Surgical correction of ametropia

By changing the optical strength of the two main optical elements of the eye - the cornea and the lens, it is possible to form a clinical refraction of the eye and thus correct myopia, hyperopia, astigmatism.

Surgical correction of refractive error anomalies was called "refractive surgery."

Depending on the localization of the operative zone, corneal, or corneal, and lens surgery is isolated.

The cornea is the most accessible biological lens in the optical system of the eye. With a decrease or increase in its refraction, the refraction of the eye as a whole changes significantly. In addition, the cornea is an eye structure that is easy to perform surgery. A healthy cornea does not have blood vessels, it quickly epithelizes, preserving transparency. Refractive surgery of the cornea does not require the opening of the eyeball and allows accurate dosage of the refractive effect.

The first refractive surgery on a transparent cornea was conducted by Colombian ophthalmologist H. Barraque in 1949. In recent years, there has been a rapid increase in the number of operations performed: up to 1.5 million surgeries are carried out annually in the world.

The purpose of the operation with myopia is to "weaken" the too strong refractive power of the eye, which focuses the image in front of the retina. This is achieved by easing the refraction of the cornea in the center from 40.0-43.0 to 32.0-40.0 D, depending on the degree of myopia. Parameters of the operation (its plan) are calculated by special computer programs. The anatomical-optic parameters of the eye and the data of its refraction are measured before the operation. The effectiveness of refractive surgery depends to a large extent on the accuracy of measuring the anatomical and optic parameters of the eye, computer calculations of the operation plan and its performance by a surgeon, and compliance with all the requirements of refractive surgery.

In order to correct myopia, apply:

• anterior radial keratotomy;
• myopic keratomileusis;
• introduction of intragenital rings and lenses.

Anterior radial keratotomy, developed by SN Fedorov in 1974, is used to correct myopia 0.5-6.0 diopters. The technique of the operation is to apply non-penetrating deep (90% thick) radial incisions of the cornea at the periphery with a dosed diamond knife. The peripheral part of the cornea weakened by notches swells under the influence of intraocular pressure, and the central section flattenes.

The diameter of the central optical zone of the cornea, which remains without cuts (3.2-4 mm), the number of notches (4-12) and their depth is chosen by the surgeon using a computer program, depending on the parameters of the eye and the age of the patient.

To correct myopic astigmatism, special operations have been developed that allow to reduce the refraction of the cornea to 4.0 dt along the meridian corresponding to the axis of astigmatism by means of metered notches applied perpendicularly or in parallel to the strongly refracting axis-tangential or longitudinal keratotomy.

The technique of performing myopic keratomileusis, developed by H. Barracker in 1964, has now changed significantly. Special microkeratomes allow accurate cutting of the superficial layers of the cornea to a depth of 130-150 microns (with a thickness of 550 microns) and form a "cap". After the second, deeper cut, the cut internal layers are removed, and the "lid" is put in place. The thickness of the removed corneal stroma "doses" the degree of flattening of the corneal center and the effect of the operation. Myopic keratomileus is used with myopia over 6.0 dptr.

Currently, the mechanical excision of the corneal stroma is replaced by evaporation with an excimer laser, and this operation is called "Lasik".

The introduction of plastic rings into the peripheral layers of the cornea and intra-coronary lenses is ineffective, so this method was not widely used in clinical practice.

The goal of corneal refractive surgery of hyperopia is to "strengthen" the weak optical apparatus of the eye, focusing the image behind the retina. To achieve this goal, the operation, developed in 1981 by SN Fedorov, is performed - thermokeratocoagulation of the cornea.

With hyperopia, it is necessary to increase the refractive power of the cornea from 40.0-43.0 to 42.0-50.0 D, depending on the degree of hypermetropia. This is achieved by exposing the peripheral part of the cornea to infrared (thermal) energy, which causes the collagen of the corneal stroma to liquefy, the ring of the peripheral part of the cornea shrinks, and the central optical zone "swells out," with refraction of the cornea intensified.

Thermal action is carried out with the help of a special thin needle (electrode), which automatically moves to the specified depth and at the time of the corneal sting, it heats up to 700-1000 "C, so the tissue is cut through the entire thickness of the cornea. Program depending on the parameters of the patient's eye.The operation allows you to correct farsightedness from 0.75-5.0 D and farsighted astigmatism (upon exposure to one of the main meridians of the astigmatic gl over) to 4.0 diopters.

At present, thanks to the use of a solid-state laser, the thermal energy has been replaced by a laser, resulting in a reduced traumatic operation. 

Lenticular refractive surgery involves several methods of affecting the refraction of the eye:

• removal of the transparent lens - refractive lenectomy with the introduction of an artificial lens or without it;
• introduction of an additional negative or positive intraocular lens into the eye.

The removal of the transparent lens for the correction of myopia was proposed by Fukala as far back as 1890, but it was not spread due to serious complications. Currently, thanks to the use of modern microsurgical techniques, the risk of complications is reduced, but the method can be used for short-sightedness not exceeding 20.0 Dpt.

For the purpose of correction of hyperopia of a high degree, the operation of replacing the transparent lens with a stronger intraocular lens of 30-48 D depends on the anatomical and optical parameters of the eye.

At present, correction of high-grade ametropia uses the technique of introducing an additional corrective lens into the eye - "glasses inside the eye". The super-thin elastic lens is inserted into the posterior chamber of the eye through a minimal incision and placed in front of the transparent lens, therefore it is called the intraocular contact lens. A negative intraocular lens allows correcting myopia to -20.0-25.0 D, a positive lens - farsightedness up to + 12.0-15.0 Dpt. Modern methods of refractive eye surgery are very effective, provide a quality stable vision and successfully replace glasses and contact lenses.

[1], [2], [3], [4], [5], [6]