Modern GP scleral lenses are now recognized as a mainstream modality to restore visual acuity and ocular surface integrity on irregular corneas. They are also considered a valid option to help soft lens wearers who have regular corneas and are struggling with fluctuating vision, contact lens-induced discomfort, or complaints about glare and haloes. Sclerals can also be a useful modality for patients who have sensitive eyes and are exposed to allergens or challenging environments.

Manufacturers have introduced many new designs and lens features to make scleral lens fitting practitioner-friendly. However, the science coming from research is not evolving at the same rate, and we still need more evidence-based elements to help us use scleral lenses more efficiently. Some concerns have been raised, and questions are still not fully answered on the long-term outcomes of scleral lens usage, especially on normal corneas.

FITTING COMPLICATIONS

Scleral lenses should evenly rest on the bulbar conjunctiva. Although scleral lenses are generally forgiving in nature, a poor fitting relationship can lead to redness and irritation. Scleral lenses that fit too tightly to the eye cause circumferential compression of the bulbar conjunctival tissue that leads to blanching of the tissue under the lens haptic, with corresponding paralimbal injection (Figure 1). This will cause the lens to be uncomfortable, reducing wear time. In addition, significant resistance will be felt during lens removal, resulting in further irritation.

Troubleshooting this complication involves flattening the peripheral curves to loosen the fit, including the curves that correspond to the paralimbal area. Flattening only the outside peripheral curves can actually make the lens fit tighter because this creates a hinge that results in compression as the outer edge is lifted. Switching lens designs is an alternative strategy because there can be significant differences in standard haptic curves for various designs.

If you observe compression but can remove the lens without resistance, it’s possible that pushing the scleral lens on too firmly during application artificially induced the noted blanching. In this case, reapply the lens with less pressure and reevaluate the fit.

A significant mismatch between the haptic back surface of a scleral lens and the sclera can create uneven bearing that will show sectorial blanching and areas of edge lift (Figure 2). This creates a fit that is uncomfortable and can lead to complications such as increased reservoir debris. A mismatch can be the result of a spherical-back-surface lens design fit on a toric sclera or a sclera that has significant amounts of irregularity. Keep in mind that some scleras do have spherical shapes, and a mismatch can result if a toric-back-surface lens design is used on a spherical sclera.

Corneoscleral topography can be used to discern the shape of the eye to be fit so that an appropriate back-surface design can be chosen. Ultimately, this eliminates guesswork, reducing revisits and remakes. Scleral topography measurements can be used to quantify toricity for toric fits and the appropriate position for front-surface toricity if a bitoric lens is necessary. There are nonrotationally symmetric scleras that are irregular and fall outside of the categories of toric shapes. Multiple meridians on the scleral back-surface haptic can be customized to fit highly irregular scleras using measurements from scleral topography. Alternatively, customized back surfaces can be designed from molding. As is the case with back-surface toricity, customized back surfaces will stabilize the lens for front-surface toricity.

Scleral obstacles, such pingueculas, can significantly alter the scleral shape and lead to redness and irritation if they are not accounted for in scleral lens design. For some cases, simply switching to a smaller-diameter lens will allow practitioners to completely avoid the obstacle altogether. When necessary, scleral lenses can be designed to “bypass” the scleral obstacle. Shallow notches of 1mm to 2mm can be beveled from the edge of the lens to avoid any contact with the surface elevation. Alternatively, a customized edge lift can be manufactured that allows the edge of the haptic to vault over the obstacle. For both notches and edge vaults, the scleral lens has to be ballasted with double-slab-off prism, back-surface toricity, or a customized back surface to maintain its proper position.

A fundamental fitting characteristic of scleral lenses is that they completely vault the corneal surface, including the limbal area. For keratoconus patients, paracentral bearing can occur if the sagittal depth of the scleral lens is less than that of the sagittal height of a specified chord diameter of the eye that is being fit (Figure 3). Isolated areas of significant bearing can result in epitheliopathy and irritation during wear. Simply increasing the vault of the lens design, by steepening the base curve or increasing diameter, will remedy this complication.

Areas of significant midperipheral bearing can also result in epithelial changes and decreased wear time secondary to discomfort. This fitting complication often occurs when using a prolate scleral lens design to fit an oblate cornea following myopic refractive surgery or a penetrating keratoplasty. Switching to a reverse geometry scleral lens design will improve the lens’ ability to vault over the midperipheral cornea while minimizing the corresponding central vault. Some manufacturers have separate prolate and oblate designs, while others have oblate designs that can be used universally for all corneal geometries.

One of the most serious complications that arises from scleral lens fitting is a lens that has significant bearing on the limbus (Figure 4). Symptoms of this include redness, irritation, and reduced wear time. This fitting complication can lead to keratitis, neovascularization, and limbal stem cell deficiency. Scleral lens bearing on the limbus results from a lens that is too small relative to the diameter of the cornea being fit. Limbal compression can be observed as a ring of paralimbal bearing with fluorescein evaluation, or bearing can be detected with anterior segment optical coherence tomography (AS-OCT). Increasing the diameter of the scleral lens—usually by increasing the optical zone (OZ) diameter or the width of the first peripheral curve, depending on the design—will all allow the scleral lens to adequately vault the limbal area.

SOLUTION INTERACTIONS

Various solutions play a pivotal role for successful scleral lens wear. The lenses have to be filled with a solution that takes up the space between the lens and the anterior ocular surface. It is generally believed that there is little to no tear exchange of the reservoir fluid. With this in mind, the solution that is instilled during scleral lens application may have many hours of contact with the surface of the eye during normal daily wear. Solutions that are used to fill the lens may contain preservatives and can cause toxic or hypersensitivity reactions resulting in redness and irritation. The source of these complications may also be residual multipurpose solutions that reside in the bowl of the lens after nightly cleaning and disinfection.

Toxic reactions will be noticed immediately, but hypersensitivity reactions can be delayed, which can make troubleshooting difficult. In fact, because a patient may have been using the same solutions for months without any problems, practitioners may erroneously conclude that redness and irritation are secondary to a fit complication. Solutions should always be considered as a possible source of patient symptoms. It is important to take a careful history and find out exactly what patients are currently using, as they may have switched solutions from what was originally prescribed.

According to the Scleral Lenses in Current Ophthalmic Practice: an Evaluation (SCOPE) study, 60.2% of practitioners are currently prescribing single-use nonpreserved saline solution to fill scleral lenses.¹ Currently, there are two commercially available products that have U.S. Food and Drug Administration approval for this application. The idea is that nonpreserved saline is essentially inert and, therefore, will not lead to complications.

Additionally, the SCOPE study also found that a majority of practitioners are prescribing peroxide care systems for cleaning and disinfection.¹ Peroxide care systems have an advantage over other multipurpose disinfecting solutions because neutralization of hydrogen peroxide eliminates the possibility of residual preservatives that can lead to toxic reactions.

MEDICAL COMPLICATIONS

Most scleral lenses are medically necessary devices that improve patients’ visual acuity or protect the surface of their eye. It is important to keep in mind that when a patient presents with redness and irritation, the source of the problem could be a medically related complication.

For example, a patient who has a full-thickness corneal transplant might be having a complication that is unrelated to scleral lens use, such as graft rejection or increased intraocular pressure. Although rare, microbial keratitis should be ruled out as a cause for patients’ symptoms. A thorough examination is necessary for any scleral patient who presents with redness and irritation to rule out medically related complications.

APPLICATION DIFFICULTY

The relatively larger diameter of scleral lenses and the fact that they have to be filled with solution prior to application can create challenges for patients to successfully apply them each day. Patients who have deep-set orbits, small apertures, tight lids, or disabilities can have increased difficulty applying scleral lenses. Oftentimes, these challenges can be anticipated during the evaluation and fitting process. Using relatively small-diameter scleral lenses can help as long as they still are able to properly vault the corneal surface.

During the teaching process, include family members or caregivers who might be able to assist patients at home during the initial learning curve. Stands that hold the plunger allow patients to use both hands to separate their lids but require them to lower their eye onto the lens. For select patients, these plunger stands can be the difference between success and failure.

During the initial training session, work with patients for 15 or 20 minutes and then send them home to practice as long as they can successfully remove the lens. At their follow-up visit, have them practice application to troubleshoot problems if they are still having difficulties or have been unsuccessful.

POOR VISION

As with other contact lenses, residual astigmatism can alter visual acuity. In the case of with-the-rule residual astigmatism (RA), consider the following elements:

• Corneal cylinder (> 3D) is not fully compensated
• Tear fluid layer (TFL) is not uniform²
• Lens translation after settling
• Lens flexure

To assess the exact cause of RA, perform topography or keratometry over the scleral lens to determine whether the lens is flexing. Use a slit beam or AS-OCT to evaluate the lens position and the tear film uniformity. Troubleshooting should be made according to the cause:

• Generate a uniform TFL by modifying lens design (OZ diameter, peripheral curves, geometry).
• Customize lens peripheral curves to improve support and alignment with the conjunctiva, especially for lenses greater than 16mm.
• Consider fitting with less clearance to reduce lens translation.
• Order a front-toric scleral lens if no other options have worked.

Manufacturers may recommend increasing lens thickness to minimize flexure. This is a misleading concept because thinner lenses do not increase RA versus thicker ones.³

Against-the-rule (ATR) RA is most likely caused by lenticular astigmatism becoming apparent after the full compensation of the corneal cylinder by the TFL. An ATR high corneal cylinder, which is not fully corrected, may also be present. In such cases, a front-toric lens design becomes the only option to fix the issue.

RESERVOIR DEBRIS

One of the major issues with scleral lenses is the presence of debris in the reservoir, which impacts visual acuity.⁴ It is important to differentiate between reservoir debris and surface deposits, most of which often occur in patients who have ocular surface diseases. Reservoir debris mainly results from mechanical trauma.

Scleral lens rubbing of the bulbar conjunctiva can generate debris. It takes a suction effect, generated by tear fluid compression in a closed chamber during lens sinking, to move released external debris into the lens reservoir. Considering the non-viscous nature of solution in the reservoir, the lipophilic debris would diffuse easily if there is enough space between the scleral lens and the limbus.

The lens should be fitted with toric peripheral curves (to align the lens in every quadrant) to lower the mechanical stress on the conjunctiva and to limit the clearance over the limbus without touching it. Thinner and smaller lenses may achieve this goal more efficiently and, in practice, are associated with reduced debris in the reservoir. Finally, the use of more viscous artificial tears in the bowl may help, acting like a barrier for debris diffusion.⁵

CORNEAL EDEMA

Theoretical models predict that scleral lenses fitted with more than 200μm of clearance and 250μm of lens thickness generate a low, chronic, transient hypoxic stress on the central cornea.^6,7 These models were proven valid through many case reports and in vivo studies in which higher clearance was associated with a 30% oxygen deprivation.⁸

The clinical significance, over time, of hypoxic stress remains unknown. Some authors will compare induced edema (1% to 3%) to physiological edema (4%) seen upon awakening.⁹ This is a misleading concept because the cornea deswells within one hour after eye opening.

On the contrary, hypoxic stress under scleral lenses remains for most of the wearing hours, at least until the clearance drops down and reaches an appropriate level (< 200μm). This becomes of prime importance when dealing with compromised corneas.

In a series of post-graft cases, Michaud and Gelles¹⁰ demonstrated that patients fitted with thick scleral lenses and higher clearance developed more than 100μm of corneal swelling. However, when refitted according to the predictive models, the corneas of the same cohort came back to baseline.

This is why, for the moment, as Watters¹¹ recommended, if you are using a 100-Dk lens material, the average contact lens and tear film combined thickness needs to be 350µm or less to satisfy both the Holden-Mertz¹² and Harvitt-Bonanno¹³ criteria. Consequently, scleral lenses must be fitted with minimal clearance, and the lens manufactured with the lowest thickness, considering the patient’s condition and the corneal profile.

NON-WETTING

Most modern scleral lenses are plasma treated, which is a deep cleaning process to remove any residual surface deposits from manufacturing. Before delivery, lenses should be soaked to condition their surfaces. In most cases, this will allow for sufficient surface wetting. In the case of patients suffering from ocular surface disorders or significant blepharitis, lenses may become coated rapidly with mucous filaments or lipophilic deposits. Some patients will also contaminate the lens surface with hand cream, cosmetic products, or mascara during the application process (Figure 5).

To troubleshoot issues with ocular surface disorders, it is important to manage ocular conditions before considering fitting scleral lenses.⁵ The lens material should be selected with the lowest wetting angle possible.

Care regimen should be also selected carefully. GP lens cleaners and conditioning solutions used as a system of two separate products may be considered. If so, it is very important to rinse the bowl carefully before filling it with nonpreserved saline, because conditioning solution may adhere, and its preservative agent may be released in the reservoir, contributing to increased risk of toxic reactions over time.¹⁴ This is why hydrogen peroxide may be a better option, with the precaution to recommend the regular formulation (without moisturizing agent).

Soft contact lens all-in-one solutions containing sodium hyaluronate (SH) may be used off-label to clean and to store scleral lenses. The SH component helps to condition the lenses, while the cleaning is less abrasive and keeps the lens surface less attractive to deposits.

A 90% water polyethylene glycol (PEG)-based polymer coating may be added to lenses when wetting issues persist. This treatment mimics the mucin layer of the tear film, improves wettability, and alleviates heavy deposition.¹⁵ Once treated, lenses should never be cleaned with an abrasive or alcohol-based cleaner. Patients also should be instructed to avoid heavy rubbing of the lens surface. Follow manufacturer recommendations regarding the cleaning regimen. As needed, this coating may be reapplied to the lens surface within the life cycle of the lens.

Patient education is of prime importance. Those suffering from ocular surface disease should be told that scleral lenses will help to restore their ocular condition over time, and deposits will habitually tend to be less present over the weeks following initial wear. In the meantime, regular lubrication with nonpreserved artificial tears may help to dilute the deposits.¹⁶ During contact lens wear, cleaning the front lens surface with a cotton swab wetted with a conditioning solution may help.

CONCLUSION

Scleral contact lenses are considered standard of care for the correction of irregular cornea patients and are widely used to treat ocular surface disorders. For many patients, their benefits outweigh the risks of wearing them. Scleral lenses are now considered for the correction of normal cornea patients for whom soft lenses failed to provide stable vision and all-day comfort, or those for whom soft lenses have a limited offering, such as presbyopic astigmatic patients. In these cases, the risk/benefit ratio should be evaluated and the lens fitted accordingly.

If scleral lenses become mainstream, troubleshooting issues will also become the day-to-day reality for many practitioners. CLS

REFERENCES

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3. Vincent S, Kowalski LP, Alonso-Caneiro D, et al. Flexure of miniscleral contact lenses: Influence of lens centre thickness. Paper presented at the 2017 British Contact Lens Association Clinical Conference & Exhibition, Liverpool, UK.
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13. Harvitt DM, Bonanno JA. Re-evaluation of the oxygen diffusion model for predicting minimum contact lens Dk/t values needed to avoid corneal anoxia. Optom Vis Sci. 1999 Oct;76:712-719
14. Johns L, Pullum K, McMahon J, Otten H, Samson J. Scleral Lenses: An International Panel Discussion. Presentation at the 2017 British Contact Lens Association Clinical Conference & Exhibition, Liverpool, UK.
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