What is Keratoconus?
If you are thinking of having keratoconus surgery, here is some useful information to consider beforehand. The word keratoconus originates from two Greek words: kerato, meaning cornea, and konos, meaning cone. 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. Keratoconus is an inherited condition and it sometimes skips generations. Its onset generally occurs during puberty and it is often related to allergies. Rubbing the eyes can cause the condition to evolve, leading one to seek out keratoconus treatment. 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. In later stages of Keratoconus, progression occurs with thinning of the central cornea and further impairment of vision.
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. Although suggestions to the contrary appeared in earlier literature, contact lenses cannot stop, prevent or control the progression of Keratoconus.
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 contact lenses, like SoftPerm or Kerasoft contact lenses, become the keratoconus treatment of choice.
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. Femsosecond assisted 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. Although this treatment is not aimed at improving vision, it stabilises the cornea and prevents further deterioration in vision. After the cross-linking Keratoconus treatment, many patients have improved vision with soft contact lenses and spectacles.
— The procedure:
Topical anesthetic will be instilled in the eye to be treated. Your corneal thickness will be measured to make sure your cornea is thick enough for treatment. If it is too thin, it may be swollen with hypotonic solution. Femtosecond laser technology is used to create a 140 micron deep intra-stromal pocket within the cornea. This allows intra-corneal administration of Riboflavin. This novel epithelium-sparing method of intrastromal riboflavin instillation is safe and effective. Because epithelium is not removed, corneal biomechanics are not affected, helping corneal restructuring. Post-operative pain is significantly reduced and visual recovery is much more rapid than with conventional cross-linking treatment. There is also a lower incidence of corneal scars, epithelial defects and keratitis.
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. These rings can improve 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.
— The procedure:
If both eyes need Keratoconus surgery, they can be done simultaneously unless you or the surgeon chooses to do them separately. It is a very safe procedure. There are no restrictions on eating, drinking or medications before surgery but you should, however, avoid alcohol and medications that may cause drowsiness. No eye make-up is permitted on the day of surgery. When you arrive, drops will be installed to numb the eye completely and you are able to lie flat on a surgical table during the entire procedure. The eyelids are retracted with a speculum so that you cannot blink or move your eyelids – this is important as you will remain awake the entire time. Femtosecond laser technology is used to create the intra-corneal tunnel in which the rings are placed. A tiny opening (less than 2 mm) is made in the cornea, intersecting the intra-corneal tunnel, through which the two ring segments are then placed in the outer edge of the cornea. All in all, the procedure takes about 15 minutes per eye. While you will feel some pressure on your eye during the procedure, you won’t feel any pain. A clear shield will be put over the eye for protection after completion while you spend some time in the recovery room – and afterwards you can go home. You will not be able to drive yourself, so remember to come with someone that can drive you home.
3. Anterior Lamellar Keratoplasty (ALK)
In most Keratoconus cases, the innermost layer of the cornea - the endothelium, is healthy. (This is the functional layer of the cornea that contains cells that pump fluid out of the cornea and maintain its clarity.) 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. Long term use of steroids can predispose to complications such as cataract and glaucoma, besides the increased risk of secondary infection.
Deep anterior lamellar keratoplasty (DALK), is a newer method of corneal surgical procedure. It is a partial thickness grapht 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. Using Femtosecond laser 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 degrees of astigmatism as compared to conventional methods.
4. Penetrating Keratoplasty (corneal transplant):
When the above mentioned treatment is not suitable for you, and a contact lens cannot be fitted satisfactorily despite all measures, the conical cornea must be replaced surgically. Keratoplasty (Corneal transplantation or grafting) is an operation in which abnormal host tissue is replaced by donor corneal tissue. Penetrating Keratoplasty is the procedure of choice, and virtually all authorities cite success rates greater than 90%. The donor tissue is fixated onto the host by means of multiple interrupted sutures.
For more information on keratoconus surgery as well as our other eye laser procedures, contact us today.