FR2626466A1 - APPARATUS FOR THE SURGICAL TREATMENT OF ASTIMAGTISM - Google Patents

Abstract

An apparatus for the surgical treatment of astigmatism is disclosed. According to the invention, it comprises a laser 1 and a former 3 for distributing the energy density in the cross section of the beam 2 of the laser; the former 3 has the form of an optical cuvette 7, the windows 8 and 9 of which are installed with the possibility of rotation about the axis 21 of the beam 2; the internal surfaces of the windows 8 and 9 are cylindrical surfaces of second order revolution; the cuvette 7 is filled with a medium 10 which partially absorbs the laser radiation. The invention applies in particular to the treatment of myopic, hypermetropic or mixed astigmatism.

Description

The present invention relates to medicine,

  more particularly to ophthalmology, and more specifically

  to astigmatism (myopic, hypermetropic and mixed), With myopia and farsightedness, astigmatism is the most widespread eye defect in the world. The correction of astigmatism to

  the use of glasses does not always ensure the quality required

  correction, whereas the use of

  tact causes some discomfort for patients. The

  the most promising method for the correction of astigmatism

  matism is the surgical modification of refraction.

  of the eye. Compared with conventional surgical procedures for astigmatism that currently exist, laser surgery presents

  clear advantages, such as complete sterility,

  mathematical ass of the results of the intervention and a

high accuracy.

  The development of reliable, easy-to-use and easy-to-manufacture devices for the surgical treatment of astigmatism by laser

  represents a major task today.

  There is known a device for the treatment of

  of astigmatism which includes a pulsed laser and a radiation energy density distribution former in the cross-section of the beam in the beam path of that laser (Report of the "IBM Science Center" ", Paris, France,

  Doc. NF 104, 1986, K. Hanna et al. "Excite Laser Refrac-

tive Keratoplasty ").

  In this device, the distribution

  the energy density of the radiation in the form of a

  than pivoting with a slot of an erected form. As a result of the action of many laser radiation pulses, for a given ratio between the moment of appearance of the radiation pulse and the angular position of the

262à466

  slot relative to the main axes of the patient's eye, there is a change in the shape of the cor surface,

  necessary for correcting astigmatism.

  However, following the use of the

  As is known above, only a part of the cornea, which is determined by the shape of the slit and by its position, is produced at the same time.

  angle at the given moment, which makes it difficult to obtain

  of smooth surfaces of a desired profile since each radiation pulse removes, from the cornea, a

  layer with vertical walls, the shape of which corresponds

  lays at the shape of the slot. Therefore, we are getting

  of the required form of the corneal surface by a sur-

  staged surface and to obtain a smooth surface, we must remove many layers of shallow depths

  prolongs the duration of the intervention and complicates its

  tion by requiring a precise fixation of the eye of the

  Holds relative to the laser's radius for a long time

  period of time. The energy of the laser radiation is used

  not very efficient, which also condionned

  an increase in the duration of the intervention. This appa-

  Known material is complicated to manufacture because it requires a high precision of preparation. slot and mechanism

  of rotation, a measure of precision of the angular position

  slot and an adaptation, with that, of the moment

  of the appearance of the pulse of the laser radiation.

  The disadvantages mentioned above reduce

  the accuracy of the results of the intervention and

  the possibility of complications.

  - The problem posed in the present invention

  to set up an apparatus for the surgical treatment of astigmatism with a construction of

  distributor of the. energy density of the

  in the laser beam cross-section which, as a result of the irradiation of the whole corneal surface, ensures a smooth surface of a desired profile, thereby reducing the duration of the laser beam. surgical intervention and increase the efficiency

of use of the radiation.

  This problem is solved by the fact that, in an apparatus for the surgical treatment of astigmatism, comprising a pulsed laser and a radiation energy density distribution former in the cross-section of the beam, this former being on the path of the radiation beam, according to the invention, the energy density distribution former has the shape of an optical cuvette whose first and second windows, located in the path of the radiation beam, are arranged with a possibility of rotation around

  the axis of the beam and are made of a trans-

  radiation of the laser, their internal surfaces being second-order cylindrical surfaces and the

  principal direction of each of them being

  pendicular b the axis of symmetry of the beam of

  This bowl is filled with a medium which partly absorbs the laser radiation. It is advantageous that the bowl is disgorging and that it communicates with a circulation system of the absorption medium provided with a means for changing the optical density of this medium. For the treatment of myopic astigmatism, it is advantageous to make the internal surfaces of the two windows of the bowl in the form of cylindrical parabolic surfaces whose convexity is turned towards the inside.

of the bowl.

  For the treatment of hypermetropic astigmatism

  sting, it is advantageous to make the internal surfaces

  the two windows of the bowl in the form of cylindrical surfaces

  circular dies whose convexity is turned towards

the outside of the bowl.

  For the treatment of mixed astigmatism, it is advantageous to make the internal surfaces of the two windows of the bowl in the form of cylindrical hyperbolic surfaces, one of which must be turned by its convexity.

  inward and outward of the bowl.

  The apparatus for the surgical treatment of

  tigmatism according to the invention can significantly reduce the duration of the intervention, ensures a high efficiency of use of the energy of the laser and gives the possibility of obtaining, at the end of the intervention, a smooth surface

and a desired profile of the cornea.

  The invention will be better understood and other purposes, details and advantages thereof will become more apparent in the

  light of the explanatory description which will follow from

  various embodiments given solely by way of nonlimiting examples, with references to the appended nonlimiting drawings in which:

  - Figure 1 shows the device for the treatment

  Surgically astigmatism according to the invention, - Figure Z shows an alternative embodiment of the windows of the optical bowl for the treatment of myopic astigmatism in isometry; FIG. 3 shows an alternative embodiment of the windows of the optical cuvette for the treatment of hypermetropic astismagtism, in isometry. FIG. 4 shows an alternative embodiment of the windows of the optical cuvette for the treatment of mixed astigmatism. in isometry; FIGS. 5a and b schematically show an eye in the treatment phase of myopic astigmatism, in sectional views made along mutually perpendicular astigmatic meridians; FIGS. 6a and b schematically show an eye during treatment of hypermitropic astigmatism,

  in sectional views along astigmatic meridians

  perpendicular work; and FIGS. 7a and b schematically show an eye in the treatment phase of mixed astigmatism,

  sectional views along reciprocal astigmatic meridians

perpendicularly.

  The apparatus for the surgical treatment of the

  tigmatism (myopia, hyperopia -at mixed) according to the

  tion, shown in FIG. 1, comprises a pulsed laser 1

  and, arranged in succession on the path 2-of its

  a trainer 3 for the distribution of energy density.

  radiation on the cross section of the beam 2, a diaphragm 4 and a lens 5 which establish the diameter of the operating area on the cornea 6 of the eye

of the patient.

  The 3-density distribution former

  the energy is formed of an optical bowl 7 whose windows

  8 and 9 which lie in the path of the beam 2 of the laser radiation 1 are made of a material transparent to the

  laser radiation, for example quartz, and their

  internal faces are cylindrical surfaces of second

  order. We understand here under the term international surface

  windows 8 and 9, the separation surface between the cavity of the bowl 7 and the material of these windows 8 and 9. The bowl 7 is filled with a medium 10 which absorbs

  partially the laser radiation and it is

  communication with a circulation system of the absorption medium 10, and it is for this reason that the

  wall of its cylindrical body It carries a connection of

  12 and an outlet connector 13. Through a pipe 14, the inlet connector 12 communicates via a gas expander, serving as a means for changing the optical density of the medium 10 (by gas pressure), with a flange to

  compressed absorption gas 16, for example ammonia.

  At the outlet connection 13 are connected successively

  a valve 17 and a device 18 for absorbing the gas.

  In the case where an environment of ab-

  liquid sorption, for which it is possible to use, for example, an aqueous solution of NaCl, the circulation system

  (not shown in the drawings) includes a

  see liquid and a pump for pumping the liquid

  in a closed circuit through the bowl 7.

  As a laser 1, it is possible to use an excimer laser with homogeneous distribution of the 'radiation energy' density in the cross section of the beam. The windows B and 9 are respectively fixed in sockets 19 and. 20 which are installed in a

  cylindrical body 11, each of which is coaxial

  with the possibility of rotation about the axis of the body 11, this axis coinciding with the axis 21 of the laser beam 2. The outer end surfaces of the sockets 19 and 20 carry a scale on behalf of the angle of rotation. The cavity of the bowl 7 is étanehéifie relative to the external medium using known means of hermetization, such as fluorinated plastic seals

  (which are not represented by convention in Figure 1).

  As windows 8 and 9, we use

  telescopic rods whose surfaces delimiting cavities

  t.6 of the bowl 7 are cylindrical surfaces of

  cond parabolic order, hyperbolic, elliptical or

circular cylinder surfaces.

  FIG. 2 shows an embodiment variant

  windows 8 and 9 of the optical cuvette for the treatment

  myopic astigmatism, where the inner surfaces 22 and 23 are in the form of parabolic cylindrical surfaces

  turned, by their convexity, towards the interior of the bowl.

  you. The main directions 24 and 25 of the surfaces 22 and

  23 respectively are perpendicular to the axis of symmetry

21 of the beam.

  By the main statement of a curvi-

  line, indicate the direction, on the surface, along

  of which the normal section curvature has the greatest

-35 worth.

  FIG. 3 shows an alternative embodiment of the windows 8 and 9, whose internal surfaces 26 and 27 have the shape of circular cylinder surfaces of which

  the convents are turned towards the outside of the bowl.

  The main directions 28 and 29 of the surfaces 26 and 27 are respectively also perpendicular to the axis 21

beam.

  FIG. 4 shows an alternative embodiment of the windows 8 and 9 of the optical bowl, the inner surfaces 30 and 31 have the shape of cylindrical surfaces.

  hyperbolic with respectively main directions

  32 and 33 perpendicular to the axis 21 of the beam.

  The surface is turned, by its convexity, towards the interior.

  of the bowl while the surface 31 is turned,

  by its convexity, towards the exterior of this bowl.

  In the variants of realization of the windows 8

  and 9 shown in FIGS. 2, 3 and 4, it is also possible to

  also use other second order cylindrical surfaces. For example, in the variant shown in FIG. 2, the windows 8 and 9 may have hyperbolic, elliptical cylindrical surfaces or circular cylinder surfaces provided that these surfaces are turned, by their convexity, towards the interior of the cylinder.

  the bowl and that the main directions are ortho-

  gonales to the axis 21 of the beam. This also applies to the variants shown in FIGS. 3 and 4, provided that the convexity of the internal surfaces of the windows 8 and 9

  must be turned in the directions indicated for the

Figures 3 and 4.

  In each case the choice of the variant

  of the bowl 7 depends on the size and type. of the astig

  matism of the patient's eye, middle parameters

  of absorption 10 which is used as well as

  manufacturing practices and minimization requirements of

  aberrations of the optical system of the apparatus according to the invention.

tion.

  The apparatus for the surgical treatment of the

  Tigmatism according to the invention operates as follows.

  We will first examine the operation of the apparatus according to the invention on an example of treatment

myopic astigmatism.

  It is known that the surface of the cornea of the normal eye can be described by the equation of a paraboloid

of revolution.

  In myopic astigmatism, the surface of the

  cornea of the eye is described by the equation of a parabo-

  elliptical loid with radii of curvature at the top in all sections smaller than in the case of an eye.normal. For the treatment of myopic astigmatism, segment 34 should be removed from the cornea of the eye.

  (Figures 5a and b) which is delimited by two

  the paraboloid surface 35 and the paraben surface

  Boloide of revolution 36 (corneal surface of the normal eye). The change in the thickness of the segment 34 to be removed on the surface of the cornea can be described by an elliptical paraboloid equation with a maximum on the axis 21 of the beam. The sections of segment 34 in astigmatic meridians reciprocally perpendicular

  (directions of maximum refraction and minimal refraction

  male of the eye) are shown in Figures 5a and b. For

  to remove segment 34 during treatment of astigmatism

  myopic system using the apparatus according to the invention ,.

  firstly, taking into account the absorption coefficient of the medium 10 of FIG. 1, the value of the angle between the main directions 24 and 25 must first be calculated.

  (figure 2) windows B and 9 (figure 1) and then

  the windows 8 and 9 by rotation of sockets 19 and 20 until the angle between the main directions

  24 and 25 of Figure 2 becomes equal to the calcu-

  and that the bisector of this angle coincides with one of the meridians astigmatisms, principal directions and more precisely-with the direction of maximum refraction of the eye. The laser I is then turned on, the beam

  2, coming out of the laser 1 with uniform distribution of the den-

  sity of the energy in the cross section of the beam, through the window 8 of the bowl 7, the space between the windows 8 and 9 which is filled with the absorption medium

  , the window 9, the diaphragm 4, the lens 5 for

  come to the cornea 6 of the eye. Since the surface areas

  these internals of the windows 8 and 9 are curvilinear, the thick-

  of the middle layer 10 in the path of the radiation beam 2 is not uniform and increases from the center

  towards the periphery of the bowl 7, and there is a direc-

  maximum growth, and perpendicular to

  this one a direction of minimal increase of the thick-

sor.

  The absorption of the radiation in the medium 10 increases from the center to the periphery of the beam 2 with a different speed in different directions. After

  have passed through the bowl 7, the beam 37 has a distribution

  non-uniform energy delivery, symmetrical with respect to reciprocally perpendicular planes whose shape and parameters are determined: by the shape of the internal surfaces of the windows 8 and 9; and by the absorption coefficient of the medium which may vary, for example, as a result of the change in the pressure of the absorption gas or the concentration of the solution if it is a liquid medium. The distribution of energy density in the cross-section of the

  beam 37 is described by an equation close to the equation

  of the elliptical paraboloid with a maximum on the axis 21 of the beam 2, the degree of approximation increasing by

  periphery to the center of the beam 2.

  Then, the beam 37 passes through the diaphragm 4 and the lens 5. (which may be absent in the case of a

  sufficiently small divergence of the laser beam) to

dye the cornea 6 of the eye.

  During the course of the intervention, the absorption medium 10 is constantly pumped through

  the cavity of the bowl 7 by means of the cireula-

  to avoid the decomposition of this medium 10 under

  prolonged action of laser radiation 1.

  It is known that the action of ultraviolet far

  biological tissue brings a photo-ablation (photo-

  evaporation) of the latter, the thickness of the layer 10 removed being proportional to the density of the energy

  for a defined range of energy density of

is lying.

  The interaction of faiaceau 37, whose distribution

  energy can be roughly described

  13 as indicated above by the equation of parabola

  The sheptic tip with maximum energy density on the axis of the bundle, with the cornea 6, causes ablation of the zone 34 of the cornea, which is delimited by an elliptical paraboloid surface and a paraboloid surface of revolution, the first being the initial surface of the patient's cornea before treatment and the

  second being the surface the cornea after the action of the ray-

  Laser 1 (Figure 1). The irradiation is performed.

  until elimination of myopic astigmatism.

  In hypermetropic astigmatism, the surface

  of the cornea of the eye is described by the equation of para-

  elliptical boloids with greater radius of curvature at the top in all sections than in the case of

  the normal eye. For the treatment of hyper-astigmatism

  30. moped, it is necessary to remove the cornea, zone 38

  (Figures 6a and b) which is delimited by two surfaces para-

  bolicles, the surface 39 of elliptical paraboloid and the surface 40 of paraboide of r.volution (corneal surface of

  normal eye). Treatment of hypermetropic astigmatism

  This is done in the same way as in the case of myopic astigmatism and that as a form

  3 of the distribution of the density of the radiation energy-

  on the transverse plane of the beam 2, we choose the

  variant of the windows 8 and 9 of the bowl 7 which is

  3. As a result, at the outlet of the bowl 7, the beam 37 has an energy distribution which can be described by a paraboloid equation.

  elliptical with its minimum on the axis 21 of the beam 2.

  the interaction of such a bundle with the cornea 6, as can be seen in FIGS. 6a and b, leads to the ablation

l from zone 38 of its surface.

  In mixed astigmatism, the surface of the

  cornea of the eye can be described by the equation of para-

  elliptical boloids with a smaller radius of curvature in the meridian of maximum refraction and greater in the meridian of minimum refraction than the radius of curvature

  of the normal eye. For the treatment of mixed astigmatism

  From the cornea, zone 41 of FIGS. 7a and b must be removed, whose thickness change on the surface

  of the cornea can be described by a para-

  hyperbolic boloide. Treatment of mixed astigmatism

  is done in the same way as for myopic or hypermetropic astigmatism

  trainer 3 of distribution of the energy density of the ray-

  In the cross-section of the beam, the variant of the windows 8 and 9 of the bowl 7, which is shown in FIG. 4, is chosen. As a result, the beam

  37 at the outlet of the bowl 7 has a distribution of den-

  which can be roughly described by the equation of the hyperbolic paraboloid. The interaction of such a bundle with the cornea 6 leads to the removal of

  zone 41 of FIGS. 7a and b, of its surface.

  The invention will be better understood by means of

  the following explanatory example of its realization.

  One of the variants of the apparatus according to

  was prepared and tested. In order to

  to modify the refraction of the eye of the rabbit, a ray-

  laser (i) (193 nm) was used, with

  uniform energy distribution, consisting of a beam.

  parallel 2 of 6 mm diameter transmitted through the energy density distribution former 3 having identical windows 8 and 9 executed in the form of telescopic lenses with surfaces representing circular cylinders and prepared from quartz, which windows are firmly installed under a vacuum in the cylindrical body of the bowl 7 so that the convexity of one of them knows

  the interior of the other being turned towards the outside

  of the bowl 7 (as shown in FIG. 4).

  The windows 8 and 9 are fixed in the sockets 19 and 20 which can pivot in the cylindrical body 11 of stainless steel. For the connections 12 and 13, the formator 3 is connected to the system provide a flow of N2O under a pressure of ix 10 to 3 x 106 Pa. The frequency of repetition of the pulses of the laser 1 is equal to 10 Hz, the energy of

  the pulse being 100 to 300 mJ.

  For an experiment on 8 eyeballs of rabbits, we obtained an artificial mixed astLgmatism, by thermocoagulation and application of cuts by means of a diamond blade scalpel. At the end of the action

  laser'au means of the apparatus according to the invention, the correct

  G5 tien of artificially induced mixed astigmatism

* in myopia intervals of 0 to 3 D and hypermetropic

  from 0 to 2.5 D has been realized, allowing to obtain a

  smooth surfaces of the cornea subjected to irradiation

  tion. The use'of the apparatus according to the invention * makes it possible to increase the accuracy of obtaining the shape

  of the corneal surface as well as to reduce net

the duration of the intervention.

262,646 '

  1. Apparatus for the surgical treatment of astigmatism, of the type comprising a pulsed laser and a

  distribution of the energy density of the ray-

  on the beam cross-section placed on the path of said beam, characterized in that the energy density distribution former 3-the form of an optical bowl (7) whose windows (8 and 9) which are in the path of the beam of radiation are installed rotatably about the axis (21) of the beam (2) and are made of a material transparent to laser radiation, their internal surfaces being cylindrical surfaces of revolution of second order and

  principal direction of each of them being

  to the axis '21) of the beam (2) of radiation, the bowl (7) being filled with a medium (iO) 'partially

transparent to laser radiation.

  2. Apparatus according to claim 1, characterized in that the bowl (7) is disgorging and communicates with a circulation system of the absorption medium (10) provided with means for changing the optical deneity of said

medium (10).

  3. Apparatus according to claim 1, characterized in that the inner surfaces of the windows (8 and 9) 1 of

  the bowl (7) have the shape of cylindrical surfaces

  Bowls whose convexity is turned inwards

of said bowl.

  4. Apparatus according to claim 1, characterized in that the inner surfaces of the windows (8 and 9) of

  the bowl (7) have the shape of circular cylinder surfaces

  eyelids with outward-facing convexity

of said bowl.

  5. Apparatus according to revendicatiôn 1, characterized in that the inner surfaces of the windows (8 and 9) of

  the bowl (7) has the shape of hyper-cylindrical cylindrical surfaces

  boliques, one of them having its convexity

  towards the inside and the other towards the outside of that

vette.