Keratoconus: Signs, Symptoms, Causes & Treatments
Keratoconus is a progressive disease of the cornea that may cause vision loss and distortion. The condition occurs when a thinning, weakened cornea loses its integrity and bulges forward into a cone shape.
When light enters the eye, the cone shape prevents correct refraction or bending of light, so the light fails to land correctly on the retina at the back of the eye. Keratoconus typically strikes young people between the ages of 10 and 25.
Severity may continue to progress for over ten years, occurring in one or both eyes.
As the affected cornea continues to thin and weaken, it becomes even more misshapen. Astigmatism and progressive myopia may occur.
Symptoms of Keratoconus
Besides a frequent need for eyeglass prescription changes, symptoms may include:
1. Blurry, distorted vision
2. Glare and light sensitivity
3. Itchy eyes
Causes of Keratoconus
An imbalance of corneal enzymes may be a possible cause. This imbalance makes the cornea prone to oxidative damage by free radicals, and toxic compounds produced during some cell functions involving oxygen. This damage from the free radicals weakens the cornea, allowing it to bulge outwards.
The condition likely has a genetic cause and may affect several family members.
Other possible keratoconus risk factors are:
1. Chronic eye irritation
2. A history of wearing improperly fitted contact lenses
3. Rubbing the eye
4. Overexposure to the sun’s UV rays
Treatment of Keratoconus
Keratoconus may respond well to treatment with eyeglasses and contact lenses in the early stages. However, this eye condition is progressive, and these treatments may fail to give adequate vision correction in the later stages.
Some options for treatment include:
1. Corneal Cross-Linking
Also called corneal collagen cross-linking or CXL, this procedure is intended to strengthen the cornea. The two basic types are called epithelium-on and epithelium-off. Epithelium refers to an upper skin layer.
In the epithelium-off procedure, the top corneal layer is removed. The tissues underneath are called the stroma. With the top epithelial layer removed, a B vitamin called riboflavin or B2 is applied to the stroma and activated with UV light.
The epithelium-on treatment doesn’t involve removing the top corneal layer. It’s also called transepithelial cross-linking. It may carry less risk of infection, involve less discomfort, and require less recovery time.
Corneal cross-linking stabilizes the cornea and is an effective treatment for keratoconus. It may also help with complications of refractive surgery like LASIK. This is because the LASIK procedure involves cutting a flap in the cornea that can sometimes cause destabilization.
Corneal cross-linking may be combined with other treatment methods to increase and enhance overall treatment results.
2. Custom Contact Lenses
These aren’t the same as regular contacts because they’re custom-made based on the patient’s precise corneal measurements. Custom lenses may be more comfortable than either gas permeable (GP) or hybrid contact lenses.
KeraSoft and NovaKone, brand name contact lenses by Bausch and Lomb, are available in the United States for mild to moderate keratoconus.
KeraSoft is a high-water silicone hydrogel lens capable of correcting up to 20 diopters of either nearsightedness or farsightedness and up to 12 diopters of astigmatism.
NovaKone is a medium-water hydrogel lens able to correct up to 30 diopters of either nearsightedness or farsightedness and as many as 10 diopters of astigmatism.
Both brands are larger than regular contact lenses to give further stability to the cornea.
Custom toric lenses for keratoconus are costly, but vision insurance may cover all or some expenses for these medically-necessary lenses.
3. Gas Permeable Lenses
For mild to moderate keratoconus, this is typically the preferred treatment. Gas permeable lenses give the best refracting surface for a keratoconus eye. This helps to correct and compensate for the irregular shape of the cornea.
It takes patience and skill to fit these lenses for a patient with keratoconus correctly. It may take several attempts to find the correct fit and require multiple return visits and fine-tuning to achieve optimal fit and vision correction.
4. Piggyback Lenses
Gas permeable lenses are made of a special silicone compound that allows oxygen to pass through. However, these lenses are rigid and generally less comfortable than standard soft contact lenses.
To increase comfort as much as possible, some eye doctors fit a gas-permeable lens over a soft silicone hydrogel lens. The soft lens acts as a cushion for the rigid lens and may decrease the discomfort of gas permeable lenses.
5. Hybrid Contact Lenses
These are combination lenses with a rigid center surrounded by a soft lens skirt. The rigid center vaults over the coned cornea and increases comfort for some keratoconus patients.
6. Scleral Lenses
The sclera is the white part of the eye. Traditional contact lenses, either hard or soft, cover only the iris or part of it. Scleral lenses have a large diameter that covers part of the sclera for better corneal stability.
Semi-scleral lenses cover less of the sclera; scleral lenses cover more. These rigid gas permeable lenses can vault over or cover the cornea’s irregular shape without putting pressure on the cone-shaped cornea.
The larger size allows scleral lenses to stay in place better than other gas-permeable lenses because they’re more resistant to slippage from blinking.
7. Prosthetic Lenses
People with advanced keratoconus will likely require more correction than a standard scleral lens can provide. Prosthetic lenses are custom-made using a process called Elevation Specific Technology.
This begins with an EyePrint impression giving precise and detailed information about the eye’s surface. An EyePrint lab then scans the impression with 3D technology.
A special machining system uses the scanned impression to make a custom contact lens as unique as a fingerprint.
Eye doctors offering this service must first be trained and certified to use the EyePrintPRO system.
8. Intacs
These are FDA-approved arc-shaped inserts placed surgically into the peripheral area of the cornea to reshape the front eye surface. Intacs are often necessary when eyeglasses and contact lenses fail.
Studies have shown that Intacs can help improve vision for keratoconus patients by as many as two lines on a standard eye chart. The Intacs procedure only takes about 10 minutes, and the inserts can be removed and exchanged if necessary.
9. Topography-guided Conductive Keratoplasty
Known as CK, this uses radio waves applied with a special device at the outside edges of the cornea’s periphery. This is guided by a computer-generated topographic map that helps to customize treatment for each patient.
10. Transplanting a Cornea
This is the last resort when all else fails. Called a penetrating keratoplasty or PK, a corneal transplant may improve vision for those who cannot tolerate rigid contact lenses. However, patients will still likely need glasses for clear vision.
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