IES930121A2 - Apparatus for use in photorefractive keratermomy - Google Patents

Abstract

An apparatus 10 comprises a support structure 100 having a first, second and third laser producing means 11, 12 and 13. The first laser means 11 produces an excimer beam which passes through an'optical system 14. The second and third 5 laser producing means 12, 13 each produces a He-Ne laser beam. A binocular view apparatus 50 is provided. Light producing means 21 is provided which together with a lens 20 forms the optical system 14. In use, a patient views a fixation light which delineates the area of an eye to be t 10 ablated. The beams from the second and third laser producing means 12, 13 are allowed to overlap on the cornea so as to coincide with the beam produced by the first laser producing means 11 thereby ensuring that the first laser producing means 11 is focused correctly in the plane of the 15 tissue to be deleted.

Description

This invention relates to an apparatus for use in photorefractive keratectomy otherwise known as PRK.

PRK is a process whereby the front surface of a cornea is reshaped so as to correct, or ameliorate the effects of, an optical error. The technique involves a process known as photoablation which removes very fine layers of cells from the front surface of the cornea, without damaging the underlying cells. In a shortsighted person, it flattens the cornea and in a longsighted person steepens the cornea. The technique uses laser energy (ultra-violet radiation at 193 nanometers) delivered to the cornea in a controlled manner usually with the aid of a computer.

IE 930121 IE 930121 - 2 Prior to the use of the laser energy, the surgeon employing the technique must first remove the epithelium which covers the surface of the cornea so that the laser energy can etch a new curvature on the front surface of the substance of the cornea. The epithelium is removed by a blunt hockey stick blade. In the majority of the procedures, the diameter of the area which is ablated is about 5mm.

It is important that the area which is to be 10 ablated is exactly central to the visual axis of the eye and further that the area is entirely free of epithelium. Non-concentric or irregular ablation will result in an induced optical error. The known apparatus shown in Figure A of the drawings essentially comprises a first means for producing a laser beam 11, and a second means for producing two laser He-Ne beams (12 and 13) and a green fixation light. The He-Ne laser beams are directed onto the cornea of the patient from the right and left side of the patient. The green fixation light is parallel to the laser beam which is used to correct the optical error. The patient observes the green fixation light. When the He-Ne beams are overlapping, the laser beam is actuated and is automatically focused precisely on the correct plane. A circular zone marker is pressed onto the surface of the cornea to delineate the area from which it is desired to remove the epithelium. The laser beam is focused onto this area free of epithelium.

There are a number of difficulties with this technique and apparatus. In order for the surgeon to observe the area delineated by the circular zone marker, an illuminating beam of light produced by a light source B is shone on the eye which illuminating beam is IE 930121 - 3 directed obliquely from one side. The intensity of the beam must be relatively strong (about 60-100 watts) which causes photophobia which, in some cases, is severe depending on the duration that the illuminating beam needs to be on and the light sensitivity of the patient.

In addition, the patient finds it difficult not to move the eye out of the range of the area visualised by the surgeon through a binocular microscope 50, and hence prevents the technique from being carried out quickly and accurately so as to overcome the problem of the corneal tissues becoming dehydrated. It is also difficult to observe the indentation left by the zone marker. One or more of these problems can result in the removal of more epithelium than is necessary, or an incorrect ablation due to tissue dehydration.

It is an object of the present invention to overcome these problems.

The invention, therefore, provides an apparatus for use in photorefractive keratectomy which comprises a first means for producing a laser beam, a second means for producing two laser He-Ne beams, means for producing a first or fixation beam of light, means for enabling the He-Ne laser beams to overlap the anterior corneal stroma of an eye so that the laser beam may be actuated to remove a predetermined quantity of stroma from the cornea, and means for producing a second beam of light capable of delineating and, illuminating a predetermined area of the cornea for enabling the mechanical removal or ablation of the delineated epithelium of the eye.

IE 930121 - 4 Preferably, means is provided for varying the diameter of the beam of light so as to enable the part of the cornea which it is desired to ablate to be delineated according to the desired diameter.

Preferably, there is interposed between the source of the beam of light and the cornea a suitable filter such as a Wratten (Trade Mark) 66 filter which helps epithelial visualization.

Preferably, means is provided for enabling 10 the laser beam and the second beam of light to be concentric relative to each other.

The invention also relates to a lens element for use in the apparatus according to the invention which element comprises a convex, planar or concave lens having located substantially centrally thereof an aperture for permitting the passage of electromagnetic radiation through the element without the radiation being influenced by the lens.

The invention will be understood in greater detail from the following description of preferred embodiment thereof given by way of example only and with reference to the accompanying drawings in which:Figure 1 is a front elevation of part of the apparatus according to the invention; Figure 2 is a partially cut-away view of the apparatus of Figure 1 of the drawings; IE 930121 - 5 Figure 2a is an elevation of a lens for use in the apparatus of Figure 1 of the drawings; Figure 2b is a plan view of the lens of Figure 2a; Figure 2c is an elevation of a light source for use in the apparatus of Figure 1 of the drawings; Figure 2d is a plan view of the light source of Figure 2c of the drawings; and Figure 3 is a side view of the apparatus of Figure 1 of the drawings.

Referring now to the drawings, there is shown an apparatus 10 according to the invention which comprises a support structure 100 on which is mounted a first laser producing means 11, a second laser producing means 12 and a third laser producing means 13.

The first laser producing means 11 is mounted so as to enable a laser or excimer beam produced by it to be directed through an optical system 14 also mounted on the support structure 100.

The second and third laser producing means and 13 are not directly associated with the optical system 14. Each laser producing means 12, 13 produces a He-Ne laser beam.

Associated with the optical system 14 and also mounted on the support structure 100 is a binocular viewing apparatus 50 for enabling a surgeon to view the images of a patients eye through the optical system 14.

IE 930121 - 6 Also associated with the optical system 14 is a means for producing a fixation light (not shown) in eluding means (not shown) for enabling the fixation light to be shone in a beam parallel with the excimer laser beam. The purpose of the fixation light is to enable the patient to visually target the laser beam. Well-known means such as a microprocessor may be used to correct any differences between the fixation light and the laser beam due to parallex error. The fixation light is usually green in colour and of relatively low power and, therefore, is not stressful to the patient.

The apparatus 10 also includes means 21 for producing a beam of light including means for enabling the beam to be directed through the optical system 14.

The optical system 14 includes a lens 20 and the light producing means 21.

The lens 20 essentially comprises a concave lens suitable for focusing the light produced by the light producing means 21 onto the cornea of a patient.

As it is desirable for the beam from the light producing means 21 and the laser beam produced from the laser producing means 11 to be concentric relative to each other, the lens 20 incorporates an opening 22 located substantially centrally of the lens 20 and through which opening may be directed the laser beam from the laser producing means 11. The lens 20 may be mounted within a suitable housing 30 of a conventional type by means of supports 31, 32.

The light producing means 21 comprises a circulating shaped housing 33 in which is housed a filament IE 930121 - 7 34. The housing terminates in legs 35, 36 through which project the respective ends 37, 38 of the filament 34.

Such a construction of the light producing means 21 is well known. The light producing means 21 is mounted in the housing 30 by means of supports 39, 40 having regard to its circular shape does not interfere with the laser beam produced by the first laser producing means 11.

If desired, conventional means (not shown) for varying the diameter of the beam of light produced by the light producing means 21 may be incorporated within the housing 30. The means for varying the diameter of the beam could be of the iris type which would not interfere with the laser beam produced by the first laser producing means 11.

In use, the patient (not shown) is positioned so that the eye of the patient which is to be treated is located below the optical system 14.

The fixation light is illuminated and the 20 patient asked to look at the fixation light. In order to delineate the area to be ablated, the light producing means 21 is actuated so as to produce a beam of low intensity light having a diameter of about 5mm with the appropriate light filter. The diameter is suitably adjusted by means of the diameter varying means. When the surgeon is satisfied that the area to be ablated is correctly delineated, the epithelium is removed with a blunt hockey stick blade.

IE 930121 - 8 Following the removal of the epithelium, the first laser producing means 11 is actuated so as to remove a predetermined quantity of anterior stroma from the cornea. The two He-Ne laser beams produced by the second and third laser producing means 12, 13 are actuated and allowed to overlap on the patient's cornea so as to be coincident with the beam produced by the light producing means 11. The He-Ne beams serve to ensure that the first laser producing means 11 is focused correctly in the plane of this tissue to be ablated.

The apparatus according to the invention provides for a more comfortable environment for the patient insofar as the relatively high intensity light beam is no longer necessary. In addition, the need for using the zone marker is no longer required which use in some cases caused additional anxiety to the patient and furthermore, the indentation mark left by it was not very easy to observe through the binocular viewing apparatus 50. The accurate delineation of the area of the epithelial removal ensures the surgeon removes no more than the necessary amount - thus decreasing the time of re-epithelialization and lessening the pain suffered by the patient.

The invention is not limited by or to the specific embodiments described which can undergo considerable variation without departing from the scope of the invention.

Claims (5)

1. . An apparatus for use in photorefractive keratectomy which comprises a first means for producing a laser beam, a second means for producing two laser He-Ne beams, means for producing a first or fixation 5 beam of light, means for enabling the He-Ne laser beams to overlap the anterior corneal stroma of an eye so that the laser beam may be actuated to remove a predetermined quantity of stroma from the cornea, and means for produc ing a second beam of light capable of delineating and, 10 illuminating a predetermined area of the cornea for enabling the mechanical removal or ablation of the delineated epithelium of the eye.

2. An apparatus as claimed in claim 1 wherein 15 means is provided for varying the diameter of the second beam of light so as to enable the part of the cornea which it is desired to ablate to be delineated according to the desired diameter. 20

3. An apparatus as claimed in claim 1 or claim 2 wherein means is provided for enabling the laser beam and the second beam of light to be concentric relative to each other. 25

4. An apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

5. A lens element for use in the apparatus 30 according to any of claims 1-4 which element comprises a convex, planar or concave lens having located substantially centrally thereof an aperture for permitting the passage of electromagnetic radiation through the element without the radiation being 35 influenced by the lens.