The advent of modern scleral lens design, manufacturing, and availability has been a boon to the specialty lens industry and eyecare practitioners alike. Their rapid utilization in the last five to seven years has led to many success stories and to their adaptation as a lens of choice in challenging cases.

However, there certainly are many questions about how a lens that covers the entire cornea, limbus, and parts of the conjunctiva affects those respective tissues over time. A recent much-debated question about scleral lenses is: Should scleral lens use be limited to diseased and irregular eyes, or is it also a viable option for normal healthy eyes? In this article, Dr. Derek Louie addresses the benefits of fitting normal, healthy eyes, while Dr. Jeffrey Sonsino addresses their use as limited to diseased and irregular eyes. (Note: Opinions expressed are those of the authors and not of Contact Lens Spectrum).

1. SHOULD PATIENTS BE PRESENTED WITH ALL OPTIONS?

Dr. Louie Yes. Uncertainty should not automatically preclude the use of a scleral lens in cases that may not be overly challenging from an anatomical or refractive standpoint. I would argue that we do our patients a disservice if all options to correct refractive error or to enhance contact lens comfort are not considered and/or presented. Practitioners are slowly adapting to the use of scleral lenses, as is evident in the market surveys that show a general increase in scleral lens fits/refits over the past several years.¹

Dr. Sonsino No, but we live in a world of beautiful shades of gray, not of black and white. Therefore, I cannot say that I will never fit a patient who has a normal cornea in a scleral lens.

In fact, I can recall a patient who has a very large horizontal visible iris diameter (HVID)—but without pathology—who failed in multiple off-the-shelf soft lenses, custom lathed soft lenses, and corneal GPs. We fit her with scleral lenses and were successful due to the customizability and ability to not interact with the cornea.

However, the key to that story was that we failed with all other simpler strategies first. Sclerals are not appropriate as a primary, secondary, or tertiary strategy for those who have no significant pathology. The pathology and limited options need to be significant enough to justify the cost, the numerous visits for fitting and evaluation, the 50% reported rate of filming and fogging, the conjunctival redness, and the hassle of application and removal tools that scleral lenses require.

Dr. Louie The resurgence of scleral lens availability and prescribing is driven mostly by modern material science and manufacturing capabilities. Over the past several years, most custom contact lens manufacturing laboratories have added modern scleral lens designs to their product lists. All of these lens designs are available in high-oxygen-permeable (Dk) or hyper-Dk materials.

Dr. Sonsino Just because we have the technology to create something complex and safe does not mean that we should deploy this strategy for the general population. This is a basic tenant in public health. Why? Because as a society, we need to balance costs with outcomes.

An example of this is lower back pain. Lower back pain is the fifth most prevalent reason for doctors’ visits.² Magnetic resonance imaging (MRI) tells a physician immediately if there is herniation of the disc, spinal stenosis, or osteoarthritis. But, the American Academy of Family Physicians recently recommended not imaging patients for back pain unless other major problems are present.^3,4 The reasoning: the costs do not justify the outcomes. This is a difficult thing to tell your patient in the chair, but it is necessary.

Dr. Louie Anyone who has low refractive error and is generally asymptomatic in commercially available daily disposable soft lenses would not likely want the extra burden of specialty lens maintenance.

Scleral lenses are applied to the ocular surface differently compared to any other contact lens that an eyecare provider can prescribe. Scleral lenses require preservative-free saline solutions, careful balance of the lenses, dexterity, and usually specialized devices to apply and remove the lenses. Generally, this extra burden of materials and solutions would not be the best or most convenient lens modality for a patient who is happy and comfortable in a commercially available soft lens or well-fit corneal GP lens.

But, what about those patients who are not happy or comfortable in any available lens design and who have a “normal/healthy” cornea? Almost daily in our practices, we see patients who are dissatisfied with their contact lens experience due to comfort and/or vision issues. Presenting the possibility of a well-fit scleral lens that retains liquid next to the cornea and could improve the visual experience, both qualitatively and quantitatively, is an exciting proposition for many existing and new contact lens wearers.

We often go around and around, order diagnostic lens after diagnostic lens, only to be disappointed or get an unacceptable result. With scleral lens optics, masking of corneal astigmatism, and a supremely stable lens, a practitioner could offer normal cornea patients who have challenging refractive errors a solution to their contact lens frustrations within one to two visits.

Dr. Sonsino To that point, I would say that if you cannot find a standard option for a patient who has no pathology, you are not trying hard enough. There are many more options for such patients than what the soft lens manufacturers produce.

Hybrid lenses are a substantial troubleshooter in the right hands. They are available with a 90% water polyethylene glycol (PEG)-based polymer coating to improve comfort for patients who have dry eyes. Or, custom-lathed soft lenses can accommodate any conceivable power, diameter, and base curve radius.

All of these strategies are available to any of us willing to invest the time and effort to learn how to drive success. And, because they are marketed to compete with off-the-shelf soft lenses, handling, ease of use, and cost to patients are all competitive.

2. WHAT ABOUT THOSE WHO HAVE DRY EYE OR OCULAR SURFACE DISEASE?

Dr. Louie There is no question that scleral lenses are beneficial for irregular corneas: keratoconus, post-transplant, ectasia, radial keratotomy, or ocular trauma. Many studies present cases of scleral lens use for irregular corneas.^5,6 However, scleral lenses are also beneficial not only in pathological dry eye patients, but also in those who have less severe symptoms and clinical signs.

It is not uncommon in a busy dry eye clinic to encounter patients who have little or no refractive error. Could a practitioner, or would a practitioner, present a contact lens as an option for management of an ocular surface disorder? Given the increased knowledge and research focused on ocular surface disorders, presenting a scleral lens as a mode of treatment should be relatively high on the differential decision-making.^7,8 It is our experience that in severe ocular surface disorder cases, intervening with a scleral lens is often a very rewarding experience for both patient and prescriber.

The two main reasons that patients drop out of contact lens wear are vision and comfort.⁹ A scleral lens could address both of these factors for some patients who have a normal corneal surface. Scleral contact lenses are well established tools in the challenging and often frustrating pursuit of solutions for patients who have ocular surface disorders.^10-12 While case reports and peer-reviewed journal articles often highlight the use of scleral lenses in extremely challenging scenarios, scleral lenses are also of use in “less challenging” ocular surface disorder or dry eye cases. These patients have essentially normal ocular anatomical profiles in their cornea and conjunctiva, but suffer from aberrant tear production in quality and/or quantity. The use of a scleral lens in these normal cornea patients can sometimes be life-changing.

Dr. Sonsino There is no doubt that patients who have severe dry eyes—such as in cases of ocular graft-versus-host disease (oGVHD), Sjögren’s syndrome, Stevens-Johnson syndrome, mucous membrane pemphigoid (MMP), exposure keratopathy, and others—benefit from scleral lenses. Their conditions are so severe that if we do nothing, they run the risk of severe complications.

If you fit enough scleral lenses, invariably patients who have blepharitis end up in your chair wanting them. The problem is that scleral lenses do not treat the underlying pathology. They simply exchange the surface where there is a problem.

In oGVHD, the meibomian glands atrophy, yielding very little meibum secretion on the ocular surface.¹³ When wearing a scleral lens, this lack of meibomian gland secretion manifests as fluctuating vision due to the unstable tear film on the front surface of the lens. Patients are willing to deal with this consequence because they get to keep their corneas. But, a patient who has primary meibomian gland dysfunction (MGD) or blepharitis does not have corneal perforation as a motivator to wear sclerals. So, fluctuating vision/filming and fogging is often a reason for lens dropout.¹⁴

Peer-reviewed literature on this topic is scarce, but in a small series of patients who have moderate-to-severe dry eyes, only four of the seven were successful in mini-scleral lenses.¹⁵ We can hypothesize that the rate of success in mild dry eye would be less.

3. WHAT ABOUT PATIENTS WHO HAVE A NORMAL OCULAR SURFACE/CORNEA BUT AREN’T SUCCESSFUL IN SOFT LENSES?

Dr. Louie Are corneal GPs/hybrid lenses the only option? I would argue that refitting a patient who is not comfortable or satisfied in a soft contact lens of any modality (monthly, two-week, or daily disposable) into a corneal GP contact lens is not the most common clinical decision. If comfort or dryness is the main factor for refit, then the initial experience in a corneal GP may not excite the patient.

However, it has been my experience that a diagnostic fit of a scleral lens that captures and maintains sterile saline next to the ocular surface—even when there is lens awareness and the diagnostic lens is not close in power—generally provides a positive experience for the patient. Any underlying condition could be treated concurrently.

Dr. Sonsino Refitting a patient who is not comfortable/satisfied with a soft lens into a scleral lens does not address the reason why the patient is not comfortable in the first place. In every case that I have seen in which a patient is uncomfortable in a soft lens, there is an underlying reason.

Does that patient have MGD, blepharitis, lid wiper epitheliopathy (LWE), or contact lens papillary conjunctivitis (CLPC)? If the underlying condition is MGD or blepharitis, filming and fogging will plague the wearing experience. If the answer is LWE or CLPC, a scleral lens will not fix the problem and will be just as uncomfortable. In all cases, treatment of the underlying condition is a better answer.

4. SHOULD SCLERAL LENSES BE CONSIDERED IN PATIENTS WHO HAVE HIGH AMETROPIA?

Dr. Louie Yes. With a happy patient in standard power who has no problems, there is no need for scleral/custom lenses. From a clinical decision-making process, it is unlikely that a practitioner would consider any custom lens if a patient is happy and satisfied with his or her vision in a commercially available soft contact lens. It is also important to consider the risks of neovascularization and/or limbal stem cell stress in custom soft lenses versus scleral lenses. There have been several theoretical studies on the risk of hypoxia in scleral lens wear.^16-19 Whenever approaching a new scleral lens fit, the amount of clearance, thickness of the contact lens, and material selection should be considered carefully. Studies show that ideally, prescribers should select a material greater than 125 Dk, fit the lens with less than or equal to 150 microns of clearance over the cornea, and ensure that the lens thickness is no more than 250 microns.¹⁸ These criteria are difficult for irregular cornea patients; however, it is much easier to achieve with a normal, regular cornea.

Regardless, careful eye health monitoring is required in any scleral lens wearer, particularly in the limbal region for limbal stem cell distress and corneal neovascularization. However, this is no different a consideration than for any contact lens wearer, especially those in custom soft lenses for high ametropia, for whom the lens is likely going to be thicker and potentially of a lower-oxygen-transmissibility material.

Dr. Sonsino No. The next logical lens in the continuum of care of patients who have high refractive errors and a normal cornea is not a scleral lens. The next logical lens is a second-generation hybrid lens. A well-fit hybrid lens allows a tear pump with movement, a hyper-Dk skirt with no power (making the skirt thin), and a high-Dk GP center. These properties combine to provide a simple second step if you believe that a patient should be fit with the simplest, most cost-effective contact lens that accomplishes the best outcome. If a hybrid lens does not work out for any reason, then a piggyback corneal GP over a high-Dk soft lens would be a next logical step.

The third logical step would be a custom silicone hydrogel lens manufactured by any of the GP lens laboratories. Most, if not all, GP laboratories have access to a latheable silicone hydrogel material with a Dk of 75.

5. WHAT ABOUT AN UNSTABLE CUSTOM SOFT OR GP LENS?

Dr. Louie Lens movement and/or rotation decreases visual functioning. An unstable custom soft or corneal GP lens is not a benefit to a patient even if it provides improved corneal eye health. If the patient has unstable acuity with any contact lens, the likelihood of success decreases.

Scleral lenses don’t move. If they do, they must be refit, as a patient will suffer from midday fogging and, most likely, lens awareness and discomfort.¹⁴ Fitting a spherical scleral lens for a patient who has high regular or irregular astigmatism can provide improved visual stability and comfort. The tear layer between the lens and cornea will correct any corneal astigmatism, without the variability of lens movement or rotation. This simple fact is perhaps why there is a higher percentage of refits to scleral lenses than to bitoric corneal GP lenses.¹

Dr. Sonsino This scenario is the perfect reason to fit a hybrid lens. Hybrid lenses are cost competitive with soft torics, have easy handling without tools, come equipped with a PEG coating, are six-month replacement lenses, and have equivalent comfort (after two to three days when well fit).

I recognize that not everyone is an expert in hybrid lenses and is able to drive this success. My answer to that is to invest the time to develop that expertise; many practitioners have, and you can too.

Developing hybrid lens expertise goes hand-in-hand with scleral or other specialty lens expertise. Why not develop a skill that can be used in the widest variety of patient care scenarios as possible?

Dr. Louie Practitioners must also consider the cost of an annual supply of custom soft lenses and the fact that spherical/bitoric GP lenses can be uncomfortable and difficult to adapt to. Patient experience drives acceptance in contact lens wear. This can be observed in clinical situations and has been written on extensively elsewhere.^20-23

Many clinicians employ topical anesthesia when dispensing or assessing corneal GP lenses. In our experience, this is unnecessary and even unwanted in scleral lens evaluations. It is important to demonstrate what a scleral lens feels like on patients’ eyes so that they can compare this sensation to their existing lens modality. Often, the comfort of a scleral lens is surprising based on patients’ pre-conceived notions of material and lens size.

Dr. Sonsino As I mentioned earlier, the second step after bitoric GP failure is to add a piggyback lens. The third strategy after bitoric GP piggyback failure is to use a custom soft toric lens, either hydrogel or silicone hydrogel. That totals four strategies to be used before a scleral lens, again taking into consideration cost, convenience, ease of fit, etc.

Dr. Louie A piggyback system is just as cumbersome or more so than a scleral lens. And, the cost is prohibitive for some, with an annual supply of daily disposables in addition to the cost of the corneal GP. If patients aren’t using a daily disposable, then, at the very least, they are purchasing twice the amount of cleaning and disinfecting solutions annually, or two different care solutions.

Dr. Sonsino Application of a corneal GP lens piggybacked over a daily disposable lens is much less cumbersome compared to application of sclerals. Piggyback lenses do not require tools to apply or remove them, which is a big deal to many patients. The dexterity required to balance a scleral lens, fill it with solution, lean over, and miss the lids without trapping an air bubble is a skill that takes many months to master. In fact, most practitioners whom we teach in workshops have trouble with application and removal of sclerals. Additionally, if patients misplace a scleral removal tool, you are getting a call at midnight to meet them at the practice.

How are you pricing your materials? In my practice, inclusive of professional fees, the price of a piggyback GP with daily disposables is less than one-third the price of sclerals. I think that this is generally reflective of most practices across the country.

Dr. Louie My argument would still be timing and cost. A custom soft lens may take as many or more visits as a well-fit scleral lens on a normal cornea. How often have we seen patients who have required two to three diagnostic toric soft lenses that are not working well, or the thickness and comfort of a custom soft lens is not acceptable to the patient?

A cornea without physical irregularity of shape may still be a challenging fit in mass-produced lenses. Corneal sagittal height, HVID, lid anatomy, and tear production are all factors when considering any contact lens for a patient. Some or all of these variables may influence the successful wear of any contact lens, including soft contact lenses.²⁴

Dr. Sonsino Custom soft lenses are available in any diameter, base curve, sagittal depth, optic zone, power, and thickness conceivable by the designer. With that body of options, it is very possible to fit any eye that does not succeed with off-the-shelf lenses.

6. WHAT ABOUT MULTIFOCAL SCLERAL LENSES?

Dr. Louie This is a new frontier, and there are exciting options for practitioners. A scleral multifocal lens is an amazing option to offer patients who are spending more time on a computer (lower blink rate and incomplete blinking), but require near/far optics that are stable. In many new scleral lens designs, you can specify the optic zone for near and far options. For patients who have regular astigmatism and are good candidates for a multifocal contact lens, a scleral lens could be a better option compared to a bitoric multifocal corneal GP or a custom soft toric multifocal that provides “soft lens” optics.

Dr. Sonsino It is well known that even with toric haptics, most sclerals center inferior-temporally over the cornea. There are a number of papers that describe this phenomenon due to the scleral asymmetry being, on average, steeper temporally than nasally.^25,26 Scleral lenses, because of their bulk, literally fall down the hill. Until decentered optics become available in sclerals, the gold standards for multifocals are still corneal GP and soft lens options.

7. ARE CONSIDERATIONS DIFFERENT FOR A SCLERAL LENS THAN FOR ANY OTHER CUSTOM SOFT OR GP LENS?

Dr. Louie Whenever prescribing a specialty lens or custom-designed lens, the number of variables and the complexity increase; oxygen permeability of the material selected, complexity of fit, complexity of lens maintenance, replacement schedule of the lens, material compatibility with the ocular surface, and solution compatibility with the immune system are all important factors. These considerations are no different in a patient wearing a scleral lens compared to a patient wearing a quarterly replacement soft lens or corneal GP lens.

Scleral lenses do require a more systematic approach to prescribing. Any scleral lens is a custom lens and cannot be ordered empirically from a manufacturer at this time. However, newer instrumentation that can obtain scleral topography can aid in designing or customizing the peripheral areas of some scleral lenses. Optical coherence tomography (OCT) can also be used to analyze vault in specific areas of a scleral lens.²⁷ However, none of these instruments are necessary to prescribe any modern scleral lens design. What is necessary is a diagnostic set. Currently, there are no scleral lenses that can be accurately ordered without a diagnostic lens, at least for over-refraction.

Dr. Sonsino Scleral topographers and OCT are wonderful additions to a scleral practice, but these devices do not come free. Practitioners set the cost of scleral lenses based partially on the cost of the equipment needed to drive success with the modality. This is simple economics. Soft lenses, hybrids, and corneal GPs may all be ordered empirically, saving chair time and cost. With this issue, you need to ask yourself a very honest question. Are you fitting patients who have normal corneas in scleral lenses to justify (and pay for) the shiny new OCT you bought, or is this lens truly in your patients’ best interest? Hopefully, you have a patient population to justify the costs of these devices on their own merits.

Dr. Louie None of these instruments are necessary to design and prescribe scleral lenses. In a practice utilizing scleral lenses often, the instruments could be useful.

Careful follow-up is required. Designing and troubleshooting a scleral lens requires a systematic approach and usually at least one follow-up visit. However, with some experience, there should be no need for more follow-up appointments than with any other custom lens design that is being considered.

Dr. Sonsino It is not the follow up that adds visits to the scleral fit and evaluation. It is the actual fit and evaluation. In the best of hands, the average scleral fit and evaluation takes four to six visits.²⁸ We can argue that with the modern generations of lenses, the number of visits required to achieve success has improved. But, we can also argue that if practitioners are not spending visits mastering the vault that meets Michaud et al’s criteria,¹⁶ haptic alignment, and toric over-refractions, then success with sclerals declines.

Dr. Louie I disagree with the number of visits required to properly fit a scleral lens. With toric diagnostic lenses included in many sets, getting the sagittal height and amount of toricity optimized is easier than ever. The power of the lens can also be optimized with a quick spherical retinoscopy and over-refraction.

If a patient is being refit into a corneal GP or hybrid lens, additional time for re-education about materials, application and removal, and cleaning and disinfecting may be necessary. For any new contact lens wearer of any sort, staff or prescriber time is always necessary to educate the patient on best contact lens practices and habits.

CONCLUSION

Dr. Louie Scleral lenses should not be discounted for patients who have “healthy” eyes and should be considered for any patient who isn’t successful in traditional, commercially available, non-custom soft lenses. I reiterate my opening statement that these wouldn’t be the go-to lens in a busy commercial practice or for a patient who is happy and healthy in a commercially available soft lens. However, there is a consistent number of frustrated patients, and patients who drop out of lens wear, who could be well served with scleral lenses despite having a “normal” refractive error and “normal” corneas.

Dr. Sonsino Scleral lenses should not be mainstreamed for normal corneas. There is a continuum of care with any condition, whether it be keratoconus or a cornea without pathology. As responsible practitioners, we should be aiming for the most cost-effective, simplest strategy that will yield the maximum in safety, comfort, and vision. All of these factors need to be balanced when we are helping our patients make decisions on the best contact lens strategies. Currently, scleral lenses are the most expensive strategy with a downside in application and removal from the patients’ perspective. From the practitioners’ perspective, the fitting skill and expertise necessary to achieve maximal results are roadblocks.

Now, there is even a startup company marketing direct-to-consumer scleral lenses to patients who have normal corneas. After sending in a copy of a current habitual contact lens prescription, a patient reports to a network practitioner for evaluation. The company pays the practitioner a small fitting fee, and the patient pays a subscription model monthly payment to the company for the lenses. Apparently, this company seems to believe that it has taken the complexity out of scleral lenses. If that is possible, I have not seen it. In the best of hands, a proper scleral evaluation takes numerous visits, and this is why scleral lenses are more costly. Will internet consumers and, just as importantly, the novice practitioners in the company’s network who accept its reimbursement tolerate this? We’ll see.

Many practitioners are starting to label themselves as scleral fitters. Although I fit more sclerals compared to most practitioners, I do not call myself a scleral fitter. I pride myself on being a problem-solver who uses all types of lenses to satisfy my patients. In my practice, with my patients who have normal corneas, I am able to achieve maximal results using all of the top technology in contact lenses without having to resort to sclerals. And, you can too. CLS

REFERENCES

1. Nichols JJ. Contact Lenses 2017. Contact Lens Spectrum. 2018 Jan;33:20-25,42. Available at https://www.clspectrum.com/issues/2018/january-2018/contact-lenses-2017 . Accessed on Feb. 20, 2018.
2. American Academy of Family Physicians. Imaging for Low Back Pain. 2018. Available at https://www.aafp.org/patient-care/clinical-recommendations/all/cw-back-pain.html . Accessed on Feb. 20, 2018.
3. Chou R, Qaseem A, Owens DK, Shekelle P; Clinical Guidelines Committee of the American College of Physicians. Diagnostic imaging for low back pain: advice for high-value health care from the American College of Physicians. Ann Intern Med. 2011 Feb;154:181-189.
4. Chou R, Fu R, Carrino JA, Deyo RA. Imaging strategies for low-back pain: systematic review and meta-analysis. Lancet. 2009 Feb;373:463-472.
5. Alipour F, Rahimi F, Hashemian MN, Ajdarkosh Z, Roohipoor R, Mohebi M. Mini-scleral Contact Lens for Management of Poor Visual Outcomes after Intrastromal Corneal Ring Segments Implantation in Keratoconus. J Ophthalmic Vis Res. 2016 Jul-Sep;11:252-257.
6. Ozkurt Y, Atakan M, Gencaga T, Akkaya S. Contact lens visual rehabilitation in keratoconus and corneal keratoplasty. J Ophthalmol. 2012;2012:832070.
7. Craig JP, Nelson JD, Azar DT, et al. TFOS DEWS II Report Executive Summary. Ocul Surf. 2017 Oct;15:802-812.
8. Jones L, Downie LE, Korb D, et al. TFOS DEWS II Management and Therapy Report. Ocul Surf. 2017 Jul;15:575-628.
9. Richdale K, Sinnott LT, Skadahl E, Nichols JJ. Frequency of and factors associated with contact lens dissatisfaction and discontinuation. Cornea. 2007 Feb;26:168-174.
10. Bavinger JC, DeLoss K, Mian SI. Scleral lens use in dry eye syndrome. Curr Opin Ophthalmol. 2015 Jul;26:319-324.
11. Jacobs DS, Rosenthal P. Boston scleral lens prosthetic device for treatment of severe dry eye in chronic graft-versus-host disease. Cornea. 2007 Dec;26:1195-1199.
12. Yuksel E, Bilgihan K, Novruzlu, Yuksel N, Koksal M. The Management of Refractory Dry Eye With Semi-Scleral Contact Lens. Eye Contact Lens. 2016 May 19. [Epub ahead of print]
13. Engel LA, Wittig S, Bock F, et al. Meibography and meibomian gland measurements in ocular graft-versus-host disease. Bone Marrow Transplant. 2015 Jul;50:961-967.
14. Walker MK, Bergmanson JP, Miller WL, Marsack JD, Johnson LA. Complications and fitting challenges associated with scleral contact lenses: A review. Cont Lens Anterior Eye. 2016 Apr;39:88-96.
15. Alipour F, Kheirkhah A, Jabarvand Behrouz M. Use of mini scleral contact lenses in moderate to severe dry eye. Cont Lens Anterior Eye. 2012 Dec;35:272-276.
16. Compañ V, Oliveira C, Aguilella-Arzo M, Mollá S, Peixoto-de-Matos SC, González-Méijome JM. Oxygen diffusion and edema with modern scleral rigid gas permeable contact lenses. Invest Ophthalmol Vis Sci. 2014 Sep 4;55:6421-6429.
17. Giasson CJ, Morency J, Melillo M, Michaud L. Oxygen Tension Beneath Scleral Lenses of Different Clearances. Optom Vis Sci. 2017 Apr;94:466-475.
18. Michaud L, van der Worp E, Brazeau D, Warde R, Giasson CJ. Predicting estimates of oxygen transmissibility for scleral lenses. Cont Lens Anterior Eye. 2012 Dec;35:266-271.
19. Weissman BA, Ye P. Calculated tear oxygen tension under contact lenses offering resistance in series: piggyback and scleral lenses. Cont Lens Anterior Eye. 2006 Dec;29:231-237.
20. Caffery B, Dogru M, Jones LW, et al. Contact Lens Comfort. Optom Vis Sci. 2016 Aug;93:790-792.
21. Naduvilath T, Papas EB, Lazon de la Jara P. Demographic Factors Affect Ocular Comfort Ratings During Contact Lens Wear. Optom Vis Sci. 2016 Aug;93:1004-1010.
22. Sulley A, Young G, Hunt C. Factors in the success of new contact lens wearers. Cont Lens Anterior Eye. 2017 Feb;40:15-24.
23. Woods CA, Bentley SA, Fonn D. Temporal changes in contact lens comfort over a day of wear. Ophthalmic Physiol Opt. 2016 Nov;36:643-648.
24. Stapleton F, Tan J. Impact of Contact Lens Material, Design, and Fitting on Discomfort. Eye Contact Lens. 2017 Jan;43:32-39.
25. Barnett M, Fadel D. Scleral Lenses: The Benefits of Toric Landing Zones. Contact Lens Spectrum. 2017 Nov;32:36-41. Available at https://www.clspectrum.com/issues/2017/november-2017/scleral-lenses-the-benefits-of-toric-landing-zone . Accessed on Feb. 22, 2018.
26. DeNaeyer G, Sanders DR, van der Worp E, Jedlicka J, Michaud L, Morrison S. Qualitative Assessment of Scleral Shape Patterns Using a New Wide Field Ocular Surface Elevation Topographer: The SSSG Study. J Cont Lens Res Sci. 2017 Nov; 1:12-22.
27. Yeung D, Sorbara L. Scleral Lens Clearance Assessment with Biomicroscopy and Anterior Segment Optical Coherence Tomography. Optom Vis Sci. 2018 Jan;95:13-20.
28. Pecego M, Barnett M, Mannis MJ, Durbin-Johnson B. Jupiter Scleral Lenses: the UC Davis Eye Center experience. Eye Contact Lens. 2012 May;38:179-182.