Marjan Farid, MD and Allison R. Jarstad, DO
The anterior chamber intraocular lens (ACIOL) implant was introduced in 1952 as the original Baron IOL. An important advantage over the posterior chamber IOL (PCIOL) is that the ACIOL can be placed into an eye after both intra- or extracapsular cataract extraction, regardless of the status of the capsular bag. This revolutionized cataract surgery by making secondary IOL implantation feasible in the absence of capsular support. ACIOLs also minimized IOL dislocation if capsular support was questionable at a time when suturing to the iris or sclera was not yet routine.1 However, early ACIOLs were associated with significant intraocular complications. After trial and error with many variations of lens styles over the course of decades, the modern ACIOL design offers a significant advantage over older IOL styles. Although still associated with intraocular complications in some eyes, modern ACIOLs have proven to be an excellent option for the anterior segment surgeon, especially when posterior capsular support is lacking or the patient cannot tolerate a prolonged surgery.
The imperfections of early closed-loop and rigid, single-piece ACIOL designs led to a variety of complications, giving the ACIOL a negative reputation. Earlier ACIOL models were most notorious for causing endothelial decompensation, uveitis-glaucoma-hyphema syndrome, and cystoid macular edema, but other reported complications included pupillary block, corneal blood staining, late secondary glaucoma, IOL dislocation, and corectopia.2,3 Specific design flaws often were not identified until after lenses were removed and the lens features studied in detail. Patterns of ocular complications became associated with certain lens properties, such as improper IOL size, steep anterior vaulting within the anterior chamber, inadequate polishing of the surface of the IOL, and inflexibility or excessive flexibility. As different IOL designs were linked to adverse ocular effects, innovative improvements were made to both the design and manufacturing process in the attempt to eliminate further complications. However, as more ACIOLs were released into the market, significant confusion over the ideal IOL design developed. In fact, in the late 1980s, more than 3 decades after the first ACIOL was introduced, there was a greater selection of ACIOLs than ever before as ophthalmologists searched to create a lens that would be well tolerated in the eye and void of iatrogenic complications.
It was not until Dr. Charles Kelman’s 1982 release of the Multiflex ACIOL, an updated flexible design with 4-point haptic fixation, that complication rates declined significantly. The modern flexible, open-loop, single-piece polymethylmethacrylate (PMMA) ACIOL that is used today has been modeled after Dr. Kelman’s Multiflex lens. In the 1990s, the rate of ACIOL removal was reported between 0.06% and 0.16%.4 Studies have shown that the modern ACIOL has similar best spectacle-corrected visual acuity compared to PCIOLs and poses no greater risk than PCIOLs after IOL exchange, especially when there is absence of capsular support.5 Although complications can still be seen with the modern ACIOL, its design has stood the test of time and is much better tolerated than older ACIOL models.
Despite the growing current trend to fixate lenses to the sclera or iris, there certainly is still a role for the modern flexible, open-loop ACIOL. Some may opt for an ACIOL over scleral fixation because of the ease and speed of implantation, especially for an elderly patient who cannot tolerate a longer operative time or in a busy surgical practice requiring a quick case turnover time. Hill reported that ACIOL placement takes approximately 8 to 16 minutes compared to 35 to 60 minutes to suture a PCIOL to the sclera, which is technically more challenging and may be out of the scope of practice for some anterior segment surgeons.6 If deciding between placing an ACIOL vs returning to the operating room at a later date for a secondary iris- or scleral-fixated IOL, immediate correction of aphakia by placing an ACIOL may be the better option, especially if the patient cannot tolerate a second surgery because of either physical or financial constraints.
It may be that some complications occur in eyes receiving ACIOLs because of the intraoperative challenges leading one to place an ACIOL in the first place rather than from the lens itself. Other complications are related to ocular trauma from poor lens implantation technique. Endothelial cell loss can occur when placing the IOL if the entry incision is too small or inadequate amounts of viscoelastic are used to protect the endothelium, resulting in long-term corneal edema. Studies have shown that rates of common complications such as elevated intraocular pressure and pseudophakic bullous keratopathy are actually similar between eyes receiving an ACIOL and those undergoing placement of a scleral-fixated IOL.7 Flexible, open-loop ACIOLs have also been shown to be safe and effective after cataract surgery complicated by vitreous loss.8 Reports of similar visual outcomes between secondary ACIOLs and scleral-fixated IOLs after complicated cataract surgery further support the notion that some of the complications seen in eyes with an ACIOL are due to the long-term effects of a complicated cataract surgery with vitreous loss or posterior capsule violation.5
The modern flexible, open-loop, Kelman-style ACIOL has been shown to be better tolerated than older models. The major difference between older and newer models is the presence of flexible haptics with 4-point fixation. This allows excellent, stable fixation without excessive movement of the lens, which results in less trauma to the intraocular anatomy. When IOLs are poorly sized, the haptics do not sit in the correct anatomical position, and late complications can arise. Haptic migration into the peripheral iridotomy can result in corectopia or uveitis-glaucoma-hyphema (UGH) syndrome (Figure 55-1). Movement of the ACIOL can also lead to long-term endothelial decompensation. The modern Kelman-style ACIOL is made in multiple sizes and fits a greater range of anterior chambers due to the flexible haptics, avoiding some of the problems associated with a poor lens fit. Newer lenses also go through a standardized finishing process, which includes polishing the PMMA surface to rid the lens material of jagged edges. In contrast, older lenses were made out of material that was unable to be polished to a smooth surface, leading to iris chafing and hyphema.
Despite the many reported complications with ACIOLs, including the modern day Kelman-style lens, placement of an ACIOL can be successful if the appropriate lens is placed in the right patient. Careful surgical planning and patient selection is critical for success.
Because many complications are thought to be due to poor positioning of the IOL at the time of initial insertion, it is imperative to understand proper placement techniques and exclude eyes that are poor candidates for an ACIOL. Ideally, the lens haptics should sit in the angle resting directly on the scleral spur, without causing the iris to fold over itself. A flexible, open-loop haptic with 4-point fixation combined with flexible, open-loop haptics is an ideal choice because it prevents fibrous overgrowth over the haptic and erosion into the angle structures (discussed in detail later).9
ACIOLs should not be placed in eyes with inadequate angle support from peripheral anterior synechiae, congenital abnormalities, or anterior segment trauma where there is extensive iris atrophy or damage.3,10 Additionally, they should be avoided in eyes with uncontrolled glaucoma and in eyes with a shallow anterior chamber. When a large peripheral iridotomy is present, these lenses should be placed cautiously with the haptics positioned away from the iridotomy because the haptics can migrate and dislocate through the peripheral iridotomy. ACIOLs should be avoided in patients with baseline endothelial cell compromise, such as patients with Fuchs’ endothelial dystrophy. In younger patients, including the pediatric population and young adults, the risk of long-term endothelial cell failure must always be considered, and the endothelial cell count should be measured prior to lens placement. Ideal candidates for ACIOLs are older patients with adequate endothelial cell counts and the absence of diseased endothelium, patients who cannot tolerate a prolonged surgery, and patients on anticoagulants with an increased risk of bleeding from an iris- or scleral-fixated lens.9
One benefit of choosing an ACIOL over scleral fixation is that there is no risk of suture erosion or exposure through the conjunctiva, which puts the patient at risk for endophthalmitis. ACIOL placement also avoids an anterior vitrectomy when the vitreous face is still intact.7,11 However, in eyes that are at risk of anterior chamber collapse (as in patients with high myopia and collagen disorders associated with excessively thin, flexible sclera) or eyes with a small palpebral fissure or tight orbit (as seen in some patients of Asian ethnicity), Chan et al recommend doing a pars plana vitrectomy prior to ACIOL placement.7 This deepens the anterior chamber, allowing the lens to sit further away from the corneal endothelium.
Most commonly, ACIOLs are implanted when there is not enough capsular support for a PCIOL. Many studies have shown comparable visual acuity and complication rates between IOLs placed in the anterior chamber and PCIOLs fixated to the sclera.7,9,10,12,13 In a report by the American Academy of Ophthalmology in 2003, there was insufficient evidence to demonstrate the superiority of one lens type or fixation site over another in the absence of capsular support, leaving the option of ACIOL, scleral-fixated PCIOL, or iris-fixated PCIOL available according to the preference of the surgeon in such cases.10
Even if one does not routinely implant ACIOLs, understanding the complications associated with these lenses will prepare the comprehensive ophthalmologist to avoid placing this lens in a poor candidate and to manage patients who are referred with ACIOL–associated problems. It is imperative that modern cataract surgeons not only familiarize themselves with the role for ACIOL placement and the most common complications but also understand the surgical technique for ACIOL placement, repositioning, and explantation.
Problems Associated With Anterior Chamber IOLs
The most common reasons for removing an ACIOL are corneal edema, uveitis, glaucoma, hyphema, and macular edema. Other complications such as astigmatism and iris trauma are seen, even with modern designs. One study reported the rates of complications from ACIOLs with open-loop haptics, which included an average rate of endothelial cell loss of 20%, pupillary block (4.8%), transient elevated intraocular pressure from retained viscoelastic (3.6%), persistent glaucoma (2.4%), hyphema (2.4%), and corneal decompensation (2.4%).12
Pseudophakic bullous keratopathy was the most common cause for IOL explantation in the mid-1980s according to Doren et al and can present within 3 months or many years after the placement of an ACIOL.14 Pseudophakic bullous keratopathy is seen in a variety of situations, usually from the lens abutting the cornea endothelial cells, creating cell loss and leading to corneal edema (Figure 55-2). Oversized and stiff ACIOLs vault anteriorly and harm corneal endothelial cells. Undersized IOLs move within the anterior chamber, and extremely flexible IOLs intermittently arc anteriorly during eye rubbing and make contact with the corneal endothelium. Aggressive eye rubbing can also push the cornea posteriorly, creating contact between the endothelium and the IOL. Pseudophakic bullous keratopathy is also seen after the endothelial cells are traumatized during the initial IOL implantation process. Liberal use of viscoelastic while inserting an ACIOL and an adequately sized incision will help protect the IOL from coming into contact with the corneal endothelial cells.15