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 Dallas 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.
When keratoconus become more severe (which usually takes a long time however on occasion can happen rather quickly), the cornea can begin to swell and form scar tissue. This scar tissue can result in even further visual distortion and blurred vision.
Treatment for Keratoconus
In the early stages of the disease, standard eyeglasses and soft contact lenses will usually correct the nearsightedness and astigmatism experienced by the patient. As the disease progresses however, glasses and soft contact lenses may no longer correct vision and soft lenses may become uncomfortable. This is when other forms of vision correction will be recommended.
Gas Permeable and Scleral Contact Lenses At the more advanced stage of keratoconus rigid gas permeable (RGP) contact lenses, scleral or semi-scleral lenses may be used for increased comfort and visual acuity. Since they are more rigid, RGP and scleral lenses are able to create a smooth, round shape around the cornea, creating a smoother surface for better vision. Scleral or semi-scleral lenses have a larger diameter which covers the entire cornea and reaches over into the white part of the eye, which is known as the sclera. Many patients find these more comfortable than regular RGPs and find that they move around less when the eyes move. The main disadvantage of these rigid lenses is that for some, they are somewhat less comfortable than soft lenses and they must be continually refit as the shape of the eye changes.
Whether it is glasses or contact lenses being used to correct vision, patients will likely have to undergo many tests and prescription changes as their vision needs change.
Intacs Intacs are small, surgically implanted plastic inserts which are placed on the cornea to flatten it back to shape. Usually they are able to restore clear vision, with the continued use of glasses. Intacs are often recommended when contact lenses and eyeglasses are no longer able to correct vision adequately. Intacs take about 10 minutes to insert and can delay the need for corneal transplant.
Corneal Crosslinking (CXL) In corneal crosslinking, a UV light and eye drops are used to strengthen and stiffen the cornea which helps to reduce bulging and restore the cornea to its natural shape.
Corneal Transplant When corneal scarring occurs and eyeglasses and contact lenses no longer help, doctors may suggest a corneal transplant to replace the corneal with healthy donor tissue to restore vision. Most patients will still require eyeglasses or contact lenses for clear vision following the transplant.
Keratoconus is a condition that requires ongoing treatment by a qualified eye doctor. If you or a loved one suffers from this disease make sure that you find an eye doctor that you like and trust to accompany you on this journey.
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Q&A for Keratoconus
What is Keratoconus?
Keratoconus is when the cornea pushes out, begins to be more “cone like,” and begins to thin at the apex of the cone. As the cornea begins to thin, it takes on a more cone-like conformation.
Are some people more likely to develop it?
Anyone can have the disease, however if you have a close family member with it, you are statistically more likely to develop it.
Excessive eye rubbing is one of the few known causal links for keratoconus, so we generally advise against it. The general saying is, “Not everyone who rubs their eye will get keratoconus, but everyone who has keratoconus has a history of eye rubbing.” Allergies are thought to play a role in the triggers to rub too hard to too frequently for some patients.
How would someone know if they have it?
Symptoms are typically visual distortion. Patients often first become aware when their vision changes very rapidly over a short period of time as the cornea begins to protrude and distort light.
How do you as a practice diagnose Keratoconus?
Retinoscopy is a simple early detection tool. The doctor uses a handheld device to shine a light inside the eye, and can see and evaluate the quality of the light as it passes through the cornea. Additionally, corneal topography can identify if the cornea is protruding abnormally. We use the gold standard of corneal topography called the Medmont E300 on all of our contact lens patients to map the shape of their cornea. There are also corneal findings linked to keratoconus, that can be seen under our slit lamp during a routine exam.
What consequences can occur if Keratoconus is left untreated?
At best, the patient might suffer with a very poor quality of vision… At worst, the cornea might protrude so far, and become so thin that it could perforate (pop) at which point, emergency surgery would be needed to salvage the eye.
How do you treat Keratoconus? Are there risks involved in the treatment?
The good news is that the treatment for keratoconus has come a long way! It used to be that the only way to “cure” it was to get a corneal transplant. Now, a transplant is considered to be a last resort reserved only for the patients who get dangerously close to perforation.
Here, as soon as keratoconus is detected, you will be referred to a corneal surgeon for a procedure known as corneal crosslinking to stabilize your cornea and prevent further progression. After recovery, you can be fitted for a special type of contact called a scleral contact.