Scleral Lenses for Keratoconus Treatment
Keratoconus is a genetic ophthalmic dysfunction that causes a symmetrical or bilateral protrusion in the naturally dome-like shape of the cornea. When the light rays fall onto this conical shaped cornea, they deflect through the bulging cornea and form an obscure and distorted image. This distortion makes it difficult for the eye to concentrate on the object, and the person might also experience sharp light streaks, halos, vibrant hues and star bursts. These symptoms are the basic diagnostic indicators of Keratoconus, and the sight and vision defects caused as a result of them are ideally treated through sclera lenses to fix flaws and aberrations as far as a person’s vision is concerned.
What are Scleral Lenses?
Scleral Lenses are large, rigid, and transparent gas permeable lenses having an extended diameter range of 14mm-20mm. What distinguishes them from regular contact lenses is their extended diameter that environs the entire external corneal surface, with its edges reaching out to the scleral part of the eye. This outreach and extension of the lens surface overcomes the corneal protrusion or Keratoconus and artificially retains the original dome-like shape of the cornea.
Scleral lenses are particularly effective in overcoming vision disorders caused by Keratoconus. This is because their surface overlaps the cornea and allows the light to deflect naturally and form a perfect, accurate and undistorted image. However, the efficacy of such lenses depends a great deal on the shape and size dimensions of the cornea and the human eye.
Types of Scleral Lenses
Scleral Lenses do not come in a definite standard size. Depending upon the physical attributes of the human eye and the state of Keratoconus, scleral lens dimensions vary according to every person’s eye structure. Thus, they are prescribed after an intricate and elaborate evaluation and examination of the eye. Depending upon the size variations, the most common types of scleral lenses include:
Mini-Scleral Lenses
The scleral lenses with a diameter range of 14.5mm-18mm are classified as mini-scleral lenses. Since the diameter of an average human cornea measures around 11.5mm–11.9mm, even the smallest size of mini-scleral lenses sufficiently extends from over the cornea to the scleral region.
Corneo-Scleral Lenses
Corneo-scleral lenses fall in the same size brackets as the regular GP contact lenses. The diameter of corneo-scleral lenses varies from 13mm-15mm.
Semi-Scleral Lenses
Semi-Scleral lenses are large diameter lenses that are generally prescribed in extreme keratoconic conditions. The diameter of semi-scleral lenses measures up to 20 mm and the lens rests over the corneal bulge and extends further to cover a significant part of the sclera.
Custom Scleral Lenses
Custom scleral lenses are often prescribed when generic scleral lenses cannot provide great vision and comfort. Additionally, they can minimize\remove Higher-Order Aberrations (HOA) – glare, starburst, halos, double vision, and blurry vision . Custom scleral lenses use different techniques to design a custom fit for each individual eye. Examples of custom scleral lenses include, EyePrint PRO which uses a molding technique to design the lens and PVR PROSE which utilizes Optical coherence tomography (OCT) to design the lens.
Efficacy of Scleral Lenses against Keratoconus and Associated Vision Defects
As mentioned earlier, Keratoconus and other corneal dysfunctions cause aberrations, obscurity and other vision defects. Unfortunately, Keratoconus is an irreversible process and once the natural dome-like shape of the cornea starts to bulge forward and gets thinner at the edges, the protrusion cannot be stopped.
In such a situation, a specifically prescribed and perfectly fitting scleral lens is an effective countermeasure against the visionary defects caused by corneal dysfunctions. They remove vision obscurity, aberration, hues and light effects and ensure a natural refraction of light rays to form a perfect and undistorted image.