Troubleshooting Scleral Lenses
A successful fit can be life-changing, but practitioners must address the challenges of this lens type.
|Jeffrey Sonsino, OD, FAAO, is an assistant professor at Vanderbilt Eye Institute in Nashville, TN. He is a Diplomate in Contact Lenses of the American Academy of Optometry, a council member of the AOA Cornea and Contact Lens Section, and a fellow of the Scleral Lens Education Society.|
|Muriel Schornack, OD, FAAO, is a consultant in the department of ophthalmology at the Mayo Clinic in Rochester, MN. She holds the rank of assistant professor in the Mayo Medical School. She is a founding member of the Scleral Lens Education Society and serves on the organization’s Board of Directors. She is also a member of the GPLI Advisory Council.|
By Jeffrey Sonsino, OD, FAAO, & Muriel Schornack, OD, FAAO
Scleral lenses can be life-changing for patients who have severe ocular surface disease or corneal irregularity. Although scleral and corneal GP lenses are manufactured from similar materials, unique fitting characteristics of scleral lenses create entirely new troubleshooting challenges that are not encountered when fitting corneal lenses. Increased sagittal depth allows the lenses to vault the cornea, but also changes the interactions between the lids and the lenses and changes the dynamics of lid closure. Differences between corneal and scleral lenses in total surface area and fluid dynamics surrounding the lens may require adjustments in care recommendations for scleral lenses. Additional challenges result from our inability to accurately map the contour of the anterior ocular surface region where the lenses actually land.
Primary indications for scleral lenses include protecting the ocular surface in ocular surface disease, improving ocular comfort in ocular surface conditions, and visual rehabilitation in patients who have corneal irregularity. Each of these indications can lead to specific challenges with scleral lens prescription and management. Many of these problems fall into one of the following general categories: wetting problems, limited wear time, comfort complaints, handling issues, challenges achieving an optimal fit, and complications related to care products and practices.
Wetting Problems and Limited Wear Time
A nonwetting lens will result in both discomfort and less-than-optimal vision. The lid wiper (epithelial tissue at the margin of the tarsal conjunctiva that contacts the corneal surface during the blink) is relatively sensitive to any irregularity. Areas of poor wetting or actual deposits on the lens surface will cause discomfort due to friction as the lid wiper moves over the lens surface. Areas of poor wetting will also compromise the quality of vision, in the same way that a nonwetting car windshield can obscure visibility during a rainstorm. Vision is described as hazy, variable with the blink, and blurred. Patients may say that they have a dirty or deposited lens.
Not surprisingly, scleral lens surface issues tend to be most troublesome in patients who have severe ocular surface disease. We must realize, and clearly explain to patients, that scleral lenses do not actually cure the condition for which they are being prescribed. The goal of scleral lens therapy in such cases is to protect the ocular surface. However, the lens surface will now be as compromised as the ocular surface was before the initiation of scleral lens therapy.
For example, a patient who has severe meibomian gland dysfunction (MGD) may have a significantly reduced tear breakup time (Figure 1). If the patient is fit with a scleral lens, the ocular surface will be protected, but tear breakup time will not improve. The oxygen-permeable materials from which scleral lenses are manufactured are relatively hydrophobic and will easily attract surface deposits in these cases. The front surface of the lens will become desiccated, and the lens will likely become uncomfortable. Aggressive management of MGD before and during the scleral lens fitting process will increase the likelihood of success.
Figure 1. A nonwetting scleral lens (a) on a patient who has severe untreated meibomian gland dysfunction (b). After the initial scleral lens fitting and before the dispense, this patient was instructed to perform aggressive lid hygiene.
Patients who have aqueous deficiency are frequently using lubricant drops by the time they present for scleral lens fitting. While scleral lens wear may improve ocular comfort in these patients, advising them to continue to use lubricant drops over their scleral lenses may help to preserve lens surface integrity.
There are ways to optimize the maintenance of a comfortable lens surface. Attention to relatively simple details in lens manufacture, handling, and wear can increase a patient’s chances of success with scleral lens wear.
Occasionally, friction induced by the lathe can expose the lens to excessive heat during the manufacturing process. In such cases, lens surfaces simply will not wet, regardless of steps that you may take to attempt to improve surface quality. If nonwetting areas appear on the lens surface immediately after application, it is likely that the lens was overheated during fabrication. When this happens, new lenses need to be ordered.
Scleral lens patients exhibit the same variability in tear film composition as do patients who wear corneal lenses, so you need to carefully evaluate the ocular response to a particular material. If surface wetting remains an issue after aggressive management of underlying ocular surface disease, it may be helpful to try a different lens material. You can choose among materials with different wetting properties. Table 1 lists GP materials currently available in button sizes large enough to accommodate full scleral lenses.
Materials with lower wetting angles have less hydrophobic lens surfaces. Patients who have lipid-related surface disease, such as MGD, should be more successful with a lens that has a lower wetting angle. The front surface of any of these materials should be plasma-treated for all scleral lenses. Plasma treatment is not a coating; it is a process that removes impurities from the front surface of the lens. Plasma-treated lenses must be shipped and kept wet at all times and cannot be cleaned with abrasive GP cleaning solutions such as the Boston Cleaner (Original Formula, Bausch + Lomb), but are safe with GP multipurpose solutions (MPSs). Some manufacturers can re-treat lenses if the surface quality degrades with time.
Before handling lenses, practitioners and patients should wash their hands with non-oily soaps. Any soap that contains lanolin or another moisturizing agent can leave a residue on the hands that can then be transferred to the lenses. Likewise, any plunger, tool, or device that comes into contact with the surface of the lens during application should be cleaned in a way that leaves no residue that could compromise the lens surface. Disinfecting the face of the plunger with an alcohol swab may clean the device very effectively, but any alcohol residue could potentially disrupt the hydrophilic-conditioned lens surface. To help maintain the conditioned lens surface, dip the plunger surface that comes into contact with the lens into the scleral lens storage solution.
|Diffusion Coefficient and Wetting Angle of GP Lens Materials Available for Sclerals*|
|Boston Equalens II||85||30°|
|*March 2012, Tyler’s Quarterly|
During wear, the front surface of the lens may be lubricated with nonpreserved artificial tears or rewetting drops. However, if hydrophobic regions have already developed on the lens surface, lubricant drops alone may not restore surface quality. Moistening a cotton swab with saline or conditioning solution and gently swabbing the lens surface may remove lipid deposits. Remember that a full scleral lens (18.0mm or more in diameter) will cover most of the ocular surface, making it impossible for patients to cause corneal damage with this technique. If lubricant drops and surface swabbing do not improve surface wettability, patients will need to remove, clean, recondition, and reapply the lens. Some patients, especially those who have severe ocular surface disease, will need to proactively remove lenses during the day before the front-surface dryness becomes troublesome. For example, if patients notice that their lenses predictably become dry at about the same time each day, they can remove, clean, recondition, and reapply lenses before they become uncomfortable.
Figure 2. Application bubble that was obvious to the patient because of decreased comfort and vision.
Figure 3. Metabolic waste products accumulated in the post-lens tear reservoir. Dr. Rob Breece described this as the “Toxic Swamp” behind the lens.
Comfort and Handling Issues
Scleral lenses rest upon relatively insensitive conjunctival tissue, move very little, and generally fit under the upper and lower lids. Lack of corneal contact, along with minimal lid interaction, results in excellent comfort for most patients. However, some patients may report lens sensation or even frank discomfort with scleral lens wear.
Many patients report lens awareness immediately after diagnostic lens application early in the fitting process. They generally do not describe this sensation as pain, but may indicate that the lens feels large or bulky. Indeed, the combination of the lens thickness (0.3mm or more) and the depth of the post-lens fluid reservoir (up to 0.5mm) displaces the upper lid anteriorly. Reassure patients that this sensation is normal, and that it generally abates rapidly with lens wear.
Listening carefully to a patient’s description of lens sensation or irritation with lens wear during the fitting process can be of great help in designing lenses that provide an optimal fitting relationship. Excessive edge lift tends to yield a sensation that patients may describe as “scratchy.” However, if the lens edge embeds itself into conjunctival tissue, many patients describe a “tight” sensation. Patients may even be able to localize the sensation that they are experiencing to a particular quadrant or eye region. Immediately after lens application, it may be difficult to visualize potential problem areas of the flange with slit lamp evaluation, but an astute patient can describe conjunctival sensation in areas of suboptimal alignment very quickly. Patient descriptions can help guide your slit lamp evaluation of the alignment of the flange with the conjunctival surface.
Application can be challenging for new scleral lens wearers. Even with a well-fit lens, many patients may have difficulty applying the lens without an entrapped air bubble during the first weeks of wear (Figure 2). Patients who have limited visual potential may have difficulty seeing an entrapped air bubble, but corneal tissue will become desiccated beneath a bubble relatively quickly. This will give rise to a “dry eye” sensation. Using a more viscous agent such as Celluvisc (Allergan) to fill the bowl of the lens before application may be more forgiving compared to using saline as the patient learns how to handle the lens. If the patient continues to have difficulty applying the lens without entrapped bubbles after becoming adept at lens handling, the sagittal depth of the lens may need to be reduced.
Figure 4. Temporal decentration as evidenced on anterior segment OCT (a) and fluorescein inspection (b). Common solutions for this problem are flattening the intermediate curves, moving to a reverse geometry design lens, or increasing the overall lens diameter and optic zone diameter. This case was solved (c) by flattening the intermediate curves (and slightly steepening the base curve).
High degrees of scleral irregularity may allow air bubbles to enter into the post-lens fluid reservoir even after bubble-free application. If a patient reports good initial comfort after application, but subsequently realizes that bubbles have become entrapped after a period of wear, air may be entering the fluid reservoir beneath the flange. Carefully examine the flange after several hours of wear in such cases. Frequently, air bubbles may be visible beneath one or two quadrants of the flange. These bubbles will eventually work their way into the post-lens fluid reservoir, where they will coalesce and cause discomfort or reduced vision. Toric or quadrant-specific flanges can often improve the seal between the lens and the conjunctival surface.
Most scleral lenses are not fenestrated, but are instead fluid-ventilated. While the ideal scleral lens fit features at least some degree of tear exchange, the post-lens fluid reservoir is not replenished as rapidly as is the tear lens behind a corneal lens. With time, oxygen dissolved in the fluid reservoir is depleted, and corneal metabolic waste products begin to accumulate in the reservoir (Figure 3). This can also cause discomfort after several hours of lens wear. Periodic removal, rinsing, and lens reapplication with fresh saline may improve comfort and reduce the risk of possible hypoxia complications.
Lens Fitting Challenges
Achieving complete corneal clearance, good centration, and reasonable scleral alignment can be challenging with large-diameter lenses. The sheer mass of the lens, along with downward pressure from the upper lid, can result in inferior or temporal decentration. If the lens decenters excessively, visual performance will suffer because the optic center of the lens no longer corresponds to the patient’s visual axis. Decentration may induce higher-order aberrations that cannot be corrected with a simple spherocylindrical over-refraction. Decentration is particularly troublesome for patients who wear a lens in one eye only. The fluid reservoir essentially creates a base-down prism when the lens decenters inferiorly. This can cause vertical diplopia. Furthermore, the posterior surface of an inferiorly decentered lens may rest upon superior corneal tissue. Contact with corneal tissue may eventually lead to epithelial damage and patient discomfort (Figure 4).
It may be difficult to completely eliminate inferior decentration, particularly if a patient has unusually heavy or tight upper lids. One way to determine whether the lids are pushing the lens downward is to manually retract the upper lid. If the lens immediately rises into position, assume that interaction with the lids is contributing to lens decentration. In such cases, minimizing sagittal depth or elevation of the center of the anterior lens surface may help to minimize decentration.
If the lens remains decentered when the upper lid is retracted, the fitting relationship between the lens haptic and the sclera must be addressed. Careful evaluation of conjunctival vasculature beneath the landing zone can provide clues for optimizing alignment. If you see sectoral vascular impingement at the lens edge, a toric flange may help to improve centration. Vascular impingement around the entire lens periphery would indicate that the landing curve should be flattened. Mild vascular impingement at the junction between the final zone of the corneal chamber and the first landing curve would suggest a steeper flange. Increasing overall diameter or corneal chamber diameter will maintain the sagittal depth while flattening the anterior contour of the lens. A reverse geometry design, in which the first peripheral curve radius is steeper compared to the base curve radius, may create a wider corneal chamber diameter.
Figure 5. Patient with symblepharon due to ocular cicatricial pemphigoid and severe dry eye symptoms (a). A notch measuring 6mm chord length by 2mm depth was used to avoid the elevation of the symblepharon (b).
Lens dislocation can occur if abnormalities are present in the conjunctival tissue that overlies the sclera, or if scleral contour is markedly abnormal. The presence of a pinguecula, an elevated bleb, symblepharon, or a scleral patch graft make it difficult to achieve a sealed fit. Although a scleral lens may stay in position when the patient is in primary gaze, movement of the patient’s eye in the direction of the elevation can disrupt the capillary attraction that holds the lens in place. Once the seal is broken, air bubbles can become entrapped beneath the lens, or the lens may dislodge entirely. If the elevated tissue is near the limbus, designing a lens with a larger diameter may allow the lens to vault or bridge the irregularity and land on more regular peripheral tissue. If elevation of conjunctival tissue is located beyond the limbus, a smaller lens may be more appropriate. It may also be possible to incorporate a notch or truncation to avoid the elevation (Figure 5). In general, smaller notches are preferable to larger notches because a wide or deep notch may compromise the integrity of the seal between the flange and the conjunctiva. A notched lens needs to be applied in the correct orientation, and toricity on the flange may be necessary to prevent unwanted rotation.
Figure 6. Scleral lens entrapping 180 degrees of loose conjunctiva (a). After the lens was removed, corneal neovascularization beneath the entrapped conjunctiva was evident (b).
Negative pressure beneath the lens following the blink can draw loose conjunctival tissue over the limbus into the corneal chamber. This tissue may become entrapped beneath the lens just inside of the haptic. Limited entrapment in a single quadrant may be of little clinical significance. However, more pronounced entrapment may cause discomfort. Severe entrapment may even result in neovascularization within the region of the cornea that is covered by conjunctival tissue (Figure 6). Flattening the lens (bringing it close to the ocular surface) over the region in which entrapment occurs frequently solves this issue. However, if significant conjunctivochalasis exists, surgical resection of redundant conjunctiva may be indicated during the scleral lens fitting process.
Recommendations for scleral lens care and handling have evolved during the past several years. While early scleral lens wearers may have been instructed to use standard MPS products for cleaning, disinfection, and even lens application, most scleral lens experts now agree that using nonpreserved care products is advisable. Patients who experience mild conjunctival hyperemia or excessive accumulation of debris in the post-lens fluid reservoir may achieve more successful lens wear if they store their lenses in a hydrogen peroxide-based cleaner rather than in a traditional GP lens conditioning solution.
Perhaps even more important than the conditioning or soaking solution is the fluid with which the bowl of the lens is filled before lens application. Nonpreserved saline is frequently recommended, but patients who are sensitive to the buffering agent in bottled nonpreserved saline may prefer to fill the lens with 0.9% NaCl, available by prescription in 5ml vials typically used in nebulizers. Although the use of inhalation saline for scleral lens application is off-label, many patients find this product to be convenient, comfortable, and relatively cost-effective.
Recommend care products for patient characteristics and conditions.
Certainly, recommendations for care products need to be based upon individual patient characteristics and conditions. Some patients find lens application easier if the bowl of the lens is filled with a more viscous product, such as Celluvisc. In other patients, autologous serum placed in the lens bowl prior to application appears to facilitate healing of epithelial defects and maintenance of epithelial integrity. A scleral lens may function as a drug delivery device in cases in which it may be desirable to maintain medication contact with the ocular surface over an extended period of time.
Evidence-based guidelines for best practices in scleral lens prescription and management have yet to be developed. We do not yet know how these lenses may affect the ocular surface, nor do we fully understand the significance of various clinical observations. We cannot, as of yet, accurately capture images of the contour of the sclera beneath the landing zone of these lenses in a clinical setting, and have yet to define ideal fitting relationships between the lenses and the eye’s anterior surface. Questions have been raised about the possibility of significant corneal hypoxia during scleral lens wear. As our understanding of scleral lenses continues to develop, we will be able to address specific issues that arise with scleral lens wear with greater certainty and accuracy. For further information on scleral lenses, and for ideas and discussion on additional troubleshooting tips, visit the Scleral Lens Education Society website (https://www.sclerallens.org/). CLS