Scleral lenses were first introduced in Germany in 1887 (van der Worp et al, 2018). They were made of blown glass and used the following year for vision correction purposes. Because these lenses were impermeable to gas (i.e., induced hypoxia), they were reserved for extreme cases of corneal disease.

Since these scleral contact lenses were first introduced, the eyecare community has made great strides with regard to materials and designs as well as with its understanding of how to fit these life-changing lenses (Harthan et al, 2018). The following article includes a summary of some of the current hot topics within the scleral contact lens research arena.

Who Is Fitting Scleral Lenses?

Scleral lenses were once primarily fit in referral centers (hospitals and university-based practices) and were mostly reserved for patients who had advanced corneal ectasias; however, scleral lenses are now most commonly fit in private practice (Nau et al, 2018). They are also now commonly used to manage dry eye and relatively uncomplicated refractive errors in addition to post-surgical patients and patients who have ectasias (Nau et al, 2018). Scleral lens fitters tend to be younger because scleral lens fitting is now commonly taught in schools, which is a change from the past. The majority of fitters are relatively new to the modality, with most having fewer than 50 fits in their career (Nau et al, 2018).

What Is an Appropriate Starting Lens?

The most common starting lens is one that has an overall diameter between 15.1mm and 16.5mm; this diameter is likely related to the fitting sets available to practitioners (Pucker et al, 2019). Whether scleral lens fitters start with smaller or larger diameters is likely related to the severity of the disease that they most commonly encounter. After selecting a lens, it needs to be applied to the eye and evaluated. Survey data suggest that average scleral lens fitters prefer an initial starting central corneal clearance of 277µm and a final central corneal clearance of about 195µm (Pucker et al, 2019). Likewise, survey data suggest that more than 300µm of central corneal clearance is excessive, while less than 100µm provides insufficient central corneal clearance (Harthan et al, 2018).

In addition to evaluating central corneal clearance, practitioners should also evaluate limbal clearance and lens edge lift to ensure a healthy fit. Data suggest that more than 200µm of limbal clearance may be excessive, while less than 50µm of limbal clearance may be insufficient (Harthan et al, 2018).

Data furthermore suggest that small amounts of conjunctival blanching (due to a tight peripheral edge) may be acceptable. Clinical experience, however, suggests that blanching should be minimized as much as possible through lens fit adjustments, because poorly fitting lenses may become uncomfortable. Conjunctival prolapse should also be avoided, as it has the potential to damage limbal stem cells, though this issue is also sometimes unavoidable (Harthan et al, 2018).

What Is a Patient’s Initial Experience?

Scleral lens wear comes with some unique perceptions and care issues. Preliminary survey data suggest that 72.7% of neophyte scleral lens wearers have no hesitations about trying this technology, which is surprising considering that scleral lenses are large-diameter GP lenses (Bickle et al, 2019). This same survey reported that 63.6% of subjects needed only one visit to learn how to use their lenses, while it took 9.2% of subjects three or more visits to learn how to use them (Bickle et al, 2019). The ease of using this modality is likely influenced by the physical state of each subject. Likewise, 68.2% of subjects found it easy to learn how to use scleral lenses, though 36.4% of subjects had trouble with application bubbles during the first week of lens wear (Bickle et al, 2019). This survey also reported that about 70% of subjects believed that it was easy to apply and remove their lenses after one week, and more than half of the included subjects preferred using an inserter for applying the lenses compared to other methods such as using their fingers or an O-ring (Bickle et al, 2019).

How Frequently Are Complications Associated with Scleral Lenses?

Practitioner survey data suggests that the most common emergent corneal complications are corneal edema (0.45%), neovascularization (0.28%), infiltrates (0.17%), toxic keratopathy (0.17%), bullae (0.10%), and microbial keratitis (0.08%), while the most common emergent conjunctival complications are giant papillary conjunctivitis (0.16%), conjunctivochalasis (0.2%), and hyperemia (0.01%) (Schornack et al, 2016). Alternatively, most practitioners have at least encountered patients who have experienced minor complications such as poor lens wetting and midday fogging (Pucker et al, 2019); these are most commonly treated by having patients remove, clean, and reapply their lenses (Pucker et al, 2019).

Do Scleral Lenses Induce Clinically Meaningful Hypoxia?

Proper oxygen transmission is essential to corneal health. Thankfully, modern scleral lens materials are highly gas-permeable and are able to readily transfer oxygen to the tears and subsequently to the cornea (Michaud et al, 2012). Nevertheless, the tears themselves are a significant barrier to oxygen transmission. So, under most fitting situations, the cornea is subjected to a minor hypoxic state (Michaud et al, 2012; Kim et al, 2018). During open-eye lens wear conditions, the cornea swells about 2% (which is approaching the closed-eye state with no lens wear). When an eye is closed with a scleral lens on it (such as with overnight wear), the eye is under an unacceptable hypoxic state (Kim et al, 2018). Furthermore, with greater central corneal clearances, the tear reservoir is more likely to have more white blood cells (hypoxia-induced inflammation), which may be promoting midday fogging (Postnikoff et al, 2019).

What Causes Midday Fogging?

Midday fogging is a unique minor complication associated with scleral lenses. While the exact cause is still unknown, the two leading theories suggests that particulate matter builds up within the tear reservoir, resulting either from excess tear exchange or from lens seal off (McKinney et al, 2013; Skidmore et al, 2019). In either case, particulate matter may stem from tear biomolecules (lipids and/or proteins) or from inflammatory cells secondary to hypoxia (Walker et al, 2016; Postnikoff et al, 2019). Poor tear exchange as a primary cause is supported by sclerals having a tear exchange rate that is 0.42% per minute after 30 minutes; this rate is considerably less than that of a non-lens-wearing eye (34.2% per minute) (Paugh et al, 2018). Nevertheless, Skidmore et al (2019) did not find a significant difference in tear exchange rates between subjects who did (0.11% per minute ± 0.59% per minute) and did not (0.42% per minute ± 0.67% per minute) have midday fogging. This lack of significant difference may have been related to high inter-subject variability. Therefore, fogging may be best avoided by fitting lenses closer to the cornea (i.e., helps avoid hypoxia), that are smaller in diameter (i.e., helps avoid scleral toricity), and that are fit with good peripheral alignment (i.e., toric haptics may help improve peripheral fitting relationship) (Postnikoff et al, 2019; Consejo et al, 2019).

Conclusion

Scleral lenses have made great strides since their inception. They are typically safe when a proper care regimen is followed (Zimmerman and Marks, 2014; Schornack et al, 2016). They are used in a variety of practice settings and can be used to treat a range of ocular surface conditions (Nau et al, 2018).

While fitting trends and practitioners’ understanding of scleral lens-associated complications and their treatments are maturing, more research is still needed to fully understand the best way to fit this modality. CLS

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