SPECIFICATIONLaser apparatus for ophthalmic surgeryThe present invention concerns an ophthalmic surgery laser apparatus.
The apparatus is usable, for example, in therapy on the clouded posterior capsule after lens implantation, in treatment of glaucoma by pressure operation between the anterior and posterior chambers, and for surgery on tendons and other parts in the vitreous body.
In artificial lens surgery, the lens is implanted in the eye between the anterior and posterior chambers, anterior to the posterior capsule. In the majority of cases the posterior capsule becomes clouded postoperatively to present so-called postglaucoma. Postglaucoma is treated by posterior capsule surgery, that is by bombarding the posterior capsule with a laser beam at the clouded point. The energy density of the laser beam is extremely high at the focus, of the order of 1012 watts per cm2.
This high energy density gives rise to plasma formation, which tends to proceed in the direction from which the laser beam arrives, i.e. towards the artificial lens. Damage to the artificial lens is frequently caused by the plasma, even including cracking of the lens, and in many instances another artificial lens operation to implant a new lens is necesary.
The object of the present invention is to provide apparatus that can be used to eliminate the drawback described, and allow posterior capsule surgery to be done without dmaging the artificial lens.
According to the present invention ophthalmic surgery laser apparatus comprises a slit lamp having a lens system, an operating laser attached to the slit lamp, means for directing an operating beam from the operating laser onto the optical axis of the slit lamp, an aiming laser, means for directing an aiming beam from the aiming laser onto the optical axis of the slit lamp, and an adjustment means for adjusting the focus of the operating beam independent of the slit lamp's focus and of the focus of the aiming beam, preferably to lie behind the latter.
Thanks to the invention, the focus of the operating laser beam can be adjusted with reference to the focus of the aiming laser beam, preferably to lie behind the latter, as seen from the eyepiece of the slit lamp. In this case, the power of the plasma produced by the operating laser beam in the posterior capsule or in the inner parts of the eye will be attenuated before it meets the artificial lens, and the artificial lens will not suffer any damage.
Preferably the aiming beam is reflected by the aid of a mirror placed on the optical axis and which is asymetrical with reference to a straight line perpendicular to the optical axis, so that the light of the aiming laser as seen at the object of surgery through the slit lamp indicates by its asymmetry the position of the object with reference to the focus of the aiming beam.
The invention will be better understood from the following description of a specific embodiment thereof, given by way of example only with reference to the accompanying drawing, wherein:~Figure 1 is a schematic elevational view of a laser apparatus according to the invention; andFigures 2a and 2b illustrate on an enlarged scale the focussing of the operating laser beam and of the aiming laser beam in the eye when using an apparatus according to Fig. 1.
Fig. 1 shows an ophthalmic surgical laser apparatus, comprising a conventional slit lamp 1, e.g. a cornea microscope. The lens system 2 of the slit lamp comprises among others an objective 21 and an eyepiece 22; the optical axis has been indicated by the reference numeral 3. A surgical laser 4 is attached to the slit lamp, the laser beam 5 being carried onto the optical axis 3 of the slit lamp 1 by reflection with the aid of a dielectric mirror 21. The apparatus also comprises an aiming laser 6, the laser beam 7 thereby produced being carried onto the optical axis 3 of the slit lamp 1 with the aid of an annular reflecting mirror 14 having a non-reflecting central aperture 1 3.The mirrors 21 and 14 reflect the laser beams, desirably through an angle of 90 , onto the optical axis of the slit lamp, and they are focussed after leaving the objective 2', normally at the focus 10 of the objective.
As taught by the invention, the apparatus has been provided with an adjustment means 8 for effecting free adjustment of the focal point 9 of the laser beam 5 from the operating laser 4, that is, for its adjustment independent of the focal point 10 of the slit lamp and of the focal point 11 of the aiming laser's laser beam, preferably to be located behind the latter as viewed from the eyepiece 22.
Thus, referring now to Fig. 2a, the focal point 9 of the operating laser beam 5 can be directed to lie behind the focal point 11 of the aiming beam 7 by a distance a which may be, for example, 0.1-1 mm. In this case, when the operating laser beam is shot and when it causes plasma formation within the eye, the plasma cannot cause any damage in the lens 31. In Fig. 2a, the focus 11 of the aiming beam 7 and the focus 10 of the slit lamp coincide.
Fig. 1 shows the way in which the laser beam 7 of the aiming laser 6 is reflected onto the optical axis of the slit lamp 1 with the aid of the mirror 14 which is placed on said axis and which possess asymmetry with reference to a straight line 13 perpendicular to the axis (in the Figure, at right angles to the paper). In this case the asymmetry is provided by forming a gap 16 in the annular mirror. Thus, the beam of the aiming laser visible at the object of surgery through the slit lamp will by its asymmetry indicate the position of the object with reference to the focus 11 of the aiming laser. The situation is illustrated by Fig. 2b.
When the object A is located anterior to the laser beam focus 11 as viewed from the eyepiece 22 and the aiming beam strikes the object, the aiming beam will create an image 141 of the shaded mirror 14 on the object, the asymmetry of said image corresponding to the asymmetry of the light reflected by the mirror 14. When the object is located at the focus 11, the aiming beam is correspondingly seen through the eyepiece 22 as a point, with diameter for instance 50 #m. When the object is located behind the focus 11, the aiming beam produces the image 142 on the object with the asymmetry of the image seen inverted, in Fig. 2b with a gap 16 in the annular aiming beam pointing upward when in an image anterior to the focus 11, the gap 16 points downward.
The annularly shaped, assymetrically shaded mirror 14 shown in Figs. 1 and 2b and intended for reflecting the aiming beam 7 is particularly advantageous. The aiming beam consists of a ray bundle arranged in annular form, and the back reflections from outside the focus area, e.g. from the eye surface or from the contact glass are minimal because the viewing is with the eyepiece through said annular mirror. At the same time the foccussing is highly accurate.
In the- embodiment depicted in Fig. 1, the adjusting means 8 for adjusting the focus 9 of the operating laser beam 5 consists of a lens displaceable in the direction of the beam.
A convenient laser for use in the invention is an Nd-YAG laser, of wavelength 1064 nm.
The laser is of the Q-connected and integrated type, in other words, the crystal 18, laser mirrors 19 and tuner light source 20 have been packed to form a compact entity maintaining its tunig. Alternatively, a laser of theHeNe type may be used.