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

INTRODUCTION

The implantation of intraocular lenses (IOLs) into the human eye reached its 50th anniversary in 1999. Looking back to the various IOLs implanted into the anterior or posterior chamber, we are aware of various complications associated with different IOL designs, materials, and positions. These complications can be shortor long-term.

The implantation of IOLs in the phakic eye (phakic IOLs) is a relatively new technique to correct primarily high ametropia. The time lapse between introduction of new lens designs is short, thus surgeon’s experience with one specific lens is back to zero when new lenses are presented that overcome a specific complication, but keep in mind, however, that new problems inevitably arise.1 Currently, only a few long-term studies are available with phakic IOLs, thus regular reassessment of the complication spectrum is necessary, as new studies will be published. Complications of phakic IOLs documented in the literature as well as those encountered in the authors’ own experiences are summarized and discussed in this chapter.

ANTERIOR CHAMBER

ANGLE-SUPPORTED

PHAKIC INTRAOCULAR LENSES

The certain complication spectrum of angle-supported anterior chamber phakic IOLs (AC phakic IOLs), which were mainly developed by Baïkoff from France, is related to their design as they are positioned in the anterior cham-

ber where there is potential risk for damage to the endothelium, and as they are supported in the sclerocorneal angle with possible damage to the angle and iris (pupillary block, pupil ovalization, chronic uveitis). Positioning the phakic lens away from the crystalline lens might reduce the risk of cataract formation compared to posterior chamber phakic IOLs. Below, specific complications of the angle-supported AC phakic IOLs are discussed.

Endothelial Cell Loss and

Anterior Chamber Depth

The main concern about AC phakic IOLs is loss or damage to the endothelial integrity. An exact preoperative examination should exclude those patients with low endothelial cell count or those with shallow anterior chambers because the risk of cell loss increases as the distance between phakic IOL and the endothelium decreases. A 7-year follow-up study by Alió et al reports on an early postoperative loss of endothelial density of 38%, gradually decreasing to about 0.5% per year after the second postoperative year.2 In this study, the Chiron ZB 5M/ZB 5MF (Chiron, Claremont, Calif) was investigated for 7 years and the Morcher ZSAL-4 (Morcher GmbH, Stuttgart, Germany) for only 4 years. The total percentage of endothelial loss over 7 years was 8.4%. Other studies have confirmed the initial significant loss of endothelial cell and reduction of this tendency in the second postoperative year.3-5 Alleman et al found a 12% loss for the Bausch & Lomb NuVita (Rochester, NY) at 2 years. Baïkoff et al found a 4.8% loss at 3 years with the ZB 5M, and Perez-Santonja

Figure 9-1A. Deposits on AC phakic IOL. Protein deposits on AC phakic IOL 1 month postoperatively (34-year-old female).

Figure 9-1B. Deposits on AC phakic IOL. Anterior chamber hemorrhage after AC phakic IOL implantation (courtesy of E. Rosen, Manchester, Great Britain).

et al found a 4.2% loss with the Morcher ZSAL-4. All of these AC phakic IOLs were polymethylmethacrylate (PMMA) rigid IOLs. The numbers are not yet published for the new flexible AC phakic IOLs, such as the CIBA Vision Vivarte (foldable optic with PMMA haptics) (CIBA Vision, Atlanta, Ga) or the Alcon foldable AC phakic IOL (hydrophobic acrylate) (Alcon Surgical, Fort Worth, Tex). However, meticulous long-term follow-up of each patient is at the moment necessary for any AC phakic IOL to detect those individuals with significant damage to the endothelium and to explant the phakic IOL whenever clinically necessary.

Pigment Dispersion

and Lens Deposits

Although no definite incidence for these conditions is reported in the literature, these conditions are seen in clinical practice (Figure 9-1A). They normally do not negatively affect visual acuity and thus no further procedure— except for regular clinical observation—is necessary. Surgical intervention might be necessary in single individual cases. Besides pigment dispersion, intraoperative hemorrhage (Figure 9-1B) may lead to erythrocyte deposits on the IOL and intraocular pressure (IOP) elevation. The bleeding either originates from vessels in the scleral tunnel or from the intraoperative iridectomy.

Chronic Inflammation and Uveitis

As the angle-supported AC phakic IOL is positioned directly in front of the iris, chronic inflammation and pigment dispersion are possible, as the pupil movement might induce some friction with the IOL. Perez-Santonja et al reported on two of 23 treated eyes presenting with slight chronic inflammation during the first 6 months.5 Allemann

et al removed one of the 21 implanted IOLs due to a chronic postoperative inflammatory response associated with ocular hypertension.3 Alió et al observed acute postoperative iritis in 4.6% of 263 AC phakic IOLs.2 As with other complications, if the conservative treatment does not succeed, lens removal should be considered to avoid long-term risk to the vision.

Pupil Ovalization and Iris Retraction

Ovalization of the pupil is a specific complication of angle-AC phakic IOLs (Figures 9-2A and 9-2B). The position of haptics in the sclerocorneal angle and their size might lead to mild deformation of the iridosclerocorneal architecture, resulting in iris retraction and pupil ovalization. Mild to medium deformation of pupil shape (see Figure 9-2A) as reported by Alió et al in 10.3% of their large series of 263 eyes2 does not affect the refractive, the cosmetic, or the optical results of the surgery. Severe ovalization causes glare and is unacceptable from a cosmetic point of view (see Figure 9-2B). Alió et al observed this condition in 5.9%, which led to lens explantation in two cases. Allemann and coworkers reported eight oval pupils (>0.5 mm) in a series of 21 eyes.3 Perez-Santonja et al observed four cases in a series of 23 eyes.5

Iris retraction with oval pupil deformation remains a concern of the angle-supported phakic IOLs. This matter, together with potential damage to endothelial cells, is the major objection against the current lens designs. Topical use of miotic agents should be considered in the early postoperative phase if pupil ovalization associated with glare is detected.

Intraocular Lens Rotation

Rotation of the angle-supported phakic IOLs might occur due to undersizing. In fact, Allemann et al report that 80% of eyes showed greater than 15 degrees of rota-

Figure 9-2A. Pupil ovalization following AC phakic IOL implantation. Moderate ovalization.2

Figure 9-2B. Pupil ovalization following AC phakic IOL implantation. Severe “cat pupil”-like ovalization.2

tion in 2 years, and 60% had rotated between years 1 and 2, implying some instability in the anterior chamber.3 Perez-Santonja observed rotation in 43.5% of 23 treated eyes.5

Induced Astigmatism

Surgically induced astigmatism is of significance because patients request acceptable unaided postoperative visual acuity. The surgeon needs to consider the preoperative amount and axis of astigmatism in order to decide whether to use a 5 to 6 mm incision size with a PMMA lens (eg, Phakic 6 [Ophthalmic Innovation International Inc, Ontario, Canada]) or to implant a foldable phakic IOL (eg, Vivarte) through a small incision. If a significant astigmatism is induced by the surgery, further refractive surgical procedures (eg, suture revision or removal, limbal relaxing incisions, or even excimer laser surgery) might be considered.

Glare and Halos

One disadvantage of AC phakic IOLs is that they are positioned in front of the pupil, with edge effects as a potential source of optical aberrations. Furthermore, the relation of pupil size and center to the optic of the lens is a crucial factor that should be evaluated and discussed preoperatively. Sometimes the AC phakic IOL optic center and the pupil center are not coincident. In cases in which the scotopic pupil size is significantly larger than the optic of the lens, the surgeon should be very cautious with the implantation of phakic IOLs because this will probably result in postoperative glare and subjective discomfort. The incidence of glare is dependent on the size of the optic, which varies in different lens designs and generations. The acceptable relationship between AC phakic IOL optic and scotopic pupil size remains to be determined. Incidence of glare and halos is reported in the literature to be between 10% at the 7-year follow-up2 and 80% as observed by Allemann and coworkers.3 However, in a recent study, the

NuVita IOL had a special optic edge design to prevent glare. A study performed by Maroccos et al showed that all tested phakic IOLs (ie, NuVita, Artisan, Implantable Contact Lens [ICL] [STAAR Surgical AG, Nidau, Switzerland]), in particular ICL (posterior chamber phakic IOL) and NuVita (angle-supported AC phakic IOL), lead to a decreased visual performance during night time due to glare and halos.6 Topical use of miotic agents should be considered in the early postoperative phase if the patient feels disturbed by these phenomena.

Glaucoma

The risk of acute angle glaucoma is well known from aphakic anterior chamber IOLs; therefore, a peripheral iridectomy is recommended for this IOL. With phakic anglesupported anterior chamber IOLs, the risk will not be less, particularly because the continuously growing natural lens is still in the eye. Ardjomand et al observed one case of pupillary block after implantation of an angle-supported AC phakic IOL that was successfully treated with neodymium:yttrium-aluminum-garnet (Nd:YAG) iridotomy.7 The authors recommend two very important steps to prevent the potential complication of acute angle glaucoma for angle-supported and other types of phakic IOLs:

1.Removal of all viscoelastic substance from the anterior segment at the end of the procedure is mandatory. A coadhesive viscoelastic substance like Healon (Pharmacia, New York, NY) is the authors’ preference

2.The authors recommend preoperative iridotomy, as performed by most surgeons, by means of Nd:YAG laser or intraoperative iridectomy with scissors or vitrector cutters to forestall acute pupillary block glaucoma

Particularly with foldable angle-supported phakic IOLs, the need for a peripheral iridectomy has been discussed amongst experienced refractive intraocular surgeons. However, only long-term experience will show if surgeons can abandon this important step of the procedure.

Figure 9-3. Nuclear cataract in an eye with an AC phakic IOL (courtesy of Jorge L. Alió,Alicante, Spain).

Figure 9-4. Endophthalmitis after AC phakic IOL implantation (courtesy of Jorge L. Alió,Alicante, Spain).

Figure 9-5. After AC phakic IOL implantation (Bausch & Lomb, NuVita lens), diagnostic mydriasis is possible (33- year-old female).

Other factors of postoperative elevated IOP may be due to steroid medication, which should be carefully observed and treated with conversion to nonsteroidal antiinflammatory drugs, if still necessary, and topical antiglaucomatous medication.

If a chronic IOP elevation develops otherwise, the angle needs to be examined for synechia formation and other pathologies, and IOL removal should be considered when necessary.

(3.4%).2 All cataracts were nuclear and the calculated Kaplan-Meier survival curves for cataract development show that more than 90% of subjects would be expected to remain cataract free after 98 months.

General Risks of Intraocular

Procedures and Vitreoretinal

Procedures

Implantation of phakic IOLs is an intraocular procedure with potential risk of endophthalmitis (Figure 9-4), as in every intraocular surgery. Preoperative use of antibiotics, intraoperative care sterility, and meticulous postoperative follow-up examinations may help to prevent this severe complication and to treat it as early and as aggressively as possible. Only a few vitreoretinal complications have been reported after implantation of phakic IOLs.8,9 Exact preoperative and regular postoperative examination of the posterior segment by indirect ophthalmoscopy or Goldmann 3-mirror lens will help to detect and treat retinal breaks in this patient group, which is in danger of vitreoretinal pathologic conditions because of severe myopia in most cases. In the authors’ experience, sufficient pupil dilation for retinal examination without any risk of pupil deformation or IOL decentration is feasible following AC phakic IOL implantation (Figure 9-5).

Cataract Formation

As the AC phakic IOL is positioned away from the lens, cataract formation is of less significance when compared to posterior chamber phakic IOLs. Because cataract formation in the highly myopic, who represent the vast majority of the treated patients, is more frequent than in the general population, discriminating between a myopiaassociated cataract and a surgically-triggered or hastened cataract is difficult (Figure 9-3). Alió et al reported on nine cataract removals during the 7-year follow-up of 263 eyes

IRIS-FIXATED ANTERIOR CHAMBER

PHAKIC INTRAOCULAR LENSES

The iris-fixated IOL is marketed in Europe as the Artisan (Ophtec BV, Groningen, Netherlands) and outside Europe as the Verisyse (Advanced Medical Optics, Irvine, Calif). The “lobster-claw“ design has been used since 1978 for pseudophakic IOLs, mainly for secondary implantation in aphakic eyes.10 Since 1986, the Worst-Fechner IOL has been implanted in phakic eyes for the correction of high

Figure 9-6A. First generation iris-claw lens (Worst-Fechner), 11 years after implantation (61-year-old female). Slit lamp image. Note the slight decentration.

Figure 9-6B. First generation iris-claw lens (Worst-Fechner), 11 years after implantation (61-year-old female). The confocal microscopic image of the endothelium reveals severe endothelial cell loss (700 cells/mm2).

myopia and subsequently hyperopia (Figure 9-6A).11 The original design was modified in 1991 to assure a sufficient vault between the IOL optic and the iris. This IOL design bears potential risks to the corneal endothelium, a problem that is common for all AC IOLs. Another concern is the fixation in the sensitive iris tissue, which has the potential to cause pigment dispersion or intraocular inflammation as well as decentration or deformation of the pupil.

Endothelial Cell Loss

and Anterior Chamber Depth

Damage to the endothelium can occur mostly because of the IOL’s direct contact with the inner surface of the cornea, either during implantation or by postoperative changes in IOL position. Another possibility for postoperative endothelial damage may be subclinical inflammation with direct toxicity to the endothelium.

In 1991, Fechner et al described the first results of this lens after a 12-month follow-up.12 Five of 109 eyes suffered endothelial cell loss by surgical trauma and five eyes had progressive endothelial cell loss that caused corneal edema in one eye (Figure 9-6B).

Menezo et al examined the influence on the corneal endothelium of 111 eyes over 4 years in a prospective study.13 They found the largest percentage of cell loss in the first 6 months after implantation and concluded that the main cause for endothelial cell loss is surgical trauma. Endothelial cell pleomorphism and polymegathism did not change significantly after surgery. One phakic IOL that was placed too superiorly caused corneal edema and had to be removed. Other studies yielded similar results.14-17 Maloney et al found no difference in mean

endothelial cell count between the preoperative state and 6 months postoperatively.18

In contrast to these findings, Perez-Santonja et al reported continuous endothelial cell loss with a decrease of 17.6% 24 months after surgery.19 All authors agree that preoperative endothelial microscopy is mandatory. Patients with endothelial damage or an endothelial cell count below 2000 cells/mm2 should not receive an AC phakic IOL.

The height of the Artisan lens and the potential closeness to the cornea increase with the dioptric power. Therefore, a sufficient anterior chamber depth (ACD) for the calculated IOL is necessary. The distance between the implant and the corneal endothelium should not be less than 1.5 mm.

Pigment Dispersion and Lens Deposits

The optic of the iris-claw phakic IOL is vaulted anteriorly to prevent iris chafing. Pop et al performed postoperative ultrasonic biomicroscopy of the IOL haptics of myopic and hyperopic phakic IOLs and found no evidence for irritation of the iris pigment epithelium by the IOL haptics within a follow-up period of 24 to 371 days.20,21 Occasionally, pigment cells are visible on the IOL optic in the early postoperative period due to surgical trauma (Figures 9-7A and 9-7B), but as of the writing of this text, there is no evidence of chronic pigment dispersion or pigment glaucoma as a typical complication of this type of phakic IOL. However, in the US Food and Drug Administration Phase III trial for the hyperopic iris-claw phakic IOL, there were reports of three patients who had pigment dispersion or pupillary membrane formation due to iris touch.1 This may be a problem more for the hyperopic than the myopic iris-claw phakic IOL.

Figure 9-7A. Iris pigment defects at the site of enclavation may be one source for dispersed iris pigment (30-year-old male).

Figure 9-8A. Inflammatory reaction after iris-claw lens implantation. Dense fibrin coating of the phakic IOL 1 week postoperatively (34-year-old female).

Chronic Inflammation and Uveitis

The possibility of chronic inflammation has always been a major concern with the iris-claw lens, as this IOL is fixated directly in the iris tissue and causes pressure or shear forces when the eye is moving (Figures 9-8A and 9-8B). This could lead to injury or increased permeability of the iris vessels with breakdown of the blood-aqueous barrier and chronic release of inflammatory mediators. This has been repeatedly examined using different technologies. Two studies that were performed using iris angiography showed no leakage of the iris vessels.12,22

Studies conducted using a laser-flare cell meter came to diverging results. Fechner et al12 found no elevated flare levels in 109 eyes with at least 12 months of follow-up. Perez-Santonja et al found elevated flare levels compared to a normal population in 30 eyes at 12, 18, and 24 months after surgery.23 Gross et al found no significantly elevated flare after 6 months17 in a study with 44 eyes. In all of the studies, clinically relevant inflammation could only be

Figure 9-7B. Iris pigment defects at the site of enclavation may be one source for dispersed iris pigment (47-year-old female). Both A and B are 3 months postoperatively.

Figure 9-8B. Inflammatory reaction after iris-claw lens implantation. Persistent deposits 3 months after implantation (37-year-old male).

detected in individual cases. Nevertheless, careful postoperative monitoring of inflammatory signs is necessary. If persistent intraocular inflammation occurs that is not sufficiently treatable with drugs, the removal of the implant must be considered.

Pupil Ovalization and Decentration

Pupil ovalization or irregularity can occur if the fixation of the haptics is performed asymmetrically. No progressive pupil ovalization has been reported so far. Maloney et al report pupil irregularities in 14.0% of 130 eyes on the first day after surgery and 1.2% of 84 eyes after 6 months.18 As the enclavation is performed in the peripheral iris, pupil dilatation is limited after implantation of the IOL. However, the authors have been able to perform regular fundus examination in all eyes with phakic iris-fixated IOLs (Figures 9-9A and 9-9B).

Figure 9-9A. After iris-claw AC phakic IOL implantation (Artisan/ Verisyse), diagnostic mydriasis is possible (25-year-old female) 12 months after implantation.

Figure 9-10. Traumatic dislocation of an iris-claw AC phakic IOL (courtesy of D. Annen, Switzerland).

The Artisan/Verisyse phakic IOLs are centered on the pupil. This can lead to difficulties if the pupil itself is decentered and if the optical axis is not in the middle of the pupil (see Figure 9-6A). Postoperative decentration is possible if the enclavation is not sufficient. Menezo et al report 13.5% decentration, but only one case in which a second intervention was necessary due to double vision.22 Perez-Santonja et al found a decentration greater than 0.5 mm in 43% of the examined eyes.19 Perez-Torregrosa et al found a mean decentration of 0.47 with respect to the pupil center in 22 eyes using a digital imaging system.24 If the IOL is fixated properly, no postoperative decentration or rotation of the optic should occur. The authors recommend performing the enclavation step of the operation in a physiological situation (ie, the anterior chamber is not too flat and not too deep).

Postoperative dislocations due to blunt ocular trauma have been described (Figure 9-10).18,25 In the authors’ experience, they observed only one case of possible phakic IOL dislocation in a patient with very thin iris tissue.

Figure 9-9B. After iris-claw AC phakic IOL implantation (Artisan/Verisyse), diagnostic mydriasis is possible (24-year- old male) 3 months after implantation.

However, before the IOL could have been completely dislocated, a second intervention was performed and the iris enclavation was repeated with more iris tissue. This phakic IOL has been stable in the eye for more than 6 months.

Intraocular Lens Rotation

Rotation of iris-fixated phakic IOLs is not expected due to the permanent enclavation in the iris tissue and it has not been described. Therefore, this design is particularly interesting for toric phakic IOL designs.

Induced Astigmatism

Because the iris-claw lens is not foldable, it requires an incision that approximately equals the optic diameter (5.0 or 6.0 mm). This is likely to induce postoperative astigmatism (Figure 9-11A to 9-11C). There are several ways of influencing postoperative astigmatism: incision on the steep corneal meridian; use of clear corneal, posterior limbal, or scleral tunnel incisions (Figures 9-12A to 9-12C); adjustment of the sutures during surgery; or selective suture removal after surgery. According to the literature, surgically induced astigmatism is less than one might expect. Menezo et al found no significant increase of postoperative astigmatism.22 Alió et al15 found a mean induced astigmatism of 1.48 0.89 D for the hyperopic Artisan IOL with correction of primary hyperopia and 1.85 1.19 D with correction of secondary hyperopia after corneal refractive surgery. Maloney et al reported a mean decrease in astigmatism of 0.3 D after 6 months.18 In the authors’ experience, the induced astigmatism for the Artisan IOL implanted through a 6-mm superior posterior limbal incision was 1.93 0.49 D.26 Therefore, we currently adjust our incision according to the preoperative astigmatism. The introduction of foldable models of the iris-claw lens could further reduce the amount of induced astigmatism. With the toric models, larger amount of astigmatism can be managed.

Figure 9-11A. Induction of corneal astigmatism due to a 6-mm superior limbal incision (35-year-old male). Preoperative topography.

Figure 9-11C. Induction of corneal astigmatism due to a 6-mm superior limbal incision (35-year-old male).

Figure 9-11B. Induction of corneal astigmatism due to a 6-mm superior limbal incision (35-year-old male). Corneal topography 1 week postoperatively.

Figure 9-12A. Six-mm superior limbal incision for iris-claw lens implantation (36-year-old male).

Figure 9-12B. The scleral tunnel helps to avoid induction of corneal astigmatism (36-year-old male).

Figure 9-12C. Loosening of sutures and induction of pannus tissue 3 months after implantation of an iris-claw lens (47- year-old female).

Figure 9-13A. Different optic diameters of the iris fixated AC phakic IOL (30-year-old male), 5-mm optic in the right eye (17 D).

Figure 9-13B. Different optic diameters of the iris fixated AC phakic IOL (30-year-old male), 6-mm optic in the left eye (12 D).

Glare and Halos

Phakic IOLs are often implanted in eyes of comparatively young patients with a large scotopic pupil diameter. This can result in glare phenomena if the pupil is larger than the IOL optic. A study conducted by Maroccos et al6 showed significantly less glare and smaller halos for the Artisan IOL than for other phakic IOLs, especially for the 6.0-mm optic. This was attributed to the larger IOL optic (6 mm vs 5 mm) and the fixation of the IOL in the iris, which causes less dilation of the pupil. Therefore, the 6.0-mm optic iris-fixated phakic IOL seems to be preferable over the 5.0-mm optic. Unfortunately, this is not always possible due to the greater thickness of these optics and possible damage to the corneal endothelium in a given ACD (Figures 9-13A and 9-13B). The power of the 6.0-mm optic is -15.5 D for myopia. For hyperopia the range is +1.0 to +12.0 for both optic types. Landesz et al report two of 38 patients that required pilocarpine eye drops because of halos after implantation of the 5.0-mm optic Artisan lens.16 Maloney et al recorded mild to moderate glare in 18 eyes (13.8%) and severe glare in one eye (0.8%) of 130. A lens with 5.0-mm optic was exchanged for a lens with 6.0-mm optic in three eyes, with no further glare noticed afterward.18

Cataract Formation

Cataract formation due to the iris-claw lens is very unlikely because it is inserted over a miotic pupil without contacting the crystalline lens. Until now, clinically relevant cataract formation has not been reported in association with the iris-claw lens. Perez-Santoja et al only detected a loss of lens transmittance of 1.03% after 18 months by fluorophotometry that had no influence on visual acuity.19

Other Complications

Menezo et al describe one case of permanent wide dilation of the pupil causing decreased postoperative visual acuity because of glare.22 Hyphema in the early postoperative phase due to iris trauma is occasionally described.16,18,22 Iris bleeding can also be caused by preoperative Argon or Nd:YAG laser treatment of the iris to mark fixation points for the IOL enclavation.

As for all other intraocular procedures, every precaution must be taken to avoid infectious endophthalmitis. Likewise, thorough examination of the posterior segment for vitreoretinal pathologies is mandatory, although there have been no vitreoretinal complications with the iris-claw lens reported so far.

Glaucoma

Because the anterior chamber angle is not affected by the haptics of the iris-claw IOL, lens size-related secondary glaucoma is not practically possible. A peripheral iridectomy or iridotomy is necessary for the prevention of a pupillary block. In several studies and in the authors’ experience, there were some cases of elevated IOP in the early postoperative period that resolved without further damage and were probably related to steroid medication.15,16,18,27

POSTERIOR CHAMBER

PHAKIC INTRAOCULAR LENSES

Implantation of posterior chamber phakic intraocular lenses (PC phakic IOLs) in phakic eyes has proven to be an effective and predictable refractive technique for surgical treatment of high myopia.28-30 In some cases, even high hyperopic eyes can be treated with PC phakic IOLs.28,31