Ophthalmologic device for breaking down eye tissue

#The present invention relates to an ophthalmological apparatus for the breakdown of eye tissue. The invention relates, in particular, to an ophthalmological apparatus which comprises a base station having a light source for generating light pulses, and an application head which can be mounted on an eye, which application head is provided with a light projector for the focussed projection of the light pulses for punctiform breakdown of eye tissue, and having movement drivers for moving the light projector in a feed direction and in a first scanning direction.

#Instances of ametropia such as myopia (short-sightedness), hyperopia (longsightedness or far-sightedness) or astigmatism can nowadays be permanently corrected by refractive surgical treatment. Refractive surgical treatments are surgical operations on the eye which change the optical refractive power of the eye with the aim of bringing it as close to a desired value as possible. One of the most important methods in refractive surgery is so-called laser-assisted in situ keratomileusis (LASIK) in which the interior of the cornea is removed with the aid of a computer-controlled eximer laser after a corneal flap has previously been partially severed and folded away. In order to produce the corneal flap, use is made of mechanical microkeratomes in which a driven scalpel cuts the corneal flap. Recently, such corneal flaps can also be cut with the aid of strongly focussed femtosecond laser pulses, which have pulse widths of typically 100 fs to 1000 fs (1 fs=10−15 s). The risks existing during use of a mechanically oscillating scalpel are avoided by the use of a femtosecond laser. Such a system is marketed, for example, by IntraLase Corp, in Irvine, Calif., USA under the name of Pulsion FS Laser. The overall size of the known systems having femtosecond lasers is comparable to the overall size of an eximer laser, the disadvantage being that the space required for the eximer laser is required once again in the treatment room for the femtosecond laser system. In addition, after the cutting of the corneal flap by the femtosecond laser system the patient must be transferred to the eximer laser. The overall size of the fentosecond laser is determined, inter alia, by the light source used, the scanner technology and the attendant beam guidance systems.

#The laser beam is focussed inside a large stationary lens system by means of beam-deflecting optical elements onto the tissue areas of the eye to be separated. For design reasons, the maximum achievable numerical aperture (NA, proportional to half the sine of the aperture angle of the objective) of the focussing optical system is limited in this case (typically NA=0.2-0.3). For a given work area, for example the entire cornea, the scanning optics (typically f-Theta optics) requires a minimum working distance. In conjunction with the required movement and the achievable size of the beam-deflecting optical elements, the working distance determines a design limit for the diameter of the scanning optics. A further upper design limit for the diameter follows from instances of shadings or collisions with body parts (eyebrows, nose). Even in the case of large diameters, it is always possible to illuminate only a subarea of the optics with a scanning laser beam. The result of this is an upper design limit for the effective useful numerical aperture of the optics. High apertures are desirable because with high NA it is possible to produce small focal points, and thus a smaller cutting zone per pulse. Less gas is produced per pulse in smaller cutting zones than in large cutting zones. More precise cuts can be made by means of smaller gas bubbles since, inter alia, the cutting zones are not substantially deformed by the internal gas pressure. In addition, high NAs require disproportionately less energy per pulse to make a cut. With a lower energy, there is also a reduction in the cavitation bubbles produced by the laser pulse, and this additionally has a positive effect on the cutting quality. Furthermore, the retina is subject to less stress from the more strongly diverging beams downstream of the focal point, given high NAs. A further advantage is that for high NA local contaminants in the vicinity of the corneal surface have less effect in reducing the intensity at the focus.

#A design of the present invention is described below with the aid of an example. The example of the design is illustrated by the following attached figures:

#FIG. 1 shows a block diagram which schematically illustrates an ophthalmological apparatus which has an application head which is connected to a base station via an articulated arm.

#FIG. 2 shows a diagrammatic cross section of the articulated arm with an optical transmission system fitted therein.

#Mutually corresponding components are denoted in FIGS. 1 to 8 by identical reference symbols.

#In FIG. 1, the reference numeral 1 denotes an ophthalmological apparatus which comprises a base station 11 and an application head 3 which are interconnected via an articulated arm 13.

#The base station 11 is of mobile configuration and has a lockable running gear 18. In addition, the base station 11 has a height adjusting means 17 which enables the height of the base station 11 to be adjusted. The base station 11 also comprises an electronic control module 15 which is set up to receive control signals from a user via a foot switch 19 arranged externally in relation to the housing of the base station 11. The control module 15 can also be operated and controlled by a user via a display and operating unit 14. The base station 11 further has a vacuum pump 16, a light source 51, a scanner 52 and a rotation element 54 which are controlled by the control module 15. The control module 15 also controls the movement drivers 57 of the application head 3.