What is Keratoconus?
Keratoconus is a condition in which the shape of the cornea, which is usually round, is shaped like a rugby ball, developing a cone-shaped bulge, resulting in diminished vision. The symmetrical curvature of the cornea is distorted by an abnormal thinning of its central and inferior paracentral areas. It usually starts at around puberty and progresses slowly thereafter. The progression may be slow but continuous for years and then stabilise permanently, or periods of progression may alternate with periods during which it appears to have stopped.
It is uncommon for the condition to progress after the affected individual has attained the age of 40 years. The factors governing the progression and stabilisation of Keratoconus are not known. The condition is always bilateral and asymmetric – meaning that it affects both eyes, but not equally. Rubbing the eyes can cause the condition to evolve. The presenting symptom is impaired vision due to irregular, myopic astigmatism. Due to the asymmetrical nature of the condition, one eye is usually worse than the other, with higher astigmatism. Visual acuity is usually much better with hard contact lenses than with glasses, especially in more advanced stages of Keratoconus. Unfortunately, the wearing of contact lenses does not prevent the progression of the condition.
How can it be treated?
Keratoconus correction has always been a challenge, however, in the early stages, spectacles or soft contact lenses can correct the refractive error.
If Keratoconus progresses and there is a higher degree of irregular astigmatism, spectacles are at best, of limited use, and then hard contact lenses or special hybrid contact lenses become more effective in improving vision.
In advanced Keratoconus, contact lenses may become inadequate because they cannot be tolerated or they fail to bring about significant visual improvement because of stromal scarring or other pathological change. In cases like this, surgery is indicated. In advanced cases with severe corneal irregularity, corneal transplant may be the last surgical alternative.
1. Corneal Cross-linking with Riboflavin
A number of clinical studies have demonstrated that progressive Keratoconus and iatrogenic ectasia can be stabilised by corneal cross-linking. UV radiation in combination with Riboflavin initiates molecular cross-linking of corneal collagen. Thus progressive corneal thinning is slowed down or even stopped. Biomechanical strength of corneal tissue is improved. Femtosecond laser technology can be used to create an intra-stromal pocket within the cornea into which the Riboflavin is safely and effectively administered. Although this treatment is not aimed at improving vision, it stabilises the cornea and prevents further deterioration in vision. After the cross-linking treatment, many patients have improved vision with soft contact lenses and spectacles.
Trans-epithelial corneal cross-linking with ricrolin (without de-epitheliazation) is also available at the Tygervalley Eye & Laser Centre. This cross-linking technique allows treatment of younger patients (under the age of 10) and patients with thin corneas.
2. Kera/Ferrara Rings:
Kera/Ferrara rings are tiny plastic semicircular rings surgically implanted into the cornea to flatten the corneal surface and improve vision in patients with Keratoconus. Femtosecond laser technology is used to create the intra-corneal tunnel in which the rings are placed. These rings can improve soft contact lens wear in most patients. Implantation does not affect the central optic zone, does not involve the removal of any tissue, and can be reversed if vision changes, thus preserving all future options for vision correction or adjustment.
*Imagine your cornea as a tent with a curved top. If you push out the sides of the tent, the top flattens. Similarly, when Kera/Ferrara rings are placed in the sides of the cornea, they flatten it just enough to correct the problem.
3. Anterior Lamellar Keratoplasty (ALK)
In most Keratoconus cases, the innermost layer of the cornea – the endothelium, is healthy. However in full thickness corneal transplantation procedures (conventional corneal grafting surgery) this layer is also sacrificed and replaced with donor tissue. The body senses this layer as being foreign and attempts to reject this tissue. Hence post operative steroid medications are necessary for a long time post-operatively to prevent rejection of the corneal graft.
Deep anterior lamellar keratoplasty (DALK), is a newer method of corneal surgical procedure. It is a partial thickness graph that selectively removes the diseased anterior layers of the cornea and preserves the two healthy innermost layers, the endothelium and Descemet’s membrane. As the inner layers are retained the body does not recognize the donor tissue, hence there is less risk of rejection, and steroid medications need not be continued for a long duration.
4. Penetrating Keratoplasty (corneal transplant):
When the above mentioned treatments are not suitable for you, and a contact lens cannot be fitted satisfactorily despite all measures, the conical cornea must be replaced surgically. Penetrating Keratoplasty (Corneal transplantation or grafting) is an operation in which abnormal host tissue is replaced by donor corneal tissue. Using Femtosecond laser technology allows both the donor and recipient corneal tissue to be cut at precise depths and in various patterns. This customized technology is used in order to improve surgical outcomes and wound healing. Patients experience more rapid visual recovery and reduced degress of astigmatism as compared to conventional methods.
For more information on keratoconus surgery as well as our other eye laser procedures, contact us today.