Title: Orthokeratology Lenses
Author: Reese Loveless, OD
Keywords/Main Subjects: Orthokeratology, contact lenses
What is Orthokeratology?
Orthokeratology is the use of specialty gas permeable contact lenses to reshape the surface of the cornea, providing correction of refractive error. The lenses are worn at night and reshape the eye so that vision correction is not needed during the day. Although referred to as contact lenses, orthokeratology lenses are more correctly referred to as a form of treatment. Fitting an orthokeratology lens requires certification, which is obtained from the lens manufacturer of the lens design being fit.
What is an Orthokeratology Lens?
Orthokeratology lenses differ from standard gas permeable lenses in both their wear schedule and their design. (See Figure 1)
Where traditional contact lenses are worn throughout the day, orthokeratology lenses are worn while the patient is sleeping. As the patient sleeps, the lens works to mold or reshape the corneal epithelium to correct for the patient’s refractive error.
When comparing designs of lenses, traditional GP lenses have a central base curve and progressively flatter peripheral curves. In contrast, an orthokeratology lens has a flat central base curve and gets steeper in the periphery. Although lens design varies between lens brands, there are generally three zones that make up an orthokeratology lens:
- The treatment zone
- The reverse curve or return zone
- The alignment zone
Together, these zones work to change the contour of the corneal epithelium to make it flatter in the center, steeper para-centrally, and help the lens stay centered over the pupil.
The treatment zone is the central portion of the lens that flattens the corneal epithelium centrally. The base curve is a key aspect of the treatment zone, but is not typically modified to change the fit of the lens on the eye. Each type of lens will have a different fitting philosophy in determining the proper base curve for optimal treatment, so it’s important to refer to the fitting guide to determine the correct base curve.
Once the proper base curve has been determined, you will only need to make a change if you find inadequate or excessive refractive treatment. Generally, it will not need to be changed if there is an adjustment needed to the fit of the lens.
Reverse Curve/Return Zone
The reverse curve zone works to bring or “return” the treatment zone of the lens closer to the cornea, allowing for the desired applanation. Not only does it help in applanation of the treatment zone, it is also a key component in achieving a centered fit.
The alignment zone is in the periphery of the lens. It is critical in the stability of the contact lens fit. This zone contours to the cornea and helps with centration and movement of the lens. Although some movement of the lens is acceptable, too much movement can result in improper centration and treatment.
Who are candidates for orthokeratology?
Orthokeratology lenses are approved to treat up to 5.00-6.00D of myopia and 1.50-1.75D of astigmatism, depending on the brand of the lens.1 However, the best results tend to be achieved with little to no astigmatism and lower amounts of myopia. Conversely, poor results are more likely in patients with higher amounts of astigmatism and/or irregular/asymmetric astigmatism.
In addition to falling within the parameters listed above, good candidates should be strongly motivated, willing to maintain proper hygiene and care of the lenses, and willing to have multiple follow-ups in order to ensure proper lens fitting and treatment.
What are the benefits of orthokeratology?
Orthokeratology provides a reversible way to treat myopia. It allows patients to go throughout the day without the need for spectacle or contact lens correction. This makes it a great option for athletes and other individuals that would like clear vision during the day. It is also a benefit for those not interested in permanent refractive correction.
One common use for these lenses is to help slow the progression of myopia. Although not currently FDA approved for this purpose, there have been numerous studies indicating that orthokeratology lenses may be successful in reducing myopia progression up to 40-60%.1-3
What are the potential complications of orthokeratology?
Similar to other corneal gas permeable lenses, there are risks with wearing orthokeratology lenses. Of main concern is microbial keratitis. Although it may seem like a microbial infection is more likely with a lens that is worn while sleeping, studies actually show a similar incidence of microbial keratitis when compared to other lenses.2 When handling and wearing contact lenses, good hygiene is always critical. Washing hands before inserting/removing lenses, cleaning and storing lenses in the appropriate disinfecting solution, avoiding direct water contact to the eyes while wearing lenses, and maintaining a clean storage case are some of the best ways to prevent possible infections.
Other complications can result from an improper fit, such as corneal defects and irritation. Patients may also experience halos and ghosting around lights as a result of the corneal reshaping. These symptoms may be more noticeable in low light conditions when pupil size increases, or if they have larger pupil sizes in general.
How do you fit an orthokeratology lens?
Obtaining a proper fitting lens is crucial, not only to avoid complications, but also to the success of correcting refractive error. Key to this process is a baseline corneal topography, the patient’s manifest refraction, and the customized design of the lens. Horizontal visible iris diameter (HVID) and pupil size are also important considerations. Designing the lens can be accomplished either empirically or diagnostically; this is largely determined by the brand of lenses being fit.
Empirical fit lenses are designed with the help of a lab consultant, using the above parameters. No trial lenses are involved, and the first lens on the patient’s eye is custom made for them. Changes can then be made to improve treatment, centration, movement or other concerns.
When fitting diagnostically, a lens from the trial lens fitting set is placed on the eye based on the above parameters and the fitting guide. Once a lens is selected, the lens is then placed on the eye and evaluated with fluorescein to check for an appropriate fit. A custom lens is then designed based on the fitting evaluation and overrefraction of the trial lens.
In either case, the ideal end result would have a defined treatment zone that is centered over the pupil, with appropriate return and alignment zones. On fluorescein evaluation, a bullseye pattern should be seen, as pictured in Figure 2, with defined zones.
A poor fitting lens does not have well-defined areas, is not centered on the pupil, and/or has unacceptable applanation.
Not only would you want to verify that the lens has a good fit physically, having a topography map that performs a subtractive comparison of the treated cornea to the untreated cornea is vital. This information shows how much correction has been achieved and in which areas of the cornea the change has occurred (Figure 3).
Poorly fitting orthokeratology lenses can also be seen when doing a subtractive mapping. In cases of inadequate treatment, there may be an “island” of central steepening in the treatment zone (Figure 4).
In cases where the lens is decentered, a “smile” may be observed from a superiorly decentered lens, resulting in inferior steepening (Figure 5). Similar patterns can be seen from an inferiorly decentered lens or a horizontally decentered lens.
Consulting the fitting guide for the specific lens being used will help to provide more precise instructions on which parameters to change to correct for these fitting errors. In general, to adjust for inadequate refractive treatment, changes are made to the base curve of the lens. Decentration of the lens can be corrected for with changes to the alignment zone.
As stated previously, fitting orthokeratology lenses requires a dedicated patient who is willing to have multiple follow-ups.
Each follow-up generally consists of obtaining a case history of the patient’s lens routine (including wear time and lens hygiene), checking the patient’s unaided visual acuity, checking the refractive error, updating the corneal topography, assessing the fit of the lens, and checking the over-refraction while wearing the lenses.
The first follow-up should be the morning after the first night of wear, and the patient should present to the office wearing the lenses. This will allow the practitioner to evaluate how the lenses are fitting throughout the night, measure the amount of treatment achieved, and assess for any complications. Although treatment lasting throughout an entire day usually isn’t achieved for a week or two, the patient should still notice an improvement throughout the first part of the day.
At subsequent follow-ups it is usually not required for the patient to wear the lenses to the appointment. However, having the patient bring their lenses to each appointment is very beneficial if there is concern over the fit of the lens, lenses being switched, or other complications.
Follow-up visits are usually held after one week of wear, then one month, three months, six months, and then about every six months to a year following that. For children wearing the lenses for myopia control, tighter follow-ups are recommended.
Orthokeratology lenses are specialty contact lenses that provide qualifying patients with a temporary, non-surgical option for correction of their refractive error. Unlike traditional contact lenses, these lenses are worn throughout the night, allowing the patient to go throughout the day without need for refractive correction.
Complications related to orthokeratology lenses are rare and can be best prevented by maintaining proper lens hygiene, proper wearing of lenses, and following up regularly with the lens provider.
Orthokeratology is a safe, effective means to provide clear vision during the day and reduce dependence on glasses and traditional contact lenses.
Free resource for more information on Orthokeratology:
Certification and fitting guides are available through these web addresses:
- Michael, L. J. (2019). Contemporary Orthokeratology. Retrieved from https://contemporaryorthokeratology.com/
- Lipson, M. J., & Koffler, B. H. (2019). Orthokeratology for Managing Myopia Progression in Children. Advances in Ophthalmology and Optometry, 4, 75–87. doi: 10.1016/j.yaoo.2019.04.004
- Tran, H. D., Tran, Y. H., Tran, T. D., Jong, M., Coroneo, M., & Sankaridurg, P. (2018). A Review of Myopia Control with Atropine. Journal of Ocular Pharmacology and Therapeutics, 34(5), 374–379. doi: 10.1089/jop.2017.0144
Figure 1: Chan, Paco. Orthokeratology Lens (Ortho-k Lens). SwissCoat Better Vision [serial online] July 2017. Available at https://blog.swisscoat.com/en/orthokeratology/. Accessed April 28, 2020.
Figure 2: JubeAO / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)
Figure 3: Collar, Cesar Villa. Overnight orthokeratology: the treatment and control of childhood myopia comes of age. Health & Medicine [serial online] 2018. Available at https://researchoutreach.org/wp-content/uploads/2019/08/Cesar-Villa-Collar.pdf. Accessed April 28, 2020.
Figure 4: Orthok outcomes: Central Islands. Vimeo [Online video] 2014. Available at https://vimeo.com/79661244. Accessed April 28, 2020.
Figure 5: Orthok outcomes: Smiley Faces. Vimeo [Online video] 2014. Available at https://vimeo.com/79666422. Accessed April 28, 2020.