Ashish Gangwar, B.Optom

Optometrist, Dr. Shroff’s Charity Eye Hospital, New Delhi, India

Orthokeratology refers to the creation of specially designed rigid gas permeable contact lenses to reduce or eliminate refractive error temporarily by reshaping the corneal curvature. ⁽¹⁾ It is based on the reverse geometry principle. Ortho k lenses exert pressure on the corneal surface and reshape the cornea by pushing the epithelial cells towards the periphery. Flattening of cornea reduces the axial length and focusing power of the eye. Research shows that the corneal reshaping decreases peripheral hyperopic defocus and therefore increases peripheral myopic defocus to likely reduce stimuli for axial elongation and myopia development. ⁽²⁾

Figure 1: Reverse Geometry Contact Lens design.
(Source – IACLE module E3 myopia control and orthokeratology 2016-July-1)

Lenses are inserted before going to sleep and removed in the morning. As the therapy progresses and the cornea is molded, the lenses give good unaided vision for a longer period. Gradually the lens wearing time may be decreased to a level which gives the desired reduction in myopia.

Ortho K lens diameters are usually larger than conventional gas permeable design and typically between 10-11 mm to optimize the size of the treatment zone. GP materials of high dk 85 units are used to avoid lack of oxygen permeability. Ortho K works best on a large diameter. ⁽³⁾ Ortho K results in corneal sphericalization and can correct up to -4D of myopia, ≤ 1.50D with the rule astigmatism and ≤0.75D against the rule astigmatism. ⁽⁴⁾ Higher refractive error correction is possible, but outcome is less predictable.

While fitting the Ortho K lenses, soft contact lenses should be suspended for a few days and GP lenses for 4 weeks before fitting so that the cornea can regain its original shape. Corneal topography should be done. The initial fitting and refractive changes should be checked after 1 hour of lens wear so that the practitioner can gain information about the patient’s response. If the fit is acceptable then the patient can wear it overnight and further evaluation should be done the next day. While fitting the initial goal of the practitioner is a well centered lens. Ideal fit includes 3-4 mm of central bearing. There should be a wide, deep tear reservoir around the central bearing zone. There should be good concentration. Up to 0.3 mm movement with blink is acceptable. ⁽⁵⁾

When the whole world is struggling to find the best possible way to correct mild to moderate myopia, Ortho K seems to be a productive solution as it gives freedom from contact lens and glasses during daytime. Only overnight lens wear is required. There is no age limit to use ortho K lenses. It is a safe and reversible therapy without surgery. Although Ortho K is one of the best ways to correct and control myopia, it is contraindicated in case of anterior segment disorders, and it cannot correct high refractive error fully.

Research recommends Ortho K retards myopia better than atropine. While comparing the myopia control effect, it is found in a study the use of Ortho K lenses resulted in smaller changes in axial length than the use of 0.01% and 0.05% atropine. Ortho K treatment may reduce the degree of myopia and can control its progression especially in young children. ⁽⁶⁾

In conclusion, Orthokeratology can be used to correct myopia and its progression. It is an effective, safe method and reversible process.

References:

1. Swarbrick, H. A. (2006). Orthokeratology review and update. Clinical and Experimental Optometry, 89(3), 124-143.
2. Li, X., Friedman, I. B., Medow, N. B., & Zhang, C. (2017). Update on orthokeratology in managing progressive myopia in children: efficacy, mechanisms, and concerns. Journal of Pediatric Ophthalmology & Strabismus, 54(3), 142-148.
3. Vincent, S. J., Cho, P., Chan, K. Y., Fadel, D., Ghorbani-Mojarrad, N., González-Méijome, J. M., … & Jones, L. (2021). BCLA CLEAR-Orthokeratology. Contact Lens and Anterior Eye, 44(2), 240-269.
4. Carracedo, G., Espinosa-Vidal, T. M., Martínez-Alberquilla, I., & Batres, L. (2019). The topographical effect of optical zone diameter in orthokeratology contact lenses in high myopes. Journal of Ophthalmology.
5. Iacle module E3 myopia control and orthokeratology 2016-July-1
6. Tsai, W. S., Wang, J. H., & Chiu, C. J. (2020). A comparative study of orthokeratology and low-dose atropine for the treatment of anisomyopia in children. Scientific Reports, 10(1), 1-8.