While troubleshooting is essential to a successful orthokeratology (ortho-K) practice, adequate patient selection is the ultimate step in preventing and avoiding classic pitfalls. This article is intended to provide a complementary analysis to the two preceding articles authored by the same contributors. Following a comprehensive review of the theoretical concepts that offer a deeper knowledge about the aetiology of myopia and its progression, it is imperative to select patients appropriately and to obtain valid clinical data. This is essential for determining the most suitable ortho-K design for the individual patient’s unique characteristics.
The subsequent focus will be on the optimization of ortho-K lenses, with a particular emphasis on the more or less frequent fitting issues. More precisely, because the fitting process has evolved over the years from trial fitting based on fluorescein pattern to a more empirical-based lens selection with a topography-aided algorithm, this article will focus on the problems that arise at follow-ups instead of the initial fitting stage.1-3
We acknowledge that certain concepts may appear to be more advanced than others; however, this article has been written with the intention of reaching a more extensive audience, ranging from novices to experts.
 |
| Fig. 1. Summary of decentration troubleshooting.Click image to enlarge. |
Among troubleshooting issues, the centration of the molding effect is usually the first step to assess. The practitioner can evaluate if the treatment is localized on the pupil center by looking at the differential map on topography. Differential maps can also be helpful to assess the amount of defocus generated and the proportion of defocus in the pupil.4,5 This evaluation should use the tangential map. Using the pre-treatment elevation map can help predict the decentration.6,7
Even though a small decentration can enhance the myopia control effect, there is a limit to accepting a decentered treatment zone.8 A significant decentration can decrease the quality of vision by adding ghosting, glare and flare, as well as induce residual astigmatism and affect the success of ortho-K wear.9 Aiming for a smaller peripheral ring of addition in the pupil in the context of myopia control is better.10-19 The lens can be decentered upward, downward or laterally.
 |
| Case #2’s topography map showing skewed radial axes on the axial map, and an oval cone on the tangential map (top). The final FlexLens ARC fit (bottom).Click image to enlarge. |
 |
| Fig. 2A. Fluorescein pattern of a spherical landing zone ortho-K design on a toric cornea. Arrow is showing an inadequate inferior alignment in the inferior quadrant.Click image to enlarge. |
 |
| Fig. 2B. Anterior segment OCT epithelial map showing the supero-temporal decentration of the lens treatment seen in Figure2A. Click image to enlarge. |
High Rider/Smiley Face
A treatment zone that is decentered upward is called a high rider or “smiley face,” which is usually the result of a flat alignment zone with insufficient sagittal height. It can result from improper initial keratometry evaluation and overestimating corneal eccentricity.
To solve this, the alignment or the reverse curves can be steepened, or the return zone depth and landing zone angle can also be increased. For a computer-based lens design, the sagittal depth can be increased directly in the software and done on one or multiple zones, depending on the platform.
Low rider/frowny face
In opposition, a low rider or “frowny face” is a treatment zone that shows a treatment zone decentered inferiorly. It is the result of a landing zone being too steep. Like a high rider, it can result from improper initial keratometry evaluation and underestimating corneal eccentricity.
To solve this, the alignment or the reverse curves can be flattened, or the return zone depth and landing zone angle can also be decreased. For a computer-based lens design, the sagittal depth can be reduced directly in the software and done on one or multiple zones, depending on the platform.
Lateral rider
A lateral rider is a treatment zone that shows a decentration laterally, most often in the nasal area. It usually happens because of the difference in elevation between the temporal and the nasal cornea. The best way to solve that problem is to move to a quadrant-specific design that allows for a landing zone in every quadrant or, even better, with a fully customized design assisted by topography. If you don’t have access to these types of technology, you can increase the total diameter of the lens and have a flatter landing zone curve.
Elevation as the key
To solve any situation above, remember to always think about elevation. With a regular cornea, there is a link between curvature and astigmatism as a 25µm elevation difference between principal meridian equals -1.25D of astigmatism at 8mm chord.20 This is considered the threshold for going to a toric landing zone. Hence, switching between a spheric to a toric or a toric to a spheric peripheral landing zone, depending on the situation, should be the first step in problem-solving, as most decentration is related to improper corneal elevation difference evaluation.
Table 1 shows the different sagittal depth heights of a customized ortho-K lens designed with keratometry and eccentricity. The table highlights that an error of 0.1 on the eccentricity value does not translate to the same mistake in elevation if there is high or low eccentricity combined with flat or steep keratometry. For 40.00D, using an eccentricity of 0.1 instead of 0.2 will give an error of only 12µm. For 40.00D, the same difference in the eccentricity of 0.1 at 0.8 vs. 0.9 will create a gap of 31µm. It is even worse with a K value of 46.00D ateccentricity 0.8 vs. 0.9 with an error of 50µm. As a rule of thumb, it is easier to make a mistake of elevation in the lens design with a steep cornea with high eccentricity. Keep in mind that a 10µm difference can have an impact on lens centration.
 |
| Fig. 3A. Imprint of a contact lens design showing a clear supero-temporal decentration and lens adhesion.Click image to enlarge. |
 |
| Fig. 3B. The topography related to the image of Figure 3A shows a center treatment zone by erroneous analysis. Click image to enlarge. |
Central Zone Height
Another type of complication can be linked to the elevation of the lens in the back optic zone. The central sagittal height can be too deep or too shallow. If it is too limited, it can create a central zone of staining, leading to corneal erosion. This anomaly can be solved by increasing the sagittal depth in that zone or manipulating the reverse curve to have a higher central zone. It is sometimes called a false central island, as it can mimic its appearance on corneal topography.
In contrast, if the central sagittal depth is too high, it can create a true central island that can be seen on the topography as a warmer zone in the central expected flatter blue zone. It is a zone of central molding that will retake its shape during the day. Patients usually complain about a decrease in vision as the day advances. In its subtle form, software analysis often misses it, as it is interpreted as inconsistent data compared to the surroundings. Detection of the central island can be enhanced with Fourier-based profilometry or epithelial map of anterior segment OCT.
Visual Acuity Concerns
Any complaints about the quality of vision can be tricky in the case of myopia control. The goal is to induce spherical aberration, which can be challenging for patients in darker environments or activities like driving at night. One needs to discern what is inherent to the mechanism of ortho-K correction versus an anomaly that can be improved. In the presence of an effective myopia control effect in older teenagers, increasing the central zone diameter molding to improve the quality of vision in a dim environment is possible. Keep in mind that this will reduce the slowing effect on eye growth.
Every decentration that reduced visual acuity should be assessed, whether a high, a low or a lateral rider. Moreover, central sagittal elevation (central staining or central island) can also decrease the quality of vision, which can be significant for the patient. University clinic guidelines imply to reach a minimal monocular visual acuity of 20/25, understanding that 20/20 is achievable binocularly.
The most common cause of acuity complaints is under or overcorrection, which is primarily caused by an over- or underestimated keratometry reading at the initial visit, assuming that the refraction is accurate. It can also be caused by an unresponsive or overresponsive cornea with extremebiomechanical properties. To fix this issue, a modification of the back optic zone radius is necessary. Remember that if you need to add -1.00D of correction, you might need to change the radius by -1.50D, as the modification of the curvature of the lens doesn’t fully translate into the molding effect.21 In other words, the lens shape never equals the corneal reshaped profile after appropriate lens wear. This is why topographic maps analysis must be done at every visit to estimate the true impact of the lens on the cornea.
Determining where the visual complaints happen during the day can help to identify their cause. A patient complaining of not seeing well for a couple of hours after removal in the morning can be indicative of an overcorrection/hyperopia in the morning. It can also be caused by improper removal of the lens. If the lens adheres to the cornea and the patient removes it with a rubber removal tool, it can induce a suction that creates a significant central staining that is located in the center of the pupil. This kind of central staining can significantly alter the vision until the complete healing of the epithelium will happen in a couple of hours, depending on the width and the deepness of the lesion.
If the patient complains about decreased vision in the afternoon or later, once a central island is ruled out, it is usually because of molding regression. Depending on the biomechanics of the cornea, the central zone can move back to its original shape too fast. Increasing the compression factor or Jessen factor is usually the way to solve that problem. It can also be related to insufficient sleeping time. The patient should sleep between seven and eight hours to have the optimal treatment effect in terms of central vision quality. Also ask if the patient is taking a nap. Napping, even only 30 minutes without the lens, can make the cornea return to normal faster.
If you don’t see a well-defined topography treatment despite the patient telling you that they have worn the lens, suspect napping or noncompliance. In younger patients, this can happen when commuting to your clinic for an evaluation. For patients that take a real nap in the afternoon, it is recommended to wear the lens even if it is for 30 minutes.22
The other issue related to the quality of vision can be a symptom of halos. Once you rule out every possibility mentioned earlier, consider the size of the pupil rater rather than modify the lens parameters. The peripheral plus ring can create significant halos if the pupil is too big in a dark environment. It can be improved by prescribing a brimonidine drop to be used as needed or by prescribing small myopic glasses to enhance that aspect. A subtype of patients symptoms of halos even during the days in the presence of a pupil size that varies a lot between the photopic and scotopic stages. Low-dose atropine (0.025% or 0.05%) can be prescribed to decrease movement amplitude and alleviate the vision disturbance. The goal here is to facilitate neuroadaptation by having less variation in pupil size.
 |
| Fig. 4. Significant central staining created by an inadequate central sagittal height that needs to be managed. Click image to enlarge. |
Corneal Physiology Anomalies
By affecting the corneal epithelium with the ortho-K designs, multiple anomalies can happen. One of the most common over time is the development of an iron line around the treatment zone.23-26 This condition is benign and does not require any intervention. It is a sign of treatment stability and is visible in almost all patients over time. Every practitioner should teach his patient how to manage an adherent lens. This situation can be scary for the patient when it happens. If the lens is improperly removed, it can also create minor erosion that is uncomfortable. Asking the patient to instill artificial tears before removal and to move the lens using the lower lid can relieve adherence and facilitate the removal process.Conjunctival abrasion can happen if the edge of the lens is too steep and the lens moves outside of the cornea on a much flatter scleral zone during the rapid eye movement sleep phase. The patient will complain of pain and localized redness. In those situations, the edge lift of the lens should be increased to avoid that complication.
Peripheral staining is another problematic situation the first time you encounter it. If the staining is relatively superficial, there is no need to change anything. If it is associated with a steep landing zone and a description of adherence, the landing zone must be flattened. Over time, some patients stopped using the artificial tear drop before removal or used less viscous brands. Backchecking what they use at every visit can save a lot of chair time. A more viscous artificial tear versus a saline solution is better for comfort and protecting the epithelium.27
Another aspect related to compliance is the deposit on the lens. Proper lens surface cleaning is mandatory for safety and successful lens wear. Replacing the lens on a timely schedule can prevent multiple complications and avoid many troubleshooting complications before they happen. As the lens ages, its curves also change and can alter the quality of the intended molding effect. A layer of protein can also accumulate in the reservoir curve and decrease the hydraulic pressure necessary to obtain an optimal treatment effect.28 It is typical for a lens to have a steeper landing zone curve as it ages. The lens can also develop a biofilm, inducing ocular surface inflammation and increasing the risk of microbial keratitis.29 Hydrogen-peroxide disinfection systems are efficient in controlling microbial contamination on the lens surface.30 The use of cold chemical options are as efficient if used in conjunction with a cleaner.31
Giant papillary conjunctivitis can develop even outside the allergic seasons with or without a deposit on the lens surface. Proper follow-up checkups should include palpebral eversion. Careful cornea examination is mandatory to screen for small subepithelial infiltrate. In this situation, it might be time to renew the lens. Both inflammatory processes can be managed with lens replacement and proper use of topical medication. If there is significant corneal erosion, remember to add a last-generation fluoroquinolone to cover for opportunistic microbial keratitis.
As with every contact lens wearer, compliance is an issue.32 Remember that despite all the risks, ortho-K is relatively safe compared to the benefits of myopia control and the improved quality of life.20,33-42
 |
| Fig. 5. Conjunctival abrasion created by a lens decentration overnight with an insufficient peripheral edge lift. Click image to enlarge. |
Takeaways
Solving ortho-K lens fitting problems starts with the acquisition of reliable data on corneal curvature and profile as of the refraction. The impact of the lens on the corneal surface should be evaluated at each visit by comparing the baseline topography with that acquired at the time of the follow-up. Finally, a rigorous eye health assessment and a periodic reminder of lens care rules should become routine. If these conditions are respected, ortho-K lens wear should bring no surprises.
Dr. Simard is in private practice at Clinique d’Optométrie Bélanger and is a clinical instructor at Université de Montréal since 2002. He is a fellow of the AAO, the International Association of Contact Lens Educators and the BCLA. His research interests include myopia control, orthokeratology, aberrometry and scleral lenses. Dr. Simard co-holds a patent for a contact lens design that controls the development of myopia and axial length. He co-authored Managing Myopia One Child at a Time, now translated in five languages (Dougmar Publishers). After completing a cornea and contact lenses residency at the University of Montreal School of Optometry in 2008, Dr. Gagnon joined the attending clinician team. He also gives lectures to optometry and pharmacy students. he practices general optometry and contact lenses at Opto-Réseau Terrebonne. He is a fellow of the AAO. Dr. Michaud is full professor and former dean of the School of Optometry at the L’École d’optométrie de Université de Montréal. He is a diplomate of the AAO and a fellow of the BCLA, the Scleral Lens Education Society and the European Academy of Optometry. He is also certified by the International Academy of Orthokeratology and Myopia Management. Dr. Michaud was named GPLI Educator of the year in 2023. He has received honoraria from Bausch + Lomb, CooperVision, Johnson & Johnson and Alcon
1. Maldonado-Codina C, Efron S, Morgan P, et al. Empirical vs. trial set fitting systems for accelerated orthokeratology. Eye Contact Lens. 2005;31(4):137-47.
2. Chan KY, Cheung SW, Cho P. Clinical performance of an orthokeratology lens fitted with the aid of a computer software in Chinese children. Cont Lens Anterior Eye. 2012;35(4):180-4.
3. Lu D, Gu T, Weiping L, et al. Efficacy of trial fitting and software fitting for orthokeratology lens: one-year follow-up study. Eye Contact Lens. 2018;44(5):339-43.
4. Marcotte-Collard R, Simard P, Michaud L. Analysis of two orthokeratology lens designs and comparison of their optical effects on the cornea. Eye Contact Lens. 2018;44(5):322-9.
5. Guo B, Wu H, Cheung SW, Cho P. Manual and software-based measurements of treatment zone parameters and characteristics in children with slow and fast axial elongation in orthokeratology. Ophthalmic Physiol Opt. 2022;42(4):773-85.
6. Chen Z, Xue F, Zhou J, et al. Prediction of orthokeratology lens decentration with corneal elevation. Optom Vis Sci. 2017;94(9):903-7.
7. Xu Q, Li Y, Li X, et al. Corneal elevation asymmetry vector: Viable predictor of severe one-year-averaged orthokeratology lens decentration. Cont Lens Anterior Eye. 2024:102337.
8. Chen R, Chen Y, Lipson M, et al. The effect of treatment zone decentration on myopic progression during prthokeratology. Curr Eye Res. 2020;45(5):645-51.
9. Chen J, Huang W, Zhu R, et al. Influence of overnight orthokeratology lens fitting decentration on corneal topography reshaping. Eye and Vision. 2018;5(1):5.
10. Guo B, Cheung SW, Kojima R, Cho P. One-year results of the Variation of Orthokeratology Lens Treatment Zone (VOLTZ) Study: a prospective randomized clinical trial. Ophthalmic Physiol Opt. 2021;41(4):702-14.
11. Guo B, Cheung SW, Kojima R, Cho P. Variation of Orthokeratology Lens Treatment Zone (VOLTZ) Study: a two-year randomized clinical trial. Ophthalmic Physiol Opt. 2023;43(6):1449-61.
12. Michaud L, Simard P, Marcotte-Collard R, Ouzanni M. Defining the Montreal Experience: a customized approach to myopia control. Part I - basic principles and treatment algorithm. Cont Lens Anterior Eye. 2022;45(1):101633.
13. Zhou Y, Li H, Hao J, et al. The efficacy of orthokeratology lenses with smaller back optic zone diameter in myopia control: a meta-analysis. Ophthalmic Physiol Opt. 2024;44(6):1215-23.
14. Li N, Lin W, Zhang W, et al. The effect of back optic zone diameter on relative corneal refractive power distribution and corneal higher-order aberrations in orthokeratology. Cont Lens Anterior Eye. 2022:101755.
15. Chen M, Zhang R, Zhu C, et al. Analysis of corneal surface shape following overnight orthokeratology with different optical zone diameters. Front Med (Lausanne). 2024;11:1421361.
16. Chen M, Liu X, Xie Z, et al. The effect of corneal refractive power area changes on myopia progression during orthokeratology. J Ophthalmol. 2022;2022:5530162.
17. Ding W, Jiang D, Tian Y, et al. The effect of the back optic zone diameter on the treatment zone area and axial elongation in orthokeratology. Cont Lens Anterior Eye. 2024;47(2):102131.
18. Wang W, Deng J, Wang F, et al. Study of association between corneal shape parameters and axial length elongation during orthokeratology using image-pro plus software. BMC Ophthalmol. 2024;24(1):163.
19. Rong D, Zhao Z, Wu Y, et al. Prediction of myopia eye axial elongation with orthokeratology treatment via dense I2I based corneal topography change analysis. IEEE Trans Med Imaging. 2024;43(3):1149-64.
20. Vincent SJ, Cho P, Chan KY, et al. CLEAR - Orthokeratology. Cont Lens Anterior Eye. 2021;44(2):240-69.
21. Lau JK, Vincent SJ, Cheung SW, Cho P. The influence of orthokeratology compression factor on ocular higher-order aberrations. Clin Exp Optom. 2020;103(1):123-8.
22. Pérez-Corral J, Cardona G, Pinero DP, et al. Should overnight orthokeratology patients wear their lenses during their afternoon nap? Eye Contact Lens. 2021;47(2):91-7.
23. Cho P, Chui W-S, Mountford J, Cheung SW. Corneal iron ring associated with orthokeratology lens wear. Optom Vis Sci. 2002;79(9):565-8.
24. Rah MJ, Barr JT, Bailey MD. Corneal pigmentation in overnight orthokeratology: a case series. Optometry. 2002;73(7):425-34.
25. Liu C-F, Lee J-S, Sun C-C, et al. Correlation between pigmented arc and epithelial thickness (COPE) study in orthokeratology-treated patients using OCT measurements. Eye. 2020;34(2):352-9.
26. Huang PW, Yeung L, Sun C-C, et al., Correlation of corneal pigmented arc with wide epithelial thickness map in orthokeratology-treated children using optical coherence tomography measurements. Cont Lens Anterior Eye. 2020;43(3):238-43.
27. Carracedo G, Villa-Collar C, Martin-Gil A, et al. Comparison between viscous teardrops and saline solution to fill orthokeratology contact lenses before overnight wear. Eye Contact Lens. 2018;44 Suppl 1:S307-11.
28. Ouzzani M, Simard P, Marcotte-Collard R. Analysis of corneal topographic changes after 12 months of customized orthokeratology use in myopic children. Cont Lens Anterior Eye. 2022;45(1).
29. Lo J, Kuo M-T, Chien C-C, et al. Microbial bioburden of orthokeratology contact lens care system. Eye Contact Lens. 2016;42(1):61-7.
30. Datta A, Tomiyama ES, Richdale K. Microbial bioburden of orthokeratology and hydrogel contact lenses and storage cases using a hydrogen peroxide disinfecting system: a pilot study. J Cont Lens Res Sci. 2021;5(1):e19-31.
31. Pastrana C, Huete-Toral F, Privado-Aroco A, Carracedo G. Efficacy of different disinfecting methods for contact lenses against Acanthamoeba castellanii. Cont Lens Anterior Eye. 2024:102326.
32. Jun J, Zhiwen B, Feifu W, et al. Level of compliance in orthokeratology. Eye Contact Lens. 2018;44(5):330-4.
33. Bullimore MA, Johnson LA. Overnight orthokeratology. Cont Lens Anterior Eye. 2020;43(4):322-32.
34. Gispets J, Yebana P, Lupon N, et al. Efficacy, predictability and safety of long-term orthokeratology: an 18-year follow-up study. Cont Lens Anterior Eye. 2021:101530.
35. Cheng X, Brennan NA, Toubouti Y, Greenaway NL. Safety of soft contact lenses in children: retrospective review of six randomized controlled trials of myopia control. Acta Ophthalmol. 2020;98(3):e346-51.
36. Hiraoka T, Sekine Y, Okamoto F, et al. Safety and efficacy following 10-years of overnight orthokeratology for myopia control. Ophthalmic Physiol Opt. 2018;38(3):281-9.
37. Hu P, Zhao Y, Chen D, Hailong N. The safety of orthokeratology in myopic children and analysis of related factors. Cont Lens Anterior Eye. 2021;44(1):89-93.
38. Liu YM, P Xie. The safety of orthokeratology - a systematic review. Eye Contact Lens. 2016;42(1):35-42.
39. Bullimore MA, Mirsayafov DS, Khurai AR, et al. Pediatric microbial keratitis with overnight orthokeratology in Russia. Eye Contact Lens. 2021;47(7):420-5.
40. Hiraoka T, Matsumura S, Hori Y, et al. Incidence of microbial keratitis associated with overnight orthokeratology: a multicenter collaborative study. Jpn J Ophthalmol. November 16, 2024. [Epub ahead of print.]
41. Gifford KL. Childhood and lifetime risk comparison of myopia control with contact lenses. Cont Lens Anterior Eye. 2020;43(1):26-32.
42. McAlinden C, Lipson M. Orthokeratology and contact lens quality of life questionnaire (OCL-QoL). Eye Contact Lens. 2018;44(5):279-85.
