Keratoconus is a congenital disease of the cornea (autosomal dominant or auosomal recessive) and it belongs to the large group of corneal dystrophies (hereditary determined pathological changes of the cornea). The disease is characterised by a thinning and conuslike protrusion of the cornea due to alterations in the corneal structure. At first, the protrusion occurs in the inferior parts but later it affects also the central part of the cornea.
Keratoconus mostly happens to be bilateral but often the progression is asymmetrical. First symptoms generally start during puberty or early adolescence. In most cases patients realise a decrease in vision, or an increasing myopia with a significant progression of astigmatism can be found. The incidence of keratoconus in the general population is about 1 in 2000.
When examined under / with mangnification (so called slit lamp examination) the disease shows specific and typical changes. There is an increase in iron precipitations coming from the tear film (Fleischer's ring). Further advanced cases show a visible thinning of the inferior third of the cornea and so called Voigt's striae. Due to an increased content of water there can be opacifications of the corneal stroma which are associated with a significant drop in visual acuity.
In far progressed / advanced cases one can even see the conuslike protrusion of the cornea with the naked eye. (see above)
Other equipment such as corneal topography (visualisation of the corneal surface and measurement of curvature and refractive power of different parts of the cornea) can be used to diagnose early cases and, during follow up, can help to measure / estimate a possible progression.
It has to be said that the prognosis can vary a lot. At all times the progression of the disease can stop spontaneously. And if there is a progression the speed of a possible worsening is different in each patient. Everything is possible from quick progression already in early adolescence to a slow development which up to a high age doesn't lead to any significant symptoms.
There is no cure in the classic sense since the disease is some kind of "stuck in our gens". However, as mentioned above, a spontaneous stop of progression is possible at any time. In progressing / advancing cases rigid contact lenses can improve visual acuity, yet they can not stop the process.
Even a few years ago, the only therapeutic option for advanced cases with significant reduction of visual acuity was the transfer of corneal tissue (penetrating keratoplasty) to achieve a better vision.
Recently a new procedure has been developed at our hospital which is supposed to stop the progression of keratoconus. This procedure is called Cornea Cross Linking and is performed since 1999 as part of a clinical trial / study (approved by the ethic committee). It usually is performed as day surgery.
The aim of the treatment is to stabilise the cornea. The main part of the corneal tissue (stroma) is built from single collagen fibres which are linked /connected. With this specific treatment of the corneal stroma (removing of the superior protective layer, application of the photosensitizer Riboflavin (vitamin B2) and 30 min radiation of the corneal tissue with UVA light) further links between the collagen fibers can be induced, so called cross links. Therefore the single fibres form a "denser network" which leads to an increase in the overall stability of the cornea.
After in the meantime more than 3 ½ years, our results show that none of the treated patients showed any more progression of keratoconus within that time.
Due to the newness of the procedure there are no long term (10 or 15 year) results yet. At this moment in time, however, there are no clues for possible late complications or unwanted side effects. Therefore we are optimistic that - as long as a keratoconus is diagnosed early enough - a stabilisation of clinical findings and visual acuity can be achieved without a corneal transplant.
Keratoconus is a mostly bilateral degeneration which leads to a conuslike protrusion of the cornea. In the early 19th century it was named by Mr. Ammon. The disease is characterised by a progressive thinning of the cornea, Voigt's striae (vertical lines) and ruptures of Descemet- as well as Bowman membrane. Roughly 21% of all patients will eventually need a cornea transplant. The cause of the disease is still unknown - according to M. Kohlhaas (Dresden). Enzyme variations in the epithelium with an increased expression of lysosomal and proteolytic enzyms and changes in the stromal matrix (imbalance between keratan- and dermatansulfat) are discussed.
The incidence of keratoconus is about 1/2000. The ectasia generally starts during puberty. A genetic predisposition is very likely. The amount of family run diseases varies in literature between 5% and 20%. The hereditary pattern can be autosomal dominant as well as autosomal recessive. Various ocular and non-ocular disorders can be combined with keratoconus, i.e. atopic dermatitis and keratitis, keratoconjunctivitis vernalis (up to 35%), Down Syndrome (with an incidence of 5-15%) and Ehlers-Danlos-Syndrome.
Hints for a keratoconus: frequent changes of refraction in patients history (increase in myopia and astigmatism), distorted light reflex during sciascopy and the slit lamp findings of an inferiorly located apex of the cone and a beginning irregular astigmatism.
Treatment options include glasses, rotation symmetrical or not rotation symmetrical contact lenses, epikeratophaky (no used anymore), lamellar and penetrating keratoplasty, so called intacs (intracorneal ring segments) and collagen cross linking with Riboflavin and UVA light. The treatment of keratoconus with collagen cross linking is based on a significant stiffening of the corneal stroma due to photochemical cross linking of the collagen fibres. This procedure is performed under topical anaesthesia. After an epithelium abrasio, Riboflavin (vitamin B) is applied to the corneal surface and it is exposed to 365nm UVA light for 30min. During the follow up of the 48 patients (60 eyes) so far treated with collagen cross linking none of the patients showed any more progression (follow up time 1-38 month). In 81.7% of the patients a regression of the maximal K-values of -2.87 +/-2.56 dpt (0.18 to 9.97 dpt) could be seen. Post surgical visual acuity rose by 1.4 +/- 2.04 lines of Snellen. No unwanted side effects such as opacification of the lens or loss of endothelial calls could be found. Only during the first 2 to 3 months after the cross linking a slight superficial corneal haze occurred. Generally this minor haze disappears without any treatment, but, if wanted, a supportive therapy with soothing ointment or with a local steroid (i.e. Efflumidex or Vexol) can be used.
Collagen cross linking which only stiffens the anterior 200-250µm of the cornea modifies to biomechanical characteristics of the cornea. Deeper layers are not damaged. This procedure stopps the progression of the keratectasia. Therefore the number of penetrating keratoplasties could be significantly reduced in the future. The treatment is relatively easy and low in costs.
Conclusion: Keratoconus patients have to be checked / examined every 6-12 month. If the findings are stable a treatment with glasses or contact lenses is sufficient. If there is a progression an early cross linking treatment is recommended / indicated.
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If you are looking for more information about keratoconus feel free to have a look at our slide show. There we demonstrate again the characteristics of keratoconus as well as explain the various diagnostics and treatment options.