Inside the overlap between scleral lenses and dry eye

Image credit: AdobeStock/megaflopp

Dry eye disease is the most common multifactorial ocular surface disease that affects patients of all ages.¹ Signs and symptoms of dry eye disease occur because of disruption of ocular homeostasis in the patient’s tear film. This can occur due to deficiency of the aqueous, the mucin, the meibum, or a combination of multiple etiologies.¹

Treatment for dry eye disease is often multifaceted, with the use of multiple forms of heat therapy and/or pharmacological drugs. For patients with more advanced signs or symptoms of dry eye disease, scleral lenses are a tertiary treatment option for patient cases that are more difficult to treat.¹

Scleral lenses are a type of large gas permeable contact lenses that vault over the corneal surface and rest on the patient’s conjunctiva and sclera. Scleral lenses are most commonly used to correct refractive error for patients with irregular corneal astigmatism. Scleral lenses are less commonly fit as a treatment for patients with basic refractive error or ocular surface disease.² However, therapeutic uses of scleral lenses are becoming more popular due to their ability to serve as a reservoir of lubrication for the cornea and to prolong pharmacological treatment time on the ocular surface.

Many different brands of scleral lenses may be used for refractive correction and/or ocular surface protection. It is up to the practitioner to determine which type of scleral lens to fit onto their patients to optimize the management of their symptoms. Although there is not a clear-cut methodology agreed upon between practitioners for fitting scleral lenses for therapeutic purposes at this time, there are a few specific considerations to take into account when designing the scleral lens fit.

The first consideration is determining an appropriate diameter for the scleral lenses. Scleral lens diameters are often chosen based on the horizontal visible diameter of the patient’s eyes. However, depending on the etiology and severity of the patient’s ocular surface disease, scleral lenses that are larger in diameter may be indicated to offer additional protection for the patient’s anterior segment.⁸ Some examples of patients who may benefit from significantly larger lenses are those with graft-vs-host disease, neurotrophic keratitis, and more.¹

Once a sufficient diameter has been chosen, considerations need to be made for the depth of clearance in mm over the patient’s cornea. Generally, in patients who have complex ocular surface disease and need oxygen, fitting scleral lenses that have a shallower vault could prove beneficial to the patient’s oxygen transmissibility.⁹ For patients with typical scleral lens–fitting philosophies, practitioners often aim for a clearance of 200 to 300 mm over the central cornea after lens settling. An estimated 100 mm of postlens tear film can be expected to be absorbed by the cornea or leaked out as the scleral lens settles over several hours from initial lens insertion.^1,9 Overvaulting of the scleral lenses can potentially cause corneal compromise through hypoxia, which can result in corneal neovascularization and corneal edema.

Additional considerations to manage corneal hypoxia can be determined through the scleral lens material. Hyper-Dk materials are an essential component of scleral lenses to ensure adequate oxygen transmission. Newer hyper-Dk materials continue to emerge through new technology and innovation, with the highest-Dk gas permeable lens available at a Dk greater than 200.¹⁰

Close monitoring of the patient’s corneal health must occur when fitting scleral lenses for therapeutic purposes. During the fitting process, it is often important to see the patient after multiple hours of lens wear to determine whether there is adequate scleral vault after lens settling and to observe the appearance and effect of lens edges. Adjustments must be made for lenses that cause excessive impingement along the lens edge or inadequate clearance over the limbal region.

In terms of evaluating the need for any changes to the lens edge, it is especially imperative that the scleral lenses themselves do not cause significant edge impingement after multiple hours of wear. Blanching of blood vessels underneath the lens edge can be caused by either the toe or the heel of the scleral lens edge. If the toe of the lens edge is to blame for the blanching, the lens edge is too steep and needs to be flattened. If the heel of the lens edge is to blame for the blanching, the lens edge is too flat and needs to be steepened.¹¹ In both cases, patient symptoms may include discomfort after a few hours of wear and a persistent impression ring and/or redness after lens removal.

Another determination for the need of lens adjustment is the presence of suction upon lens removal. This often manifests itself as difficulty of scleral lens removal with removal plungers. The patient may even hear a popping sound upon lens removal. This excessive suction can damage the patient’s ocular surface by causing additional insult to the conjunctiva and further exacerbate symptoms of irritation on the ocular surface, thereby resulting in excessive mucus production.¹² Besides adjusting the edges of the scleral lens to reduce suction, certain scleral lens manufacturing companies have optional additions to the design of the lens, such as channels or microvaults, that can reduce the amount of suction the lens has on the patient’s cornea.

An additional consideration that may be cause for adjusting the fit of the scleral lens is conjunctival prolapse. This occurs when there is excessive negative pressure underneath the scleral lens and the conjunctiva (often redundant conjunctiva) pulls toward the center of the cornea and covers the limbal area in that region of the lens to attach to the cornea.¹² This can put the patient at risk for vascularization and corneal scarring if the limbal region in that area and peripheral cornea shows evidence of hypoxia. In these cases, reducing the limbal vault may be indicated.

The fitting of edges along the conjunctiva is even more difficult when the patient has a lot of debris in their tear film, such as mucus. Often, the presence of debris is a sign and symptom of their ocular surface disease. The practitioner must ensure that the lens does not suction too much but is also not so loose that the patient’s tear film debris can seep in through the lens edge into the postlens tear film. Significant debris in the postlens tear film underneath the scleral lens can cause visual discomfort and fogging. The patient may present with an excessive need to refill the bowl of the scleral lens multiple times a day. Vital dyes such as lissamine green or sodium fluorescein can be excellent diagnostic tools when painted over the surface of the lens to determine the presence of leakage.¹² If the dye rapidly seeps into the fluid reservoir of the lens, this is an indication to the fitter that the edges are not well aligned and likely need to be steepened.

An additional consideration for fitting patients with therapeutic scleral lenses is the scleral lens filling solution. Although most patients who are fit with scleral lenses for refractive purposes can be successful with a simple preservative-free 0.9% sodium chloride solution as their scleral filling solution, additional suggestions can be beneficial for patients with more complex ocular surface disease. A scleral lens filling solution that has additional electrolytes could be beneficial for patients with dry eye disease.¹³ There is also the possibility of adding a drop of preservative-free artificial tears or a more viscous preservative-free gel tear into the bowl of the lens for additional comfort. Some practitioners are adding additional pharmacological agents in the bowl of the scleral lens, as well as a vehicle for drug delivery that offers prolonged contact with the patient’s ocular surface. However, this delivery method for therapeutic purposes has not been widely studied at this time and research is still ongoing.¹⁴

It is important to pay closer attention to these additional considerations when fitting patients with scleral contact lenses for therapeutic purposes. At each follow-up visit, the practitioner should be looking for clinical signs of improvement in dry eye disease (eg, improvements in punctate staining, decrease in tear osmolarity, increase in tear breakup time).¹⁵ These signs should be evaluated alongside the patient’s subjective symptoms. Of course, diagnostic testing will vary depending on its availability and the practice setting in which the eye care practitioner works. The use of scleral lenses can potentially improve the signs and symptoms of ocular surface disease, but it is important that we do not induce additional damage to the eye with a poor-fitting scleral lens.

Although scleral lenses are still most often prescribed for visual correction of irregular corneas, their use as a therapeutic agent has increased over the past few years. Minimal published research has been completed in terms of measuring the efficacy of therapeutic scleral lenses depending on the patient’s ocular surface disease, but their increased use and interest among eye care practitioners will likely prompt an increase in their use for therapeutic purposes in the coming years. When patients have experienced multiple treatment failures for dry eye disease, consider prescribing or referring the patient for a scleral lens fitting as an adjunctive treatment option.

References:

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