Increasing the use of scleral lenses may benefit a larger patient base.
In 2021, eye care professionals estimated that scleral lenses accounted for approximately 14% of the gas permeable (GP) lenses they prescribed, according to Contact Lens Spectrum GP and Custom Soft 2021 Annual Report.1 Although contact lenses remain the dominant GP lens design, scleral lenses are becoming increasingly popular among practitioners for a variety of corneal conditions.
Because scleral lenses are fitted to arch over both the cornea and the limbus and land on the sclera, the resulting tear reservoir offers a plethora of advantages over traditional contact lenses. These include superior vision, improved comfort and better protection of the ocular surface. Scleral lenses are generally considered an option for patients with irregular corneas; however, they are also excellent options for patients with severe ametropia and dry eye syndrome.
As scleral lenses have become commonplace in many practices, manufacturers have created simple fitting guides. When fitted empirically, regardless of manufacturer, all scleral lenses follow the same 4 basic guidelines.
1. Choose a diagnostic lens
Choosing the right diagnostic lens is crucial and involves 2 key steps: selecting the appropriate design and selecting the diameter. An elongated design is ideal for regular corneas or patients with corneal ectasias (eg, keratoconus and pellucida marginal degeneration). An oblate design is ideal for patients who have had refractive surgery (eg, LASIK, photorefractive keratectomy, or radial keratotomy). Occasionally, topography reveals a corneal pattern that clearly does not fit into either category (eg, post-transplant). If so, try on both designs and determine which fits you best based on fit guidelines 2-4.
Selection of the appropriate diameter should be guided by the horizontal visible iris diameter (HVID) of the patient. This can be measured manually with an HVID ruler or slit lamp beam or obtained from measurements provided by a topographer. Once the appropriate diameter and design have been selected, choose a manufacturer-recommended starter lens based on the patient’s corneal condition or keratometry values. When in doubt, choose a lens in the middle of the mount assembly.
2. Assess apical and limbal clearance
Once the initial diagnostic lens is placed on the eye, assess the apical clearance. Most manufacturers recommend an apical clearance of 100-250 μm after the lens has settled for approximately 30 minutes. Limbic clearance is just as important as apical clearance. Ideally, aim for 50-100 μm.
Apical and limbal clearance can be assessed with sodium fluorescein and blue light using the diffuse slit lamp beam and more accurately assessed with white light and an optical section. Additionally, the anterior segment feature on an ocular coherence tomograph (OCT) can help quantify the exact amount of clearance both apically and limbically.
3. Assess the landing zone
After achieving the appropriate apical and limbal clearances, assess the scleral landing zone, which is the peripheral system of the scleral lens. The lens should be aligned with the sclera and show no edge lifting or vessel whitening.
4. Add power
The last step is to add the over-refraction. It is wise to add spherical over-refraction initially and then add spherocylindrical over-refraction once the final lens fit has been established.
In a perfect world, following these 4 steps would provide every patient with an exact fit and exceptional vision (Figure 1). In reality, while the actual fitting of scleral lenses is simple, the troubleshooting issues are more difficult. Here are some of the most common fitting challenges.
Whitening of conjunctival vessels
This is caused by localized pressure on the conjunctiva and can be quadrant, meridian, or circumferential specific. Patients typically report the following after removal: discomfort often extending into the next day, rebound hyperemia, and/or impression ring. Bleaching can be divided into 2 categories:
1. Conflict occurs along the outermost curve of the lens, causing the lens to sink into the conjunctiva. This cuts off circulation to the conjunctival vessels.
2. Compression occurs along the inner scleral landing curves and causes whitening of the conjunctival vessels below the lens (Figure 2).
It is important to note that impact and compression can occur simultaneously. The most common causes of conjunctival vessel blanching are peripheral obstructions (eg, pterygium, pinguecula, or filter bullae) and scleral asymmetry. To solve this problem, the easiest solution is to flatten the periphery of the lens in the whitening area.
For peripheral obstructions, the fix can be a bit more complex. Creating a notch around or a microvault above the obstruction will ensure a tailored design that promotes overall eye health and prevents unnecessary interaction with the obstruction.
This is caused by a flatter lens fit than the scleral profile and can also be quadrant, meridian or circumferential specific. Patients will typically report lens awareness in the area of edge lift and potentially experience blurred vision due to buildup of bubbles and/or debris under the lens. The edge lift can be visualized with a slit lamp and appears as a shadow below the lift area (Figure 2).
Because the sclera is more spherical closer to the limbus and more toric towards the periphery, larger diameter scleral lenses may be more difficult to fit than smaller diameter ones. The Scleral Shape Study Group (SSSG) has uncovered additional information regarding scleral shape. Approximately 65% of patients in the study achieved the best fit with a back surface quadrant-specific or freeform scleral lens design, 30% achieved the best fit with toric landing zones, and only 6% achieved the best fit by using a scleral lens with a spherical landing zone.2
Many manufacturers offer fitting sets that include diagnostic lenses with toric back haptics and quadrant-specific haptics, making fitting these lenses much more accessible than in the past. Given the SSSG results, most patients would benefit from these lens designs, and management of areas of whitening and/or edge lift would be minimized by using more personalized haptics. For patients with particularly irregular scleral profiles, free-form designs created from a scleral profilometer or an impression-based design may be the best option.
This is due to the limbal curve being too flat, usually causing a compression ring and/or limbal staining. Limbic support can lead to corneal hypoxia and neovascularization. For this reason, no level of limbic support can be tolerated. Sharpening the limbic curve, steepening the base curve, and increasing the overall diameter are all effective options for remedying this problem. Limbic support is particularly problematic in corneal transplant patients as it can potentially lead to rejection (picture 3).
This is caused by entrapment of the conjunctiva near the limbic region between the scleral lens and the cornea. It is most commonly seen in elderly patients and is often completely benign. Prolapse monitoring is usually all that is needed. However, if neovascularization or synechia develops, decreasing lens diameter and/or decreasing limbal clearance may improve prolapse (Figure 4).
Studies have reported that 26% to 46% of scleral lens wearers experience fogging in the middle of the day.3 The exact etiology of this phenomenon is unknown, but it is likely associated with peripheral misalignment, where the lens is either too loose or too tight.
Fortunately, now that toric haptics are becoming more conventional, practitioners are better equipped to tackle asymmetrical scleral profiles. However, despite a perfectly aligned periphery, some scleral lens wearers still experience fogging in the middle of the day. Other suggestions include treating any ocular surface disease (OSD) before fitting, maintaining an appropriate amount of limbal clearance (50-100 μm), and using a viscous solution mixture without preservative and saline solution without preservative.
Because scleral lenses are designed to land on the sclera and not interact with the cornea, corneal staining is rare. A localized spot of coloring usually indicates a rolling area that would require increased clearance in that area. Diffuse corneal staining is usually a toxic reaction to entrapment of product stored under the lens. This may include filler solution, cleaning solution, or topical eye drops. Simply asking the patient about their daily contact lens routine will likely reveal the culprit.
Finally, mechanical damage to the cornea during insertion and/or removal can also cause corneal staining. Additional instructions on proper application and removal may prevent future incidents.
Mucoid, lipid or protein deposits normally cause poor wetting (Figure 5). These deposits can be caused by untreated OSD or external factors such as makeup, face creams and hand soaps. Encourage patients to apply makeup and face creams after lens insertion and to use only mild, moisturizer-free soaps for hand washing. Material choice also plays a role in proper wetting, so finding the right balance between oxygen permeability and wetting angle is imperative.
Additionally, treating the lens with plasma and Tangible Hydra-PEG can improve wettability and reduce deposits. Finally, practitioners should encourage patients to gently scrub the front surface with non-abrasive cleansers to further reduce deposits.