All contact lenses, whether large or small, rigid or soft, generally address one of two goals; optical correction or therapeutic rehabilitation. For patients who have healthy corneas of average curvature, diameter, and refractive need, optical correction can be achieved with mass-produced soft contact lenses. But, when it comes to irregular corneas and ocular surface disease, providers need specialty contact lenses to overcome the unique challenges presented by these conditions.

IRREGULAR CORNEAS

Irregular corneal profiles can range in shape from oblate to hyper prolate (Figure 1), but all present with irregular astigmatism as a result of trauma, disease, dystrophy, or surgical complication. Table 1 lists common indications. The resultant higher-order aberrations from the asymmetric corneal shape cannot be adequately corrected with spectacles or traditional soft contact lenses. The primary function of specialty lenses for this population is to mask the abnormal corneal surface, reducing the associated aberrations and improving visual acuity.

Additionally, lenses should provide adequate comfort for all hours of wear and, most importantly, should not adversely affect ocular health. Irregular corneas are as unique as a fingerprint, and thus there is no such thing as one size (or rather, one lens) fits all. As a result, practitioners need to be knowledgeable of the various contact lens modalities and to be proficient in fitting each type of lens to improve the likelihood of success.

SPECIALTY LENS OPTIONS FOR IRREGULAR CORNEAS

Corneal GP Lenses Corneal GP lenses are the classic choice to mask corneal surface irregularities and to improve visual acuity. Using corneal GP lenses on a cornea that has very minor irregularity is similar to fitting them for refractive correction on a normal cornea.

However, fitting corneal GPs becomes increasingly difficult as the corneal surface becomes more irregular. A corneal elevation difference of 350 microns was a significant factor for success when fitting a corneal GP lens on an irregular cornea; differences greater than 350 microns indicated the use of a scleral lens.¹ When fitting a corneal GP lens, an apical-bearing fitting relationship can lead to complications such as corneal epitheliopathy or scarring. Corneal warpage has been documented as a result of corneal GP wear.² This can alter baseline measurements in progressive corneal ectatic disease, making disease progression difficult to determine based on anterior curvature changes alone. Furthermore, individuals fit with a flat or apical-bearing fitting relationship were more prone to develop apical scarring.³ An apical-clearance or a three-point-touch approach can maintain the corneal integrity (Figure 2).

Diameters and curve widths of GP lenses are variable or fixed depending on the chosen design. Generally, a centrally located irregularity can be managed with a smaller overall diameter (OAD) and a smaller back optic zone diameter (BOZD). As the apex becomes more peripherally located, creating more inferior-superior asymmetry, a larger OAD and BOZD are appropriate.⁴ Lens geometry is variable and should be selected primarily based on the corneal profile, i.e., use reverse geometry lens designs for more oblate or peripherally steep corneal profiles, and use prolate geometry for prolate or centrally steep profiles. Peripheral curve profiles can include the use of toric or quadrant-specific changes, useful to reduce edge lift or bearing and to improve lens centration. In eyes with corneal opacity, corneal GP lenses have proven useful in surgical versus non-surgical decision-making.⁵

Custom Soft Lenses For individuals who are unable or unwilling to tolerate corneal GP lenses, custom soft lenses may provide adequate vision and improved levels of comfort.⁶ Unlike their mass-produced counterparts, these lenses are not limited to the typical parameter constraints of the normal corneal population. Custom soft lenses are lathe-cut and can be produced in an extensive range of base curve radii, diameters, hydrogel or silicone hydrogel materials, and nearly endless refractive powers. In some designs, the lens optics can incorporate variable eccentricity and even multifocal options to meet the needs of these patients.

The designs available are all unique. In general, they are available with either double slab-off or prism-ballast stabilization for toric optics, full-diameter or central thick zones (Figure 3), and either a variable base curve or base curve and peripheral curves that can be modified independently. In a dual-curve design, the base curve is used to create alignment with—or to gently touch—the apex of the cornea, and the peripheral curve is used to control movement and centration. Also, dual-curve designs make it easy to create reverse geometry lenses to accommodate oblate corneal shapes. In a few designs, the peripheral curve can incorporate a quadrant-specific design to improve lens centration.

Additionally, lens thickness can be significantly increased to create a pseudo-rigidity, which can mask corneal irregularity. Success of these lenses depends on the severity of the irregularity. They can provide similar vision to a corneal GP with less epithelial disruption,⁷ and they can maintain consistent levels of comfort from application to removal.⁸ Some of these lenses can have a cosmetic or prosthetic option added, which can be useful to improve cosmesis and to reduce glare. Oxygen transmissibility should be considered with increased thickness, as corneas with reduced function or high hypoxia concerns, such as post-corneal transplant, should be avoided.

Piggyback (PB) Lens Systems For patients experiencing reduced comfort or minor epitheliopathy with a best-fit corneal GP, a PB lens system can be utilized. This approach seems to be often overlooked, as utilization is approximately only 2% in keratoconus patients.⁹ The GP lens improves visual acuity, while the underlying soft lens provides corneal protection, cushioning the cornea from the GP lens and improving comfort. The PB lens system may be best utilized when other options have failed; a GP lens is the appropriate first lens option.

There are commonly two approaches to fitting a PB lens system. First, a corneal GP lens is fit; then, a best-fit, near-plano-powered soft lens is placed underneath. This arrangement will minimally affect the fitting relationship and power of the GP lens. The second method is to fit a soft lens first, using the spherical power of the soft lens to artificially change the anterior surface curvature. With good centration of the soft lens, lens power changes can create a more prolate (plus lens power) or oblate (minus lens power) surface to aid in lens fitting. A minus lens may be more appropriate in keratoconus applications, as it artificially flattens the anterior surface.¹⁰ As for the refractive power changes induced, approximately 21% of soft lens power translates to changes in GP lens power.¹¹

Patients may be apprehensive to adopt this modality due to the perceived difficulty of wearing and caring for two lenses. Daily disposable lenses can be used to reduce the burden of caring for another lens, assuming that an appropriate soft lens fitting relationship can be achieved.

Excessive edge lift or lens fluting results from insufficient sagittal depth, which can be mitigated with a larger diameter and/or a steeper base curve. The sagittal depths of mass-manufactured soft lenses have been studied; this data can act as a helpful guide to select a soft lens.¹² However, if excessive edge lift or lens fluting is still observed with mass-produced soft lens options, a thin custom soft lens can be used to improve the fitting relationship.

Other soft lens options, such as a cosmetic/prosthetic soft lens or a soft lens with a central excavation (allowing the GP lens to rest in a depression in the soft lens surface), can be used to improve cosmesis, reduce glare, or improve lens centration (Figure 4). Importantly, PB lens systems using low-oxygen-permeable materials may result in hypoxia complications; therefore, it has been suggested that hyper-oxygen-permeable lens materials should be used for both the GP and the soft lens.¹³

Hybrid Lenses Hybrid lenses utilize a GP center with a soft lens skirt, so they have characteristics of both GP and soft lenses. Various hybrid lens designs exist, with multiple geometries to accommodate a variety of corneal shapes. Globally, there are several designs and manufacturers of hybrid lenses; in the United States, there is one manufacturer that offers multiple designs, with the OAD and GP diameter fixed in each. The GP portion of the lens uses base curve or variable sagittal depth based on reverse geometry to align with—or vault over—the corneal surface or apex, respectively. The soft skirt can be ordered in a few base curve radii, usually flat, medium, and steep. This can aid in adjusting lens movement, tear exchange, and lens centration and can also influence alignment of the GP portion of the lens. The lens material varies by design, with both high- (soft) and hyper- (GP) oxygen-permeable materials utilized in newer designs.

Optically, all U.S.-based hybrid lenses are available with spherical powers, and the lenses designed for normal corneas are available with multifocal optics as well. Nau reported an improvement in lens comfort with hybrid lenses in comparison to corneal GP lenses.¹⁴ Hybrids can produce improved vision and comfort over corneal GPs in cases of lens decentration and lens intolerance.¹⁵ Of note, quality of life is similar with corneal GP, soft, and hybrid lenses.¹⁶ Lens application technique is crucial with hybrid lenses, as forceful application will flatten the soft skirt and create GP lens seal off, suction, and difficulty with removal (Figure 5).

Scleral Lenses When the corneal irregularity is extreme, scleral lenses may be preferred over other lens designs. These lenses vault the cornea and limbus, aligning with the sclera and overlying conjunctiva. Scleral lenses can overcome nearly any corneal irregularity and should be considered as an option prior to referral for corneal transplantation. Individuals who have keratoconus and who otherwise would have undergone corneal transplantation secondary to contact lens failure can achieve success with these lenses.¹⁷

The Scleral Lenses in Current Ophthalmic Practice Evaluation (SCOPE) study reviewed practitioner prescribing habits for scleral lenses and reported corneal irregularity as the primary use, followed by ocular surface disease and uncomplicated refractive error.¹⁸ These lenses are available with an abundance of unique modifications depending on design. Overall diameters and curvature can be variable or fixed. Scleral lenses can be modified via changes in base curve or sagittal depth. Some designs compensate for changes to individual curves; this allows for a single parameter to be changed without affecting the rest of the lens. Their geometry can accommodate prolate and oblate corneal profiles, and the haptics can incorporate toric, quadrant-specific, and elevation-specific changes. These lenses have sparked innovation in the form of 3D scanned impressions and profilometry devices specifically made to map the ocular surface to identify scleral shape. The derived data can then be used to guide the fitting process or even to create unique, elevation-specific lenses for a patient (Figure 6).

Scleral lens optics can incorporate nearly limitless spherical and astigmatic powers. Optical stabilization is provided by double slab-off, prism-ballasted, or asymmetric haptics that align to the ocular shape, preventing lens rotation. In addition, many are available with highly customizable multifocal options, some with the ability to displace the optics to improve optical centration over the pupil. Furthermore, a few have variable front-surface eccentricity to reduce higher-order aberrations. Custom higher-order-aberration-correcting optics have been well documented in the literature and are finally becoming commercially available.¹⁹

Although scleral lenses have proven to be highly successful in improving optics for severe corneal disease, they have limitations—specifically in patients who have reduced endothelial cell function, such as after penetrating keratoplasty or in patients who have Fuchs’ dystrophy.²⁰ Concerns have been raised about scleral lens wear and its effect on intraocular pressure, but more research is needed to confirm this finding.²¹

OCULAR SURFACE DISEASE

Ocular surface disease comprises a multitude of disease states that ultimately compromise ocular surface tissue integrity. The scope of ocular surface disease is tremendous. The intricacies of the various pathophysiologies and etiologies are detailed in the Tear Film and Ocular Surface Society (TFOS) Dry Eye Workshop (DEWS) II report.²² Specialty lenses for ocular surface disease primarily provide ocular protection, acting as shields to mechanical or exposure damage. This protection aids in wound healing, pain relief, and the prevention of tissue dissection. The TFOS DEWS II report places therapeutic contact lens options as part of step 3, alongside autologous or allogenic serum and oral secretagogues.²³ Utilization of these lenses may be in addition to—or in lieu of—other forms of therapy. Frequently, contact lens therapy is initiated prior to long-term steroid, amniotic membrane graft, or surgical intervention.²³

The wear strategy of a therapeutic lens is variable depending on the disease state and severity. Traditionally, there are two options for therapeutic contact lenses: bandage/therapeutic soft lenses and scleral lenses.

SPECIALTY LENS OPTIONS FOR OCULAR SURFACE DISEASE

Bandage/Therapeutic Soft Lenses A few mass-produced lenses, all of which are manufactured in silicone hydrogel material and are approved for extended wear, have a therapeutic indication from the U.S. Food & Drug Administration (FDA). Of these three lenses, two are approved for 30 days of continuous wear, while the third is approved for seven days. These are readily available and simple to fit on patients who have average corneal characteristics.

Certain conditions such as irregular corneas, keratoprosthesis, and bleb leaks will require more customized soft lenses with variable diameter or base curve radii, although off-label use of these lenses is necessary for management.^24,25 The use of a topical antibiotic is indicated for prophylaxis, and the most common indication is for postoperative corneal wound healing.²⁶ Bandage contact lenses can also be used as a retention system for dehydrated amniotic membranes (note that dehydrated membranes are labeled only for wound coverage). For chronic conditions such as bullous keratopathy or recurrent corneal erosions, extended wear is an excellent option. For patients who are unable to apply or remove lenses, in-office lens replacement can be performed with monthly follow-up evaluation (Figure 7).

Therapeutic Scleral Lenses The use of scleral lenses for therapeutic indication was popularized in the United States after the development of large-diameter GP lens buttons. Scleral lenses provide mechanical protection and continuous corneal hydration throughout all hours of lens wear. This provides patients with significant symptom relief in cases of severe ocular surface disease when primary treatments have failed.²⁷

Scleral lens therapy can be used on a variety of ocular surface disease states and has become widely accepted by practitioners. Several GP lens materials have an FDA indication for use in ocular surface disease. Scleral lenses can reduce the need for ocular lubricants, thereby decreasing the burden of treatment and improving quality of life.²⁸ In addition, these lenses may achieve success for patients who otherwise may require surgical interventions such as partial/full tarsorrhaphy.²⁹

Scleral lens wear has been shown to provide rapid ocular surface healing and improved vision, the benefits of which can be maintained even after cessation of lens wear.^30,31 Risk versus benefit should always be assessed in these patients prior to wear and continuously during wear. High-risk applications of scleral lenses, such as extended wear for wound healing in persistent epithelial defects, has proven to be successful.³² Figure 8 shows a case of a persistent epithelial defect managed with therapeutic scleral lens wear. A two-lens strategy was implemented in which the lens was changed every 12 hours while allowing the unworn lens to disinfect in un-neutralized hydrogen peroxide. The lens was rinsed and filled with nonpreserved sterile saline, then a drop of nonpreserved moxifloxacin was added to the reservoir for prophylaxis. Follow-up care was frequent and highly regimented.³³ Defect resolution occurred in six days; the patient then continued daily wear.

Similarly, scleral lenses have been used as drug delivery devices. Topical bevacizumab has been used in the lens reservoir to significantly reduce corneal neovascularization.³⁴

The challenges of therapeutic scleral lens wear include the same challenges as scleral lens wear for other indications, in particular the potential for reduced endothelial function. Additionally, severe ocular surface disease patients may present with symblepharon or reduced fissure size, which may make the lens fitting process more challenging. Unlike readily available therapeutic soft lenses, scleral lenses will need to be designed to fit. In this population, extra care must be exercised to not interfere with the limbus, especially in cases presenting with limbal stem cell deficiency.

CONCLUSION

It is important for practitioners to keep in mind that contact lenses are part of the comprehensive management of irregular corneas and ocular disease. It’s not just about fitting a lens to an eye. At each visit, the health of the cornea and ocular surface should be evaluated in addition to the lens-to-cornea fitting relationship and the lens itself. Relationships with comanaging practitioners are paramount to success, especially with complex ocular surface diseases in which multifactorial ocular and systemic variables are common. With proper management of the underlying condition, practitioners can utilize the various specialty lens modalities—and a little imagination—to overcome nearly any challenge. CLS

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