Scleral contact lenses are the fastest growing specialty lens modality in recent years, likely a result of improved designs and materials.1 Market growth has also increased because scleral lenses were once reserved for patients with complex ocular surface diseases, but new technologies have allowed for expanded indications to include patients with dry eyes and even patients with normal eyes.1,2
Despite a surge in scleral lens fitting and related research, the literature still lacks a comprehensive description of the pathologies associated with scleral lenses, probably because scleral lens use is rare compared with soft contact lens use.3 That said, most practitioners consider scleral lenses a relatively safe and an effective means for correcting refractive error.1,2,4 The goal of this article is to summarize the clinically important literature related to the pathological conditions (minor and serious) associated with scleral lenses and, when possible, to provide a description of the potential mechanisms leading to these complications along with means by which to treat and prevent them from occurring.
Midday fogging, a condition whereby tear reservoir particulate matter distorts vision, is possibly the most common scleral lens complication. Approximately 20% to 33% of all scleral lens wearers experience midday fogging,5 although additional research is needed to determine its true frequency. Patients experiencing midday fogging indicate that their vision is blurred. If present, the symptom will likely worsen throughout the day unless the patient self-treats.5 Midday fogging can be visualized with a slit-lamp biomicroscope and with anterior segment optical coherence tomography.5 When clinically visualized, midday fogging presents as a particulate matter that is trapped between the lens and the ocular surface (Figure 1).6 Although the identity of the fogging material is unknown, the material and its origins have been of great interest to the clinical and scientific communities.
Tear lipids and tear inflammatory molecules are the primary fogging candidates.6,7 While no causative mechanisms has been uncovered, we hypothesize that if tear lipids are the fogging culprit, excessive tear lipids may accumulate in the tear lacrimal lens after the sloughing off of the cornea when peripheral lens seal-off is present. Alternatively, a poorly fitting lens back surface may result in gaps between the lens and the eye, which may allow for an excessive influx of meibomian gland lipids or debris into the tear reservoir. If the fogging material is primarily inflammatory, it could result from hypoxic seal off, mechanical interaction with the cornea/limbus/conjunctiva, hypoxia secondary to an excessively steep lens/thick lacrimal lens, or secondary to dry eye disease.6,7
Midday fogging does not generally prevent scleral lens wear, particularly when prescribed for highly motivated patients such as those with a corneal ectasia, though this condition can be a nuisance, requiring persistent mitigation.4,5 Specifically, patients experiencing midday fogging will need to alleviate the fogging regularly by removing their lenses, cleaning them, refilling them with new nonpreserved saline, and then reapplying them to the eye, a routine that requires patients to carry their care products with them throughout the day.5 Anecdotally, fogging has also been improved by applying a thick preservative-free artificial tear to the contact lens bowl before applying the lens and by altering the lens fit.5 (Note: this is off-label use, but helps to avoid the preservatives found in rewetting drops.) We have also noticed that a poorly wetting lens may mimic midday fogging; we have found that cleaning the lens can alleviate the poor wetting and improve vision. A surface coating or plasma treatment also may be helpful. Additional research is needed to truly determine if these actions improve the patient’s experience and to identify other treatment and prevention options.
Infective and Noninfective Complications
Schornack and colleagues used a survey to estimate the frequency of prescriber-reported noninfective corneal complications associated with scleral lens use. They determined that 0.45%, 0.28%, 0.17%, and 0.10% of wearers develop corneal edema, corneal neovascularization, toxic keratopathy, and bullae, respectively.9 Similarly, they estimated the frequency of conjunctival complications and determined that 0.16%, 0.02%, and 0.01% of wearers develop giant papillary conjunctivitis, conjunctivochalasis, and hyperemia, respectively.9
We have routinely noticed toxic keratopathy/superficial punctate keratitis, which we found were most likely caused by a solution hypersensitivity reaction. In spite of instructions to use only preservative-free saline or preservative-free artificial tears to fill the lens bowl, a small number of patients, upon presenting with an inflammatory episode, admit to filling their lenses with preserved saline, multipurpose solutions, or even tap water. With one exception where the patient required an antibiotic, all of these cases resolved when the patients stopped using inappropriate solutions and switched to nonpreserved saline solution.
Infiltrative keratitis is rare (~0.2%) in scleral lens wearers.5,9 Each of us has had a single case. One case appeared to be contact lens-associated red eye, which resolved after the patient temporarily stopped wearing the lenses. The other case was associated with the use of a multipurpose solution to fill the lens bowl, and this resolved after the patient switched to preservative-free saline.
The rate of infective keratitis (~0.1%) associated with scleral lens use is also believed to be relatively low.9 Zimmerman and Marks documented one corneal ulcer that was thought to be secondary to poor care and compliance.10
We have had three patients with non-healing sterile corneal ulcers referred to us for scleral lenses. All three patients were fitted with scleral lenses but, out of concern for the development of microbial keratitis, all of them were instructed to add one drop of topical antibiotic to the solution used to fill the lens at the time of application. In all three cases, the ulcer ultimately resolved without infection, indicating that, in spite of altered physiology under the lens, scleral lenses can aid in the treatment of severely compromised corneas.
Innovations in scleral lens materials (primarily materials with better oxygen transmissibility) are the most important reason for the exponential market growth of scleral lenses in modern practice.1 Specifically, oxygen transmissibility (Dk/t) is a material property that describes oxygen’s ability to transmit through the thickness of the material.8 Historically, the Holden-Mertz criteria have been used to determine the minimal amount of oxygen transmissibility needed to avoid contact lens-induced corneal swelling during open-eye (24.1) and closed-eye (87.0) conditions.11 Oxygen transmissibility is most affected by the lens material, although oxygen’s ability to reach the ocular surface is also affected by central corneal clearance (lacrimal lens) and overall lens diameter.12
One of the easiest methods for increasing oxygen flow to the ocular surface is to prescribe a scleral lens made from a highly transmissible (Dk/t > 100) material.12 Be aware, however, that higher Dk materials generally result in lenses with decreased wettability. Therefore, lens surface wetting should be monitored, because poor lens wetting could result in variable vision.13
Relatedly, scleral lenses tend to be thicker than 300 μm, which, as previously described, affects oxygen’s ability to reach the ocular surface.12 While scleral lens thickness should be minimized when possible to allow maximum oxygen transmissibility and to avoid hypoxic conditions, a scleral lens needs to be sufficiently thick to avoid lens flexure (variable vision) and breakage.14,15
The central corneal clearance of a scleral lens (tear reservoir thickness between the cornea and the lens) can have as much or more impact on oxygen’s ability to reach the cornea than the material and lens thickness.15 Specifically, the transmissibility of tears is about 80, which is lower than most scleral lens materials.12 Thus, the amount of oxygen reaching the corneal surface is inversely proportional to the thickness of the lacrimal lens. This suggests that a scleral lens should be fit as close to the cornea as possible while avoiding corneal and limbal touch.
Recent research indicates that, on average, experienced scleral lens fitters prefer a central corneal clearance of 277 μm at dispensing and a central corneal clearance of 195 μm after lens settling.16 Additional research is needed to determine the ideal central corneal clearances for avoiding corneal hypoxia during daily wear, although the literature currently suggests that most available lens/fitting combinations result in some corneal hypoxia or swelling.12,15 While no evidence exists that modern scleral lenses produce clinically meaningful hypoxia, additional research is needed to determine the long-term consequences of scleral lens-induced hypoxia.
Overall lens diameter and, more specifically, the diameter of the chamber may influence the amount of oxygen reaching the cornea.17 A larger lens chamber diameter will have greater sagittal depth and, if not properly compensated for by flattening the base curve, may result in increased clearance (thicker lacrimal lens).17 A larger chamber usually requires a wider landing zone, a larger overall diameter, and a thicker lens. Therefore, when fitting scleral lenses, one should select a lens with the smallest chamber size that provides corneal clearance at the limbus, minimize lens thickness, and fit the lens as close to the cornea as possible.
By design and definition, scleral lenses are meant to vault the cornea and rest on the bulbar conjunctiva somewhere beyond the limbus.6 In a significant number of cases, however, there is some corneal bearing. While it has been hypothesized that scleral lens corneal bearing just inside the limbus may affect corneal health, limbal bearing’s long-term impact on the health of limbal stem cells has yet to be fully elucidated.5 With that said, it would seem logical to avoid or lessen corneal bearing whenever possible. Some cases of corneal bearing are relatively easy to fix by increasing the lens chamber size. In other words, increasing the optic zone diameter or the widths of the peripheral curves that are inside the conjunctival/scleral landing zone will increase limbal/cornea clearance.
Scleral lenses have a tendency to center low and slightly temporally. This decentration may be caused by pressure from the upper eyelid pushing the lens downward, or it may result from the asymmetrical topography of the sclera pushing the lens temporally.18 This type of lens decentration results in corneal touch just inside the limbus in the superior nasal quadrant. Increasing the chamber size may not resolve the corneal bearing if the lens is simply further decentered until the landing comes into contact with the superior nasal cornea.
One possible strategy to increase corneal clearance at the limbus is to steepen the curve that makes up the outside edge of the chamber. The outside edge of this curve makes contact with the sclera while the inside edge should clear the cornea at or just inside the limbus. Steepening this curve will elevate that inside edge and should reduce the amount of corneal touch. We find that a perfectly centered scleral lens is somewhat rare. In most cases, the best achievable fit still results in some mild corneal touch in the superior nasal quadrant.
Another issue in scleral lens fitting is conjunctival entrapment/prolapse, whereby loose bulbar conjunctiva is pulled into the lens chamber and onto the cornea.5 The amount of limbus being covered by conjunctiva is usually limited to parts of 1 or 2 quadrants; however, it is possible to have 360 degrees of conjunctival prolapse.
Much like scleral lens corneal touch, it is unknown whether or not conjunctival tissue covering the cornea inside the limbus is a significant issue and, if so, the degree of physiological compromise being caused by it. There is one report of neovascularization in the area where the conjunctiva covered the cornea, indicating that this condition is undesirable.5 One of the authors has successfully reduced conjunctival prolapse by reducing the lens chamber diameter (increasing chamber diameter made the condition worse) and bringing the landing closer to the limbus where the bulbar conjunctiva is evidently more adherent to the underlying sclera than the lens. The problem becomes one of balance, where a large chamber may result in significant conjunctival prolapse, while reducing the chamber size may result in an unacceptable amount of corneal touch.
A significant number of patients wearing scleral lenses will experience problems with the fit of the landing zone on the sclera/conjunctiva where there is excessive edge lift or conjunctival blood vessel blanching, indicating a lens that is fit too loose or too tight, respectively. Excessive edge lift often will be accompanied by lens movement, discomfort, and excessive particulate matter inside the chamber, while a too-tight lens periphery will often result in a visible white outer ring around the edge of the lens. In cases where the sclera is mostly spherical, the landing zone curves may simply be steepened to decrease unwanted edge lift or flattened to reduce the pressure on the conjunctival vessels and lessen the “white ring” effect. In many cases, however, scleral lenses with toric peripheral curves or more advanced scleral lenses such as those with quadrant-specific or mold-designed peripheral curves may be needed to achieve an adequately aligned peripheral landing zone and comfortable fit.
In spite of having a relatively hypoxic corneal environment and a severely reduced tear exchange, scleral lenses cause surprisingly few serious complications.5,12,15 In fact, these lenses seem to perform well as bandage lenses for many patients with seriously compromised corneas. Improved, higher-Dk materials may make scleral lenses even safer in the future. Meanwhile, more research will help us better understand midday fogging, the long-term effects of low-grade corneal hypoxia, and the fitting issues associated with current scleral lenses.
- Harthan J, Nau CB, Barr J, et al. Scleral lens prescription and management practices: The SCOPE Study. Eye Contact Lens. E-pub: April 6, 2017.
- Bergmanson JP, Barnett M, Naroo SA. Scleral gas permeable lenses have come of age. Cont Lens Anterior Eye. 2016;39(4):247-248.
- Nichols JJ. The Contact Lens Event of 2016. Contact Lens Spectrum; January 2017.
- Bergmanson JP, Walker MK, Johnson LA. Assessing scleral contact lens satisfaction in a keratoconus population. Optom Vis Sci. 2016;93(8):855-860.
- 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;39(2):88-96.
- Carracedo G, Serramito-Blanco M, Martin-Gil A, Wang Z, Rodriguez-Pomar C, Pintor J. Post-lens tear turbidity and visual quality after scleral lens wear. Clin Exp Optom. E-pub Jan. 26, 2017.
- McKinney A, Miller WL, Leach N, Polizzi C, van der Worp E, Bergmanson J. The cause of midday visual fogging in scleral gas permeable lens wearers. Invest Ophthalmol Vis Sci. 2013;54(15):5483.
- Papas EB. The significance of oxygen during contact lens wear. Cont Lens Anterior Eye. 2014;37(6):394-404.
- Schornack M, Harthan J, Barr JT, Shorter E, Nau A, Nau CB. Complications of Scleral Lens Wear. Poster presented during ARVO 2016; Abstract 1467.
- Zimmerman AB, Marks A. Microbial keratitis secondary to unintended poor compliance with scleral gas-permeable contact lenses. Eye Contact Lens. 2014;40(1):e1-4.
- Holden BA, Mertz GW. Critical oxygen levels to avoid corneal edema for daily and extended wear contact lenses. Invest Ophthalmol Vis Sci. 1984;25(10):1161-1167.
- 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;35(6):266-271.
- Bennett ES. How important are lens oxygen ratings? They are one of many performance factors. Cornea. 1990;9 Suppl 1:S4-7; discussion S8.
- Compan V, Aguilella-Arzo M, Edrington TB, Weissman BA. Modeling corneal oxygen with scleral gas permeable lens wear. Optom Vis Sci. 2016;93(11):1339-1348.
- Compan V, Oliveira C, Aguilella-Arzo M, Molla S, Peixoto-de-Matos SC, Gonzalez-Meijome JM. Oxygen diffusion and edema with modern scleral rigid gas permeable contact lenses. Invest Ophthalmol Vis Sci. 2014;55(10):6421-6429.
- Bickle KM, Jones-Jordan LA, Kuhn J, et al. Practitioner Assessment of Scleral Contact Lens Central Corneal Clearance. American Academy of Optometry 2017;Abstract.
- Giasson CJ, Morency J, Melillo M, Michaud L. Oxygen tension beneath scleral lenses of different clearances. Optom Vis Sci. 2017;94(4):466-475.
- van der Worp E. A Guide to Scleral Lens Fitting, 2nd edition. [monograph online]. Forest Grove, OR: Pacific University; 2015. Available at: http://commons.pacificu.edu/mono/10/ .