Keratoconus
What is keratoconus?
Keratoconus is a non-inflammatory, progressive disorder of the cornea. The cornea is the transparent front surface of the eye that provides most of the eyes optical power. Together with the lens, the cornea refracts light, and as a result helps the eye to focus. With keratoconus, the cornea becomes thinner and irregular in shape. The diseased area bulges outwards causing an increase in myopia (short-sightedness) and astigmatism (abnormal corneal curvature) leading to poor vision. Symptoms include blurred vision, distortion, glare and possibly double vision. Frequent changes in spectacle prescription may be noticed. Keratoconus usually starts around puberty with a slow progression; however the rate of progression varies between patients. It usually affects both eyes but one eye may be affected more than the other.
How is it diagnosed?
Most cases of keratoconus are detected during an eye examination. There are visible signs in the cornea and these can be seen with a slit-lamp (a type of microscope). A scan of the eye with a corneal topographer (a device that measures the curvature of the cornea) is often used in the diagnosis of the disease and to monitor the disease progression.
How many people are affected?
Keratoconus is a rare condition. The number of patients affected varies between 1 in 3,000 and 1 in 10,000 depending on geographic location.
What causes keratoconus?
The cause is unknown. However keratoconus has both systemic and ocular associations. Some of the systemic associations include Downs, Turner, Ehlers-Danlos and Marfan syndromes, atopy, osteogenesis imperfecta and mitral valve prolapse. Ocular associations include vernal keratoconjunctivitis, blue sclera, aniridia, ectopia lentis, Leber congenital amaurosis and retinitis pigmentosa.
What are the treatments available?
- Spectacles and soft contact lenses:
At the very early stages of the condition, spectacles or soft contact lenses may correct the induced myopia and astigmatism. However small changes in the disease will have a dramatic effect on your spectacle prescription. - Rigid contact lenses:
As the condition progresses and the cornea continues to thin and change shape, rigid contact lenses can be used to correct the vision more adequately. These contact lenses must be carefully fitted and require frequent checkups. Lens changes may be required to maintain good vision. Unfortunately contact lenses do not stop nor slow the progression of the disease. - Corneal collagen cross linking with riboflavin (C3-R®):
The cornea is made of collagen (connective tissue) and in keratoconus the anchors between collagen fibres are weak. This treatment strengthens the collagen structure in the cornea preventing the cornea from bulging out. The treatment is relatively non-invasive and involves application of a custom-made riboflavin eye drop and then exposure of the eye to UV light. The result is increased cross linking of the collagen fibres in the cornea. - Intrastromal corneal rings (Intacs™):
Intacs prescription inserts are particularly useful for patients who are contact lens intolerant or to defer the need for corneal graft/transplant surgery. It is a good surgical option as it has a lower rate of complications compared with corneal transplant surgery. The corneal implants are flexible, crescent-shaped rings that are made of PMMA (polymethylmethacrylate). Placement around the periphery (sides) of the cornea causes gentle re-shaping and flattening of the central cornea. The surgical procedure is usually preformed under local anaesthesia but this depends on the patient. There are various implants available with a range of thicknesses for different degrees of correction. An incision is made in the cornea with a special probe or a laser to create a channel and the plastic implants are then inserted into the channels. Some patients may require contact lenses following this surgery; however the tolerance to the lenses should be better. The implants can be removed or exchanged if necessary without affecting the central cornea. The Intacs cannot be felt, are no more visible than a contact lens and require no maintenance. Based on the results of a large scale European study, Intacs received regulatory approval (CE Mark) for use in the treatment of keratoconus. They are supported by more than ten years of clinical studies and have received NICE approval in the UK and FDA approval in the US.
C3-R treatments can be combined with Intacs to flatten the cornea more so than with Intacs alone. The C3-R treatment aims to stabilize keratoconus from progression and the Intacs reverse the keratoconus steepening that has already occurred. - Keratoplasty:
In approximately 10%-20% of keratoconus patients the cornea may become extremely steep, thin and irregular and the vision cannot be improved sufficiently with the above techniques. In these severe cases, a corneal transplant may be required. This is a surgical procedure that replaces the diseased cornea with healthy donor tissue. Where previously keratoplasty was carried out as a full thickness corneal transplant, where possible the endothelial surface is retained and only the anterior (front) surface of the cornea is replaced as a lamellar or deep lamellar graft. Visual recovery after a full thickness transplant takes a long time and complications such as rejection can occur. Lamellar grafts have quicker visual recovery times but with either operation there is a significant possibility that the eye may still need to be fitted with a contact lens.
For more information regarding keratoconus:
UK Keratoconus Self Help and Support Group
The National Keratoconus Foundation
The Keratoconus Center
References:
Mencucci, R., Mazzotta, C., Rossi, F., Ponchietti, C., Pini, R., Baiocchi, S., Caporossi, A. and Menchini, U., 2007. Riboflavin and ultraviolet A collagen crosslinking: in vivo thermographic analysis of the corneal surface. Journal of Cataract & Refractive Surgery, 33 (6), 1005-8. Wollensak, G., Aurich, H., Pham, D.T. and Wirbelauer, C., 2007. Hydration behavior of porcine cornea crosslinked with riboflavin and ultraviolet A. Journal of Cataract & Refractive Surgery, 33 (3), 516-21. Kymionis, G. and Portaliou, D., 2007. Corneal crosslinking with riboflavin and UVA for the treatment of keratoconus. Journal of Cataract & Refractive Surgery, 33 (7), 1143-4. Colin, J., 2006. European clinical evaluation: use of Intacs for the treatment of keratoconus. Journal of Cataract & Refractive Surgery, 32, 747-755. Hustler, A., Manna, A., Morris, S., Obi, A. and Horgan, S., 2007. Intacs for the correction of keratoconus.Journal of Cataract and Refractive Surgery, 33 (8),1354. Rabinowitz, Y.S., 2007. Intacs for keratoconus. Current Opinion in Ophthalmology, 18 (4), 279-283. Kymionis, G.D., Siganos, C.S., Tsiklis, N.S., Anastasakis, A., Yoo, S.H., Pallikaris, A.I., Astyrakakis, N. and Pallikaris, I.G., 2007 Long-term Follow-up of Intacs in Keratoconus. American Journal of Ophthalmology, 143 (2) 236-244. Mohammadpour, M., 2007. Penetrating Keratoplasty for Keratoconus. Ophthalmology, 114 (10) 1952. Paula Grigorian A., 2007. Extended long-term outcomes of penetrating keratoplasty for keratoconus. Evidence-Based Ophthalmology,8 (1) 12-13. Watson SL, Ramsay A, Dart JK, Bunce C, Craig E. Comparison of deep lamellar keratoplasty and penetrating keratoplasty in patients with keratoconus. Ophthalmology. 2004 Sep;111(9):1676-82.
