Myopia Profile


The contrast theory in myopia: Q&A with Prof. Earl Smith, Marcella McParland and Jill Woods

Posted on April 22nd 2024 by Professor Earl Smith

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In this article:

In this article, we speak to research optometrists Professor Earl Smith, Dean at the University of Houston College of Optometry, Marcella McParland who is Vice President of Clinical, Medical and Professional Affairs at SightGlass Vision™  and Jill Woods, Head of Clinical Research at CORE, Centre for Ocular Research & Education, University of Waterloo in Canada about the contrast theory and the CYPRESS clinical trial which explored the use of the SightGlass Vision™  Diffusion Optics Technology™  (DOT™ ) spectacle lenses for myopia control.

What is contrast?


In the context of vision, contrast describes the differences in color (color contrast) or brightness (luminance contrast) over time or between adjacent objects. Contrast is critical for the detection of objects on a background of a different luminance or color. The human visual system, beginning in the retina, is organized to detect contrast and is more sensitive to contrast than to absolute luminance.

Why is contrast important when it comes to myopia?


It has been well established that eye growth and refractive development is a visually guided process.1 The primary visual signals that influence eye growth are derived from defocus and contrast,1,2 and are processed locally within the eye.3 Many of the retinal neurons are, in essence, contrast detectors. 

There are many examples of how variations in contrast can influence refractive development. In primates, imposing significant reductions in retinal image contrast under outdoor ambient lighting conditions produces hyperopia. In humans, abnormally high retinal contrast signalling evident in familial myopia promotes myopia progression. These findings suggest a potential therapeutic use of contrast management in myopia control. Recent well-structured clinical trials have demonstrated that mild reductions in retinal contrast imposed by spectacle diffusion lenses can slow the progression of myopia in children.

While there is still much to learn about the role of vision in regulating refractive development, contrast management represents a promising new approach to myopia management.     

What is artificial and natural contrast?


Our eyes are exposed to a range of contrast levels in normal everyday life. 

Artificial contrast describes higher contrast visual stimuli and environments made by humans: for example, books with dark text on a white background or digital devices and also modern urban environments. 

Natural contrast refers to lower contrast stimuli evident in the natural world: for example, the countryside or a football field and are made up of different shades of green and blue sky with clouds.  

How does artificial and natural contrast influence myopia?


We have observed a connection between contrast levels in different environments and myopia progression. 

Higher levels of education, greater amounts of near work and urban environments are established myopia risk factors5 and are all sources of higher, artificial contrast. Contrast theory states that high artificial contrast overstimulates the retina (particularly the bipolar cells which are the first retinal cells to detect contrast), leading to an overstimulation of eye growth and myopia progression.

Increased time outdoors is protective against the onset of myopia6 and may help control myopia progression.7 The natural outdoor environment provides a lower, natural contrast visual experience. This natural contrast elicits lower-level retinal activity that does not appear to cause an acceleration of eye growth. 

DOT spectacle lenses are designed to slow myopia progression by slightly lowering retinal contrast to mimic more natural contrast.

What is the CYPRESS clinical trial?

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The purpose of the CYPRESS clinical trial was to evaluate the safety and efficacy of DOT spectacle lenses in reducing the progression of juvenile myopia. It was a multicentre, randomised, controlled clinical trial that enrolled 256 children aged 6-10 years across 14 North American clinical sites. The original 3-year study was extended for 1 year and the Control group was retained throughout. I led the data collection at the Centre for Research and Education (CORE) at the University of Waterloo.

What were the key learnings from the CYPRESS clinical trial?

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The CYPRESS clinical trial provides robust evidence that DOT lenses are safe and effective in children from age 6. 

Of particular interest are the results of the children starting the study at age 6-7 years because these children are likely to progress to high levels of myopia and there is a paucity of efficacy data available for this young age group. After 3 years, myopia progression was slowed by 0.84 D in cycloplegic SER and 0.32 mm in axial length in the 23 6–7-year-old children who wore DOT lenses. This benefit continued to year 4, for the 61% who enrolled into the one-year extension study.

The CYPRESS clinical trial expands the evidence-base for myopia control spectacle lenses and has several unique aspects, as the only spectacle lens study to demonstrate myopia control efficacy in a multicentre clinical trial with North American children from age 6. 

These results support the hypothesis that myopia progression can be slowed by managing contrast.

Our research team at CORE have also investigated the choroidal response with DOT lenses, which will be presented at the 2024 Association for Research in Vision and Ophthalmology (ARVO) conference in May.

DOT spectacle lenses are pending FDA approval & are not available for sale within the United States.

Meet the Authors:

About Professor Earl Smith

Prof. Earl Smith has been ranked ninth in the world among optometrists by Clinical and Experimental Optometry, the peer-reviewed optometric journal in Australia.

In a remarkable career as a globally acclaimed scientist and professor, his work in myopia is radically changing how vision care practitioners help children see the world.

Over a career in myopia research spanning 30 years, Prof. Smith has systematically unraveled how visual experience influences refractive error development. His original idea that peripheral defocus strongly impacts the rate at which eyes grow is the scientific foundation for all the optical methods of myopia control in use today. 

Prof. Earl Smith has been an integral part of the University of Houston College of Optometry (UHCO) since 1978. As UHCO Dean, he facilitated the growth of the college into a leading global center for optometry. 

About Marcella McParland

Marcella McParland graduated as an optometrist from Manchester University in 1986 and has worked in  private practice, hospital settings and in the contact lens industry. She is passionate about education, leading many largescale educational and digital initiatives in Europe, Middle East and Africa (EMEA). Marcella has authored clinical articles and presented at European and International conferences. She is Past President of the BCLA, past EUROMCONTACT Board member and holds fellowships for American Academy of Optometry, International Association of Contact Lens Educators and the BCLA. Her current interests are in silicone hydrogel materials and myopia management solutions for children.

About Jill Woods

Jill Woods is Head of Clinical Research at CORE, Centre for Ocular Research & Education, University of Waterloo in Canada, which she joined in 2005. Her role involves overseeing clinical research trials from concept to final report, managing the workload of the clinical research team and oversight of administrative and regulatory processes. She is involved in contact lens & dry eye research, with particular interest in presbyopia, contact lens comfort & controlling myopia progression. 

Jill completed her Optometry degree in London, UK and her Master’s in Waterloo, Canada. Previous experience includes her own private practice, low-vision hospital work, clinical teaching.  

This content is brought to you thanks to unrestricted educational grant from


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