Contact lenses are widely used for correcting common refractive errors, allowing millions to achieve clear vision without spectacles. While conventional soft and rigid lenses address standard conditions, some anatomical or disease-related conditions require a more specialized approach. Scleral lenses are a valuable vision correction tool in this context. These lenses are notable for their large diameter, which allows them to bypass the sensitive front surface of the eye. Scleral lenses are custom-designed to provide improved clarity and superior comfort for individuals whose ocular conditions cannot be adequately managed with conventional options.
Defining Scleral Lenses and Their Unique Mechanism
Scleral lenses are distinct from traditional contacts due to their large size, typically ranging from 15 to 24 millimeters in diameter, and their construction from highly oxygen-permeable materials. Unlike standard lenses that rest directly on the central cornea, scleral lenses are designed to extend outward and land gently on the sclera, which is the white, less sensitive tissue covering the eye. This unique architecture is the foundation of their therapeutic function.
The most significant characteristic of a scleral lens is its ability to “vault” completely over the entire corneal surface without touching it. This design creates a small, dome-shaped gap between the back surface of the lens and the front of the cornea. This vault ensures that the lens provides a smooth, stable optical surface without causing irritation to the highly innervated corneal tissue.
Before insertion, the lens bowl is filled with a sterile, preservative-free saline solution. Once applied, this fluid remains trapped in the vault, creating a continuous, therapeutic reservoir of moisture over the cornea. This fluid layer not only fills in any surface irregularities to ensure clear vision but also provides constant hydration, acting as a protective bath for the compromised ocular surface.
Eye Conditions Requiring Scleral Lenses
The most frequent reason for prescribing scleral lenses is the presence of an irregularly shaped cornea, such as with the condition known as keratoconus. Keratoconus causes the cornea to progressively thin and bulge into a cone shape, severely distorting vision that cannot be corrected by glasses. The scleral lens vaults over this irregular cone, and the saline fluid layer neutralizes the uneven surface to create a smooth, new refracting surface, dramatically improving visual acuity.
Scleral lenses are also highly effective for managing severe ocular surface diseases, including chronic dry eye syndrome and conditions like Sjögren’s syndrome. For these patients, the constant saline reservoir acts as a continuous moisture chamber, shielding the eye from environmental irritants and preventing the tear film from evaporating too quickly. This prolonged hydration supports the health of the corneal epithelium, which is often damaged by severe dryness.
Additional candidates include those with complications following refractive surgeries like LASIK or PRK, which can sometimes result in corneal ectasia or irregular astigmatism. Scleral lenses provide a stable fit and superior vision correction for eyes with scarring from trauma or infection, or those that have undergone corneal transplant procedures. Because the lens rests on the sclera, it maintains stability even over a compromised corneal shape, which standard lenses cannot achieve.
Comparison to Standard Lenses and Daily Care
Scleral lenses offer a comfort advantage over traditional rigid gas permeable (RGP) lenses because they rest entirely on the sclera, which is far less sensitive than the cornea. Their larger diameter also contributes to greater stability on the eye, minimizing movement and reducing the glare or light sensitivity that can occur with smaller, unstable lenses. While soft lenses are pliable and conform to the cornea, they do not offer the same vaulting mechanism or the optical correction necessary for highly irregular surfaces.
Due to their size and the need to retain the saline fluid, the application and removal of scleral lenses require specialized techniques. Patients typically use a small, handled suction cup, often called a plunger, to safely insert and remove the lens while keeping the saline intact. This method is a departure from the finger-based techniques used for standard soft lenses and requires dedicated training with an eye care professional.
Rigorous daily maintenance is mandatory for scleral lens wearers to ensure both comfort and eye health. The lens must be cleaned and disinfected each evening using approved solutions, similar to other reusable contacts. Crucially, the fluid reservoir must only be filled with sterile, preservative-free saline immediately before insertion, as using preserved solutions can cause irritation and toxicity to the cornea. This regimen differs from the care needed for most conventional lenses.