26 November 2020 Author : Bernardo Feijóo The cornea is the convex outer layer of eyeball, covering the iris, pupil, and anterior chamber, and that continues in the sclera. Under normal conditions it is transparent and has no blood vessels. The main functions of the cornea are to protect the eyeball and, together with the lens, refract the light, which helps to focus images on the retina. Keratoconus is a progressive deformation of the cornea, in which it becomes progressively thinner and deformed - it takes on the shape of a cone - which leads to decreased vision. It is a bilateral disease, that is, it affects both eyes, but not necessarily in the same way. Keratoconus is rare before adolescence and tends to stabilize in the 3 rd or 4 th decade of life. Causes of keratoconus This disease can have several causes (it has a multifactorial etiology) and is associated with genetic predisposition. Down syndrome, ocular allergy and connective tissue diseases can predispose to the development of keratoconus. Rubbing the eyes can also weaken the cornea and promote the development of keratoconus. Symptoms The first most frequent symptoms of keratoconus are complaints of decreased vision, for example: Image distortion for close or distant objects; Double vision using only one eye; Greater sensitivity to light; Ghost images; Eye irritation. In children or adolescents who already wear glasses, the development of keratoconus can manifest itself as a rapid increase in myopia or astigmatism, which often cannot be completely corrected with the glasses. Diagnosis The ophthalmologist makes the diagnosis of keratoconus based on complaints, the eye examination, and the results of a corneal topography. Corneal topography assesses the shape and thickness of the cornea. The repetition of a corneal topography over time allows the ophthalmologist to conclude whether the disease is progressing or is stable. Keratoconus treatment The treatment of keratoconus has two objectives : Stabilize the disease progression, that is, try to interrupt the progressive deformation of the cornea; Improve the patient vision. Currently, the first objective is achieved with a treatment called corneal collagen crosslinking. Corneal collagen crosslinking This surgical procedure consists of applying riboflavin to the cornea followed by exposure to ultraviolet light A (UVA). This establishes bonds chemically stronger between the collagen fibers of the cornea and increases its stiffness, which counteracts the deformation caused by the keratoconus. This treatment is thus effective in preventing the progression of keratoconus . Glasses and contact lenses To improve vision , the first step is to use glasses or soft (hydrophilic) contact lenses. In the initial or mild forms of keratoconus, glasses may be sufficient to eliminate symptoms and allow a clear vision. In cases with glasses where vision is not satisfactory, semi-rigid contact lenses are recommended. In cases where adaptation to contact lenses is not achieved or vision is not satisfactory, surgical options can be considered. Surgery with intra-stromal corneal ring segments These rings are segments of an inert plastic-like material that are introduced in the corneal thickness with the aid of a femtosecond laser. The goal is to regularize the surface of the cornea , which can improve vision in moderate keratoconus. It can also facilitate further adaptation of contact lenses. Corneal transplant Corneal transplantation is the last-line treatment for cases where the other options do not allow the patient to have a satisfactory vision. Corneal transplantation consists of replacing the central portion of the diseased cornea with a donor cornea, which has a normal shape, an adequate thickness and normal transparency. The transplant can include: All layers of the cornea, called penetrating keratoplasty; Only the most anterior layers of the cornea that are deformed, called anterior lamellar keratoplasty. In this case, the risk of rejection is lower. Prognosis Although keratoconus can progress very quickly in children and adolescents, the disease tends to stabilize with age and rarely progresses after the age of 40. With the emergence of new therapies that can stabilize the disease from its early stages, early diagnosis becomes very important to avoid having to resort to more invasive surgical therapies, such as corneal transplant. Meet the ophthalmology team from Hospital da Luz network. The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
