Keratoconus is a progressive eye disease in which the cornea thins and bulges into a cone-like shape, losing its roundness. The eventual cone shape deflects light which enters the eye towards the light-sensitive retina. The result is distorted vision.
Keratoconus can occur in one or both eyes. Keratoconus is relatively rare. If it does occur the onset usually begins in the teens or early twenties.
Symptoms of Keratoconus
Keratoconus may be difficult to detect and it typically develops slowly with few cases proceeding rapidly. As the cornea gradually becomes irregular in shape, progressively nearsightedness and irregular astigmatism increase. This creates problems such as distorted and blurry vision. Glare and light sensitivity as well. Keratoconic patients often need prescription changes every time they visit their eye doctor.
Causes of Keratoconus
The weakening of the corneal tissue which leads to keratoconus appears to be from an imbalance of enzymes in the cornea. The enzyme imbalance makes the cornea susceptible to oxidative damage from free radicals, causing weakness and corneal bulge.
Risk factors for this type of oxidative damage and weakening of the cornea include genetic predisposition, which explaining why keratoconus often affects multiple members of the same family. Keratoconus is also connected to ultraviolet (sun) overexposure, excessive eye rubbing, a history of poorly fit contact lenses along with chronic eye irritation.
For mild forms, eyeglasses or soft contact lenses help. As the severity of the disease progresses and the cornea thins and increasingly distorted shape, glasses or soft contacts will no longer provide adequate vision correction.
Treatments for moderate to advanced keratoconus include:
Gas permeable contact lenses. If eyeglasses or soft contact lenses cannot control keratoconus, then gas permeable (GP) contact lenses are usually the effective. Rigid materials enable the GP lenses to dome over the cornea, replacing the irregular shape with a smooth, uniform refracting surface thus improving vision.
There is a comfort cost though because GP contact lenses can be less comfortable to wear compared to soft lenses. Fitting of the contact lenses on keratoconic corneas are also challenging and more time-consuming. Expect frequent office visits for fine-tuning and fitting of the prescription, especially as the keratoconus continues to progress.
Piggybacking lenses. Some practitioners advocate “piggybacking” two different types of contact lenses on the same eye to better fit the gas permeable contact lens over the cone-shaped cornea. Some patients may find this a bit uncomfortable. The GP lens is fitted on top of the soft contact lens which sits on the eye. The approach is thought to increase patient comfort as the soft lens acts as a cushion under the rigid second lens, the GP lens.
Hybrid contact lenses. Hybrid contact lenses are a relatively new design combining highly oxygen-permeable rigid center with a soft peripheral lens “skirt.” Manufacturers claim their hybrid contacts provide crisp optics of GP lenses alongside wear- comfort rivaling soft contact lenses. Hybrid lenses are available in a wide variety of parameters to provide optimal fit which conforms best to the irregular shape of a keratoconic eye.
Scleral and semi-scleral lenses. These are gas permeable contact lenses which have a large diameter allowing the edge of the lenses to rest on the white part of the eye -the sclera. These lenses will also dome over the irregularly shaped cornea, allowing for a most comfortable fit. They will move less during eye blinks. Scleral lenses cover a larger portion of the sclera, whereas semi-scleral lenses cover a smaller white (eye) area.
Intacs. These are tiny plastic inserts which are surgically inserted just underneath the eye surface in the periphery of the cornea helping to reshape the cornea. The result, clearer vision. Intacs may be advised when keratoconus patients no longer can obtain functional vision with contact lenses or eyeglasses.
Studies show that Intacs can improve the spectacle-corrected visual acuity (BSCVA) of a keratoconic eye by an average of two additional lines on a standard eye chart. The implants have the additional advantage of being removable and changeable. The surgical procedure takes 10 minutes. Intacs might delay but will not prevent the required corneal transplant, if keratoconus progresses.
Corneal crosslinking. This procedure, “CXL” for short, strengthens corneal tissue slowing or preventing the bulging of the eye surface. In turn this procedure can reduce the need to undergo a corneal transplant.
There are two types of corneal crosslinking: epithelium-off and epithelium-on. Epithelium-off crosslinking is where the outer portion of the cornea (epithelium) is removed to allow entry of riboflavin, a B vitamin, to the cornea. Once administered, the riboflavin is activated with UV light. With the epithelium-on method (transepithelial crosslinking), the corneal surface is left intact.
Neither procedure is FDA-approved. However, multiple clinical trials are currently underway. Although cross-linking may already be common in some countries — few doctors in the United States will perform the procedure until it is FDA-approved. For that reason, it’s also not covered by insurance. The procedure costs $2,500 per eye, not including the contacts or eye drops.
Corneal transplant. Some people with keratoconus cannot tolerate a rigid contact lens, or they are beyond the point of contact lenses or known therapies providing acceptable vision. The last resort remedy may be a corneal transplant, also called a penetrating keratoplasty (PK or PKP). Note that after successfully completing a cornea transplant, most keratoconic patients will still need glasses or contact lenses for clear vision.
Scleral contact lenses are rigid contact lenses are larger than traditional contacts. This allows them to only touch the eye on the white part, or sclera, hence the name.
Scleral contact lenses are excellent for people who have compromised corneas, whether it be from trauma, corneal dystrophies such as keratoconus, or severe dry eye.
If traditional rigid contact lenses and soft contact lenses have not worked due to comfort or clarity of vision, scleral contact lenses can often be an option that allows a patient to return to contact lens wear.
Scleral lenses can treat many forms of corneal dystrophies (keratoconus, pellucid marginal degeneration, macular corneal dystrophy), severe dry eye (a scleral locks a tear reserve onto the front of the eye preventing the cornea from drying out) as well as post trauma or surgery that have affected the cornea, such as corneal transplants, corneal lacerations, etc.
The main difference between scleral lenses is size. If a corneal has more severe deformation, whether, from surgery or trauma, a larger lens is needed to vault over the cornea and ensure the lens is only touching on the sclera.
Many instances of corneal diseases, corneal trauma or severe dry eye can be covered. Coverage varies widely by insurance, call for a consult with our insurance specialist to determine if a scleral lens benefit is offered.
Comfort and clarity of vision where traditional contacts have failed.
With proper care, a set should last several years.
Yes and no. Depends on how much the surface of the cornea has steepened as the disease progresses.
Such lenses used as prosthetic or cosmetic lenses are large soft contact lenses that allow an eye to look altered in color, size, or health. While sharing a similar name, they are completely different from a rigid scleral lens discussed here.
It is not recommended for wearers under the age 13 due to the requirements of proper care for the contacts.
A pair of scleral lenses is about $600. With proper care though they will last several years, and for many instances, the vision and comfort will far exceed any other contact lens type. While a specialty product, they offer a great value to those who have been unable to achieve crisp vision through any other type of correction.
Yes, because a scleral lens does not move on the eye and does not touch the cornea, sclerals are supremely comfortable. This comfort is immediate (there is no adaptation period as in regular rigid gas permeable contact lenses) and long term.