What is keratoconus?
The cornea is the clear surface on the front of the eye and is critical for focusing light into the back of the eye where the light is captured and sent to the brain.
Instead of a smooth cornea, bulging from keratoconus causes a “cone” shaped cornea that distorts light as it enters the eye (above). In fact, in Greek Keratoconus literally means cornea, Kerato, that is cone shaped, Conus.
What are the symptoms of keratoconus?
Glare and halos around lights
Difficulty seeing at night
Eye irritation or headaches associated with eye pain
Increased sensitivity to bright light
Sudden worsening or clouding of vision
risk factors
Genetics. Patients with a family history of keratoconus or with certain systemic disorders, such as Down syndrome, are at a higher risk of developing keratoconus.
Chronic eye inflammation. Constant inflammation from allergies or irritants can contribute to the destruction of corneal tissue that may result in developing keratoconus.
Eye rubbing. Chronic eye rubbing is associated with developing keratoconus. It may also be a risk factor for disease progression.
Age. Keratoconus is often discovered in the teenage years. Generally, young patients with advanced keratoconus are more likely to need some form of surgical intervention as the disease progresses.
Associated conditions. Having certain conditions, such as retinitis pigmentosa, Down syndrome, Ehlers-Danlos syndrome, hay fever and asthma.
GRADING SCALE OF KERATOCONUS
Grading the types of keratoconus is largely based on where the area of bulging (or cone) is located on corneal topography.
Essentially, corneal topography measures the elevation of the cornea similar to geographic topography that shows hills and valleys on a map. Topography is color coded with cooler colors (blues) being flatter and hotter colors (orange and reds) showing steepening from Keratoconus.
A normal topography shows a very regular and uniform corneal surface without any significant steepening.
TYPES OF KERATOCONUS
Forme Fruste Keratoconus
The mildest form of keratoconus is called Forme Fruste Keratoconus. Forme Fruste Keratoconus is sub-clinical and symptom free.
With this form, the disease is present but either very early/mild or has already stopped progressing completely. Here you can see the red inferior and asymmetrical steepening present on the topography.
This form of Keratoconus is extremely common and no treatment for this condition is indicated.
Nipple Cone
A Nipple Cone is a small isolated area of bulging at (or very near) the center of the cornea. Here you can see the relatively small but very pronounced area of bulging in red.
Although the area of corneal bulging is small, nipple cones often cause substantial distortion of vision because the area of corneal bulging is very near or in the pupil. The pupil location is denoted with the black circle.
This type of Keratoconus needs correction through Specialty Contacts. Depending on severity, the ideal treatment options could be specialty small diameter hard lenses, hybrid lenses, or scleral contact lenses.
Oval Cone
An Oval Cone is the most common form of keratoconus we encounter. Here the area of bulging is much larger and is mostly commonly seen inferior and temporally (toward the ear) on the cornea. Often there is a sagging appearance to the corneal on general observation.
While the area of thinning and bulging is down on the cornea, the corneal distortion does extend into the center part of the cornea and vision will be substantially decreased with glasses and soft contact lenses.
This type of Keratoconus would be be corrected through the use of Scleral Contact Lenses or possibly a Hybrid Contact Lens.
Globus Cone
A Globus Cone is simply defined as expansive corneal thinning and bulging affecting over 75% of the cornea (as seen here). This is the most severe form of Keratoconus. Globus Cones are more likely than other types of Keratoconus to require a corneal transplant called a Penetrating Keratoplasty (PKP).
Due to the extensive area of thinning, this type of keratoconus is likely only correctable through a large diameter Scleral Contact Lens.
Severity of Keratoconus
Corneal Steepening
To grade Keratoconus by curvature, corneal topography is used to measure the absolute steepest part of the cornea at the height of the cone.
Mild Keratoconus = steepest corneal curvature of ≤ 48.00D
Moderate Keratoconus = steepest corneal curvature of 48.00D to 53.00D
Advanced Keratoconus = steepest corneal curvature of ≥ 53.00D
Corneal Thinning
The average corneal thickness is about 555 μm (or a little over half a millimeter). Thinning at the bulging cone can lead to corneal break down, scarring, loss of vision, and additional complications that can lead to a Penetrating Keratoplasty (corneal transplant). Therefore, corneal thinning is often measured for monitoring progression and staging of the disease.
Mild Keratoconus = Lowest corneal thickness of ≥ 500μm
Moderate Keratoconus = Lowest corneal thickness of 300μm – 500μm
Advanced Keratoconus = Lowest corneal thickness of ≤ 300μm
WHAT ARE THE TREATMENT OPTIONS FOR KERATOCONUS?
Corneal Crosslinking (clx)
Early detection of keratoconus is so important now that viable options are available aimed to stop progression. Corneal Cross Linking uses riboflavin (vitamin B2) and ultraviolet light to greatly strengthen and stabilize the collagen network of the cornea.
Numerous studies show that CXL successfully halts the progression and severe complications of Keratoconus by at least 93%!
Historically, about 12 – 20% of patients developed complications that required a corneal transplant. This surgery is known as a Penetrating Keratoplasty or PKP (right) and uses donor tissue to replace the thinned and scarred part of the cornea.
At Reimbold Eye Group, we preform annual topography screenings for keratoconus on every patient. With new treatments such as CLX available, we believe early detection is of the upmost importance.
Specialty contact lenses
The reason that Keratoconus causes blurry vision is because of the irregular corneal surface distorting incoming light. Glasses will only help to mild degree because light still needs to travel through the irregular cornea, after the glasses. Similarly, soft contact lenses will drape across the irregular surface and often times not greatly improve vision.
As a result, mainstay of correction for decades has been some form of hard contact lenses. Specialty hard lenses hold their shape as they sit on the front surface and cover over the irregular cornea. At the same time, the tears fill in the space between the lens and the bulging cornea forming a new smooth front surface. In essence, this creates a new, prosthetic cornea resulting in vastly improved quality of vision.
