RU2209054C1 - Ophthalmic surgical laser device - Google Patents

Abstract

FIELD: medical engineering. SUBSTANCE: device has laser with parametric light generator inside of resonator device having in- series-connected output parametric mirror partially transparent for signal wave and completely reflecting for excitation wave, non- linear crystal element directed in synchronism direction for producing signal wave in bandwidth of 1930-1950 nm, internal parametric mirror transparent for excitation wave and deaf for signal wave forming parametric light generator, the first active element, member for rotating polarization plane to 90 deg, lens having focal length of F₀, the second active element, electro-optical shutter and end reflector like mirror deaf for excitation wave or like prism roof. Focal length F₀ of the lens is selected from known relation. EFFECT: enhanced effectiveness of cataract treatment. 1 dwg

Description

 The invention relates to ophthalmology and can be applied, in particular, in the surgical treatment of cataracts.

 Known ophthalmic surgical laser systems for the treatment of cataracts, which use solid-state lasers on various crystals.

The following requirements apply to ophthalmic surgical laser systems for cataract treatment:
- the wavelength of the laser radiation should lie in the IR (1800-10000 nm) spectral range, where the radiation is effectively absorbed by biological tissues;
- the duration of the pulses should be no more than 50 ns to ensure the evaporation (ablation) of tissues without thermal effects on surrounding tissues.

 Known ophthalmic surgical laser installation, including a laser based on yttrium aluminum garnet doped with erbium (AIH: Er) [1]. The laser has a wavelength of 2.94 μm, a pulse duration of 200 μs, a pulse energy of 5-50 mJ, and a pulse repetition rate of 10-100 Hz. The disadvantage of this setup is the low rate of destruction of dense catarrhal nuclei, which is associated with the non-optimal laser pulse duration. The disadvantage of the installation is the complexity of the design of the system for delivering radiation to the surgical field, which uses unstable to laser radiation and expensive optical fiber.

 Ophthalmic surgical laser installations are also known, including a holmium doped yttrium aluminum garnet laser (AIG: Ho) with a wavelength of 2.08 μm [2]. The disadvantage of these installations is also the low fragmentation rate of dense catarrhal nuclei, associated with a low absorption coefficient of radiation.

 The disadvantage of all used ophthalmic surgical laser systems is that they can only work at a fixed wavelength, which is determined by the active medium of the laser used, and the set of parameters of the laser radiation pulses (wavelength, duration, energy, repetition frequency) is not optimal for microsurgery.

 Known lasers with parametric conversion of the frequency of the radiation, which allow you to smoothly tune the wavelength of the radiation or work with a fixed wavelength within the tuning range. These lasers consist of a pump laser (usually an IR laser using neodymium-containing crystals) and a parametric light generator (ASG). An ASG consists of a nonlinear crystalline element oriented in the direction of synchronism for generating a signal wave, which is placed in an optical resonator formed by an output parametric mirror partially transparent for the signal wave and a parametric mirror deaf for the signal wave. In CGS, pump radiation is converted to longer-wave radiation [3].

 A well-known laser operating in the Q-switching mode with intracavity CGP: wavelength 1571 nm, pulse repetition rate up to 100 Hz, pulse energy up to 30 mJ, pulse duration 5 ns [4]. The disadvantages of this laser include a limited average radiation power (one laser head and induced effects in the laser optical circuit).

 Closest in technical essence to the invention is an ophthalmic surgical laser unit for removal of catarrhal tissue [4]. As a radiation source, it used a pulsed neodymium-aluminum Yttrium garnet laser (AIG: Nd) with a tube pump operating in the free-running mode (wavelength 1444 nm, pulse energy 50-350 mJ, pulse duration 250 μs, pulse repetition rate 12 -30 Hz) with a fiber-optic system for delivering radiation to the surgical field.

 The disadvantage of this installation is the increased likelihood of complications when removing dense cataracts, such as local edema of the cornea, increased intraocular pressure due to an increase in the time of surgery.

 At the same time, there is a need for an ophthalmic surgical laser unit with an optimal radiation wavelength, short duration and high pulse repetition rate.

 The objective of the invention is the creation of an ophthalmic surgical laser unit that allows for the treatment of cataract to destroy dense catarrhal nuclei in a short time while reducing traumatic effects on the eye.

где L= a+b; F₁ и F₂ - фокусные расстояния термических линз, наведенных излучением ламповой накачки в активных элементах, а - расстояние от линзы до концевого отражателя; b - расстояние от линзы до выходного параметрического зеркала, I_{н пор} - пороговая плотность энергии параметрического генератора света; I_пред - лучевая прочность электрооптического элемента.To solve the problem in an ophthalmic surgical laser system, including a pulsed solid-state laser with a pumped lamp and a fiber-optic system for delivering radiation to the operating field, a laser with a parametric light generator inside the resonator was used, including a sequentially located parametric output mirror partially transparent to the signal wave and completely reflecting for the pump wave, a crystalline nonlinear element oriented in the direction of synchronism for the generation of a signal wave in the range 1930-1950 nm, an internal parametric mirror transparent for the pump wave and blank for the signal wave, forming a parametric light generator, the first active element, a 90 ^o polarization plane rotator, a lens with a focal length F ₀ , the second active element electro-optical shutter consisting of two polarizers and the electrooptical element therebetween, and an end reflector in the form of mirrors, blind to the pump wave, or as a roof-prisms, wherein the focal length of the lens F ₀ is chosen Xia the relation

where L = a + b; F ₁ and F ₂ are the focal lengths of thermal lenses induced by the radiation of a tube pump in the active elements, and is the distance from the lens to the end reflector; b is the distance from the lens to the output parametric mirror, I _{n pore} is the threshold energy density of the parametric light generator; I _pre - beam strength of the electro-optical element.

An essential distinguishing feature of the present invention from the prototype is the replacement of the AIG: Nd laser operating in the free generation mode with an ASG laser operating in the cavity Q-switched modulation mode, the radiation wavelength of which is combined with the local absorption maximum of catarrhal nuclei in the range 1930-1950 nm. At the same time, qualitatively new installation properties were achieved:
- the pulse duration fell into the nanosecond range and therefore the thermal effect on the surrounding tissue is significantly reduced;
- the energy of impulses required for ablation decreased and, therefore, the traumatic effect on the eye decreased;
- the maximum pulse repetition rate (with two active elements and two pump lamps) increased, which led to a reduction in the time of the operation.

 Moreover, by increasing the distances a and b, it is possible to reduce the peak power of the pulses by increasing the duration of the radiation pulses (while remaining in the nanosecond range) to a value that allows transmission of radiation pulses with the required energy through the optical fiber without damaging the latter.

 The advantage of the installation is also that an optical fiber made of quartz, transparent to the working wavelength of the laser, can be used.

 The drawing shows a schematic optical diagram of the proposed laser installation.

где L= a+b; F₁ и F₂ - фокусные расстояния термических линз, наведенных излучением ламповой накачки в активных элементах, а - расстояние от линзы до концевого отражателя; b - расстояние от линзы до выходного параметрического зеркала; I_{н пор} - пороговая плотность энергии параметрического генератора света; I_пред - лучевая прочность электрооптического элемента.The laser cavity is formed by an output parametric mirror 1, deaf for the pump wave and partially transparent for the signal wave, and end reflector 2, made either in the form of a mirror deaf for the pump wave, or in the form of a prism-roof, the edge of which lies in the plane of the drawing. The crystalline nonlinear element 3 is oriented in the direction of synchronism for generating a wavelength in the range 1930-1950 nm. The internal parametric mirror 4 completely transmits pump radiation and completely reflects the signal wave. The first active element 5 is of a cylindrical shape made of a crystal activated by Nd ions and having a cubic crystal lattice (AIG: Nd, HCHG: Cr, Nd, HCHG: Cr, Nd, etc.) grown in the [001] direction, oriented so that the crystallographic axes X and Y make an angle of ± 45 ^o with the plane of the drawing. If a crystal is grown in the [111] direction, then its azimuthal orientation can be arbitrary. In the case of the use of active elements from uniaxial crystals AI: Nd, ILF: Nd, etc. element 5 is oriented so that the plane of polarization of radiation lies in the plane of the drawing. The element itself is placed in a illuminator containing a reflector and a pump lamp. The second active element 6 is placed in the same illuminator as element 5. If it is from a cubic crystal, then it is oriented in the same way as element 5. If element 6 is from a uniaxial crystal, then its plane of radiation polarization should lie in the plane perpendicular to the plane of the drawing. Between the active elements 5 and 6, there is a 90 ^° rotator of the plane of polarization of the pump radiation 7 for mutual compensation of the birefringence thermally induced by the radiation of the pump lamps in the active elements. Next to the active element 6 is placed lens 8, the role of which is to adjust the total lens with a focal length F ₀ selected from the relation:

where L = a + b; F ₁ and F ₂ are the focal lengths of thermal lenses induced by the radiation of a tube pump in the active elements, and is the distance from the lens to the end reflector; b is the distance from the lens to the output parametric mirror; I _{n pore} is the threshold energy density of a parametric light generator; I _pre - beam strength of the electro-optical element.

The electro-optical shutter operating according to the λ / 2 scheme consists of an electro-optical element 9 and two polarizers 10 and 11, which transmit radiation in a plane perpendicular to the plane of the drawing. You can also use polarizers with a transmission plane in the drawing plane, then you should rotate the active elements 5, 6 (if they are from uniaxial crystals) and the nonlinear element 3 by 90 ^o around its geometric axis parallel to the axis of the resonator. Swivel mirrors 12 can reduce the longitudinal dimensions of the laser.

 The laser radiation exiting through the mirror 1 is focused by the lens 13 into the optical fiber 14, through which the radiation is transmitted to the patient. The optical fiber ends with a laser tip with a working needle, which is a hollow tube containing a light guide extending from the distal end of the tube by 0.5-2 mm.

The role of lens 8 is to adjust the total lens with equivalent focal length
F $\genfrac{}{}{0ex}{}{\text{-1}}{\text{Σ}}$ = F ₁ ^-1 + F ₂ ^-1 + F ₀ ^-1 . (2)
The correction of the total lens is made from the following considerations.

Из уравнений (2) и (3) следует определение для нижней границы оптической линзы 8:

Другим условием работы лазера является нахождение его резонатора в области устойчивости, которая достигается при F_Σ<L/2, где L=a+b. Поэтому нижнюю границу для F₀ определяют из неравенства 2/L-F₁ ^-1-F₂ ^-1≥F₀ ^-1.From the calculation of the radiation caustics in the resonator, consisting of two flat mirrors with an asymmetrically located lens, it follows that the cross-sectional areas of the pump radiation S ₃ on element 3 and S ₉ on element 9 are related as
S ₉ / S ₃ = (F _Σ -a) / (F _Σ -b). (3)
According to the results of experimental studies of the operating modes of a laser with an intracavity CGP, it was determined that the radiation strength of element 9 with a 30% margin should be greater than the threshold energy density of the pump radiation pulses I _{p then} corresponding to the threshold for CGM generation:

From equations (2) and (3) follows the definition for the lower boundary of the optical lens 8:

Another condition for the laser to work is to find its cavity in the stability region, which is achieved at F _Σ <L / 2, where L = a + b. Therefore, the lower bound for F ₀ is determined from the inequality 2 / LF ₁ ^-1 -F ₂ ^-1 ≥F ₀ ^-1 .

The values of I _before , I _{n pores} , F ₁ and F _{2 are} determined by calculation or experimentally.

 The proposed installation works as follows.

In the pulse-periodic mode, during each pulse of the pump lamp (discharges through the lamps are carried out synchronously) with a closed electro-optical shutter, the inverse population accumulates in the active elements 5 and 6. When a high-voltage trigger pulse is applied to the electrodes of the electro-optical element 9, the gate opens and is generated in the resonator pump radiation pulse. With a slight delay relative to its beginning, a signal wave pulse is generated in the CBC, the duration of which depends, in particular, on the cavity length L = a + b. If the energy of the pulses of the output laser radiation is sufficient to destroy dense catarrhal nuclei when leaving the fiber, but optical damage to the fiber is observed, then the cavity shoulders a and b should be increased and the lens with F ₀ corresponding to relation (1) should be selected again. In this case, the duration of the radiation pulses will increase, and the peak power will decrease to a value safe for this type of optical fiber. The pulse repetition rate is chosen close to the limit, determined by the allowable electric power of the pump lamps in order to reduce the time of the operation.

 A laser needle is inserted through the corneal paracentesis into the anterior chamber of the eye. The working needle is brought as close to the surface of the lens as possible and the generation of laser pulses is turned on. A gradual destruction of the substance of the lens occurs. At the same time, the lens fragments are aspirated. After the nucleus of the lens "breaks" into several fragments, they are alternately destroyed and aspirated. Then make the leaching of the remains of the crystalline masses according to the standard method.

To confirm the effectiveness of the proposed device, a setup was tested that included a laser based on AIG elements: Nd размером5x65 mm in size, a nonlinear KTP element (phase angle θ = 55 ^° , φ = 0 ^° ), an electro-optical element made of a LiNbO ₃ crystal, and ⌀400 μm optical fiber from quartz. For 15 ns pulse width were selected L = 1,7 m, a = 0.7 m, b = 1 m. Experimentally identified values F ₁ = F ₂ = 5 m, I _{n pores} = 100 MW / cm ^2, I _pre = 100 MW / cm ² . According to the formula (1) 1.67 m≤F ₀ ≤10 m, therefore, a lens with F ₀ = 2 m was selected.

 Installation tests were carried out on rabbits. The energy of the radiation pulse at the fiber output was 16–18 mJ, the wavelength was 1.942 μm, and the frequency was 50 Hz. The clear rabbit lens was removed using a laser system. Through the oppositional corneal incision, a dense human lens core was implanted into the capsular bag, removed during extracapsular cataract extraction. Then, the implanted dense nucleus was removed using a laser system and an aspiration system.

 Thus, the proposed ophthalmic surgical laser unit allows you to destroy dense catarrhal nuclei in the treatment of cataracts, which confirms its effectiveness.

Sources of information
1. "Phacolase ^TM The ErYAG Laser System", prospectus of Aesculap-Meditec GmbH.

 2. T. Kecik, D. Kecik, J. Kasprzak, A. Pratnicki, Z. Jankiewicz, A. Zajac, "Experimental studies on the usage possibilities of the holmium laser in cataract surgery". Proc. SPIE, vol. 2781, pp. 34-39, 1996.

 3. Akhmanov S. A., Khokhlov R.V. "Parametric amplifiers and light generators", Uspekhi Fizicheskikh Nauk, 1966, v. 88, issue 3, p. 439.

 4. RF patent 2101817, H 01 S 3/10.

 5. S. N. Fedorov, V.G. Kopaeva, Yu.V. Andreev, A.V. Belikov, "Results of 1000 laser cataract extractions", Ophthalmosurgery, 3, 1999, pp. 3-14 - prototype.

Claims (1)

An ophthalmic surgical laser system including a pulsed solid-state laser pumped by a lamp and a fiber-optic system for delivering radiation to the surgical field, characterized in that the pulsed solid-state laser is made in the form of a laser with a parametric light generator inside the resonator and contains a sequentially located parametric output mirror, partially transparent for a signal wave and completely reflecting for a pump wave, a crystalline nonlinear element oriented along synchronism systematic way for generating the signal wave in the range of 1930 ... 1950 nm, the internal parametric mirror transparent for the pump wave and the signal wave blind for forming the optical parametric oscillator, a first active element 90 ^o -vraschatel polarization plane, a lens with a focal length F _0, the second active element, an electro-optic shutter, consisting of two polarizers and the electrooptical element therebetween, and an end reflector in the form of mirrors, blind to the pump wave, or as a roof-prisms, wherein the focal The distance F of the lens is selected from the relation ₀

where L = a + b;
F ₁ and F ₂ are the focal lengths of thermal lenses induced by the radiation of a tube pump in the active elements;
a is the distance from the lens to the end reflector;
b is the distance from the lens to the output parametric mirror;
I _{n pore} is the threshold energy density of a parametric light generator;
I _pre - beam strength of the electro-optical element.