Myopia

Myopia

Myopia (short-sightedness) is one of the major causes of vision impairment in young populations around the world.  Although it is known that myopia occurs due to excessive axial growth of the eye, the mechanisms that lead to this increased eye growth in human myopia development and progression are still not clearly understood.  Recent decades have also seen dramatic increases in the prevalence of myopia in young populations in many developed nations around the world, with myopia reaching epidemic levels in young populations in developed East Asian cities.  The rising global prevalence of myopia provides a strong catalyst to better understand myopia and its development in human eyes and for the development of effective interventions for myopia control.

Our research aims to better understand the environmental factors involved in the development and progression of myopia, and to expand our knowledge of the ocular changes linked to myopia.

Light and eye growth

We utilize high resolution ocular imaging, and novel wearable sensor technology coupled with innovative experimental paradigms, in order to provide new insights into a range of factors involved in human myopia.  Our current projects in the myopia field aim to further our knowledge in the following broad areas:

  • The impact of light exposure on human eye growth and myopia.
  • The role of the choroid (the vascular tissue that provides oxygen and nutrients to the retina) in human myopia and eye growth
  • The impact of near-work on ocular parameters in myopia
  • The role of the optical characteristics of the eye in myopia development
  • Interventions to control myopia development
  • The interaction between diurnal and seasonal factors and eye growth

Our work using wearable sensors capable of measuring light exposure and physical activity provides new knowledge on the typical patterns of light exposure in myopia, and demonstrates associations between ambient light exposure and the rate of growth in the human eye.  The data in the lower panel of the figure to the right, collected as part of the role of outdoor activity in myopia study (ROAM study), show the average light exposure over the course of the day in myopic and non-myopic children, demonstrating significantly greater daily light exposure in non-myopic children.

The Choroid

Using high-resolution optical coherence tomography (OCT), we are able to reliably image and measure the human choroid in-vivo (top left).  Our work examining the choroid in myopia has demonstrated substantial choroidal thinning associated with myopia in childhood (bottom left).  Dynamic changes in the choroid are also observed over time, and these changes also appear to be linked to the rate of eye growth in childhood (right). This suggests that short-term choroidal variations appear to be providing a biomarker associated with eye growth and myopia.

Studies with animals have shown that retinal image blur can lead to predictable changes in choroidal thickness and eye growth.  Our work in this area aims to understand how the human eye responds to imposed image blur, through the use of high resolution imaging techniques and short-term image blur experimental methods.  We have provided the first evidence that, similar to other animal species, the length of the human eye also responds to imposed defocus consistent with the eye detecting the sign of blur.  Thse changes appear to be driven by choroidal thickness changes.  Our current work aims to expand our understanding of the eye’s response to blur, including studies examining the time course and spatial distribution of change, and the influence of the autonomic nervous system upon the eye’s response to blur.

 

Changes in axial length for various subject groups, in response to the amount of exposure time to defocus

 

Near Work

Performing close-up visual tasks has long been considered a potential risk factor in the development and progression of myopia. Our research utilizes high resolution, non-invasive imaging to better understand the ocular changes that occur when we perform near work. These studies demonstrate that near work is accompanied by a small magnitude transient increase in the length of the eye, and that aspects of these near work induced changes appear to be altered in eyes with myopia (e.g. the transient eye elongation takes longer to recover to normal in myopic eyes, see top panel of figure below). These eye length changes appear to be in-part driven by changes in choroidal thickness (bottom panel of figure below), and our work continues to examine the potential changes in other ocular structures such as the sclera in near work.


Further Reading

(2016) Ocular and environmental factors associated with eye growth in childhood. Optometry and Vision Science, 93(9), pp. 1031-1041. (https://eprints.qut.edu.au/105528/)

, , , & (2015) Longitudinal changes in choroidal thickness and eye growth in childhood. Investigative Ophthalmology and Visual Science, 56(5), pp. 3103-3112. (https://eprints.qut.edu.au/93313/)

, , , & (2015) Regional changes in choroidal thickness associated with accommodation. Investigative Ophthalmology and Visual Science, 56(11), pp. 6414-6422. (https://eprints.qut.edu.au/89266/)

, , , , & (2014) Axial elongation associated with biomechanical factors during near work. Optometry and Vision Science, 91(3), pp. 322-329. (https://eprints.qut.edu.au/67904/)

, , , & (2013) Choroidal thickness in myopic and non-myopic children assessed with enhanced depth imaging optical coherence tomography. Investigative Ophthalmology and Visual Science, 54(12), pp. 7578-7586. (https://eprints.qut.edu.au/67898/)

, , & (2013) Hyperopic defocus and diurnal changes in human choroid and axial length. Optometry and Vision Science, 90(11), pp. 1187-1198. (https://eprints.qut.edu.au/63732/)

, , , & (2013) Retinal and choroidal thickness in myopic anisometropia. Investigative Ophthalmology and Visual Science, 54(4), pp. 2445-2456. (https://eprints.qut.edu.au/58971/)

, , & (2012) Axial length and choroidal thickness changes accompanying prolonged accommodation in myopes and emmetropes. Vision Research: an International Journal for Functional Aspects of Vision, 72, pp. 34-41. (https://eprints.qut.edu.au/55082/)

, , & (2012) Monocular myopic defocus and daily changes in axial length and choroidal thickness of human eyes. Experimental Eye Research, 103, pp. 47-54. (https://eprints.qut.edu.au/55086/)

Read, Scott A., Collins, Michael J., & Sander, Beata. (2010) Human optical axial length and defocus. [QUT ePrint record will be available shortly.].