Overview
Keratoconus occurs when your cornea — the clear, dome-shaped front surface of your eye — thins and gradually bulges outward into a cone shape.
Your cornea, the transparent outer lens of your eye, or “windshield,” typically has a dome shape that resembles a ball. The building occasionally loses its ability to maintain its round shape and protrudes outward in the shape of a cone. The term for this is keratoconus.
Collagen, a tiny protein fiber in your eye, aids in stabilizing your cornea. These fibers can’t maintain their form when they get weak. Your cornea gradually begins to resemble a cone.It happens when you don’t have enough protective antioxidants in your cornea. Its cells produce harmful byproducts, the same way a car puts out exhaust. Normally, antioxidants get rid of them and protect the collagen fibers. But if levels are low, the collagen weakens and the cornea bulges.
Causes
The specific cause of keratoconus is unknown. According to researchers, some people are more likely to be born with it.
Several things may have a link to the condition:
- Family history: If someone in your family has this condition, you have a greater chance of getting it yourself. If you have it, get your children’s eyes checked for signs starting around age 10.
- Age: It usually starts when you’re a teenager. But it might show up earlier in childhood or not until you’re 30. It can also affect people 40 and older, but that’s less common.
- Certain disorders: Studies have found a connection between keratoconus and systemic conditions such as Down syndrome, Ehlers-Danlos syndrome, osteogenesis imperfecta, and retinitis pigmentosa.
- Inflammation: Inflammation from things like allergies, asthma, or atopic eye disease can break down the tissue of the cornea.
- Eye rubbing: Rubbing your eyes hard over time can break down the cornea. It can also make keratoconus progress faster if you already have it.
- Race: One study of more than 16,000 people with keratoconus found that people who are Black or Latino are roughly 50% more likely to get it than people who are white.
Symptoms
Your vision is altered in two ways by keratoconus:
The smooth corneal surface becomes wavelike when the cornea transforms from a ball to a cone. Astigmatism that is irregular is what this is.
Your vision becomes more nearsighted as the front enlarges. This means that only up close can you see stuff clearly. Anything that is too far away appears blurry.
An eye doctor may spot the signs during an eye exam. You should also mention symptoms like:
- Double vision when looking with just one eye
- Objects both near and far that look blurry
- Bright lights that appear to have halos around them
- Light streaks
- Triple ghost images
- Blurry vision that makes it hard to drive
Risk factors
These factors can increase your chances of developing keratoconus:
- Having a family history of keratoconus
- Rubbing your eyes vigorously
- Having certain conditions, such as retinitis pigmentosa, Down syndrome, Ehlers-Danlos syndrome, hay fever and asthma
Complications
In some circumstances, your cornea may quickly enlarge, resulting in an abrupt reduction in vision and corneal scarring. This is brought on by a disorder that causes the cornea’s internal lining to tear, allowing fluid to enter the cornea (hydrops). The swelling typically goes down on its own, but a scar that impairs your eyesight may develop.
Your cornea may develop scars as a result of advanced keratoconus, especially in the areas where the cone is most noticeable. A corneal scar exacerbates vision issues and may necessitate corneal transplant surgery.
Diagnosis
Your eye doctor (ophthalmologist or optometrist) will examine your eyes and perform an eye exam in order to identify keratoconus. He or she might perform additional exams to get a better idea of your cornea’s shape. There are several tests to identify keratoconus.
- Eye refraction. In this test your eye doctor uses special equipment that measures your eyes to check for vision problems. He or she may ask you to look through a device that contains wheels of different lenses (phoropter) to help judge which combination gives you the sharpest vision. Some doctors may use a hand-held instrument (retinoscope) to evaluate your eyes.
- Slit-lamp examination. In this test your doctor directs a vertical beam of light on the surface of your eye and uses a low-powered microscope to view your eye. He or she evaluates the shape of your cornea and looks for other potential problems in your eye.
- Keratometry. In this test your eye doctor focuses a circle of light on your cornea and measures the reflection to determine the basic shape of your cornea.
- Computerized corneal mapping. Special photographic tests, such as corneal tomography and corneal topography, record images to create a detailed shape map of your cornea. Corneal tomography can also measure the thickness of your cornea. Corneal tomography can often detect early signs of keratoconus before the disease is visible by slit-lamp examination.
Treatment
The severity of your keratoconus and how rapidly it is progressing will determine how you are treated. In general, there are two ways to treat keratoconus: by reducing the disease’s progression and by enhancing your vision.
Corneal collagen cross-linking may be advised to slow or stop the progression of your keratoconus if it is already present. You might not require a corneal transplant in the future thanks to this more recent procedure. However, neither keratoconus nor vision are improved by this treatment.
The degree of keratoconus determines whether you can improve your vision. Contact lenses or eyeglasses can be used to treat mild to moderate keratoconus. The likelihood of this being a long-term remedy increases if your cornea becomes stable over time or as a result of cross-linking.
Some keratoconus patients experience advanced disease-related corneal scarring or difficulty wearing contact lenses. Surgery for cornea transplantation may be required in these patients.
Lenses
- Eyeglasses or soft contact lenses. Glasses or soft contact lenses can correct blurry or distorted vision in early keratoconus. But people frequently need to change their prescription for eyeglasses or contacts as the shape of their corneas change.
- Hard contact lenses. Hard (rigid, gas permeable) contact lenses are often the next step in treating more-advanced keratoconus. Hard lenses may feel uncomfortable at first, but many people adjust to wearing them and they can provide excellent vision. This type of lens can be made to fit your corneas.
- Piggyback lenses. If rigid lenses are uncomfortable, your doctor may recommend “piggybacking” a hard contact lens on top of a soft one.
- Hybrid lenses. These contact lenses have a rigid center with a softer ring around the outside for increased comfort. People who can’t tolerate hard contact lenses may prefer hybrid lenses.
- Scleral lenses. These lenses are useful for very irregular shape changes in your cornea in advanced keratoconus. Instead of resting on the cornea like traditional contact lenses do, scleral lenses sit on the white part of the eye (sclera) and vault over the cornea without touching it.
Surgery
If you have severe corneal thinning, corneal scarring, poor vision even with the strongest corrective lenses, or difficulty using any form of contact lenses, surgery may be necessary. Surgical alternatives include the following, depending on the location of the bulging cone and the seriousness of your condition:
- Penetrating keratoplasty. If you have corneal scarring or extreme thinning, you’ll likely need a cornea transplant (keratoplasty). Penetrating keratoplasty is a full-cornea transplant. In this procedure, doctors remove a full-thickness portion of your central cornea and replace it with donor tissue.
- Deep anterior lamellar keratoplasty (DALK). The DALK procedure preserves the inside lining of the cornea (endothelium). This helps avoid the rejection of this critical inside lining that can occur with a full-thickness transplant.
The success rate of cornea transplants for keratoconus is normally quite high, but graft rejection, blurred vision, infection, and astigmatism are all potential side effects. After receiving a corneal transplant, wearing hard contact lenses is typically more comfortable and is frequently used to treat astigmatism.