Keratoconus and the Human Eye
Keratoconus is a degenerative disease occurring as a result of the congenitally weak cornea, which, usually in puberty, becomes more progressively curved than usual. Over time this brings to simultaneous corneal thinning and steepening, increase in diopter – especially astigmatism, and decreased visual acuity.
In the beginning, wearing eyeglasses enables relatively good vision, whereas in progressive stages due to the irregular change of corneal shape, there is a need to wear gas permeable or conventional hard lenses. Some 20% of patients will need cornea transplants (keratoplasty) to form the normally shaped cornea and regain the possibility of solid vision with glasses or contact lenses.
What Is Keratoconus?
Kerаtoconus is a progressive disease of the cornea on both eyes but usually affecting one more than the other. Keratoconus is the weakening of collagen tissues that make up the cornea. The weakening of the cross-links between collagen molecules leads to the deformation of the corneal surface. It thins and bulges outward into a cone shape. Eyesight worsens – firstly, as a result of irregular astigmatism and myopia (short-sightedness), and secondly because of corneal scars.
A healthy cornea has a smooth dome shape. In the case of keratoconus, the cornea is of bad quality and its structure simply isn’t strong enough, so it yields slowly and bulges into the shape of a cone. This eye condition is called keratoconus.
What Causes Kerаtoconus?
The cause of keratoconus is unknown but doctors believe it is a genetic weakness of the collagen protein, the main structural component of the cornea. Some studies indicate that keratoconus affects a few people within a family, and it happens more often to people with certain health problems, especially allergies. Chronic eye rubbing can certainly worsen and, in cases of a strong allergy, even cause keratoconus.
Keratoconus usually occurs in the teenage period, but it can also start in childhood or before the age of 30. Also, an interesting fact is that the progression of keratoconus stops around the age of 35, except in rare cases of marginal pellucid degeneration.
A person with keratoconus may not notice that his eyesight slowly worsens because it usually starts on one eye, whereas the other still unaffected eye functions completely normally. Most people suffer from keratoconus on both eyes, but not always with the same intensity.
Can Kerаtoconus Impair Vision?
Changes in the shape of the cornea worsen eye acuity, so people wear glasses or contact lenses to achieve clear vision. In worst cases, when the cornea is completely distorted and bulges out, the doctor does a cornea transplant, which is the only way to help the patient regain vision. Luckily, that is much rarer – about 20% of the patients can expect such a decline. Usually, these are patients whose keratoconus started earlier, even before puberty.
Keratoconus can be dangerous if laser correction of vision is performed – either LASIK or PRK. The cornea of the diseased eye is not strong enough to undergo laser treatment, so even stable non-progressive keratoconus can be disrupted with such additional thinning, which brings to galloping progression of the disease and often to cornea transplant! For this reason, persons with keratoconus are not good candidates for laser vision correction.
How Is Keratoconus Diagnosed?
Keratoconus is diagnosed with a thorough eye examination and talk to the patient. The symptoms indicating keratoconus are: often change of glasses, double vision in one eye, sensitivity to light, halos, blurred vision, and bad night vision.
To diagnose keratoconus, the doctor measures corneal curvature and thickness using topography, tomography, and pachymetry of the cornea. Corneal topography can display even discrete changes in the initial bulging of the posterior corneal surface before the disease progresses, in other words – before thinning and bulging of the anterior corneal surface.
A doctor diagnoses the condition after a full eye examination and talks regarding medical history and symptoms. It is also advisable that all close and distant relatives examine the risky age, so the doctor can recognize and even treat possible keratoconus on time.
How Is Kerаtoconus Treated?
Only a doctor with extensive experience in the treatment of such ocular diseases (the so-called anterior segment diseases) can recommend the right treatment for the patient’s keratoconus. The treatment consists of two levels which are applied simultaneously: first, monitor the corneal structure and shape, as well as to stiffen it with corneal collagen cross-linking (CXL) in case of keratoconus progression. Second is an optical correction, which is the improvement of better vision with some optical aids.
Usually, people start with glasses with cylinders. If these glasses do not provide adequate vision, the doctor suggests gas permeable or scleral contact lenses. If the disease does not progress, surgery isn’t necessary except in case of inadequate vision acuity with any optical aids.
If optical aids don’t work, once the cornea has already been treated by CXL, it is possible to try with limited topography-guided laser treatment to slightly regularize the corneal surface (topo-guided PRK). As a last resort, the doctor can choose cornea transplant (keratoplasty), more specifically Deep Anterior Lamellar Keratoplasty (DALK) or perforating keratoplasty (in which the entire thickness of the cornea is removed and replaced by transparent corneal tissue).