Paper title: IMI: Accommodation and Binocular Vision in Myopia Development and Progression
Authors: Nicola S. Logan (1), Hema Radhakrishnan (2), Fiona E. Cruikshank (2), Peter M. Allen (3), Praveen K. Bandela (4,5), Leon N. Davies (1), Satoshi Hasebe (6), Safal Khanal (7), Katrina L. Schmid (8), Fuensanta A. Vera-Diaz (9), James S. Wolffsohn (1)
- School of Optometry, Aston University, Birmingham, United Kingdom
- Division of Pharmacy and Optometry, School of Health Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Vision and Hearing Sciences Research Centre, School of Psychology and Sports Sciences, Anglia Ruskin University, Cambridge, United Kingdom
- Brien Holden Vision Institute, Sydney, New South Wales, Australia
- School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia
- School of Optometry, Aston University, Birmingham, United Kingdom
- Department of Ophthalmology, Kawasaki Medical School, Kurashiki, Okayama, Japan
- School of Optometry, University of Alabama at Birmingham, Birmingham, Alabama, United States
- New England College of Optometry, Boston, Massachusetts, United States
Date: Apr 2021
Reference: Logan NS, Radhakrishnan H, Cruickshank FE, Allen PM, Bandela PK, Davies LN, Hasebe S, Khanal S, Schmid KL, Vera-Diaz FA, Wolffsohn JS. IMI Accommodation and Binocular Vision in Myopia Development and Progression. Invest Ophthalmol Vis Sci. 2021 Apr 28;62(5):4. (Link to open access paper)
It has been thought that myopic children show greater and more frequent lags in accommodation than emmetropic children and where there is a higher accommodative demand, there will be a larger lag of accommodation giving rise to hyperopic defocus, diffuse blur and a stimulus to axial length growth. However, higher lags of accommodation have also been seen in children after myopia has already developed, therefore making elevated accommodative lag a poor predictive factor for myopia. Lags of accommodation may not give poor image quality in combination with other factors such as pupil size and chromatic aberrations, suggesting there is no causal link with myopia development or progression.
Increased AC/A ratios have been found prior to myopia onset. A higher AC/A ratio has corresponded with increased lag of accommodation in myopic children and may bring about esophoria for near, but there has been no association found with esophoria and faster myopic progression rates in studies using bifocal or progressive add spectacles.
Aberrations within the eye may provide a clue; spherical aberration acts as a defocus cue in the central visual field and changes with accommodation. Increased accommodative lag and negative spherical aberration during prolonged near work periods may provide poorer image quality for myopes then for emmetropes who experience lower lags.
Further image degradation may be due to myopes demonstrating increased contrast adaptation and reduced sensitivity to defocus blur compared to emmetropes. This can be a result of prolonged periods of near work (high contrast text), leading to perceptual blur and consequently myopia.
Prolonged accommodation for a near distance has been found to give near induced transient myopia: a delay in relaxing the accommodation for distance viewing. The retinal defocus provided is larger, and continues longer, for late-onset and progressing adults and children.
Closer working distances are common in children and reduce further with increased concentration. This leads to higher lags of accommodation which reduce image quality with higher spatial frequencies.
There is little strong current evidence associating accommodation and binocular status with the development and progression of myopia.
Animal studies have shown the emmetropisation process may be disrupted by hyperopic defocus, leading to myopia. In humans, retinal blur from accommodative lag is more common in myopes and the increased hyperopic defocus it provides may be a result of myopia, rather than a cause.
Esophoria at near may be a result of under-accommodation and a feature of myopia, rather than a cause.
A deeper understanding of the role accommodation and binocular vision plays in myopia development and progression is needed so that evidence-based targeted intervention methods can be produced.
What does this mean for my practice?
Despite the lack of support for a role of accommodation so far, eyecare practitioners should continue to assess the binocular status of myopes, and those at risk of myopia, to ensure they have a clear retinal image. Myopes may be more likely to show unstable accommodative responses, which in turn would impede clear image formation and accommodation helps reduce hyperopic defocus.
Closer working distances are common in children and reduce further with increased concentration. This leads to higher lags of accommodation which reduce image quality with higher spatial frequencies. Children should be encouraged to maintain a further working distance to reduce their lag of accommodation.
What do we still need to learn?
The optical mechanisms involved in accommodation and convergence in near work tasks and the changes in the choroid due to the ciliary body need to be further explored to explain their roles in myopia development and progression.
Title: IMI Accommodation and Binocular Vision in Myopia Development and Progression
Authors: Nicola S. Logan, Hema Radhakrishnan, Fiona E. Cruikshank, Peter M. Allen, Praveen K. Bandela, Leon N. Davies, Satoshi Hasebe, Safal Khanal, Katrina L. Schmid, Fuensanta A. Vera-Diaz, James S. Wolffsohn
The role of accommodation in myopia development and progression has been debated for decades. More recently, the understanding of the mechanisms involved in accommodation and the consequent alterations in ocular parameters has expanded. This International Myopia Institute white paper reviews the variations in ocular parameters that occur with accommodation and the mechanisms involved in accommodation and myopia development and progression. Convergence is synergistically linked with accommodation and the impact of this on myopia has also been critiqued. Specific topics reviewed included accommodation and myopia, role of spatial frequency, and contrast of the task of objects in the near environment, color cues to accommodation, lag of accommodation, accommodative-convergence ratio, and near phoria status. Aspects of retinal blur from the lag of accommodation, the impact of spatial frequency at near and a short working distance may all be implicated in myopia development and progression. The response of the ciliary body and its links with changes in the choroid remain to be explored. Further research is critical to understanding the factors underlying accommodative and binocular mechanisms for myopia development and its progression and to guide recommendations for targeted interventions to slow myopia progression.
Ailsa Lane is a contact lens optician based in Kent, England. She is currently completing her Advanced Diploma In Contact Lens Practice with Honours, which has ignited her interest and skills in understanding scientific research and finding its translations to clinical practice.