implantation Marvin L Kwitko, MD Artificial lens

Transcription

1 Marvin L Kwitko, MD Artificial lens implantation Cataract formation is one of the major causes of blindness. More than 400,000 persons in the United States and about 10% of that number in Canada, most of them elderly, undergo surgery each year for the removal of opacified lenses in their eyes. Following surgery, such patients are usually fitted with extra thick cataract glasses or contact lenses. The normal lens of the eye consists of crystal-clear gelatinous protein encased in a capsule. It lies behind the circular, colored iris, fixed by a series of suspensory ligaments called zonules. Because it is naturally pliable, the lens can automatically lengthen or shorten to focus at varying distances in much the same way that the zoom lens of a camera operates. Cataracts develop when the lens Marvin L Kwitko, MD, FRCS(C), is attending ophthalmologist, St Mary's Hospital and Sir Mortimer Davis Jewish General Hospital, Montreal. He received his MD degree from the University of Western Ontario in London, Ont. protein undergoes changes in molecular structure that cause it to lose its pristine transparency and gradually become opaque. The process can be caused by exposure to radiation, certain toxic chemicals, genetic factors, or some systemic diseases. However, cataracts usually occur, like the graying of the hair, as a natural part of the aging process. While cataracts almost always affect both eyes, they often develop at quite different rates, and only the lens in the most advanced state of disease is removed in the initial operation. The average operation takes about one hour, the eye patch is removed the next day, and the patient can be discharged from hospital and sent home in less than a week if all goes well during the postoperative period. The healing process generally takes about six weeks, during which time eyedrops are instilled once or twice a day. The surgery is therefore simple and safe, but the aftermath can be troublesome. The thick spectacles worn by cataract patients magnify images by 25%. The cosmetic appearance is bad, doorways appear curved, peripheral vision is restricted, and objects seem to be closer than they reaily are. When a patient still has one normal eye, the distortions produced by the spectacle lens and the difference of 25% in image size make useful binocular vision impossible. A contact lens produces far less AORN Journal, July 1978, Val 28, 1 47

2 Table 7 Comparison found in the use of intraocular lenses, contact lenses, and spectacles Visual fields Image size magnification 24-hour use Good uncorrected vision Flare Prismatic displacement Binocularity (use of both eyes) Depth perception Useful in work environments with dust and chemicals Suitable for patients with tremor, neurosis, conjunctival problems, etc Requires dexterity on the patient s part Useful for the remainder of the patient s life lntraocular lens Full 1 Yo-2% Almost always a 5% Contact lens Full % Frequently About 50% t likely Spectacles Limited 30%-33% Rarely Likely distortion and permits adequate peripheral vision, but these lenses require a high degree of manual dexterity, which older people often lack. They cannot be used in a dusty environment, and patients with ocular allergies and those having a medical eye condition such as glaucoma cannot wear them. Many patients, particularly the aged, find them a nuisance to care for and uncomfortable as well. Because of these problems, many cataract patients give up wearing contact lenses even though they may have worn them successfully at the beginning. The artificial plastic lens implant, however, provides vision of a quality that nearly matches the natural lens and is just as unobtrusive. The benefits and disadvantages of these three possible corrective measures for vision following cataract surgery are listed in Table 1, and the procedure is outlined step by step in Table 2. The history of lens implantation goes back to 1949 when Harold Ridley of England implanted the first artificial acrylic lens in an eye that had undergone a cataract operation. It captured the imagination of ophthalmologists everywhere, for this brilliant concept, if successful, would solve many of the problems of the cataract patient. Unfortunately, Ridley s lens and the ones that followed produced so many complications that by 1957 the procedure had been largely abandoned. It remained for Cornelius Binkhorst to reevaluate the whole concept and come up with a functional artificial lens. Binkhorst s first implant took place in Holland in 1958; his design or some modification of it is now used for practically all of the lenses implanted following an intracapsular cataract extraction (Fig 1). Binkhorst later modified his lens for use in younger patients, particularly those with severe ocular trauma involving the lens. This lens was called the irido-capsular lens (Fig 2). At the same time, Epstein in South Africa designed the Maltese cross lens, 48 AORN Journal, July 1978, Vol28, 1

3 i Fig 1. Binkhorst's first lens design, the "iris-c1ip"lens for use in intracapsular cataract surgery. The original design has been modified and is stillin use today. All dimensions in diagrams are in millimeters. Fig 2. Binkhorst's modification of the original lens design, the "irido-capsular" lens is used primarily in the extracapsular cataract surgery and phacoemulsification. n fl PLAN SIDE VIE w EL E VA Ti0 N IMPLANT IN SlTU Fig 3. Epstein "Maltese Cross" lens. This lens is used primarily in older patients. AORN Journal, July 1978, Vol28, 1 49

4 loo., Loopsand 7.5 RAD 2 Fig 4. Fyodorov Sputnik lens. This tens is useful in all age groups where lens implants are indicated. - Fig 5. Fyodorov lens, implanted in a case of a young man who developed a cataract after severe trauma to the eye. All Dimensions in Millimeters Fig 6. Worst Medallion lens. The suture fixes the lens and prevents dislocation during dilatation of the pupif for fundus examination. 50 AORN Journal, July 1978, Vol28, 1

5 Fig 7. Worst "platinum clip" lens. The clip prevents lens dislocation and is useful when a suture is not practical in a given case. Fig 8. Worst "smgle loop" lens. This lens can be implanted through a relatively small cataract incision. TJ,-w>r Fig 9. Kwitko lens design. This lens can be used in a wide selection of cases. AORN Journal, July 1978, Val 28, 1 51

6 Table 2 lntracapsular cataract extraction with lens implantation 1. Preparation is with iodophor sol. 2. For anesthesia, a retrobulbar block is given. Intravenous medications are given by the anesthesiologist to control relaxation. 3. The eye is massaged by the nurse intermittently for ten minutes or more until the time the surgery begins. more than ten minutes of massage need be given for extracapsular cataract extraction. 4. Lid speculum is placed. 5. Superior rectus suture is placed. 6. Limbus-based flap is made. 7. Limbus is cleaned and cauterized. 8. Surgical incision is made with two-thirds thickness groove perpendicular to the sclera-corneal at 10 o clock and 2 o clock, scleral at 12 o clock. 9. Sutures are preplaced at 11 o clock and 1 o clock and looped out of the wound medially and laterally. Anterior chamber is entered at 1 1 o clock. Corneal scleral incision is made. The iris suture is placed superior to sphincter, one-third distance between pupil and angle. Suture is placed from right to left, full thickness iris at 12 o clock. Lens is extracted with a cryoprobe. Pupil is controlled with Miochol used with Millipore filter. Anterior chamber is maintained with air injection. 16. The lens is inspected, loops are checked for position, optical segment is checked for precipitates, and lens is irrigated well with balanced salt solution. 17. Sutures are placed from back to front on left hole and front to back on right hole. 18. Lens is placed. If right-handed, the surgeon will place the right loop under the iris first, then the left loop in one sweeping slow motion, if possible. If the pupil is too miotic, one will engage the right loop under the iris and drop the lens in the anterior chamber. The left loop will then be placed with a fine notched spatula and a fine iris hook if necessary. All of these movements are made under visual control. If hemorrhage or pigment clouds the anterior chamber, all movements are stopped until this is controlled by irrigation. The use of an irrigation lens inserter would be helpful. At all times, if possible, the anterior chamber is maintained with air or fluid. 19. Suture tie is placed and checked to make sure the suture is not crossed. The end with the needle should be to the right, the anterior end. A square knot is made. The suture remains slightly loose around the lens. This should be placed visually if possible, either through closed or open which has gained a measure of acceptance in several centers in the United States (Fig 3). Modification of these early artificial lenses became necessary because of complications, namely irreversible edema of the cornea due to trauma by either the lens itself or the support structures and dislocation of the lens when the pupil was dilated to visualize the ocular fundus. Fyodorov of the USSR in 1972 designed the Sputnik lens, which eliminated many of these complications because of its geometric design (Fig 4). This lens may also be used in the case of traumatic cataracts (Fig 5). Worst of Holland chose to insure fixation first by suturing the lens to the iris (Fig 6) and later using a safety-pin device to fix the lens situated in front of the iris to the support structures located behind (Fig 7). Other modifications of this lens have also been introduced (Fig 8). Taking advantage of technical ad- 52 AORN Journal, July 1978, Val 28, 1

7 cornea. The second knot will not tighten the suture. The third knot is made and is now between lens and iris. 20. The knot is cut by pulling on the suture end with tying forceps. The suture is cut flush with the edge of the lens. The knot will then retract under the lens surface. If it does not, it is pushed under with a fine spatula. 21. Chamber depth is controlled. The preplaced sutures are tied and air is injected into the anterior chamber. Any lens centering needed can be done at this time. 22. Peripheral iridectomy is done at this time so that (1) during lens insertion there is a complete iris diaphragm and no chance of vitreous herniation through an iridectomy, and (2) if hemorrhage occurs at this time, it will not prevent lens insertion. 23. Wound is closed with running shoelace tie with the knot buried at 2 o'clock. This is done by placement of the first suture on the scleral side only and the last suture through the corneal side only. 24. The air in the chamber is replaced with balanced salt solution. 25. Lens is inspected. The lens must be placed precisely at this time. lf it is not, it must be manipulated with a fine spatula until it is centered. amount of gravity or pupillary action will do the centering later. 26. Conjunctival closure is made with a running mattress stitch from left to right. 27. Medication is administered, and the patch and shield are applied. vances made in the past, in 1974 Kwitko fashioned a new lens style (Fig 91, which has been uniformly successful in avoiding complications. Kwitko has been performing this operation in Canada routinely since The most suitable material now available is the highly transparent light, polymethyl methacrylate. This material does not pose great problems in processing, and it has been shown to retain its chemical composition and transparency for an extended period as much as 40 years in constant surroundings. Visual acuity loss from opacification of the crystalline lens is restored in the most natural manner with the artificial lens implant. The visual field approaches normal and binocular vision is obtained. The pupil has a diameter of 3 to 3.5 mm in the normal state; with the newer style fixation devices, almost full pupillary dilation may be achieved. The natural human lens has a light transmission of only 65% to 80% in patients over age 60. An artificial intraocular lens has a light transmission of 92% to 94%. In addition, the quality of the optical surfaces of the artificial lens is better than that of the natural lens surface in the older patient. Since the lens cannot change its shape for focusing as a normal, youthful lens does, the patient must wear the appropriate conventional glasses to compensate, in much the same way that the presbyope must use reading glasses. The artificial lens cannot be installed in the eye of all cataract patients. A patient showing undue agitation under local anesthesia, prolongation of the operative time in a patient who is less than a good surgical risk, excess vitreous pressure or actual loss, and any deformation of the iris onto which the artificial lens is attached at time of surgery are some of the situations that preclude the use of this technique. The eye surgeon must always demonstrate good medical judgment as to when not to implant a lens in order to avoid serious complications. Since the lens implant operation is relatively new to many operating rooms in rth America, it is important for OR nurses to become aware of the technicalities of the procedure. AORN Journal, July 1978, Vol28, 1 53