RU2228730C1 - Method for removing high-degree myopia at availability of thin cornea - Google Patents

Abstract

FIELD: medicine, ophthalmology. SUBSTANCE: one should carry out a two-stage LASIC interference. At the first stage one should conduct a multi-zonal ablation at decreasing myopia degree up to low-degree myopia. In 3-5 wk during the second stage one should prescan an optic tract to detect optic aberrations of both the highest and the lowest order. Repeated LASIC interference should be performed by taking into consideration all detected aberrations to obtain emmetropic refraction. The method enables to achieve refraction effect by keeping the structure and integrity of thin cornea. EFFECT: higher efficiency of operation. 1 cl,1 ex

Description

The invention relates to refractive ophthalmic surgery and is intended to eliminate high myopia in the presence of a thin cornea.

The task of eliminating myopia of a high degree in the presence of a thin cornea seems quite relevant and largely unsolved. The use of modern refractive laser technologies for the correction of myopia is limited by the thickness of the cornea. In accordance with this, the elimination of high myopia in the presence of a thin cornea requires the development of special methodological approaches.

A known method of surgical correction of high myopia, including automated lamellar keratoplasty (ALA) (Buratto L., Brint SF ALK with the eximer laser: better than ALK alone // Ocular Surgery News, March, 1, 1995, p. 5-6) .

However, when using this method, it is impossible to achieve complete correction of high myopia with a thin and flat cornea, since thinning of the cornea by the ALA method of less than 200 μm can lead to serious complications in the postoperative period (keratoconus).

One of the ways to eliminate this drawback is the method according to patent RU 2121328, 10.11.1998 - a method of surgical correction of high myopia with a thin and flat cornea, which consists in placing a ring-shaped intrastromal implant in the stromal bed, the thickness of which in the center exceeds the depth of the specified bed on the calculated value depending on the initial and planned refraction and on the initial thickness of the cornea, but not more than 150 microns. Then the superficial corneal flap is returned to its original position.

The intrastromal ring-shaped implant for the implementation of the method is made in the form of a ring with a flat lower surface and a convex upper surface with a thickness of the ring in the center from 0.15 to 0.3 mm and a ratio of the maximum ring diameters, external and internal, to the minimum ring diameters, external and internal in the range of 1.02-1.05.

The ring-shaped intrastromal implant is made of an elastic, optically transparent material intact to the tissues of the eye, for example, collagen.

To achieve maximum refractive effect, the thickness of the ring in the center should exceed the depth of the formed corneal bed by no more than 150 μm, since otherwise there is a deficiency of the surface sheet and its uneven fit to the implant.

However, the accuracy of the effect is more than 1 diopter, while it is not possible to correct astigmatism, in addition, cases of implant rejection have been described.

There is a method of surgical correction of high myopia in the presence of a thin cornea, in which keratotomy with a maximum volume is preliminarily performed, after not less than 6 months, the epithelial layer of the central part of the cornea is first removed with a flat laser beam of a UV laser with an pulse energy of 80 to 250 mJ / cm ² , a frequency of 5-10 Hz, a pulse duration of 15 ns, a diameter of 3.5-5.0 mm, then the corneal stroma is vaporized by UV-laser radiation with an energy per pulse of 230 to 250 mJ / cm ² , a frequency of 5 -10 Hz, duration a pulse width of 15 ns, a half-width of the Gaussian energy distribution σ (sigma) from 1.8 to 2.2 and a diameter of 3.5-5.0 mm, while the remaining thickness of the cornea should be at least 250 mm (RU 2154451, 08.20.2000 )

With high and superhigh degree myopia and a thin cornea of 415-500 microns in the center, neither keratotomy nor excimer laser keratectomy, performed independently, leads to a sufficient and complete refractive effect.

In this method, keratotomy with a maximum volume (knife) is preliminarily performed, which partially eliminates the existing myopia. Then, after at least 6 months, laser intervention is performed. At the same time, part of the refractive effect provided by keratotomy is achieved by acting on the periphery of the cornea, while another part, associated with laser intervention, by acting on its central zone. The total refractive effect of the two-stage combined surgery is immeasurably greater than with a separate keratotomy or excimer laser keratectomy. It ensures the achievement of high visual functions without correction in a complex group of previously incurable refractive patients.

With keratotomy, to achieve the greatest effect, the maximum amount of surgery is performed, including the maximum possible depth, length and number of keratotomy incisions. The refractive result of the intervention, taking into account these parameters, is calculated and predicted in advance using a special computer program.

However, the interval between keratotomy and PRK is too large, while keratotomy leads to a lifelong restriction of the patient in relation to physical activity, creates an increased risk in case of possible subsequent injuries. In addition, manipulation is painful for the patient and may produce late refractive changes.

It is known to conduct the combined operation of specialized laser keratomileusis (LASIK) after photorefractive keratectomy.

However, when LASIK is performed after photorefractive keratectomy, there is a risk of stretching, tearing and sliding of the corneal epithelium under the pressure of the head of a moving microkeratome. The reason for this is the uneven fixation of the epithelium in different zones and the degree of thinning. In addition, due to pre-performed photorefractive keratectomy, which ended unsuccessfully and led to the appearance of a fleur that entailed LASIK surgery, the corneal cut surface may be less smooth than it could be on an unoperated cornea, and this in turn leads to an increase in the possibility of amplification optical aberrations. According to our data, in addition, the frequency of damage to the epithelium during specialized laser keratomiliasis after photorefractive keratectomy is rather high, about 67% (see "LASIK" J. G. Pallikaris, D. S. Siganos, SLACK Incorporated, 1999, p. 305-309).

In essence, repeated refractive operations are aimed at eliminating residual unplanned myopia: radial keratotomy + LASIK (RU 2147425, 04/20/2000) or elimination of complications: repeated LASIK (RU 2147854, 04/27/2000).

The closest analogue of the proposed method can be the above-described method of the same purpose, including a two-stage intervention - keratotomy and subsequent evaporation of the corneal stroma by UV-laser radiation (RU 2154451, 08.20.2000).

The task of the invention is to develop a two-stage intervention LASIK in the correction of high myopia and thin cornea.

The technical result of the proposed method is to obtain a high refractive effect.

The technical result is achieved due to a two-stage metered elimination of myopia at both stages with the simultaneous elimination of optical aberrations of higher and lower order at the second stage of the intervention.

As mentioned above, repeated LASIK was used earlier to eliminate the complications that arose.

In the proposed method, at each of the two stages, LASIK is used to correct myopia, while the aberrations that occurred at the first stage are eliminated at the second together with the planned residual myopia. It is such a two-stage intervention that allows you to get a good refractive effect in patients with high myopia and a thin cornea.

The method is as follows. The patient determines cooperative clinical refraction, scans the optical tract of both eyes and reveals the presence of lower-order optical aberrations - spherical and cylindrical, as well as higher-order aberrations, and measures the thickness of the cornea using keratopachymetry. Scanning is carried out by the NIDEK OPD-SCAN device, which is a “wavefront” aberrometer and operating on the principle of “infrared microscopy”. The device scans the entire optical path of the eye at 1440 points. After that, the ablation depth is theoretically calculated for conventional ablation, multizonal and personalized. As you know, conventional ablation eliminates myopia and astigmatism. Multizonal ablation is a variant of conventional ablation, characterized by a lower ablation depth, while corneal thickness is “saved”. Personalized ablation eliminates myopia, astigmatism and high-order optical aberrations (coma, dystrophy, etc.), individual for each particular eye. Personalized ablation consists of customized (eliminates myopia and astigmatism) and segmental (eliminates optical aberration). The required residual corneal thickness should be at least 250 microns. The estimated thickness of the flap is 150 microns. Thus, the ablation depth (L) should not exceed L≤N-400. In patients with a thin cornea, neither normal nor personalized ablation can be performed in full.

At the first stage, according to standard LASIK technology, an intervention is performed, and multizonal ablation is calculated so that, as a result of the first stage, astigmatism is completely neutralized and myopia is partially neutralized (planned residual myopia can be about -2 D). After 3-5 weeks, a repeated scan of the optical path is carried out, with an increase in the initial level of higher order optical aberrations by approximately 17-18%. Pachymetry is repeated and a possible corneal thinning is determined. Based on the rescan data, an operating data file is compiled taking into account the correction of residual myopia and higher order optical aberrations. According to the standard method, a corneal flap is raised and personalized ablation is performed, while aberrations of the lower (simple residual myopia) and higher (preoperative and induced during the first stage) orders are neutralized.

Example. Patient K., 29 years old. Preoperative Clinical Refraction:

OD 003 sph - 14.5 cyl - 2.5 ax 0 = 0.7;

OS 003 sph - 15.25 cyl - 1.75 ax 0 = 0.6.

An OPD scan of both eyes revealed the presence of higher order optical aberrations (in addition to lower order aberrations - sph., Cyl).

Keratopachymetry (N) to the center. zone: OD = 572 μm, OS = 567 μm. Theoretically calculated ablation depth with 6.0 mm / 7.0 mm zones (optical / transition zones):

1) Normal ablation: OD = 218.2 microns; OS = 217.1 μm.

2) Multizonal ablation: OD = 147.1 μm; OS = 142.2 μm.

3) Personalized ablation (based on OPD data - scan - a): OD = 241.2 microns; OS = 238.6 μm.

Thus, theoretically, when conducting multizonal ablation, the ablation depth decreases by OD = 71.1 μm; OS = 74.9 μm.

The required residual corneal thickness should be at least 250 microns. The estimated thickness of the flap is 150 microns. Thus, the ablation depth (L) should not exceed L≤N-400. In this particular case, neither ordinary nor personalized ablation can be carried out in full.

The first stage of LASIK standard technology carried out the first stage of the operation. We calculated multizonal ablation in such a way that, as a result of the first stage of the operation, completely neutralize astigmatism and partially neutralize myopia (planned residual myopia of -2.0 D - does not fit into the sphere).

Estimated data:

OD: sph - 12.5 cyl - 2.5 ax 0; ablation depth = 133.1 μm;

OS: sph - 13.25 cyl - 1.75 ax 0; ablation depth = 128.2 μm.

As a result of the first stage of the operation, the planned refraction was achieved (on the third day):

OD 0.4 sph - 2.0 = 0.7,

OS 0.4 sph-2.0 = 0.6.

After 5 weeks, a second OPD scan of both eyes was performed, an increase in the initial level of optical aberrations of higher orders by 17-18% was revealed. Refraction (after 5 weeks):

OD 0.3 - 0.4 sph - 2.0 = 0.7,

OS 0.3 sph - 2.0 = 0.6.

Pachymetry: OD = 439 μm, OS = 439 μm.

Thus, another 39 microns can be removed on the right eye, 39 microns on the left eye.

Based on the latest OPD scan data, an operating data file was compiled taking into account the correction of residual myopia and higher order optical aberrations.

The ablation depth by 6.0 / 7.0 mm zones calculated by a computer was

OD = 36 μm, OS = 40 μm.

37 days after the first operation, the second stage of the operation was performed on both eyes. Corneal flaps were raised according to standard procedures and personalized ablation was performed. During the second operation, aberrations of the lower (simple residual myopia) and higher (preoperative and induced during the first stage) orders were neutralized.

VISUS on the 3rd day after the second stage of the operation:

OD = 0.8,

OS = 0.8.

Thus, the proposed method of two-stage keratomileusis allows to achieve emmetropic refraction in patients with a high degree of myopia and a thin cornea.

Claims (2)

1. A way to eliminate high myopia in the presence of a thin cornea, including two-step LASIK intervention, in the first stage, multizonal ablation is performed with a decrease in the degree of myopia to a myopia of a weak degree, and after 3-5 weeks at the second stage, optical aberrations of higher and lower order, and then repeatedly carry out LASIK taking into account the identified aberrations to obtain emmetropic refraction. 2. The method according to claim 1, characterized in that the aberrations are detected by scanning the optical path.