How does orthokeratology lens wear impact the tear film?

Paper title: Influence of overnight orthokeratology on tear film and meibomian glands in myopic children: a prospective study

Authors: Ruan, Jing (1); Zhang, Yu (2); Chen, Yueguo (3)

1. Department of Ophthalmology, Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, 49 North Huayuan Road, Haidian District, Beijing, 100191, China.
2. Department of Ophthalmology, Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, 49 North Huayuan Road, Haidian District, Beijing, 100191, China. zhangyured@sohu.com.
3. Department of Ophthalmology, Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Peking University Third Hospital, 49 North Huayuan Road, Haidian District, Beijing, 100191, China.

Date: Apr 2023

Reference: Ruan J, Zhang Y, Chen Y. Influence of overnight orthokeratology on tear film and meibomian glands in myopic children: a prospective study. BMC Ophthalmol. 2023 Apr 3;23(1):136

[Link to open access paper]

Orthokeratology (ortho-k) lenses incorporate reverse geometry surfaces to temporarily reshape the anterior corneal tissue with overnight wear. They are increasingly used for reducing myopia progression in children.

The success and comfort of any contact lens wear is closely related to tear film quality. Due to the close fit of orthokeratology lenses and the wear schedule needed to achieve the treatment effect for myopia control, the integrity of the ocular surface is important.

This prospective study investigated whether ortho-k lenses wear influenced the ocular surface environment or meibomian gland function in children.

• Thirty-three children with monocular myopia who had been prescribed ortho-k lens wear for at least 1 year to their myopic eye at the Peking University Third Hospital, Beijing were recruited to the study. Their emmetropic eyes served as the control group.
• The children were fit with one of three lens designs (Lucid, Paragon CRT or Euclid) to their myopic eye. All were advised to wear the lens every night over the study period, to use the same daily cleaning, protein removal and preservative-free lubricating solutions and were followed for regular follow-up examinations. 

Baseline examinations included non-invasive assessment of the tear film quality and quantity, using an OCULUS Keratograph 5M. Lid eversion and infra-red light was used to image the appearance and position of the meibomian glands. Folllow-up every 3 months included corneal topography, lens fit and clearance evaluation, slit-lamp biomicroscopy and repeating the original tear film assessment tests.

• The participants (girls n = 18, boys n = 15) had a mean age of 12.43yrs. They wore an ortho-k lens in their myopic eye for 18mths. 
• At baseline, the mean spherical equivalent in the ortho-k group was -2.11D. No significant differences were seen for the baseline spherical equivalent refraction, non-invasive tear break-up times (NITBUT) or keratometry values.
• At the 1-yr follow-up, the first non-invasive tear break-up times were 6.15 and 6.18 seconds for the ortho-k wearing and control eyes, respectively and average tear break-up times were 6.85 and 6.79 seconds, respectively. Tear meniscus height was measured as 18.74 and 18.65µm for the ortho-k wearing eyes and the control eyes.

Up to 1/3 loss of meibomian glands was seen for 90.9% and 93.9% for the treatment and control group, respectively. The differences between the two groups were found to be statistically insignificant.

This study found that for children wearing Ortho-K lenses continuously for a year, there was no significant impact on their tear film quality or meibomian gland function. This study is unique in that the control group consisted of the contralateral eyes of the participants.

• The results confirm those found from a previous study that also evaluated meibomian gland function and dry eye in Ortho-K wearers. Kyung et al found that although some meibomian gland changes were seen in a small number of wearers, there were no significant changes in tear break-up times for children wearing Ortho-K lenses over a 3-yr period.¹

Non-invasive methods of evaluating the ocular surface integrity were utilised in this study. This would be the ideal method for practitioners to monitor tear film stability changes, where possible.

Ortho-K lens fitting for myopia control is increasingly popular. These results provide reassurance for eyecare practitioners that treatment benefits are not being outweighed by ocular surface issues.

Tear film stability is not due to optimally functioning meibomian glands only, and measuring features such as tear break-up time and tear meniscus heights are only part of the picture of tear film differences with lens wear.

• Other studies have examined the tear film osmolarity of ortho-k wearing adults, finding that lens wear caused osmolarity changes which improved again once wear was ceased,² and that ortho-k lens wear actually improved dry eye symptoms.³

This suggests further research is needed to confirm what impact long-term Ortho-K lens wear may have on all aspects of the tear film and the ocular surface and if they may be reversible. 

Limitations of this study include:

• A relatively small number of participants.  
• A prospective design was used, meaning data on NITBUT and meibomian gland function prior to the study was not available for comparison
• Different brands of lens design were used, which may have caused different responses to varying materials and fit designs.
• An average follow-up time of approx. 18mths. Ortho-k lenses are often worn for many years for myopia control. A longer study could confirm if tear film changes occur after longer wear periods.

Title: Influence of overnight orthokeratology on tear film and meibomian glands in myopic children: a prospective study

Authors: Ruan, Jing; Zhang, Yu; Chen, Yueguo

Purpose: Orthokeratology lenses, which are worn overnight, are recommended for reducing myopia progression. They lie on the cornea and can influence the ocular surface by temporarily reshaping the corneal surface through a reverse geometry design. This study investigated the effect of overnight orthokeratology lenses on tear film stability and meibomian gland status in children aged 8-15 years.

Methods: This prospective, self-controlled study included 33 children with monocular myopia who were prescribed orthokeratology lenses for at least one year. The experimental group (ortho-k group) comprised 33 myopic eyes. The control group comprised the emmetropic eyes of the same participants. Tear film stability and meibomian gland status were measured using a Keratograph 5M (Oculus, Wetzlar, Germany). Paired t-tests and Wilcoxon signed-rank tests were used to compare the data between the two groups.

Results: At the one-year visit, the non-invasive first tear film break-up time (NIBUTf) values were 6.15 ± 2.56 s and 6.18 ± 2.61 s in the experimental and control groups, respectively. The lower tear meniscus height was 18.74 ± 0.05 μm and 18.65 ± 0.04 μm in these groups, respectively. No significant difference was observed in loss of meibomian glands or non-invasive average tear film break-up time between the experimental and control groups using Wilcoxon signed-rank tests.

Conclusions: The stability of the tear film and meibomian gland status were not significantly affected by wearing orthokeratology lenses overnight, indicating that continuous use of orthokeratology lenses for 12 months has a minimal effect on the ocular surface. This finding can help guide the clinical management of tear film quality with respect to the use of orthokeratology contact lenses.

[Link to open access paper]