There are many reasons to consider offering orthokeratology or to want to increase the amount of orthokeratology fitting done in practice. The potential benefits to both patients and practice are numerous. Patients enjoy excellent vision without the hassle of wearing contact lenses or glasses during the day, and practitioners are able to provide a service that builds patient loyalty and improves practice profitability.

With current U.S. Food and Drug Administration (FDA) limitations in orthokeratology approval (orthokeratology is currently approved to treat only up to –6.00D of myopia and up to –1.75D of astigmatism), it can be difficult to find “perfect” candidates to grow an orthokeratology practice. However, as long as the practitioners and patients are both comfortable with off-label prescribing of orthokeratology lenses, there are many opportunities for orthokeratology fits within a practice’s current patient base (Table 1). Thinking “outside-the-box” when it comes to orthokeratology candidacy will reveal a large number of untapped potential patients without the need for aggressive or expensive marketing efforts.

ORTHOKERATOLOGY FOR MYOPIA CONTROL

While growing in popularity, myopia control still has a long way to go to become the standard of care in most eyecare practices. With pharmacological approaches, contact lenses, and lifestyle modifications, there are enough options in the eyecare professionals’ armament to give each potentially progressive myope who enters a practice an appropriate option for controlling their future level of myopia. Orthokeratology offers an opportunity for many young myopes to enjoy both freedom from spectacles/daily contact lens wear and the more long-term benefit of myopia control.

What prevents many patients from being offered orthokeratology services is prescription limitations, although research suggests that more patients are good candidates for orthokeratology than is commonly thought. A novel study by Charm and Cho suggests that even partial reduction of myopia via orthokeratology in patients who have moderate-to-high myopia resulted in significant reduction of axial length elongation (63% slower) compared to spectacle lens-wearing control subjects.¹ This study was performed with children ages 8 to 11 years who had spherical equivalent refractions of at least –5.75D and myopia equal to –5.00D or more. Children this age and with this type of refraction are usually considered “too far gone” to be fit in orthokeratology; however, with parental understanding and consent to off-label use of FDA-approved orthokeratology lenses, they may still be fit to slow further progression and possibly avoid high-myopia-induced ocular pathology. Furthermore, reducing a child’s refraction from high myopia to low or moderate myopia can be useful in many other ways; for example, they would be less disabled if they lost or broke their glasses while playing, and they would have thinner, more cosmetically appealing spectacle lenses.

When attempting to correct higher amounts of myopia with orthokeratology, it may be necessary to use multiple lenses with increasingly flat base curves until the desired level of correction is achieved. This helps to avoid overly aggressive initial flattening that can result in lens instability/decentration and possibly even central corneal abrasions. Additionally, full treatment zone size will generally decrease as higher amounts of flattening are pursued. This can lead to complaints of visual distortion, halos, or glare in lower light conditions when pupil size increases. Conversely, a smaller treatment zone and larger area of peripheral myopic defocus can be beneficial by providing a stronger myopia control effect. Large, steep corneas are the best choice for higher levels of myopia correction; it can be very difficult to accomplish significant myopia reduction on a small, flat cornea.²

Myopia control for young myopes who have notable cylinder in their spectacle refraction is also possible with orthokeratology as long as good centration can be achieved during overnight wear. Multiple studies have confirmed that toric orthokeratology can be effective for both vision correction^3-5 and also for myopia control.^6-7 Most of the work being performed in this area is on myopic patients who have cylinder no greater than –4.00D, and it is generally limited to with-the-rule cylinder to prevent lens decentration during overnight wear. Other challenges to incorporating this into practice include the limited availability of true toric orthokeratology lens designs, particularly in the United States.

Toric periphery orthokeratology lens designs are somewhat easier to come by, but the usefulness of these designs is more in achieving lens centration than central cylinder reduction. If a patient has a small central area of corneal cylinder, some may be corrected with a spherical design alone. If corneal cylinder is limbus-to-limbus, ensuring overnight lens centration becomes increasingly difficult without a meridian-specific design.

BINOCULARITY, ACCOMMODATION, AND ORTHOKERATOLOGY

It is well known that contact lens wear in general can be better compared to spectacle wear for certain binocular vision issues. For example, correction of anisometropia to minimize aniseikonia in contact lenses is common. Other spectacle lens-induced effects such as magnification or minification or unwanted prism can often be avoided with contact lenses as well, and orthokeratology correction should be included in the possible lens options considered to address these types of issues.

Beyond this, some studies demonstrate other potentially beneficial binocular effects from orthokeratology lens wear. Ren et al found that in patients who have low-to-moderate myopia, orthokeratology correction decreased both accommodative lag and high accommodative convergence/accommodation (AC/A) ratio after one year of follow up compared to a spectacle lens-wearing control group.⁸ Gifford et al report findings showing that orthokeratology lens wearers present with more exophoria and lower accommodative lags when compared to a control group of soft contact lens wearers.⁹

Another study suggests some increased exophoria in orthokeratology patients (but no changes in other binocular testing) compared to their binocular status prior to beginning orthokeratology treatment.¹⁰ However, effects were found only in the first three months of treatment and were not present at a long-term follow up (after three years). While relatively small studies, these results are intriguing. If future studies are performed to confirm that orthokeratology is able to improve the accommodative/convergence relationship, this may have many potential clinical applications.

ORTHOKERATOLOGY IS FOR ADULTS, TOO

While many practitioners think of young myopes as their ideal orthokeratology patients, it can be argued that adults are often easier to fit and can have their visual needs satisfied with corneal reshaping. Any adults who have mild or moderate myopia, low hyperopia, and/or minimal cylinder and are interested in reducing their dependency on glasses or contact lenses during the day could be considered for orthokeratology.

When monovision presbyopic correction is appropriate or desired by a patient, orthokeratology should be considered. Many of today’s presbyopes who have active lifestyles would gladly consider the opportunity to limit their refractive correction to overnight wear only. For low-to-moderate myopes, it may be possible to wear one orthokeratology lens in the dominant eye only. In some patients, due to a relatively small treatment zone size, a “pinhole” visual effect can be achieved and near vision maintained throughout early-to-moderate presbyopia. Additionally, presbyopic orthokeratology designs exist that can create annular multifocal or inferior bifocal-type zones on the cornea.¹¹ As orthokeratology usage and design demand increases, the growing presbyopic market may find better access to options like these.

Candidacy for orthokeratology monovision does not have to be limited to myopes, however, as low hyperopes can also do very well with orthokeratology correction.¹² Even if full monovision correction is not achievable due to a higher magnitude of hyperopia, presbyopic patients who have experienced a decline in distance vision from the emergence of latent hyperopia may be content to simply correct the distance hyperopia to be less dependent on glasses, with reading glasses then needed only occasionally throughout the day. Additionally, this is a far better choice compared to refractive surgery while the hyperopic changes are ongoing until the patient reaches absolute presbyopia.

The “bull’s-eye” fluorescein fitting pattern of hyperopic orthokeratology appears similar to that of myopic orthokeratology peripherally, but centrally it shows pooling as opposed to apparent bearing. Centration is critical, as is achieving limited lens movement during overnight wear; similarly, follow up is done much like that of a myopic orthokeratology lens fit. Hyperopic orthokeratology lens designs are now available in the United States and in many cases are no more difficult to fit than myopic orthokeratology is, although central corneal steepening can be a slower and less dramatic process compared to central flattening (Case 1 below).

CASE 1 – A 51-year-old female who had an entering refraction of +0.25 –0.50 x 107 OD and plano –0.50 x 091 OS presented with the complaint of ongoing blur at near and a desire to reduce her dependency on reading glasses. She agreed to try orthokeratology with a target of +2.00D OS only (monovision).

Diagnostic fitting demonstrated excellent centration and a reasonable amount of central pooling and midperipheral bearing (Figure 1). She had very little refractive effect after one night of wear, but gradually achieved approximately +1.50D OS after three weeks of overnight use.

The patient was quite happy with this result socially, but she noted that she still needed +1.00D reading spectacles OU for work. However, this was acceptable because she enjoyed the benefits of blue-blocking spectacles at the computer and felt that binocular correction was beneficial when using multiple screens.

Astigmatism in adult patients also may not be as much of a contraindication as is generally thought. Even when toric orthokeratology correction is not pursued, as long as lens centration can be achieved, an adult patient may be quite happy with a plano or near-plano spherical equivalent refraction after orthokeratology treatment. It is not unusual to encounter patients who have undergone refractive surgery or cataract extraction and are quite happy with their uncorrected vision despite notable cylindrical refraction. When the restriction of having no cylinder is removed from potential orthokeratology patient consideration, more numerous orthokeratology fittings can be pursued.

DRY EYE AND ORTHOKERATOLOGY

Regardless of a patient’s age, orthokeratology is a viable alternative to soft and GP contact lenses worn during the day when dryness is a concern. Numerous studies have investigated patient comfort both subjectively and objectively, with some recent studies showing more confirmatory results. Carracedo et al performed a study of both current silicone hydrogel contact lens wearers and new contact lens wearers who were fit into orthokeratology lenses.¹³ They found that Ocular Surface Disease Index (OSDI) questionnaire scores improved significantly compared to baseline in the initially silicone hydrogel-wearing patients after one month of orthokeratology wear. Perhaps more interesting was the finding of a significant increase in goblet cell density in these same patients after one month as well. This may indicate that lessening interaction with conjunctival goblet cells by changing from larger silicone hydrogel lenses to corneal GP/orthokeratology wear could positively influence tear film quality.

In another study comparing silicone hydrogel and orthokeratology lens wearers, subjective symptoms measured using the Dry Eye Questionnaire (DEQ) again were better in the orthokeratology group.¹⁴ Additionally, objective measurements of bulbar redness, limbal redness, and conjunctival staining were worse in the silicone hydrogel group of patients.

Reasons for improved comfort in orthokeratology lens designs are still not fully understood, but they are likely multifactorial. With wear primarily overnight, issues that occur during daytime contact lens wear are eliminated. Dehydration of soft lens materials, exposure to environmental factors such as wind, dirt, or allergens, and tear film disruption from daytime contact lens wear can all be avoided with orthokeratology. Treatment of dry eye during the day can be easier and/or more comfortable when contact lenses are not being worn; for example, not needing to remove contact lenses increases the likelihood that patients will comply with using hot compresses or thicker, lipid- or gel-based artificial tears. Conversely, dry eye patients should be educated to not instill any ointment or thick gels into their eyes prior to orthokeratology lens application at bedtime.

ORTHOKERATOLOGY AFTER REFRACTIVE SURGERY

Patients who experience myopia regression following refractive surgery can be resistant to returning to daily spectacle or contact lens wear. Additionally, dryness following eye surgery may be exacerbated by daytime contact lens wear. Offering these patients a solution such as orthokeratology is often a welcome answer to the blur following a disappointing refractive surgery procedure.

When assessing candidacy for orthokeratology after a refractive procedure, look for corneal topography to be fairly regular and for the treatment zone to be well-centered. Highly oblate corneas or decentered steep or flat islands will not allow for adequate lens centration while sleeping. If available, pre-surgical keratometry can be used to determine the first orthokeratology lens fitting parameters. If not available, estimated keratometry values calculated from the mean keratometry value of the peripheral cornea can be used effectively.¹⁵ Case 2 (below) presents an example of a patient who experienced myopia regression after laser-assisted in situ keratomileusis (LASIK) and was fit in orthokeratology lenses.

CASE 2 – A 46-year-old female presented for her annual examination after having LASIK surgery approximately one year prior. Her pre-operative refraction was OD –6.00 –0.25 x 115, OS –5.50 –1.50 x 082. Her refractive goal for the surgery was to achieve mild monovision, approximately –1.50D OD and plano OS.

Her entering visual acuities at the one-year postoperative examination were 20/30 OU at distance and 20/20 OU at near, with complaints of distance blur and difficulty driving at night. Her refraction was –1.25 –0.50 x 177 (20/20) OD and –0.50 –0.50 x 028 (20/20) OS.

After extended discussion, she decided to attempt orthokeratology OS only to improve her distance vision. Lenses were selected based on pre-surgical keratometry readings, and diagnostic lens fitting showed good centration and edge alignment. There was visible central pooling, as expected after LASIK (Figure 2). Central sagittal depth was adjusted to address this, and a light but adequate central “bull’s eye” pattern was achieved.

Visual acuity after one week of wear was 20/20^-1 OS and OU at distance and was 20/20 OU at near with good reported adaptation and comfort. The patient noted much improved distance vision and was very happy to avoid returning to spectacle or soft contact lens wear.

THE FUTURE OF ORTHOKERATOLOGY

The future holds other exciting options to allow increasingly more patients access to orthokeratology. Corneal cross-linking is still a relatively new procedure with applications that have yet to be fully discovered. It may be possible to combine this with orthokeratology treatment to permanently shape a myopic cornea or perhaps to not just halt, but also to reverse, keratoconus progression.16 Scleral lenses have the potential to provide better centration of orthokeratology lens treatments, which could open up a world of refraction correction possibilities. There is still much that needs to be learned about scleral lenses in general, however, including their long-term effects on goblet cell density, meibomian gland function, oxygen transmission requirements to the cornea through the lens and tear layer (particularly during overnight wear), and more before this type of orthokeratology could be attempted.

As long as patients (and parents) understand and agree to off-label use of lens designs, and adequate lens centration can be achieved during overnight wear, orthokeratology does not have to be limited to only a small number of perfect candidates. Setting reasonable expectations through patient education is critical to ensuring successful outcomes, particularly in more complicated cases. If contact-lens-fitting practitioners make an effort to consider orthokeratology for a wider range of candidates, more patients will benefit from this unique and effective modality for vision correction. CLS

REFERENCES

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