Overview of Orthokeratology

Overview of Orthokeratology
Tara Y. T. Chen, Dr. Austin Mardon

What is orthokeratology?
    Orthokeratology is a treatment for myopia progression that uses rigid, gas-permeable contact lenses to reshape the cornea (Villa-Collar et al., 2019). Contact lenses are worn overnight and specialized to fit the eye shape of each patient (Charm, 2017). 

How are the contact lenses designed?
Each contact lens is unique to the patient. Corneal topography is a diagnostic tool that creates various three-dimensional maps of the corneal surface. Some maps include an axial map for corneal power, tangential map for corneal shape and curvature maps (Charm, 2017). These maps are used to identify corneal asymmetries because patients with irregular corneas, keratoconus or a decentred corneal apex are not candidates for the treatment (Charm, 2017). 
The patient may need to undergo several lens fitting sessions before the practitioner can design a perfect-fitting contact lens (Charm, 2017). Additionally, since each patient’s eyelid force is different, new lenses are tested overnight to assess whether further lens corrections are needed to adjust for a looser or tighter eyelid (Charm, 2017). 

Benefits
Orthokeratology can treat a moderate range of diopters (D). 90% of low-to-moderate cases of myopia (-0.75 D to -5.00 D) have been treated by orthokeratology (Charm, 2017). The contact lenses achieve this by flattening the centre of the cornea and steepening the paracentral cornea (Charm, 2017). After wearing the lens for one night, patients can experience an improvement in vision by 60% (Charm, 2017). Continuously wearing the lenses results in constant levels of improved vision (Charm, 2017). Moreover, 50% of mild cases of astigmatism (below 1.50 D) have been treated by orthokeratology (Charm, 2017). 
    Although patients of any age can undergo this treatment, it is most effective in young children between 6 to 8 years old (Villa-Collar et al., 2019). Young children tend to have milder cases of myopia and the ability to prevent myopia progression is longer lasting compared to that of adults (Villa-Collar et al., 2019). Additionally, Zhao et al. (2018) have shown that after three months of orthokeratology treatment, children had a significantly improved quality of life due to increased self-confidence, convenience in playing sports and increased time being active outdoors (Zhao et al., 2018). 

Risks
    When removing the rigid, gas-permeable contact lenses, corneal abrasions may occur. This is especially common in long-term orthokeratology patients and the centre of the cornea is often damaged (Chan et al., 2008). To counteract this risk, artificial tears may be applied before the patient removes the lenses (Chan et al., 2008).
    Additionally, some studies revealed a risk of microbial keratitis, a corneal bacterial infection, in orthokeratology patients (Charm, 2017). This occurs when practitioners are inadequately trained or when patients are not informed of proper lens sanitation procedures. To avoid this risk, clinics offering orthokeratology should be informed of updated training courses and sanitation procedures to properly educate their patients (Charm, 2017). 
    Although visual acuity is improved with orthokeratology, there is a reduction in the patient’s ability to identify slight changes in shading and patterns of objects (Charm, 2017). Some patients also see glares and halos in dimly lit environments (Charm, 2017). However, these phenomena are often temporary and do not appear after the first treatment week (Charm, 2017).

Conclusion
    Overall, orthokeratology is a beneficial method to stabilize myopia progression and astigmatism in children and adults (Villa-Collar et al., 2019). A fitted contact lens is specifically designed for each patient’s unique cornea shape and diopter (Charm, 2017). Although there are a few risks related to infections and corneal abrasions, proper lens sanitation procedures and lens application habits can minimize discomfort (Charm, 2017).  

References
Chan, B., Cho, P., & Cheung, S. W. (2008). Orthokeratology practice in children in a 
university clinic in Hong Kong. Clinical & experimental optometry, 91(5), 453–460. https://doi.org/10.1111/j.1444-0938.2008.00259.x
Charm J. (2017). Orthokeratology: clinical utility and patient perspectives. Clinical 
optometry, 9, 33–40. https://doi.org/10.2147/OPTO.S104507
Villa-Collar, C., Carracedo, G., Chen, Z., & Gonzalez-Méijome, J. M. (2019). Overnight 
Orthokeratology: Technology, Efficiency, Safety, and Myopia Control. Journal of 
ophthalmology, 2019, 2607429. https://doi.org/10.1155/2019/2607429
Zhao, F., Zhao, G., & Zhao, Z. (2018). Investigation of the Effect of Orthokeratology 
Lenses on Quality of Life and Behaviors of Children. Eye & contact lens, 44(5), 335–338. https://doi.org/10.1097/ICL.0000000000000529

Biographies
Tara Y. T. Chen is a third-year undergraduate student studying medical sciences at the University of Western Ontario in Canada. In the past, she has presented her research on psoriasis treatments at the Western Student Research Conference 2021 and has written several science academic books. 
Dr. Austin Mardon is an assistant adjunct professor at the John Dossetor Health Ethics Centre at the University of Alberta, and the founder and director of Antarctic Institute of Canada.