Lens File: Myopia done the MyCon way

It is very doubtful that anyone in the optical world has not heard that we are on the verge of a myopia epidemic. The study from Holden et al in 2016¹ predicts that potentially 50% of the world’s population will be myopic by the year 2050.

Why should this matter? Why are we concerned about this shift towards myopia? A large reason is the associated risks of other conditions that come with being myopic.  

Studies by Bullimore & Brennan;² Flitcroft;³ Haarman et al,⁴ show these risks increase dramatically according to the level of myopia. Table 1 shows why, when it comes to myopia management, each dioptre matters. 

^{Table 1: Risk of developing certain diseases according to myopia level (adapted from Flitcroft, 2012)}

Risk indicators 

The risk of myopia can be split into two categories: modifiable and non-modifiable. Non-modifiable factors relate to the genetic predisposition of an individual and cannot be controlled.

Essentially, these are ethnicity and genetics. Donovan et al,⁵ showed that Asian people are at a higher risk of myopia development, with Sankaridurg et al,⁶ showing that the mean cumulative progression of myopia over three years is about 35% higher than for Caucasians (figure 1).  

^{Figure 1: Myopia prevalence over time (age and region) (adapted from Sankaridurg et al, 2021)}

A major risk factor in the progression of myopia is the prevalence of myopia within the biological parents of children. A child with two myopic parents has a 35-60% risk of also being myopic (Wu & Edwards, 1999, figure 2).⁷  

^{Figure 2: Myopia prevalence in children by number of myopic parents (adapted from Mew-May Wu & Edwards, 1999; Mutti et al, 2002)}

Modifiable factors relate to lifestyle and visual health and are key to managing risk and maximising treatment efficiency. It is important to realise that many of these risk factors have been increased by the Covid-19 outbreak and the way society has changed the way in which it lives.

Two important factors to consider are:  

1.  Near vision tasks. The more time a child spends on close work activities, such as homework, reading and/or mobile devices, the higher the risk of developing and increasing myopia. Decreasing the number of near tasks and increasing the working distance wherever possible is key to visual health. 
2. Outdoor time. Studies have shown that an increase in time spent outside is a natural blocker of axial elongation, especially in pre-myopia.⁸ At least 80 to 120 minutes outside are shown to mitigate the impact of myopia progression (Sherwin et al).⁹ 

Causation 

There are many theories about what causes the progression of myopia, with recent thoughts being on the relationship between the peripheral retina and axial length. When a child has a refraction and standard myopic lenses are supplied, while the image is formed on the central retina, in the periphery the image would be formed behind (Tabernero et al)¹⁰ and a peripheral hypermetropia generated (Smith).¹¹  

This peripheral stimulus would instigate a growth in the axial length and cause the image at the central retina to become out of focus. A further refraction would be conducted, a higher myopic prescription would be found, and the vicious circle would continue (figure 3).  

^{Figure 3: A Myopia correction with standard lenses}

Therefore, standard single vision lenses are not the answer to myopia progression and specialised lenses are needed. MyCon uses freeform surfacing to create a differently shaped surface to ensure light in the periphery is focused in front of the retina and removing the axial length growth stimulus (figure 4).

^{Figure 4: Myopia correction with MyCon lens}

The design of MyCon is the cumulation of a long history of scientific research in the field of myopia by experts and is protected by Rodenstock IP. A lens based on the principles of MyCon has been clinically tested in a trial conducted over five years outside of all Covid-19 lockdowns.  

This long-term study has shown that a lens like MyCon reduces the progression of myopia (Tarutta et al,¹² figure 5).  

^{Figure 5: Results of the clinical study carried out with lenses based on the principles of MyCon
(adapted from Tarutta et al, 2019)}

Lens Design 

MyCon is a perifocal defocus lens with a horizontal asymmetric design. The perifocal defocus is created along the horizontal meridian, leaving the vertical meridian as the nominal refracted value for the child (figure 6).  

There are some distinct advantages to this design. With a ‘clear’ vertical section, the lens is better matched to the physiology of a child whose gaze tends to be directed upwards much more than an adult. The lens can be fitted into a frame with a more natural pantoscopic angle rather than trying to fit a frame to zero degrees of tilt.  

^{Figure 6: Chart showing the power distribution of the MyCon lens}

With a blended perifocal defocus, there are no ‘elements’ on the lens to be noticed by others. Coupled with a wide power range and indices to match, a great aesthetic result can be achieved for the child.  

The availability of MyCon is shown in table 2.

^{Table 2: MyCon availability (July 2023)}

• Andrew Copley is head of professional services and product at Rodenstock. 

References

1. Holden BA, Fricke TR, Wilson DA et al. Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050. Ophthalmology. 2016; 123:1036-42. 
2. Bullimore MA, Brennan NA. Myopia Control: Why Each Diopter Matters. Optom Vis Sci 2019;96:463-5. 
3. Flitcroft DI. The complex interactions of retinal, optical and environmental factors in myopia aetiology. Prog Retin Eye Res. 2012;31:622-60. 
4. van Leeuwen R, Haarman AEG, van de Put MAJ, et al. Association of Rhegmatogenous Retinal Detachment Incidence With Myopia Prevalence in the Netherlands. JAMA Ophthalmology Published Online First: 25 November 2020. doi:10.1001/jamaophthalmol.2020.5114 
5. Donovan LS, P, Ho A, Naduvilath T, Smith EL, 3rd, Holden BA. Myopia progression rates in urban children wearing single-vision spectacles. Optom Vis Sci. 2012;89:27-32. 
6. Sankaridurg P, Tahhan N et al. IMI Impact of Myopia. Investigative Ophthalmology & Visual Science April 2021, Vol.62, 2. 
7. Wu MM, Edwards MH. The effect of having myopic parents: an analysis of myopia in three generations. Optom Vis Sci 1999;76(6):387-92. 
8. Torii H, Kurihara T, Seko Y, Negishi K, Ohnuma K, Inaba T, Kawashima M, Jiang X,  Kondo S, Miyauchi M, Miwa Y, Katada Y, Mori K, Kato K, Tsubota K, Goto H, Oda M, Hatori  M, Tsubota K. Violet Light Exposure Can Be a Preventive Strategy Against Myopia  Progression. EBioMedicine. 2017 
9. Sherwin JC, Reacher MH, Keogh RH, et al. The association between time spent outdoors and myopia in children and adolescents: A systematic review and meta-analysis. Ophthalmology 2012;119:2141–51. doi:10.1016/j.ophtha.2012.04.020 
10. Tabernero J, Vazquez D, Seidermann A, Uttenweiler D & Schaffel F. Effects of myopic spectacle correction and radial refractive gradient spectacles on peripheral refraction. Vis Res 2009; 49: 2,176-2,186. 
11. Smith EL, 3rd. Prentice Award Lecture 2010: A case for peripheral optical treatment strategies for myopia. Optom Vis Sci. 2011;88:1029-44 
12. Tarutta EP,  Proskurina OV,   Iomdina EN. The Myopia Control in Real Clinical Practice: The Results of an Expert Study. 2019. DOI: 10.17116/oftalma201913505146