fig1 shows an eye 10 to be treated comprising a lens 12 , an iris 14 and a cornea 16 . the corneal area 16 a to be treated with laser radiation ( e . g . excimer laser radiation having a wavelength of 193 nm ) is hatched in fig1 . fig1 is a vertical section through the eye 10 . fig2 shows a top view of the eye 10 to be treated and the arrangement of three radiation sources 20 , 22 , 24 for the auxiliary radiation used for determining the eye position . neither the camera system nor the actual laser treatment beam are shown separately in the figures . they correspond to the above - mentioned prior art . the description following hereinbelow is therefore limited to the auxiliary radiation and its arrangement with respect to the eye . each individual radiation source 20 , 22 , 24 consists of a plurality of individual light - emitting diodes ( leds ) 26 . the leds emit radiation in the infrared region having a wavelength of 810 nm . for the camera ( not shown ) a daylight filter is used . the camera used can e . g . be a black - and - white camera . for achieving good measurement results with respect to the eye position , it is important to obtain a high contrast between the pupil ( dark ) and the iris ( bright ). this is achieved by means of the auxiliary radiation of the radiation sources 20 , 22 , 24 , which is described here . in the embodiment shown , each radiation source 20 , 22 , 24 comprises twelve individual ir leds which are interconnected so as to define an array of 3 × 4 leds . fig1 shows one of the radiation sources ( radiation source 24 ) so that the individual leds 26 can be seen . the two outer led rows , which each consist of four leds , have e . g . a radiation angle of ± 8 °, whereas the inner row , which comprises four leds , has a radiation angle of ± 20 °. the radiation angle referred to corresponds approximately to the divergence angle of the radiation lobe . the above - mentioned choice of radiation angles permits mixing of the radiation within an array ; this proved to be advantageous with regard to a shadow - free and homogeneous illumination . a choice of different radiation angles within one radiation source is preferably used in the case of all three radiation sources 20 , 22 , 24 . the radiations produced by the individual leds are combined so as to form one composite beam 30 , 32 , 34 . the resultant beams can be seen from fig1 and 2 as far as their positioning relative to one another and relative to the eye 10 to be treated is concerned . in the horizontal representation according to fig2 the actual laser treatment beam ( not shown separately ) extends at right angles to the plane of the drawing ; its axis is designated by reference numeral 18 . the illuminating beams ( auxiliary beams ) 30 , 32 , 34 extend slightly inclined to the horizontal plane and at an angle α relative to the axis 18 of the laser treatment beam . fig1 shows the angles between the illumination beams 30 , 32 and the laser treatment beam 18 , viz . the angles α 1 and α 2 . the above applies accordingly to the third radiation source 24 . the angles α 1 , α 2 are in a range of 40 to 60 °. the distance d between the exit aperture of the illuminating beams 30 , 32 , 34 and the top tangential plane of the cornea to be treated is approx . 20 to 150 mm , preferably approx . 30 to 100 mm . it will be particularly advantageous to achieve light admission of the ir light outside of the treatment zone 16 a by means of the above - described oblique incidence of the illuminating radiation . this will guarantee that no substantial change in the conditions for the illuminating radiation will occur during the treatment . during the treatment , the transmission of the cornea may change drastically within the treatment zone 16 a . in the case of the illumination system described and shown in fig1 and 2 , such a change does not have any substantial influence on the illuminating radiation and , consequently , the determination of the eye position . in addition , disturbing but unavoidable reflections of the ir illuminating radiation on the corneal surface are displaced into the peripheral area of the cornea where they will not disturb the evaluation of the determined contour of the pupil . fig1 and 2 also show a preferred arrangement of the radiation sources relative to one another . two radiation sources 20 , 22 are arranged such that the illuminating beams 30 , 32 emitted by them form an angle p when projected onto a horizontal plane . the angle β is an acute angle , preferably in the range of from 25 to 70 °, better still in the range of from 35 to 65 °. the third radiation source 24 is then arranged in such a way that its radiation 34 extends approximately in the area of the angle bisector 36 of the angle β between the two other beams . this will lead to optimum illumination and best results with regard to the determination of the eye position when the camera images are being evaluated .
a device for the medical treatment of the eye with laser radiation uses auxiliary radiation for determining the eye position . with the aid of the auxiliary radiation , pictures are taken by means of a solid state image camera for determining eye movements and for causing the laser treatment radiation to follow accordingly . infrared radiation sources , which are arranged in a triangle above the eye to be treated , are used for the auxiliary radiation .