Control program for a device for photorefractive corneal surgery of the eye
AssigneeWavelight Laser Technologies GmbH
InventorsMichael Mrochen, Maik Kaemmerer, Theo Seiler
Life of this patent
Estimating the term…
Abstract
In a control program, according to which a laser-beam spot is guided, while being controlled with respect to position and time, over a cornea to be corrected photorefractively, so as to ablate a predetermined ablation profile therefrom, the effect of the angle between the laser earn and the corneal surface on the energy density of the laser-beam spot incident on the corneal surface and/or on the fraction of the laser-beam energy incident on the corneal surface which is reflected away, is taken into account when generating the control program.
Claims9
A computer readable media including a control program, according to which a laser-beam spot is guided, while being controlled with respect to position and time, over a cornea to be corrected, so as to ablate a predetermined ablation profile therefrom, comprising:
- instructions to take into account the effect of the angle between the laser beam (68) and the corneal surface on the energy density of the laser-beam spot incident on the corneal surface,
- wherein the time interval the laser-beam spot is incident on the corneal surface at an incident point (58) of the corneal surface is increased as a function of the distance (r) of the incident point (58) of the laser-beam spot centre on the cornea (54) from an axis running parallel to the laser-beam direction which axis meets the corneal surface at a right angle (z axis),
- wherein the effect of the distance r of the incidence point (58) of the laser-beam spot centre on the cornea (54) from an axis running parallel to the laser-beam direction which meets the corneal surface at a right angle (z axis), is taken into account, and account is taken of the fact that the energy density F of the emitted laser-beam spot of radius rs is reduced to F/kl(r), in the case of a cornea assumed to be hemispherical with radius R, when incident on its curved surface (54), where
- k1
-
- (
- r
- )
- =
- A
- eff
-
- (
- r
- )
- A
- 0
- =
- A
- eff
-
- (
- r
- )
- π
- ·
- r
- s
- 2
- and
- A
- eff
-
- (
- r
- )
- =
- ∫
- -
- rs
- rs
-
- ∫
- rs
- 2
- -
- x
- 2
- +
- r
- -
- rs
- 2
- -
- x
- 2
- +
- r
-
- 1
- +
- (
- ⅆ
- ⅆ
- x
-
- f
-
- (
- x
- ,
- y
- )
- )
- 2
- +
- (
- ⅆ
- ⅆ
- y
-
- f
-
- (
- x
- ,
- y
- )
- )
- 2
-
- ⅆ
- x
-
- ⅆ
- y
- with
- z=f(x,y)=f(r)=√{square root over (R2−x2−y2)}=√{square root over (R2−r2)},
- r=(x2+y2)1/2
- where x, y, z are the coordinates of the incidence point (58) of the laser-beam spot centre in a Cartesian coordinate system, in which the origin lies at the sphere centre of the cornea which is assumed to be hemispherical.
A computer readable media including a control program, according to which a laser-beam spot is guided, while being controlled with respect to position and time, over a cornea to be corrected photorefractively, so as to ablate a predetermined ablation profile therefrom, comprising:
- instructions to take into account the effect of the angle between the laser beam and the corneal surface on the fraction of the laser-beam energy incident on the corneal surface which is reflected away,
- wherein the effect of the distance r of the incidence point (58) of the laser-beam spot centre on the cornea from an axis running parallel to the laser-beam direction, which meets the corneal surface at a right angle (z axis) is taken into account,
- wherein account is taken of the fact that, in the case of the cornea assumed to be hemispherical with radius R, the unreflected fraction of the energy density F of the laser-beam spot incident on the curved surface is given as (1-k2(r))·F, where
- k2
-
- (
- r
- )
- =
- q
- ⊥
- 2
-
- (
- r
- )
- +
- q
- ∥
- 2
-
- (
- r
- )
- 2
- with
- q
- ⊥
-
- (
- α
- 1
- )
- =
- n
- 2
- -
- sin
- 2
-
- (
- α
- i
- )
- -
- cos
-
- (
- α
- i
- )
- 1
- -
- n
- 2
- q
- ∥
-
- (
- α
- 1
- )
- =
- n
- 2
-
- cos
-
-
- (
- α
- i
- )
- -
- n
- 2
- -
- sin
- 2
-
- (
- α
- i
- )
- n
- 2
-
- cos
-
- (
- α
- i
- )
- +
- n
- 2
- -
- sin
- 2
-
- (
- α
- i
- )
- where π/2-α1 is the angle between the laser beam and the corneal surface, where
- α
- 1
-
- (
- r
- )
- =
- α
-
-
- tan
- (
- r
- R
- 2
- -
- r
- 2
- )
- with 0≦r2<R2,
- and n is the empirically determined refractive index of the cornea at the wavelength of the laser beam which is used.
A computer readable media including a control program according to which an intensity of a laser-beam is controlled, while being controlled with respect to position and time, over a cornea to be corrected, comprising:
- instructions for determining a reduction in an energy density of the laser-beam incident on a corneal surface due to an angle between the laser beam and the corneal surface;
- instructions for determining a fraction of the laser-beam energy incident on the corneal surface that is reflected away;
- and
- instructions for adjusting the intensity in response to the determined fraction and reduction;
- wherein the time interval the laser-beam spot is incident on the corneal surface at an incident point of the corneal surface being increased as a function of he distance of the incidence point of the laser-beam spot center of the cornea from an axis running parallel to the laser-beam direction which axis meets the corneal surface at a right angle;
- wherein the energy density F of the emitted laser-beam spot of a radius rs is calculated as being reduced to F/k1(r), in the case of a cornea assumed to be substantially hemispherical with radius R, when incident on its curved surface (54), where
- k1
-
- (
- r
- )
- =
- A
- eff
-
- (
- r
- )
- A
- 0
- =
- A
- eff
-
- (
- r
- )
- π
- ·
- r
- s
- 2
- and
- A
- eff
-
- (
- r
- )
- =
- ∫
- -
- rs
- rs
-
- ∫
- rs
- 2
- -
- x
- 2
- +
- r
- -
- rs
- 2
- -
- x
- 2
- +
- r
-
- 1
- +
- (
- ⅆ
- ⅆ
- x
-
- f
-
- (
- x
- ,
- y
- )
- )
- 2
- +
- (
- ⅆ
- ⅆ
- y
-
- f
-
- (
- x
- ,
- y
- )
- )
- 2
-
- ⅆ
- x
-
- ⅆ
- y
- with
- z=f(x,y)=f(r)=√{square root over (R2−x2−y2)}=√{square root over (R2−r2)},
- r=(x2+y2)1/2
- where x, y, z are the coordinates of the incidence point (58) of the laser-beam spot centre in a Cartesian coordinate system, in which the origin lies at the sphere centre of the cornea.
A computer readable media including a control program according to which an intensity of a laser-beam is controlled, while being controlled with respect to position and time, over a cornea to be corrected, comprising:
- instructions for determining a reduction in an energy density of the laser-beam incident on a corneal surface due to an angle between the laser beam and the corneal surface;
- instructions for determining a fraction of the laser-beam energy incident on the corneal surface that is reflected away;
- and
- instructions for adjusting the intensity in response to the determined fraction and reduction;
- wherein the time interval the laser-beam spot is incident on the corneal surface at an incident point of the corneal surface being increased as a function of the distance of the incidence point of the laser-beam spot center of the cornea from an axis running parallel to the laser-beam direction which axis meets the corneal surface at a right angle;
- wherein an unreflected fraction of the energy density F of the laser-beam spot incident on the curved surface is calculated by the formula (1-k2(r))·F, where
- k2
-
- (
- r
- )
- =
- q
- ⊥
- 2
-
- (
- r
- )
- +
- q
- ∥
- 2
-
- (
- r
- )
- 2
- with
- q
- ⊥
-
- (
- α
- 1
- )
- =
- n
- 2
- -
- sin
- 2
-
- (
- α
- i
- )
- -
- cos
-
- (
- α
- i
- )
- 1
- -
- n
- 2
- q
- ∥
-
- (
- α
- 1
- )
- =
- n
- 2
-
- cos
-
-
- (
- α
- i
- )
- -
- n
- 2
- -
- sin
- 2
-
- (
- α
- i
- )
- n
- 2
-
- cos
-
- (
- α
- i
- )
- +
- n
- 2
- -
- sin
- 2
-
- (
- α
- i
- )
- where π/2-α1 is the angle between the laser beam and the corneal surface, where
- α
- 1
-
- (
- r
- )
- =
- α
-
-
- tan
- (
- r
- R
- 2
- -
- r
- 2
- )
- with 0<r2<R2,
- and n is the empirically determined refractive index of the cornea at the wavelength of the laser beam which is used.
Dependencies are inferred from the claim text.