Corneal neovascularization is a disease in which the blood vessels of the limb grow into the stroma of the cornea. Clinically, the pathology is manifested by a decrease in visual acuity up to blindness, visualization of vessels in the form of “red twigs” on the surface of the cornea, violation of binocular vision. Biomicroscopy of the eye, visometry, keratometry, ultrasound of the eye are used for diagnosis. Surgical tactics are reduced to keratoplasty, keratoprosthetics, laser coagulation or photodynamic therapy. Conservative treatment is based on the instillation of glucocorticosteroids into the conjunctival cavity, their subconjunctival and parabulbar administration.
H16.4 Corneal neovascularization
Neoangiogenesis of the cornea is a widespread pathology in practical ophthalmology. According to statistics, about 40 million patients worldwide need a corneal transplant due to the development of complications of this disease. It is proved that normally only 0.01% of endotheliocytes are at the stage of division. In a state of chronic hypoxia, this indicator increases tenfold. In 14.5% of patients, there is a persistent decrease in visual functions. The risk of developing blindness is about 20-25%. The disease occurs with the same frequency among men and women. Geographical features of the distribution are not noted.
There are many factors that lead to this disease. All of them have a single mechanism of development, since enhanced angiogenesis is a compensatory reaction of tissues to oxygen deficiency. The main causes of neovascularization:
- Traumatic injuries. As a result of injuries (wounds, burns of the eyes) or surgical interventions in the cornea, orbital conjunctiva and limb, scar defects are formed, which lead to deep neovascularization.
- Chronic keratitis. Prolonged course of inflammatory processes (keratitis, keratoconjunctivitis) it causes hypoxia of the membranes of the eye and provokes neoangiogenesis.
- Degenerative-dystrophic changes. Multiple ulcerative defects and recurrent erosions stimulate vascular proliferation due to thickening of the cornea and insufficient oxygen supply to the deep layers.
- Long-term wearing of contact lenses. The disease develops due to a mechanical obstacle in the way of oxygen supply. At high risk or the first symptoms of pathology, the patient is recommended to use lenses with high oxygen permeability and alternate them with wearing glasses.
Normally, the cornea is the shell of the eyeball, devoid of blood vessels. Its blood supply and trophism are provided by a vascular network located in the limbic region. The trigger factor for the development of the disease is regional hypoxia, in which insufficient oxygen enters the cornea. This leads to increased secretion of nitric oxide, which is manifested by the expansion and increased permeability of blood vessels at the border of the sclera and cornea. Proteolytic degradation of the basement membrane and plasminogen activation contribute to the proliferation of endothelial cells. Enhanced formation of endotheliocytes, mobilization of pericytes and smooth muscle cells underlie corneal neovascularization.
From a clinical point of view , ophthalmologists distinguish the following forms of corneal neovascularization:
- Superficial. Vessels from the limbic region pass unchanged to the cornea.
- Deep. The vessels, moving from the peripheral to the central parts, grow into the thickness of the cornea. The middle and deep layers of the stroma are affected. Scleral and episcleral vessels have the form of parallel threads.
- Mixed. The process of neovascularization affects the entire thickness of the shell.
Enhanced angiogenesis leads to the proliferation of blood vessels on the surface of the cornea, which entails a decrease in its transparency. In the initial stages of the disease, visual acuity decreases slightly. If the neovascularization process reaches the central zone, the patient completely loses sight. The narrowing of the visual fields is accompanied by a violation of spatial perception. Photopsies and metamorphopsies may occur. Patients with corneal neovascularization complain of the appearance of dark spots or “shrouds” in front of the eyes, note increased fatigue when performing visual work.
With a unilateral process, binocular vision is disrupted. Adaptation to monocular vision with damage to the optical part is difficult in mature patients. Due to the constant discomfort caused by interference in front of the eyes, a headache occurs. Many patients use colored lenses to reduce the severity of visual changes, which further aggravates the clinical symptoms. The prolonged course of the disease leads to a change in the radius of curvature of the cornea, its thickening, which causes an increase in the index of refraction and distortion of vision.
The most common complication of corneal neovascularization is total vascular opacity. In addition to changing the normal color of the eyes, the eyesore leads to blindness. Patients with this pathology are at risk of developing inflammatory and infectious diseases (keratoconjunctivitis, keratitis). Pathological neovascularization is often complicated by hemorrhage in the anterior chamber of the eye. Rarely, intensive angiogenesis is the cause of hemophthalmos. In the later stages, polymegatism develops, in which an irreversible change in the size of endotheliocytes is observed.
In order to make a diagnosis, an external examination and a complex of ophthalmological studies are carried out. The germination of blood vessels in the form of “red threads” is visually determined. Ophthalmological examination provides:
- Visometry. Measuring visual acuity is a basic diagnostic method. Depending on the degree of vascular proliferation, visual acuity varies from a slight decrease in visual functions to their complete loss.
- Biomicroscopy of the eye. The technique allows to study the degree of transparency of the optical media of the eye, to identify signs of inflammatory and dystrophic changes. With a superficial form, the blood flow in the newly formed vessels is determined.
- Keratometry. The study makes it possible to study the structure of the cornea, to determine how much the radius of its curvature has changed.
- Ultrasound of the eyes. The purpose of the ultrasound examination in the In-mode is to identify secondary changes associated with the progression of neovascularization.
In the early stages, the elimination of the etiological factor eliminates the progression of the disease or reduces the severity of clinical manifestations. Newly formed arterioles become desolate and take the form of barely noticeable “ghost vessels”. Conservative therapy is reduced to instillation of glucocorticosteroids into the conjunctival cavity or to parabulbar and subconjunctival administration. Surgical treatment is used for far-reaching forms and includes:
- End-to-end keratoplasty. The technique is used when vessels grow into the cornea in a limited area. After removal of the altered corneal area, donor material is sewn in its place.
- Keratoprosthetics. This is the method of choice in the treatment of patients with a deep form of neovascularization or with a complicated course of pathology due to the occurrence of a total vascular cataract. Keratoprosthesis is installed only 3 months after implantation of the support plate.
- Laser coagulation of neovessels. Gradual coagulation of endothelial channels and capillaries from the central part to the periphery is carried out. The technique is more effective in the superficial variant of the disease. In the late postoperative period, vascular recanalization is possible.
- Photodynamic therapy. The method is based on light-induced chemotherapy. The photosensitizer selectively accumulates in tissues with increased proliferative activity.
Prognosis and prevention
The prognosis for life with corneal neovascularization is favorable, the prognosis for visual functions depends on the degree of vascular germination. In most cases, timely treatment ensures complete restoration of visual acuity. Specific preventive measures have not been developed. Non-specific prevention includes compliance with safety regulations in production conditions, monitoring the duration of wearing contact lenses during the day. A patient who wears lenses should consult a specialist at least once a year and choose lenses with a high oxygen transmittance.