Ординатура / Офтальмология / Английские материалы / Phakic Intraocular Lenses_Hardten, Lindstrom, Davis_2004

110 Chapter 11

The ZSAL-4

Pérez-Santonja and Zato also developed an angle-sup- ported, single-piece PMMA, anterior chamber phakic IOL based on the Kelman Multiflex lens.29 Their first generation lens, the ZSAL-1 phakic refractive lens, was introduced in 1991. Successive generations of lenses altered the anterior angulation of the lens as well as changed the optic. In 1994, Pérez-Santonja and Alió developed the fourth and current generation lens, the ZSAL-4, that was based on the previous models.29

Morcher GmbH (Stuttgart, Germany) manufactures and markets the ZSAL-4 as Model 93A. The diameter of the optic is 5 mm. The optic design is anterior plano/posterior concave and has a multifaceted edge designed to reduce refracted glare. A 19-degree haptic angulation reduces potential iris contact and allows central clearance from the crystalline lens of approximately 1.0 mm. The phakic IOL has long Z-shaped haptics to increase haptic flexibility and decrease compression forces against angle structures. The overall length of the lens is 13.0 mm, and the lens power ranges from -6 to -22 D. A ZSAL-4/PLUS model is available (Morcher Model 99C) with a 5.3-mm optic and 22.7-degree haptic angulation.

The details of surgical placement of the ZSAL-4 are similar to those of the NuVita lens. The ZSAL-4, with its 5-mm optic, will require an approximately 5.5-mm incision. The ZSAL-4 lens became available in Europe in January 1995.

Others

The Vivarte is a foldable anterior chamber lens marketed by CIBA Vision (Duluth, Ga). They claim the lens’ three-point fixation in the anterior chamber increases its stability. The lens is CE approved in Europe, and US FDA clinical trials are ongoing.

Ophthalmic Innovations International, Inc (Ontario, Canada) markets the Phakic 6 anterior chamber angle-sup- ported phakic IOL. Its PMMA design resembles the design of the ZSAL-4 lens. It is manufactured with a 6-mm optic and is available in total lengths of 12 to 14 mm. The power range is -2 to -25 D and +2 to +10 D. The company claims that its heparin-surface modified phakic IOL reduces synechiae. The lens has the European CE mark.

IOLTech (La Rochelle, France) has designed the GBR, an anterior chamber phakic IOL with a foldable optic and rigid three-point fixation haptics similar to the Vivarte. Its 5.5-mm optic is available in powers from -7 to -25 D. This lens can be implanted through a 3.2-mm incision. This lens has the European CE mark.

Although inferences can be drawn by comparing these newer models to existing models, there is, as yet, no peerreviewed studies to support their efficacy and safety.

RESULTS

Phakic IOL surgery has developed significantly since Strampelli’s initial attempt to implant a minus power anterior chamber lens in myopic eyes.1 Each of the major classifications of phakic lenses has undergone significant revisions, ever since Fechner’s modification of the Worst irisclaw lens and Baïkoff’s modification of the Kelman Multiflex anterior chamber IOL in the mid-1980s.15- 17,26,30,31 These revisions are driven by the results of the ongoing US FDA and international clinical trials as well as by unpublished experience. Manufacturing processes are improving and materials are in evolution. As more of a particular model spreads to surgeons of all skill levels, specialized instruments are developed and “pearls” are shared that allow higher rates of successful implantation. With large groups of data, nomograms and refractive outcomes are improved. Attention can be paid to the effect these lenses have on qualitative vision parameters and the higher order aberrations their insertion induces.

Faced with this rapidly enlarging and improving arena, a fair comparison among these lenses can be exceedingly challenging. The development and use of improved models often occurred within the data collection period of a single study.32-34 Except where noted and in order to present a fair comparison, only the studies reporting results from the latest version of each of the lenses have been included in the review. The reader is encouraged to turn to the original literature for details on lens model specifics and details of the surgeries.

Refractive Outcomes

Myopic Results

The major clinical studies showing refractive outcomes for the correction of high myopia with phakic IOLs are detailed in Table 11-1. Each of the studies was published in 1997 or later and is, in general, a nonrandomized consecutive case series. Of the 1344 eyes included in the table, the experience with the Artisan lens represents the largest proportion of eyes (61%). The design and implantation of the Artisan lens has been unchanged since its modification from the Worst-Fechner lens in 1991, and, thus, the follow-up from Artisan implantation is also the longest. For the reasons mentioned above, only studies including the latest generation of lenses are included (ie, the ICL MV4, the PRL 101, the Artisan 204 and 206, the ZSAL-4, and the NuVita MA20). The ICL and Artisan studies enrolled eyes with lower degrees of myopia than the PRL, ZSAL-4, and NuVita. This context should be recognized when interpreting much of the refractive and outcomes data. The lens power nomograms and the surgical complication rates for the very high myopes are more

Table 11-1

MYOPIA

CORRECT

TOENS

LNTRAOCULAR

IHAKIC

PA

OFMPLANTATION

INVOLVING

IERIES

SASE

CAJOR

M

Safety

Efficacy

Safety

problematic than with the moderate and high myopes. The studies with the ICL and Artisan lenses have approached the lower myopes—as low as -3 D with the ICL and -4.88 D with the Artisan. This may be because the increased experience clinicians have gained with these two lenses allows them to feel more confident with the low myope.

Regarding the predictability and visual acuity results, every effort was made to adjust or eliminate the appropriate data when residual myopia for enhanced near vision was intended. Often the degree of myopia that these phakic IOLs are able to correct is limited by the maximum manufactured dioptric power. The data were not corrected for this factor. This issue should not be overlooked because expanding the range of these lenses to fully correct the highest myopes involves more than simply increasing the dioptric power of the optic. Mechanical limitations that cause the lens to rub against adjacent crystalline lens, iris, or endothelium are distinct concerns. Moreover, the quality of vision and spherical aberrations may reduce the effectiveness of these phakic IOLs at extreme dioptric powers.

The other studies achieve good refractive outcomes with mildly myopic endpoints. On average, 55% achieve a postoperative refraction within 0.5 D of the attempted, while up to 92% are within 1 D of attempted. The ICL and Artisan lenses have impressive results, with approximately 30% to 50% achieving an uncorrected visual acuity (UCVA) of 20/20 or better and 70% to 90% achieving a UCVA of 20/40 of better.

At first glance, the NuVita study by Allemann et al appears to have a poorer refractive outcome.35 The data presented in the original manuscript, however, indicate that the preoperative visual acuity was worse than the other studies—no eye had a preoperative best-corrected visual acuity (BCVA) better than 20/30, and the mean preoperative logarithmic BCVA was only 20/50.

The efficacy index is defined as the postoperative decimal UCVA divided by the preoperative decimal BCVA. Although not strictly mathematically correct, this index gives an indication of the refractive outcome at a glance. Larger indices are the desired outcome.

As a whole, this modern, latest generation of phakic IOLs seems remarkably safe. On average, loss of one line of visual acuity occurs in about 5%, while <1% of eyes lose two or more lines of vision. About one-third of patients gain two or more lines of vision. In one remarkable study by Menezo et al, not one eye of 94 eyes implanted with the Artisan lens lost any lines of visual acuity.34 At 3 years after surgery, 5% showed no gain in lines of BCVA, 13% gained one line, 23% gained two lines, 31% gained three lines, 26% gained four lines, and 2% gained five lines. The safety index is defined as the postoperative decimal BCVA divided by the preoperative decimal BCVA. All indices were greater than 1.

Hyperopic Results

The major studies involving the implantation of a phakic IOL to correct hyperopia are detailed in Table 11-2. The studies involve a total of 126 eyes published since 1998. Only the latest models of phakic IOL are included (ie, the ICL HV3, the PRL 200, and the Artisan 203). No peer-reviewed publications exist for the correction of hyperopia with an anterior chamber angle-supported phakic lens that is currently in production. Mean follow-up is less than that for the myopic phakic IOL group. Average preoperative spherical equivalent was +5.61 D. Rosen et al included an eye with a refraction of just +2.25 D sphere.8

Mean postoperative refractions are well within the 0.5 D steps in which the lenses are manufactured. Predictability is very good, and the percentage of eyes within 0.5 D and 1 D of the targeted refraction is 70% and 93%, respectively; results that, in most cases, exceed the myopic data. UCVAs are very good and the efficacy indices (defined earlier) are also very good.

Correction of high hyperopia with phakic IOLs seems to be a relatively safe procedure, with an average of 7% losing one line of BCVA and 1.8% losing two or more lines of BCVA. An average of 17% gained two or more lines of BCVA. All reported safety indices were greater than 1.

Toric Results

The only peer-reviewed publication describing the surgical outcomes of a toric phakic IOL was recently published.36 The Artisan Toric model can correct concurrent myopia and hyperopia, and the outcomes are listed in the appropriate tables. In the study, the average magnitude of the refractive astigmatism was reduced from 3.7 D preoperatively to 0.7 D postoperatively.

Complications

As with cataract surgery, the list of potential complications with phakic IOL surgery is long. Virtually every structure in the eye is at risk in the operative or postoperative period. Retrospective and prospective studies have identified the most common complications (Table 11-3). Some complications, such as glare and halos, are shared among all types of lenses, whereas other complications are more lens-specific.

Whenever the cornea is incised—whether penetrated or perforated—some degree of regular or irregular astigmatism can be induced. With the self-sealing clear corneal incisions used to place the ICL, induced astigmatism is much less likely than with incisions as large as 6.5 mm to implant either the Artisan lens or an angle-fixated phakic IOL. Only a few published reports quantify the induced regular astigmatism associated with phakic IOL implantation. In the largest series of published eyes with the Artisan lens, Budo et al reduced the mean preoperative astigma-

Table 11-2

AOF

IMPLANTATION

INVOLVING

SERIES

CASE

MAJOR

HYPEROPIA

CORRECT

TOENS

LNTRAOCULAR

IHAKIC

P

Safety

Efficacy

Table 11-3

SERIES

CASE

MAJOR

INOMPLICATIONS

CEPORTED

R

LENS

INTRAOCULAR

PHAKIC

AOF

IMPLANTATION

INVOLVING

Table 11-3 (Continued)

tism of 1.23 D to 0.84 D postoperatively.37 The induction of irregular astigmatism would manifest itself as a decrease in the UCVA, but especially the BCVA. Budo et al report 1.2% of the eyes in their series lost two or more lines of BCVA. The remainder of the data in Tables 11-1 and 11-2 suggest that there are no large increases in irregular astigmatism after implanting phakic IOLs. No study has specifically looked at irregular astigmatism with retinoscopy, topography, or wavefront aberrometry.

Even the gentlest of anterior segment surgeries results in an immediate postoperative loss in endothelial cell numbers, leading to a decrease in the density of the cells. An immediate decrease in central endothelial cell densities has been recorded after the insertion of all types of phakic IOLs. Although the immediate effect on the endothelial cell density is not as great as it is with phacoemulsification, the concern in this patient population (with a mean age much younger than those undergoing phacoemulsification) really should be the long-term endothelial loss initiated by the insertion of a phakic IOL. The chronic loss of endothelial cells is mediated by chronic or intermittent touch of the phakic IOL to the posterior cornea or can be the endpoint of chronic, low grade iridocyclitis induced by the phakic IOL. By recording serial measurements on the same patients and by examining the morphologic features of the endothelial cells, investigators have concluded that the bulk of the endothelial loss happens initially, with minimal loss thereafter. The studies with the longest fol- low-up of each of the lenses show a 12% loss at 4 years with the ICL,38 a 13% loss at 4 years with the Artisan,39 and a 9% loss at 7 years with the ZSAL-4.27

Pupil irregularity is a complication of principally the anterior chamber phakic IOLs. With the current generation of anterior chamber phakic IOLs, pupil ovalization rates of 16% to 40% can be expected. These are progressive and probably related to chronic irritation of the phakic IOL footplates in the anterior chamber angle. Better sizing of the lenses and redesigned haptics that spread the force more evenly in the angle will be features of the next generation of phakic IOLs. A small percentage of eyes with the Artisan lens will show a nonprogressive irregular pupil related to improper iris enclavation. In one large study, 4% reported minor surgical difficulties inserting the lens.19

Pigment dispersion or deposits on the phakic IOL can be associated with pigmentary glaucoma. This complication seems to be related to the level of contact between the phakic IOL and the uvea. Arne et al40 reports pigment deposits on the periphery of the ICL optic in 100% of this series of 58 ICLs. In two of the eyes (3.4%), increased intraocular pressure necessitated the chronic use of topical beta blockers. Pigment dispersion has been reported in the

iris-fixated and angle-fixated models, but to a lesser degree.

IOL decentration is reported at a low incidence with the self-centering design of the ICL. Decentration with the Artisan is dependent on the skill of the surgeon to enclavate the lens in the proper position. Improper enclavation is a complication that can lead to an irregular pupil, phakic IOL decentration, and glare. In the hands of the clinicians currently using the lens, decentration is reported at a rate of 1% to 13%.

Pupillary block glaucoma seems to be a feature primarily of the posterior chamber lenses. This complication is reducing in incidence as clinicians learn to make two large iridotomies or iridectomies prior to implantation of the lens. If the iris defects are made 90 degrees apart, both cannot be blocked simultaneously should the lens rotate. This is particularly important with the PRL.

The occurrence of any lens opacity—whether visually significant or not—is listed in Table 11-3. The risk of cataract is highest with the posterior chamber lenses. In a comprehensive retrospective review of the two latest myopic models of the ICL, Sanders et al demonstrate a marked reduction in the incidence of cataract with the newest generation of ICLs that have the increased vaulting over the crystalline lens (ICM-V4).41 Their data come from eyes enrolled in the US FDA clinical trial for myopia. The publication notes 15 anterior subcapsular opacities greater than “trace” density in 523 eyes receiving the ICLV4 model. Of these 15, six were associated with the ICL being removed and reinserted at surgery. Four cataracts were deemed “clinically significant.” Bloomenstein et al, who implanted only the ICL-V4 model, noted that 18 of 86 eyes (21%) in their study had “asymptomatic anterior subcapsular changes.”42 They note that the changes are nonprogressive and “appear more like a scratch on the surface of the anterior capsule.” The Artisan lens also carries a risk of anterior subcapsular cataracts as well as anterior nuclear vacuoles associated with the trauma of insertion.

The presence of glare and halos is a feature primarily of the Artisan and angle-fixated lenses. The Artisan is manufactured in models with optics of 5 and 6 mm in diameter. In every study that has examined the association, more subjective complaints are associated with the 5-mm optic model than the 6-mm optic model. The 6-mm lens is not made above -15.5 D because the optic thickness at that dioptric power would place the lens edge too close to the corneal endothelium. The anterior location of the anglefixated lenses necessitates a smaller optic, and this is thought to be the cause of the glare complaints. The ZSAL-4 and NuVita lenses have optic edge modifications in an attempt to control this symptom.

118 Chapter 11

CONCLUSIONS

In general, the results are encouraging. The group of patients approached with phakic IOLs are challenging, indeed, with myopia up to -29 D and hyperopia up to +18 D. Refractive outcomes are very good with a high proportion of patients within 1 D of their intended target and with a UCVA of 20/40 or better. The efficacy ratios approach 1.00 in the hyperopic cases and often exceed it with the myopic cases. As surgeons continue to gain experience with these lenses, surgical nomograms will get more accurate, and the variables that control refractive outcomes will become clearer. Phakic IOL surgery is also reasonably safe. In this challenging set of eyes with high refractive errors, the vast majority of patients do very well with a significant portion gaining lines of BCVA. Safety indices in all reviewed studies were greater than 1.00.

Every new technique, new instrumentation, or new technology needs the accumulation of postoperative data over time to reveal potential faults. Phakic IOL technology seems to be a perfect example of this concept. None of the lenses are perfect, but each has improved markedly over the past 15 years as dictated by the results of large clinical studies. As these lenses gain US FDA approval and more lenses gain the European CE mark, choosing a lens may depend more on surgeon preference and lens availability than solid evidence that one phakic IOL is the best. Successive generations of lens will continue to improve on the efficacy and safety of the current generation. Time is required to evaluate the risk, and these lenses should be used with caution.

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54.Alió JL, de la Hoz F, Ruiz-Moreno JM et al. Cataract surgery in highly myopic eyes corrected by phakic anterior chamber angle-supported lenses. J Cataract Refract Surg. 2000;26:1303-1311.