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Cataracts and Cataract Operations (First of Two Parts)*

      Cataract operations are commonly performed in either a primary-care or a tertiary-care center. A plethora of information (some of which is unfounded) has been disseminated in the lay news media about the advances in the surgical techniques of cataract removal. This article reviews some of the recent concepts about the formation of cataracts and the modern approaches for their extraction. It is directed at the nonophthalmologic primary-care physician who refers patients for evaluation or performs the ancillary tests in preparation for a cataract operation. Space limitations prevent a complete review of the subject. Some of the controversial aspects of cataract surgical procedures are addressed objectively, but bias is unavoidable.
      Given a long life-span, a person is more likely to undergo a cataract operation than most other surgical procedures.
      • Sommer A
      Cataracts as an epidemiologic problem.
      In 1982, more than 600,000 cataract operations were performed in the United States.
      • Stark WJ
      • Leske MC
      • Worthen DM
      • Murray GC
      Trends in cataract surgery and intraocular lenses in the United States.
      No other operation dominates a surgical subspecialty as do cataract procedures in ophthalmology; no other operation in medical practice is probably as frequently dramatically successful.
      During the past few years, technologic advances in cataract operations have profoundly affected the practice of ophthalmology. Experienced surgeons have made extensive changes in operative techniques and have ultimately accepted the intraocular lens, which had been condemned just 2 decades earlier. The ease of communication, the demands of patients, and the innovativeness of many surgeons have brought about a tremendous explosion of information. Although scientific data have been disseminated through medical symposiums and medical literature, they sometimes appear initially in the lay literature or on television. Strong personal opinions, aggressive investigative reporting, and an enthusiastic market frequently cloud the facts about the modern approaches in cataract surgical procedures.
      Against this background, this article was written to familiarize the nonophthalmologic physicians with the current concepts of formation of cataracts, the techniques of cataract operations, and the methods of optical correction postoperatively. Cataract surgical procedures are often the backbone of a practice in general ophthal mology and frequently determine the economic status of a physician. Each surgeon's approach to patients with cataracts and individual surgical techniques for cataracts may be unique. Any surgeon can collect scientific documents to support multiple disparate opinions about any one subject, and occasionally some surgeons become unduly defensive about their particular mode of operation. This article cannot be written without introducing bias concerning the topics, emphases, and references selected. This review will not be an all-inclusive report but will present highlights and new directions in cataract surgical procedures.

      DEFINITION OF A CATARACT

      The normal crystalline lens is located behind the iris in the pupillary space and is supported by zonules or elastic ligaments that extend from the ciliary body to the equator of the lens (Fig. 1). This lens consists of several cellular layers that overlie a nucleus. It is unique because of its avascularity, low water content, regular crystalline arrangement, anaerobic metabolism, and low energy demands. It is approximately 9 mm in diameter and 4 mm thick but varies in size with accommodation of the eye during focusing (in younger persons). With aging, both the nucleus and the cortical zones of the lens enlarge because new fibers are formed in the cortical zones of the lens and because the older fibers become more compressed and dehydrated in the nucleus. In addition, the metabolic activity changes: protein becomes more insoluble; calcium, sodium, potassium, and phosphate all increase in concentration; the amount of glutathione decreases; and the water content varies. The yellow brown pigment of the lens increases, perhaps because of oxidation of tryptophan by ultraviolet sunlight.
      • Zigman S
      The role of sunlight in human cataract formation.
      The unfolding of protein molecules, the cross-linking of sulfhydryl groups, and the conversion of soluble to insoluble proteins all reduce the transparency of the lens.
      Figure thumbnail gr1
      Fig. 1Diagram of anatomy of the eye, with special emphasis on structures affected by cataract surgical procedures.
      A cataract is an opacity or clouding of the normally transparent crystalline lens. As described, it can be part of the normal aging process. Depending on the location and the size of the opacification, vision is blurred or an annoying glare is produced, especially around lights. Complex biochemical processes may contribute to the formation of cataracts in humans, and no therapy effectively alters these biochemical processes.
      • Kador PF
      Overview of the current attempts toward the medical treatment of cataract.
      In a recent study, aspirin was touted, although that study was inconclusive.
      • Cotlier E
      Senile cataracts: evidence for acceleration by diabetes and deceleration by salicylate.
      Currently, no method of clearing the opacity or preventing its progression exists except for surgical removal. Eyedrops, laser therapy, and systemic medication are ineffective.

      CAUSES OF CATARACTS

      Cataracts may be classified on the basis of cause, age at onset, location, or degree of opacification. Cataracts can occur as congenital or developmental anomalies but most commonly are acquired defects. Those present at birth may be of genetic origin or maternal origin (from rubella, syphilis, or amniocentesis). In cataracts of genetic origin, the parents of the affected infant frequently have a similar type of cataract. During the developmental stages, cataracts may occur in relationship to inborn errors of metabolism (diabetes, galactosemia, homo cystinuria, and Lowe's syndrome [oculocerebrorenal syndrome]), chromosomal abnormalities (trisomy 13, 18, or 21), and syndromes of unknown cause (for example, idiopathic hypoparathyroidism, atopic dermatitis, and myotonic dystrophy). Developmental cataracts can also be associated with other ocular abnormalities that may be of more serious concern.
      Acquired cataracts may be caused by trauma, toxins, or metabolic defects; may be associated with other ocular disease; or may be related to the aging process. Traumatic injury to the lens in the form of a blunt or sharp mechanical injury may cause immediate or delayed (after months or years) formation of cataracts. Physical trauma from irradiation (ionizing, beta, or infrared), electric current, or glassblowing may be associated with delayed formation of cataracts. Evidence of the role of sunlight and, specifically, near-ultraviolet light in the photochemical generation of fluorescent pigments and formation of cataracts is accumulating.
      • Lerman S
      Avoidance of extreme exposure and the use of protective lenses are suggested for those exposed to near-ultraviolet irradiation.
      • Zigman S
      The role of sunlight in human cataract formation.
      • Wojno T
      • Singer D
      • Schultz RO
      Ultraviolet light, cataracts, and spectacle wear.
      In diabetes mellitus, excessive glucose may diffuse into the lens from the aqueous humor; aldose reductase in the lens converts the glucose into sorbitol, which cannot escape from the lens and acts as an osmotic agent that draws water into the lens. This process is potentially reversible in the early stages and explains some of the episodes of fluctuation in vision which are experienced by those who have uncontrolled diabetes. Toxic substances associated with formation of cataracts include MER-29 (triparanol), copper, iron, naphthalene, dinitrophenol, and paradichlorobenzene, but toxicity can also occur in association with use of chlorpromazine (anterior axial pigment) and corticosteroids (typical posterior subcapsular cataracts). Cataracts associated with other intraocular disease are called complicated or secondary cataracts and are seen particularly in association with intraocular inflammation (uveitis), glaucoma, and retinitis pigmentosa.
      Senescent cataracts, by far the most common type of cataract, are usually seen in association with the aging process but may also occur at a relatively early age. They are classified on the basis of location and stage of development (Fig. 2). Nuclear cataracts are an exaggeration of the normal aging changes in the lens nucleus and are accompanied by increasing myopia, spherical aberration, and yellowish or brownish discoloration of the nucleus. They are termed “hard cataracts” in contradistinction to the softer cortical cataracts, which begin as clefts that separate fibers and appear clinically as radial spokes or shields around the nucleus. Subcapsular cataracts can form on the anterior or the posterior capsule.
      Figure thumbnail gr2
      Fig. 2Types and locations of cataracts. A, Congenital zonular cataract in various layers of lens nucleus. B, Congenital coronary cataract in cortex of lens. C, Common nuclear sclerotic cataract of aging. D, Posterior subcapsular cataract, frequently seen in middle-aged persons, E, Immature cortical cataract with beginning hydration of lens. F, Total white opacification of cortex with mature or “ripe” cataract. G, Morgagnian cataract with totally liquefied cortex and floating nucleus. H, Hypermature cataract with wrinkled capsule and loss of cortical fluid.
      The posterior subcapsular cataracts are the most disabling because of their central location; they produce a glare that interferes with reading and outdoor activities. The posterior subcapsular cataracts are associated with use of corticosteroids (either topical or systemic); these cataracts, however, are also the most commonly acquired type of cataract in a middle-aged person.
      Once a cataract begins in any of these locations or for any of the described reasons, it can either remain stationary or, more likely, develop through stages until it is “ripe.” An immature or developing cataract has cortical or nuclear changes that cause variations in visual acuity. A mature cataract is characterized by total opacification of the cortex and thus is associated with poor visual acuity. It usually appears totally white. The cataract may further progress to an intumescent stage (in which it is imbibed with water and swollen) or to a hypermature stage (in which the fluid has leaked out of the capsule and a wrinkled capsule remains). A morgagnian cataract is a lens with a totally liquefied cortex and the nucleus lying in a dependent position. Leakage of denatured protein through the capsule may cause a mild inflammatory reaction within the eye in association with glaucoma and may necessitate removal of the lens to alleviate the condition.

      EVALUATION FOR CATARACT OPERATION

      Cataracts in Children.

      The treatment of a cataract in a young child depends on the cause of the cataract, whether it is unilateral or bilateral, the presence of other ocular or systemic disease, the degree to which it interferes with vision, and the ability of the patient to adjust to optical correction.
      • Parks MM
      Visual results in aphakic children.
      Children with small cataracts in the main axis of vision may obtain good vision by seeing around the opacity if the pupils are kept dilated (Fig. 2). These cataracts frequently do not progress.
      If the cataracts are bilateral and severe, removal of the lens is necessary for development of the normal visual fixation reflex. The current concepts of functional amblyopia necessitate a clear visual axis during the important formative years of the visual apparatus.
      • Von Noorden GK
      • Crawford MLJ
      The sensitive period.
      Ocular nystagmus occurs if the cataracts prevent the development of the fixation reflex during the first 3 months of life, and this condition further handicaps the processing of visual information.
      • Rogers GL
      • Tishler CL
      • Tsou BH
      • Hertle RW
      • Fellows RR
      Visual acuities in infants with congenital cataracts operated on prior to 6 months of age.
      Once nystagmus develops, it persists even if the cataracts are subsequently removed, and affected patients rarely have vision better than 20/200 (6/60), which constitutes legal blindness. If an operation is indicated, the cataracts should be removed from both eyes before 3 months of age and ideally within the first few days or weeks of life. The child should be fitted with a contact lens or aphakic glasses as soon as possible for maximal stimulation of the developing macula. Fairly good results can be obtained in patients with bilateral cataracts.
      If a child has a unilateral cataract, the situation is considerably altered. If the patient has one normal eye or one with good useful vision, good vision is unlikely to develop in the eye with the cataract, either with or without a cataract surgical procedure. For any attempt at visual rehabilitation, the procedure must be performed as early as feasible (within weeks), the patient must wear an aphakic correction (usually a. contact lens), and occlusion therapy (with a patch) must be applied to the normal eye to stimulate development of visual potential in the aphakic eye. Therapy must be continued during the early years of visual development, and care must be taken to avoid causing amblyopia in the good eye. Complete cooperation from the parents isessential. Before deciding on surgical removal of the cataracts, the parents should understand that forcing the child to use the contact lens and occlusion therapy may cause social damage or psychologic damage in their relationship with the child. A recent study reported good visual acuity with an aggressive early approach,
      • Beller R
      • Hoyt CS
      • Marg E
      • Odom JV
      Good visual function after neonatal surgery for congenital monocular cataracts.
      but these results have not generally been reproducible. Intraocular lenses are being used in special circumstances in children, although amblyopia and other problems related to intraocular lenses remain a persistent problem.
      • Hiles DA
      Visual acuities of monocular IOL and non-IOL aphakic children.
      A newer approach has been a refractive corneal operation (epikeratophakia),
      • Friedlander MH
      • Safir A
      • McDonald MB
      • Kaufman HE
      • Granet N
      Update on keratophakia.
      which will be discussed later in this article.
      Patients with congenital cataracts frequently have other general medical diseases or ocular diseases (such as myopia, retinopathy, or nystagmus). Glaucoma, retinal detachment, and secondary membranes are frequently late complications that hamper the visual success of the procedure, and this outcome fosters a conservative approach to unilateral cataracts by most practicing ophthalmologists.
      • Toyofuku H
      • Hirose T
      • Schepens CL
      Retinal detachment following congenital cataract surgery. I. Preoperative findings in 114 eyes.
      • Phelps CD
      • Arafat NI
      Open-angle glaucoma following surgery for congenital cataracts.

      Cataracts in Adults.

      The major indication for surgical removal of cataracts in adults is the need to improve vision.
      • Wong WW
      Indications for cataract surgery: psycholinguistic considerations.
      Removal of cataracts (even though they are not far advanced) may be necessary in several other circumstances—for example, to facilitate the visualization of the ocular fundus (in order to monitor glaucoma or in preparation for photocoagulation therapy in diabetic retinopathy), to remove a foreign body embedded in the lens, to prepare for vitrectomy and surgical repair of retinal detachment, or for a variety of pathologic conditions in which the lens is threatening the viability of the eye. The last-mentioned conditions include phacolytic glaucoma (in which the fluid of the lens escapes and causes intraocular inflammation and glaucoma), rupture of the lens that causes phacoanaphylactic endophthalmitis (a reaction that results from prior sensitization to lens protein), or swelling of the lens and consequent crowding and compromising of the anterior structures of the eye. Both the physician and the patient must have a clear understanding of the objective of the surgical procedure so expectations are appropriate.
      No absolute or exact visual requirements can be cited for recommendation of a routine cataract operation. The decision for surgical intervention depends on the patient's needs, the desired activity and recreational level of the patient, the symmetry of the disease process, conditions of the other ocular structures, the general health of the patient, and appropriate informed consent with reasonable expectations of the patient. One useful approach is to consider this elective procedure from the stance of the devil's advocate: can the patient function with the present level of vision, and can the patient and physician stand by their decision in the face of a serious complication that may lead to permanent blindness? Patients in the working age group (for example, physicians and surgeons) may have their livelihood threatened by decreased visual acuity or loss of binocular vision, and consideration of cataract extraction in patients with 20/30 or 20/40 vision is not rare. The posterior subcapsular cataract, which occurs particularly frequently in middle-aged persons, can profoundly affect reading vision, whereas the nuclear sclerotic cataract affects distance vision.
      If the patient believes that visual performance is adequate, surgical correction should not be considered. An exception to this general rule is the presenile or senile patient who lives alone or in a nursing home and who may be coping with multiple medical or social problems and does not realize the extent of the visual loss. Under these circumstances, it is gratifying to restore vision and provide a new life for these elderly patients. Balancing these successes, however, are the elderly persons who have associated ocular disease (such as macular degeneration, glaucoma, or retinopathy) that cannot be accurately assessed preoperatively. Even though cataract removal is technically successful, vision in these patients remains limited, and frustration and depression prevail.
      With the availability of newer and better surgical techniques for cataract removal, in conjunction with an aging population and increasing patient demands, a more liberal trend has evolved in performing cataract operations. In some patients, cataract extraction does not appreciably improve the quality of life. Tissue is not generally available for postoperative analysis, and even if it were present, visual function cannot be determined on the basis of a pathologic examination.
      If the patient has a unilateral cataract, the decision to proceed with operative removal is even more complicated for the patient and the physician. In this circumstance, the patient must use a contact lens or an intraocular lens postoperatively in the affected eye to restore binocular vision. Although an active person may require this binocular vision, such an outcome is not necessarily appropriate for an elderly patient confined to a nursing home or a wheelchair who may not even appreciate the improved visual acuity. Certain broader social and financial issues may be forced into the decision-making process in the future.
      The final decision about surgical removal of cataracts depends on the age and the occupation of the patient; the skill, experience, and surgical philosophy of the surgeon; and the expectations of the patient or the environment in which the patient lives.

      CORRECTION OF APHAKIA

      Aphakia (a Greek-derived word meaning without a lens) is the term used for the condition of an eye after surgical removal of a cataract. Determining what prosthetic optical device is necessary before useful vision can be restored is of paramount importance, for both the patient and the surgeon, in the consideration of a cataract operation. Options for the patient to consider are aphakic spectacles, contact lenses, or intraocular lenses (Fig. 3). Each has its indications, advantages, and disadvantages. Refractive keratoplasty may be available in the future.
      Figure thumbnail gr3
      Fig. 3Methods of optical correction of aphakia. A, Thick aphakic spectacles worn in front of eye. B, Contact lens worn on surface of eye. C, Intraocular lens placed within eye. D, Refractive keratomileusis of cornea to correct aphakia. E, Refractive keratophakia with use of donor lenticule to alter refraction of cornea. F, Epikeratophakia with donor lenticule sutured onto surface of cornea.

      Aphakic Spectacles.

      Aphakic spectacles are the simplest, safest, and oldest form of optical correction, but apart from these factors, they have no other advantages.
      • Editorial
      The adjustment to aphakia.
      Because the spectacles are positioned far in front of the eye, image size is magnified 25% and spatial orientation is false. The spherical aberration from the thick lenses causes a parabolic world of vision, with straight lines transformed to curves and a pincushion distortion effect; as the patient looks across a field of gaze, objects change shape. The peripheral visual field is restricted, primarily because of the prismatic effect of the periphery of the thick lens. The aphakic spectacle frame must be carefully adjusted because small movements of the glasses cause a substantial change in the effective dioptric power of the lens. Lightweight, aspheric, plastic lenses have been developed to alleviate some of these problems, but modern patients generally do not like these visual annoyances, and some patients cannot adjust to these bulky glasses. This technique of optical correction is now generally limited to patients who do not qualify for implantation of an intraocular lens or who cannot tolerate a contact lens. An aphakic spectacle over one eye cannot be used together with a thin glass over the other eye because the image magnification on the retina with the aphakic spectacle would cause distortion and confusion in comparison with the eye with the thin lens.

      Contact Lenses.

      Contact lenses have an optical advantage over aphakic spectacles because they are placed closer to the eye. The 7% image magnification can be tolerated and coordinated with the other unoperated eye to give binocular vision. With contact lenses, patients have essentially a full field of vision. The hard contact lenses are particularly effective in superficially scarred corneas because they provide a better refractive surface, and they are practical in the younger active patient. The fitting of contact lenses is a definite art, and a poorly fit lens is a frequent problem.
      Hard, semihard (gas-permeable), and soft contact lenses are available for the aphakic patient, and advantages, disadvantages, and compromises are associated with each type of lens.
      • Ruben M
      Review: contact lens in practice.
      Hard contact lenses are made of polymethyl methacrylate. Semihard lenses are made of various compounds that allow oxygen and other gases to permeate the lenses. Soft contact lenses are made of a variety of hydrophilic plastic polymers. The main disadvantages of contact lenses are that many patients do not possess the manual dexterity necessary to insert and remove them and, under certain conditions (for example, a dusty or outdoor environment), they are not well tolerated. Additionally, the eye may become intolerant of the contact lens or develop hypersensitivity reactions to the lens or the contact lens solutions. Corneal ulcers or infections occasionally occur.
      High-water-content and thin lenses have been developed for extended wear. Two to 3 months may elapse before removal and cleaning are needed.
      • Martin NF
      • Kracher CP
      • Stark WJ
      • Maumenee AE
      Extended-wear soft contact lenses for aphakic correction.
      They are more convenient for the elderly patient because manipulation is unnecessary. Although they provide more stable vision, they also necessitate frequent follow-up, periodic replacement, and more expertise by the contact lens technician. They are usually unsuccessful in patients with insufficient tear lubrication, inflammation of the eyelids (blepharitis), or vascularized corneas and are unsafe in patients who cannot appreciate the early development of complications.

      Intraocular Lenses.

      If a lens is inserted within the eye close to the location of the original lens, the eye will regain near-normal vision. In the field of ophthalmology, the intraocular lens has been the single greatest development for patients with cataracts. The intraocular lens causes minimal magnification and spatial disorientation, and peripheral vision is good. This device is most convenient for the patient because no manual dexterity and no replacement are necessary. It is especially ideal in elderly patients with arthritis, mentally retarded persons, patients in a dusty environment, and patients with macular degeneration (who have lost their central vision and need as much peripheral vision as possible).
      In comparison with other corrective methods for aphakia, insertion of an intraocular lens demands greater skill of the surgeon and is generally more traumatic to the eye because of the additional handling of tissue. There are risks to the delicate endothelial cell membrane that lines the back of the cornea and whose pumping action keeps the cornea clear. More endothelial cell damage can occur intraoperatively
      • Katz J
      • Kaufman HE
      • Goldberg EP
      • Sheets JW
      Prevention of endothelial damage from intraocular lens insertion.
      and on a chronic basis with this procedure than with a routine cataract operation.
      • Liesegang TJ
      • Bourne WM
      • llstrup DM
      Short- and long-term endothelial cell loss associated with cataract extraction and intraocular lens implantation.
      Additional risks are associated with the intraocular lens, including the potential for uveitis, glaucoma, or dislocation of the implant. Long-term data on intraocular lenses are still lacking, especially because of the frequent changes (presumably improvements) in design, materials, sterilization, and surgical techniques.

      Refractive Keratoplasty.

      Keratomileusis (a Greek-derived word meaning sculptured cornea) and keratophakia (“corneal lens”) are surgical procedures used to modify the radius of the corneal curvature and to correct the large refractive errors produced by removal of a cataract.
      • Barraquer JI
      Keratomileusis and keratophakia in the surgical correction of aphakia.
      These extraocular surgical procedures eliminate the dependence on a prosthetic device such as an intraocular lens or a contact lens (Fig. 3). Keratomileusis is an autoplastic operation in which the corneal thickness in the zone of the optical axis is decreased. A round corneal disk of parallel faces and predetermined thickness is resected from the anterior layer of the operated eye and hardened by freezing. The tissue disk is cut meticulously on a lathe to give the necessary dioptric power, and the new disk (called a lenticule) is replaced on the globe and sutured. In keratophakia, an adequately shaped lenticule is obtained from the stromal tissue of a donor cornea. This lenticule is placed intralamellarly within the operated cornea to thicken and modify the radius of the anterior surface.
      Both procedures necessitate great precision in cutting. Current techniques use computerized equipment with a microtome, a cryolathe, and a surgical keratometer all within the operating room. These techniques are difficult and tedious to learn, even for experienced surgeons.
      Pioneered for years by Barraquer of Bogota, Colombia, keratomileusis and keratophakia have recently been introduced into the United States.
      • Swinger CA
      • Barraquer JI
      Keratophakia and keratomileusis: clinical results.
      Simpler variations of these techniques have been developed, such as the technique of epikeratophakia, in which an onlay donor graft, which has been prefrozen and lathed, is sutured onto the surface of the cornea after the corneal epithelium has been removed.
      • Friedlander MH
      • Safir A
      • McDonald MB
      • Kaufman HE
      • Granet N
      Update on keratophakia.
      In other approaches, hydrophilic materials or precut donor corneas have been used to replace the donor corneal lenticules.
      • McDonald MB
      • Koenig SB
      • Friedlander MH
      • Hamano T
      • Kaufman HE
      Alloplastic epikeratophakia for the correction of aphakia.
      This rapidly developing technology holds considerable interest for the cataract and corneal surgeon alike but is still experimental.

      INTRAOCULAR LENSES

      History of Intraocular Lenses.

      Because of the dominance of intraocular lenses in the field of cataract surgery, reviewing the history of these lenses seems worthwhile. The intraocular lens should be fixated in the eye without any movement, should be chemically nontoxic, should avoid mechanical damage to other ocular structures, and must be sterile. Some of these principles are obvious, and others have evolved during the history of the use of intraocular lenses.
      Although several centuries ago a few investigators attempted to insert an intraocular lens in the eye,
      • Jaffe NS
      • Calin MA
      • Hirschman H
      • Clayman HM
      the modern era of intraocular lens surgical procedures began with Harold Ridley (England), who noted in 1949 that the plexiglass used for airplane canopies was well tolerated in the eyes of several Royal Air Force pilots who had been injured during World War II. Plexiglass is a polymethyl methacrylate plastic manufactured as Perspex CQ by Imperial Chemical Industries of England. Most intraocular lenses today are derived from Perspex CQ or from molded lenses supplied by Rohm and Haas of West Germany. Ridley placed his initial intraocular lenses behind the iris and within the posterior chamber, but these lenses were heavy and poorly designed and were associated with dislocation, uveitis, and glaucoma.
      • Ridley H
      Intra-ocular acrylic lenses: 10 years' development.
      Within a few years, other lenses for placement in the anterior chamber were designed by Ridley, Strampelli (Italy), Dannheim (Germany), and Barraquer (Spain), but these lens designs caused considerable damage to the cornea or the anterior chamber of the eye and gave the procedure a poor reputation.
      • Choyce DP
      The evolution of the anterior chamber implant up to, and including, the Choyce Mark IX.
      Between 1957 and 1963, Choyce (England) designed several modifications of the anterior chamber lenses with improved success.
      • Choyce DP
      The evolution of the anterior chamber implant up to, and including, the Choyce Mark IX.
      Binkhorst (Holland) developed an iris clip lens supported by the pupillary aperture with two loops in front of and two behind the iris; he reported a much higher success rate than had previously been attainable.
      • Binkhorst CD
      • Leonard PAM
      Results in 208 iris-clip pseudophakos implantations.
      Other investigators used a variety of struts, loops, and other devices to fixate on the iris or with the addition of a suture; the better iris-supported lenses were designed by Epstein (South Africa), Fyodorov (Russia), and Copeland (United States).
      • Epstein E
      Modified Ridley lenses.
      The excellent results obtained by Binkhorst and an edifying communitywide study done in Miami, Florida, with the Copeland lens,
      • Duffner LR
      • Wallace WK
      • Stiles WR
      The Miami cooperative community study on the Copeland intraocular lens (pseudophakos).
      which was orchestrated by Jaffe, were the main thrust for the introduction of intraocular lenses in the United States. There were, however, early outspoken critics.
      Recognizing firm fixation as an essential feature of intraocular lenses, Binkhorst later used an intraocular lens supported in the pupillary space within the lens bag after extracapsular surgical removal of cataracts.
      • Binkhorst CD
      Iris-clip and irido-capsular lens implants (pseudophakoi): personal techniques of pseudophakia.
      This design provided more stability and eliminated the excessive movement of the vitreous and iris diaphragm, which he thought damaged intraocular structures. Worst (Holland) developed his medallion lens, which was fixated to the iris with a suture and could be used with both an intracapsular and an extracapsular cataract operation.
      Choyce persisted with his modifications of the anterior chamber lens through a series from Mark I to Mark IX, and the reported results were good.
      • Choyce DP
      The Choyce Mark VIII anterior chamber implant.
      Because insertion of this lens necessitated the fewest changes from the cataract operation most popular in the United States at that time (intracapsular cataract operation), the anterior chamber lens of Choyce became the most popular implant. The demand for the anterior chamber lens in the United States temporarily outstripped the ability of the manufacturer to maintain quality control; the rough edges and warping of some of these lenses were associated with uveitis, glaucoma, and hyphema.
      • Ellingson FT
      The uveitis-glaucoma-hyphema syndrome associated with the Mark VIII anterior chamber lens implant.
      Later modifications in design of anterior chamber lenses were made by Tennant, Kelman, and Azar (all from the United States). With use of different principles of fixation, more flexible anterior chamber lenses with multiple variations have recently been developed.
      Independently, Pearce (England)
      • Pearce JL
      Experience with 194 posterior chamber lenses in 20 months.
      • Pearce JL
      Sixteen months' experience with 140 posterior chamber intraocular lens implants.
      and Harris (United States) concluded that the posterior chamber was an ideal location for fixation of a lens implant. This approach necessitated an extracapsular cataract operation. Optically, the implant was closer to the location of the original lens in the eye and theoretically produced better image resolution and size. There was also less chance of damaging the corneal endothelium or chamber angle. With the Shearing lens (United States), the posterior chamber lens was substantially modified by using flexible loops that could rest against the ciliary body behind the iris for support or within the lens bag.
      • Shearing SP
      A practical posterior chamber lens.
      Numerous modifications of these flexible loop designs for the posterior chamber have been developed.
      The current arsenal of intraocular lenses in the United States consists of several variations of posterior chamber lenses with loops of different flexibility and size and several anterior chamber lenses with both rigid and flexible loops (Fig. 4). The iris-fixated lenses have generally been replaced by other lenses.
      • Stark WJ
      • Leske MC
      • Worthen DM
      • Murray GC
      Trends in cataract surgery and intraocular lenses in the United States.
      Figure thumbnail gr4
      Fig. 4Styles of intraocular lenses. A, Different anterior chamber lenses for implantation after intraocular cataract extraction or extracapsular cataract extraction. B, Different iris clip lenses for implantation after intracapsular cataract extraction or extracapsular cataract extraction. C, Posterior chamber lenses for implantation after extracapsular cataract extraction only. D, “Universal” lens for implantation in anterior chamber (after extracapsular cataract extraction or intracapsular cataract extraction) or in posterior chamber (after extracapsular cataract extraction).

      Indications for Intraocular Lenses.

      Although implantation of intraocular lenses is a routine procedure in the United States today, it was controversial just a few years ago. In 1978, the federal government mandated a study of all patients in the United States who had undergone insertion of an intraocular lens.
      • Worthen DM
      • Boucher JA
      • Buxton JN
      • Heyreh SS
      • Lowther G
      • Reinecke RD
      • Spencer WH
      • Talbott M
      • Weeks DF
      Interim FDA report on intraocular lenses.
      • Worthen DM
      • Boucher JA
      • Buxton J
      • Lowther G
      • Talbott M
      Update report on intraocular lenses.
      • Stark WJ
      • Worthen DM
      • Holladay JT
      • Bath PE
      • Jacobs ME
      • Murray GC
      • McGhee ET
      • Talbott MW
      • Shipp MD
      • Thomas NE
      • Barnes RW
      • Brown DWC
      • Buxton JN
      • Reinecke RD
      • Lao C-S
      • Fisher S
      The FDA report on intraocular lenses.
      Initially, the recommended guidelines were conservative; Jaffe suggested that the surgical procedure be restricted to one eye of a patient who was older than age 65 years and was unlikely to succeed with use of a contact lens.
      • Jaffe NS
      Indications and contraindications.
      • Jaffe NS
      Suggested guidelines for intraocular lens implant surgery.
      Because of a longer life-span and greater mobility of the elderly patients, enhanced patient awareness, technologic advances in cataract operations and intraocular lens implantation, a more aggressive surgical approach, and impressive results,
      • Worthen DM
      • Boucher JA
      • Buxton JN
      • Heyreh SS
      • Lowther G
      • Reinecke RD
      • Spencer WH
      • Talbott M
      • Weeks DF
      Interim FDA report on intraocular lenses.
      • Worthen DM
      • Boucher JA
      • Buxton J
      • Lowther G
      • Talbott M
      Update report on intraocular lenses.
      • Stark WJ
      • Worthen DM
      • Holladay JT
      • Bath PE
      • Jacobs ME
      • Murray GC
      • McGhee ET
      • Talbott MW
      • Shipp MD
      • Thomas NE
      • Barnes RW
      • Brown DWC
      • Buxton JN
      • Reinecke RD
      • Lao C-S
      • Fisher S
      The FDA report on intraocular lenses.
      a more liberal attitude has developed toward surgical implantation of intraocular lenses.
      • Jaffe NS
      The way things were and are: changing indications for intraocular lens implantation.
      More than 600,000 cataract operations were done in the United States in 1982, and almost 500,000 involved an intraocular lens.
      • Stark WJ
      • Leske MC
      • Worthen DM
      • Murray GC
      Trends in cataract surgery and intraocular lenses in the United States.
      At present, an intraocular lens is offered by some surgeons as a reasonable choice to patients of almost any age (except children) if success with a contact lens is unlikely. The Food and Drug Administration is considering the approval of intraocular lenses for patients older than 18 years of age. The lens may be inserted in one eye, or if both eyes need correction, an interval of several months between the procedures is recommended. Simultaneous bilateral cataract operations are generally discouraged.
      For individual surgeons, the indications for use of intraocular lenses are still evolving and expanding, and the age of patients in whom most ophthalmologists will use an intraocular lens has decreased from 65 to 60 to 55 years, and some ophthalmic surgeons will implant an intraocular lens in any patient older than 18 years. Although intraocular lenses are being used in children in a limited protocol, their use is questionable because of the long-term effects on the developing eye.
      • Hiles DA
      Visual acuities of monocular IOL and non-IOL aphakic children.
      The contraindications are becoming better defined as experience accumulates. Patients with only one useful eye, active uveitis, rubeosis iridis, proliferative diabetic retinopathy, severe myopia, or severe glaucoma are not candidates for implantation of an intraocular lens, in the opinion of most surgeons. More controversial is the use of an intraocular lens in the presence of mild glaucoma, corneal endothelial disease, nonproliferative diabetic retinopathy, a small anterior segment, a predilection for retinal detachment, and postoperative problems such as bleeding, loss of vitreous, or a damaged iris. If the patient has had a poor result in the first eye or does not want an intraocular implant, it should not be inserted.
      Some patients are unable to wear a contact lens successfully or cannot tolerate aphakic spectacles after a technically successful cataract operation. Under selective circumstances, an intraocular lens can be placed in the eye during a second operation. This secondary implant is still controversial, although it is increasing in frequency in the United States. The visual results and complications are worse than if the implant had been inserted during the initial procedure, primarily because of the need for manipulation of the vitreous in about 20% of patients.
      • Kraff MC
      • Sanders DR
      • Lieberman HL
      • Kraff J
      Secondary intraocular lens implantation.

      Material for Intraocular Lenses.

      With the popularity of intraocular lenses, there has been a competitive surge in technologic improvements in the design and manufacture of these lenses. Intraocular lenses have evolved to high-optical-quality, durable, lightweight products with smooth edges and polished surfaces. The optic material, polymethyl methacrylate, is suitable for lathe cutting, casting, injection, or compression molding. The polymethyl methacrylate allows the transmission of near-ultraviolet light, which is a potential source of retinal damage;
      • Mainster MA
      Spectral transmittance of intraocular lenses and retinal damage from intense light sources.
      currently available lenses can effectively filter ultraviolet light. Class is heavier than these materials but does have an optical advantage;
      • Barasch KR
      • Poler S
      A glass intraocular lens.
      its major disadvantage is that it may shatter when the new ophthalmic (yttrium-aluminum-garnet) lasers are used.
      The optical and supporting structures all can be molded from polymethyl methacrylate, or the supporting haptics (prongs) can be attached. These haptics are made of polymethyl methacrylate, polyimide, Dacron, nylon 6 (Supramid), nylon 66, or polypropylene (Prolene). This last substance is most resistant to hydrolysis but may have loss of tensile strength with prolonged exposure to ultraviolet light.
      • Fechner PU
      • Hartmann E
      • Wehmeyer K
      Ultraviolet light and suture material.
      Metal loop lenses (made of platinumiridium, titanium, and stainless steel) have been tried but are no longer used because of associated problems with uveitis, corneal edema, lens dislocation, and iris erosions, difficulties probably related to the additional weight.
      • Shepard DD
      The dangers of metal-loop intraocular lenses.
      The lenses are buffed and polished to remove all of the rough edges and are then sterilized. Dry heat sterilization, autoclaving, and γ-irradiation are inappropriate because of damage to the polymethyl methacrylate monomer.
      • Drews RC
      Inflammatory response, endophthalmitis, corneal dystrophy, glaucoma, retinal detachment, dislocation, refractive error, lens removal, and enucleation.
      The only successful methods are chemical sterilization by either sodium hydroxide (wet sterilization) or ethylene oxide gas (dry sterilization). There is a risk of contamination with neutralizing solution, as witnessed by a lot contamination with the fungus Paecilomyces lilacinus
      • Pettit TH
      • Olson RJ
      • Foos RY
      • Martin WJ
      Fungal endophthalmitis following intraocular lens implantation: a surgical epidemic.
      and with Pseudomonas aeruginosa.
      • Gerding DN
      • Poley BJ
      • Hall WH
      • LeWin DP
      • Clark MD
      Treatment of Pseudomonas endophthalmitis associated with prosthetic intraocular lens implantation.
      Since the publication of these reports, use of ethylene oxide has been the only method of sterilization permitted by the Food and Drug Administration in the United States. It has been associated with some inflammation due to residual ethylene oxide gas, immune sensitization, polishing compounds, or a reaction of ethylene oxide with a monomer in polymethyl methacrylate.
      • Stark WJ
      • Rosenblum P
      • Maumenee AE
      • Cowan CL
      Postoperative inflammatory reactions to intraocular lenses sterilized with ethylene-oxide.
      The glass intraocular lens is inert and has an additional advantage of being autoclavable.

      Calculation of Intraocular Lens Power.

      In order to achieve comfortable binocular vision, the postoperative refractive error of the operated eye must be matched with that of the unoperated eye. The available intraocular lens powers usually range from + 10 to + 25 diopters, as measured in the aqueous humor. Initially, estimates based on the prior refraction were used to judge the necessary intraocular lens power, but large errors resulted. Later, theoretical formulas based on Gullstrand's geometric optical model of the eye were introduced.
      • Gullstrand A
      • Fritz KJ
      Intraocular lens power formulas (letter to the editor).
      These formulas for calculating the correct intraocular lens power were influenced by three variables: the corneal power, the length of the eye, and the position of the implant in the eye.
      • Hoffer KJ
      Preoperative cataract evaluation: intraocular lens power calculation.
      The corneal power is derived from a measurement of the radius of the curvature of the central 3 mm of the anterior corneal surface with a keratometer. The axial length of the eye is measured by applanation or immersion ultrasonic equipment. With use of A-scan ultrasonography, the mean (+ SD) axial length of the eye is 23.65 ± 1.35 mm.
      • Hoffer KJ
      Biometry of 7,500 cataractous eyes.
      If the instrument is properly aligned along the visual axis and the appropriate sound velocity is used, the measurements can be exceedingly accurate. The location of the intraocular lens within the eye cannot be measured preoperatively, so it is estimated by using a variety of different formulas based on the design of the lens, and these formulas are later modified depending on clinical experience.
      Several variations of the theoretical formula have been proposed by Binkhorst
      • Binkhorst RD
      The optical design of intraocular lens implants.
      and others. The lens calculation formulas can be applied to nomograms or can be programmed on simple hand-held calculators. Although there are strong proponents of these theoretical formulas,
      • Hoffer KJ
      Preoperative cataract evaluation: intraocular lens power calculation.
      regression formulas that have analyzed the data of large numbers of patients who have previously undergone a cataract operation have been developed and may be more accurate. The most popular regression formula is that of Sanders and associates.
      • Sanders D
      • Retzlaff J
      • Kraff M
      • Kratz R
      • Gills J
      • Levine R
      • Colvard M
      • Weisel J
      • Loyd T
      Comparison of the accuracy of the Binkhorst, Colenbrander, and SRK™ implant power prediction formulas.
      These formulas have improved our ability to choose the appropriate implant power considerably, but some inadequacies still remain and are usually corrected by wearing thin glasses. Most patients require bifocals because the eye of a patient with an intraocular lens, just as the eye of an older patient with a natural lens, will usually not accommodate.
      • Nakazawa M
      • Ohtsuki K
      ™ Apparent accommodation in pseudophakic eyes after implantation of posterior chamber intraocular lenses.

      PREOPERATIVE EVALUATION

      Medical Examination.

      A brief medical examination or contact with the patient's referring physician before a cataract operation is important to determine the general health of the patient, to identify any coexisting systemic disease that may influence the decision for surgical intervention, and to consider the life expectancy of the patient. Certain medical diseases may be associated with important ocular complications. The presence of bronchitis, pronounced obesity, ischemic heart disease, or diabetes mellitus and the use of systemic corticosteroids, immunosuppressive agents, or anticoagulants are important to note so the surgeon can anticipate and respond to the variables that may result. Any infection elsewhere (especially of the skin) should be resolved preoperatively. If possible, this elective operation should not be performed concurrently with other procedures or at the time of hospitalization for another reason because of the presence of hospital organisms and the inability of elderly patients to comprehend and adhere to instructions related to recovery from totally different medical problems.
      Laboratory evaluation depends on the requirements of the anesthesiologist. With currently available techniques, the procedure can generally be done under local anesthesia within 1 hour, with minimal medication and stress to the patient.

      Ocular Examination.

      A history of ocular trauma, inflammation, glaucoma, retinal disease, amblyopia, or any previous serious ocular disease immediately indicates the possibility of a less-than-perfect visual result and warrants additional preoperative counseling. A history of complicated cataract extraction in one eye is important to note in preparation for surgical correction of the second eye.
      A complete examination of the eye is needed to determine the presence of coexisting ocular disease. A moderate or opaque cataract may preclude adequate examination of the retina, but various tests may aid in evaluating the function of the macula and the peripheral retina. Some of the simpler tests for evaluation are the afferent pupillary response (Marcus Gunn phenomenon), Amsler grid testing, photostress, light-projection discrimination, color perception, the entoptic phenomenon, or the Haidinger brush test.
      • Sinclair SH
      • Loebl M
      • Riva CE
      Blue field entoptic phenomenon in cataract patients.
      More exquisite laboratory evaluation can be done with ultrasonography, laser interferometer fringe testing,
      • Goldmann H
      • Chrenková A
      • Cornaro S
      Retinal visual acuity in cataractous eyes: determination with interference fringes.
      potential acuity meters,
      • Guyton D
      New instrument offers prediction of post-operative vision in mild cataract.
      electroretinography, or the visual evoked response.
      Slit-lamp biomicroscopy of the anterior segment will detect corneal opacities, corneal endothelial disease, inflammation, posterior synechiae, or dislocation of the lens, all of which influence the decision about surgical intervention and the outcome. The corneal endothelial cells pump fluid out of the cornea, and their health ensures the transparency of the cornea. These cells do not regenerate after damage but rather spread to fill the defects. By using the slit lamp with the technique of specular reflection, the endothelial cell density' of the cornea can be estimated;
      • McIntyre DJ
      Comparative endothelial biomicroscopy.
      the finding can be interpreted as representative of the entire corneal endothelial surface in an unoperated eye, and hence the functional reserve of the corneal endothelium can be anticipated. Clinical specular microscopy has been developed for endothelial cell photography at high magnification (X 200) to study the endothelial cell counts accurately preoperatively and after various intraocular procedures.
      • Sugar A
      Clinical specular microscopy.
      • Bourne WM
      • Kaufman HE
      Specular microscopy of human corneal endothelium in vivo.
      Both contact and noncontact methods of photographing the corneal endothelium have been developed. This technique has helped immensely in comparing, judging, and monitoring the safety of new techniques as well as assisting in the decision about individual patients.
      After the ocular examination, the ophthalmologist should discuss with the patient and the family the need for or alternatives to a cataract operation; the likelihood of considerable improvement; the role of preexisting medical disorders; the surgical techniques for cataract removal; the type of optical correction; the duration of hospitalization, convalescence, and adjustment; and the possible complications intraoperatively, immediately postoperatively, and late postoperatively. The patient should have confidence in the surgeon, and the surgeon should comprehend the expectations of the patient; if either confidence or comprehension is less than complete, this elective procedure is best delayed.

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        Update report on intraocular lenses.
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        Spectral transmittance of intraocular lenses and retinal damage from intense light sources.
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        A glass intraocular lens.
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