Keratoconus – dystrophic changes of the cornea, leading to its conical deformation, impaired and decreased vision. With keratoconus, visual acuity is progressively reduced, the image of objects is distorted, highlights and halos appear, monocular diplopia, sometimes pain syndrome and corneal opacity. Diagnosis consists in skiascopy, biomicroscopy, ophthalmometry, computer keratometry, coherent tomography. Microsurgical techniques of cross-linking, implantation of corneal rings, keratoplasty are used for the treatment of keratoconus.
In ophthalmology, keratoconus is diagnosed in 0.01% – 0.6% of cases. The disease occurs with the same frequency among representatives of different races and both sexes. The first manifestations usually occur in adolescence and early adolescence and then slowly progress. Sometimes keratoconus develops at a later date – in 25-30 years. With keratoconus, the structure and shape of the cornea changes: it becomes thinner and deformed according to the type of cone, which leads to the development of myopia and irregular astigmatism. Keratoconus is usually bilateral and asymmetric.
The question of the etiology remains debatable. As part of the study of the causes of corneal degeneration, several hypotheses have been put forward – hereditary, endocrine, metabolic, immunological, etc. In modern science, the hereditary-metabolic theory of keratoconus development is gaining an increasing number of supporters. This theory connects the occurrence of corneal changes with hereditary fermentopathy, which can be activated during the period of endocrine restructuring, under the influence of immunological disorders, general diseases, etc.
The research revealed a correlation between keratoconus and bronchial asthma, eczema, hay fever, atopic dermatitis, corticosteroid use, Addison’s disease, corneal microtrauma, retinopathy pigmentosa, keratoconjunctivitis, traumatic or viral keratitis, Leber congenital amaurosis, Down syndrome, Marfan syndrome and other diseases. There is an adverse effect on the cornea of ultraviolet rays, dustiness of the air, radiation radiation.
In recent years, due to the spread of excimer laser vision correction (LASIK), the frequency of iatrogenic keratoectasia and related cases of subsequent keratoconus has increased.
With keratoconus, multiple biochemical changes are detected in the deformed cornea; the content of collagen decreases, the concentration of keratin sulfate decreases, the total protein content decreases and the number of non-protein structures increases, collagenolytic and gelatinolytic activity increases, associated with the insufficiency of enzymes and proteinase inhibitors. As a result of a decrease in antioxidant activity, destructive aldehydes and/or hieroxynitrites are formed in the cornea.
It is believed that the process of corneal degeneration begins in the basal cells of the corneal epithelium or at the site of its transition to the stroma. The weakness of the corneal epithelium and stroma is accompanied by a decrease in the elasticity of the cornea, an increase in its rigidity and, as a result, irreversible stretching and cone–shaped deformation – the development of keratoconus.
According to the mechanism of occurrence, primary and secondary keratoconus are distinguished. The development of secondary keratoconus in most cases is caused by iatrogenic causes (iatrogenic keratectasia). In 95% of cases, keratoconus is bilateral, in 5% – unilateral.
The nature of the course of the disease may be progressive or stationary. In a separate form, researchers distinguish acute keratoconus.
Several variants of keratoconus staging have been proposed; among them, the Amsler classification is the most common, according to which stages IV of ophthalmopathology are distinguished. The first stage is characterized by irregular astigmatism, corrected by cylindrical lenses; visual acuity can be 1.0-0.5. Astigmatism in the second stage is also corrected, but is more pronounced; visual acuity in the range of 0.4 – 0.1. The third stage of keratoconus is accompanied by thinning and protrusion of the cornea; visual acuity is reduced to 0.12-0.02, correction is possible only with the help of hard contact lenses. With the development of the fourth stage of keratoconus, conical deformation and clouding of the cornea are pronounced, visual acuity is 0.02-0.01 and cannot be corrected.
Manifestations of keratoconus are caused by conical deformation of the cornea and are associated with the development of myopia and irregular astigmatism, the axes of which are constantly changing with the progression of the disease. This leads to a gradually increasing decrease in vision and monocular diplopia (double vision). Changes occur first in one eye, then in the other.
A patient with keratoconus is often forced to contact an ophthalmologist for the selection of glasses, however, the prescribed eyeglass correction in these cases is poorly tolerated and does not give its effect. This is due to a rapidly progressive decrease in visual acuity, so a person sees not as well in newly made glasses as in the process of their recent selection. Over time, it becomes impossible to use soft contact lenses because they do not adhere to the cornea.
With keratoconus, the patient can see a multi-contour image of objects, distortion of letters when reading, halos around light sources. Sometimes there is increased photosensitivity and constant eye irritation. At the beginning of the disease, a decrease in twilight vision is more pronounced, in the future vision worsens even in good lighting. Rapid eye fatigue, itching and burning sensations are noted. In the late stages of keratoconus, the cone-shaped deformation of the cornea is noticeable to the naked eye.
Keratoconus, as a rule, progresses slowly, within 10-15 years; in 50% of patients, it can stop at an early stage and go into long-term remission. In 5-7% of cases, the course of the disease is complicated by acute keratoconus, in which there is a sudden rupture of the descemet shell with the release of watery moisture into the corneal layers. Clinically acute keratoconus is accompanied by the development of corneal edema and the appearance of pain syndrome. After about 3 weeks, the acute process subsides, and scars form on the cornea. As a result, the deformation of the corneal surface may decrease, and vision may improve somewhat.
The examination begins with a standard visual acuity check, which allows you to identify its decrease to one degree or another. Repeated selection of glasses reveals a sharp asymmetric increase in refraction, the need to switch from spherical to cylindrical lenses to achieve acceptable visual acuity, a change in the axis of cylindrical lenses. Refractometry in keratoconus reveals abnormal astigmatism and myopia caused by corneal protrusion.
During diaphanoscopy of the eye, the keratoconus is determined as a wedge-shaped shadow on the iris. Skiascopy in keratoconus reveals the presence of a “springy”, “leaf-shaped” shadow caused by incorrect astigmatism. With the help of ophthalmometry, signs of conical deformation of the cornea are determined – distortion, characterized by a fracture and a disparity of horizontal marks, a change in the angle between the main meridians, etc. With the transparency of the eye media, ophthalmoscopy is performed.
The most accurate information about the parameters of the cornea in keratoconus can be obtained thanks to keratotopography and photokeratometry (computer keratometry). The latter method makes it possible to estimate the radius, toricity, asymmetry, eccentricity and to identify the conical deformation of the cornea at the subclinical stage.
During biomicroscopy of the eye with keratoconus, structural non-inflammatory changes of the cornea are determined: the appearance of nerve endings in its central zone, rarefaction of the corneal stroma, changes in endothelial cells, opacities in the bowman shell, thickening, cracks, ruptures of the descemet membrane, keratoconus lines, etc.
In specialized ophthalmological clinics, methods of computer corneal topography, optical coherence tomography of the cornea, and endothelial microscopy of the cornea are used to detect keratoconus.
Taking into account the nature of the course of keratoconus (speed of progression, tendency to relapse), treatment can be differentiated: non-surgical or surgical.
Conservative treatment of keratoconus consists in correcting vision with the help of semi-rigid lenses (hard in the center, soft in the periphery), which, as it were, press the cone of the cornea. In the initial stages, especially with a non-progressive, stable course of keratoconus, eyeglass correction can also be effective. Courses of vitamin therapy, tissue therapy, immunomodulators and antioxidants are prescribed; eye drops (taurine), subconjunctival and parabulbar injections of ATP, methylethylpyridinol. With keratoconus, physiotherapy (magnetotherapy, phonophoresis with tocopherol, etc.) is effective. procedures).
With the development of acute keratoconus, urgent care is required: instillation of mydriatics into the eye (mezaton, mydriacil, etc.), the imposition of a pressure bandage on the eye in order to prevent corneal perforation.
A relatively new, well-proven method of conservative treatment of keratoconus is corneal cross-linking, which consists in removing the surface epithelium from the cornea, instilling riboflavin solution on it and subsequent irradiation with UV rays. This procedure allows you to strengthen the cornea, increase its resistance to deformation, stop the development or achieve regression of keratoconus. After corneal cross-linking, the usual eyeglass and contact correction with soft lenses becomes possible.
At the initial stage of keratoconus, with a sufficient thickness of the cornea, it is possible to perform an excimer laser procedure (FRK + FTC), which allows to correct astigmatism, increase visual acuity, strengthen the anterior layers of the cornea and slow down the progression of keratectasia.
In some cases, in order to reduce corneal deformation, thermokeratoplasty is used – the application of a coagulator to the periphery of the cornea of chiseled applications that allow for flattening of the cornea.
In keratoconus surgery, the method of implantation of corneal rings is used. Stromal (corneal) rings change the surface of the cornea, normalize refraction and stabilize the cornea.
The classic operation is through-or layer-by-layer keratoplasty, involving the removal of one’s own cornea and implantation of a donor graft in its place. Keratoplasty is accompanied by almost 100% graft engraftment and allows you to adjust visual acuity to 0.9-1.0 in about 90% of cases. End-to-end keratoplasty can be undertaken even in the terminal stage of keratoconus.
Prognosis and prevention
In most cases, the course is slowly progressing and relatively favorable. Sometimes the progression can stop and stabilize at any stage of keratoconus. The later the keratoconus appeared, the slower its course and the better its prognosis.
Complications of pathology may include the development of acute keratoconus, opacification and perforation of the cornea. In the postoperative period, postoperative astigmatism of a high degree may occur, requiring contact correction.
In order to exclude the possibility development, it is necessary to treat those disorders that can contribute to the occurrence of corneal deformity – allergic, immune, endocrine, inflammatory, etc.