The keratoconus (KCN) is a degenerative eye disease of progressive character, manifesting as a characteristic cone-shaped curving of the cornea, associated with irregular thinning of the corneal layer known as the stroma, resulting in cone-shaped swelling and significant loss of vision. In fact, the visual consequences of this condition include a significant reduction in visual acuity of varying degrees, image distortion and increased sensitivity to glare and light in general. Moreover, conventional spherocylindrical spectacle lenses cannot adequately correct this pathological refractive condition.
Generally, keratoconus tends to occur during puberty (late adolescence for males and before the age of 20 for females) and may progress until the age of 30-40. Beyond this age, it is very rare for there to be progression. In rare cases, keratoconus may occur at a later age, for instance as a result of hormonal changes, such as during pregnancy. The manifestation and progression of the disease are vary and are very often asymmetrical between the two eyes of the same patient, although it is never a unilateral disease. In general, it is estimated that the incidence of keratoconus can vary between 50 and 230 cases every 100,000 people (about 1/2,000).
An interesting fact is that keratoconus was probably known from the earliest days of ophthalmology. Originally, this pathology had names other than 'keratoconus', such as hyperkeratosis or cone-shaped cornea, all of which described the presence of a deformed cornea. The first adequate description of keratoconus, however, dates back to the early 18th century, when it appeared in Nottingham's fundamental treatise. Possible treatments were also suggested at that time: Photinos Pannas (1831-1902), a professor at the University of Paris, presented a management approach based on the use of glass contact lenses.
What are the causes of keratoconus?
The causes of keratoconus are not known. Several associations have been identified, including the use of rigid gas-permeable contact lenses, chronic rubbing of the eyes, Down syndrome, and certain connective tissue diseases. However, keratoconus often occurs without being associated with other ocular or systemic diseases. Keratoconus is also considered a hereditary disease. In fact, at least 6% to 8% of reported cases have a positive family history or show evidence of familial transmission.
Evaluation and diagnosis of keratoconus
Today, several ocular imaging techniques, including corneal topography and optical coherence tomography (OCT), have improved our ability to diagnose keratoconus early. Corneal topography is the main diagnostic test for detecting the pathology. In fact, colour-coded corneal curvature maps generated by corneal topography can offer visualisation of the irregularity of the corneal surface. Recently, the use of anterior segment optical coherence tomography (OCT) has also been progressively introduced in the clinical diagnosis of keratoconus.
How is keratoconus treated?
The options available for the management of keratoconus depend strongly on the stage of the disease and its progression. If the disease is stabilised, more emphasis is placed on correcting vision. If the disease is progressing, the emphasis is on slowing and stopping the disease.
Among the therapeutic approaches, custom-designed soft contact lenses can provide some control of the primary aberrations associated with keratoconus. Rigid gas permeable contact lenses (RGP) and scleral lenses are the most suitable therapeutic solutions for mild to advanced keratoconus. However, it may happen that these types of lenses are not well tolerated by patients. Alternatives include hydrogel contact lenses, piggy back lenses or scleral contact lenses.
Corneal collagen cross-linking is a minimally invasive, outpatient parachirurgical procedure that has proven effective in halting the progression of keratoconus, especially in cases diagnosed early.
Finally, the cornea transplant is required is considered the last resort when the cornea has become too thin and the symptoms of the pathology are severe. In this case, the cornea is replaced completely (penetrating keratoplasty) or partially (lamellar keratoplasty) with corneal tissue from a healthy donor.
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