Although the reduction in posterior capsule opacification (PCO) rates with the vertical edge of the AcrySof MA60BM (Alcon Laboratories, Fort Worth, TX) has been unprecedented and pleasantly surprising, the drawbacks of the vertical edge design have become apparent. A few patients who had these vertical-edge IOLs implanted have returned with complaints of edge glare or unwanted images. In my experience, these frustrating subjective observations were voiced by 60 to 70% of patients 1 week after surgery, but only a fraction of these patients had symptoms 1 month postoperatively. In the late 1990s, Richard Lindstrom, MD, observed that the 1-week postoperative visit was not useful in otherwise uncomplicated cases. With the deletion of this visit, the majority of patients experienced these flashes, and then accommodated to their presence without comment before the final visit at 3 to 4 weeks.
EDGE DESIGN PHENOMENA
With relatively simple ray tracings, Jack Holladay, MD, has demonstrated that round edges distribute light rays over a significantly larger retinal area than sharp edge designs (Figure 1).1 The rounded IOL edge reduces the peak intensity of the reflected glare image by diffusing the reflected light, thus diminishing the potential for unwanted optical images. In contrast, the sharp edge creates a coherent, internally focused reflected image. How patients became acclimated to these images remains poorly understood. In the early postoperative course, this probably represented a retinal downregulation relative to these flashes, or perhaps bilateral implantation ended the visual dissimilarity. Later, the developing capsular bend and anterior capsule fibrosis helped by creating an optical barrier at the edge of the lens. For the few patients that did not have resolution, unfortunately, miotic therapy appeared to have no benefit.
A more perplexing problem is the presence of negative dysphotopsias. James Davison, MD, identified both positive (glare, halos, and streaks) and negative (dark shadows in the temporal field) optic phenomena in square-edge IOLs with shiny edges, but not in round-edge IOLs.2 He also reported less dysphotopsia in a square-edge acrylic IOL with nonreflective edges than with shiny edges. Several theories have been discussed in roundtable and panel forums, but no published studies have identified the source of the dark temporal field.
Finally, a third, rather transient phenomenon was observed with the specific optic design and high-index acrylic of the MA60BM. Many patients with good early clarity described a “jiggling” of the image in the very early postoperative period. The IOL would display a faint pseudophakodenesis, but this movement was not inconsistent with other IOL types or designs. Kerry Assil, MD, recently proposed that this subjective jiggling represents a fourth Purkinje image originating on the posterior optic surface, then reflected back off the nearly plano anterior optic surface and onto the retina (personal communication, January 2002). As the movement of this image subsides with capsular contraction, it blends with the visual environment.
NO IOL IS IMMUNE
Sharp vertical edges were first noticed to generate unwanted images well over a decade ago with positioning holes in the optic. IOLs were modified to accommodate smaller incisions, and ovoid PMMA lenses were developed with smaller, 5.0-mm width perpendicular to the axis of insertion. Masket et al,3 as well as Waller and Steinert,4 found the truncated edges to have considerably higher incidences of unwanted images than round IOLs. In the early investigative phase of the CeeOn 911 IOL (Pharmacia Corporation, Peapack, NJ), Dr. Masket again identified the truncated edge as responsible for unwanted dysphotopsias in the form of reflections and halos.3
The highly sporadic and absolutely subjective nature of these unwanted images makes objective measurements difficult. In the best effort published to date, Rob Tester, MD, reported that whereas specific unwanted images were more prevalent with certain types of IOLs, no IOL was free of these issues.5 Specifically, postoperative patients fitted with the AcrySof 6.0-mm (MA60BM) and 5.5-mm (MA30BA) (Alcon Surgical, Fort Worth, TX), the AMO 6.0-mm silicone (SI-40, Allergan, Irvine, CA), the STAAR (Monrovia, CA) plate haptic, and a 5.5-mm and 6.0-mm PMMA were surveyed and the results were compared for glare symptoms to a control group of 50 patients with presbyopia. The telephone interview involved approximately 50 patients with each IOL type.
In my opinion, it was not surprising that the strong association of the AcrySof lenses with the presence of positive dysphotopsias was attributed to the truncated lens edge. The responses were quite revealing about our assumptions regarding the presence or absence of symptoms in the general pseudophakic population. Approximately 10% of the IOL study group had ceased night driving due to unwanted light-related problems, with no statistical difference among lens types. The control group, with its younger median age, actually had more problems driving in bright sunlight or toward oncoming headlights than any IOL group studied. Only the patients fitted with the AcrySof and SI-40 lenses had generally higher reported problems with glare and increased light sensitivity compared to the presbyopic controls.
MANAGING UNWANTED IMAGES
Overall, these investigators found the patients to be quite satisfied with the outcomes of the surgery, despite the presence of the unwanted light images. Dr. Tester et al stressed their observation that the more active lifestyle a patient enjoys, the more likely they are to place themselves in a situation in which these images may be noticed. For example, the higher symptoms associated with the SI-40 were attributed to the greater likelihood that patients with this lens were still actively driving at night.
Since the publication of Dr. Tester's article, Okihiro Nishi, MD, has shown the ability of the SI-40 to consistently induce a capsular bend.6 As he had surmised in earlier efforts, this work demonstrated that the speed of capsular bend formation with the SI-40 was a factor in allowing it nearly the same PCO prevention benefit as the MA60BM. With the relatively surprising finding of unwanted images with the round-edge SI-40, one is left to wonder if unwanted images are inherently associated with the ability of an unmodified IOL edge to rapidly induce a capsular bend adequate for reducing PCO.
Relation of Optic Size
Optic size has proven a bit more challenging to correlate with dysphotopsias. Dr. Davison was unable to correlate the smaller optic size of the MA30BA with greater severity of symptoms than the MA60BM, as the proportion of symptomatic patients was identical to his proportion of specific implant.2 Hwang and Olson7 found the 6.0-mm optics of the SI-40 and MA60BM to have higher levels of general patient satisfaction with regard to general glare symptoms than the smaller 5.5-mm MA30BA. In regard to specific unwanted images, these investigators found edge design to be more highly correlated than the differences in optic size. Although design has been implicated as the primary source of dysphotopsias, the acrylic material of the MA60BM may also contribute to unwanted images. Jay Erie, MD8 reported that an unequal biconvex IOL design manufactured of a high refractive index (RI) material (1.55 RI) had the potential to generate more surface-reflected glare and unwanted optical images than an equibiconvex IOL made with a lower RI material (1.43 RI). Just as the prevention of PCO appears to be the result of several factors, including surgical technique and IOL design, the absolute frequency and severity of dysphotopsias are also the result of interactions between edge design and higher-RI materials.
Unanswered Questions
Although the MA60BM and MA30BA have borne the brunt of evaluation with regard to dysphotopsias due to optic configuration, vertical edge, and high index of refraction, several questions remain unanswered. For example, how would lenses of identical configuration but differing material and differing indices of refraction compare with regard to unwanted optical images? These issues may never be fully answered, but, fortunately, as the research has progressed, solutions to these difficult challenges are becoming available.
Advances in Edge Design
Worldwide, the absolute numbers of patients who have undergone an IOL exchange in an attempt to alleviate these symptoms is almost negligible relative to the total number of implants.2, 9, 10 The subjective patient responses to unwanted images made it questionable whether the PCO-reducing benefits of a vertical edge were clinically worthwhile.
Fortunately, the lingering issue of unwanted images is encouraging new innovation for altering the vertical edge. Alcon Surgical has modified the AcrySof MA60BM by frosting its edge, and placing the bulk of the power of the optic on the anterior surface. This modification was made to offer improved optical performance and ease of folding. The new lens, the AcrySof MA60AC, kept the traditional three-piece vertical edge design, now time-tested for its PCO reduction. The hydrophobic acrylic material remains unchanged, with the same higher refractive index. This lens is thinner than the original MA60BM, and the optic folds nicely without warming (Figure 2).
The second generation AcrySof lens, the Single-Piece SA60AT IOL, became available to surgeons before the MA60AC. As discussed earlier, this lens has a one-piece design with planar acrylic haptics and an anterior dominant optic configuration. The vertical edge is also frosted in an attempt to reduce the incidence of dysphotopsias, while keeping the PCO reduction benefit. It is also formed from the same hydrophobic acrylic material with the higher index of refraction, and also folds well without warming due to the thinner optic.
Although patient reports of peripheral flashes have fallen dramatically with the frosted edge, one drawback that the new design has failed to overcome is the negative dysphotopsias. Dr. Davison recently reported explanting two of the SA60AT lenses due to this phenomenon.11 Again, the causative issue of the dark crescent is in question, but without a fundamental answer. I am unaware of any reports of explantation of the MA60AC for unwanted photic problems.
Allergan Surgical released the modified Sensar acrylic lens in mid-2001, and the new Clariflex third-generation silicone lens in late 2001. The modified edge design, termed OptiEdge, incorporates a sharp vertical edge at the posterior border of the optic. Rather than continue the vertical edge along the entire optic rim, it features a total of three edge configurations (Figure 3). The anterior edge is rounded, and the middle section is slightly canted. The effect of these three surfaces is a lack of significant reflecting surface along the edge of the optic (Figure 4), and clinically, much fewer and shorter-lived patient complaints regarding dysphotopsias. Otherwise, the new lenses are rather similar. They have a traditional three-piece design with equiconvex optics. The RI of the acrylic is 1.47, and the silicone, 1.46, further reducing the potential for dysphotopsias. These two lenses provide an opportunity to compare the effects of these different materials on PCO.
Summary
Understanding the healing process of the capsular bag after cataract removal and IOL implantation helps to further the investigation toward the elimination of PCO. While the primary factors for reducing PCO are related to the surgical technique, the choice of IOL becomes just as important. Available three-piece IOLs with vertical barrier edges, posterior haptic angulation, and posterior optic convexity, can rapidly initiate a capsular bend that serves as our best current defense against the need for Nd:YAG laser capsulotomy. The only apparent drawbacks of this vertical edge design are dysphotopsias. New IOL edge designs have now become available to both preserve the barrier edge effect and improve patient satisfaction by reducing both PCO and dysphotopsias. With these new edge designs available, further analysis of the remaining unwanted images will hopefully drive next-generation design modifications to allow for truly asymptomatic cataract surgery with the potential for clear posterior capsules.
1. Holladay J, Lang A, Portney V: Analysis of edge glare phenomena in intraocular lens edge designs. J Cataract Refract Surg 25:748-752, 1999
2. Davison JA: Positive and negative dysphotopsia in patients with acrylic intraocular lenses. J Cataract Refract Surg 26:1346-1355, 2000
3. Masket S: Truncated edge design, dysphotopsia, and inhibition of posterior capsule opacification. J Cataract Refract Surg 26:145-147, 2000
4. Waller S, Steinert RF: Symptomatic intraocular reflections from oval intraocular lens implants. Am J Ophthalmol 116:374-376, 1993
5. Tester R, Pace NL, Samore M, Olson RJ: Dysphotopsia in phakic and pseudophakic patients: Incidence and relation to intraocular lens type. J Cataract Refract Surg 26:810-816, 2000
6. Nishi O, Nishi K, Akura J: Speed of capsular bend formation at the optic edge of acrylic, silicone, and poly(methylmethacrylate) lenses. J Cataract Refract Surg 28:432-437, 2002
7. Hwang I, Olson R: Patient satisfaction after uneventful cataract surgery with implantation of a silicone or acrylic foldable intraocular lens. Comparative study. J Cataract Refract Surg 27:1607-1610, 2001
8. Erie JC, Bandhauer MH, McLaren JW: Analysis of postoperative glare and intraocular lens design. J Cataract Refract Surg 27:614-621 2001
9. Mamalis N, Spencer T: Complications of foldable intraocular lenses requiring explantation or secondary intervention—2000 survey update. J Cataract Refract Surg 27:1310-1317, 2001
10. Farbowitz MA, Zabriskie NA, Crandall AS, et al: Visual complaints associated with the AcrySof acrylic intraocular lens. J Cataract Refract Surg 26:1339-1345, 2000
11. Davison J: Explanting the AcrySof single-piece IOL. EyeWorld 6:67, 2001
