al. 2017

Ophthalmic Physiologic Optic

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PurposeTo determine if human accommodation uses the eye's own monochromatic aberrations to track dynamic accommodative stimuli.MethodsWavefront aberrations were measured while subjects monocularly viewed a monochromatic Maltese cross moving sinusoidally around 2D of accommodative demand with 1D amplitude at 0.2 Hz. The amplitude and phase (delay) of the accommodation response were compared to the actual vergence of the stimulus to obtain gain and temporal phase, calculated from wavefront aberrations recorded over time during experimental trials. The tested conditions were as follows: Correction of all the subject's aberrations except defocus (C); Correction of all the subject's aberrations except defocus and habitual second‐order astigmatism (AS); Correction of all the subject's aberrations except defocus and odd higher‐order aberrations (HOAs); Correction of all the subject's aberrations except defocus and even HOAs (E); Natural aberrations of the subject's eye, i.e., the adaptive‐optics system only corrected the optical system's aberrations (N); Correction of all the subject's aberrations except defocus and fourth‐order spherical aberration (SA). The correction was performed at 20 Hz and each condition was repeated six times in randomised order.ResultsAverage gain (±2 standard errors of the mean) varied little across conditions; between 0.55 ± 0.06 (SA), and 0.62 ± 0.06 (AS). Average phase (±2 standard errors of the mean) also varied little; between 0.41 ± 0.02 s (E), and 0.47 ± 0.02 s (O). After Bonferroni correction, no statistically significant differences in gain or phase were found in the presence of specific monochromatic aberrations or in their absence.ConclusionsThese results show that the eye's monochromatic aberrations are not necessary for accommodation to track dynamic accommodative stimuli.

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“…Accommodation is thought to respond to signals (cues) that are either environmental or inherent to the eye. Some of the signals inherent to the physiology of the human eye that may affect accommodation responses are: retinal image blur from monochromatic (Campbell and Westheimer, 1960, Stark and Takahashi, 1965, Tucker and Charman, 1979), and chromatic aberrations (Kruger et al, 1993, Kruger and Pola, 1986), and microfluctuations in accommodation (Charman and Heron, 1988, Charman and Heron, 2015). Some of the environmental signals are luminance, interposition, perceived distance, and apparent size (Ittelson and Ames, 1950, Johnson, 1976, Kotulak and Morse, 1995, Kruger and Pola, 1987, Toates, 1972).…”

Section: Introductionmentioning

confidence: 99%