August 2, 2021
By Nina Tahhan, PhD, MPH, BOptom, Senior Research Scientist at BHVI
Orthokeratology (OK) is the practice of reshaping the cornea with rigid gas permeable contact lenses to temporarily reduce or eliminate refractive error. Modern OK lenses can be worn overnight, enabling wearers to go about their day without the need for vision correction. The practice has been gaining increasing popularity worldwide, particularly in Asia, due to emerging evidence that it can retard myopia progression. Today, it is regarded to be one of the most effective myopia control strategies available. This study by Hiraoka et al., 2012, reports on the efficacy of OK for myopia control over a 5-year period. Currently, this is the longest period of time a randomized controlled trial investigating myopia control efficacy of OK has been reported in the literature.
The study recruited 59 children between 8-12 years of age with myopia between -0.50D to -5.00D. Twenty-nine of the participants were fitted with four-zone reverse geometry lenses, and the other 30 subjects wore spectacles and acted as a control group. All participants were reviewed every 3 months over a 5-year period where axial length, refraction, and visual acuity measurements were taken. Twenty-two out of 29 subjects wearing OK lenses and 21 out of 30 of the spectacle-wearing group completed the 5-year study.
The increase in axial length was significantly lower in the OK group (0.99 ± 0.47 mm) compared to the control group (1.41 ± 0.68 mm) over a 5-year period. The greatest difference in axial length change between the groups was in the first 3 years. In the last 2 years of the study, the level of axial elongation was not significantly different between OK and control groups. The myopia control findings from this study support findings from other randomized controlled trials with OK lenses. However, previous studies were limited to 2 years duration. This study also demonstrated very few adverse effects with the lenses. Over the 5 years, 3 participants were observed to have superficial punctuate keratopathy, and one participant had a small corneal erosion with the OK lenses. All of these were completely resolved after 1 week of discontinuation of lens wear.
The authors note that certain issues remain unclear regarding OK and myopia control, including the optimal duration of lens wear and whether any rebound effect may occur after discontinuation. Hence, further studies are required to answer these questions.
Long-Term Effect of Overnight Orthokeratology on Axial Length Elongation in Childhood Myopia: A 5-Year Follow-Up Study
Takahiro Hiraoka; Tetsuhiko Kakita; Fumiki Okamoto; Hideto Takahashi; Tetsuro Oshika
Purpose: Our prospective study was conducted to compare axial length elongation in myopic children receiving long-term overnight orthokeratology (OK) treatment to those wearing spectacles as controls.
Methods: There were 59 subjects enrolled in this study. The OK group comprised 29 subjects who matched the inclusion criteria for OK. The control group comprised 30 subjects who also matched the inclusion criteria for OK but preferred spectacles for myopia correction. Axial length was measured periodically for 5 years using an IOLMaster device, and the time course of changes was evaluated and compared between the groups.
Results: A total of 43 subjects (22 and 21 in the OK and control groups, respectively) completed the 5-year follow-up examinations. At baseline, the mean age ± SD was 10.04 ± 1.43 and 9.95 ± 1.59 years, the spherical equivalent refractive error was −1.89 ± 0.82 and −1.83 ± 1.06 diopters (D), and the axial length was 24.09 ± 0.77 and 24.22 ± 0.71 mm in the OK and control groups, respectively, with no significant differences between the groups. The increase in axial length during the 5-year study period was 0.99 ± 0.47 and 1.41 ± 0.68 mm for the OK and control groups, respectively, and the difference was statistically significant (P = 0.0236, unpaired t-test). The annual increases in axial length were significantly different between the groups for the first (P = 0.0002), second (P = 0.0476), and third years (P = 0.0385), but not for the fourth (P = 0.0938) and fifth (P = 0.8633) years. There were no severe complications throughout the study period.
Conclusions: The current 5-year follow-up study indicated that OK can suppress axial length elongation in childhood myopia.
Hiraoka, T., Kakita, T., Okamoto, F., Takahashi, H., & Oshika, T. (2012). Long-term effect of overnight orthokeratology on axial length elongation in childhood myopia: a 5-year follow-up study. Investigative ophthalmology & visual science, 53(7), 3913-3919.
Dr. Nina Tahhan, PhD, MPH, B.Optom, is a Senior Research Scientist at BHVI and Conjoint Lecturer at UNSW. Nina’s professional experience includes: clinical, public health, and epidemiological research, delivery of eye care education, and clinical research management in contact lenses, including orthokeratology research. Nina also has a history of delivering eye care to disadvantaged communities around Australia and in developing countries.