Definition

Keratoconus is a degenerative pathology of the cornea characterized by progressive thinning and fatigue of the corneal stroma. Clinical onset – usually bilateral – occurs in young age, in the second-third decade of life.

Symptomatology

The first symptom of keratoconus is reduced visus due to irregular astigmatism and high order optical aberrations induced by the apex of the cone.
Photophobia, glare from light sources, monocular diplopia and frequent eye redness may be symptoms.
Keratoconus has an estimated average incidence of 1 case per 2000 people and can occur in families. An association of keratoconus with noninflammatory connective tissue disorders has been observed, including Elhers-Danlos syndrome and osteogenesis imperfecta syndrome.
In patients suffering from keratoconus, the presence of isolated eye diseases can be noted: a classic example is retinitis pigmentosa.

Diagnostics

Keratoconus is diagnosed by physical examination of the eye and corneal topography.  
Topography allows the computerized reconstruction of the corneal curvature and allows both an early diagnosis, in the preclinical stage of keratoconus, and the study of the evolution and staging of the pathology. The clinical examination also makes use of corneal pachymetry, through which it is possible to measure corneal thickness: a corneal thickness, central or paracentral, less than 450 microns is considered pathological.
Currently an examination that integrates topography and pachymetry is corneal tomography that can be performed with instruments that use a scheimplfug camera or a corneal OCT.
In addition, biomicroscopic examination reveals in the early stages of keratoconus signs of superficial stromal layers (scarring of Bowman's membrane) or deep striae (Vogt's striae) and, in late cases, corneal ectasias. If the apex of the cone is generally located at the visual axis, there is a significant reduction in the patient's visual performance.  

Therapy

In the early stages, the treatment of keratoconus makes use of the correction of the visus through glasses or contact lenses, which in any case never slow down the progression of the cone.
The only therapeutic option that can slow or even stop the progression of keratoconus is corneal cross-linking. The technique aims to increase the mechanical rigidity of corneal tissue, weakened by corneal degeneration, by generating new chemical bonds between the collagen molecules of the stroma of the cornea, according to a chemical process called photopolymerization. There are two different types of treatment:
- the standard cross-linking (epi-off) with which the corneal epithelium is initially removed to facilitate the absorption of riboflavin and subsequent irradiation with ultraviolet rays;
- the transepithelial cross-linking (epi-on) where absorption and irradiation occur without the removal of the corneal epithelium; this technique is, therefore, more suitable for people with corneas too thin that could not undergo the previous classical procedure.
The results from the introduction, a few years ago, in the clinical practice of cross-linking have demonstrated the efficacy and safety of the treatment. On average, a significant flattening of the keratoconus apex (average of 1-2 diopters) was observed, with a simultaneous improvement in visual acuity with contact lenses of one or two Snellen lines.
The surgical indication is aimed at early stage evolutionary keratoconi with a slight reduction in the best natural or correct visus with contact lenses and with a corneal thickness greater than 400 microns. The operation is performed on an outpatient basis under topical anesthesia (with anesthetic eye drops); at the end of the procedure a therapeutic contact lens is placed on the cornea which is removed after 3-4 days from the operation as soon as the epithelium is intact.
Post-operative medical therapy is topical and uses antibiotic and anti-inflammatory eye drops. During the first 2-3 days after surgery, a sense of foreign body or eye burning may occur due to the process of corneal re-epithelialization.
Once the epithelium has healed, any discomfort ceases and the patient can return shortly to wear the contact lens, always on the recommendation of the ophthalmologist.

Another method to achieve an improvement in the quality of vision in patients with keratoconus is the insertion of intrastromal corneal rings. It is important to underline that this treatment is not intended to halt the progression of the disease, but only to improve vision in patients with already stable keratoconus.
Finally, in those patients suffering from keratoconus who, despite treatment by cross-linking, do not obtain a satisfactory stabilization or vision, corneal transplant (keratoplasty) is necessary.