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IS ORTHO-K POSSIBLE WITH CORNEO-SCLERAL LENSES?
DADDI FADEL, DOPTOM, & CARY M. HERZBERG, OD
The evolution of scleral lenses in the past 10 years has led us to think about scleral lenses for normal eyes because of the benefits that have been obtained when fitting scleral lenses for irregular and diseased corneas. At the same time, we could consider whether there is an indication for scleral lenses for orthokeratology (ortho-k).
For some time, we have heard about the possibility of using mini-scleral lenses as an ortho-k treatment. Using corneo-scleral lenses for ortho-k was first presented by Dr. Cary Herzberg at the 2004 Global Orthokeratology Symposium. In 2006, he registered a patent for a dedicated design of corneo-scleral lenses for orthokeratology (Herzberg, 2006). In 2010, Dr. Herzberg established that mini-scleral lens designs are very safe and useful for ortho-k treatment and that they almost create a well-centered treatment zone (Herzberg, 2010).
In one case report of an off-label use of scleral lenses for ortho-k, Yin (2014) affirmed that these lenses provide superior comfort, better centration, more stability, and the possibility to have an increased treatment zone size. But, no study to date has determined optimal fitting characteristics, the indications of the treatment, the myopia control effects, and the complications of this use of scleral lenses.
Therefore, the questions we must ask ourselves are: Why should we fit scleral lenses for ortho-k rather than corneal reverse geometry lenses (RGLs)? Which design should we fit? Can we fit a standard corneo-scleral or mini-scleral design with a very flat optic zone, or is it necessary to design a lens specifically dedicated for this purpose? Is it essential to fit a mini-scleral lens with a reverse zone that has a reservoir for a faster reshaping of the cornea? What are the overnight wear effects of ortho-k scleral lenses?
It’s interesting and relevant to note that corneal RGLs (for ortho-k) and scleral lenses have the presence of a “landing zone” in common that is functional for centering and stabilizing both types of lenses.
Indications to Fit Ortho-k Sclerals
The indications for using scleral lenses for ortho-k might be related to the contraindications of a corneal ortho-k lens because of scleral lenses’ greater stability. These indications might include high corneal astigmatism (>1.75D), against-the-rule and oblique astigmatism, high myopia (especially when associated with a small cornea), irregular astigmatism, and when the cylinder component is higher compared to the spherical component. But as usual, it’s important to evaluate the benefit-to-risk ratio.
Which Design to Fit
In the preliminary phase of a current study, the first lenses fit on three eyes were standard mini-sclerals and standard corneo-sclerals with a flat back optic zone (Fadel, 2016). The mini-scleral lens (8.60mm base curve radius [BCR], 15.0mm total diameter [TD]) was inferiorly decentered and bearing on the superior cornea (Figure 1). The corneo-scleral lens (8.20mm BCR, 14.6mm TD) was slightly superiorly decentered, bearing on the central cornea. The corneo-scleral lens was acting as a corneal lens because there was no scleral landing (Figure 2). The patterns observed with scleral and corneo-scleral lenses were almost all the same in the three eyes.
Figure 1. Mini-scleral lens with inferiorly decentration bearing on the superior cornea (A). Prismatic fluid layer showing bearing on the superior cornea (B).
Figure 2. Corneo-scleral lens slightly decentered superiorly. This lens is acting as a corneal lens and has no scleral landing area, but only central bearing (A and B).
The corneo-scleral lens was fit for two days in a daily wear regimen. The corneal map after eight hours of lens wearing showed an insufficient flattening effect (Figure 3).
Figure 3. A corneal map before the treatment (A), and after two days of standard flat corneo-scleral lens fitting in a daily wear regimen that shows an insufficient flattening effect (B).
Because of the insufficient corneal shaping attained with the corneo-scleral lenses, the researchers assumed it was necessary to use a dedicated design with a reverse curve zone and a corneal landing zone to create a negative pressure and hydrodynamic forces to induce a central cornea flattening and mid-peripheral steepening, reducing the corneal power (Mountford, 2004).
The resulting lens design was a corneo-scleral lens with five zones: optic, reverse, corneal landing, limbal, and scleral landing. The fluorescein pattern immediately after the lens application showed a centered lens. After four days with daily wear, the fluorescein pattern still showed a centered lens with a wide treatment zone (7mm), covering the entire dilated pupil in scotopic vision (Figure 4).
Figure 4. The fluorescein pattern immediately after the reverse corneo-scleral lens application, showing a centered lens (A). After four days with daily wear, the pattern shows a still centered lens with a wide treatment zone (7mm) covering the entire dilated pupil in scotopic vision (B).
The clearance was evaluated in different gaze directions. Looking straight, the central clearance was about 10µm; there was no central bearing. Over the limbal area, the clearance was about 50µm, which permits high oxygenation to this sensitive tissue (Figure 5). Looking up and down, the clearance in the reverse zone was about 100µm (Figure 6). In the temporal-superior area, it appeared that limbal bearing existed. We believe that in some cases it would be necessary to have a double reverse zone, vaulting the limbus to keep it safe.
Figure 5. Central (A) and limbal (B) clearance evaluation. Looking straight, the central clearance is about 10µm, so there was no apical bearing (A). Over the limbal area, the clearance was about 50µm (B).
Figure 6. Clearance evaluation in different gaze directions, looking down (A) and up (B). The clearance in the reverse zone was about 100µm.
The corneal map showed a significant (0.20mm/1.00D) flattening effect after only four hours of daily wear (Figure 7). In one case, a central island was evident after four days’ wear (Figure 8). But, this issue can be handled just like those encountered with corneal ortho-k lenses.
Figure 7. Corneal map before the fitting (A) and after only four hours of daily wear showing a significant flattening effect (B).
Figure 8. In one case, a central island was evident after four days’ wear.
Overnight Effects of Scleral Ortho-k Lenses
The most significant complications/risks of overnight wear of scleral lenses are corneal swelling and corneal inflammation, including microbial keratitis. Despite these risks, overnight wear of scleral lenses was reported in several cases for the treatment of chronic epithelial defects (Pullum and Buckley, 1997; Romero-Rangel et al, 2000; Rosenthal et al, 2000; Tappin et al, 2001) and keratinized lid margin (Pullum and Buckley, 1997).
Tappin et al (2001) have also contemplated overnight use of scleral lenses for corneal exposure, post-radiotherapy complications, trichiasis, Stevens-Johnson syndrome, recurrent corneal epithelial erosion, and congenital or postsurgical lid defects. None of these cases of wearing sclerals overnight reported any overnight swelling (Pullum and Buckley, 1997; Romero-Rangel et al, 2000; Rosenthal et al, 2000; Tappin et al, 2001).
A study on corneal swelling with overnight use of scleral lenses was conducted by Smith et al (2004) on three patients with healthy eyes, fitting an 800µm thick lens with a clearance between 200µm to 300µm. This study showed corneal swelling in three subjects from 4.9% to 10.2%. The overnight swelling was greater than that induced by daily wear, which was almost 2.4% to 3.5%. A fourth volunteer agreed to participate to the study despite daily wear swelling in excess of 5%. This subject showed greater overnight swelling, almost 17.5%.
However, there is still a lack of knowledge of the corneal physiological response of overnight scleral lens wear and a reluctance to use scleral lenses in overnight wear (Schein et al, 1990; Pullum and Buckley, 1997) despite success in the treatment of several ocular diseases (Pullum and Buckley, 1997; Romero-Rangel et al, 2000; Rosenthal et al, 2000; Tappin et al, 2001). Nevertheless, with corneo-scleral lenses for ortho-k, the clearance, even in the reverse area, is only about 100µm, so the overnight swelling using thinner lenses might be minimal.
In the end, the researchers concluded that sclerals should be considered in overnight use only if they offer a unique therapeutic attribute and when patients can’t be rehabilitated with other forms of lenses. Additionally, sclerals shouldn’t only be considered for visual rehabilitation.
The risk of corneal inflammation, including microbial keratitis, in overnight wear with scleral lenses might be the same as those with corneal ortho-k lenses. In one case study, it was reported that microbial keratitis resulted from fitting scleral lenses for treatment of neurotrophic keratitis secondary to herpes simplex keratitis (Zimmerman and Marks, 2014). However, it turns out that the subject developed microbial keratitis due to inappropriate compliance that could have been avoided with education on the proper use of contact lens care solutions, case replacement, and hygiene rules.
The use of scleral lenses for ortho-k has been reported for the past 10 years. Practitioners fitting these lenses have affirmed that they are better centered, more stable, provide a wider optic zone, and are safe. But, there is no study to demonstrate these characteristics.
As mentioned earlier, after fitting the three patients with different lenses, we determined that a standard scleral lens with a flat optical zone has an insufficient flattening effect; a reverse zone is necessary to create negative pressure to facilitate a greater and faster flattening effect.
But, we still have unanswered questions: Is a double reverse zone necessary to protect the limbus? And, what are the overnight wear effects of reverse corneo-scleral ortho-k lenses? Further studies and considerations are necessary. CLS
For references, please visit www.clspectrum.com/references and click on document #253.
Dr. Fadel is a specialist in contact lenses for irregular cornea, scleral lenses, and orthokeratology. She has a contact lens private practice in Italy where she designs special customized contact lenses. She is the founder and president of the Italian Academy of Scleral lenses (AILeS), board member of the Italian Academy of contact lense (AILAC), and a member of Scleral Lens Education Society (SLS).
Dr. Herzberg holds a patent on the first scleral orthokeratology design. He is co-founder, president, board member, and fellow of the International Academy of Orthokeratology & Myopia Control (IAOMC); and the founder, president, and a board member of the American Academy of Orthokeratology and Myopia Control (AAOMC), formerly The Orthokeratology Academy of America (OAA). He is an advisory board member of the GP Lens Institute (GPLI) and a former contact lens design consultant to C&H Contact Lens. He has received travel funding from Paragon Vision Sciences.