Modern overnight orthokeratology (ortho-k) effectively reduces low to moderate myopia1–4 and has the potential to slow myopic progression.2,5 Thus, ortho-k is becoming increasingly popular as a means of myopic reduction and myopic control, especially in places where the prevalence of myopia is high.6 The rates of myopic progression in children wearing ortho-k lenses were reported to be about 50% of the rates in children wearing spectacles or contact lenses.2,5
However, information concerning the mechanism by which ortho-k slows myopic progression, the critical age of intervention, or whether the myopic control effect will last after ceasing lens wear is currently not available. The main concerns of parents who enrolled their children for ortho-k are the following: What would happen to the refractive errors of their child if the child ceased lens wear after ortho-k treatment for myopic control for a period of time? Will the refractive errors increase drastically (rapid increase within days or weeks after ceasing lens wear)? Would the refractive errors catch up with the amount of myopia that would have been present if the child has never received ortho-k treatment? This is a case report about a young girl who has worn ortho-k lenses for a period of time for myopic control, who ceased lens wear for a period of time and used spectacles for vision correction, and then resumed ortho-k lens wear. We monitored changes to her refraction and axial length (AL).
This young girl was 6 years old when she was enrolled in ortho-k for myopic control. Her parents enrolled her because of their concern about myopic progression as she had a history of myopic progression of about 1.00 diopter (D) per year. Her mother reported that she was first found to be myopic (about −1.50 D in both eyes) when she was about 4 years old. Her pretreatment subjective refraction was OD −2.75 − 1.00 × 10 and OS −3.25 − 0.75 × 7. She was fitted with a pair of five-curve reverse geometry lenses targeted for full myopic reduction. The lenses were made of Boston XO material (eLens; E&E Optics, Hong Kong) with a five-zone design (lens parameters: matched flat K = 43.25 D, fitting curve = standard, alignment curve = −10 μm, peripheral curve = 12.5 mm, lens diameter = 10.6 mm, target = 3.00 D). The lens parameters for the right and left lenses were the same. After 2½ years of ortho-k treatment, the mother and the girl consented to a three-phase assessment of ortho-k wear (phase I, 8 months), spectacles lens only wear (phase II, 6½ months including 1 month of washout period; ortho-k was resumed sooner because of the increased rate of axial elongation during this phase), and resumed ortho-k wear (phase III, 6 months including 1 month of stabilization period when ortho-k was resumed). A pair of new ortho-k lenses targeted for full myopic reduction was used in phase III. The girl did not return for data collection until about 2 months after resuming ortho-k lens wear.
During the investigation period (phases I to III), refractive errors, visual acuities (VAs), AL, and external ocular health were monitored on a monthly basis. At each visit, subjective refraction and AL measurements (IOLMaster; Carl Zeiss, Germany) were made. Ocular health was monitored by slitlamp biomicroscopy.
Changes in Refractive Errors
Table 1 summarizes the refractive or residual errors and AL measurements over the 21-month study period. The residual refractive errors during phase I were not more than ±0.25 D in spherical power and not more than 0.50 D in cylinder power. The monocular-unaided VA was 20/30 or better at all visits, and the parameters of ortho-k lenses worn before and during phase I were unchanged. After stopping the treatment, refractive errors returned to the pretreatment level within 2 weeks and stabilized within 1 month (i.e., the refractive errors were not different at two consecutive visits after ceasing lens wear). At the end of phase II, the refractive errors were OD −3.50 − 1.50 × 175 and OS −4.50 − 1.50 × 180, indicating increases of 0.75 D (OD) and 1.25 D (OS) in myopia. The parameters of the new pair of ortho-k lenses used in phase III were not different from those worn in phase I except that the target reduction was increased for full reduction. Although the cylinder powers in the residual refraction were slightly higher in phase III than in phase I, the unaided VAs were not significantly affected and were 20/30 or better at most of the visits.
Changes in AL
Fig. 1 shows the AL measurements during the three phases of study. ALs were 24.68 mm (OD) and 24.89 mm (OS) at the beginning of phase I. In phase I, AL increased by 0.02 mm (OD) and 0.03 mm (OS) per month. In phase II, including 1 month of washout period, AL increased by about 0.06 mm (OD and OS) per month of spectacle wear. These changes were about double the rates of change in phase I. In phase III, no increases in AL were observed in both eyes during the period of resumed ortho-k lens wear.
In view of the significantly faster increase in myopia during the spectacle lens wear phase compared with ortho-k lens wear phases, the parents decided to let the girl continued with ortho-k treatment after completion of phase III. The girl is now, at the time of writing this report, about 12 years old, and she is still wearing ortho-k lenses.
This case demonstrates that axial elongation was faster in a myopic child when wearing spectacles compared with when wearing ortho-k lenses. Edwards7 monitored the refractive changes of 7 year olds over 5 years and showed that myopic progression was greatest between the ages of 9 and 11 years. However, Hyman et al.8 monitored the myopic progression in 6- to 11-year-old myopic children and found that younger children had the highest myopic progression over 3 years. Saw et al.9 also reported that the rate of axial elongation decreases with age in a group of 7- to 9-year-old myopic children in Singapore.
In the current case report, the child started the ortho-k lens wear when she was about 6 years old. She was only about 9 years old when ortho-k lens wear was temporarily ceased (phase I), and hence, myopic progression was expected to be still active. This was evidenced by the increases in AL and refractive errors when she stopped ortho-k lens wear. Comparing the changes in AL when the child was wearing ortho-k lenses to when she was wearing spectacles, the increase in AL was at least 50% slower when she was wearing ortho-k lenses. This was in agreement with the findings of the Longitudinal Orthokeratology Research in Children (LORIC)2 and the Corneal Reshaping and Yearly Observation of Nearsightedness (CRAYON)5 studies where the increase in axial elongation of the eyes of children wearing ortho-k lenses were about 50% less than those wearing spectacles (LORIC) or soft contact lenses (CRAYON).
Although AL increased significantly faster in phase II, nevertheless, axial elongation was not drastic. One month after ceasing ortho-k lens wear, her refractive errors were stabilized at OD −3.00 − 1.50 × 5 and OS −3.50 − 1.50 × 170. The spherical equivalent refractive errors were 0.50 D and 0.625 D more than the values in the OD and OS, respectively, at baseline (OD, −2.75 − 1.00 × 10; and OS, −3.25 − 0.75 × 7) before she commenced ortho-k treatment about 3 years ago. Unfortunately, we did not have her pre-ortho-k AL data for comparison. When she ceased ortho-k lens wear and returned to wearing spectacles, her AL started to increase at faster rates. At the end of the spectacle-wear period, her refractive errors were OD −3.50 − 1.50 × 175 and OS −4.50 − 1.50 × 180. The increases in myopia during the 6-month spectacle-wear period were 0.50 D (OD) and 1.00 D (OS). Fan et al.10 reported the rate of myopic progression (spherical equivalent) in myopic children in Hong Kong to be 0.63 D per year, whereas a more recent study11 reported the rate to be 0.90 D per year. The differences in the values reported may be because the former included children from 5 to 16 years old whereas the latter included only children from 6 to 12 years old. The increases noted in this case report in phase II were perhaps not unexpected as the child has a history of fast myopic progression before ortho-k treatment. We did not know the actual rate of myopic progression before ortho-k treatment except that, as the parents reported, it was about 1.00 D per year. The corresponding increases in AL during this period were about double those measured during phase I when the girl was wearing ortho-k lenses [i.e., on average 0.06 mm per month in each eye vs. 0.02 (OD) mm and 0.03 mm (OS) per month during 8 months of treatment]. When the child resumed ortho-k lens wear (phase III), no further increases in AL were observed in either eye in the subsequent 6 months of lens wear. The child was about 10½ years old at the end of phase III.
A time period between two consecutive phases was necessary to allow the effect from the prior treatment (in the case of switching from ortho-k to spectacles) to wash out or the new treatment (in the case of switching from spectacles to ortho-k) to stabilize. A subtle increase in AL during the transition from phase I to phase II and a decrease in AL from phase II to phase III were observed. Additional studies will be needed to confirm whether a more rapid early rate of axial elongation, which suggests a small “rebound effect,” is a repeatable characteristic of stopping ortho-k. There has not been any report investigating the short-term effect of ortho-k on AL. González-Méijome et al.12 reported a short-term reduction of 9.08 μm in central corneal thickness after 3 h of ortho-k lens wear and a recovery of 5.33 μm 3 h after ortho-k lens removal. However, this net transient reduction of 3.75 μm in corneal thickness cannot explain the rapid rebound and the subtle decrease in AL observed when the girl stopped and resumed ortho-k lens wear, respectively, in the current case. Changes observed in this little girl may be particular to her only or may reflect changes that would be observed when switching between spectacle wear and ortho-k. Further work is still required to confirm how ortho-k effect myopic reduction and myopic control.
After resuming ortho-k treatment in phase III, AL did not show significant change in either eye. However, changes in AL in the two eyes were very different from what were observed during phase I. By phase III, the girl was 10 years old. It may be that myopic progression rate had naturally attenuated with increased age. This factor cannot be neglected, and a study with control of the age effect is warranted to further investigate the changes observed in this case report.
The results of this case, whilst providing a positive insight into what could happen after ceasing ortho-k treatment for myopic control, is nevertheless an anecdotal report on a single patient. Therefore, it is important that this case is not taken as a representing proof that myopia will not drastically increase or catch up with what they were expected to be if the eyes had never underwent ortho-k treatment. Additional research is required before a firm conclusion about the effects of ceasing ortho-k lens wear can be drawn.
When a myopic child who had been wearing ortho-k lenses for myopic control ceased lens wear and was switched to spectacles, small net amounts of axial elongation were observed. These took place at a faster rate relative to the ortho-k lens wear period. Ortho-k lens wear appeared to slow myopic progression for this child.
We thank Ms. Jane Lau for referring this patient and PolyU for facilities supported by research grant (J-BB7P).
School of Optometry, The Hong Kong Polytechnic University
Hung Hom, Kowloon, Hong Kong SAR
1. Walline JJ, Rah MJ, Jones LA. The Children's Overnight Orthokeratology Investigation (COOKI) pilot study. Optom Vis Sci 2004;81:407–13.
2. Cho P, Cheung SW, Edwards M. The Longitudinal Orthokeratology Research in Children (LORIC) in Hong Kong: a pilot study on refractive changes and myopic control. Curr Eye Res 2005;30:71–80.
3. Cheung SW, Cho P, Chui WS, Woo GC. Refractive error and visual acuity changes in orthokeratology patients. Optom Vis Sci 2007;84:410–6.
4. Mika R, Morgan B, Cron M, Lotoczky J, Pole J. Safety and efficacy of overnight orthokeratology in myopic children. Optometry 2007;78:225–31.
5. Walline JJ, Jones LA, Sinnott LT. Corneal reshaping and myopia progression. Br J Ophthalmol 2009;93:1181–5.
6. Swarbrick HA. Orthokeratology review and update. Clin Exp Optom 2006;89:124–43.
7. Edwards MH. The development of myopia in Hong Kong children between the ages of 7 and 12 years: a five-year longitudinal study. Ophthalmic Physiol Opt 1999;19:286–94.
8. Hyman L, Gwiazda J, Hussein M, Norton TT, Wang Y, Marsh-Tootle W, Everett D. Relationship of age, sex, and ethnicity with myopia progression and axial elongation in the correction of myopia evaluation trial. Arch Ophthalmol 2005;123:977–87.
9. Saw SM, Chua WH, Gazzard G, Koh D, Tan DT, Stone RA. Eye growth changes in myopic children in Singapore. Br J Ophthalmol 2005;89:1489–94.
10. Fan DS, Lam DS, Lam RF, Lau JT, Chong KS, Cheung EY, Lai RY, Chew SJ. Prevalence, incidence, and progression of myopia of school children in Hong Kong. Invest Ophthalmol Vis Sci 2004;45:1071–5.
11. Cheng D, Schmid KL, Woo GC. Myopia prevalence in Chinese-Canadian children in an optometric practice. Optom Vis Sci 2007;84:21–32.
12. González-Méijome JM, Villa-Collar C, Queiros A, Jorge J, Parafita MA. Pilot study on the influence of corneal biomechanical properties over the short term in response to corneal refractive therapy for myopia. Cornea 2008;27:421–6.