Efficacy and safety of orthokeratology

Compared to other treatments, ortho-k has the most substantial volume of evidence supporting its effectiveness in controlling myopia and is considered the most effective monotherapy intervention by eye care practitioners.¹ However, there are still gaps in the evidence base regarding the long-term safety, the influence of demographic factors such as age, gender, and ethnicity on ortho-k’s efficacy, and a comprehensive understanding of adverse events associated with its use. Two recent research publications provide new insights on the efficacy and safety of orthokeratology.

Current research highlights the effectiveness of ortho-k in managing myopia, with robust evidence indicating its capability to reduce axial elongation of the eye. Systematic reviews and meta-analyses have consistently shown that ortho-k lenses can decrease myopia progression by about 0.25 mm over two years compared to single-vision spectacle or contact lens wearers.^2-4 Additionally, factors such as age,^5,6 gender, baseline refractive error,^7-9 and ethnicity may impact the treatment's efficacy, yet research in these areas is limited due to small sample sizes and a scarcity of multicentre studies with diverse populations, as well as being confounded by conflicting results across studies.^6,8,10-11 

Ortho-k is largely deemed safe.^12,13 Reports suggest an annual 20% incidence of adverse events, ranging from relatively frequent cases of corneal staining to very rare sight-threatening complications such as microbial keratitis,^14-16 but many studies lack detailed definitions and comprehensive reporting of these events, especially over the long term.¹⁷ Ortho-k can be commenced in children as young as 6-years old and has the potential to be a lifelong form of vision correction even after myopia control is no longer required. Given this, a deeper understanding of their safety and effectiveness is crucial for optimal patient care.

A study by Santodomingo-Rubido et al employed data from three prospective clinical trials conducted in Hong Kong and Spain to evaluate the efficacy of ortho-k lenses in slowing myopia progression in children.¹⁸ The trials collectively included 243 subjects aged 6 to 12 years with varying degrees of myopia and astigmatism, who were randomly assigned to wear either ortho-k lenses or single-vision spectacles. In all studies, subjects used Menicon Z Night ortho-k lenses and were followed for two years with regular check-ups and axial length measurements were taken using the Zeiss IOLMaster device. The primary endpoint was the cumulative reduction in axial elongation over the study period. 

The key findings of the study revealed:

• Significant Reduction in Axial Elongation: Ortho-k lenses significantly reduced the rate of axial elongation compared to single-vision spectacles. Mean reduction of 0.24 mm over two years.
• Efficacy During First Year: 62.5% of the treatment effect was observed during the first year of lens wear.
• Variable Efficacy: 41.5% of ortho-k users experienced very low levels of myopia progression of 0.30mm or less over the two-year period. 7.9% of subjects exhibited no axial elongation, defined as 0.02mm or less. However, approximately 25% showed no benefit from the treatment, defined as 0.59mm or more axial length growth over 2 years. 
• Influence of Demographic Factors: The better outcomes observed in older Hong Kong Chinese children with higher baseline myopia, as compared to the lesser benefit seen in younger white European children, were specific to a subgroup analysis of orthokeratology subjects. This subgroup analysis compared those who showed full myopia control efficacy (axial elongation ≤0.02 mm) from those with no myopia control efficacy (axial elongation >0.59 mm) but did not include the entire cohort. However, differences in efficacy based on subjects’ age, gender, baseline refractive error, or ethnicity were deemed not significant (p > 0.05).

Research paper: Santodomingo-Rubido J, Cheung SW, Villa-Collar C; ROMIO/MCOS/TO-SEE Groups. A new look at the myopia control efficacy of orthokeratology. Cont Lens Anterior Eye. 2024 Jun 20:102251 [LINK]

In this study, the safety of ortho-k lenses was evaluated using data from the same three prospective clinical trials conducted in Hong Kong and Spain.¹⁷ Subjects were followed for two years with regular check-ups, and adverse events and slit-lamp findings were recorded. Care solutions MeniCare Plus and Menicon Progent were used in all three studies. The main safety endpoints in this study were comparing the number of adverse events and slit-lamp findings graded ≥ 2 between the orthokeratology group and the control group. The key findings of the study revealed:

• Discontinuation Rates: Approximately 20% of children using orthokeratology lenses stopped wearing them, mainly due to issues with lens fitting, such as insufficient correction of myopia and poor lens centration. In comparison, about 25% of children wearing spectacle lenses discontinued their use, largely because they sought myopia control treatments.
• Adverse Event Incidence: Between 10% and 20% of children using orthokeratology lenses experienced adverse events over the course of a year, with fewer than 10% of these events being directly related to the lenses themselves. Most adverse events were minor and resolved without any loss of best-corrected visual acuity.
• Slit-Lamp Findings: The rate of slit-lamp findings graded ≥ 2 was comparable between children wearing orthokeratology lenses and those wearing spectacles.
• Comparison with Daily Wear Soft Contact Lenses: When comparing the safety of overnight orthokeratology lenses with daily wear soft contact lenses worn by children, the incidence of anterior eye adverse events was similar, though slightly higher for overnight orthokeratology lenses. Adverse events likely to be related to contact lens wear (given in per 100 patient years of lens wear) in soft contact lens studies ranged from 3.4 – 20.7,^15,19-21 whereas ortho-k ranged from 7.7 – 42.7^15-17 with this study finding 8.4 for ortho-k. 

Research paper: Santodomingo-Rubido J, Cheung SW, Villa-Collar C; ROMIO/MCOS/TO-SEE Groups. The safety of orthokeratology contact lens wear in slowing the axial elongation of the eye in children. Cont Lens Anterior Eye. 2024 Jul 12:102258. [LINK]

Subjects were randomized to receive either overnight orthokeratology or spectacle lenses in only one of the three studies analysed, and only one study employed a single-masked design. Additionally, the limited range of variables tested (age 6–12 years, mean spherical refractive error up to −6.00D, and ethnicity limited to Hong Kong Chinese and White European) may not fully represent the broader population. The study's analysis was constrained by a relatively short total subject-time exposure to orthokeratology lens wear (214 patient-years), which means the incidence rate of adverse events in regular clinical practice is not yet firmly established. Long-term data across a number of clinical practices in Russia reinforces that incidence of microbial keratitis in ortho-k wearers are similar to daily wear soft contact lenses.¹³ More longer-term studies and a wider diversity of subjects would address these current gaps in research.

The studies provide valuable insights into both the efficacy and safety of ortho-k for myopia control in children. The findings demonstrate that ortho-k can effectively slow myopia progression, though efficacy can vary over time. Despite some adverse events, the majority were non-significant and resolved without lasting effects on vision, supporting the overall safety of ortho-k lenses. While there are limitations related to study design and the range of variables tested, these results offer a solid foundation for eye care practitioners to make informed decisions and counsel patients on the benefits and risks of ortho-k lenses. Further research, particularly long-term and multicentre studies, is needed to address the remaining gaps and enhance our understanding of ortho-k's role in myopia management.