Keratoconus is a rare eye disorder in humans that can occasionally lead to blindness but may significantly impair vision.
What is Keratoconus?
Keratoconus is a condition in which the normally round shape of the cornea becomes distorted, developing a protruding cone-like bulge that causes significant visual impairment. This distortion is similar to looking at a street sign through the window of your car during a heavy rainstorm. Typically, the distortion develops slowly and may progress to varying degrees, from moderate to severe. As keratoconus develops, the cornea becomes both bulging and thin, its pattern becomes irregular, and sometimes, scars may form.
Keratoconus is generally a treatable condition, but to understand what keratoconus is, it's necessary to first comprehend the structure and function of the cornea in the visual process.
The Cornea
The eye is enclosed within a white and tough outer layer called the sclera. The cornea is the transparent front part within this layer, allowing the light waves that we see to pass through as they enter the eye. The surface of the cornea is where light begins its journey into the eye. The cornea's role is to gather and focus visual images. Positioned at the front like a car's windshield, it's vulnerable to external elements.
The cornea is shaped with such precision that only the most expensive hand-crafted lenses can match its accuracy. Its curvature and structure are crucial for proper function, just as its transparency is important. If the surface or clarity of the cornea is damaged, vision is disrupted.
Despite appearing as a single transparent layer, the cornea is composed of five distinct tissue layers, each with a unique role. The thin outermost layer called the epithelium, acts as a barrier against corneal and eye infections. Damage to the epithelium can be a precursor to the penetration of infectious agents into the middle (stromal) layer of the cornea, composed of collagen fibers and proteins. The innermost layer, the endothelial cells, is responsible for maintaining corneal hydration and thickness.
While we can live with large blemishes on our skin without problems, except for cosmetic concerns, the cornea is different. Even a small scar can impair vision. Regardless of other functions of the eye, a scarred, cloudy, or distorted cornea will affect vision.
What Causes Keratoconus?
As previously explained, keratoconus is characterized by the bulging of the cornea, usually in a round shape, which results in visual distortion. The phenomenon of keratoconus has been recognized for over two hundred years, although it wasn't accurately described or distinguished from similar corneal problems until the mid-20th century.
The reasons for this condition are still unknown despite our prolonged familiarity with it. Over time, a substantial body of research has accumulated, proposing various theories.
One scientific perspective suggests that keratoconus is primarily developmental (genetic) in origin. This implies that it's a result of abnormal growth, a congenital defect in its essence. Another viewpoint considers keratoconus as a degenerative condition. A third hypothesis posits that keratoconus is secondary to another disease process. This idea arose from the fact that it can be found in children with Down syndrome or recurrent eye inflammations, often affecting both eyes.
The basis for the genetic theory of keratoconus is supported by research indicating that around 13% of treated individuals have family members who suffer from the disease. If there is no evidence of keratoconus appearing across several generations in the family, there is only a 1 in 10 chance that your offspring will suffer from some degree of keratoconus.
Who Is Affected by Keratoconus?
The true prevalence of keratoconus is not known. It is not considered one of the common eye diseases, but it is certainly not rare. An estimated one in every 2000 individuals in the general population is affected by this condition. It usually presents in young individuals during puberty or late teenage years. It is widespread across the globe without any distinct geographical, cultural, or societal pattern.
Symptoms and Signs
The initial symptom of keratoconus for a patient is blurred and distorted vision. In its early stages, this can be corrected with eyeglasses, which require frequent changes to address changes in short-sightedness and astigmatism. The process of thinning and corneal bulging tends to stabilize around age 40. Using corneal topography, a device that maps the cornea's surface, keratoconus can be diagnosed and the progression of the distortion tracked. To obtain accurate corneal topography, avoid wearing contact lenses for a week before the test. In some cases, the thinning process may rapidly progress, causing sudden blurring of vision in one eye, which will disappear within weeks or months. This phenomenon is called "acute hydrops" and is caused by sudden fluid accumulation in the stretched cornea. In advanced cases, localized scar tissue may develop around the corneal bulge, exacerbating the visual impairment.
How Is Keratoconus Treated?
The goal of treatment is to correct vision. In mild cases, this can be achieved using eyeglasses. However, most individuals with keratoconus require contact lenses to achieve satisfactory vision correction. In severe cases, corneal transplantation may become necessary.
Contact Lenses
As mentioned, in the early stages of keratoconus, eyeglasses can be used for short-sightedness and mild astigmatism correction. As the disease progresses, continuous thinning and corneal bulging create a distinct astigmatism. This shape cannot be corrected using eyeglasses and is often best managed with contact lenses. Various types of contact lenses have been developed to correct the different aspects of vision distortion related to keratoconus. The most common type is the "rigid gas permeable" (RGP) lens. These lenses have several qualities that make them ideal for keratoconus:
- They correct almost all forms of short-sightedness and astigmatism related to keratoconus.
- They allow the cornea to receive oxygen directly through the lens.
- They are easy to handle, remove, and clean.
- They can be precisely fitted to the unique shape of the affected eye.
Proper fitting of contact lenses for keratoconus requires significant expertise and care. It may involve trials and frequent lens changes due to subtle and unexpected changes in the corneal shape.
In addition to RGP lenses, there are other types of contact lenses available, such as custom soft lenses, hybrid lenses (rigid center with soft periphery), and scleral lenses. It's important to note that advancements and innovations in contact lens technology are ongoing. If you've tried a certain type of contact lens in the past and it didn't work well due to discomfort or inadequate vision correction, it's highly recommended to consult your eye doctor periodically to stay informed about the latest developments in keratoconus treatment.
It should be remembered that successful contact lens wear results in significant visual improvement for many individuals with keratoconus. Many have found ways to effectively incorporate contact lenses into their daily lives, pursuing education, career goals, sports activities, and leisure without significant disruption. Despite this, contact lenses do not cure keratoconus and do not alter the course of the disease.
Corneal Rings
When there is a developing intolerance to contact lenses or when contact lenses frequently dislocate, corneal ring implantation can be considered. The corneal ring is a piece of plastic in the shape of a semicircle that is implanted into the cornea through a small incision. Its purpose is to flatten the cornea so that the contact lens sits better on the cornea and doesn't fall off. Corneal rings assist in achieving this goal for some patients and also improve vision with glasses for a small subset of patients. The improvement in vision with glasses is marginal, and therefore, implanting rings solely to get rid of contact lenses is not recommended. Corneal rings are not intended to halt the progression of keratoconus.
Cross-Linking
The goal of treating patients with keratoconus is to improve visual acuity. In less severe cases, this can be achieved with glasses, and in more advanced cases, contact lenses are needed. When there is a developing intolerance to contact lenses or when contact lenses frequently dislocate, corneal ring implantation can be considered. The corneal ring is a piece of plastic in the shape of a semicircle that is implanted into the cornea through a small incision. Its purpose is to flatten the cornea so that the contact lens sits better on the cornea and doesn't fall off. In severe cases (around 20% of keratoconus patients), corneal transplantation may be necessary. Despite a success rate of 95% for corneal transplantation performed for keratoconus, this procedure carries serious risks, as do all surgeries. Even if corneal transplantation resolves the underlying irregularities of the corneal surface, glasses or contact lenses will generally be required for vision correction.
All of the above treatments are intended to improve visual acuity, but they do not halt the progression of keratoconus. Collagen cross-linking is the only treatment so far that aims to stop the progression of keratoconus. This method combines riboflavin (Vitamin B2) and ultraviolet A (UVA) radiation to strengthen the collagen fibers that make up most of the cornea's thickness. This innovative technique is still in the research stages. Published study results suggest that over approximately 7 years, keratoconus progression was halted in most cases after cross-linking treatment, and in some cases, corneal flattening occurred.
The treatment is performed in a surgical room under local anesthesia. The removal of the corneal epithelium, the outermost layer of cells, is followed by the application of riboflavin drops to the eye for several minutes. Subsequently, the eye is exposed to UVA light for 30 minutes. After the treatment, a soft contact lens is placed on the eye for 3 days. The improvement in visual acuity to a pre-operative level may take several weeks.
The lowest complication rate is high, and most complications are mild. In cases of complication following the treatment, such as corneal infection or herpes reactivation, additional antibiotic or antiviral treatment may be required. Minimal corneal haze may develop, disappearing after about 3 months.
We hope and believe that as a result of the treatment and the chemical change in the corneal structure, the progression of the disease will be halted.
Corneal Transplantation
Approximately 20% of keratoconus patients may require corneal transplantation. In this procedure, a large part of the keratoconus patient's central cornea is removed and replaced with a healthy cornea from a recently deceased donor. There are eye banks that specialize in preserving healthy corneas from donors and respond to requests from eye surgeons in need of these corneas. This is a highly organized and advanced system. Corneal transplantation surgeries are the most common and have a high success rate. The likelihood of rejection is lower than for any other transplanted organ, and lifelong immunosuppressive medications are not required due to the lack of blood supply to the cornea.
Despite a success rate of 95% for corneal transplantation performed as a treatment for keratoconus, this procedure carries serious risks, as do all surgeries. In cases where the graft does not succeed, additional transplants may succeed. Rare cases involve the recurrence of keratoconus in the transplanted cornea or complete loss of vision due to the surgery. Generally, the option of corneal transplantation is considered in cases where contact lenses cannot be fitted or do not sufficiently improve vision.
Even if a new corneal transplant resolves the underlying irregularities of the corneal surface, glasses or contact lenses will generally be required for vision correction. In many cases, hard contact lenses will be necessary to correct the corneal distortion that sometimes occurs following transplantation surgery, regardless of the surgeon's expertise.
What Is Involved in Corneal Transplantation?
Eye surgeries have reached an impressive level of success, efficiency, and relative comfort. Corneal transplantation surgery is the most successful among all transplant surgeries, and the techniques are continuously improving. Generally, the surgery is performed on an outpatient basis, under general or local anesthesia. Sometimes, a hospital stay for one night is recommended. After the surgery, the patient should be assisted in getting home and then maintain a calm lifestyle for several days. The pain or discomfort that most transplant recipients feel after the surgery is remarkably mild. The duration of absence from work varies greatly from person to person and depending on the type of work. Generally, individuals return to non-strenuous work after one or two weeks.
During the surgery, the surgeon uses a trephine, a high-tech device similar to a cookie cutter, to remove the distorted cornea of the recipient and cut a similar round piece from the donor cornea. The surgeon then places the donor corneal piece in the recipient's cornea and sutures them together. Throughout these actions, the surgeon uses surgical microscopes to closely monitor the process. The suture thread used for suturing is much finer than a hair, and a non-crossed eye may not even see it.
Usually, the bandages are removed a day after the surgery, but the vision will not yet be clear. It will take a few months for the vision to stabilize, and glasses or contact lenses can then be prescribed. The duration varies significantly from person to person, so the periods mentioned above should be seen as general frameworks.
Living with Keratoconus
In the end, people learn to live with keratoconus, whether surgery is needed or not. Individuals react differently to the knowledge that they have keratoconus, and group discussions often help to gain insight and confidence. Lack of knowledge often leads to fear. The best psychological remedy may be to share experiences with others who have undergone similar circumstances. In conversations with keratoconus patients, similar issues arise, but almost each person experiences unique challenges.
The common experience for all was, of course, vision deterioration or weakening in one or both eyes. Almost everyone reported experiences with contact lenses, ranging from complete satisfaction to discomfort, and recognizing their dependency on the proper functioning of their contact lenses.
Specific cases presented a rich variety of disease progression patterns. There are patients who, despite being diagnosed at a young age, still experience relatively mild limitations, and on the other hand, rare cases that included multiple surgeries and numerous eye doctors.
The results obtained from those who underwent corneal transplant surgeries are generally excellent. Most of the patients reported meeting with their eye doctors two or three times a year.
From a medical point of view, the most important thing is to maintain continuous contact with the eye doctor and to meticulously follow their instructions. From an emotional and psychological perspective, it's important to understand the nature of keratoconus, develop a positive attitude, learn to live with the condition, and freely discuss it with family members and friends. If possible, it's important to talk to others who suffer from keratoconus. Such conversations can be very beneficial.
Some keratoconus patients report severe visual disturbances due to the condition of the cornea. Despite this condition, these individuals have achieved significant accomplishments in their activities.
Understandably, some people keep their condition a secret, fearing it might hinder them from obtaining a job or promotion. However, it's important to emphasize that keratoconus shouldn't prevent you from achieving your goals. People who successfully manage their limitations due to keratoconus develop their own coping mechanisms. These include wearing eyeglasses while driving, having spare contact lenses, and planning trips in advance, even within the city, as reading street signs can often be a challenge. Taking time during the day to remove contact lenses and rest the eyes is essential.
You should react promptly to any change in your eye condition or vision. If you experience blurring, itching, irritation, tearing, or any discomfort, it's important to consult an eye doctor immediately. Such symptoms might indicate an issue with your contact lens tolerance or the need for re-fitting. Of course, you should also maintain regular eye care and avoid using any substances that you haven't received from your eye doctor. Women should be cautious when using makeup. Anyone with keratoconus must wear protective eyewear when swimming, gardening, or engaging in sports activities. If you have a relationship with another specialist doctor, such as an internist, it's important to inform them about your keratoconus as well.