RU2479294C1 - Method for providing improved corneal organ-sparing in excimer laser correction of vision - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention refers to medicine, namely ophthalmic surgery. Excimer laser correction of vision is conducted by sequential layered corneal ablation by pulse staring excimer laser light. The exposure is generated by the light characterised by smooth spatial profile of energy deposition in the entire area of a surgical field at deflection amplitude max. 1% of the calculated irradiance in the exposed area. A transition from an intact surface of stroma to the operation area (incision) is presented in the form of a step no more than 6 mcm.

EFFECT: method enables conducting excimer laser correction of ametropia with providing corneal organ-sparing as measured by a greater postoperative corneal thickness with no refractive regression and enhancement for the purpose of recurrent operations.

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Description

The invention relates to the field of ophthalmic surgery.

A known method of surgical correction of ametropia (myopia) of a high degree in the presence of a thin cornea according to the patent of the Russian Federation 2402306, A61F 9/008. According to the invention, the first stage of photorefractive keratectomy (registered trademark - Trans-PRK ^® ) is preliminarily performed in the form of exposure to the cornea from an excimer laser with a wavelength of 193 nm, a pulse duration of 15 ns, and a pulse repetition rate of 5 to 10 Hz. By sequential layerwise ablation of corneal sections, the first stage of the operation is initially performed with correction of not more than 80% of the initial myopia by the action of pulsed radiation from a non-scanning excimer laser with a Gaussian radial distribution of the energy density in the beam cross section with parameters: standard deviation of the energy density distribution in the range from 2.3 to 1.8 mm , the value of the amplitude of the energy density at the center of symmetry of the pulse in the range from 180 to 220 mJ / cm2, the diameter of the laser zone from 5 to 7 mm, then, after 8-12 months, the second stage is carried out with the correction of the remaining myopia by a similar laser exposure with the following parameters: standard deviation of the energy density distribution in the range from 2.5 to 1.9 mm, the value of the energy density amplitude in the center of symmetry pulse in the range from 190 to 230 mJ / sq. cm, the diameter of the laser exposure zone from 5.1 to 8 mm.

The known method is based on the fact that:

During the time between the first and second stages, a fibrocellular membrane is formed on the cornea, covered with corneal epithelium. The thickness and strength of the membrane significantly exceed the initial characteristics of the bowman shell evaporated during the first stage (see E. A. Kasparova. Diagnosis and treatment of early keratoconus. Eye, 2001, No. 2). At the same time, the external curvature of the cornea, and therefore the refractive effect of the first stage, does not change significantly.

However, this invention has significant drawbacks: despite the formation of a fibrocellular membrane in the postoperative period after each stage of the operation, the cornea becomes thinner by 5 to 50 percent of the initial value. This is a negative factor that determines the reduced physical strength of the eye compared to the initial one, as well as the reduction in the physiological reserves of the cornea for possible subsequent surgical interventions;

- edge effects at the border of the surgical field can cause postoperative opacification of the annular type of fibroplasia, which, without interfering with central vision, can nevertheless negatively affect the course of postoperative healing of the cornea.

The technical result of the invention: excimer laser correction of ametropia with organ cornea preservation, expressed in postoperative increase in the thickness of the cornea without refractive regression and the expansion of functionality for repeated surgical interventions.

The technical result is achieved by the fact that in the method of excimer laser correction of ametropia, which consists in sequential layer-by-layer ablation of the cornea by pulsed radiation of a non-scanning excimer laser, the effect is produced by radiation with a smooth spatial profile of energy exposure over the entire area of the surgical field with an amplitude of deviation of not more than 1% of the calculated density energy in the impact zone, and the transition from the untouched surface of the stroma to the area of operation (insert) is performed as a step of magnitude hydrochloric not more than 6 microns.

The set of essential distinguishing features proposed by the authors is necessary and sufficient for the unique achievement of the task.

The authors did a great job, which allowed us to determine the necessary degree of smoothness of the spatial energy profile of the excimer laser effect on the cornea.

Firstly, based on the fact that the ablation depth is proportional to the logarithm of the energy density, the proper geometric correspondence of the obtained ablation profile to the calculated one is ensured only if the amplitude of the micro-scale (an order of magnitude smaller than the size of the operation zone) unevenness of the energy profile does not exceed 5% of the calculated values in the affected area. When this value is exceeded, the physical roughness of the resulting surface becomes significant. This, in turn, causes the appearance of optical inhomogeneities in the area of operation, which reduces the quality of vision.

Secondly, during ablation of the corneal layers, in addition to the physical uniformity (smoothness) of the obtained surface, the uniformity of the heat load on the same microscale throughout the operation area is very important. This follows from the fact that the degree of damage to stromal cells is proportional to their overheating. And heating the corneal tissue is directly proportional to the amount of energy absorbed. Accordingly, direct proportionality, in contrast to the logarithmic dependence, determines a more stringent condition for the necessary uniformity of the energy profile, in which neighboring sections of the cornea on the microscale will experience the same radiation (and, therefore, thermal) effect. It was experimentally established that the amplitude of the roughness of the energy profile should not exceed 1% of the calculated value of the energy density in the impact zone. Exceeding this value causes negative effects: a delay in postoperative epithelization, an increase in the duration of blepharospasm and an increased likelihood of haze within the surgical field.

Thirdly, it has been experimentally established that in the case of an abrupt incision into the stroma at the edge of the surgical field (transition from the surgical area to the intact cornea), the likelihood of annular opacification along the edge of the surgical field increases sharply with increasing incision. Empirically established a cut-in limit of 6 micrometers.

The method is as follows.

The cornea is exposed to a beam of a non-scanning excimer laser with a wavelength of 193 nm, a pulse duration of 15 ns, a pulse repetition rate of 5 to 10 Hz and a beam width equal to the diameter of the operation zone. The operation is carried out by sequential layer-by-layer ablation of corneal sites by the action of pulsed radiation from a non-scanning excimer laser with parameters: the diameter of the laser exposure zone from 5.1 to 8 mm, the amplitude of the energy density in the operation zone in the range from 180 to 220 mJ / cm2 and the micro-scale irregularity of the energy profile beam no more than 1% of the calculated value of the energy density in the area of the operation, and the transition from the untouched surface of the stroma to the area of operation (insert) is performed as a step of magnitude no more than 6 microns.

The proposed method is characterized by the following clinical examples: Example 1. Patient G., 37 years old.

Condition before surgery:

Visual acuity in the distance: Vis OD = 0.05 Sph -6.5 D = 1.0

Vis OS = 0.05 Sph -5.5 D = 1.0

Corneal thickness OD / OS: 470/490 μm.

Diagnosis: stationary myopia of an average degree of both eyes.

06/29/2011 - The operation in accordance with the proposed invention:

Condition after surgery (4 months):

Visual acuity in the distance: Vis OD = 1.0 Vis OS = 0.8

Corneal thickness OD / OS: 466/488 μm, the cornea is transparent.

Example 2. Patient J., 30 years old.

Condition before surgery:

Visual acuity in the distance: Vis OD = 0.05 Sph -5.00 D = 1.0

Vis OS = 0.05 Sph -5.00 D = 1.0

Corneal thickness OD / OS: 465/476 μm.

Diagnosis: stationary myopia of an average degree of both eyes.

10.27.2010 - The operation was carried out in accordance with the proposed invention:

Condition after surgery (1 year):

Visual acuity in the distance: Vis OD = 0.9 Vis OS = 1.0

Corneal thickness OD / OS: 536/544 μm, the cornea is transparent.

Example 3. Patient E., 24 years old.

Condition before surgery:

Visual acuity in the distance: Vis OD = 0.02 Sph -3.25 D Cyl -1.00 D Ax 175 = 1.0

Vis OS = 0.02 Sph -4.00 D Cyl -0.75 D Ax 5 = 1.0

Corneal thickness OD / OS: 440/445 μm.

Diagnosis: moderate stationary myopia, complex myopic astigmatism in both eyes.

12/28/2010 - The operation was carried out in accordance with the proposed invention:

Condition after surgery (10 months):

Visual acuity in the distance: Vis OD = 1.0 Vis OS = 1.0

Corneal thickness OD / OS: 484/514 μm, the cornea is transparent.

Using the proposed invention on the Profile-500 installation made it possible to confirm an unambiguous positive solution to the claimed technical problem: excimer laser correction of ametropia (myopia) with corneal organ preservation, expressed as a postoperative increase in the thickness of the cornea without refractive regression and expansion of functionality for repeated surgical interventions.

Claims (1)

A method of increasing the cornea’s organ preservation during excimer laser correction of ametropia, which consists in sequential layer-by-layer ablation of the cornea by pulsed radiation of a non-scanning excimer laser, characterized in that the effect is produced by radiation with a smooth spatial energy profile over the entire area of the surgical field with a deviation amplitude of not more than 1% of the calculated value of the energy density in the impact zone, and the transition from the pristine stroma surface to the operation zone Fill in the form of a step with a size of not more than 6 microns.