Ординатура / Офтальмология / Английские материалы / The Art of Phacoemulsification_Mehta, Alpar_2001

IMPLANTATION TECHNIQUES OF ACRYLIC FOLDABLE IOL & ITS CLINICAL RESULTS 283

Fig. 26.48: An eye at 3 years after the implantation of acrylic foldable IOL. While anterior capsular margin is slightly opaque and there are some cell proliferation outside the optic, posterior capsule retains complete clarity

posterior capsule but the anterior capsule remains clear for years (Figs 26.47 and 48).

With the acrylic foldable IOL, pearl type PCO occurs in some cases (Fig. 26.49), but fibrosis type PCO is rarely seen. In general, pearl type PCO is easier to dissect with Nd:YAG laser than fibrosis type PCO. Moreover, acrylic foldable IOL is highly resistant to the Nd:YAG laser damage.1 Thus, posterior capsulotomy is safely performed on acrylic foldable IOL with the least risk of “pit” formation on the optic, which is a rather common observation with silicone IOLs.19

Centration of the acrylic foldable lens is also excellent. Figure 26.50 demonstrates the degree of decentration measured in 18 silicone, 23 PMMA and 22 acrylic foldable IOLs at 6 months, postoperatively.

These features of acrylic foldable IOL, i.e. lower PCO rate and better centration, seem to be attributable, at least in part, to the strong adhesion of this lens to the lens capsules. An experimental study has shown that acrylic foldable IOL adhered to the capsule most strongly, followed by PMMA IOL, while silicone IOL showed no adhesion.17 Histologic observation suggested that acrylic foldable IOL inhibited the lens epithelial cells (LECs) and lens fibers at the optic edge from proliferating and migrating toward the center of the posterior capsule (Fig. 26.51).

Adhesion of the anterior capsule to IOL optic is another factor (Fig. 26.52). A recent study has shown that a phenomenon called capsular capture, in which parts of the IOL optic slip out of the capsular bag and the edge of the anterior

286 THE ART OF PHACOEMULSIFICATION

On the other hand, strong, thick anterior capsular fibrosis and phimosis may affect capsular shrinkage and result in tighter wrapping of the capsular bag around the entire IOL. Regarding surgical technique, creating a well-centered CCC smaller than the optic of an IOL is crucial, so the capsular edges along the entire circumference are in apposition to the IOL optic. This may allow creation of an optimal capsular bend at the sharp, rectangular optic edges.24

CON C L US ION

Acrylic foldable IOL is the most inert lens in the eye that the author has ever seen. In addition to the advantageous characteristics mentioned in this chapter, postoperative inflammation has also been found to be less with acrylic foldable IOL.18 One possible drawback of this lens is the relatively large incision size when compared to that of silicone IOL. However, with the advent of newer and more sophisticated wound architectures as well as the introduction of the 5.5 mm diameter optic lens, this drawback is far outweighed by the advantages. The introduction of new injector system will further add to the advantageous feature of this lens. As shown in the recent statistics, acrylic foldable IOL has been dramatically gaining its popularity among the cataract surgerons,26,27 and this trend will continue in the coming years.

R E F E R E N C E S

1. Koch DD: Alcon AcrySofTM acrylic intraocular lens. In Martin RG, Gills JP, Sanders DR (Eds):

Foldable Intraocular Lenses. Slack: Thorofare, 1993.

2. Shugar JK: Implantation of AcrySof acrylic intraocular lenses. J Cataract Refract Surg 22:1355-59, 1996.

3. Steinert RF, Deacon J: Enlargement of incision width during phacoemulsification and folded intraocular lens implant surgery. Ophthalmology 103:220-25, 1996.

4. Mackool RJ, Russell RS: Effect of foldable intraocular lens insertion on incision width. J Cataract Refract Surg 22:571-74, 1996.

5. Kohnen T, Lambert RJ, Koch DD: Incision sizes for foldable intraocular lenses. Ophthalmology 104:1277-86, 1997.

6. Miller KM, Grusha YO, Ching ECP: Injecting the Alcon MA30BA lens through a Staar 1-MTC- 45 cartridge. J Cataract Refract Surg 22:1132-33, 1996.

7. Milazzo S, Turut P, Blin H: Alterations to the AcrySof intraocular lens during folding. J Cataract Refract Surg 22:1351-54, 1996.

8. Vrabec MP, Syverud JC, Burgess CJ: Forceps-induced scratching of a foldable acrylic intraocular lens. Arch Ophthalmol 114:777, 1996.

9. Carlson KH, Johnson DW: Cracking of acrylic intraocular lenses during capsular bag insertion.

Ophthalmic Surg Lasers 26:572-73, 1995.

10.Pfister DR: Stress fractures after folding an acrylic intraocular lens. Am J Ophthalmol 121:572-74, 1996.

11.Lee GA: Cracked acrylic intraocular lens requiring explantation. Aust NZ J Ophthalmol 25:71-73, 1997.

12.Baldeschi L, Rizzo S, Nardi M: Damage of foldable intraocular lenses by incorrect folding forceps.

Am J Ophthalmol 124:245-47, 1997.

13.Bee JA: Cracking of acrylic intraocular lenses during capsular bag insertion. Ophthalmic Surg Lasers 27:327, 1996.

IMPLANTATION TECHNIQUES OF ACRYLIC FOLDABLE IOL & ITS CLINICAL RESULTS 287

16.Neuhann TH: Intraocular folding of an acrylic lens for explantation through a small incision cataract wound. J Cataract Refract Surg 22:1383-86, 1996.

17.Oshika T, Nagata T, Ishii Y: Adhesion of lens capsule to intraocular lenses of polymethylmethacrylate, silicone and acrylic foldable materials: an experimental study. Br J Ophthalmol 82:549-53, 1998.

18. Oshika T, Suzuki Y, Kizaki H et al: Two year clinical study of a soft acrylic intraocular lens.

J Cataract Refract Surg 22:104-109, 1996.

19.Newland TJ, Auffarth GU, Wesendahl TA et al: Neodymium:YAG laser damage on silicone intraocular lenses—a comparison of lesions on explanted lenses and experimentally produced lesions. J Cataract Refract Surg 20:527-33, 1994.

20. Hayashi K, Hayashi H, Nakao F et al: Capsular capture of silicone intraocular lenses. J Cataract Refract Surg 22:1267-71, 1996.

21.Apple DJ, Solomon KD, Tetz MR et al: Posterior capsule opacification. Surv Ophthalmol 37:73116, 1992.

22. Nagamoto T, Hara E: Lens epithelial cell migration onto the posterior capsule in vitro. J Cataract Refract Surg 22:841-46, 1996.

23.Nishi O, Nishi K, Sakanishi K: Inhibition of migrating lens epithelial cells at the capsular bend created by the rectangular optic edge of a posterior chamber intraocular lens. Ophthalmic Surg Lasers 29:587-94, 1998.

24.Nishi O, Nishi K: Preventing posterior capsule opacification by creating a discontinuous sharp bend in the capsule. J Cataract Refract Surg 25:521-26, 1999.

25.Nagata T, Watanabe I: Optic sharp edge or convexity—comparison of effects on posterior capsular opacification. Jpn J Ophthalmol 40:397-403,1996.

26. Leaming DV: Practice styles and preferences of ASCRS members—1998 survey. J Cataract Refract Surg 25:851-59, 1999.

27.Oshika T, Amano S, Araie M et al: Current trends in cataract and refractive surgery in Japan— 1997 survey. Jpn J Ophthalmol 43:139-47, 1999.

288 THE ART OF PHACOEMULSIFICATION

J Stuart Cumming

Before discussing the modified plate lens, the mini-loop lens and the accommodating lens, it is necessary to understand the advantages and disadvantages of standard plate lenses.

The STAAR Surgical 4004 Sulcus Plate Lens

This first silicone lens was developed and designed for sulcus placement. Its commercial life preceded capsulorrhexis and thus implantation was in conjunction with a beer-can capsulotomy. Care had to be taken to ensure that the thin haptics were placed in the sulcus. Misplacement of one or both haptics into the bag resulted in the “Z-syndrome” with severe tilting of the optic necessitating lens exchange. This was the major complication of this lens design.

Other complications resulted from its sulcus placement which placed the lens plates in close proximity to the iris. This could result in chafing and iris pigment dispersion and, in rare cases, pigmentary glaucoma.

In my experience with implantation of 600 of these lenses, these complications, with the exception of the Z-syndrome, did not cause serious clinical problems necessitating lens exchange. As a result of the Z-syndrome complication of the 4004 STAAR plate lens, the company thickened the plate to 0.25 mm. This occurred at the same time that Gimbel and Neuhann discovered the anterior capsulotomy technique of capsulorrhexis. The implantation of the modified plate lens, the STAAR surgical model 4203, allowed the lens with the thicker and stiffer plates to be implanted into the capsular bag with capsulorrhexis without the complication of the Z-syndrome.

THE MINI-LOOP PLATE AND ACCOMMODATING LENSES 289

The STAAR Surgical and Chiron Vision 4203 and C10: Identical Plate Lenses

The lenses are 10.5 mm long, the approximate length of the empty capsular bag. The haptics are 0.25 mm thick, thick enough to prevent buckling with fibrosis but still sufficiently resilient to allow the haptics to flex with fibrosis of the anterior capsular rim, with its resultant end-to-end compression of the plates. Since the fibrosed anterior capsule is tough and leather-like, the plates cannot vault anteriorly. Thus, they flex in a posterior direction, placing the optic of the lens up against the vitreous face.

Thecomplicationsofmoderncataractsurgeryareretinaldetachment,cystoidmacular edema (CME) and opacification of the posterior capsule. Opening the opacified capsule

with a YAG laser further increases the risk of retinal detachment and CME.1

The capsular bag in a 70-year-old is approximately 5.0 mm deep, yet the IOL occupying this space is at the most only 1.3 mm thick. A space is therefore left that is filled with aqueous if the optic locates posteriorly or by the enlargement of the vitreous cavity allowing movement of the solid vitreous forward if the optic locates anteriorly. An IOL locating anteriorly greatly increases the mobility of the solid vitreous and can result in retinal detachment and CME.2

It is a reasonable assumption that designing an IOL that locates in the posterior part of the capsular bag, thereby stabilizing the vitreous, will result in a low incidence of both retinal detachment and CME. The posterior location of the plate IOL is caused by shrinkage of the capsular bag during fibrosis, “shrinkwrapping” the lens. This exerts end-to-end pressure on the plates, which flex. They cannot flex anteriorly because of the fibrosed leather-like anterior capsule and therefore they flex posteriorly. This pulls the elastic posterior capsule tightly against the posterior convex surface of the optic, greatly reducing the rate of opacification of the capsule with a resultant decrease in the need for a YAG capsulotomy2,3 further reducing the risk of retinal detachment and CME.

We know that the incidence of retinal detachment with intracapsular cataract surgery was 3.5 percent and with uncomplicated extracapsular surgery with some containment of the vitreous, it was less than 1 percent. The incidence of retinal detachment has been reported to be much less than this and with a very low incidence of CME and opacification of the posterior capsule1-3 with the currently available plate hepatic lenses from STAAR Surgical, Model 4203, and Chiron Vision, Model C40.6 At Anaheim Eye Medical Group, both plate and loop lenses were implanted. The charts of pseudophakic patients who developed a retinal detachment were examined over a seven-year period. There were 16 detachments: all sixteen were in patients implanted with a loop lens, five of these were implanted into a torn capsular bag without vitrectomy. The remaining 11 were implanted into an intact bag with capsulorrhexis—exactly the same procedure as the plate lens implantations. During this period of time, there were 1857 loop lenses implanted versus more than 3000 plate lens implantations. There is, therefore, a significant reduction in the incidence of retinal detachment with the posterior-locating and thus vitreous-stabilizing plate lens.

The identical plate haptic silicone IOL’s, Chiron Vision’s Model C10 and STAAR Surgical’s Model C4203, therefore have major advantages over loop lenses. These

Figure 27.1 demonstrates two highly significant findings: (i) the 1.3 mm thick optic of the plate lens consistently locates in the posterior part of the 5.0 mm deep bag space, thereby stabilizing the vitreous, and (ii) the optics of the plate lenses have a much smaller spread along the axis of the eye than the optics of long loop lenses.

With plate lens implantation, 50 percent of the time, the vitreous cavity is shortened; therefore, its volume is decreased, and in cases where the vitreous

cavity is lengthened by as much as only 0.75 mm, this distance corresponds to less than 5 percent of its preoperative length. On the other hand, the long-

loop lenses decrease the vitreous length 20 percent of the time. Eighty percent of the time, the vitreous cavity length is increased; the largest increase in length is 2.17 mm. The anterior location of a large percentage of long-loop lenses, therefore, increases the mobility of the remaining solid vitreous.

The spread of the location of plate lenses in this study was 1.45 mm and the loop lense spread 3.15 mm. Approximately 1.0 mm change in location of the optic can change the effective power of the lens by as much as 2.0 diopters. Because of the large spread in the location of the optic along the axis of the eye, the ‘A’ constant of plate lenses should be more meaningful than loop lenses and the uncorrected acuities are superior.2 Many of the refractive surprises encountered with long-loop lenses can therefore be accounted for by the location of the optic—in myopic surprises in the anterior, and hypermyopic surprises in the posterior range of the spread of optic locations along the axis of the eye.

The Mini-Loop Lens Design

The mini-loop lens was designed to maintain the advantages of plate lenses and yet allow the lens to fixate in the bag. The plates into which the mini-loops are anchored are 10.5 mm from end-to-end and 0.25 mm thick—the same length and thickness as the STAAR 4203 and Chiron C40 plate lenses.

The mini-loops, made of either polyimide or silicone, project from each end of the plates by 0.5 mm, giving the lens an overall length of 11.5 mm.

The capsular bag is between 10.0 and 10.5 mm in diameter and the sulcus is about 10.5 mm in diameter. The lens is therefore slightly longer than either. The loops therefore project minimally from the ends of the plates but enough to gently engage the periphery of the capsular bag or sulcus. Silicone has a specific gravity close to that of the aqueous and is therefore weightless within the eye. Gentle pressure on the periphery of the bag will therefore hold the lens in position until the lens is fixed in position by fibrosis around the loops. The loops are designed to exert as little pressure as possible on the periphery of the bag since this part of the bag is close to being in contact with the highly-vascular ciliary muscle which, despite the fact that the eye is aphakic, constricts just as the pupil does when patients change their fixation from far to near, and relaxes when fixation changes from near to far. Long-loop lenses have overall loop lengths from 12.0 to 14.0 mm—much longer than the bag space. These long loops, especially