Keratoconus

O keratoconus is a progressive deformation of the cornea. It becomes prominent in the shape of a cone.

The cornea becomes thinner and more prominent, taking on the shape of a cone (ectasia or prominent dilatation), which leads to a decrease in vision, due to the appearance of irregular astigmatism. It is sometimes associated with myopia. It can be distinguished from other corneal ectasias, such as pellucid marginal degeneration, by the location of the cone, which is positioned in a central temporal direction and coincides with the area of lesser corneal thickness.

This is a pathology which normally affects both eyes (bilateral) although it can be asymmetrical (one eye with a developed cone and the other eye still almost normal). In the initial phase, vision can be corrected with glasses, but as the keratoconus the cornea becomes more and more prominent and therefore thinner, developing an irregular astigmatism. In the more advanced stages of the disease, it is expected that the vision with glasses is not very satisfactory and contact lenses are an alternative, so that the patient can obtain better vision.

O keratoconus is quite common, being the most common corneal ectasia worldwide. It is estimated that 1 person in 1000 is diagnosed with keratoconus. This pathology generally appears in adolescence and tends to stabilise in the third or fourth decade of life. Since keratoconus is a degenerative pathology, it usually develops progressively and there is usually an increase in astigmatism from its initial phase to its more advanced stages.

The origin of keratoconus is considered multifactorial, that is, there are a set of genetic and environmental factors that lead to its development. Ethnicity, family history and the existence of other systemic and ocular pathologies are considered to be risk factors. There are studies that indicate that constant eye rubbing may be associated with the development of keratoconus, due to the mechanical action exerted on the cornea.

The main symptom of keratoconus are complaints of decreased vision, associated with the appearance of myopia, astigmatism and some refractive instability, that is, the need to frequently change the glasses' graduation. In addition to this, patients usually report:

• Ghost images;
• Luminous halos;
• Photophobia (increased sensitivity to light)
• Eye irritation;
• Double vision.

The early diagnosis of keratoconus is fundamental for a correct follow-up of the pathology.

The ophthalmologist can diagnose keratoconus through observation at the doctor's surgery and through examinations such as biomicroscopy, supported by the use of complementary means of diagnosis.

Currently, corneal topography is excellent for the diagnosis and characterisation of keratoconus as it is a test that allows a detailed mapping of the shape and thickness of the cornea.

There are some characteristic signs of keratoconus that can be observed by the ophthalmologist during his assessment, facilitating the diagnosis. It is known that the most common characteristic of this pathology is the decrease in corneal thickness, at central or paracentral level, and a cone-shaped protrusion in the cornea, which is more noticeable mainly in more advanced stages of the pathology. Other signs can be observed in moderate to advanced keratoconus, such as Munson's sign (lower eyelid in a "V" shape when the patient looks downwards). With the biomicroscope, it is possible to observe, Rizzuti's sign (conical light reflex in the nasal cornea when illuminated temporally), Fleische's ring (iron deposits at the base of the cone), Vogt's streaks observed in the corneal thickness.

In very advanced stages of keratoconus complications may arise, such as corneal hydrops - due to rupture of the endothelium, with passage of aqueous humour and consequent oedema and opacification of the cornea.

The main objectives ofkeratoconus treatment are to improve the patient's quality of life through better visual function and to try to prevent the progression of the pathology.

There are various ways of treating vision defects, which must be adapted to each case.

The use of contact lenses, when it is no longer possible to obtain good vision with glasses. There are different types of lenses (hydrophilic, semi-rigid, semi-rigid and scleral) which must be adapted according to the stage of keratoconus in question and the patient's tolerance.

Crosslinking is a surgical treatment that has the main purpose of stabilising the keratoconus and preventing its evolution, as it makes the collagen more resistant, increasing the rigidity of the cornea, which becomes more resistant to possible deformations. The surgery consists of applying drops of riboflavin (vitamin B2) on the cornea, followed by exposure to ultraviolet light A. The reaction results in the strengthening of the collagen

Intrastromal ring implantation surgery is another resource with the aim of regularising the corneal surface and thus reducing the associated refractive error, especially irregular astigmatism. It consists of implanting ring segments made of a biocompatible material into the corneal thickness.

The surgery of corneal transplant is the last therapeutic option in cases of keratoconus. Corneal transplant consists of the total or partial replacement with a totally healthy and transparent cornea.