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

In addition to the phakic intraocular lenses (IOLs) discussed in the previous chapters, several new designs are currently under investigation. These include the I-CARE (Corneal, Paris, France), Kelman Duet (Tekia Inc, Irvine, Calif), and ZSAL-4 Plus (Morcher GmbH, Stuttgart, Germany) anterior chamber lenses.

I-CARE

This anterior chamber, angle-fixated phakic IOL (currently undergoing a multicenter trial in Europe) is designed to correct myopia and hyperopia ranging from -5.0 to -20.0 diopters (D) for myopia and +3.0 to +10.0 D for hyperopia D (lens power available in 0.5-D steps). The lens, made of 26% hydrophilic acrylic with an ultraviolet (UV) filter, is available in four lengths: 12.0, 12.5, 13.0, and 13.5 mm. The manufacturer recommends an anterior chamber depth of at least 3.4 mm and an endothelial cell density of at least 2000 cells/mm2.

Unique Features

This lens has a 5.75-mm optic and is foldable, allowing injection through a 3.2-mm incision. The unique haptics feature a symmetrical design with two 0.9-mm “feet” on each haptic that evenly distribute forces and minimize angle occlusion (Figures 17-1 to 17-3). The vaulting is calculated so that the surfaces maintain the maximum possible distance from both the anterior capsule (0.84 mm) and the corneal endothelium (2.07 mm to optic center).

Ten I-CARE lenses have been implanted at the time of this writing in patients with myopia ranging from -11.0 to -17.0 D. With 8 month follow-up, all cases are within 1 D of intended correction with no significant complications.1

KELMAN DUET IMPLANT

This unique two-piece anterior chamber, angle-fixated phakic IOL was designed by Charles Kelman, MD and Tekia Inc to treat myopia from -8.0 to -20.0 D (Figure 17- 4). The polymethylmethacrylate (PMMA) haptics feature a tripod design that is inserted first, separately from the optic, through a 1.5-mm incision.

Unique Features

Figures 17-5A to 17-5H show the implantation technique for the Kelman Duet. Three mm and 1 mm incisions are made through clear cornea at the 3:00 and 9:00 positions, respectively (Figure 17-5A). Viscoelastic is introduced into the anterior chamber (Figure 17-5B). The haptic assembly is snaked into the anterior chamber through the 3-mm incision (Figure 17-5C), and angle placement is verified with gonioscopy (Figure 17-5D). The silicone optic is loaded in the injector right side up with the attachment tabs folded upward (Figure 17-5E). The optic is injected into the anterior chamber (Figure 17-5F). A hook is then used to grasp each optic tab and engage it into its respective haptic (Figures 17-5G and 17-5H). This design not only allows insertion of an anterior chamber

Figure 17-1. I-CARE phakic IOL features a 5.75-mm optic and haptics with 0.9 mm “feet,” which minimize angle occlusion but provide good stability (courtesy of Alessandro Mularoni).

Figure 17-3. I-CARE phakic IOL showing good centration with dilated pupil (courtesy of Alessandro Mularoni).

Figure 17-2. I-CARE phakic IOL demonstrating minimal angle touch of haptic foot (arrow) (courtesy of Alessandro Mularoni).

Figure 17-4A. Kelman Duet implant features an asymmetric, tri- pod-shaped PMMA haptic and a separate 5.5-mm silicone optic (courtesy of Tekia Inc).

Figure 17-4B. The assembled Kelman Duet implant (courtesy of Tekia Inc).

Figure 17-5A. Implantation technique for Kelman Duet implant system. Three-mm and 1-mm incisions are made through clear cornea at the 3:00 and 9:00 positions, respectively (courtesy of Tekia Inc).

Figure 17-5B. Implantation technique for Kelman Duet implant system. Viscoelastic is introduced into the anterior chamber (courtesy of Tekia Inc).

Figure 17-5D. Implantation technique for Kelman Duet implant system. Angle placement is verified with gonioscopy (courtesy of Tekia Inc).

Figure 17-5C. Implantation technique for Kelman Duet implant system. The haptic assembly is snaked into the anterior chamber through the 3-mm incision (courtesy of Tekia Inc).

Figure 17-5E. Implantation technique for Kelman Duet implant system. The silicone optic is loaded in the injector right side up with the attachment tabs folded upward (courtesy of Tekia Inc).

Figure 17-5F. Implantation technique for Kelman Duet implant system. The optic is injected into the anterior chamber (courtesy of Tekia Inc).

Figure 17-5G. Implantation technique for Kelman Duet implant system. A hook is then used to grasp each optic tab and engage it into its respective haptic (courtesy of Tekia Inc).

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Figure 17-5H. Implantation technique for Kelman Duet implant system. A hook is then used to grasp each optic tab and engage it into its respective haptic (courtesy of Tekia Inc).

lens through a small incision, thus minimizing potential induced astigmatism, but also allows for subsequent exchange of the optic through the same small incision should the patient’s refractive error change in later years. Because this system is designed to treat high myopia, the ease of optic exchange may make the lens particularly attractive for young patients.

Clinical Results

European trials are underway, with six lenses placed by Jorge L. Alio, MD. All patients experienced an improvement in best-corrected visual acuity of one to two Snellen lines.2 US clinical trials are anticipated to begin in 2003.

ZSAL-4 PLUS

This lens is the fifth generation in an evolving series of vaulted, conventional, angle-supported anterior chamber lenses. The precursor to this series was the ZB lens, designed by Joly et al,3 and consisting of a modified Kelman 4-point fixation Multiflex lens with a biconcave optic. This lens was associated with high endothelial cell loss.4,5 Baïkoff modified the lens by increasing the lenscorneal space by 0.6 mm. The new lens, the ZB 5M, reduced the endothelial cell loss but encountered night vision problems and pupil ovalization.6,7

In an effort to avoid these complications, PerezSantonja and Zato developed a vaulted, convex-concave angle-supported lens. Figure 17-6 describes the first four iterations of the ZSAL lens design. The first iteration, ZSAL-1, was a prototype with the lens angulated anteriorly 15 degrees. Although the ZSAL-2 and 3 increased the angulation to 17 and 18 degrees, respectively, the posterior edge of the optic was still too close to the iris. The

Figure 17-6. The first 4 iterations of the ZSAL lens design. A. The first iteration, ZSAL-1, was a prototype with the lens angulated anteriorly 15 degrees. B. and C. Although the ZSAL-2 and 3 increased the angulation to 17 and 18 degrees, respectively, the posterior edge of the optic was still too close to the iris. D. The fourth generation, ZSAL-4, was changed to a plano-concave design with a 19-degree anterior angulation (reprinted with permission from Perez-Santonja JJ, Alio JL, Jimenez-Alfaro I, Zato MA. Surgical correction of severe myopia with an angle-sup- ported phakic intraocular lens. J Cataract Refract Surg. 2000;26(9):1288-1302).

fourth generation, ZSAL-4, was changed to a plano-con- cave design with a 19-degree anterior angulation.

Clinical Results

A recent study examined implantation of the ZSAL-4 lens in 23 eyes of 16 patients with a mean preoperative refractive error of -19.56 D (range: -16.75 to -23.25).8 Postoperatively there was a mean two line improvement in best corrected acuity. Mean endothelial cell loss was 4.18% at 24 months. The new design afforded a reduction in night halos but still suffered from pupil ovalization (Figure 17-7), IOL rotation, and low-grade postoperative uveitis. These remaining complications appear to be related to problems with the haptic-angle interaction. With this in mind, a fifth generation ZSAL-4 Plus was designed with a thinner connecting bridge between the optic and the first footplate and a thicker connecting bridge between both footplates to increase haptic flexibility and disperse compression forces against angle structures. In addition, the ZSAL-4 Plus features an effective optical zone enlarged to 5.3 mm from 5.0 mm in the previous version, hopefully affording further reduction in night time visual disturbances.8

SUMMARY

The IOL implant for cataract surgery underwent many iterations before optically effective, biocompatible, and surgically efficient foldable lenses were created. Indeed, the latest generation of IOLs are pushing the envelope of

Figure 17-7. Pupil ovalization 2 years after implantation of ZSAL-4 phakic intraocular lens (reprinted with permission from Perez-Santonja JJ, Alio JL, Jimenez-Alfaro I, Zato MA. Surgical correction of severe myopia with an angle-sup- ported phakic intraocular lens. J Cataract Refract Surg. 2000;26(9):1288-1302).

small incisions and new optic designs that correct higher order aberrations. Similarly, phakic IOL designs are still in their early generations, with many innovative modifications that will improve their safety and efficacy to come. In Chapter 21, we will examine some of these new designs as well as some innovative ideas for future generations of refractive IOLs.

Other Types of Phakic Intraocular Lenses 175

REFERENCES

1.Cimberle M. Corneal injectable phakic IOL demonstrates good stability and visual outcome. Ocular Surgery News [serial online]. Available at: http://www.osnsupersite.com. Accessed July 22, 2003.

2.Angelucci D. Innovation Spotlight: Two-piece phakic lens may correct high myopia. Eye World [serial online]. Available at: http://www.eyeworld.org. Accessed July 22, 2003.

3.Joly P, Baïkoff G, Bonnet P. Mise en place d’un implant negative de chamber anterieure chez des sujets phakes. Bull Soc Ophth Fr. 1989;89:727-733.

4.Mimouni F, Colin J, Koffi V, Bonner P. Damage to the corneal endothelium from anterior chamber intraocular lenses in phakic myopic eyes. Refract Corneal Surg. 1991;7:277-281.

5.Saragoussi JJ, Cotinat J, Renard G, et al. Damage to the corneal endothelium by minus power anterior chamber intraocular lenses. Refract Corneal Surg. 1991;7:282-285.

6.Baïkoff G, Arne JL, Bokobza Y, et al. Angle-fixated anterior chamber phakic intraocular lens for myopia of -7 to -19 diopters. J Refract Surg. 1998;14:282-293.

7.Alio JL, de la Hoz F, Perez-Santonja JJ, et al. Phakic anterior chamber lenses for the correction of myopia; a 7-year cumulative analysis of complications in 263 cases. Ophthalmology. 1999;106:458-466.

8.Perez-Santonja JJ, Alio JL, Jimenez-Alfaro I, Zato MA. Surgical correction of severe myopia with an angle-support- ed phakic intraocular lens. J Cataract Refract Surg. 2000;26:1288-1302.

We began using the technique of bioptics in 1996 and have continuously adjusted the indications since then according to our results.

In 1995 we chose to not use anterior chamber lenses any more and to only employ the phakic posterior chamber intraocular lens (IOL) (Implantable Contact Lens [ICL]) (STAAR Surgical AG, Nidau, Switzerland) (Figure 18-1). We used to correct residual astigmatism and myopia with radial keratotomy or arcuate keratotomy. Then we began to perform ablations with laser in-situ keratomileusis (LASIK) so we also used this to correct residual defects after ICL.

After these first cases of bioptics, we have widely expanded the technique. Using a foldable lens implanted through a 2.8- to 3.0-mm incision, the astigmatism induction is minimal, so we can propose to the patient a second procedure to treat the pre-existing astigmatism. Because we observe visual acuity quality and quantity improvement in our patients, we often offer bioptics to patients after their preoperative examination.

Initially, we thought this combined technique was a very good option for those young patients with extreme refractive errors, avoiding the complications related to clear lensectomy.

We have shared our experience in other publications and congresses, and we have demonstrated that this technique presents significant advantages. It is essential to properly select the patients, and careful surgical technique in experienced hands achieves the desired results.

Bioptics implies two different procedures in two different planes of the eye, so patient inclusion criteria depends on many factors.

•The first procedure, intraocular, is the ICL implantation

•The second procedure, corneal, is LASIK, laser epithelial keratomileusis (LASEK), or photorefractive keratectomy (PRK)

Usually, we perform this surgery in patients who are older than 19 years of age with refractive stability, excluding severe general pathologies, such as immunosuppression or diabetes, vitreoretinal pathologies, cataract, glaucoma, uveitis, or other intraocular inflammatory disease.

To perform the superficial corneal procedure, it is necessary to have proper pachymetry and to exclude any patients with severe dry eye; corneal dystrophy; corneal degenerations, such as keratoconus; and infections, such as herpes.

We have observed that hyperopic patients achieve refractive stability at an earlier age than myopic patients.

We utilize this procedure in patients with a spherical equivalent larger than -10 diopters (D) in myopic eyes and more than +5.00 D in hyperopic ones.

Although some patients with high myopia (-10 to -15 D) have been corrected with laser surgery, we prefer to correct patients with high myopia with this double procedure because a laser ablation of this magnitude will result in a small transition and optical zone. Laser consumes corneal tissue, and in high corrections can decrease the

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Figure 18-1. ICL V4 model.

quality of vision. Some eyes may not have enough corneal tissue to retreat in the case of undercorrection without a high risk of inducing iatrogenic ectasia.

When using laser in hyperopic patients with more than +5.00 D or corneal curvature superior to 48.00 D, we can generate tear film disruption, changes in stromal architecture, and corneal irregularity that diminishes visual quality and comfort.

In hyperopic patients we have to keep in mind their age and the potential degree of their accommodation influencing the refraction. We always have to perform the refraction under cycloplegia because young patients usually have strong accommodation. When accommodation is significant, we can induce an accommodative myopic result in cases in which we correct the whole refractive error. This situation is very uncomfortable for the patient. In patients with strong accommodation we prefer to use LASIK to correct only a part of the refractive error based upon two measurements: subjective and cycloplegic refraction (see Case Report: Accommodation in a Hyperopic Patient on p. 179).

The situation mentioned below and results obtained with new and improved software for laser treatment of hyperopia have led us to decrease the use of implants in hyperopic patients. In general, we can satisfy all patient needs using only LASIK. In the above case we tried to correct the entire hyperopic error, but the patient continued to have significant levels of accommodation inducing measured myopia. Nowadays, in young patients we do not correct the whole hyperopic defect to prevent this problem.

In this group of patients we have in mind work activity. In artists or office workers (ie, those who rely on near vision), residual myopia can be helpful, but in pilots or drivers this myopia can be dangerous and uncomfortable.

It is also very important to not forget the anterior chamber depth and white-to-white (W-to-W) measurement when we select the surgical procedure. Intraocular implants are not recommended in patients with shallow anterior chambers and small eyes.

There are some patients that have special characteristics and that do not meet the parameters mentioned above. In this group we only implant the ICL and we do not perform LASIK. We can classify them as follows:

A.Patients with thin corneas. Within this group we include patients that primarily present with low pachymetry and patients with postsurgical reduction of corneal thickness (eg, eyes previously operated with laser that present with regression or in which the initial refraction increases).

B.Forme fruste keratoconus. In this group of patients, as in keratoconus, we can correct the spherical part of their refractive defect with the phakic IOL. The astigmatism cannot be corrected with laser so we prescribe glasses. This technique allows reduction of the total defect, which is especially useful in patients with contact lens intolerance and discomfort with glasses due to the severity of the refraction.

In situations that are not at risk of corneal ectasia, it is possible to employ arcuate incisions, adding one suture 90 degrees away from the incisions to increase the corrective effect of the incisions.

C.Keratoconus status I or II, stable, or slowly progressive. This group presents the same limitations as patients with forme fruste keratoconus, but another option is to put in intracorneal rings to correct residual astigmatism.

D.Children with high anisometropia and contact lens intolerance. Although we try to avoid this surgery in very young patients, this procedure could be an interesting alternative to prevent amblyopia. In these cases, if there is a residual defect, the second part of the surgery (laser) is performed when the child reaches refractive stability (see Case Report: Child With Anisometropia on p. 179).

E.Postepikeratophakia. The residual corneal bed after this technique typically does not allow the use of laser to correct myopic residual refraction even though it is typically low.1

Additionally, in patients that have had penetrating keratoplasty we utilize bioptics to correct high residual refractive defects. In these cases the graft has to be stable with no signs of rejection. We proceed first with the ICL implant, having evaluated the corneal endothelium with specular microscopy and trying to perform a very careful and quick surgical procedure in order to minimize trauma to the cornea. We perform the flap 6 months or more after removing all graft stitches. One month later we measure the refraction and proceed with the laser ablation. We perform LASIK in two steps because the fibrous ring in the graft-host interface sometimes induces refractive changes, especially astigmatism.

In our experience, no patient has presented corneal rejection after both procedures.

PREOPERATIVE WORKUP

We first perform UCVA, BCVA, keratometry, corneal topography (anterior and posterior corneal surface) with the Orbscan topographer (Orbtek Inc, Salt Lake City, Utah), ultrasonic and slit lamp pachymetry (CompuScan, P-Storz Instrument Company, St. Louis, Mo), noncontact specular microscopy (Konan Noncon Robo, Hiogo,

Japan), ultrasonography and ecometry, biomicroscopy, applanation tonometry, anterior segment infrared picture (Anterior Segment Analysis System-EAS 1000, Nidek, Japan), dilated eye fundus, contrast sensitivity test, and corneal sensation evaluation. If necessary, gonioscopy and B-scan ultrasonography can be performed. Prior to the implant, we also require a routine physical examination and blood analysis, coagulation, and EKG.

As we said above, it is very important to observe anterior chamber depth and W-to-W measurements in hyperopic eyes in order to avoid complications after implanta-