Prof Carly Lam on Myopia ProgressionCarly Lam, Professor of the School of Optometry, The Hong Kong Polytechnic University (HKPU) has studied myopia for 30 years. She and her colleague, Professor Chi-ho To, are the brains behind MiyoSmart Defocus Incorporated Multiple Segments (DIMS) spectacle lenses, which was based on the concept of the defocus incorporated soft contact (DISC) lens and developed in collaboration with Hoya. mivision recently caught up with Prof Lam on the Gold Coast, where she was speaking to optometrists at the Eyecare Plus conference. Q: How did your DISC research lead to DIMS? We started with animal work and found that myopia defocus can retard eye growth. From this proven effect, we wanted to make a lens for human use that could correct refractive error, while at the same time having a myopic defocus signal for myopia control. We considered a lens with two foci (like a bifocal) but that would induce prismatic jump, and poor adaption, so the best solution was a contact lens (CL), with a concentric ring design. A trial proved that it worked. Some drawbacks with the CL version were compliance in children and variable wear time – we found five to eight hours of wear were needed to make the treatment more effective. The team therefore decided that a spectacle lens was the best solution. The problem was, with differing positions of gaze, the visual axis moved off the centre of the lens, making this problematic, causing blur and so on. Therefore, the defocus zone/s had to be tiny so as not to affect vision too much. We talked to various companies and although Hoya initially said it could not be done, after six-months, they’d come up with a solution that met with our requirements. Results from trials between 2014 and 2017 were good and children wore them full time, for around 15 hours. The visual performance was as good as single vision lenses and there were no issues with dizziness or distortion. Q. Where do you think we are heading, in terms of our knowledge and management of myopia? As mentioned, the myopia control affect is influenced by the original retinal profile and the amount of defocus required for optimal control. We therefore need to measure the peripheral refraction. A specially designed autorefractor can use eccentric fixation targets to measure eccentric positions and peripheral refraction – we may start seeing these used more widely. Since DIMS lenses appeared, people have also become more aware of the importance of measuring axial length to monitor and control progression. We are also increasingly aware that eye shape affects possible treatment options and defocus, necessitating regular measurement. And we know choroidal thickness starts increasing within weeks of patients starting to wear DIMS lenses and continues for two years… choroidal thickening is a permanent change (as far as the current data shows). Q. Do you know what causes this choroidal thickening? I am not sure what is going on at the molecular level, but as we know in myopia and progressive myopia, all the layers of the eye are stretched, making all layers thinner. As the retina and choroid stretch, the risk of myopia related complications increases, so increasing choroidal thickening is in a way, protective. Similarly, by slowing down the rate of progression of myopia (and ultimate level of myopia), we are preventing the related thinning of the choroid (and retina), which we all too often see. Q. For the future, should axial length measurement be the standard of care? There are multiple factors for consideration. Axial length is a good monitoring tool, but I want to see us looking at prevention not just control. For myopia prevention, AXL is not as good a parameter as refraction. We see refractive error in the +0.75 to +1.75 range as a potential to becoming myopic. However, for the same level of refraction we see varying AXLs, which is because refractive error can be influenced by the lens and cornea too. Q. Historically we’ve recommended children have a first eye exam by age four or six. In your experience is this still appropriate? Children should visit the optometrist well before they become myopic. Studies comparing European babies with babies in Hong Kong, show differences in age of onset and indeed pre-myopia and levels of hyperopia. One year old Italians refract at +2.50D, while Hong Kong babies at age one are only -1.00D Q. Is this the effect of genetics, environment, or diet, or something else? There are certainly genetic and environmental factors involved. Several high-risk factors have also been identified for example, parental refraction status, age of onset, duration of myopia etc. Read more about MiyoSmart and the evidence to support its efficacy on page 67 of this issue of mivision. Reference: 1. Zhang, H.; Lam, C.S.Y.; Tang, W.C.; Leung, M.; Qi, H.; Lee, P.H.; To, C.-H. Myopia Control Effect Is Influenced by Baseline Relative Peripheral Refraction in Children Wearing Defocus Incorporated Multiple Segments (DIMS) Spectacle Lenses. J. Clin. Med. 2022, 11, 2294. https://doi.org/ 10.3390/jcm11092294
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