Keratoconus: What Is It?
May. 12, 2019 | By Dr. Brill | In: Medical Eye Care
Before defining what keratoconus is, we need to describe how light travels through the eye. The first surface that light hits is the tear film. A clean and healthy tear film allows light to next travel through the cornea, which is a clear, dome-shaped structure that covers the colored part of the eye. The normal cornea has an aspherical shape, like an ellipse, to allow for a better, clearer image on the inside back part of the eye called the retina. If the cornea is scarred from moderate to advanced keratoconus, then light is distorted and cannot focus properly on the back of the eye due to a lot of light scatter.
Photo credit: Dr. Edward Boshnick (eyefreedom.com)
People who have distorted vision often are very sensitive to light. That distortion may even causes them to favor the better-seeing eye. When only one eye is being used, the fellow eye is being suppressed. The brain decides to favor the better-seeing eye so that double vision will not prevail. This also means that keratoconics will also lose their sense of depth perception because both eyes must be used equally in order to have 3D vision. By 3D vision, we don’t mean for 3D movies, but for seeing depth to help while driving and parking a car, playing sports, and having comfortable everyday vision.
Keratoconus describes the condition where the front of the eye is misshapen and actually takes on the contour of a cone. In other words, the front of the eye is pointy and not regular. Light passing through the conical part of the cornea is distorted and cannot be focused well with glasses. This can be very frustrating for people who need to see clearly out of both eyes. One of the first signs of keratoconus is blurred vision that is not well-corrected with spectacles. If you are one who rarely thinks that the glasses your get are accurate after going to several well-respected doctors and purchasing quality eyewear, ask them if you may have keratoconus.
How do I know if I have Keratoconus?
Most often, patients will be unaware that they have keratoconus. There is no pain or symptoms associated with this condition. Many patients with keratoconus tend to allergies and itchy eyes, as well as a clinically dry eye. A commonality among patients with keratoconus is that they are “eye rubbers”. This eye rubbing activity may seem normal and ordinary due to chronic allergies and symptoms of dry eye disease. It is thought that the rubbing activity may weaken the collagen structure of the eye to facilitate its shape change.
So, if your vision has been difficult to correct well with glasses and you find yourself constantly itching them, you need to be checked for keratoconus. Likewise, if you have seen several doctors who “just cannot get your prescription right”, think about getting checked for keratoconus.
Symptoms of Keratoconus
- Blurry vision not correctable by glasses
- Halos around lights
- Night vision difficulty and glare
- Doubling or overlapping of images
- Eyestrain and eye headaches
- Variable eyeglass prescriptions
- Itchy or dry eyes prompting eye rubbing
Methods of Layperson Diagnosis
There are several methods that doctors use to diagnose keratoconus. It could be as easy as having the patient look downwards and having the doctor carefully view the contour of the cornea as it interfaces with the lower eyelid. This is commonly referred to as having “Munson’s Sign.” You can do this at home with an observant assistant. No equipment is necessary.
Here is how to do this: have your assistant take photographs of the lower eyelid contours of several normal people with good vision. Do this by looking downwards while holding your upper eyelid against the upper brow bone. Have your other models do the same procedure. The keratoconic eye will have a relatively pointier contour to the apex of the cornea as it connects to the lower eyelid. Do you have a pointy cornea?
Now that you are an expert observer of corneal contour, try looking straight ahead and have someone take a side profile of the front of your eye with the highest magnification possible. Just looking at the side profile of the cornea will allow for a gross observation of a conically-shaped eye.
Methods of Professional Diagnosis
The absolutely best way to diagnosis keratoconus is by taking a photograph of the corneal topography of the cornea with an instrument cleverly enough called a corneal topographer. One of the best instruments used for diagnosis of the disease, as well as for custom-designing specialty contact lenses, is the Australian-made Medmont Topographer.
This is what Brill Eye Center uses to gain excellent sub-micron-level (a micron is one thousandth of a millimeter) accuracy. This also allows your contact lens doctor to quantify the level of distortion and the position of the conically-shaped portion of the cornea. Most often, the bulgy or pointy part of the defective cornea is in the lower portion. Picture a clockface. It will be located between 4 and 8 o’clock. If the pointiest contour of the cornea is dead-center, we often refer to it as an apical cone.
While we used to think that the incidence of keratoconus in the general population was one in 12,000, some expert researchers think it may be as low as one in 200. This change in thought process is due to the greater presence of topography measuring devices. Keratoconus tends to run in families. If there is a family history of keratoconus, it is wise to have every family member screened by topographical analysis. Short of doing this professional analysis, think about if you have a family member like “Uncle Joe, who never could see well.”
Can Keratoconus be prevented?
Unfortunately, there is no way to prevent keratoconus. If you have a family history of keratoconus, it would be very helpful to get your eyes screened early on in life by having your corneal topography analyzed. Of course, avoiding chronic eye-rubbing is important as well.
Allergies can now be addressed by special eyedrops that have a combination of an antihistamine and mast cell stabilizer in them. Also, autoimmune conditions like asthma often cause chronic eye rubbing and itching. Treating the source of the allergies may be one of the best ways to prevent eye rubbing and keratoconus. Prescription and non-prescription eye drops exist that can get rid of the itchy sensation in as little as 3 seconds. Some prescription eyedrops that are the most potent are Pazeo, Lastacaft, and Bepreve. Over-the-counter drops mostly contain the generic drug called ketotifen. Try to avoid the irritating preservative called benzylkonium chloride, abbreviated BAK.
While prevention of keratoconus is ideal, addressing early keratoconus by making a diagnosis in childhood is the next best thing. Corneal Crosslinking, described below, can be applied to slow the progression of corneal thinning and steepening, if found early enough.
At this point, all children should be screened by age 5, however, there is no international standard to encourage this professional activity.
How is it treated?
Common Keratoconus treatments
- Glasses, if possible, if vision can be corrected to 20/40 or better. Often, the prescription may not even be measurable by your doctor or be so strong to not be easily tolerated.
- Contact lenses: Soft, hybrid, smaller corneal gas permeable, larger scleral gas permeable, or piggyback lens designs (rigid over soft).
- Intacs, a semi-circular piece of plastic surgically implanted in the middle thickness of the cornea in an effort to flatten the steepened portion of the cornea.
- Corneal-Crosslinking or Holcomb C-3R, a chemical that is placed on the cornea and cured with UV light to stiffen the cornea
- Corneal transplants, a cookie cutter portion of a donor cornea that is donated after someone dies that has to be properly tissue-typed (like a blood transfusion) and transplanted into the recipient cornea from which the cookie-cutter “button” is received.
These modalities are not cures. The goal is to improve the level and quality of vision to lessen the effects on everyday activities of daily living.
Spectacle Correction of Keratoconus
The first line of defense for keratoconus is trying to get good glasses. It is common for the prescription for glasses to be difficult to determine for the optometrist because the vision is made blurry by the distorted shape of the eye. If the distorted portion of the cornea extends into the central pupillary zone, there will be more problems with correcting the eye for better vision.
The pupil is the dark circle surrounded by the colored part of the eye called the iris. Light travels through the pupil to get back to the retina to be processed by the brain. If light is uniform and not distorted as it travels through the pupil, vision will generally not be affected in the daytime but it will deteriorate at night when the pupils enlarge or dilate.
Glare, starbursts, streamers of light, curved lines that look like a “pincushion” or “barrel” distortion are not tolerated and make glasses impossible to wear and yield good vision. If pupils are only two or three millimeters in diameter, there is a lesser likelihood that central vision will be affected — at least for a while.
Larger pupils will be very deleterious to vision sooner, especially at night. If glasses are no longer tolerated because the prescription is too strong or clear visual acuity is not possible, the next step would be a trial or demonstration of specialty contact lenses.
The last decade has brought tremendous advancements in vision correction by means of contact lenses. This is due to the ability of computer-aided design (CAD) coupled with CNC (computer numeric controlled) three-axis laboratory manufacturing lathing techniques.
In other words, Brill Eye Center has the capability to analyze how a contact lens design will fit the diseased cornea with a virtual lens design in advance of actually fitting the lens. This is a very advanced use of available technology. Of course, analyzing the custom-made lenses on the diseased eye is the real acid-test, not to mention how well vision can be restored.
Four objectives for fitting contact lenses for patients with keratoconus are:
- Improved visual function to help manage activities of daily living
- Improved comfort that permits all day healthy wearability
- Good biocompatibility of the lens design to allow sufficient oxygen to the corneal surface and avoid further corneal tissue compromise
- Improved optics to mitigate the corneal surface irregularities from a keratoconus-induced misshapen eye or corneal scarring from permanent changes to the corneal collagen
Soft Lens Correction of Keratoconus
The purpose of wearing a contact lens for keratoconus would be to create a new regular front surface to the distorted cornea that will allow excellent correctible visual acuity.
Most often, better optics are achieved by creating a more spherical front surface to the eye. Soft lenses can be tried first due to the availability of disposable lenses or diagnostic lenses designed for fitting cones. Custom soft lenses for keratoconus are also an option. The lenses can be made of a breathable soft lens material that tends to be thicker, about the same thickness of the cornea, and have steeper fitting curves to parallel the pointier curves of the keratoconic eye.
There are several brands of specialty soft lenses that work well for many less-advanced keratoconic eyes. They can possibly offer greater comfort for patients who are intolerant of the more rigid lenses. They can correct for the increasing amounts of astigmatism (curvature difference on the cornea) and fit over the bulging keratoconic cornea. The center thickness may be designed to be about five times the center thickness of soft disposable lenses. This enhanced thickness profile will help offset the front surface irregularities that cause sources of glare referred to as higher order aberrations. Three of these brands are SoftK, NovaKone, and Kerasoft IC.
Corneal Gas Permeable Lenses
Rigid lenses are generally the best choice to create better optics of the cornea and mask a bulging, pointy, or distorted ocular surface. They have been the mainstay of keratoconus contact lens fitting for decades. Special designs have very steep back surface curves and aspheric optics in order to parallel the shape of the very curvy eyes.
Newer designs often have “relief” curves to allow lenses to vault the cornea, but are thinner and lighter at the same time. These lenses are usually smaller in diameter than soft lenses, typically, 8.0 to 11.5 mm in diameter. They are referred to as “corneal” lenses because they fit within the confines of the corneal diameter, which is usually about 12mm (about half of an inch), plus or minus one millimeter. The cone is often described by its location. They are usually referred to as upper (superior), central, apical “nipple” cones, versus the most common lower-placed (inferior) cones.
Scleral Keratoconus Lenses
It can be scientifically determined which type of rigid lenses to use for fitting over the cone by critically measuring a topographical “elevation” map. This eliminates guesswork of what will or will not work in a computer-aided design before any diagnostic fitting even occurs.
If the difference in the steepest elevation and the flattest elevation of the eye is too great, larger lenses will need to be used. These larger diameter lenses, called “scleral lenses” will be more stable on the eye by not moving very much upon blinking and offer excellent comfort.
While scleral lenses are measurably more difficult for doctors to design and fit to the patient, they also represent the upcoming trend of treatment.
FYI: Most doctors do not fit these lenses and do not have the experience to do it well or expeditiously.
The scleral lens is a “sealed system” with a layer of sterile saline filling the concavity of the lens and bridging over the cone with just the right amount of suction. Too tight and the eye will get red, angry and uncomfortable. If there is not enough suction, lenses can attract and trap cellular and other debris under the lenses causing decreased vision and behind-the-lens fogging.
Special handling is necessary to properly care for these more complex-designed lenses. Not every doctor is conversant with the scleral lens fitting techniques and processes. Demonstration lenses are often tried on the affected eye to see how the lenses fit before designing a more custom-fit lens. It may take several fitting sessions and reorders to get the fitting relationship just right for successful wear.
As seen on keratoconus internet support groups, patients are often frustrated by inexperienced providers, and are looking to invest in healthy scleral lens fit that allows great physiology and vision.
For the last 38 years, Brill Eye Center has proudly been serving Mission, KS and the surrounding communities with top-notch eye care solutions. And, for the last 10 years, we’ve been able to improve the lives our keratoconus patients with state-of-the-art scleral lens technologies.
Hybrid Keratoconus Lenses
Other lenses, called “hybrid lenses” have a central rigid lens and a surrounding soft lens “skirt.” Variations of these lenses have been around since the 1980s, the first of which were called Saturn lenses. The newest iterations of these lenses are under the SynergEyes brand name. Hybrid lenses offer the comfort of a soft lens with the optics of a rigid lens. The materials now have excellent oxygen permeability of both the rigid center and soft skirt to make for a healthier lens wearing environment.
Application and removal of SynergEyes lenses require special training and can be somewhat challenging for patients with less dexterous hands. Special contact lens solutions are indicated for hybrid lenses to ensure that the surfaces are properly cleaned and disinfected. This is also true for scleral lenses
Who do I see to get it diagnosed?
To get properly diagnosed, see your optometrist who has experience in diagnosing and fitting all of the various types and designs of lenses. Dr. Raymond Brill, OD, MBA, FAAO, FOAA has been fitting these special lenses for forty plus years, and has all of the diagnostic instrumentation and try-on lenses to expedite the fitting process to save you time and facilitate your success.
What types of invasive surgical treatments are there?
Other than contact lenses, you should know about a relatively new process in the U.S. called “corneal cross-linking” or Holcolm C-3R (done by Dr. Boxler-Wachler). This involves scraping the cornea (Epi-off) first or softening the cornea (Epi-on), then applying a solution of riboflavin. This is followed by a calibrated exposure to ultraviolet light several times. This process strengthens and stiffens the cornea so that it will not bend as much and limit the progression of the cone.
Candidates will generally be under the age of 35 years old. Keep in mind, this is not a treatment that eliminates keratoconus, or allows for better vision. Contact lenses will generally still need to be applied.
Another surgical treatment involves the implantation of semicircular rings into the middle of the cornea to stiffen the cornea and perhaps flatten the front curvature. Success varies with this technique and it makes fitting contact lenses more difficult. The intra-stromal corneal rings are called Intacs.
Lastly, if the cornea is too thin or perforates, a corneal transplant will need to be performed. The donor corneas come from recently deceased individuals who have donated them after a proper immunological tissue match. Contact lenses will eventually need to be fitted over the transplanted corneal tissue to create a smooth and regular surface and achieve good optics several weeks or months after the corneal transplants have healed adequately. Many fewer corneal transplants are being performed today due to the advent of sophisticated contact lens designs described above.
Where can I find more information about keratoconus?
The National Keratoconus Foundation is a great place to start. They offer unbiased information, support and advocacy for patients. Schedule your personalized keratoconus evaluation at Brill Eye Center today to get a more individualized discussion of what needs to be done, if anything, to permit improved vision and activities of daily living.
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