WHAT IS KERATOCONUS
AND WHAT ARE THE TREATMENT OPTIONS?
Keratoconus is an irregular protrusion of the cornea, the clear surface over the colored part of the eye. It is similar, structurally, to the crystal of a watch. If this crystal or windowpane is not smooth, the light will not bend evenly and an irregular image will be formed. Like looking through a bumpy piece of glass.
Keratoconus is a slowly progressive condition often presenting in the teen or early twenties with decreased vision or visual distortion. This condition is typically not associated with redness, inflammation or other “acute” symptoms and therefore may go undetected for long periods of time. Over 90% of patients have involvement of both eyes, though it is not unusual for there to be asymmetric changes, with one eye being more involved than the other. In most cases the cornea is the only part of the eye that is abnormal. Family history of keratoconus is seen occasionally.
During the early stages of this disease, vision may still be correctable to 20/20 with glasses. The only clue to a keratoconus diagnosis may be from corneal measurements or a corneal topography map (see maps to the right). A topographical map of the cornea will show the high and low spots on the cornea, much like a topographical map of the earth will show the mountains and oceans.
As this disease progresses, vision will no longer be correctable with glasses. Iron will deposit around the base of the protrusion. The tissue will thin and a Vogt’s Striaes may develop (photo 2 below). In severe cases, a temporary painful condition called acute hydrops (see photo left) may occur when water rushes into the thinned area of the cornea. This can lead to severe scarring (photo 1 below). Corneal transplant or penetrating keratoplasty surgery should be considered if other treatment methods fail.
About 1/ 2000 people will develop keratoconus. Most people will have a mild or moderate form of the disease. Less than 10% of keratoconics will develop the most severe form. It typically is diagnosed in the late teens or twenties. However, many people have been diagnosed in their mid to late thirties; this is usually a more mild form of the disease. It is common for one eye to precede faster than the other and the eyes may go for long periods of time without any change and then change dramatically over a period of months.
What is the cause of Keratoconus?
The cause of Keratoconus is unknown. Certain allergic and arthritic disorders, Down’s syndrome, chronic eye rubbing and contact lens wear have occasionally been associated.
What are the symptoms of Keratoconus?
The typical patient with undiagnosed keratoconus complains of deteriorating vision, usually in one eye first, both at distance and near. Near visual acuity may improve if the patient squints or holds printed material closer. Keratoconus patients often report multiple images, or ghosting of images and often relate a history of frequent refractive correction changes without much improvement in visual acuity. Patients may also report irritating symptoms such as intolerance to glare, photophobia and a recurrent foreign body sensation.
Even with appropriate contact lens correction, keratoconus patients often report fluctuating vision throughout the day and from day to day, although the measurements of visual acuity in keratoconus patients are highly repeatable.
The treatment approach to keratoconus follows an orderly progression from glasses to contact lenses to corneal transplantation. Glasses are an effective means of correction mild keratoconus. As the cornea steepens and becomes more irregular, glasses are no longer capable of providing adequate visual improvement. Corneal transplant surgery is indicated when a patient cannot wear contact lenses for an acceptable period of time or when the vision, even with contacts, is unsatisfactory. Over 90% of corneal transplants are successful with the majority of patients obtaining vision of 20/40 or better afterwards with either glasses or contact lenses.
A gas permeable contact lens is the most highly effective way to manage keratoconus and 90% of all cases can be managed this way indefinitely. If the cornea becomes too scarred or painful, a corneal transplant may be necessary.
Most mild cases can be treated with glasses and or gas permeable contact lenses. In more advanced cases the cornea more distorted and specifically designed keratoconic contact lenses become necessary. Even though Keratoconus does not cause blindness most patients go on to needing contact lenses. Less than 10% of patients will require a corneal transplant.
The use of gas permeable contact lenses has been the mainstay of the optical management of keratoconus. These lenses, manufactured in a large variety of unique designs, provide a regular surface over the cornea to neutralize the distortion brought on by the irregular cornea. No one design is best for every type of keratoconus. Since each lens design has its own unique characteristics, the practitioner needs to carefully evaluates the needs of the individual and find the lens that offers the best combination of visual acuity, comfort and corneal health.
Rigid lens fitting in keratoconic eyes is however, by no means simple. Numerous lenses are often required, fitting a keratoconic eye is an art as much as a science.
Normal design Keratoconic lenses
- Standard rigid lens designs are the simplest fitting choices and achieve their best level of success in early or mild KC. They are generally spherical in curvature and can achieve excellent fitting profiles with sharp clear visual results.
- Aspheric lens designs gradually flatten from the center toward the periphery, approximating the steep cone vs. flat periphery curvature relationship seen in keratoconus. These designs are indicated for small to moderate nipple cones. The goal of this lens is to vault the apex of the cone, or lightly touch it, and align the more normal peripheral cornea. Because the nature of an aspheric lens allows for plus power in the periphery, presbyopic keratoconics may find this lens preferable if the fit is acceptable. The lens needs to center for the optics to work.
Specialty design keratoconic lenses
- Epicon contact lens developed for Keratoconus and difficult to fit patients!
NOTICE: AS OF 07-12-02 SPECIALTY ULTRAVISION, THE COMPANY THAT MAKES THE EPICON LENS HAS GONE OUT OF BUSINESS. I DO NOT KNOW THE FUTURE OF THIS LENS AT THIS TIME BUT WILL KEEP YOU POSTED AS MORE INFORMATION BECOMES AVAILABLE.
- Rose K Keratoconic lens: Rose K lens is probably the most widely fitted keratoconus lens worldwide and achieves an 85% first fit success in the UK. The Rose K lens design is a fully flexible lens that works well on early to advanced keratoconus patients. Complex lens geometry, combined with the enhanced material benefits of Boston ES™, makes the Rose K lens the good fit enhancing patient comfort and visual acuity. Multiple parameters make fitting the Rose K lens possible for most keratoconic eyes.
- McGuire lens system: This is an aspheric lens design specifically set up to put minimal pressure on the central cone by vaulting it and distributing the bearing pressure to the more healthy peripheral cornea.
- Harrison Keratoconus: The newest addition to the Flexlens Keratoconus soft lens system, Harrison Keratoconus Lenses provide the design features of rigid keratoconus lenses and the other benefits.
- Tricurve Keratoconus lens: This lens is a soft contact lens designed with a thick center that creates more rigidity to maintain visual acuity.
- Piggyback Lens System: This lens is a two lens system: a soft lens that rests on the cornea, with a center area hollowed out to accommodate a small gas perm lens. This design is an attempt to ensure centration of the rigid lens over the central cornea and maintain a comfort level similar to a soft lens.
- Menicon Decentered OZ design: This lens has four spherical curves on the back surface of the lens with the optical zone decentered approximately 1mm. This is a good design for a low, sagging cone.
- Super Nova KC, by Innovations In Sight, Inc. is a soft, tri-curve lens design with a thick center that allows the lens to maintain its shape on the irregular corneal surface.
- Computer assisted contact lens: These designs are available from some laboratories. Because they are designed from corneal topography, and the keratoconic cornea can have changes in curvature that are too detailed for the corneal map to reveal, this type of design may or may not work when the lens is placed on the eye and interacts with the ocular environment.
CORNEAL TRANSPLANT or PENETRATING KERATOPLASTY
A corneal transplant may be needed when vision cannot be corrected satisfactorily using other procedures such as contact lenses and glasses, or if painful swelling cannot be relieved by medication. When the cornea becomes “opaque” or gray/white (see right photo) from disease or injury or painful from swelling or blisters, it no longer functions as the “clear window” of the eye. It then acts more like a “soapy” window which you cannot clearly see through. Even if the rest of the eye is healthy, a cloudy cornea will obstruct clear vision. Of all the transplant surgery done today (hearts, lungs, kidneys, etc.) corneal transplants are by far the most common and successful.
Once you and your eye care provider has decided a corneal transplant is necessary, your name is put on a waiting list for a donor cornea, usually this wait is short. Most eye banks are able to provide tissue for transplant surgery scheduled in advance for a specific day.
Before a donor cornea is released for transplant, the eye bank tests the human donor for clarity and for the viruses that cause Herpes Simplex and AIDS. Your surgeon may request that you have a physical examination and other special tests prior to surgery. If you usually take medications, ask your surgeon if you should continue them.
A corneal transplant, also known as a corneal graft, or as a penetrating keratoplasty, involves the removal of the central portion called a button (see right photo) of the diseased cornea and replacing it with clear healthy donor button. The donor cornea button is sewed into the defect created by removal of the diseased cornea. If cataracts are present, it is removed at this time. Tiny hair-thin sutures or stitches are used to anchor the graft to the host tissue (see sequence below).
The surgery itself is painless and usually done on an outpatient basis. The operating time is approximately 60-90 minutes, followed by a short recovery time. In most cases you will be allowed to go home soon afterward.
Recovery following the transplant:
The postoperative recovery is a long one, but in most cases, resumption of normal activities may occur soon after surgery with some reasonable limitations. For example, lifting heavy objects or strenuous exercise must be avoided until directed otherwise by the physician. Until the eye has healed, glasses or an eye shield must be worn to protect the eye. The sutures used to sew the donor cornea in place are barely visible and do not cause pain. It is normal for the eye to feel scratchy or irritated for the first few days following surgery. As the cornea heals, some of the stitches used to sew the donor tissue into place are removed. This can be done quite easily in the doctor’s office.
The final improvement in vision is gradual and occurs six to twelve months post-operatively. Once the cornea stabilizes, improved vision is usually enjoyed. The results and success in restoring vision usually depend more on the state of the original disease than the actual surgical manipulation. In quantitative terms success rates vary from 90-95 percent.
In spite of the most advanced surgical techniques and the most expert surgeon you can choose, complications can and do occur. The most serious complications such as loss of vision or the eye itself are uncommon. The lesser complications are usually treatable.