The present invention relates to a method of and apparatus for adjusting the tension m sutures, and more specifically to those which are used in ophthalmic surgical procedures .

In general medical practice, when sutures are used to hold together the edges of a wound, in order to minimise the formation of scar tissue, it is important to ensure that the edges of the wound just butt together. In the case of ophthalmic surgery there is included the additional requirement that distortion of the eyeball can affect its optical performance and hence the quality of vision of the patient. A high level of skill is required which can result in considerable stress to the surgeon, particularly m a busy practice.

The present invention provides a method and apparatus which enables the tension in sutures to be adjusted after they have been inserted.The main advantage is the consequent reduction in post-operative distortion (astigmatism) m the patient, but also there is a reduction in the stress to the surgeon and the production of minimum scarring to the patient is facilitated.

According to the present invention there is provided a method of adjusting the tension in sutures made of a thermoplastic material comprising the operation of irradiating the suture with laser radiation of an intensity sufficient to soften but not melt the sutura and maintaining the irradiation of the suture until a desired tension in the suture has been achieved.

Also according to the present invention there is provided an apparatus for adjusting the tension m a

suture made of a thermoplastic material, wherein there is included means for producing a beam of laser radiation having an elongated cross-section with dimensions approximately equal to those of a suture the tension in which is to be adjusted and means for superimposing the beam of laser radiation upon the suture the tension in which is to be adjusted.

Some thermoplastic materials shrink initially when heated, some merely soften prior to melting, and others do both according to the temperature to which they are heated or the original tension in them. The present invention can be used with sutures of all the above types, but preferably uses sutures made of a material which equilibrates to a single tension at a given temperature. That is to say, if the original tension in the suture is greater than the equilibrium tension, it relaxes until that value is reached, if the original tension in the suture is less than that value, the suture shrinks until the equilibrium tension is reached.

A preferred material for the sutures is polyamides, coloured so as to improve the absorption of the laser radiation.

Suitable lasers include argon-ion and carbon dioxide lasers, particularly the former because they produce radiation in the visible region of the spectrum, which assists in aligning the laser radiation with the suture. On the other hand, the output radiation from a carbon dioxide laser is eye safe.

An example of the invention will now be described, by way of example, with reference to the accompanying drawings in which

Figure 1 shows diagrammatically the use of the invention following an ophthalmic surgical procedure; and

Figure 2 illustrates diagrammatically an apparatus for carrying out the invention.

Referring to Figure 1 of the drawings, an incision 1, made m the cornea 2, of an eye 3, is closed by sutures 4 in the usual way. The sutures 4 are made of a polyamide or other thermoplastic material, such as polypropylene or polyester, and, as is usual, have a diameter of about 20 microns. A beam of radiation 5 from an argon ion laser, which is not shown, is brought to a line focus commensurate in size with the sutures 4 and superimposed upon a suture 4 the tension in which is to be adjusted.

The curvature of the cornea 2 of the eye 3 is monitored by a surgeon who is carrying out the suture tension adjustment, by observing the reflection in the eye 3 of a system of illuminated translucent and opaque rings 6, known as a Placido disk, in the usual way. The surgeon is represented schematically by another eye 7. Any distortion of the surface of the cornea 2 of the eye 3 produces a corresponding distortion of the reflection of the system of circles 6 projected on the eye 3. For convenience, the Placido disk 6, laser beam 5 and surgeon, eye 9, are shown widely separated. In practice the angular separation is much smaller.

The surgeon having satisfied himself that the laser beam is aligned accurately upon a given suture 4, subjects the suture 4 to pulses of laser radiation of about 100 ms duration and at power levels of between 10 and 100 mW. After each pulse of laser radiation, the distortion of the surface of the cornea 2 of the eyeball

3 is checked by the surgeon 9 and the power level of the laser radiation is adjusted. The pulses of laser radiation cause the loosening of tight sutures and shrinkage m loose sutures, so tightening them. The higher the power level of the pulses, the greater the respective loosening or tightening effect.

The process is carried out until the surgeon is satisfied that the distortion of the surface of the cornea 2 of the eye 3 is minimised. The process may need to be carried out more than once as relaxation/healing of the eye which has been operated upon takes place.

Referring to Figure 2 of the Drawings, an apparatus for carrying out the invention comprises an optical fibre 20 which transmits laser radiation from an argon-ion laser, which is not shown, to a focusing and directing head 21. In the focusing and directing head 21 are a bi¬ convex lens 22, a first plano-convex focusing lens 23, a second plano-convex focusing lens 24 and a beam splitter 25. The plano-convex lenses 23 and 24 produce a line focus, approximately 1.5mm long and 50μ wide, of the laser beam at the eye 4 of a patient 26. These dimensions correspond to the normal dimensions of an ophthalmic suture. Conventional laser beam delivery systems produce laser energy distributions which are approximately circular m form. Such a form is not appropriate to the present invention because if the laser spot is small enough so as not to impinge on the eye of the patent, then only a small region of the suture will be treated, with a high risk of rupturing the suture - indeed, lasers have been used for this purpose - or, on the other hand if the laser spot is large enough to cover the suture, then a relatively large area of the patient's eye will be irradiated as well. Not only does this pose a risk of damage to the patient, but it is wasteful of

laser energy

The focusing and directing head 21 is held in a mounting 27 which can be moved towards or away from the eye 4 to be treated to bring the laser beam 5 to a focus on the eye 4, or sideways to enable one eye, or the other, of the patient to be treated to be selected for attention. These motions are shown as x and y, respectively. Crude adjustment of the position of the focus of the laser beam 5 in the vertical direction z is provided by means of an adjustable head rest 34 for the head 26 of the patient whose eye 4 is to be treated. The mounting 27 is also such as to enable the directing and focusing head 21 to be tilted about a vertical axis to control the horizontal pointing of the laser beam 5 (0 _y ) , about an horizontal axis to control the vertical pointing (0 _Z ) of the laser beam 5 and rotated about its optical axis to enable the azimuth 0 of the line focus of the laser beam 5 to be varied. Attached to the mounting 27 is a hood 28 which includes a number of lights 29, a translucent screen 30 which has a set of Placido 31 rings upon it and a television camera 32 which is positioned to view the patient's eye, the reflection of the placido rings, and the position of the laser beam on the eye. The camera 32 is connected to a monitor 33 which traces, displays, and if required, stores data relating to the position of the line focus of the laser beam 5.