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

Figure 10-1. A sutured wound after Artisan IOL implantation.

THE FIRST POSTOPERATIVE VISIT

The first postoperative visit involves removing the shield and cleaning any debris on the eyelids. The author instructs the patient on keeping his or her eyelid margins clean. The author likes to follow the cleaning of the eyelids with a drop or two of topical antibiotic.

It is important to tell the patient that blurry vision is not unusual. The author tells them that he will do a good exam and make sure everything is just fine but not to worry about blur. The author has also told patients preoperatively that not everyone gets their final vision with one phakic IOL surgery and that they may need a laser enhancement or an astigmatic keratotomy postoperatively. With this candid preoperative discussion, they are not so worried if they have some blur the first postoperative day.

A brief history is first taken as far as what his or her comfort level and vision is. The uncorrected vision is checked with and without pinhole by the staff. If the vision is reasonable (ie, 20/60 or better), the staff will also check the IOP with a Tonopen (Medtronic, Jacksonville, Fla) after instillation of fresh topical anesthesia drops. These results are documented in the record and then the author sees the patient. If the IOP is elevated, it could be retained viscoelastic, malignant glaucoma, or pupillary block glaucoma. These must all be kept in mind when treating a postoperative IOP rise.

The author is positive and upbeat with the patient no matter what his or her mood is. He also wants to remain very patient if he or she is at all frustrated that his or her vision is not where he or she is hoping it would be. The author knows that the patient will feel better after a thorough exam and explanation. If the vision is not good, the author likes to do a refraction (if there is not much corneal edema) to see if the reduced vision is correctable with lenses. If the patient has blurry uncorrected vision, this

Figure 10-2. A sutureless wound after STAAR ICL placement.

step (ie, the refraction) can be very comforting to him or her. In actuality, phakic IOL surgery is typically more atraumatic than cataract surgery and there should be minimal corneal edema. Thus, these patients will often have day 1 postoperative vision that has them quite excited about this whole process. Phakic IOL surgery is one of the most gratifying surgeries the author performs.

The author first reviews the vision and IOP measurements and then does a slit lamp exam. Just prior to the slit lamp exam, he looks at the patient’s external orbit to assess for any redness or swelling that could imply an allergic reaction to the povidone-iodine prep or to the tape used on the shield. The author looks at the corneal wound with the slit lamp and makes sure it is watertight. If it is an Artisan lens (Ophtec BV, Groningen, Netherlands), there are typically sutures that are assessed for tension also (Figure 10-1). In the case of a foldable phakic IOL, such as the Implantable Contact Lens (ICL) (STAAR Surgical AG, Nidau, Switzerland), these lenses can often be placed in a sutureless fashion and thus assessing for water tightness is the main portion of the wound exam (Figure 10-2). After assessing the wound, the author looks at the cornea, starting from the surface and going in a posterior direction. The epithelium is examined and then the stroma. If there is corneal edema, it is graded on a I to IV scale. Descemet’s membrane is then evaluated to make sure it is not detached due to a complication during surgery. The endothelium is examined to see if there was any endothelial touch during surgery.

After assessing the cornea, examine the anterior chamber for depth and cellular reaction. Because all phakic IOLs can cause pupillary block, it is important to check at the first day postoperative visit that this has not happened by

Figure 10-3. Two patent PIs are very important with any phakic IOL. Mild pupillary ovalization can be seen early in the postoperative period of the Artisan phakic IOL due to extreme miosis from the carbachol.

Figure 10-4. The STAAR ICL is vaulted to reduce contact between the natural lens and the IOL.

Figure 10-6. Scheimpflug photo of the STAAR ICL verifies vault of the IOL over the natural lens.

Figure 10-5. Slit lamp exam of the distance between the posterior surface of the STAAR ICL implant to the anterior surface of the crystalline lens. Note the appropriate distance between the two.

checking the IOP and performing a quality slit lamp exam. A pressure elevation can occur after phakic IOL implantation from retained viscoelastic or pupillary block can occur from a nonpatent peripheral iridectomy (PI). If the IOP elevation is high enough and prolonged enough, an atonic pupil can occur, with resultant iris stromal atrophy and permanently dilated pupil.12,15,16 Assessing the PI with retroillumination is important because the surgeon has to make sure it is patent (Figure 10-3). A laser PI is typically smaller than a surgical PI and assessing patency can be more challenging. Nevertheless, it is very important that the red reflex be seen through the laser PI upon retroillumination. If it cannot be documented that the PI is patent, it is suggested that either the PI is made larger or a laser PI is created in a different location. Some surgeons will rou-

tinely place two PIs at separate quadrants in the superior iris to further minimize the risk of a nonpatent PI, creating an angle closure glaucoma attack.

After assessing depth and patency of the PI, assess and document the cellular (flare and cell) reaction. There is typically not much inflammation with phakic IOLs as compared to cataract surgery. The author does like to focus further back and make sure there is no vitreous reaction.

In the case of the Artisan lens, the author likes to assess the distance from the anterior surface of the implant to the posterior cornea. He also likes to assess the distance between the posterior surface of the IOL to the anterior surface of the crystalline lens. If the lens is a posterior chamber IOL, such as the STAAR ICL, it is beneficial to examine the distance between the implant and the crystalline lens (Figures 10-4, 10-5, and 10-6).

At this point, the centration of the implant is documented (Figure 10-7). The pupil center can shift based on the IOP. Therefore, if the pressure is very low after surgery, the IOL may not be as nicely centered as thought at the end of surgery. This is why intraoperatively the author likes to make sure he has normalized the IOP before making his final assessment on implant centration.

It may be noted at the first day postoperatively that with the Artisan lens the pupil is not totally round in all cases. This is particularly true if the pupil is still constricted from the miotic used intraoperatively and the postoperative inflammation. This is not unusual and is typically

Figure 10-7. A well-centered Artisan lens.

from the fact that the iris is being held (ie, “enclavated”) by the haptics of the Artisan lens. Hence, in the meridian of the enclavation, the pupil cannot constrict as much as the rest of the pupil (Figure 10-8). When the pupil is physiologic in size, it should look normal in shape unless too much iris tissue was enclavated.

It is also important with a foldable IOL to document that there are no tears in the implant since this can occur during placement into the eye from the folder. Making sure there is no foreign material that was inadvertently placed into the eye during surgery is also important at the slit lamp.

The author then likes to finish the slit lamp exam by looking at the crystalline lens to make sure it is nice and clear with no evidence of trauma. If there was lenticular touch during surgery, a localized opacity in the anterior lens can occur. These are typically localized and nonprogressive and are more common in a posterior chamber phakic IOL. Nevertheless, any new lens opacity needs to be followed to assess whether or not it will be progressive.

After a complete slit lamp exam, the results are communicated to the patient and the postoperative instructions are then reviewed to make sure the patient is following them well.

THE 1 WEEK POSTOPERATIVE VISIT

If everything looks routine at the first postoperative visit, the author will see the patient at 1 week postoperatively with instructions to call if anything seems unusual (eg, pain, redness, or decreased vision) so that he can see them immediately. The main worry is the development of any endophthalmitis in the first week. If this does occur, there should not be a delay in diagnosis or treatment.

At the 1 week visit the author takes a history to see how the vision is doing and how comfortable the eye feels. He

Figure 10-8. The iris is being held (ie, “enclavated”) by the haptics of the Artisan lens and in the meridian of the enclavation; therefore, the pupil cannot constrict as much as the rest of the pupil, which can cause pupil irregularity with constriction. An oval shape to the pupil is typically not noticed at physiologic pupil size unless too much iris tissue was enclavated.

also reviews the medication schedule and makes sure the patient is wearing his or her shield when he or she sleeps. The author also rechecks the vision and performs a manifest refraction. It is of note that it is not unusual for the best-corrected visual acuity (BCVA) to actually improve after phakic IOL placement. This is felt to be, at least in part, due to image magnification.14

In general, everything that was performed at the slit lamp at 1 day postoperatively is repeated 1 week postoperatively. The IOP is checked again to make sure there is not an early steroid response. It is expected that any cellular response that was noted at the 1 day visit is less at this visit. If there is an increase in anterior chamber reaction and the vitreous is quiet with no other signs of infection, the steroid drops are increased in frequency and consideration is given to putting the patient on a stronger steroid drop.

If there is anything unusual detected at the 1 week visit, a repeat visit is scheduled in the next days to weeks to make sure it is not progressive. Otherwise, if the exam is routine at this visit, the patient is instructed to use the antibiotic drops until he or she is 10 days postoperative and to use the steroid drops in a gradual taper for 2 weeks.

It is worth noting that if the patient is blurry at this visit and is having a hard time driving or working, a temporary lens prescription can be provided to help them function.

THE 1 MONTH POSTOPERATIVE VISIT

It is at this visit that the patient is typically off all drops and a quality assessment can be done as to the final outcome of the procedure. If the IOL was an Artisan lens,

sutures were placed, and there is residual cylinder, selective suture removal can begin if the positive cylinder is in the axis of the sutures. The author typically waits 2 weeks to see the full effect of the suture removal before considering whether or not to remove another.

If corneal edema is persistent at this visit, one needs to consider the health of the corneal endothelium. If IOP is normal, there is no persistent inflammation, and there is still corneal edema, an endothelial cell count is indicated to assess number and morphology of the endothelial cells. With modern day surgical technique and quality phakic IOLs, this should be a rare occurrence.

If any lens opacities were noted at previous visits, they should be followed closely to assess whether or not they are progressive.17 The Lens Opacity Classification System (LOCS) III can be useful in following early lens opacities and for documentation.18 In the STAAR ICL United States clinical trials, a change in LOCS III score of more than one unit from baseline was felt to be indicative of significant lens change.19

After the refractive error is stable, one can consider whether or not an enhancement is indicated.

WHEN TO ENHANCE

If a patient has significant cylinder preoperatively, an astigmatic keratotomy (AK) can be performed preoperatively, intraoperatively, or postoperatively. AK is very effective in lessening astigmatism before or after phakic IOL placement. One can also place the incision at the time of lens implantation in the steep axis of the cylinder to lessen the astigmatism somewhat.

When to perform an astigmatic keratotomy procedure is dependent on the approach taken for the IOL placement. If it is an Artisan lens and a 6.0-mm incision is used with the wound sutured, the author suggests waiting until 3 months after suture removal. This is done with a few visits in a row separated by at least a few weeks to document that the refractive cylinder is not changing. If it is a smallincision, sutureless procedure, such as with the STAAR ICL or other foldable phakic IOL, then 3 months postoperatively is a reasonable time to consider AK. Again, refractive stability should be documented.

If one chooses to perform a spherical (with or without cylinder) laser enhancement with PRK or LASIK, one should wait a bit longer after the phakic IOL procedure. The author suggests waiting at least 6 months to perform PRK and 1 year to perform LASIK after an Artisan procedure. He would also suggest waiting 3 months for PRK and 6 months for a LASIK enhancement after a small incision sutureless procedure.

One also needs to keep in mind that certain tracking devices, such as the tracker on the LADARVision laser

(Alcon, Fort Worth, Tex) track the pupil edge and can be affected by the reflections of an implant. If this laser cannot track, then the laser enhancement cannot be performed.

LONG-TERM CONSIDERATIONS

As studies continue to be conducted on the long-term risks of phakic IOLs, there appears to be good predictability with a low risk of major complications.13,20,21 As with any intraocular surgery, the long-term effects on the retina are important to consider. Myopes are already at an increased risk of developing retinal detachment when compared to the general population. Myopes are at an even greater risk of retinal detachment after intraocular surgery when compared to postoperative nonmyopic individuals.

CONCLUSION

Phakic IOLs have made tremendous progress over the past 20 years in terms of safety and efficacy. With proper attention to details, including postoperative care, the risk- to-benefit ratio becomes very acceptable for the individual desiring refractive surgery. By following the above principles for phakic IOL postoperative care, and with the surgeon’s experience with the postoperative care of the cataract patient, these patients should do quite well in the long run. Phakic IOL surgery is coming of age, becoming a mainstream option for patients seeking quality surgical vision correction.

REFERENCES

1.Hersh PS, Steinert RF, Brint SF. Photorefractive keratectomy versus laser in situ keratomileusis: comparison of optical side effects. Summit PRK-LASIK Study Group. Ophthalmology. 2000;107:925-933.

2.Holladay JT, Dudeja DR, Chang J. Functional vision and corneal changes after laser in situ keratomileusis determined by contrast sensitivity, glare testing, and corneal topography. J Cataract Refract Surg. 1999;25:663-669.

3.Goes FJ. Photorefractive keratectomy for myopia of -8.00 to -24.00 diopters. J Refract Surg. 1996;12:91-97.

4.Davidorf JM, Zaldivar R, Oscherow S. Results and complications of laser in situ keratomileusis by experienced surgeons. J Refract Surg. 1998;14:114-122.

5.Holland SP, Srivannaboon S, Reinstein DZ. Avoiding serious corneal complications of laser assisted in situ keratomileusis and photorefractive keratectomy. Ophthalmology. 2000;107:640-652.

6.Geggel HS, Talley AR. Delayed onset keratectasia following laser in situ keratomileusis. J Cataract Refract Surg. 1999;25:582-586.

7.Tsai RJ. Laser in situ keratomileusis for myopia of -2 to -25 diopters. J Refract Surg. 1996;13:S427-S429.

8.Knorz MC, Liermann A, Seiberth V, et al. Laser in situ keratomileusis to correct myopia of -6.00 to -29.00 diopters. J Refract Surg. 1996;12:575-584.

9.Asetto V, Benedetti S, Pesando P. Collamer intraocular contact lens to correct high myopia. J Cataract Refract Surg. 1996;22:551-552.

10.Zaldivar R, Davidorf J, Oscherow S. Posterior chamber pha-

kic intraocular lens for myopia of -8 to -19 diopters. J Refract Surg. 1998;14:294-305.

11.Sanders DR, Brown D, Martin R, et al. Implantable contact lens for moderate to high myopia. Phase I FDA clinical study with 6 month follow-up. J Cataract Refract Surg. 1998;24:607-611.

12.Baikoff G, Colin J. Intraocular lenses in phakic patients.

Ophthalmol Clin North Am. 1992;4:789.

13.Baikoff 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.

14.Guell JL, Vazquez M, Gris O, et al. Combined surgery to correct high myopia: iris-claw phakic intraocular lens and laser in situ keratomileusis. J Refract Surg. 1999;15:529-537.

15.Fechner PU, Strobel J, Wiechmann W. Correction of myopia by implantation of a concave Worst iris-claw lens into phakic eyes. Refract Corneal Surg. 1991;7:286-298.

16.Fechner PU. Correction of myopia by implantation of minus optic (Worst iris-claw) lenses into the anterior chamber of phakic eyes. Eur J Implant Refract Surg. 1993;5:55.

17.Fink AM, Gore C, Rosen E. Cataract development after implantation of the STAAR Collamer posterior chamber phakic lens. J Cataract Refract Surg. 1999;25:278-282.

18.Chylack LT Jr, Wolfe JK, Singer DM, et al. The Lens Opacities Classification System III. The Longitudinal Study of Cataract Study Group. Arch Ophthalmol. 1993;111:831836.

19.Sanders DR, Vukich JA, Doney K, Gaston M, Implantable Contact Lens in Treatment of Myopia Study Group. U.S. food and drug administration clinical trial of the implantable contact lens for moderate to high myopia. Ophthalmology. 2003;110:255-266.

20.Fyodorov SN, Zuev VK, Tumanyan ER, et al. Analysis of long-term clinical and functional results of intraocular correction of high myopia. Ophthalmosurgery. 1990;2:3-6.

21.Menezo JL, Cisneros A, Hueso JR, et al. Long-term results of the surgical treatment of high myopia with WorstFechner intraocular lenses. J Cataract Refract Surg. 1995;21:93-98.

INTRODUCTION

Phakic intraocular lenses (IOLs) are refractive devices used primarily for the elective correction of higher levels of ametropia. Because phakic IOLs are generally used in an elective capacity and in a setting where the patient may have several surgical as well as nonsurgical options, a clear understanding of the results is imperative. With a complete understanding of the known outcomes, including risks and benefits, the patient and surgeon can make an informed decision concerning phakic IOLs and with regard to other refractive options.

Implanting an anterior chamber IOL in a phakic eye to correct high myopia was developed and then abandoned by Strampelli1 and Barraquer2 in the 1950s. Interest has recently been revived by Fechner, van der Heijde, and Worst,3 who used an iris-fixated lens, and by Joly, Baïkoff, and Bonnet,4 who used an angle-supported lens whose style resembled the Kelman-style multiflex anterior chamber lens. Many phakic IOL designs have emerged since 1983. Today, the designs can be classified according to the way that they are fixated in the eye: anterior chamber angle, iris, and posterior chamber.

The general comparison of the major phakic IOLs are outlined by virtue of several tables presented in this chapter. It is exceedingly difficult to draw a fair, direct, and accurate comparison between different designs of phakic IOLs. Frequent design revisions mean that a particular lens model is not implanted in any great numbers or for any great length of time, as newer revisions of the lens are introduced that correct the weaknesses of the preceding

generation of lenses. In fact, in many of the reviewed papers, several versions of the same lens are grouped for a collective analysis of the refractive outcomes and complications, with some papers making no mention whatsoever of the version of the lens implanted. None of the papers directly compare any two lenses currently in production. No lens is currently approved for use by the US Food and Drug Administration (FDA).

MAJOR PHAKIC

INTRAOCULAR LENSES

Posterior Chamber

The Implantable Contact Lens

The Implantable Contact Lens (ICL) is a posterior chamber lens based on the original design introduced by Fyodorov5 and developed by STAAR Surgical AG (Nidau, Switzerland).6 The first ICLs made by STAAR Surgical were implanted in human eyes in Europe in 1993,6,7 and more than six distinct lens designs have been manufactured and implanted during clinical studies.6,8,9

The lens has a single-piece plate haptic design and is made of a porcine collagen/hydroxymethacrylate copolymer (34% water and <0.1% collagen). The optic of the lens is 5.5 mm in diameter and is manufactured in an anterior concave/posterior concave design for correcting myopia and an anterior convex/posterior concave design for correcting hyperopia. The central optic thickness of the

108 Chapter 11

myopic model is only 60 µm, and the optical zone varies between 4.5 and 5.5 mm, depending on the strength of the lens. The latest, and currently only produced, model to correct myopia is the ICM V4 (STAAR Surgical, Monrovia, Calif). This new ICL model was recently introduced to increase the gap between the ICL and the crystalline lens and is presumed to offer better vaulting over the crystalline lens than the previous model (ie, ICM V3). This vaulting is obtained by decreasing the radius of curvature of the posterior face of the ICL. Implantation of this lens began in November 1998. The current model to correct hyperopia is the ICM V3 (STAAR Surgical, Monrovia, Calif).

The foldable lens may be implanted through a clear corneal incision as small as 2.8 mm and under topical anesthesia. Under the protection of viscoelastic, the lens initially unfolds in the anterior chamber with the haptics residing in the anterior chamber angle. With the aid of a widely dilated pupil and simple specialized instruments, each footplate of the plate haptic is tucked into the posterior chamber. Atraumatic surgical technique places the lens in the ciliary sulcus without touching the native, crystalline lens. The myopic lens is manufactured in powers of -3 to -20 D, and the -20 D lens corrects about 15 D of myopia. The hyperopic lens powers range from +1.5 to +20 D, with the +20 D lens correcting about +12 D at the spectacle plane.

Success with the lens depends in large part on the vaulting of the phakic IOL over the crystalline lens. Ideally, the vaulting of the lens is about 100% of corneal thickness, or approximately 500 µm. This vaulting is governed by the length of the phakic IOL and the sulcus-to-sulcus distance. Currently, no good method exists to accurately measure the sulcus diameter; therefore, adjusted white-to-white measurements are used as a surrogate. The lens is manufactured in total lengths ranging from 11 to 13 mm. Choosing a lens that is too short for the required sulcus- to-sulcus span can result in a decreased or absent vault over the crystalline lens. Subsequent cataract formation can result from either chronic intermittent touch to the anterior capsule or blocking of aqueous flow that bathes the anterior aspect of the crystalline lens.10,11 Choosing a lens that is too long for the eye can result in chronic iris chafing and attendant pigment liberation with possible pigmentary glaucoma. A lens that is too long for the eye can also vault the phakic lens into the pupil, increasing the risk of pupillary block glaucoma or angle crowding. All phakic IOL manufacturers recommend either an iridectomy or an iridotomy to prevent pupillary block glaucoma. Clinicians, anticipating that all the aqueous will flow through the defects, have learned to place two large iris defects. Placing them 90 degrees apart guards against one of them being occluded by the lens haptic should the lens rotate.

US FDA clinical evaluations started in 1997, and the myopic and hyperopic ICL models are currently in Phase

III FDA trials.9 A toric ICL is also under US FDA clinical trials.

The Phakic Refractive Lens

The Phakic Refractive Lens (PRL), manufactured by Medennium, Inc (Irvine, Calif) and distributed by CIBA Vision (Duluth, Ga), has been in development since 1987. The PRL has a single-piece plate design and is made of silicone. Like the ICL, the PRL is designed for implantation in the posterior chamber for the correction of myopia and hyperopia. Its distinction is that it is designed to float on the crystalline lens; there are no feet to its plate haptics.

The myopic PRL model 101 is 11.3 mm long with an optical zone that varies from 4.5 to 5.0 mm according to the lens’ dioptric power. The hyperopic PRL model 200 has an overall length of 10.6 mm with an optical zone of 4.5 mm. Hyperopic and myopic models are 6 mm wide. The thickness of the PRL optic is dependent on the dioptric power, with a maximum of 0.6 mm. The myopic lens is manufactured in powers ranging from -3 to -20 D and corrects up to -23 D. The hyperopic model is made from +3 to +15 D and corrects a maximum of +11 D. An older myopic model (PRL 100) with a 10.8 mm length used in some of the studies is not available today.

The PRL is introduced into the posterior chamber through a 3.0- to 3.5-mm clear corneal incision and stabilized between the iris and the crystalline lens without contacting the anterior capsule.

The lens has secured Europe’s Conformité Européenne (CE) mark, and US FDA Phase III clinical investigations are ongoing.

Iris-Fixated

The Artisan Lens

The original iris-claw lens was developed by Worst and was designed to be used for the correction of secondary aphakia after cataract surgery. The lens has been implanted in approximately 300,000 aphakic eyes worldwide after being introduced in 1978. However, these early iris-fixat- ed lenses had a propensity to form synechiae to the mobile aphakic pupillary margin and, thus, carried an increased risk of cystoid macular edema and corneal decompensation.12 By 1986, Worst and Fechner modified the existing iris-claw lens into a negative-powered biconcave lens to be used in highly myopic phakic eyes.3,13 At that time, this new Worst-Fechner claw lens had an optic diameter of 4.5 mm, and a few hundred of these lenses were implanted with good refractive results.3,13-16 In 1991, the design of the optic was altered to an anterior convex/posterior concave shape to increase safety, and the diameter of the optic was increased to 5 mm to reduce halos and glare. This new lens, called the Worst myopia claw lens, has been implanted ever since.17,18 In 1997, an additional

model with a 6-mm optic diameter was added to address potential glare and halos in patients with large pupils. In 1998, the name of the lens was changed to the Artisan myopia lens. There was, however, no change in lens design; it still has an anterior convex/posterior concave optic.

The current Artisan design is a one-piece IOL manufactured of polymethylmethacrylate (PMMA) with an ultravi- olet-blocking material. The lens is marketed by Ophtec USA Inc (Boca Raton, Fla). The total length of the Artisan lens is 8.5 mm. The optic vaults approximately 0.87 mm anterior to the iris, allowing clearance from both the anterior lens capsule and the corneal endothelium. Current Artisan lenses are models 206, which has a 5-mm optic and is available in powers -3 to -23.5 D, and model 204, which has a 6-mm optic and is available in powers -3 to -15.5 D. The hyperopic model 203, with a 5-mm optic, is manufactured in powers +1 to +12 D. A hyperopic model with a larger diameter optic is under development.

The new Artisan Toric model was designed to correct spherical and cylindrical errors simultaneously. So that surgeons can implant the Toric model in the horizontal position to which they are accustomed, two models are available. In model A, the toric axis runs parallel to the claws for correction of with-the-rule astigmatism. In model B, the toric axis runs perpendicular to the claws for correction of against-the-rule astigmatism. Available powers can correct -3 to -20.5 D of myopia or from +2.0 to +12.0 D of hyperopia along with 2.0 to 7.5 D of astigmatism (power increments are 0.5 D). The Artisan Toric phakic IOL measures 8.5 mm in overall length and features a 5-mm anterior convex/posterior concave optic.

Generally, a corneal, limbal, or scleral incision is fashioned under retrobulbar anesthesia. Under the protection of viscoelastic and a pharmacologically constricted pupil, a portion of midperipheral iris is drawn into the diametri- cally-opposed claws of the phakic IOL in a process called enclavation. Enclavation is an ambidextrous procedure (ie, the right haptic is enclavated with the right hand, and the left haptic is enclavated with the left hand) and one in which care must be taken not to damage the corneal endothelium, iris insertion, or lens.

The incision needed to insert the Artisan lens is slightly larger than the diameter of the optic. Approximately a 5.5-mm incision for the 5-mm optic and 6.5 mm for the 6-mm optic is required.19 Adjusting the anterior-posterior placement of the incision as well as adjusting the tension on the sutures used to close the incision are means by which preoperative astigmatism can be reduced. The potential for increasing astigmatism or inducing irregular astigmatism also exists.

Clinical investigation of the Artisan lens began in October 1997 in the United States under FDA supervision; both myopic and hyperopic models are in Phase III. The Artisan lens carries Europe’s CE mark.

Anterior Chamber

The NuVita MA20

There are two major anterior chamber lenses in production that have published outcomes—the NuVita MA20 (Bausch & Lomb Surgical/Chiron Vision, Rochester, NY) and the ZSAL-4 (Morcher GmbH, Stuttgart, Germany).

In 1987, Baïkoff and Joly4,20,21 modified the Kelman Multiflex IOL used in cataract surgery into a negative biconcave lens for the correction of high myopia. This first generation IOL, called the Baïkoff ZB lens, was associated with an unacceptably high incidence of endothelial cell loss and with marked changes in endothelial cell morphology.12,22,23 These changes were probably caused by excessive contact between the edge of the IOL optic and adjacent corneal endothelium; a separation of only 0.71 to 1.50 mm in one study.12 Because of these endothelial problems, Baïkoff modified the design to reduce the IOL’s proximity to the cornea. The subsequent design, the ZB 5M lens, gained approximately 0.5 mm in IOL-cornea spacing in comparison with the first model.12,24,25 The ZB 5M model was used from 1990 through 1997. Numerous subsequent clinical studies26-28 demonstrated reasonable optical results and less long-term endothelial cell loss with this lens. Continued pupillary ovalization (22.6%), glare complaints (12.5%), and pupillary block (3.8%) prompted the next generation of lenses.26

To further reduce the complications, modifications were made to create the NuVita MA20. This phakic IOL employs a 5-mm optic with a treated posterior edge and a 4.5-mm optical zone to address refracted glare. The optic has an anterior convex/posterior concave design. The haptics loops have been redesigned to reduce pressure in the angle that may lead to pupil ovalization. Vaulting has been changed from a step vault to a straight continuous angulation to further minimize potential contact between the footplate and the iris, and haptic footplates better conform to iridocorneal angle geometry to disperse compression forces over a broader area.

An angle-supported phakic IOL is attractive because of the ease with which it can be inserted in the anterior chamber and fixed in the angle. Insertion of an angled-sup- ported phakic IOL should be familiar to a surgeon experienced with the insertion of an anterior chamber pseudophakic IOL. Because of their nonfoldable PMMA design, insertion of the NuVita lens requires a 5.5-mm incision. As with the Artisan lens, placement of the incision and the nature by which it is closed can reduce preoperative astigmatism or induce irregular astigmatism.

NuVita IOLs were implanted in an experimental clinical trial in 1997 and are now commercially available in Europe and South America. Bausch & Lomb Surgical has not yet brought this style of phakic IOL to the United States.