Cataract is the most prevalent ophthalmic disease. The number of persons who became blind as a result of cataract in 1998 was estimated to be about 17 million worldwide; this number was expected to double by early in the twenty-first century. Although a pharmacological preventive or therapeutic treatment for this blinding disease is being actively sought, the solution still appears to be many years away. Therefore, surgical treatment for cataracts, which increasingly includes intraocular lens (IOL) implantation, remains the only viable alternative.
Treatment of cataracts has been practiced for centuries using various surgical and nonsurgical procedures. However, avoidance of complications and attainment of high-quality postoperative visual rehabilitation were difficult in the years before the introduction of modern IOLs. Because significant dioptric power resides in the crystalline lens, its removal results in marked visual disability.
Aphakic spectacle correction has been prescribed throughout history, but spectacles are less than satisfactory because of the visual distortions inherent in such high-power lenses.
It was not until the late 1940s that the optical advantages that an IOL could provide in visual rehabilitation were understood and acted on by Ridley.
The implantation of IOLs is now a highly successful operation; the safety and efficacy of this procedure are well established. The number of IOL implants in the United States in 1998 was estimated to be 1.6 million. Implantation data from other countries are scant, but the total number of implantations per year worldwide is increasing rapidly. Studies are still needed to determine which surgical technique(s) and which IOL design(s) are safest, most practical, and most economical for high-volume use in the less advantaged areas of the world. For general discussions that review the evolution and provide clinicopathological overviews of IOLs, see Apple and coworkers and Binkhorst.
Posterior chamber IOLs were reintroduced in the mid-1970s and early 1980s, following a long period of disfavor after the Ridley lens was discontinued. Jaffe and other authors compared posterior chamber lenses with iris-supported lenses and were impressed by the superior results achieved with the former type of lens using an extracapsular cataract extraction technique. The use of posterior chamber IOLs is now clearly the treatment of choice.
Lens Design and Fixation
In 1967, Binkhorst proposed a detailed classification of the various means of fixation for each IOL type. In a 1985 update of this classification, Binkhorst listed four IOL types according to fixation sites:
Anterior chamber angle-supported lenses.
Posterior chamber angle (ciliary sulcus)-supported lenses.
By common agreement, most surgeons today differentiate lens types as follows:
Anterior chamber lenses.
Posterior chamber lenses.
From the time of Ridley’s first lens implantation to the present day, the evolution of IOLs can be arbitrarily divided into six generations ( Table 5.2.1 ).
|I||1949–1954||Original Ridley posterior chamber lens|
|II||1952–1962||Early anterior chamber lenses|
|IV||1963–1990||Intermediate anterior chamber lenses|
|V||1975–1990||Improved posterior chamber lenses|
|VI||1990 to present||Modern capsular posterior chamber lenses and modern anterior chamber lenses|
Generation I (Original Ridley Posterior Chamber Lens)
A practical application of the concept of IOLs began with Ridley, and credit for the introduction of lens implants clearly belongs to him.
Ridley’s first IOL operation was performed on a 49-year-old woman at St Thomas’ Hospital in London on November 29, 1949. His original IOL was a biconvex polymethyl methacrylate (PMMA) disc designed to be implanted after extracapsular cataract extraction (ECCE) ( Fig. 5.2.1 ).
Ridley’s procedure was initially met with great hostility by several skeptical and critical ophthalmologists. However, good results were attained in enough cases to warrant further implantation of the Ridley IOL, although dislocation of the lens ultimately proved troublesome. It is gratifying to note that Ridley, who died in 2001, lived long enough to experience the acknowledgment, respect, and honor he so fully deserved for this innovation.
Generation II (Early Anterior Chamber Lenses)
As a consequence of the relatively high incidence of dislocations with the Ridley lens, a new implantation site was considered—the anterior chamber, with fixation of the lens in the angle recess. The anterior chamber was chosen because less likelihood existed of dislocation within its narrow confines. In addition, anterior chamber lenses could be implanted after either an intracapsular cataract extraction (ICCE) or an ECCE. Also, anterior chamber placement of the pseudophakos was considered a simpler technical procedure than placement of the lens behind the iris.
Although many surgeons worked on the concept of this type of lens, Baron, in France, is generally credited as being the first designer and implanter of an anterior chamber lens ( Fig. 5.2.2A ). He first performed this procedure on May 13, 1952.
Late endothelial atrophy, corneal decompensation, and pseudophakic bullous keratopathy were observed with the original Baron lens and developed with many subsequent anterior chamber lens designs. The entity now termed uveitis–glaucoma–hyphema (UGH) syndrome was described first when ocular tissue damage occurred that was clearly the result of poorly manufactured anterior chamber lenses. It took many modifications of the haptic-loop configuration and the lens-vaulting characteristics (see Fig. 5.2.2B ) to develop an anterior chamber lens that allowed a reasonable prediction of long-term success. This was achieved largely because of the advances in lens design by Choyce of England and later by Kelman of New York.
Generation III (Iris-Supported Lenses)
Relatively frequent dislocation of the Ridley lens and an unacceptably high rate of corneal decompensation associated with the anterior chamber lenses that were available in the early 1950s caused some surgeons to discontinue implantation of IOLs entirely. However, iris-supported or iris-fixated IOLs were introduced subsequently in an attempt to overcome these problems.
Binkhorst in the Netherlands was an early advocate of iris-supported IOLs. His first lens was a four-loop, iris-clip IOL ( Fig. 5.2.3A ) design. Although Binkhorst initially believed that IOL contact with the iris would not cause problems, he soon noted that iris chafing, pupillary abnormalities, and dislocation developed with the early iris-clip lens. Also, in an effort to circumvent dislocation, Binkhorst made the anterior loops of his four-loop lens longer, but this led to increased corneal decompensation from peripheral touch.
His initial implantations were done after ICCE, but occasionally he implanted his four-loop lens following ECCE. His positive experience with this procedure prompted him to modify his iris-clip lens design for implantation following ECCE. Binkhorst’s change from ICCE to ECCE and the introduction of his two-loop iridocapsular IOL (see Fig. 5.2.3B ) in 1965 were important advances in both IOL design and mode of fixation. His and others’ experiences with the two-loop lens style and its modifications were influential in the development of modern design concepts of IOLs, including capsular bag–fixated, posterior chamber IOLs. Binkhorst’s innovative lens designs and his advocacy of ECCE came at a time when the entire future of IOL implantation was in jeopardy; they provided the major impetus that set the stage for modern posterior chamber lens implantations.
During the early years of iris-fixated IOLs, many clinical and subclinical problems emerged, such as dislocation, pupillary deformity and erosion, iris atrophy with transillumination defects, pigment dispersion, uveitis, hemorrhage, and opacification of the media. Many of these complications were the result of chronic rubbing or chafing of the iris by IOL loops or haptics. Problems were especially severe with metal loop IOLs and occurred frequently with multiple-looped lenses because uveal contact and chafing against the mobile iris tissues were unavoidable with these designs.
An increased incidence of corneal edema occurred in association with iris-supported lens designs. Corneal decompensation and pseudophakic bullous keratopathy became major indications for penetrating keratoplasty. The well-known coexistence of pseudophakic bullous keratopathy and cystoid macular edema (CME) has been termed corneal-retinal inflammatory syndrome by Obstbaum and Galin. Binkhorst’s return to ECCE, with the introduction of his two-loop iridocapsular lens in 1965 (see Fig. 5.2.3B ), brought about an almost immediate reduction in the incidence of many of these complications.
Most iris-supported lenses were biplanar, with the optic placed in front of the pupil. In general, biplanar IOLs required a larger limbal wound opening for insertion. The change to capsular fixation after ECCE provided better stability for the pseudophakos. This important modification was a forerunner to capsular sac (in-the-bag) fixation of modern posterior chamber IOLs.
At the time when iris-supported lenses were in widespread use, and until the mid-1980s in many cases, manufacturing methods and surgical techniques were less sophisticated. It is now clear that most modern, high-quality anterior and posterior chamber IOLs provide better success than the IOLs that depend on the iris for support. At present, it is the consensus of surgeons that lens explantation and/or exchange is usually the best treatment when a patient who has an iris-supported IOL develops late complications such as inflammation or corneal decompensation that does not respond rapidly to conservative therapy.
Generation IV (Intermediate Anterior Chamber Lenses)
As iris-supported IOLs underwent major modifications from the early 1950s up to the beginning of the 1980s, several designs of anterior chamber IOLs were introduced.
The problems of tissue chafing and difficulties in correct sizing associated with rigid IOLs were addressed by the development of anterior chamber lenses with more flexible loops or haptics ( Box 5.2.1 ). Unlike the ill-fated, nylon-looped lenses introduced by Dannheim in the early 1950s, the fixation elements of these anterior chamber IOLs were made from more stable polymers, usually PMMA and polypropylene. The best lenses were the various rigid and flexible, open-loop, one-piece PMMA designs, such as the three- and four-point fixation Kelman IOLs. Modifications of the latter have been in use since the late 1970s and are the styles most commonly implanted today ( Fig. 5.2.4 ). These lenses now are well designed, correctly vaulted, and properly sized and can provide excellent long-term results. As with the early generation of anterior chamber IOLs, new lens designs included both haptic (footplate) fixation lenses and small-diameter, round-looped IOLs.
Disadvantages of Closed-Loop Anterior Chamber Lenses
Lenses may be difficult to size
Lenses may have inappropriate vault-compression ratios; when a lens is compressed, it may vault anteriorly or posteriorly—either type of response can cause deleterious effects
Small-diameter loops may cause a “cheese-cutter” effect, particularly if the lens is too large; subsequent erosion and chafing can cause uveitis, including cystoid macular edema and pseudophakic bullous keratopathy
Some lenses have a large contact zone over broad areas of the angle with the potential for secondary glaucoma
The poorly finished, sharp edges of some lens models can cause chafing, which leads to sequelae such as uveitis or uveitis–glaucoma–hyphema syndrome
Synechiae formation around the small-diameter loops may make the lens difficult to remove when necessary; tearing of ocular tissues, hemorrhage, and iridocyclodialysis are possible complications of intraocular lens removal if correct procedures are not used
Advantages of Modern, Open-Loop, One-Piece, All-PMMA Flexible Anterior Chamber Lenses
Most modern lenses have an excellent finish with highly polished smooth surfaces and rounded edges from tumble polishing; tissue contact with any component of these intraocular lenses is much less likely to result in chafing damage
Sizing is less critical with flexible, open-loop designs
In contrast to a closed-loop anterior chamber intraocular lens, the vault (a well-designed, open-loop lens) is maintained even under high compression—this minimizes intraocular lens touch against the cornea anteriorly or against the iris posteriorly
Point fixation is possible, since the haptic may subtend only small areas of the angle outflow structures
Most open-loop intraocular lens designs are much easier to remove, when necessary, especially those with Choyce-like haptic or footplate fixation; the well-polished surfaces of these lenses usually do not become completely surrounded by goniosynechiae or cocoon membranes and thus can usually be removed if necessary without undue difficulty or excessive tissue damage
Although in the 1950s implantations with early anterior chamber IOLs were often disappointing, some models of anterior chamber lenses provided good success, particularly when the lens was properly sized. Two important factors that led to a higher success rate with anterior chamber IOL use are improved lens designs and manufacturing techniques.
More appropriate lens flexibility has decreased the need for perfect sizing. Increased attention has been given to the anterior–posterior vaulting characteristics of IOLs, which has reduced the incidence of intermittent touch and uveal chafing problems. Design flaws in older lens styles have been identified and these lenses removed from the market in the United States. Tumble polishing of IOLs, particularly one-piece, all-PMMA lenses, produces excellent surfaces and edges. The elimination of sharp optic or haptic edges is critical in the production of anterior chamber IOLs. This is even more true than for posterior chamber IOLs, because anterior chamber IOLs are fixated in a confined space directly adjacent to delicate anterior segment tissues.
The two major disadvantages of an anterior chamber IOL, as compared with posterior chamber lens styles, are:
The close proximity of the haptics or loops to delicate tissues such as the trabecular meshwork, corneal epithelium, angle recess, and anterior iris surface.
The difficulty often encountered in IOL sizing, particularly with rigid lens designs.
The close proximity of anterior chamber lens components to the corneal endothelium is an obvious disadvantage because of the potential for corneal decompensation and/or pseudophakic bullous keratopathy as a result of contact of the cornea with the IOL. In the past, the most common causes of pseudophakic bullous keratopathy were related to anterior chamber IOLs that were sized incorrectly, vaulted too steeply, or designed with an inappropriate amount of flexibility.
Haptics or spatula-like footplates are one of the two types of fixation elements used for anterior chamber IOLs. Haptics or footplates, popularized by Peter Choyce, are often likened to the flattened portion of a spatula and were used originally with the more rigid IOL styles. They now are used with both rigid and flexible modern anterior chamber IOLs. When IOL removal is necessary for any reason, the footplate generally slides out of the eye much more easily than does a small-diameter loop and does so with minimal tissue damage.
Small-diameter lens loops are the second type of fixation element for anterior chamber IOLs. Loops may be of either an open or a closed design. Round, small-diameter, closed loops may cause a “cheese-cutter” effect within the eye and difficulty in removal. A 360° fibrouveal encapsulation, or “cocoon,” often forms around such small-diameter, round loops as the loops become embedded in the tissues of the angle recess. If the correct explantation procedure is not used, these adhesions may result in tissue tears, hemorrhage, and iridocyclodialysis. These anterior chamber IOLs, often generically classified together as “closed-loop lenses,” do not provide the safety and efficacy achieved by other anterior chamber lens designs, such as finely polished, flexible, one-piece, all-PMMA lenses (see Fig. 5.2.4 ). By 1987 the U.S. Food and Drug Administration had placed IOLs of the closed-loop design on core investigational status. This had the effect of removing them from the market in the United States, although it did not prevent the export of such lenses.
The flexible, open-loop designs, modifications of the original Kelman anterior chamber IOLs (with Choyce-style footplates), can be well finished using tumble polishing, which provides a rounded, “tissue-friendly” surface at points of haptic contact with delicate uveal tissues. One-piece IOLs, particularly those with a footplate design, are usually much easier to explant than IOLs with round, small-diameter loops of either closed-loop or open-loop design.
Iris- or scleral-fixated, sutured posterior chamber IOLs may be used in cases formerly reserved for anterior chamber IOLs. Results are encouraging. Uncertainty still exists as to whether a retropupillary lens is superior to a modern, well-manufactured, Kelman-style anterior chamber IOL for cases such as intraoperative capsular rupture or vitreous loss or as a secondary or exchange procedure. The technique is more difficult than insertion of a single anterior chamber lens, and therefore it should be carried out only by an experienced surgeon.
Generation V (Improved Posterior Chamber Lenses)
The return to Ridley’s original concept of IOL implantation in the posterior chamber occurred after 1975. Pearce of England implanted the first uniplanar posterior chamber lens since Ridley. This lens was a rigid tripod design with the two inferior feet implanted in the capsular bag and the superior foot implanted in front of the anterior capsule and sutured to the iris. Shearing of Las Vegas introduced a major lens design breakthrough in early 1977 with his posterior chamber lens. The design consisted of an optic with two flexible, J-shaped loops. Simcoe of Tulsa publicly introduced his C-looped posterior chamber lens shortly after Shearing’s J-loop design appeared. Arnott of London was an early advocate of one-piece, all-PMMA posterior chamber IOLs. The flexible open-loop designs (J-loop, modified J-loop, C-loop, or modified C-loop) still account for the largest number of IOL styles available today ( Fig. 5.2.5 ).
One obvious major theoretical advantage that a posterior chamber IOL has over an anterior chamber IOL is its position behind the iris, away from the delicate structures of the anterior segment.
As posterior chamber lens implantation evolved, the type of fixation achieved in the early years depended largely on chance or on the surgeon’s individual preference. As Fig. 5.2.6 illustrates, several loop-fixation sites are possible with modern, flexible-loop posterior chamber IOLs. In general, the loops were anchored in one of three ways:
Both loops were placed in the ciliary region.
Both loops were placed within the lens capsular sac.
One loop (usually the leading or inferior loop) was placed in the capsular sac and the other loop (usually the trailing or superior loop) in a variety of locations anterior to the anterior capsular flap.
These fixation sites have been confirmed histologically by analyses of postmortem globes implanted with posterior chamber IOLs.
The return to posterior chamber lenses coincided with the development of improved ECCE surgery. Shearing identified four major milestones that have marked the evolution of ECCE surgery:
Microscopic surgical techniques.
Flexible posterior chamber lenses.
Without microscopic surgery, modern IOL implantation would be far more difficult. Although phaco was promoted originally because it required only a small wound, it became clear that if an IOL were to be inserted, the wound would have to be enlarged after removal of the cataract, and thus nonultrasonic surgical methods were refined. By 1974, implantation of IOLs again began to achieve significant acceptability. A natural marriage between phaco and implantation of IOLs occurred.
As noted previously, Binkhorst was one of the pioneers in the return to the ECCE procedure. Binkhorst recognized that an intact posterior capsule enhanced stability, and he also recognized the many advantages of IOL implantation within the capsular sac. Evidence continues to accumulate that CME and retinal detachment occur less frequently with ECCE than with ICCE.
The introduction of flexible posterior chamber lenses designed to be implanted following ECCE largely resolved the debate about ECCE versus ICCE clearly in favor of the extracapsular procedure.
Securing both loops in the lens capsular sac is the only type of fixation in which IOL contact with uveal tissues is avoided. Placement of a lens with one or both loops outside the capsular bag is associated with various potential complications, including decentration and uveal erosion. The consequences of uveal touch have been learned after experiences with the earlier iris-fixated IOLs. The excellent success rate now achieved with posterior chamber IOL implantation is associated with improved IOL designs and improved surgical techniques, including the meticulous placement of loops ( Box 5.2.2 ).
Intraocular lens is positioned in the proper anatomical site
Both loops can be placed symmetrically in the capsular sac as easily as in the ciliary sulcus
Intraoperative stretching or tearing of zonules by loop manipulations in front of the anterior capsular leaflet is avoided
Low incidence of lens decentration and dislocation
No evidence of spontaneous loop dislocation
Intraocular lens is positioned a maximal distance behind the cornea
Intraocular lens is positioned a maximal distance from the posterior iris pigment epithelium, iris root, and ciliary processes
Iris chafing (caused by postoperative pigment dispersion into the anterior chamber) is reduced
No direct contact by, or erosion of, intraocular lens loops or haptics into ciliary body tissues
Chronic uveal tissue chafing is avoided, and the probability of long-term blood–aqueous barrier breakdown is reduced
Surface alteration of loop material is less likely
Intraocular lens implantation is safer for children and young individuals
Posterior capsular opacification may be reduced
Intraocular lens may be easier to explant, if necessary
Posterior capsule opacification (PCO; Elschnig pearls, secondary or after cataract) is a significant postoperative complication in IOL implantation. A well-designed posterior chamber lens in the lens capsular sac provides a gentle but taut radial stretch on the posterior capsule. Of the present open-loop flexible IOLs, the one-piece, all-PMMA posterior chamber designs with posterior convex or biconvex optics appear to be especially effective in providing a symmetrical stretch. Symmetrical stretch may help minimize PCO, as it reduces the folds in the capsular sac and holds the posterior capsule firmly against the posterior surface of the IOL optic. This is sometimes termed the “no space, no cells” concept.
The quality of surgery and the accuracy of loop placement are important factors that affect the outcome of the cataract operation. Two very helpful tools are available to surgeons that make precise loop or haptic placement possible:
Ophthalmic viscosurgical devices (OVDs).
New methods to control the size, shape, and quality of the anterior capsulotomy.
The intercapsular (envelope) technique and its successor, circular continuous tear capsulorrhexis, greatly increase the ability to achieve accurate and permanent loop placement.
Generation VI (Modern Capsular Lenses—Rigid PMMA, Soft Foldable, and Modern Anterior Chamber)
By the end of the 1980s, clinical laboratory studies demonstrated clearly that cataract surgical techniques and IOL design and manufacture had shown remarkable advances. Surgical technique and IOL design and manufacture had advanced to a point at which the older techniques had given way to more modern ones, which allowed consistent, secure, and permanent in-the-bag (capsular) fixation of the pseudophakos. A marriage between IOL design and improved surgical techniques has evolved into capsular surgery. The “capsular” IOLs are fabricated from both rigid and soft biomaterials.
The many changes in surgical techniques that occurred after 1980 and into the 1990s include the introduction of OVDs, increased awareness of the advantages of in-the-bag fixation, the introduction of continuous curvilinear capsulorrhexis (CCC) ( Fig. 5.2.7 ), hydrodissection ( Fig. 5.2.8 ), and the increased use of phaco. This has allowed not only much safer surgery but also implantation through a smaller incision than was possible in the early days of extracapsular extraction.
The evolution from can-opener toward capsulorrhexis (see Fig. 5.2.7 ) was initiated by Binkhorst, who developed a two-step (envelope) technique that eventually evolved into the single-step CCC. Two clear advantages of CCC exist over the early can-opener techniques.
First, the formation of radial tears ( Fig. 5.2.9 ) is reduced, which minimizes radial tears of the anterior capsule, which in turn reduce the stability of the capsular bag and may allow prolapse of haptics out of the capsular bag through the anterior capsular tear. Second, and less commonly recognized, capsulorrhexis provides a stable capsular bag that allows copious hydrodissection, which in turn is very helpful in cortical cleanup. With a frayed, emptier capsular edge, such as seen with the can-opener technique, hydrodissection is difficult without forming unwanted radial tears.
Hydrodissection (see Fig. 5.2.8 ) was a term coined by Faust in 1984. This technique, and the many variations thereof (e.g., cortical cleavage hydrodissection, hydrodelineation), makes the surgery much simpler in that mobilization and removal of cells and cortical material are rendered much easier. The long-term risk of PCO is, in turn, clearly minimized because of the more thorough removal of cells in cortical material, especially in the region of the equatorial fornix.
Modern phaco, pioneered by Kelman, has now made possible the removal of lens material through small incisions and the implantation of IOLs through incisions down to 3 mm in length, as opposed to incisions of 11 to 12 mm length in the early days of ECCE. Many real advantages of small-incision cataract surgery exist, including safer healing (with fewer risks of complications such as inflammation), more rapid healing, and rapid recovery of visual rehabilitation (with less postoperative astigmatism).
Accompanying the developments of surgical techniques that allow secure in-the-bag implantation, IOLs have evolved that work well with these techniques—both rigid PMMA designs ( Figs. 5.2.10 and 5.2.11 ) and foldable IOLs. Fig. 5.2.10 shows an example of a modern, state-of-the-art, one-piece, all-PMMA IOL that is designed for in-the-bag implantation. These can be inserted through incisions as small as 5.5–6 mm in length and provide an excellent alternative for the surgeon who finds the almost 50-year history of PMMA as a lens biomaterial of comfort. Long-term results with these IOLs are excellent and, indeed, these lenses provide slightly better centration than do some of the more modern foldable lenses at the present time. The ideal diameter for a one-piece IOL design such as that in Fig. 5.2.10 is 12–12.5 mm, which allows it to fit perfectly into the capsular bag (which measures about 10.5 mm in diameter). The diameter of the ciliary sulcus is only slightly larger (approximately 11.0 mm) and actually decreases with age.
These rigid PMMA IOL designs have been found to be very satisfactory in pediatric IOL implantation. As 90% of the growth of the infantile globe occurs during the first 18 months to 2 years ( Fig. 5.2.12 ), it is fair to assume that “adult” 12 mm lenses can be safely implanted with the achievement of good results in children of this age and older ( Figs. 5.2.12 and 5.2.13 ). The problem in the past with IOL implantation has been that of PCO. With present techniques, this is best prevented using primary posterior capsulectomy.
Improved small-incision surgical techniques and IOL designs have resulted in a natural evolution toward foldable lenses. Most foldable lenses today are manufactured from silicone, hydrogel, or acrylic material ( Figs. 5.2.14–5.2.16 ).
The earliest designs for which clinical usage was widespread were the plate lenses known as the “Mazzocco taco.” In early years these were manufactured poorly and often not implanted properly into the capsular bag, so many complications ensued. In recent years manufacturing quality has become much better, and these lenses are now satisfactory for clinical usage ( Figs. 5.2.17 and 5.2.18 ). The best plate lenses are those with large positioning holes that allow in-the-bag synechia formation, which enhances fixation and stability.