CA1191062A

CA1191062A - Method and apparatus for corneal corrective techniques

Info

Publication number: CA1191062A
Application number: CA000418722A
Authority: CA
Inventors: Alvin E. Reynolds
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-01-04
Filing date: 1982-12-30
Publication date: 1985-07-30
Also published as: EP0083493A2; DE3276923D1; JPH0343903B2; US4490022A; JPS58118750A; EP0083493A3; EP0083493B1

Abstract

Abstract of the Disclosure A quantitative corneascope for use with a surgical micro-scope in performing corrective techniques on the eye includes a pair of hinged image projection housing members movably mounted on each side of a surgical microscope and a light and image source for reflecting partial segments of placido rings (mires) from the cor-neal surface of the eye. The microscope utilizes a beam splitter to provide multiple viewing by an operating doctor, an assistant and at television camera. The camera permits viewing of the mires as reflected from the eye, on a monitor. The monitor is provided with apparatus for generating cursor lines on the viewing surface, which cursor lines represent predetermined radii of curvature corresponding to the range of spherical eye shapes. The cursor lines may be adjusted to discrete values in this range of radii of curvature which in turn changes the spacing between the straight lines of the cursor display. The cursor lines may also be adjusted along the X-Y coordinates of the viewing surface. The use of this instrument involves placing the microscope and surgical corneascope mounted thereon over the patient's eye at a fixed distance. A focus mark is displayed on the viewing surface to accommodate this adjustment. In one type of operation, the mires are reflected from the eye and displayed on the viewing surface. The cursor lines are brought into coincidence with the mires to provide an image of the preoperative condition of the eye. This information relating to the preoperative eye condition is stored for later use.

Description

1~910~;~

This invention relates to a method and apparatus for performing corrective techniques on the eye and more particularly to a system, for use with a surgical microscope, for viewing the eye while performing corrective techniques and at the same time displaying comparative images of indicia related to the present shape of the eye and a predetermined eye shape.
Present systems for viewing the eye during surgical techniques involve the use of a surgical microscope for real time viewing and usually, intermittent keratometer measurements before, during and after surgery. This procedure is not only slow and thus time consuming, its accuracy is minimal in that equipment must be moved into and out of the surgical field with each usage~ In addition this procedure must take into account the sterile atmos-phere of the surgical location and the constant interfacing of measuring equipment with the sterile field. Such a surgical technique might typically fcllow the pattern of preoperative quan-titative keratometer measurement made to determine what effect the operative procedure has had on the eye. Next suturing is often performed to close incisions in the eye and post-operative kerato-meter readings are taken to determine the condition of the sutured eye. Each keratometer reading involves the replacement of instru-mentation within the surgical field and in precise position with respect to the eye. The preciseness of repositioning of such instrumentation will of course have an effect on the quantitive accuracy of the comparative readings. Additionally present kerato-meters measure approximately only a 3mm chord across the center of the eye. The corrective technique of concern in this application more often deals with distortions on the corneal surface between - 1 - ~

11~106~

~e2 to 12mm chords.
An improvement on the above described technique is suggested by mounting a quantitative keratometer on a suryical microscope. The Troutman keratometer exemplifies this manner of treating the problem. The Troutman device is described at pages 28 to 32 of Microsurgery of the Anterlor Segment of the Eye Vol. II, C. V. Mosby Company, 1977. The Troutman keratometer is character-ized by a twelve point light source mounted in a ring about the microscope body. Light is projected to twelve points on the cornea~
A keratometer reticle is fitted to the eye piece for the surgeons nondominent eye. It has two concentric circles for reference of the keratometer projection, and split cross hairs to align sutures and mark an astigmatic axis. The Troutman keratometer is a qualita-tive measuring instrument with a function very different from that of a keratoscope, which is designed for measuring corneal topography.
The Troutman keratometer on the other hand is designed specifically to aid the surgeon in the interpretation and correction of meridianal corneal errors. It approximates the powers of astigmatic bands by offering a comparison of reticle circles to an oval reflection of the projected light ring. Interpretation of the projection is a qualitative matter depending on the experience of the surgeon.
Keratometer mire patterns are so distorted in the early postopera-tive course as to be of little value in making determinations con-cerning refraction. Thus, no present technique or system is avail-able to facilitate accurate determination of corneal topography in a real time intraoperative situation. Also lacking is a system ~19~6;~

offering a conveniently usable comparison of real time intra-surgical data with cursor indicia indicative of a predetermined or preoperative condition.
It is therefore an object of the present invention to provide a new and improved method and apparatus for providing simultaneously on a convenient viewing surface, real time quantita-tive data relating to the present corneal topography, and predeter-mined data relating to a preoperative condition or desired corneal surface condition, with such system being arranged for use intra-operatively in conjunction with a surgical microscope.
With this and other objects in view, the present invention contemplates a quantitative keratoscope system for use with a surgical microscope in performing corrective techniques on the eye.
Partial segments of placido rings are reflected off of the eye in a meridianal pattern of mires. Cursor lines are capable of being generated and projected simultaneously on a viewing surface, with such cursor lines corresponding to known or predetermined radii of curvature of a spherical surface, these cursor lines may be moved laterally with respect to one another to vary their pattern in accordance with an infinite variety of radii of curvature within the range of corneal curvatures. The group of cursor lines may be moved along the X-Y coordinates of the viewing surface to bring them into coincidence with a real time image of the indicia repre-senting the present corneal topographic condition. The mires may be observed on the corneal surface by the operating physician and assistants as well as be projected onto a separate viewing sur-1~l9~06~

face. The equipment for reflecting mires from the corneal surface may be conveniently moved to a stowed position to allow more freedom of movement in the surgical field, and then returned to its operative position without changing the positional relationship of the keratoscope, microscope, and object corneal surface. A
focusing mark on the viewing surface and in the microscope image provides a check of this positional relationship.
Another aspect of this invention relates to a surgical techni~ue whereby a preoperative quantitative keratoscope reading is taken with the surgical microscope in its operative position.
The preoperative image of mires on the corneal surface may be recorded by bringing the cursors into coincidence with the mires and reading out digitally on the viewing surface an indication of the radius of curvature corresponding to the mires. The housing for projecting the mire to be reflected from the corneal surface may then be moved to a stowed position within the surgical field but out of the surgeon~s way to permit freedom of movement within the surgical field during the operation. At any time during the operation, such as during suturing, the mires projection housing may be returned to its exact same position in the surgical field for providing a real time image of mires on the present corneal surface. Cursor lines or other indicia corresponding to the pre-operation corneal condition may then be superimposed on the view-ing surface to provide an indication of the preoperative curvature of the corneal surface. A comparison of the preoperative curvature with the present condition permits adjustment of the sutures until 6~

the preoperative condition or an otherwise desired condition is attained, whereupon the sutures are fixed.
In still another aspect of the invention, the relative position of real time mires and predetermined or desired cursor lines can be used to compute a refractively corrected corneal sur-face configuration, and read out such computation. The cursor lines may then be set to correspond to such computed configuration.
A ring is then implanted in the corneal surface with its diameter being adjusted until the real time image and computed image are in coincidence, at which time the~ring diameter is fixed.
In yet another aspect of the invention, the meridianal orientation of the projected mires may be conveniently moved in a horizontally arcuate path to incrementally provide full viewing coverage of the corneal surface.
In summary, the apparatus and method of this invention has its particular use with a surgical microscope to perform cor-rection techniques on the eye. The instrument comprises a means to project indicia such as partial segments of placido rings onto the eye. The reflected image therefrom will provide an indication of the corneal topography. The image is viewable through the microscope. The apparatus for projecting the indicia is comprised of a pair of projecting members that extend outwardly and down-wardly from the sides of the microscope. These members are hinged to the microscope and have means for moving the projecting members between a operative, extended position, and a stored position against the body of the microscope. Means are provided for display-ing, on a viewing surface, an image related to a predetermined ~19~Z

surface shape. The indicia, that is indicative of the corneal topography is also imposed onto the viewing surface with the pre-determined image in order to permit comparison of the indicia and the image for surgical purposes.
The invention will now be described in greater detail with reference to the accompanying drawings, in which.
FIGURE 1 is an eleva-tional schematic view of a quantita-tive keratometer and corneascope mounted on a surgical microscope;
FIGURE 2 is a bottom view of a portion of the apparatus of FIGURE 1 taken along lines 2-2 of FIGURE l; and FIGURE 3 is a schematic view of a viewing surface for projeeting data from the keratometer and corneaseope, and showing indicia representing predetermined generated data for eomparison with the real time data from the surgical eorneascope and kerato-meter.
Referring first to FIGURE 1 of the drawinys, a surgical -5~ ~
,, ~191~6;~

microscope 11 is shown having a main body portion 12 movably sus-pended from an arm 13 movably supported on a st~nd 14 (partially shown) which has provisions (not shown) for positioning the micro-scope by means of foot operated switches. This arrangement elimi-nates the need for persons working in the sterile surgical field to touch the microscope, at least a portion of which, is outside the sterile field. On the body 12 of the microscope are a plur-ality of viewing positions radially arranged about the body 12 and e~uipped with (in the present case) two operator viewing positions 16, and one video camera position 17. The operator positions 16 are provided with binocular eye pieces 21 to permit the surgeon's viewing of the surgical field 18 beneath the microscope. TV camera 19 provides means for projecting the image viewed by the surgeon and/or assistants onto a remote viewing surface 22 mounted on a monitor 23. The monitor 23 is also provided with computer and signal generating means 25.
The body 12 of the microscope has a lower body portion 24 extending downwardly below the viewing positions 16 and camera position 17. The lower housing portion 24 includes the main opti-cal system of the microscope. Arranged on the lower body portion24 of the standard surgical microscope is a sleeve 26 which is mounted for rotational movement with respect to lower body portion 24. A motor unit 27 is arranged to drive the sleeve 26 in a rotational path about the lower portion 24. The motor unit 27 is mounted on lower housing portion 24 and has a gear 20 driven by the motor 27. The gear cooperatively engages an arcuate rack 15 on the 1~9~6~ , outer peripheral surface of the sleeve 26~ When the motor 27 is driven, the sleeve 26 is caused to rotate on body portion 24. A
foot operated switch may be connected by suitable wiring means to permit operation of the motor unit 27.
A projection assembly 28 is mounted on the lower end of sleeve 26 and includes a pair of projection housing members 29 which are mounted for pivotal movement with respect to the sleeve 26 from an operative position as shown in FIGURE 1 along a path shown by the dotted lines and arrows 31 to a stowed position against the lower body portion 24. Driven gears 32 connected to the housing member 29 are arranged to cooperatively engage a driv-ing gear 33 and idler 30, mounted on the sleeve 26. A motor 34, also mounted on the sleeve 26 rotates the gears and idler, in response to a foot operated control device (not shown), to cause the housing members 29 to move between the operative and stowed positions described above. FIGURE 1 also shows a spherical surface viewing object 36 positioned on a fixed surface 37 within the surgical field. A light source 51 is shown positioned on top of arm 13 of the surgical microscope. The light source can also be a source of light within the housing members 29 or, as shown in FIGURE 1, can be remote to the housing 21 and utilize fiber optic bundle 52 to transmit light from the source 51 to the interior of the housing members 29.
FIGURE 2 shows the bottom side of the housing members 29 and their cooperative relationship with the lower portion 24 of the microscope bodv 12. The gears 32 are connected to axle pins 1~L9106~

41. Pins 41 are rotatably mounted within bearing arms 42 which in turn are connected to the sleeve 26. Pins 41 are formed on or are connected to the inner ends of housing member 29 and thus the housing members 29 are caused to rotate with the pins 41 and gears 32. The radially angular configuration of the side walls 53 o~ the housing members 29 describe approximately a sixty degree segment of a circle. Between the side walls 53 the lower surface 54 of the housing members is constructed of a translucent material such as Lucite, which is covered with an opaque material such as black paint. Evenly spaced arcuate lines 56 are inscribed into the painted surface 54 to leave a translucent surface beneath the lines 56. Thus the light delivered by the fiber optics bundle 52 or other light source to the interior of housing 29 is permitted to emanate through the lines 56. This in turn causes the projection of an arcuate pattern of light lines 58 (mires) which are reflected from the spherical surface 36. Also inscribed into the opaque surface 54 is a cross mark 55 which permits focusing of the mires on the viewing surface.
Referring now to FIGURE 3 of the drawings, the monitor 23 is shown having a viewing surface 22 with indicia displayed thereon.
The image of the mires 58 and cross mark 55 reflected from the spherical surface 36 is detected by the video camera 19 and trans-mitted to the viewing surface 22 by well known video transmission techniques. It is appreciated that any of the sequential images making up the video transmission can be recorded and stored for later reference. This may be done on video tape as well as by other more precise electron' data storage techniques. Such a i~9~

stored image may be later projected onto the viewing surface either alone or compositely with another image such as a real time image. The cross mark 55 is also projected onto the viewing sur-face 22 to permit monitoring of the equipment focus on the surface 22. The computation and signal generating means 25 comprises electronic components, not described in detail here, for generating a pattern of straight lines or cursors 61 fGr projection onto the viewing surface 22. These lines may be arranged in various merid-ianal patterns such as the horizontal display depicted in FIGURE 1 or in any one of various meridinal courses shown in FIGU~E 2. By means of computing components in the signal generator 25, these cursor lines may be varied in their spacing from one another to correspond to various radii of curvature c~-aspherical surface as projected onto the viewing surface 22 from a spherical object 36 on surface 37. For example, in order to calibrate the accuracy of the cursor image 61, a spherical ball of known diameter is placed on the surface 37. Light from source 51 is reflected from the surface 36 as mires 58 which in turn are displayed on the view-in~ surface 22. The cursor lines which may be moved relative to one another on the viewing surface 22 are moved by means of a radius of curvature adjustment control knob 62 until they are in alignment with the mires reflected from the object of known diam-eter. A digital readout 63 displays a value of the cursors for that discrete separation of lines. The readout number should correspond exactly w~th the known diameter of the sphere 36. If the reading is out of correspondence, an adjustment is made electronically in ~L~9~L~6~

the signal generator and computation unit 25 to bring the read out into coincidence with the known dimension of the spherical surface 36. Control knobs 64 and 66 on the monitor 23 permit the entire field of cursors to be adjusted along X and Y coordinates respec-tively. This permits precise overlaying of the generated cursors 61 with the reflected mires 58 for comparing a known spherical dimension with the real time dimension shown by the mires.
FIGURE 3 shows the mires being projected onto surface 22 in oppositely occuring sixty degree arcuate segments formed along a horizontal meridian. The motor 27 (FIGURE 1) and rotatably arranged sleeve 26 provide a means for rotatably moving the pro-jection members 29 in either direction in a horizontal plane as viewed in FIGURE 1. Thus by moving the member 29 sixty degrees in both directions from that shown, the entire surface of the spher-ical object 36 may be scanned by the mires. This arrangement of segmented movable projection members permits the apparatus to be operated over a surgical field without impairing movement of the surgeon and assistants within the field and yet still offering the advantages afforded by the quantitative keratoscope projections.
The system described above may be used to perform keratoplasty and keratorefractive techniques for example, as follows: In a cataract operation, commonly the cataracts are removed successfully from the eye, however, refractive errors are induced as a result of asymmetry stemming from suture involvement in the cornea. The cataract incision may be tied too tightly at the time of surgery, producing with-the-rule astigmatism; or too - /o ~9~C)6~

loosely, producing wound gape thus flattening of the superior cor~
nea and against-the-rule astigmatism. The above described kerato-scope easily differentiates the localization of the suture defect in these two situations and permits quantitative correction to reform the error. ~ procedure that can he followed in such an operation might comprise reflecting mires 58 from the preoperative corneal surface, and projecting an image of the mires so reflected onto the viewing surface 22. The cursors 61 are then brought into coincidence with the mires reflected from the preoperative corneal surface. A digital reading of this discrete radius of curvature can then be read out on the display 63. Alternatively the pre-operative mires image may be stored for later viewing. The cataract operation is then performed. Before sutures are tightened, the keratoscope is again focused on the postoperative corneal surface. The cursors are set to the preoperative discrete valve or the preoperative mire image is displayed, whereupon the sutures may be manipulated to bring the postoperative corneal surface into conformity with the preoperative corneal shape. It is readily seen that modifications and variations on this and other surgical techniques can be arranged and still fall within the spirit and scope of the system described.
A keratorefractive procedure which readily lends itself to this system is described in applicant's co-pending Canadian Patent application entitled "Method and Apparatus for Corneal A Curvature Adjustment" serial No. ~ and filed on Decoe~e~, ~
198~,. This keratorefractive technique briefly involves determin-~91~6Z

ing the desired shape of a corneal surface for correcting the re-fractive error of a specific corneal surface. A plastic ring is then inserted into the corneal stroma, such plastic ring being split at one point to provide two ends open for relative movement to one another. After inserting the ring, the above described keratoscope is positioned over the eye whereupon the mires reflect-ed from the eye are projected onto the viewing surface 22. The control knob 62 is then turned until the desired numerical value of corneal curvature is displayed at 63. This then places the cursors at the desired separation to correspond to a correct corneal topography. The plastic ring is then adjusted in diameter within the corneal stroma to bring the mires into coincidence with the cursors, whereupon, the ends of the ring are fixed relative to one another to provide a corrected corneal surface.
The apparatus described herein can be used simply as a quantitative keratometer by placing the cursor marks into coinci-dence with the reflected mires and then read out the radius of curvature. In fact, any number of variations of techniques may be thought of for utilizing the system described above, as well as modifications to the system specifically described. For example, one can display two sets of mires, one being real time and another, a stored image. These can then be superimposed or otherwise compared, for example, by using cursors, to facilitate eye correction -/ ? ~

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for use with a surgical microscope to perform corrective techniques on the eye, comprising; means for projecting indicia onto the eye a reflected image therefrom being indicative of corneal topography, said image being viewable through a surgi-cal microscope, said means for projecting indicia is comprised of a pair of projecting members extending outward and downwardly from the sides of the surgical microscope and hingedly fixed to the surgical microscope and further including means for moving said projecting members between an operative, extended position and a stored position against the body of the microscope; means for displaying on a viewing surface an image related to a predeter-mined surface shape; and means for superimposing the indicia in-dicative of corneal topography onto the viewing surface with the image related to the predetermined shape to permit comparison of the indicia and image.

2. The apparatus of claim 1 and further including means for recording information indicative of the image related to a predetermined surface shape.

3. The apparatus of claim 1 and further including means for adjusting the image related to a predetermined surface shape to conform to a variety of predetermined shapes.

4. The apparatus of claim 3 wherein said predetermined shapes are spherical in nature and further including means for displaying a number indicative of the radius of curvature of said predetermined shapes.

5. The apparatus of claim 4 wherein said means for adjusting comprises means for adjusting the radius of curvature of the spher-ical shapes through an infinite range of sizes.

6. The apparatus of claim 1 and further including means for adjusting said image along vertical and horizontal coordinates in the viewing plane.

7. The apparatus of claim 1 and further including means for mounting said projecting members for rotational movement with-in a plane perpendicular to the viewing axis of the microscope.

8. Apparatus for use with a surgical microscope for per-forming corrective techniques on the eye, comprising: means movably mounted about the body of the surgical microscope for projecting indicia comprised of partial segments of placido rings onto the surface of the eye; and means for viewing the eye through the microscope to permit corrective techniques to be performed on the eye while the apparatus is in place over the eye, means to pivot said projecting indicia from an outwardly projecting opera-tive position adjacent the bottom of said microscope to a stowed position above said bottom and alongside the microscope body to permit freedom of movement below said bottom by a person perform-ing corrective techniques on the eye.

9. The apparatus of claim 8 and further including a viewing surface and means for detecting an image of the projected indicia on the eye and for displaying the detected image on the viewing surface.

10. The apparatus of claim 9 and further including means for displaying predetermined indicia on the viewing surface, such pre-determined indicia being indicative of a known corneal shape.

11. The apparatus of claim 10 and further including means for moving the predetermined indicia along horizontal and vertical coordinates on the viewing surface.

12. The apparatus of claim 8 and further including means for rotatably moving said projecting means in a plane perpendicular to the viewing axis of the microscope.

13. The apparatus of claim 10 and further including means for conveniently changing the predetermined indicia to correspond to an infinite range of corneal shapes; and means for reading out a numerical value indicative of a parameter of the corneal shape.

14. The apparatus of claim 1 wherein said projecting means includes means for selectively moving said projecting means into and away from the area in which the corrective technique is being performed.

15. A method for determining the condition of the eye com-prising: placing a surgical microscope into viewing alignment over a patient's eye; projecting indicia comprised of partial segments of placido rings onto the eye which are quantitatively related to the shape of the present corneal surface and observing a reflected image of the eye and such indicia through the microscope; display-ing an image of the indicia quantitatively related to the shape of the present corneal surface; generating an image having indicia related to the shape of a predetermined spherical surface; and superimposing the generated image onto the displayed image for comparative purposes.

16. The method of claim 15 and further including aligning the generated image with the displayed image to provide a comparative image of the present corneal surface to the predetermined spherical surface.

17. The method of claim 16 and further including recording indicia indicative of the comparative image.

18. The method of claim 15 wherein a television camera is mounted on the microscope and further including utilizing the television camera to obtain an image of the indicia related to the present corneal surface.

19. The method of claim 15 and further including generating the image related to a predetermined shape by, prior to placing the surgical microscope into alignment over a patient's eye, placing a spherical surface of known dimension under the micro-scope at the same distance as the patient's eye and utilizing the television camera to obtain an image of indicia related to a spherical surface of known dimension.

20. The method of claim 16 and further including determining the radius of curvature of the corneal surface from the compara-tive image.