Accommodation and the through-focus changes of the retinal image

Charman, W. N.

doi:10.1007/978-3-0348-7586-8_10

Cited by 6 publications

(8 citation statements)

References 42 publications

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“…The idea that the system depends on the dynamic evaluation of the changes in image structure and contrast brought about by the accommodation microfluctuations has, however, recently been revisited by Mackenzie et al . and Metlapally et al.…”

Section: Later Workmentioning

confidence: 99%

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

Charman

Heron

2015

Ophthalmic Physiologic Optic

113

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Purpose: Following the recognition, some 80 years ago, that the accommodation of the eye is not stable but fluctuates over a range of about AE0.5 D, mainly at frequencies of up to a few Hz, there has been a continuing interest in the characteristics of these microfluctuations (MFs) and their possible role in the control of accommodation. This paper reviews relevant work carried out since 1988, when we previously reviewed the same topic (Charman WN, Heron G. Fluctuations in accommodation: a review. Ophthalmic Physiol Opt 1988; 8: 153-164). Recent findings: Studies relating to the effects on the MFs of stimulus form, luminance and vergence are described, together with those of pupil diameter, age and ametropia. Important advances in the understanding of the links between the characteristics of the MFs and those of the cardiopulmonary system, higher-order aberrations and ocular depth-of-focus are outlined. Only limited progress has been made in understanding the role of MFs in accommodation control. Summary: While the dependence of the characteristics of the MFs in relation to observing conditions is now reasonably well understood, their involvement in accommodation control still needs clarification. The current consensus appears to be that any role is more likely to be concerned with maintaining an appropriate response, rather than in initiating responses to abrupt changes in stimulus vergence. Fluctuations at lower temporal frequencies (<0.6 Hz) are probably important to the control process, which may make use of the associated changes in the contrast and spatial frequency spectrum of the retinal image.

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Section: Later Workmentioning

confidence: 99%

“…The question is, then, how might such temporal changes in image contrast be used to produce or maintain a reasonably appropriate accommodation response to a typical object with a broadband spatial frequency spectrum? Early work explored some of the possible implications of this idea with aberration‐free eye models. Mackenzie et al .…”

Section: Later Workmentioning

confidence: 99%

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

Charman

Heron

2015

Ophthalmic Physiologic Optic

113

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“…If the level of accommodation to a constant stimulus is examined with good time resolution, small fluctuations in accommodation are observed, having an amplitude of about 0.1 D and a frequency spectrum extending to a few hertz 99 (Figure 4). It is thought that the low‐frequency components of these fluctuations may have a role in helping to maintain the steady‐state response 100,101 …”

Section: Accommodation In the Young Adultmentioning

confidence: 99%

“…It is thought that the low-frequency components of these fluctuations may have a role in helping to maintain the steady-state response. 100,101 When the mean steady-state response level achieved is compared with the stimulus level over the available range of accommodation, a plot of the form of Figure 5A is usually found. 20,21 There is over-accommodation ('accommodative lead') for distant objects and underaccommodation ('accommodative lag') for near objects.…”

Section: Retinal Image Quality During Accommodation Accuracy Of Focusmentioning

confidence: 99%

The eye in focus: accommodation and presbyopia

Charman

2008

Clinical and Experimental Optometry

206

136

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Current understanding of the anatomy, function and performance of the accommodative system of the young, adult human eye is outlined. Most major current models of the accommodative mechanism are based on Helmholtz's original ideas but, despite of a growing volume of related research, uncertainty continues over the relative contributions made to the overall mechanism by different ocular structures. The changes with age are then discussed. Although the amplitude of accommodation decreases steadily from later childhood, the speed and accuracy of the system within the available amplitude are little impaired until the age of about 40, when the amplitude falls below that needed for normal near work. A review of the available evidence on age-related change in the lens, capsule, ciliary body and other relevant ocular structures confirms that geometric and viscoelastic lenticular changes play major roles in the progressive loss of accommodation. Other factors may also contribute in an, as yet, unquantified way and a full understanding of the origins of presbyopic change remains elusive.

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“…In addition, there is evidence that image contrast of the 5 cyc/deg stimulus would be more significantly affected by defocus than low spatial frequency targets. 32,33 The adapting stimulus was presented at a viewing distance of 50 cm and was matched in size to the mfERG stimulus array, subtending a visual angle of 30 • horizontally and 27.8 • vertically.…”

Section: Adapting Stimulimentioning

confidence: 99%