GB2485361A

GB2485361A - Ophthalmic marking tool

Info

Publication number: GB2485361A
Application number: GB201018984A
Authority: GB
Inventors: Bruno Zuberbuhler
Original assignee: Central Manchester University Hospitals NHS Foundation Trust
Current assignee: Central Manchester University Hospitals NHS Foundation Trust
Priority date: 2010-11-10
Filing date: 2010-11-10
Publication date: 2012-05-16
Also published as: GB201018984D0

Abstract

A marking tool 50 suitable for marking a portion of an eye comprises a support 52 having first 56 and second support 57 portions with first 64 and second blades 66 respectively, each blade having a blade edge 64a, 66a for contacting a surface of an eye in use. The blade edges 64a, 66a have a substantially straight or substantially convex profile and the extent of each blade in the first direction being greater at the outboard end than at the inboard end. This tool is particularly for use in toric lens implantation to correct astigmatism. The tool may comprise measurement means to measure angles, or indication means to indicate an axis of the eye.

Description

I

Marking Tool The present invention relates to a marking tool, in particular, but not limited to, a marking tool for use in marking the eye.

Astigmatism is a disorder of the shape of the cornea of the eye. Astigmatism is where the normally generally spherical surface of the cornea becomes generally ellipsoidal (for example, similar in shape to a portion of a prolate spheroid, such as a rugby ball). Astigmatism can cause blurred and distorted vision, squinting and headaches. Astigmatism is a common condition and approximately 17% of eyes of a normal population have at least mild astigmatism. Astigmatism remains lifelong and the prevalence increases with age. Patients with higher amounts of astigmatism may require spectacles or contact lenses to achieve good visual acuity.

With increasing age, it is common for people to develop a separate condition known as a cataract. A cataract is a clouding of the normally clear lens of the eye.

The standard treatment for a cataract is an operation in which the lens which has developed the cataract (also known as a cataracteous lens) is removed and replaced by a clear monofocal artificial lens implant.

Toric lenses are a recently developed type of lens implant which may be implanted during a cataract operation (instead of a monofocal lens implant) to substantially correct any pre-existing astigmatism within the eye whilst simultaneously treating the cataract. Toric lenses have two optical components: a spherical component that corrects short-sightedness or far-sightedness (in a similar manner to the way in which monofocal lens implants function), and a toric component that can compensate for corneal astigmatism. The toric component of the lens has an axis which must be generally aligned with the axis of the corneal astigmatism of the eye so as to provide the best possible compensation for the astigmatism. In order to perform this alignment the toric lens implant is rotated relative to the eye as part of the cataract operation.

Corneal marks, which are markings made on the cornea (for example, on the corneal limbus), may be created pre-operatively or during surgery in order to assist the person carrying out the cataract operation in correctly aligning the toric lens implant in relation to the eye (or, more specifically, aligning the axis of the tone lens implant with the axis of the corneal astigmatism). A marking tool is used to make the corneal marks.

Toric lenses are a relatively new technology and, as such, the methods used by surgeons for creating corneal marks may vary between different surgeons.

Furthermore, a plurality of different instruments (including different marking tools) may be used when determining and marking the axis of the corneal astigmatism of the eye.

The use of a plurality of different instruments in combination with multi-step procedures which may vary from one surgeon to another may lead to errors being made in the corneal marking procedure. For example, the corneal marks may be made inaccurately, may be difficult to see during the operation and/or may cause unnecessary trauma to the eye. It is an object of the present invention to obviate or mitigate at least one of the problems described above. It is a further object of the present invention to provide an alternative marking tool.

According to a first aspect of the present invention there is provided a marking tool suitable for marking a portion of an eye comprising a support having first and second support portions defining a clearance therebetween, first and second blades extending from the first and second support portions respectively, each blade having a blade edge for contacting a surface of an eye in use, the blade edges of the first and second blades lying substantially along a common blade axis and the first and second blades extending both along the blade axis and away from their respective support portion in a first direction perpendicular to the blade axis, wherein each of the first and second blades have an inboard end and an outboard end, and the blade edges of the first and second blade having a substantially straight or substantially convex profile and the extent of each blade in the first direction being greater at the outboard end than at the inboard end.

The blade edges of the first and second blade may have a substantially straight or substantially convex profile in a plane which is perpendicular to the blade axis and parallel to a support axis. In some embodiments, where the support is generally annular, the support axis may be an axis around which the generally annular support extends.

The extent of each blade in the first direction may generally increase from the inboard end to the outboard end, and wherein the rate of said general increase in the extent of each blade in the first direction may generally decrease from the inboard end to the outboard end. In some embodiments of the invention, the radius of curvature of the profile of the first and second blades may generally increase from the inboard end to the outboard end.

The marking tool may comprise a measurement feature configured to, in use, measure an angle between a reference point of an eye and the blade axis.

The support may comprise an annular portion or a part-annular portion.

The clearance between the first and second support features may be defined, at least in part, by an aperture in the support.

The marking tool may comprise an indication feature configured to, in use, provide an indication of the general orientation of an axis of a substantially ellipsoidal surface of an eye.

The indication feature may comprise an annular portion or a part-annular portion supported by the support generally between the first and second support portions.

The marking tool may comprise an alignment feature configured to, in use, align the marking tool with a portion of an eye.

The portion of the eye may be the centre of a cornea of the eye.

The alignment feature may comprise an annular portion or a part-annular portion supported by the support generally between the first and second support portions.

The alignment feature may comprise a first alignment portion and a second alignment portion spaced from the first, wherein the first and second alignment portions are configured such that, in use, the first alignment portion may be aligned with the second alignment portion and a portion of an eye.

In use, there may be a line of sight between the first and second alignment portions and the portion of the eye via the clearance when the first alignment portion is aligned with the second alignment portion and the portion of the eye.

The first alignment portion may comprise a first arm and the second alignment portion may comprise a second arm, each of the first and second arms depending from the support and having a free end having a tip, and wherein, in use, the tip of the first arm is aligned with the tip of a second arm and the portion of the eye such that there is a line of sight between the tips of the first and second arms and the portion of the eye via the clearance.

According to a second aspect of the present invention there is provided a kit of parts which may be assembled to form a marking tool according to the first aspect of the present invention.

According to a third aspect of the present invention there is provided a method of providing an indication of the orientation of an axis of corneal astigmatism of an eye, the method comprising: marking a horizontal axis of the eye on a cornea or corneal limbus of the eye; measuring the angle between the horizontal axis of the eye and the axis of corneal astigmatism of the eye; using a measuring feature of a marking tool according to the first aspect of the invention to orientate the marking tool such that the angle measured by the marking tool between a blade axis of the marking tool and the marked horizontal axis is substantially the same as the measured angle between the horizontal axis of the eye and the axis of corneal astigmatism of the eye; and marking the cornea or corneal limbus of the eye by urging blades of the marking tool into contact with the cornea or corneal limbus.

According to a fourth aspect of the present invention there is provided a marking tool suitable for marking a portion of an eye comprising a support which extends around a support axis having first and second support portions defining a clearance therebetween, first and second blades extending from the first and second support portions respectively, each blade having a blade edge for contacting a surface of an eye in use, the blade edges of the first and second blades lying substantially along a common blade axis and the first and second blades extending both along the blade axis and away from their respective support portion in a first direction perpendicular to the blade axis, and a measurement feature configured to, in use, measure an angle between a reference point of an eye and the blade axis about the support axis, wherein the measurement feature comprises a first type and a second type of opposed pairs of graduations, the graduations of each of the opposed pairs of graduations being substantially the same, wherein the graduations of the first and second types of opposed pairs of graduations comprise a line and a number, the number indicating an angle between the respective graduation and the blade axis about the support axis, wherein the bottom of each of the constituent characters of the numbers of each of the graduations is at a position which is clockwise about the support axis relative to the top of the respective constituent character, and wherein graduation pairs of the second type extend less far from the support axis compared to graduations of the first type.

Alternatively, the bottom of each of the constituent characters of the numbers of each of the graduations is at a position which is anticlockwise about the support axis relative to the top of the respective constituent character.

Preferably, the number of the graduation pairs of the second type is given by dividing the angle between the respective graduation and the blade axis about the support axis by ten.

Preferably, the number of each of the graduations reads in a direction which is parallel to the direction of the line of the respective graduation.

Other preferred features of the invention will become apparent from the

description below.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic, perspective ray diagram of an optical system which comprises a lens and exhibits astigmatism; Figure 2A is a cross-section along a first axis through the lens of the optical system shown in Figure 1; Figure 2B is a cross-section along a second axis through the lens of the optical system shown in Figure 1; Figure 3 is a schematic side view of a known marking tool; Figure 4 is a schematic side view of a marking tool in accordance with an embodiment of the present invention; Figure 5 is a side view of a portion of the marking tool shown in Figure 4; Figure 6 is a further side view of a portion of the marking tool shown in Figures 4 and 5; Figure 7 is a perspective view from below of a portion of the marking tool shown in Figures 4 to 6; Figure 8 is a perspective view from underneath of the marking tool of Figures 4 to 7; Figure 9 is a view from above of the marking tool shown in Figure 4; Figure 10 shows a schematic side view of a portion of the marking tool of Figure 4 contacting a portion of an eye; Figure 11 shows a view from above of an alternative marking tool in accordance with the present invention; Figure 12 shows a view from above of a further alternative marking tool in accordance with the present invention; Figure 13 shows a view from above a yet further marking tool in accordance with the present invention; Figure 14 shows a side view of the marking tool shown in Figure 13; Figure 15 shows a blade edge profile of a blade which forms part of a marking device in accordance with the present invention; and Figure 16 shows a graph of further blade edge profiles of blades which may form part of a marking tool in accordance with an amendment of the present invention.

The cornea of an eye normally has a surface which is generally spherical.

Astigmatism is a disorder of the eye whereby the cornea of the eye is instead generally ellipsoidal (for example the cornea may have a surface which is similar in shape to that of part of a surface of a prolate spheroid, for example a rugby ball). Astigmatism can cause blurred and distorted vision.

Figure 1 shows a schematic, perspective ray diagram of an optical system 10 which experiences astigmatism due to the optical system 10 having a generally ellipsoidal lens 12. The ellipsoidal lens 12 has a surface which is that of a portion of a surface of a prolate spheroid. Figures 2A and 28 show cross-sections through the ellipsoidal lens 12 along the lines A-A and B-B respectively. It can be seen that the radius of curvature of the surface 14 of the lens 12 is greater in the direction A-A than in the direction B-B. A-A may be referred to as the major axis of the ellipsoidal surface 14 and B-B may be referred to as the minor axis of the ellipsoidal surface 14. In regular astigmatism, the major axis of the ellipsoidal surface 14 is substantially perpendicular to the minor axis of the ellipsoidal surface 14. However, is some cases of astigmatism, this need not be the case.

The ray diagram shown in Figure 1 shows a plurality of rays (for example, of light) which extend from an object 0 through the lens 12. Rays 16 and 18 which pass through the minor axis B-B of the ellipsoidal surface 14 form an image of the object 0 which is indicated as Ia. Rays 20 and 22 which extend through the major axis A-A of the lens 12 form an image which is indicated by lb. The image Ia formed by rays 16 and 18 passing through the minor axis B-B of the lens 12 is at a different position to that of the image lb formed by the rays 20 and 22 which pass through the major axis A-A of the lens 12. Due to the fact that the radius of curvature of the lens 12 is greater along the major axis A-A than along the minor axis B-B, the image Ia of the object 0 which is formed by rays which pass through the minor axis B-B is closer to the lens 12 than the image lb of the object 0 formed by rays which pass through the major axis A-A of the lens 12. Because the object 0 is imaged to different positions (for example, Ia and Ib) as a result of the part of the lens 12 the rays forming the image pass through, the image formed at any image plane which is behind the lens will be blurred and/or distorted. It follows that if an eye has a cornea which has an ellipsoidal surface (and hence exhibits astigmatism) then vision using such an eye will also be blurred and/or distorted.

A separate condition which may adversely affect the vision of an eye is the presence of a cataract. A cataract is a clouding of the normally clear lens of the eye.

This clouding may alter the refractive index of the cornea and may also increase the opacity of the cornea such that the amount of light which can pass through the cornea is reduced. A common treatment for the presence of a cataract within an eye is to remove the cataracteous lens and replace it with a monofocal artificial lens implant.

Recently, toric lens implants have been developed which can be used to replace a cataracteous lens whilst at the same time compensating, at least in part, for any pre-existing astigmatism of the eye.

Toric lens implants are shaped so that they have two optical components (i.e. a shape which affects the light passing through it in two distinct ways). A spherical component of the lens implant corrects short-sightedness or far-sightedness in a similar manner to that of known monofocal lens implants. A toric component of the lens implant may be used to compensate for astigmatism.

The toric component of the toric lens implant results in the toric lens implant having a generally ellipsoidal surface similar to that of the lens 12 shown in Figures 1 and 2. In order to compensate for the astigmatism of the eye, the toric lens implant must be aligned so that the major axis of the lens implant (equivalent to the line A-A in relation to the lens shown Figure 1 and corresponding to the direction in which the radius of curvature of the lens implant is greatest) must be aligned with the minor axis of the astigmatism of the cornea (equivalent to line B-B in relation to the lens shown in Figure 1 and being the direction in which the effective radius of curvature of the cornea is least). For simplicity, within the rest of the description, the major axis of the toric lens implant will be referred to as the axis of the toric lens implant; and the minor axis of the astigmatism of the cornea will be referred to as the axis of corneal astigmatism.

As previously discussed, in order for the tone lens implants to substantially compensate for the astigmatism of the eye, the axis of the toric lens implant must be substantially aligned with the axis of corneal astigmatism. One way in which this alignment may be performed is as follows. First, keratometry is used to determine the curvature of the surface of the cornea of an eye. This enables the direction of the major and minor axis of the generally ellipsoidal surface of the astigmatic cornea to be determined. The process of keratometry will be well understood by a person skilled in the art and as such details of this process are omitted from this description. It is common for the direction of the axis of corneal astigmatism to be measured relative to a horizontal axis of the eye. In one example of defining the horizontal axis of the eye, the horizontal axis of the eye is substantially parallel to a line which runs through the centre of both eyes of a particular subject. In another example of defining the horizontal axis of the eye, the horizontal axis of the eye is substantially perpendicular to a longitudinal axis of the face and/or nose of a subject.

The next step in aligning the axis of the toric lens implant with the axis of corneal astigmatism is that a fine slit of light is projected onto the eye such that the slit of light is aligned with the horizontal axis of the eye and passes through a central portion of the cornea. The positions at which the slit of light is projected onto the edge of the cornea (also referred so as the corneal limbus) of the eye are then marked. This can be thought of as marking the edge of the cornea of the eye at the positions corresponding to the 3 o'clock and 9 o'clock positions of a clock face. The marking of the corneal limbus in this manner may be performed under topical anaesthesia. The marked positions of the corneal limbus serve as reference points because an imaginary line between these two points defines the horizontal axis of the eye.

Because the direction of the axis of corneal astigmatism was measured during keratometry relative to the horizontal axis, the markings which have been made on the corneal limbus can be used to determine the orientation of the axis of corneal astigmatism. To this end, a marking tool is used to make a second pair of opposing marks (or markings) at the corneal limbus (either side of the cornea) which correspond to the orientation of the axis of corneal astigmatism. This is achieved by using the marking tool to make marks at the corneal limbus which have an angle between them and the marked horizontal axis of the eye which is the same as the angle between the axis of corneal astigmatism and the horizontal axis of the eye that was measured during keratometry. The marking tool may have both a measurement feature to measure the angle between the second pair of marks and the marked horizontal axis; and at least one blade which can be used to make the second set of markings. Once the second set of markings has been made the marking tool can be removed. The second pair of markings indicate the orientation of the axis of corneal astigmatism and hence provide an indication during surgery as to the orientation the toric lens implant should have such that it is aligned with the axis of corneal astigmatism.

Figure 3 shows a schematic side view of a known marking tool 30 which may be used to create markings on the cornea and/or corneal limbus to indicate the orientation of the axis of corneal astigmatism. The marking tool 30 comprises a support 32 from which a handle 34 depends. The handle 34 may be used to hold the marking tool 30 in use. The support 32 is annular (although not visible in the figure) and has a first support portion 36 (to the right as shown in the figure) and a second support portion 38 (to the left as shown in the figure). A first blade 40 and a second blade 42 extend from the first support portion 36 and second support portion 38 respectively. The first and second blades 40 and 42 each have a blade edge 40A and 42A respectively. The profile of the blade edges 40A and 42A is such that they are concave.

Each of the blades 40, 42 has an inboard end 40B, 42B and an outboard end 40C, 42C. The extent to which the blades extend from their respective support portions is greater at the outboard ends 40C, 42C than at the inboard ends 406, 426.

The combination of the outboard ends 40C and 42C of the blades extend away from their respective support portions to a greater extent than that of the inboard ends 406 and 426; and the profile of the blade edges 40A and 42A being concave means that the profiles of both of the blade edges 40A and 42A generally correspond to the profile of the outer surface of the cornea of an eye (indicated generally in dash lines within the figure).

When the marking tool is used to mark the direction of the axis of corneal astigmatism, the blades 40 and 42 are located at the desired position of the corneal limbus of the eye and then the tool is urged towards the eye such that the blade edges 40A and 42A contact and incise or form an indentation in the corneal limbus of the eye.

Due to the fact that the profile of the blade edges 40A and 42A substantially corresponds to the profile of the outer surface of the cornea of an eye, when the blades and 42 are urged into the corneal limbus of the eye, the length of the incisions or indentations created by the blades 40 and 42 may be substantially the same size regardless of the force which is applied to the marking tool 30 so as to urge it towards the eye (and hence regardless of the depth to which the blades 40 and 42 penetrate the corneal limbus).

In some situations, the fact that the length of the incisions or indentations made by the blades 40 and 42 is substantially invariant with respect to how deep the blades and 42 penetrate the corneal limbus may be disadvantageous. This is because it may be desirable to control the length of the indentations or incisions made by the blades. For example, in some applications, it has been found that, if the length of the indentation or incision made by the blades is too short then the marks may not be visible and hence it is not possible to use the marks during surgery to align the axis of the toric lens implant with the axis of corneal astigmatism. In some cases the blades may be coated with a dye before the indentations or incisions are made to increase the visibility of the marks. In this situation, if the marks are too short, the dye may wash out of the marks during the operation, thereby making the marks harder to see. The harder the marks are to see, the more difficult it will be for the person carrying out the surgery to align the axis of the toric lens implant with the axis of corneal astigmatism.

Alternatively, if the length of the indentations or incisions made by the blades are too long then excessive trauma may be caused to the cornea and/or corneal limbus.

Figures 4 to g show a marking tool 50 in accordance with an embodiment of the present invention. As can be seen most clearly in Figure 8, the marking tool 50 comprises an annular support 52. A handle 54 which may be used to hold the marking tool 50, in use, depends from the support 52. The support 52 may be considered to have a first support portion 56 (on the right as shown Figure 8) and a second support portion 57 (as shown on the left in Figure 8). The first and second support portions 56, 57 are spaced apart and define a clearance between them. In the case of this embodiment, the clearance is a generally circular aperture 58 in the support 52. In the case of this embodiment a support axis (not shown) can be defined as the axis around which the annular support 52 extends. The support 52 has a lower face 60 and an upper face 62 which are spaced along the support axis from one another.

First and second blades 64 and 66 extend from the lower face 60 of each of the first and second portions 56 and 57 of the support 52 respectively. The first and second blades 64, 66 each have blade edges 64a and 66a respectively which substantially lie along a common blade axis (not shown). The first and second blades 64 and 66 extend from the respective first and second portions 56, 57 of the support 52 in a first direction which is substantially perpendicular to the blade axis and substantially parallel to the support axis. Furthermore, the first and second blades 64, 66 extend substantially along the blade axis. In this embodiment, each of the first and second blades 64, 66 extend from an inboard end 64b, 66b, which is radially inboard of the internal diameter of the annular support 52, along the blade axis to an outboard end 64c, 66c, which is located radially outboard of the inner diameter of the annular support 52 and radially inboard of the outer diameter of the annular support 52.

The first and second blades 64, 66 are arranged such that the inboard end 64b of the blade 64 is relatively proximal to the second blade 66, whereas the outboard end 64c of the first blade 64 is relatively distal to the second blade 66. Similarly, the inboard end 66b of the second blade 66 is relatively proximal to the first blade 64, whereas the outboard end 64c of the second blade 66 is relatively distal to the first blade 64. The inboard ends 64b, 66b of the first and second blades 64, 66 lie at a radial distance relative to the support axis which is less than the radial distance at which the outboard ends 64c, 66c of the first and second blade 64, 66 are located.

Furthermore, it may be said that the inboard end 64b of the first blade 64 generally faces the inboard end 66a of the second blade 66; and that the outboard end 64c of the first blade 64 faces generally away from the outboard end 66c of the second blade 66.

In contrast to the profile of blade edges of blades of known marking tools (which are concave), the profile of the blade edges 64a, 66a of the first and second blades 64, 66 is convex.

As previously discussed, each of the blades 64, 66 extends in a first direction (in this case the first direction is substantially parallel to the support axis) away from their respective support portions 56, 57. The extent of each blade 64, 66 in the first direction is greater at the outboard end 64c, 66c than at the inboard end 64b, 66b.

Furthermore, the blades 64, 66 and the profile of the blade edges 64a, 66a are configured such that the extent of each blade 64, 66 in the first direction generally increases from the inboard end 64b, 66b to the outboard end 64c, 66c. The rate of the general increase in the extent of each blade 64, 66 in the first direction from the inboard end 64b, 66b to the outboard end 64c, 66c generally decreases from the inboard end 64b, 66b to the outboard end 64c, 66c. The radius of curvature of the profile of the first and second blades edges 64a, 66a may generally increase from their respective inboard ends 64b, 66b to their respective outboard ends 64c, 66c. In the embodiment shown the profile of the blade edges 64a, 66a is such that the profile is substantially parallel to the blade axis at the outboard end 64c, 66c of the blade 64, 66.

It will be appreciated that different blade configurations and blade edge profiles may be used in accordance with the present invention. These different blade configurations and blade edge profiles are discussed in further detail later.

Figure 9 shows the upper face 62 of the support 52. It can be seen that the upper face 62 comprises graduations 70 which are located at different angular positions around the annular support 52. The graduations 70 run from 00 to 180° in a clockwise manner from the first blade 64 to the second blade 66 and from 00 to 1800 in a clockwise manner from the second blade 66 to the first blade 64. In this manner, the graduations which indicate 0° and 180° may be said to lie on the blade axis. Each of the graduations of the present embodiment is separated from its adjacent graduations by 10°.

It can be seen that there are three types of graduation 70a, 70b, 70c which form a sequential repeating pattern of graduations 70 around the support 62. When moving around the support in a clockwise manner, the unit of sequential repetition comprises, in order, a first graduation 70a, followed by a second graduation 70b, followed by a third graduation 70c. Each graduation is opposed by a substantially identical graduation. As such, opposing graduations form pairs. Within the figure, both of the graduations marked as 70a, 70b and 7Cc form a respective pair.

It can be seen that the graduations of a first type indicated by 70a have a straight line, having a first radially inboard end and a second radially outboard end.

Adjacent the second end of the line the graduation has a number indicating the angle 0 between the blade axis 72 and the graduation 70a (in a clockwise direction from the blade axis 72 to the graduation 70a). The number which indicates the angle e between the blade axis 72 and the graduation 70a is aligned so that it runs parallel to the line of the graduation 70a. The number is also orientated such that the bottom of each of its constituent characters is located at position which is clockwise relative to the top of the respective constituent character.

A second type of graduation 70b comprises a line which has a first radially inboard end and a second radially outboard end. Adjacent the second end of the line is an arrow head.

A third type of graduation 70c has a dashed line having a first radially inboard end and a second radially outboard end.

The lengths of the lines used as part of the second and third types of graduation 70b, 70c are shorter in length than the line which is part of the first type of graduation 70a. Furthermore, the first type of graduation 70a has a greater radial extent than that of the second and third types of graduation 70b, 70c (i.e. the first type of graduation 70a extends from the inner diameter of the annular support 62 to the outer diameter of the annular support 62, whereas the second and third types of graduation 70b, 70c extend from the inner diameter of the annular support 62 only part way (in this case approximately a third of the distance between the inner diameter of the support and the outer diameter of the support) to the outer diameter of the annular support 62). The use of different types of graduation 70a, 70b, 70c which sequentially alternate around the support 62 makes it easier to differentiate between adjacent graduations.

When the marking tool 50 is in use, the graduations 70 are used to measure the angle between the blade axis 72 of the marking tool 50 (and hence the axis along which the blades will make incisions, indentations or markings) and the horizontal axis of the eye which is marked on the cornea. It follows that the graduations 70 can be considered to be a measurement feature which is used to measure the angle between a reference point of the eye (namely the markings which indicate the orientation of the horizontal axis of the eye) and the blade axis 72. It will be appreciated that any appropriate reference point of the eye may be used. The marking tool can therefore be used to create a pair of markings which indicate the orientation of the axis of corneal astigmatism. This is achieved as follows: The angle between the horizontal axis of the eye and the axis of corneal astigmatism will already have been determined by keratometry as previously described, or by any other appropriate technique. The marking tool 50 is then orientated (e.g. by rotation relative to the eye) such that the angle indicated by the graduations adjacent the marks on the cornea (which were previously made to indicate the orientation of the horizontal axis of the eye) is substantially the same as the angle between the horizontal axis of the eye and the axis of corneal astigmatism previously measured by keratometry. Once the marking tool 50 has been orientated in this manner the blade axis 72 of the marking tool will be substantially aligned with the axis of corneal astigmatism. With the marking tool 50 in this orientation the marking tool 50 is urged towards the eye such that the blades 64, 66 of the marking tool 50 contact the eye (and in particular the peripheral cornea) and create a pair of incisions (or indentations or markings) in the corneal limbus which substantially lie on the axis of corneal astigmatism and therefore indicate the orientation of the axis of corneal astigmatism. The peripheral cornea is a portion of the cornea which comprises at least part of the corneal limbus. During surgery in which a toric lens implant is implanted into an eye, the marks on the corneal limbus which indicate the orientation and location of the axis of corneal astigmatism may be used to align the axis of the toric lens implant so that it is substantially aligned with the axis of corneal astigmatism.

Figure 10 shows a schematic cross-sectional side view of part of the marking tool 50 contacting an eye 70. The marking tool 50 has been urged towards the eye 80 such that a portion of the blade edge 64a contacts a surface 82 of the eye 60. The surface 82 may be any appropriate surface of the eye such as a corneal surface or the surface of the corneal limbus. With the marking tool 50 and the eye 60 in the relative position shown in Figure 10, the region of the surface 62 of the eye 80 which is in contact with the blade edge 64a of the blade 64 is indicated by 84. The region 84 extends along the blade edge 64a from the inboard end 64b of the blade 64 towards the outboard end 64c of the blade 64. It is this region 84 of the surface 82 of the eye which will be incised (or indented or marked) if a force is applied to the marking tool so as to urge it towards the eye 80.

Because the surface 82 of the eye 80 is elastic and convex and due to the fact that the profile of the blade edge 64a is also convex, if the marking tool 50 (and hence the blade 64) is urged towards the eye 80 then the length of the region 84 of contact between the blade edge 64a and the surface 82 of the eye 80 will increase. The marking tool 50 may be urged towards the eye by increasing the force applied to the marking tool 50 in a direction that urges the marking tool 50 towards the eye. Because urging the marking tool 50 towards the eye will increase the length of the region 84, urging the marking tool 50 towards the eye will also increase the length of the incision (or indentation or marking) made by the blade. Consequentially, the degree to which the marking tool 50 is urged towards the eye 80 (and hence the force applied to the marking tool 50 in order to urge the marking tool 50 towards the eye) can be used to control the length of the incisions (or indentations or markings) made by the blades of the marking tool. This may be advantageous in certain applications, because it will enable control of the length of the markings (or indentations or incisions) made by the blades. As previously discussed, if the markings (or indentations or incisions) made by the blades in the cornea (or corneal limbus) are too shod then they may not be visible.

Whereas, if the markings (or indentations or incisions) made by the blades in the cornea (or corneal limbus) are too long then unnecessary trauma may be caused to the eye.

Figure 11 shows an alternative upper face 62a which may form part of a marking tool 50 in accordance with an embodiment of the present invention. The graduations 90 of the upper face 62a differ from the graduations 70 of the upper face 62 shown in Figure 9 in that there are only two types of different graduation 90 on the upper face 62a of the embodiment shown in figure 11 compared to the three types of graduation 70 shown in the embodiment of Figure 9. The first type of graduation 90a shown in the embodiment of Figure 11 is substantially the same as the first type of graduation 70a shown in the embodiment of Figure 9. The second type of graduation 90b shown in the embodiment of Figure 11 comprises a line with a radially inboard first end and a radially outboard second end. Adjacent the second end of the line are numbers which indicate to the angle between the blade axis and the graduation 90b in a clockwise direction divided by 10. It follows that the graduations of the second type 90b have numbers which are generally shorter than the numbers of the first type of graduation 90a because the final zero of the numbers which form part of each of the second type of graduation 90b has been omitted. The first type and second type of graduations 90a, 90b form a repeating sequence around the upper face 62a wherein the repeated unit of the sequence, in order, is a first type of graduation 90a, followed by a second type of graduation 90b, followed by a further graduation of the second type 90b.

The use of a second type of graduation 90b which differs from the first type of graduation 90a in that the numbers have been shortened (divided by 10) and shorter graduation lines have been used, results in the graduations of the second type 90b extending less far from the inner diameter of the annular support 52 towards the outer diameter of the annular support 52 compared to graduations of the first type 90a. This may, in some applications, make the first type of graduation 90a stand out more than, and/or be easier to read than graduations of the second type 90b. In certain applications, this may make it easier to determine which graduations 90 form an opposing pair. This may aid alignment of an opposing pair of graduations with the markings made to indicate the direction of the horizontal axis of the eye.

The numbers which form part of the first and second types of graduation 90a, 90b are arranged so that the bottom of their constituent characters is at a position which is clockwise relative to the top of their constituent characters. This enables the characters to be easily read as the marking tool is rotated.

Figure 12 shows an alternative marking tool 50a in accordance with an embodiment of the present invention. The marking tool 50a differs from those previously described in that it comprises an annular member 92 which is supported by arms 94 which extend radially inwards from the support 52a. The annular member 92 is supported such that it is coaxial with the annular support 52a. It follows that the annular member 92 is centred with respect to the support 52a.

The annular feature 92 may be used as an alignment feature to align the marking tool 50a with a portion of an eye when the marking tool 50a is in use. The annular member 92 may be used as an alignment feature to align the marking tool SOa with the centre of the cornea of the eye (which may be the centre of curvature of the surface of the cornea of the eye) as follows. When the marking tool 50a is held above the eye a reflection of the annular member 92 from the surface of the cornea of the eye can be observed. An example of the reflection of the annular member 92 in the cornea of the eye is indicated by dashed line 96 within the figure. Due to the curvature of the cornea surface, the marking tool will be substantially aligned with the centre of the cornea when the reflection 96 of the annular member 92 is located such that it is substantially centralised within the annular member 92. The reflection 96 of the annular member 92 is substantially centralised within the annular member 92 when the radial distance between each part of the reflection 96 and the corresponding portion of the annular member 92 is substantially constant. That is to say when the separation between the reflection 96 and the annular member 92 is substantially constant. An example of this is shown within the figure whereby the distances 98a, 98b and 98c are substantially the same.

The annular member 92 may also be used as an indication feature which may provide an indication of the general orientation of an axis of a substantially ellipsoidal surface of an eye. For example, in the case where a cornea of the eye exhibits corneal astigmatism, the surface of the cornea will be substantially ellipsoidal. If the reflection 96 of the annular member 92 is viewed in the surface of an astigmatic cornea (i.e. which has an ellipsoidal surface), then the reflection 96 will not have a generally circular shape, as would be the case if the reflection 96 were observed from a non-astigmatic cornea (i.e. one which is substantially spherical). Instead, the reflection 96 of the annular member 92 from the surface of an astigmatic cornea would be distorted such that it is substantially elliptical in shape. In this case, the minor axis of the substantially elliptical reflection 96 of the annular member 92 would be substantially aligned with the minor axis of the ellipsoidal surface of the cornea. It follows that by observing the shape of the reflection 96 of the annular member 92 (and in particular the axes of any ellipsoidal reflection) that the annular member 92 may be used to provide an indication of the axis of corneal astigmatism.

Figures 13 and 14 show a further embodiment of a marking tool SOc in accordance with an embodiment of the present invention. As best shown in Figure 14, the marking tool SOc comprises a first alignment portion 100 and a second alignment portion 102. The first alignment portion 100 comprises a first alignment arm 104 which extends from a handle 54 of the marking tool SOc. The alignment arm 104 extends from the handle 54 to a position which lies on a support axis SA of the marking tool 5Cc. The support axis SA in this embodiment is the axis around which the annular support 52c is arranged. Furthermore, the support axis SA is perpendicular to the blade axis. The similar blades 108 and 110 of this embodiment are also equidistant from the support axis SA.

The second alignment portion 102 comprises a second alignment arm 106 which extends radially inwards from a portion of the support 52c to a position on the support axis SA. Both the first alignment arm 104 and second alignment arm 106 extend to different positions on the support axis SA such that said positions on the support axis SA to which the first alignment arm 104 and second alignment arm 106 extend are spaced apart from one another.

As seen best in figure 13, both the first alignment arm 104 and second alignment arm 106 narrow to a point (or tip) at the support axis SA. Within Figure 14, the support axis runs perpendicular to the plane of the figure. For this reason, within Figure 13, the support axis SA is indicated by a cross.

In order to align the marking tool 50c with a portion of an eye, for example the centre of the cornea of an eye or the centre of the surface of the cornea, the following procedure is used. The user of the marking tool 50c observes the marking tool 50c from above (such that the user's view is equivalent to that shown in Figure 13). The marking tool SOc is then orientated such that the tip of the first alignment arm 104 substantially aligns with the tip of the second alignment arm 106 and with the portion of the eye with which it is desired to align the marking tool 50c. In practice, this will be the case when the tip of the first alignment arm 104 appears to touch the tip of the second alignment arm 106; and when the touching tips of the first and second alignment arms 104, 106 are located such that the touching tips substantially obscure at least part of the portion of the eye to which it is desired to align the marking tool SOc. When this alignment is achieved there will be a line of sight between the tips of the first and second alignment arms 104, 106 and the portion of the eye to which it is desired to align the marking tool. The line of sight will extend via the clearance between first and second support portions which support the first and second blades 108 and 110 respectively. In this case, the clearance between the first and second support portions of the support SOC (which support the first and second blades 108, 110 respectively) is defined by the central aperture 112 in the annular support 52c.

As previously discussed, the blade edges of the first and second blades of the described embodiments have a substantially convex profile. Figure 15 shows an example of a profile 120 of a blade edge in accordance with an embodiment of the present invention. The profile 120 of the blade edge is such that the blade lies below the profile 120 as shown in the figure. The profile 120 of the blade edge shown in figure 15 may be uniformly scaled such that it defines the blade edge profile of any appropriate size of blade. The profile 120 is defined by a quadratic equation of the form: y=ax2+bx+c (1) where y is a value on the vertical axis; x is a value on the horizontal axis; and a, b and c are constants. A profile which may be described by the quadratic equation is referred to as a quadratic profile. In the case of profile 120 the values of constants a, b and c are -0.60, 6.53 and 9.00. Table 1 below shows some corresponding values of x and values of y of profile 120.

Figure 16 shows a further graph showing the blade edge profile 120 which is shown in Figure 15 together with a minimum blade edge profile 122 and a maximum blade edge profile 124. The minimum blade edge profile 122 is described by a quadratic equation as shown in equation 1, where the values of a, b and c are 0.00, 3.80 and 9.00 respectively. Due to the fact that the value of a is zero (such that the profile 122 is described by a linear equation of the form y = bx + c), the minimum blade edge profile 122 may be referred to as a linear profile. The maximum blade edge profile 124 is described by a quadratic equation as shown in equation 1, where the values of a, b and c are -3.00, 17.30 and 9.00 respectively. Table 2 below shows the values of a, b and c used in equation 1 to describe the blade edge profile 120, the minimum blade edge profile 122 and the maximum blade edge profile 124. The second, third and fourth columns of table 2 show the values used for blade edge profiles 120, 122, and 124 respectively. Furthermore, Table 3 below shows some values of x and corresponding values of y of profiles 120, 122 and 124. The columns labelled by VI, Ymin and Ymax show the values of y of profiles 120, 122 and 124 respectively. In the same manner as Figure 15, the blade edge profiles 120, 122 and 124 shown in Figure 16 are such that in each case the blade lies below the respective profile 120, 122, 124 as shown in the figure. Furthermore, the blade edge profiles 120, 122, 124 shown in figure 16 may be uniformly scaled such they may each define the blade edge profile of any appropriate size of blade.

The minimum blade edge profile 122 is an example of a profile which has a minimum possible curvature. In this case, the curvature is zero such that blade edge profile 122 is a straight line. The maximum blade edge profile 124 is an example of a profile which has a maximum possible general curvature that a blade edge profile may have in accordance with an embodiment of the present invention. In preferred embodiments of the invention the blade edge profile (for example blade edge profile 120) is such that it substantially lies within an area 128 bounded by the minimum blade edge profile 122 and the maximum blade edge profile 124.

It can be seen that whilst a blade edge which has either of the profiles 120 or 122 is such that the extent of the blade is continually increasing from the inboard end of the blade to the outboard end of the blade. This need not be the case. For example the blade edge profile 124 is such that the extent of the blade (in a direction which extends away from the support portion which supports the blade) increases from the inboard end towards the outboard end until a maximum indicated by the point 126 and then decreases from the maximum point 126 to the outboard end.

The blade edge profiles 120 and 124 shown in Figures 15 and 16 are quadratic.

The profile 122 shown in Figure 16 is linear. It will be appreciated that any appropriate substantially straight or substantially convex blade edge profile may be used. Such a profile may not be linear or quadratic. The blade edge may have any appropriate shape. For example, the blade edge profile may be substantially straight or a curve which is substantially convex. Furthermore, the blade edge profile may comprise one or more points of inflection and/or one or more discontinuities.

Within the described embodiments, the support is annular and the clearance between the support portions is defined by the aperture in the centre of the annular support. It will be appreciated that the support may have any appropriate shape. For example the support may be part-annular. Within this specification a body is "part-annular" if it can be defined as being a segment of an annular structure. For example the support may be generally c-shaped, such that the support is a substantially 180° segment of an annulus. In this case, the first and second support portions are at either end of the c-shaped support. Furthermore, the clearance between the first support portion and second support portion will not be defined by an aperture, but rather by the space which separates the ends of the c-shaped support. It will be appreciated that the support may have any appropriate shape and that any appropriate configuration (for example size and/or shape) of clearance between first and second support portions of the support may be used. Furthermore, whereas the aperture through the support in the described embodiments is centrally located relative to the support, this need not be the case. For example the clearance between the first and second support portions may be defined by an aperture which is offset from the centre of the support.

In the embodiments which have been described above, the marking tool is single-piece (or unitary in construction). It is within the scope of the present invention for portions of the marking tool to be provided as separate elements. For example, the blades and handle may be detachable from the support. The ability to detach the blades from the support may enable the blades to be changed if they become worn or contaminated due to use. In the case where portions of the marking tool are provided as separate elements, it is within the scope of the invention to provide the separate elements of the marking tools as a kit of the separate elements.

It will be appreciated that numerous modifications to the above described designs may be made without departing from the scope of the invention as defined in the appended claims. * 23

Y 0 9

0.5 12 1 15 1.5 17.5 2 19.5 iS 21.5 3 23 3.5 24.5 4 25.5 4.5 26 -0.60 0.00 -3.00 6.53 3.80 17.30 Cr 9.00 9.00 9.00 w& z X Vi Ymin Ymax 0 9.0 9.0 9.0 0.5 12.1 10.9 16.9 1 14.9 12.8 23.3 1.5 17.4 14.7 28.2 2 19.7 16.6 31.6 2.5 21.6 18.5 33.5 3 23.2 20.4 33.9 3.5 24.5 22.3 32.6 4 25.5 24.2 30.2 4.5 26.2 26.1 26.1 * 24

Claims

CLAIMS: 1. A marking tool suitable for marking a portion of an eye comprising: a support having first and second support portions defining a clearance therebetween, first and second blades extending from the first and second support portions respectively, each blade having a blade edge for contacting a surface of an eye in use, the blade edges of the first and second blades lying substantially along a common blade axis and the first and second blades extending both along the blade axis and away from their respective support portion in a first direction perpendicular to the blade axis, wherein each of the first and second blades have an inboard end and an outboard end, and the blade edges of the first and second blade having a substantially straight or substantially convex profile and the extent of each blade in the first direction being greater at the outboard end than at the inboard end.
2. A marking tool according to claim 1, wherein the extent of the first and second blades in the first direction generally increases from the inboard end to the outboard end, and wherein the rate of said general increase in the extent of each blade in the first direction generally decreases from the inboard end to the outboard end.
3. A marking tool according to either claim 1 or 2 comprising a measurement feature configured to, in use, measure an angle between a reference point of an eye and the blade axis.
4. A marking tool according to any preceding claim, wherein the support comprises an annular portion or a part-annular portion.
5. A marking tool according to any preceding claim, wherein the clearance between the first and second support features is defined, at least in part, by an aperture in the support.
6. A marking tool according to any preceding claim, comprising an indication feature configured to, in use, provide an indication of the general orientation of an axis of a substantially ellipsoidal surface of an eye.
7. A marking tool according to claim 6, wherein the indication feature comprises an annular portion or a part-annular portion supported by the support generally between the first and second support portions.
8. A marking tool according to any preceding claim, comprising an alignment feature configured to, in use, align the marking tool with a portion of an eye.
9. A marking tool according to claim 8, wherein said portion of the eye is the centre of a cornea of the eye.
10. A marking tool according to either claim 8 or claim 9, wherein the alignment feature comprises an annular portion or a part-annular portion supported by the support generally between the first and second support portions.
11. A marking tool according to any of claims 8 to 10, wherein the alignment feature comprises a first alignment portion and a second alignment portion spaced from the first, wherein the first and second alignment portions are configured such that, in use, the first alignment portion may be aligned with the second alignment portion and a portion of an eye.
12. A marking tool according to claim 11, wherein, in use, there is a line of sight between the first and second alignment portions and the portion of the eye via the clearance when the first alignment portion is aligned with the second alignment portion and the portion of the eye.
13. A marking tool according to either claim 11 or claim 12, wherein the first alignment portion comprises a first arm and the second alignment portion comprises a second arm, each of the first and second arms depending from the support and having a free end having a tip, and wherein, in use, the tip of the first arm is aligned with the tip of a second arm and the portion of the eye such that there is a line of sight between the tips of the first and second arms and the portion of the eye via the clearance.