PREVIOUSLY OFFERED only by a minority of specialty contact lens-minded practition-ers, fitting of orthokeratology (ortho-k) has steadily increased over the last few decades and is now showing potential for more rapid growth due to increased interest in myopia control.¹ Ortho-k is a crucial modality the eyecare practitioner can use for myopic correction and management. As practitioners fit more patients in ortho-k for myopia control, they may find themselves offering it to patients who have other refractive needs. With more patients being interested in and benefiting from ortho-k, fitting frequency should increase, presenting a variety of fitting challenges.

Fortunately, given today’s technology in both corneal topography and ortho-k lens designs, most ortho-k fits are relatively straightforward. It is not unusual to have “first lens” fitting success if patient selection is performed carefully. The best candidates for entry-level ortho-k have low to moderate myopia, minimal with-the-rule central (rather than limbus-to-limbus) astigmatism, a well-centered corneal apex, and a reliable eight hours of sleep per night.

Patients should have reasonable expectations and be able to commit to strict lens care recommendations to avoid complications. It is critical that the initial measurements taken prior to lens design are accurate, as poor starting data will often result in unpredictable and unsatisfactory results.

COMMON PROBLEMS

When problems in ortho-k fitting arise in “easy” patients, they are often due to relatively straightforward issues with lens centration or sagittal depth. Most introductory ortho-k troubleshooting addresses several potential fitting problems:

1. Vertical Lens Decentration  The appearance of a vertically decentered treatment zone on corneal topography is colloquially referred to as “smiley face” (superior lens decentration) or “frowny face” (inferior lens decentration), depending on where the steepened tissue or “red ring” is forming, if it is not symmetrical around the corneal mid-periphery. 

There are numerous ways to address vertical decentration, but reexamining the fit of the lens “on eye” can help determine next steps. It can be easier to assess an on-eye fit after the patient has become accustomed to lens wear, due to less tearing and better cooperation under slit lamp examination. Less obvious issues with edge clearance or treatment zone size may become evident once the patient is able to better tolerate open-eye lens wear.

2. Lateral/Horizontal Lens Decentration  In the absence of vertical lens decentration, lateral decentration often indicates the need to adjust lens diameter. Ideally, the lens diameter should be at least 90% to 95% of the corneal diameter (usually determined by measuring horizontal visible iris diameter [HVID]). If the diameter is appropriate, changes in sagittal depth or edge lift can improve centration.

3. Central Islands  When lens centration is adequate but there remains a central area of corneal steepening, this is termed a central island. Some are “false,” as they (rather counterintuitively) indicate excessive lens bearing centrally with resultant epithelial damage. Central corneal staining on lens removal is evidence of this phenomenon; to adjust for this, the lens usually needs to be steepened by increasing sagittal depth or decreasing edge clearance. Other central islands are “true” in that they represent undesirable central steepening within the treatment zone. This is remedied by flattening the overall fit by either reducing sagittal depth or increasing edge lift.

TORIC PERIPHERIES

As a practitioner begins fitting more difficult ortho-k patients, new problems can arise. A common challenge (even in those who meet the U.S. Food and Drug Administration [FDA]-approved myopia and astigmatism refractive error limits) is larger astigmatic corneal shape (i.e., limbus-to-limbus corneal cylinder). As the toricity of the cornea widens to reach the more peripheral corresponding curves of the ortho-k lens, which are designed for alignment on a spherical cornea, lens “rocking” can occur during the night, resulting in poor lens centration and unusual corneal shaping.

In these patients, toric peripheral curves are necessary to properly align the cornea for best lens stability and centration. This can occur even in patients who have low corneal astigmatism (again depending on the distance away from the central cornea that the toricity extends), but it worsens as overall astigmatism increases.

It is difficult to say when toric peripheral curves are necessary based only on the pretreatment manifest refraction; a careful look at the toricity of all corneal areas will better predict this need. A general rule to follow is to employ toric peripheral curves when there is more than 1D of astigmatism centrally and/or if the toricity reaches out toward the limbus.

If not done initially, toric peripheral curves can be added as a troubleshooting option when lens centration is poor or if lens “rocking” occurs over a cylindrical cornea, resulting in an incomplete or oval-shaped treatment zone. In Figures 1 and 2, the lens exhibits uneven edge clearance and results in an oval central treatment. Adding toric peripheries can stabilize the lens and even out the treatment zone.

HIGHER MYOPIA

When fitting myopia of a higher degree (e.g., above the FDA-approved –5.00D or –6.00D, depending on design), patients may need to have guarded expectations of both the time that it will take to transition from start to completion and the potential final outcome. More visits and lens remakes may be required to reach the desired endpoint than are needed for lower degrees of myopia.

Good candidates should have sufficiently steep beginning keratometry (K) readings. If the myopia is mostly axial (with very flat K readings), it will be difficult to get a lens to flatten the cornea sufficiently to obtain the desired result. Conversely, if the cornea is very steep, the peripheral curves must be controlled well to keep the lens centered and stable, as it may tend to “teeter” on a steeper apex.

It can also be challenging to achieve an adequately large central treatment zone, as more tissue needs to move to the mid-periphery than it would with lower levels of myopia. Smaller treatment zones may be desirable for myopia control, but can create visual symptoms of blur and glare, especially at night. It is not advisable to start with a smaller treatment zone in these patients; it is better to wait to introduce this change until after a desirable fit has been established and the treatment zone has been identified as too large.

Even with modest success, however, it may be worth trying ortho-k on many young high myopes, as even a partial reduction in myopia may be beneficial in myopia control and patient satisfaction.^2,3 For these patients, the practitioner needs to be prepared to offer partial-correction soft contact lenses or glasses during the longer fitting period, and to address any increased corneal staining and discomfort with more aggressive central flattening.

HYPEROPIC ORTHO-K

Hyperopic ortho-k can be very rewarding with good patient selection. Challenges in this modality are similar to those of myopic ortho-k in that lens centration is often the biggest barrier to success. Successfully inducing steepening in the central cornea can be much more difficult than flattening, and results are often less than the dioptric amount desired. Nevertheless, a motivated patient (e.g., one desiring less dependency on reading glasses) may be pleased with even a modest amount of improvement in his or her hyperopia.

CASE EXAMPLE

A 62-year-old, healthy Caucasian female presented for contact lens fitting to reduce her dependency on glasses. She was pseudophakic with IOLs targeted for monovision (OD near), but she was wearing glasses to improve her distance vision. Her manifest refraction showed notable anisometropia of –2.00 –0.50 x 085 OD and +1.50 –0.75 x 086 OS. Previous attempts at soft lens correction OS resulted in symptoms of dryness and unstable lens rotation during daily lens wear. She had worn ortho-k lenses prior to her cataract surgery and wanted to revisit this modality; however, now she desired to utilize a hyperopia ortho-k design OS only to improve her distance vision. Her baseline topography is shown in Figure 3.

After a week of wearing her first lens overnight, she noted some visual improvement but bothersome distortions and glare. A hyperopic ortho-k pattern should show well-centered central pooling (“reverse bull’s-eye”) and minimal edge clearance. However, as shown in Figure 4, this lens showed uneven and decentered pooling and excessive inferior edge clearance. This resulted in a topography with undesirable toricity in the central visual axis (Figure 5). 

As the overall diameter of the lens was appropriate as it pertained to the patient’s corneal diameter, the next lens was ordered with reduced edge clearance and a steepened reverse curve. After a few days, this resulted in a better centered treatment zone on topography (Figure 6) and a happier patient. This treatment zone should continue to improve with more nights of wear.

MYOPIA MANAGEMENT

Numerous ways of improving myopia management with ortho-k are now being researched. Ortho-k has been shown to reduce axial elongation in children safely and effectively;⁴ however, some patients may not show as much myopic retardation or may need more aggressive treatment than others. Whether the practitioner wants to proactively maximize myopia management with the initial fit or determines later on that more aggressive treatment is needed, alterations to the ortho-k fit can be made to potentially heighten the treatment effect created.

One of the simplest ways to increase myopia management in ortho-k patients is to reduce the back optic zone/treatment zone size so that more of the midperipheral ring of corneal steepening is within the pupil. Smaller back optic zone diameters can significantly reduce axial elongation over years of wear.⁵ This may be particularly helpful in patients who have smaller pupils or excessively large treatment zone sizes that extend far beyond the pupillary area, as is shown in Figure 7. It is important to note, however, that smaller treatment zones may result in more patient complaints of glare or other visual distortions, particularly at nighttime or in dim lighting conditions.

Improving the midperipheral ring “strength” may also be necessary to improve the overall fit of the lens and to get more myopia retardation; a shallow, uneven, or incomplete ring can be a sign of poor central flattening and/or centration, and generally is accompanied by patient complaints of poor vision. Simply reducing a back optic zone cannot make up for overall poor fitting characteristics. In these cases, it may appear that lowering the sagittal depth will “squish out” the central tissue, but a steeper sagittal depth will give the tissue more room to move out to the mid-periphery.

Another method of gaining more myopia treatment from an ortho-k fit is to consider treatment zone decentration, as studies have shown that slight decentration may be advantageous so long as the patient’s vision remains acceptable.^6,7While generally it is best to aim for a well-centered ortho-k fit, this evidence may suggest that rather than aggressively addressing a reasonably decentered treatment zone with lens remakes and refits, the practitioner could instead let it remain unaltered (Figure 8).

It has also been suggested that utilizing an aspheric base curve (rather than spherical) may result in even more myopic relative peripheral defocus (particularly along the horizontal meridian) and therefore possibly better myopia treatment.⁸As research grows in these areas, the optometrist’s ability to maximize myopia management with ortho-k will continue to improve.

GENERAL TIPS

When tackling more advanced ortho-k, it is sometimes necessary to abandon and restart a fitting, despite how frustrating this can be for both practitioner and patient. It can be difficult to get a new lens to center if there is corneal molding from a prior lens that inhibits it.

Verifying patient compliance with nightly wear (and sufficient hours of sleep) can avoid erroneous assumptions of treatment failure and attempts at unnecessary problem solving. Utilizing the expertise of laboratory consultants can be invaluable to help in deciding what changes to make to a fit, particularly if the fitter is able to send topographical maps and external photography securely for shared examination of collected data.

Sometimes, a change in ortho-k lens design is required to obtain the best possible fit. One notable way that ortho-k lenses differ is in the number of total curves used in the design; this option can range anywhere from three to six curves, although most current designs utilize four or five. A four-curve design has fewer parameters to monitor and may be simpler to fit, but a five-curve design may offer more specificity while choosing initial lens parameters and subsequently more meticulous adjustments.

Lenses with four and five curves can result in significantly different corneal shaping results.⁹ If the practitioner performs ortho-k on enough patients, a fitting set may be of value, although many designs have a high rate of success with empirical ordering.

Also, as any experienced ortho-k practitioner knows, patience is a virtue. If the initial data collection is accurate and lens centration is good, other issues may resolve with a few additional nights of wear. Changing parameters too quickly can be detrimental to success in the long run. When patients are impatient, it is up to the practitioner to “stay the course” and reassure them that improvements in vision can come with more wear time.

Fitting more “difficult” ortho-k cases can result in very happy and loyal patients, but requires patience, persistence, and flexibility. While ortho-k is FDA approved within certain limits, using ortho-k for refractive errors outside of these limits is considered off-label and patients should be notified of this. Proper patient selection is extremely important, and communication among practitioner, staff, and patient is critical to success.

Having solid policies regarding follow-up requirements, warranties, and cancellation will help avoid frustration if a good fit cannot be achieved. Even in the event of failure, much can be learned from the experience and should help the practitioner improve with future patient fits rather than discourage the use of this modality.

REFERENCES

1. Brennan NA, Toubouti YM, Cheng X, Bullimore MA. Efficacy in myopia control. Prog Retin Eye Res. 2021 Jul;83:100923.

2. Charm J, Cho P. High myopia-partial reduction ortho-k: a 2-year randomized study. Optom Vis Sci. 2013 Jun;90:530-539. 

3. Lyu T, Wang L, Zhou L, Qin J, Ma H, Shi M. Regimen Study of High Myopia-Partial Reduction Orthokeratology. Eye Contact Lens. 2020 May;46:141-146.

4. Lipson MJ. The Role of Orthokeratology in Myopia Management. Eye Contact Lens. 2022 May 1;48:189-193. 

5. Guo B, Cheung SW, Kojima R, Cho P. Variation of Orthokeratology Lens Treatment Zone (VOLTZ) Study: A 2-year randomised clinical trial. Ophthalmic Physiol Opt. 2023 Nov;43:1449-1461.

6. Chu M, Zhao Y, Hu P, Chen D, Yu Y, Ni H. Is Orthokeratology Treatment Zone Decentration Effective and Safe in Controlling Myopic Progression? Eye Contact Lens. 2023 Apr 1;49:147-151. 

7. Li X, Huang Y, Zhang J, et al. Treatment zone decentration promotes retinal reshaping in Chinese myopic children wearing orthokeratology lenses. Ophthalmic Physiol Opt. 2022 Sep;42:1124-1132.

8. Liu T, Ma W, Wang J, et al. The effects of base curve aspheric orthokeratology lenses on corneal topography and peripheral refraction: A randomized prospective trial. Cont Lens Anterior Eye. 2023 Jun;46:101814.

9. 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 Sep;44:322-329.