Keratoconus: Decreased visual acuity

Keratoconus is an ectatic degeneration of the cornea. As Dr. Victoria de Rojas, director of Victoria de Rojas Instituto Oftalmológico and Head of the Ophthalmology Service of the Complexo Hospitalario Universitario A Coruña, explains, the cornea is the main lens of the ocular system, it covers the anterior segment of the eye, it is transparent and has a regular curvature. It is like the window through which images enter the eye. If its curvature is altered, vision will be impaired.

In keratoconus, the cornea undergoes a conical deformation, accompanied by thinning, which causes irregular astigmatism. Irregular astigmatism, unlike regular astigmatism, cannot be fully corrected with glasses. In very advanced cases, there is also scarring and rupture of the innermost layer of the cornea, the endothelium, which leads to a waterlogging of the cornea called hydrops.

What causes keratoconus?

The cause of keratoconus is not known for sure. There is a genetic component but this is not evident in all cases. It also occurs in association with certain diseases in which collagen is altered, such as Ehlers-Danlos disease, osteogenesis imperfecta and mitral valve prolapse. In other cases it appears in isolation.

How does it manifest itself?

Keratoconus is not present from birth, it develops throughout life, especially in adolescence, the second and third decade of life and then generally slows down its progression. The earlier it appears, the more it evolves.

The main symptom is the decrease in visual acuity caused by the appearance and increase of irregular astigmatism. In keratoconus it is a bilateral alteration although of asymmetric evolution.

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Treatment

In very early stages, it is feasible to achieve a correction with glasses. When correction with glasses does not achieve adequate visual acuity, correction with semi-rigid or hybrid contact lenses is attempted. There are special contact lenses for keratoconus and the adaptation has to be done by experts.

If contact lens wear is not possible, irregular astigmatism can be corrected with the implantation of intracorneal segments, also called “intrastromal rings”. These segments “tighten” the cornea in the most appropriate area to try to regularize it. It is not a refractive procedure, although in most cases it is possible to improve the patient’s vision without correction, it is generally necessary to adapt glasses or contact lenses for complete visual rehabilitation. If the patient is not a candidate for intracorneal ring implantation or if adequate vision is not achieved with them, then the treatment consists of a corneal transplant.

More recently, a new treatment has been incorporated which is the only one known so far that allows slowing down the evolution of the disease, corneal cross-linking, which by applying riboflavin and ultraviolet light manages to harden the corneal collagen avoiding or delaying the evolution of keratoconus.

Prevention

Keratoconus cannot be prevented, but it is advisable to take into account certain tips to avoid its progression as much as possible.

In case of keratoconus, it is advisable to keep the inflammation of the ocular surface under adequate control in those cases in which some type of ocular allergic condition is associated, which is quite frequent. Patients are also warned of the importance of avoiding ocular rubbing.

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It is important to perform periodic check-ups by a specialist ophthalmologist familiar with the treatment of the disease in order to apply the most appropriate treatment according to the stage of the disease and to perform serial topographic controls that detect minimal changes in the evolution, which will allow the early application of cross-linking in those cases in which it is appropriate.