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Decentration associated with asymmetric capsular shrinkage and intraocular lens design in a rabbit model
Decentration associated with asymmetric capsular shrinkage and intraocular lens design in a rabbit model Shunsaku Ohmi, M.D., Kenshiro Uenoyama, M.D.
ABSTRACT We evaluated intraocular lens (IOL) decentration resulting from asymmetric capsular shrinkage. In 19 eyes of 10 white rabbits, a D-shaped incision was made in the anterior capsule and one of three IOL types implanted in the capsular bag: three-piece with polypropylene haptics, one-piece all-poly(methyl methacrylate) (PMMA), or compressible disk. Eight weeks later, eyes were enucleated for assessment of IOL decentration. Mean decentration was 0. 75 mm for three-piece IOLs, 0.46 mm for one-piece IOLs, and 0.30 mm for compressible-disk lenses. Decentration was significantly less in eyes with compressible-disk lenses than in those with three-piece IOLs. Although decentration was less with the compressible-disk lens, the lens is not commonly used because of the large incision and special insertion technique required. If an open-loop IOL is to be used in eyes at risk for asymmetric capsular shrinkage, our results indicate that an aii-PMMA onepiece IOL would be preferable to a three-piece lens with a polypropylene haptic. Key Words: anterior capsulotomy, asymmetric capsular shrinkage, compressible disk lens, decentration, intraocular lens, poly(methyl methacrylate), polypropylene
Good intraocular lens (IOL) centration is obtained in many cases by in-the-bag implantation. 1- 3 Decentration often occurs when one of the fixed portions escapes from the capsular bag while the other remains within it, 1 •2 but the IOL may also become displaced postoperatively even when both fixed portions remain in the capsular bag. Asymmetric capsular shrinkage is believed to be one cause. 1 •3- 5 We previously reported that a circular and centric anterior capsulotomy helps prevent asymmetric capsular shrinkage, reducing postoperative IOL decentration.6·7 We present a comparison of decentration of three IOL types after a D-shaped anterior capsulotomy in rabbits carried out to clarify which IOL type most effectively averts decentration secondary to asymmetric capsular shrinkage.
MATERIALS AND METHODS One of three types of IOLs (Figure 1) was implanted in 19 eyes of 10 white rabbits weighing 2.5 kg to 3.0 kg: (1) three-piece with a 6.5 mm diameter poly(methyl methacrylate) (PMMA) biconvex optic, short C-type polypropylene haptics with an angle of 5 degrees, and an overall length of 13.5 mm (n = 7); (2) one-piece all-PMMA with a 6.5 mm diameter biconvex optic, modified C-type haptics with an angle of 10 degrees, and an overall length of 13.5 mm (n = 7); (3) one-piece all-PMMA compressible disk with a 6.0 mm diameter biconvex optic and a 9.0 mm outer ring that serves as a flexible, circular haptic (n = 5). The optic and the outer ring were connected with a 9-degree angulation between the two parts.
From the Department of Ophthalmology, Wakayama Medical College, Wakayarna, Japan. Presented at the Symposium on Cataract, IOL and Refractive Surgery, Boston, April 1994. Kabi Pharmacia K.K., Tokyo, Japan, provided the intraocular lenses. Reprint requests to Shunsaku Ohmi, M.D., Department of Ophthalmology, Wakayama Medical College, 7-Bancho 27, Wakayama 640, Japan. JCATARACTREFRACTSURG-VOL21, MAY 1995
293
5'
Fig. 1. (Ohmi) The three IOL designs: three-piece polypropylene haptic (left); one-piece PMMA (center); compressible disk (right).
Fig. 2. (Ohmi) A D-shaped anterior capsulotomy. The force of capsule contraction from the left is greater than the force from the right because of capsule asymmetry.
After dilation of the pupil with 0.5% tropicamide and 0.5% phenylephrine, the animals were anesthetized by an intramuscular injection of ketamine 50 mg/kg and xylazine 10 mg/kg. A linear anterior capsulotomy about 4 mm long was made from 10 o'clock to 1 o'clock with a 26-gauge injection needle cystotome. After a 3.5 mm limbal incision was made, intercapsular phacoemulsification was performed and the remaining cortex aspirated with an irrigation/aspiration tip. The limbal incision was extended to about 8.0 mm, and the capsule and anterior chamber were filled with sodium hyaluronate. With small scissors, the anterior capsulotomy was extended slightly at 10 o'clock and the IOL inserted into the capsule by the compression method. The two types of open-loop IOLs were centered by positioning the haptics toward 4 o'clock and 10 o'clock. The compressible-disk lens was centered by positioning the connective parts toward 1 o'clock and 7 o'clock. The margin of the anterior capsulotomy was held at 10 o'clock with forceps and the capsulotomy extended to 7 o'clock in a semicircle with a radius of about 3.0 mm. The flap of the anterior capsule between 1 o'clock and 7 o'clock was removed with a small scissors (Figure 2). The sodium hyaluronate was aspirated and the limbal incision closed with a 10-0 nylon suture. 294
After eight weeks, the rabbits were killed by an intravenous injection of 5% pentobarbital sodium. The eyes were enucleated and cut into halves along the equator. The anterior half of each eye was photographed on slide film from the posterior aspect. The slides were projected on a screen, and decentration of each IOL was determined by measuring the distance between the center of the anterior segment, determined from the circumference of the ciliary body and the center of the IOL optic. Figures 3 to 6 show some of the slides used for evaluation.
RESULTS Table 1 shows the degree of postoperative decentration in the eye with a D-shaped anterior capsulotomy. Any IOL that was fixed asymmetrically by in-out haptic positions was excluded from the analysis. Mean decentration (:±:SD) was 0.75 :±: 0.41 mm for three-piece IOLs, 0.46 :±: 0.21 mm for the onepiece, and 0.30 :±: 0.21 mm for the compressible disk. Lens decentration was significantly less in eyes with compressible-disk lenses than in those with threepiece IOLs (P < .05). Table 2 shows the degree of decentration toward the window of the anterior capsulotomy. Decentration to the side opposite the window of the anterior capsulotomy was observed in one of seven eyes implanted with a three-piece IOL. Mean decentration was 0.36 :±: 0.42 mm in eyes with a three-piece IOL, 0.20 :±: 0.28 mm in eyes with the one-piece lens, and 0 :±: 0.13 mm in eyes with a compressible-disk lens. There was no significant difference between groups. When eyes showing opposite decentration were excluded from the analysis (one in the one-piece group, one in the compressible-disk group), mean decentration was 0.44 :±: 0.40 mm, 0.31 :±: 0.14 mm, and 0.01 :±: 0.10,
Fig. 3. (Ohmi) A rabbit eye implanted with a three-piece IOL in which decentration was 0.46 mm. Decentration to the window of the anterior capsulotomy was 0.33 mm.
J CATARACf REFRACf SURG-VOL 21, MAY 1995
Fig. 4.
(Ohmi) A rabbit eye implanted with a one-piece IOL in which decentration was 0.49 mm. Decentration to the window of the anterior capsulotomy was 0.16 mm.
Fig. 5. (Ohmi) A rabbit eye implanted with a compressible disk lens in which decentration was 0.12 mm. Decentration to the window of the anterior capsulotomy was 0. respectively. There was no significant difference between the groups.
DISCUSSION Capsular bag contraction is thought to result when collagen fibers contract because of lens epithelial cell proliferation and metaplasia. 8 When the anterior capsulotomy is not circular, particularly when it is Dshaped, contraction will be greater on the relatively intact side of the capsule, probably decentering the IOL toward the opposite side (Figure 2). In our study, the incidence of postoperative decentration was least when compressible-disk lenses were implanted and greatest when three-piece IOLs were used. The difference in degree of decentration
Fig. 6.
(Ohmi) A rabbit eye implanted with a compressible-disk lens in which decentration was 0.24 mm. The optic portion was compressed by nodular opacification and the IOL displaced to the side opposite the expected side ( -0.24 mm).
between compressible-disk and three-piece IOLs was significant. The compressible-disk lens has an outer ring haptic. Thus, even when great force is applied to the lens from one direction, the force will be dispersed if the lens can structurally withstand it. Because of this dispersion, the tension within the capsule will be equal in every direction of the 360-degree range, making the lens more stable within the capsular bag. With open-loop IOLs, the force causing capsule contraction seems to be reduced by bending and distorting the fixed portion or by haptic rotation, with degree of postoperative decentration related to the haptic material. Polypropylene seems to lose some resilience when implanted in the eye, where the temperature is relatively high. 9 Furthermore, polypropylene is very flexible. For these reasons, polypropylene is less resistant to capsular contrac-
Table 1. Extent of postoperative decentration (mm) of IOLs in rabbit eyes after eight weeks.
Eye
Intraocular Lens Type Three-Piece One-Piece Compressible-Disk
1
0.62
0.33
0.13
2
1.43
0.49
0.68
3
0.37
0.20
0.33
4
0.24
0.87
0.12
5
1.11
0.41
0.24
6
0.46
0.48
7
0.99
In-out
J CATARACf REFRACf SURG-VOL 21, MAY 1995
295
Table 2. Decentration (mm) to the window of the anterior caps ulotomy. Minus sign indicates decentration to the opposite side. Intraocular Lens Type 1-Piece Compressible-Disk
technique required. Although the insertion technique has been improved, the lens is still harder to implant than the open-loop IOL. Many surgeons are more experienced with an openloop IOL. If an open-loop IOL is to be implanted in eyes at risk for asymmetric capsular shrinkage (e.g., when the anterior capsulotomy is not circular or centered), an all-PMMA, one-piece IOL is preferable to a three-piece lens with a polypropylene haptic.
Eye
3-Piece
1
0
0.33
0
2
0.29
0.16
0.11
3
-0.12
0.16
0.13
4
0.08
0.54
0
REFERENCES
5
1.11
-0.36
-0.24
6
0.33
0.35
7
0.84
In-out
1. Apple DJ, Kincaid MC, Mamalis N, Olson RJ. Intraocular Lenses; Evolution, Designs, Complications, and Pathology. Baltimore, William and Wilkins, 1989; 135 2. Hansen SO, Tetz MR, Solomon KD, et al. Decentration of flexible loop posterior chamber intraocular lenses in a series of 222 postmortem eyes. Ophthalmology 1988; 95:344-349 3. Rochels R, Nover A. Untersuchung zur Haufigkeit und Entstehung der dezentrierung kapselsackfixierter Hinterkammerlinsen. Klin Monatsbl Augenheilkd 1988; 193:585-588 4. Kimura W, Kimura T, Sawada T, et al. Intraocular lens decentration after two years of envelope technique ECCE. Jpn IOL Soc J 1989; 3:185-192 5. Miyake K. Some considerations on methods of anterior lens capsulotomy and mechanisms of lens capsule opacification. Jpn IOL Soc J 1989; 3:236-239 6. Ohmi S, Uenoyama K. Experimental evaluation of posterior capsule opacification and intraocular lens decentration: comparison of intraocular lenses of 12.5 mm and 14.0 mm diameter. J Cataract Refract Surg 1993; 19:348-351 7. Ohmi S. Decentration associated with asymmetric capsular shrinkage and intraocular lens size. J Cataract Refract Surg 1993; 19:640-643 8. Nishi 0, Nishi K. Fibrous opacification of the anterior capsule after cataract surgery. Jpn J Clin Ophthalmol 1991; 45:1811-1815 9. Hayano S. Intraocular lenses-on the basis of high polymers. Acta Soc Ophthalmol Jpn 1986; 90:25-42 10. Kimura W, Kimura T, Sawada T, et al. Comparison of shape recovery ratios of single-piece poly(methyl methacrylate) intraocular lens haptics. J Cataract Refract Surg 1993; 19:635-639
tion than PMMA; that is, polypropylene is more likely to deform. It has also been reported that the shape recovery capability of a three-piece IOL haptic is lower than that of a one-piece IOL haptic, even when of the same material. 10 Therefore, the greater postoperative decentration of the three-piece IOL with polypropylene haptics observed in our study can be attributed to both the lens' material and the structural features. In some cases, marked rotation from the initial position and unexpected decentration away from the anterior capsulotomy window were noted. These eyes had nodular opacification similar to that of previously reported cases; thus, we speculate that the IOL optic or haptic was compressed by opacification. In previous studies, 6 •7 we confirmed that decentration secondary to asymmetric capsular shrinkage was affected by the anterior capsulotomy shape. In addition IOL fixation technique, Zinn's zonules status, amount of residual cortex, and IOL design and material can cause postoperative decentration. 5 •10 Surgeons should select the IOL that is best for a given eye. Decentration was less with the compressible-disk lens, but this type of IOL is not commonly used because of the large incision and special insertion
296
J CATARACT REFRACT SURG-VOL 21, MAY 1995
ABSTRACT We evaluated intraocular lens (IOL) decentration resulting from asymmetric capsular shrinkage. In 19 eyes of 10 white rabbits, a D-shaped incision was made in the anterior capsule and one of three IOL types implanted in the capsular bag: three-piece with polypropylene haptics, one-piece all-poly(methyl methacrylate) (PMMA), or compressible disk. Eight weeks later, eyes were enucleated for assessment of IOL decentration. Mean decentration was 0. 75 mm for three-piece IOLs, 0.46 mm for one-piece IOLs, and 0.30 mm for compressible-disk lenses. Decentration was significantly less in eyes with compressible-disk lenses than in those with three-piece IOLs. Although decentration was less with the compressible-disk lens, the lens is not commonly used because of the large incision and special insertion technique required. If an open-loop IOL is to be used in eyes at risk for asymmetric capsular shrinkage, our results indicate that an aii-PMMA onepiece IOL would be preferable to a three-piece lens with a polypropylene haptic. Key Words: anterior capsulotomy, asymmetric capsular shrinkage, compressible disk lens, decentration, intraocular lens, poly(methyl methacrylate), polypropylene
Good intraocular lens (IOL) centration is obtained in many cases by in-the-bag implantation. 1- 3 Decentration often occurs when one of the fixed portions escapes from the capsular bag while the other remains within it, 1 •2 but the IOL may also become displaced postoperatively even when both fixed portions remain in the capsular bag. Asymmetric capsular shrinkage is believed to be one cause. 1 •3- 5 We previously reported that a circular and centric anterior capsulotomy helps prevent asymmetric capsular shrinkage, reducing postoperative IOL decentration.6·7 We present a comparison of decentration of three IOL types after a D-shaped anterior capsulotomy in rabbits carried out to clarify which IOL type most effectively averts decentration secondary to asymmetric capsular shrinkage.
MATERIALS AND METHODS One of three types of IOLs (Figure 1) was implanted in 19 eyes of 10 white rabbits weighing 2.5 kg to 3.0 kg: (1) three-piece with a 6.5 mm diameter poly(methyl methacrylate) (PMMA) biconvex optic, short C-type polypropylene haptics with an angle of 5 degrees, and an overall length of 13.5 mm (n = 7); (2) one-piece all-PMMA with a 6.5 mm diameter biconvex optic, modified C-type haptics with an angle of 10 degrees, and an overall length of 13.5 mm (n = 7); (3) one-piece all-PMMA compressible disk with a 6.0 mm diameter biconvex optic and a 9.0 mm outer ring that serves as a flexible, circular haptic (n = 5). The optic and the outer ring were connected with a 9-degree angulation between the two parts.
From the Department of Ophthalmology, Wakayama Medical College, Wakayarna, Japan. Presented at the Symposium on Cataract, IOL and Refractive Surgery, Boston, April 1994. Kabi Pharmacia K.K., Tokyo, Japan, provided the intraocular lenses. Reprint requests to Shunsaku Ohmi, M.D., Department of Ophthalmology, Wakayama Medical College, 7-Bancho 27, Wakayama 640, Japan. JCATARACTREFRACTSURG-VOL21, MAY 1995
293
5'
Fig. 1. (Ohmi) The three IOL designs: three-piece polypropylene haptic (left); one-piece PMMA (center); compressible disk (right).
Fig. 2. (Ohmi) A D-shaped anterior capsulotomy. The force of capsule contraction from the left is greater than the force from the right because of capsule asymmetry.
After dilation of the pupil with 0.5% tropicamide and 0.5% phenylephrine, the animals were anesthetized by an intramuscular injection of ketamine 50 mg/kg and xylazine 10 mg/kg. A linear anterior capsulotomy about 4 mm long was made from 10 o'clock to 1 o'clock with a 26-gauge injection needle cystotome. After a 3.5 mm limbal incision was made, intercapsular phacoemulsification was performed and the remaining cortex aspirated with an irrigation/aspiration tip. The limbal incision was extended to about 8.0 mm, and the capsule and anterior chamber were filled with sodium hyaluronate. With small scissors, the anterior capsulotomy was extended slightly at 10 o'clock and the IOL inserted into the capsule by the compression method. The two types of open-loop IOLs were centered by positioning the haptics toward 4 o'clock and 10 o'clock. The compressible-disk lens was centered by positioning the connective parts toward 1 o'clock and 7 o'clock. The margin of the anterior capsulotomy was held at 10 o'clock with forceps and the capsulotomy extended to 7 o'clock in a semicircle with a radius of about 3.0 mm. The flap of the anterior capsule between 1 o'clock and 7 o'clock was removed with a small scissors (Figure 2). The sodium hyaluronate was aspirated and the limbal incision closed with a 10-0 nylon suture. 294
After eight weeks, the rabbits were killed by an intravenous injection of 5% pentobarbital sodium. The eyes were enucleated and cut into halves along the equator. The anterior half of each eye was photographed on slide film from the posterior aspect. The slides were projected on a screen, and decentration of each IOL was determined by measuring the distance between the center of the anterior segment, determined from the circumference of the ciliary body and the center of the IOL optic. Figures 3 to 6 show some of the slides used for evaluation.
RESULTS Table 1 shows the degree of postoperative decentration in the eye with a D-shaped anterior capsulotomy. Any IOL that was fixed asymmetrically by in-out haptic positions was excluded from the analysis. Mean decentration (:±:SD) was 0.75 :±: 0.41 mm for three-piece IOLs, 0.46 :±: 0.21 mm for the onepiece, and 0.30 :±: 0.21 mm for the compressible disk. Lens decentration was significantly less in eyes with compressible-disk lenses than in those with threepiece IOLs (P < .05). Table 2 shows the degree of decentration toward the window of the anterior capsulotomy. Decentration to the side opposite the window of the anterior capsulotomy was observed in one of seven eyes implanted with a three-piece IOL. Mean decentration was 0.36 :±: 0.42 mm in eyes with a three-piece IOL, 0.20 :±: 0.28 mm in eyes with the one-piece lens, and 0 :±: 0.13 mm in eyes with a compressible-disk lens. There was no significant difference between groups. When eyes showing opposite decentration were excluded from the analysis (one in the one-piece group, one in the compressible-disk group), mean decentration was 0.44 :±: 0.40 mm, 0.31 :±: 0.14 mm, and 0.01 :±: 0.10,
Fig. 3. (Ohmi) A rabbit eye implanted with a three-piece IOL in which decentration was 0.46 mm. Decentration to the window of the anterior capsulotomy was 0.33 mm.
J CATARACf REFRACf SURG-VOL 21, MAY 1995
Fig. 4.
(Ohmi) A rabbit eye implanted with a one-piece IOL in which decentration was 0.49 mm. Decentration to the window of the anterior capsulotomy was 0.16 mm.
Fig. 5. (Ohmi) A rabbit eye implanted with a compressible disk lens in which decentration was 0.12 mm. Decentration to the window of the anterior capsulotomy was 0. respectively. There was no significant difference between the groups.
DISCUSSION Capsular bag contraction is thought to result when collagen fibers contract because of lens epithelial cell proliferation and metaplasia. 8 When the anterior capsulotomy is not circular, particularly when it is Dshaped, contraction will be greater on the relatively intact side of the capsule, probably decentering the IOL toward the opposite side (Figure 2). In our study, the incidence of postoperative decentration was least when compressible-disk lenses were implanted and greatest when three-piece IOLs were used. The difference in degree of decentration
Fig. 6.
(Ohmi) A rabbit eye implanted with a compressible-disk lens in which decentration was 0.24 mm. The optic portion was compressed by nodular opacification and the IOL displaced to the side opposite the expected side ( -0.24 mm).
between compressible-disk and three-piece IOLs was significant. The compressible-disk lens has an outer ring haptic. Thus, even when great force is applied to the lens from one direction, the force will be dispersed if the lens can structurally withstand it. Because of this dispersion, the tension within the capsule will be equal in every direction of the 360-degree range, making the lens more stable within the capsular bag. With open-loop IOLs, the force causing capsule contraction seems to be reduced by bending and distorting the fixed portion or by haptic rotation, with degree of postoperative decentration related to the haptic material. Polypropylene seems to lose some resilience when implanted in the eye, where the temperature is relatively high. 9 Furthermore, polypropylene is very flexible. For these reasons, polypropylene is less resistant to capsular contrac-
Table 1. Extent of postoperative decentration (mm) of IOLs in rabbit eyes after eight weeks.
Eye
Intraocular Lens Type Three-Piece One-Piece Compressible-Disk
1
0.62
0.33
0.13
2
1.43
0.49
0.68
3
0.37
0.20
0.33
4
0.24
0.87
0.12
5
1.11
0.41
0.24
6
0.46
0.48
7
0.99
In-out
J CATARACf REFRACf SURG-VOL 21, MAY 1995
295
Table 2. Decentration (mm) to the window of the anterior caps ulotomy. Minus sign indicates decentration to the opposite side. Intraocular Lens Type 1-Piece Compressible-Disk
technique required. Although the insertion technique has been improved, the lens is still harder to implant than the open-loop IOL. Many surgeons are more experienced with an openloop IOL. If an open-loop IOL is to be implanted in eyes at risk for asymmetric capsular shrinkage (e.g., when the anterior capsulotomy is not circular or centered), an all-PMMA, one-piece IOL is preferable to a three-piece lens with a polypropylene haptic.
Eye
3-Piece
1
0
0.33
0
2
0.29
0.16
0.11
3
-0.12
0.16
0.13
4
0.08
0.54
0
REFERENCES
5
1.11
-0.36
-0.24
6
0.33
0.35
7
0.84
In-out
1. Apple DJ, Kincaid MC, Mamalis N, Olson RJ. Intraocular Lenses; Evolution, Designs, Complications, and Pathology. Baltimore, William and Wilkins, 1989; 135 2. Hansen SO, Tetz MR, Solomon KD, et al. Decentration of flexible loop posterior chamber intraocular lenses in a series of 222 postmortem eyes. Ophthalmology 1988; 95:344-349 3. Rochels R, Nover A. Untersuchung zur Haufigkeit und Entstehung der dezentrierung kapselsackfixierter Hinterkammerlinsen. Klin Monatsbl Augenheilkd 1988; 193:585-588 4. Kimura W, Kimura T, Sawada T, et al. Intraocular lens decentration after two years of envelope technique ECCE. Jpn IOL Soc J 1989; 3:185-192 5. Miyake K. Some considerations on methods of anterior lens capsulotomy and mechanisms of lens capsule opacification. Jpn IOL Soc J 1989; 3:236-239 6. Ohmi S, Uenoyama K. Experimental evaluation of posterior capsule opacification and intraocular lens decentration: comparison of intraocular lenses of 12.5 mm and 14.0 mm diameter. J Cataract Refract Surg 1993; 19:348-351 7. Ohmi S. Decentration associated with asymmetric capsular shrinkage and intraocular lens size. J Cataract Refract Surg 1993; 19:640-643 8. Nishi 0, Nishi K. Fibrous opacification of the anterior capsule after cataract surgery. Jpn J Clin Ophthalmol 1991; 45:1811-1815 9. Hayano S. Intraocular lenses-on the basis of high polymers. Acta Soc Ophthalmol Jpn 1986; 90:25-42 10. Kimura W, Kimura T, Sawada T, et al. Comparison of shape recovery ratios of single-piece poly(methyl methacrylate) intraocular lens haptics. J Cataract Refract Surg 1993; 19:635-639
tion than PMMA; that is, polypropylene is more likely to deform. It has also been reported that the shape recovery capability of a three-piece IOL haptic is lower than that of a one-piece IOL haptic, even when of the same material. 10 Therefore, the greater postoperative decentration of the three-piece IOL with polypropylene haptics observed in our study can be attributed to both the lens' material and the structural features. In some cases, marked rotation from the initial position and unexpected decentration away from the anterior capsulotomy window were noted. These eyes had nodular opacification similar to that of previously reported cases; thus, we speculate that the IOL optic or haptic was compressed by opacification. In previous studies, 6 •7 we confirmed that decentration secondary to asymmetric capsular shrinkage was affected by the anterior capsulotomy shape. In addition IOL fixation technique, Zinn's zonules status, amount of residual cortex, and IOL design and material can cause postoperative decentration. 5 •10 Surgeons should select the IOL that is best for a given eye. Decentration was less with the compressible-disk lens, but this type of IOL is not commonly used because of the large incision and special insertion
296
J CATARACT REFRACT SURG-VOL 21, MAY 1995