Equipment for the correction of presbyopia by remodelling the corneal surface by means of photoablation

Abstract: The invention relates to equipment for the correction of presbyopia by means of corneal surface modelling by photo-ablation, of the type which uses a laser beam (16) (excimer laser) which is masked with a special mask (5) in such a way as to strike surfaces (19) of the cornea (3) in a sickle-shape configuration and located in proximity to the lower area of the pupil rim (20), on which surfaces (19) a removal action of very small-thickness uniform tissue layers is effected.

Description: The invention relates to equipment for the correction of presbyopia by remodelling the corneal surface by means of photo-ablation. The prior art document EP-A-0 207 648 embraces the use of special laser equipment able to generate a radiation beam capable of vaporising in an extremely regular and precise way very thin layers, of microscopic thickness (measured in um) of the eye cornea tissue. Such equipment is used for the remodelling of the corneal curvature to correct hyperopia, myopia and astigmatism. To this end the prior art teaches the use of diaphragms and masks which have the task of permitting the laser beam to reach and ablate the corneal surface in pre-established areas. By the use of masks and diaphragms, whose apertures can be controlled and co-ordinated with programmed laser beam application times, it is possible to realise a kind of step-shaped "sculpting" of the cornea through a succession of photo-ablated excisions of uniform single-layers, of differing lengths, from the cornea itself. The principal aim of the present invention is the perfection of a device which, by exploiting the above-described technology, permits of realising an effective correction of presbyopia. The invention, as described in the claims which follow, solves the problem by proposing the use, in conjunction with an excimer laser, of a template or shaped mask so equipped as to permit of a special modelling by photo-ablation of a part of the cornea surface situated close to the lower part of the pupil rim. An advantage of the invention is its substantial simplicity. Further characteristics will better emerge from the detailed description which follows, of a preferred but not exclusive embodiment of the invention, here illustrated purely in the form of a non-limiting example in the enclosed drawings, in which: Figure 1 shows a schematic section along plane II-II of the following figure 2; Figure 2 shows a right-side schematic view of figure 1; Figures 3 and 4 show, in enlarged and altered scale, a part of figure 1 represented in two different operative configurations. With reference to the drawings, 1 indicates a diaphragm, or mask applied to an eyeball 11. The mask 1 comprises a structure having the function of a frame 5, envisaged to permit of leaning directly on the eyeball 11, on which frame 5 an organ with mask function 1 is envisaged comprising two flat plates 12 and 13 arranged one above the other and glided to slide along the same plane, but in opposite directions with respect to the frame 5. The two plates 12 and 13 are therefore reciprocally constrained by a mechanism by means of which their contemporaneous symmetrical movement with respect to the frame 5 is produced according to the directions indicated (and vice-versa) by the two arrows 14 and 15. In particular, the first plate 12 is partially shaped with a slit in the form of a circular arc, said slit edge being destined to define the rim or curved edge 22 of the aperture 10 of the mask 1. The plate 13 has instead a convex shaping in the form of a circular arc, which arc rim defines the rim or edge 23 of the said aperture 10. In particular, the radius of the curved edge 23 is greater than the curvature radius of the curved edge 22 so that the aperture 10 in any intermediate position assumed by the two plates 12 and 13, has a sickle-shape configuration. The diameters of the two circular arcs constituting the edges 22 and 23 are determined in such a way as to be similar to the diameter of the pupil opening. The mask 1 is arranged so as to direct, through its aperture 10, a laser beam 16 on an area 19 of the corneal surface 3, which area 13 is situated in proximity to the lower part of the pupil rim 20. The operation is performed according to a succession of operative phases which initially envisage that the two plates, 12 and 13, should be reciprocally positioned at the minimum distance so as to identify the minimum value of the aperture 10. Subsequently, a progressive reciprocal distancing between the two plates 12 and 13, activated with a pre-established sequence of tiny relative movements according to the two arrows 14 and 15, is performed up until the maximum value of the said aperture 10 is reached. The laser beam 16, for example produced by an excimer laser, is synchronised with the pre-established values of the aperture 10. With every different value of the said aperture 10, the laser beam 16 strikes a pre-established surface of the cornea which surface, in the example, comprises internally the surface defined by the preceding aperture 10 value. Some phases of the entire sequence are schematically represented in figs. 3 and 4, in which the step-like modelling of the corneal areas involved in the laser beam 16 action is shown. At the end of the operation, the area of the cornea near the lower rim of the pupil, indicated in the figure with the number 19, has been remodelled with a sort of shaped recess, which is more or less accentuated depending on the degree of defect correction required. The remodelled area thus constitutes a zone of the cornea which functions differently from the rest of said cornea, like in fact a lens with a different focal length which focal length permits of focussing on near objects. The particular conformation of the corneal area 19, as well as its positioning on the lower pupil rim 20, permit, in the case of presbyopia, of a notable improvement in near sight without however disturbing longsight ability. With the aim of minimising the longsight disturbance, the area 19 and thus the shaping of the aperture 10 is proportioned to the diameter of the pupil and in particular the edge 23 of the plate 13 whose diameter is about the same as that of the pupil rim 20. Thanks to the symmetry of the movement of the two plates 12 and 13 and to the positioning of the aperture 10 with respect to the pupil, the sickle-shaped recess realised on the corneal surface has its deepest point at about the level of the pupil rim 20. For the correct functioning of the entire operation, the mask 1 is equipped with a suction system arranged in the lower part of the frame 5, that is, immediately below the two plates 12 and 13.

Claims: Equipment for the correction of presbyopia by means of modelling of the corneal surface by photo-ablation comprising: a laser capable of generating a pulsed laser beam (16) which is able to remove, with each impulse, a thin layer of tissue from the corneal surface; a mask (1) having a frame (5) and a masking organ arranged so as to mask the said laser beam (16) and to expose, at every impulse or application of said laser beam (16) a pre-established surface area of the cornea, wherein said mask (1) has an aperture (10) corresponding to the lower pupil rim (20), said aperture (10) being variable and geometrically defined by at least two principal curved edges (22) and (23) reciprocally facing and arranged in such a way as to give the said aperture (10) a form defined by a first curved edge (22) having its curve externally convex, and a second curved edge (23) having its curve externally concave. Equipment as in claim 1, wherein said first edge 22 has a curvature which is greater than that of the said second edge 23. Equipment as in claim 2, wherein said edges 22 and 23 are circular arcs. Equipment as in claim 3 wherein said masking organ with mask function 1 comprises two flat plates 12 and 13, able to be guidedly slid one on the other along the same plane, but in opposite directions to one another with respect to the said frame 5; its being envisaged that the said first plate 12 is shaped with a slit in the form of a circular arc, which plate 12 edge is destined to define the said first edge 22 of the said aperture 10; its being furthermore envisaged that the said second plate 13 has convex shape according to another circular arc which plate 13 is destined to define the said second edge 23 of the said aperture 10.

Inventors: NIZZOLA GUIDO MARIA, NIZZOLA, GUIDO MARIA
Applicants: NIBATEC SA, NIBATEC S.A.
Application year: 1991
Main classification: A61F9
IPC codes: A61F9, A61F2