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Cartridge cracks during foldable intraocular lens insertion
Cartridge cracks during foldable intraocular lens insertion Arun D. Singh, MD, Ting Fang, MD, Roger Rath, MD ABSTRACT Purpose: To assess the incidence of cartridge cracks during foldable intraocular lens (IOL) insertion and to determine factors that play a role in the development of these cracks. Setting: Leesburg Regional Ambulatory Surgical Care Center, Leesburg, Florida, USA. Methods: Small incision cataract surgery was performed in 350 consecutive cases. A foldable silicone IOL (AIIergan Medical Optics Sl-40) was inserted in all cases using the Unfolder'M cartridge and 3 viscoelastic agents: sodium hyaluronate (HealonQ!), Vitra~) and sodium chondroitin sulfate-sodium hyaluronate (Viscoa~). Results: Cartridge cracks occurred in 52 eyes (14.86%). Almost all cracks (98.1%) occurred in cases in which Healon was used to load the IOL. In each case of a cracked cartridge, there was evidence of the plunger overriding the optic edge. Conclusions: We recommend the use of chondroitin-based viscoelastic agents to load the Sl-40 foldable IOL to minimize the risk of cartridge cracks. Modifications in the design of the IOL inserter may eliminate the problem of cartridge cracks. J Cataract Refract Surg 1998; 24:1220-1222
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mall incision cataract surgery is now the preferred method of cataract removal. 1 Incision size significantly influences the visual outcome; therefore, recent advances in cataract surgery have minimized the incision size. 2•3 Various foldable intraocular lenses (IOLs) and devices for inserting them are available to achieve all the benefits of small incision cataract surgery. 4 Complications during cataract surgery and IOL insertion are well known. 5 An unusual complication of cracked cartridges during insertion of the Staar M4203 VF IOL using the 1-SMC-45LP cartridge was From the Department of Ophthalmology, University of Florida, Gainesville (Singh, Fang), and Lake Eye Associates, Leesburg (Rath), Florida, USA. Ron Apedaile, Grand IsW.nd Video Productions, Grand IsW.nd, Florida, produced the illustrations. Reprint requests to Roger Rath, MD, 601 East Dixie Avenue, Medical Plaza #201, Leesburg, Florida 34748, USA. 1220
recently described. 6 In this paper, we describe our experience with cracks in the Unfolder'IM cartridge (Allergan) during insertion of the Allergan Sl-40 foldable silicone lens.
Patients and Methods Phacoemulsification through a 2.8 mm dear corneal incision was performed in 350 consecutive patients. Each patient received a foldable Sl-40 lens, which was inserted with the Unfolder cartridge. All steps in the surgery, including loading and inserting the IOL, were performed by 1 surgeon (R.R.). Sodium hyaluronate (Healon®, Vitrax®) was used to place the IOL in the cartridge in 150 cases and 50 cases, respectively; sodium chondroitin sulfate-sodium hyaluronate (Viscoat®) was used in 50 cases. Each IOL was loaded into the cartridge per the manufacturer's instructions. In brief, the viscoelastic
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CARTRIDGE CRACKS WITH FOLDABLE IOLs
(Healon, Viscoat, or Vitrax) was injected into the tube of the cartridge along both troughs. The IOL was loaded across the central ridge; the leading haptic pointed forward into the tube and the trailing haptic extended from the back of the cartridge. Just before insertion, the cartridge's handpiece screw was engaged until the rod pushed the leading haptic of the IOL. · After the cartridge tube was inserted into the incision, the screw mechanism was used to push the optic forward.
Results Mild, clinically insignificant stress lines were observed just after delivery of the optic (Figure 1) in approximately 60 to 75% of cases with the use of all 3 viscoelastic agents. In 52 cases, full-thickness cartridge cracks were observed. Fifty-one cracks (98.1 %) occurred when Healon was used to load the IOL (Table 1). One cartridge cracked with the use of Viscoat, and none cracked with Vitrax. In addition, in each case of a cracked cartridge, there was evidence of the plunger (Softip TM sheath) overriding the trailing optic edge (Figure 2). In 50 cases, this was detected before the cartridge was inserted into the incision (Figure 3). In 2 cases, the cartridge cracked intraocularly and was associated with shearing of the IOL; this necessitated IOL exchange (Figure 4).
Discussion In this series, the incidence of cracks in the Unfolder cartridge was about 15% (52 of 350). Most cracks occurred while the cartridge tube was still extraocular, indicating that incision size does not effect the crack by pinching the cartridge tube and increasing the lateral stress.
Figure 1. (Singh) Stress lines (arrows) in the cartridge.
Almost all cases of cartridge cracks (98%) were associated with Healon as the cartridge lubricant. Healon possesses a property of "pseudoplasticity" because of its long, flexible, molecular structure? Pseudoplasticity implies changing viscosity with shear rate. At a low shear rate, there is high viscosity; as the shear rate increases, the viscosity drops as the molecules align in the direction of the flow. In other words, greater force is required to initiate the flow ofHealon than to maintain the flow. 7 With Healon as the lubricant, there could be initial resistance that could raise the lateral stress imposed on the cartridge walls, leading to the extension of stress lines into a full-thickness crack. Viscoat, which has chondroitin sulfate as a component, possesses a constant viscosity. The sodium hyaluronate in Vitrax has a lower molecular weight and a higher concentration than that in Healon. Vitrax is similar to Viscoat in
Table 1. Distribution of cartridge cracks with the 3 viscoelastic agents.
Viscoelastic Agent
Number of Cases
Cases with Cracks 51*
Healon
150
Viscoat
150
Vitrax
50
0
*Associated with IOL shearing, necessitating IOL exchange, in 2 cases
Figure 2. (Singh) Extension of stress lines into a full-thickness crack in the cartridge wall.
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CARTRIDGE CRACKS WITH FOLDABLE IOLs
Figure 3. (Singh) Override of the Softip sheath (large arrow) and the trailing edge of the optic with anticipated cartridge crack and IOL shear (small arrow). In this case, the crack was anticipated and the IOL was not inserted. However, the insertion maneuver was completed extraocularly to document the occurrence of the crack.
Figure 4. (Singh) Cartridge crack associated with intraocular shearing of the IOL (arrow).
properties; it is a dispersive viscoelastic material rather than a cohesive one. Surface interaction between silicone and the components of various viscoelastic agents may also play a role in generating lateral stress. We observed that in each case of a cracked cartridge, there was evidence of the plunger overriding the trailing optic edge. The override of the Softip sheath on the optic led to increasing lateral stress on the tube wall and, eventually, to a full-thickness crack. If the plunger advanced over one third of the optic diameter (about 2.0 mm) past the trailing optic edge, the cartridge was likely to crack. The override is probably secondary to increased initial resistance because of Healon and also the rounded anterior surface of the Softip sheath. The complication of intraocular cartridge crack can be anticipated if undue resistance to the forward movement of the IOL is detected or if the override of the sheath and the trailing edge of the optic is noted. When this occurs, further maneuvers should be stopped and the IOL reloaded (after examining the IOL under the microscope for damage) into a fresh cartridge. After insertion, the foldable IOL should be examined carefully for damage caused during the insertion. Healon and the foldable injectable SI-40 IOL are commonly used in small incision cataract surgery. Combining them, there is the possibility of a cartridge crack, with resulting IOL damage. The use of a viscoelastic material that is viscoretentive (i.e., Viscoat and Vitrax) at the outset of surgery yet easily extractable
(i.e., Healon) at the close of surgery without associated intraocular spikes would be ideal. We think the override of the Softip sheath and the trailing edge of the optic can be minimized by using a chondroitin-sulfate-based viscoelastic material. Improvements in the design of the IOL inserter are also needed to eliminate the problem of cartridge cracks.
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References 1. Learning DV. Practice styles and preferences of ASCRS members-1997 survey. J Cataract Refract Surg 1998; 24:552-561 2. Brim SF, Ostrick DM, Bryan JE. Keratometric cylinder and visual performance following phacoemulsification and implantation with silicone small-incision or poly(methyl methacrylate) intraocular lenses. J Cataract Refract Surg 1991; 17:32-36 3. Oshika T, Tsuboi S, Yaguchi S, et al. Comparative study of intraocular lens implantation through 3.2- and 5.5mm incisions. Ophthalmology 1994; 101: 1183-1190 4. Kohnen T, Lambert RJ, Koch DD. Incision sizes for foldable intraocular lenses. Ophthalmology 1997; 104: 1277-1286 5. Apple DJ, Mamalis N, Loftfield K, et al. Complications of intraocular lenses. A historical and histopathological review. Surv Ophthalmol1984; 29:1-54 6. Habib NE, Singh J, Adams AD, Bartholomew RS. Cracked cartridges during foldable intraocular lens implantation. J Cataract Refract Surg 1996; 22:630-632 7. Liesegang TJ. Viscoelastic substances in ophthalmology. Surv Ophthalmol 1990; 34:268-293
J CATARACT REFRACT SURG-VOL 24, SEPTEMBER 1998
S
mall incision cataract surgery is now the preferred method of cataract removal. 1 Incision size significantly influences the visual outcome; therefore, recent advances in cataract surgery have minimized the incision size. 2•3 Various foldable intraocular lenses (IOLs) and devices for inserting them are available to achieve all the benefits of small incision cataract surgery. 4 Complications during cataract surgery and IOL insertion are well known. 5 An unusual complication of cracked cartridges during insertion of the Staar M4203 VF IOL using the 1-SMC-45LP cartridge was From the Department of Ophthalmology, University of Florida, Gainesville (Singh, Fang), and Lake Eye Associates, Leesburg (Rath), Florida, USA. Ron Apedaile, Grand IsW.nd Video Productions, Grand IsW.nd, Florida, produced the illustrations. Reprint requests to Roger Rath, MD, 601 East Dixie Avenue, Medical Plaza #201, Leesburg, Florida 34748, USA. 1220
recently described. 6 In this paper, we describe our experience with cracks in the Unfolder'IM cartridge (Allergan) during insertion of the Allergan Sl-40 foldable silicone lens.
Patients and Methods Phacoemulsification through a 2.8 mm dear corneal incision was performed in 350 consecutive patients. Each patient received a foldable Sl-40 lens, which was inserted with the Unfolder cartridge. All steps in the surgery, including loading and inserting the IOL, were performed by 1 surgeon (R.R.). Sodium hyaluronate (Healon®, Vitrax®) was used to place the IOL in the cartridge in 150 cases and 50 cases, respectively; sodium chondroitin sulfate-sodium hyaluronate (Viscoat®) was used in 50 cases. Each IOL was loaded into the cartridge per the manufacturer's instructions. In brief, the viscoelastic
] CATARACT REFRACT SURG-VOL 24, SEPTEMBER 1998
CARTRIDGE CRACKS WITH FOLDABLE IOLs
(Healon, Viscoat, or Vitrax) was injected into the tube of the cartridge along both troughs. The IOL was loaded across the central ridge; the leading haptic pointed forward into the tube and the trailing haptic extended from the back of the cartridge. Just before insertion, the cartridge's handpiece screw was engaged until the rod pushed the leading haptic of the IOL. · After the cartridge tube was inserted into the incision, the screw mechanism was used to push the optic forward.
Results Mild, clinically insignificant stress lines were observed just after delivery of the optic (Figure 1) in approximately 60 to 75% of cases with the use of all 3 viscoelastic agents. In 52 cases, full-thickness cartridge cracks were observed. Fifty-one cracks (98.1 %) occurred when Healon was used to load the IOL (Table 1). One cartridge cracked with the use of Viscoat, and none cracked with Vitrax. In addition, in each case of a cracked cartridge, there was evidence of the plunger (Softip TM sheath) overriding the trailing optic edge (Figure 2). In 50 cases, this was detected before the cartridge was inserted into the incision (Figure 3). In 2 cases, the cartridge cracked intraocularly and was associated with shearing of the IOL; this necessitated IOL exchange (Figure 4).
Discussion In this series, the incidence of cracks in the Unfolder cartridge was about 15% (52 of 350). Most cracks occurred while the cartridge tube was still extraocular, indicating that incision size does not effect the crack by pinching the cartridge tube and increasing the lateral stress.
Figure 1. (Singh) Stress lines (arrows) in the cartridge.
Almost all cases of cartridge cracks (98%) were associated with Healon as the cartridge lubricant. Healon possesses a property of "pseudoplasticity" because of its long, flexible, molecular structure? Pseudoplasticity implies changing viscosity with shear rate. At a low shear rate, there is high viscosity; as the shear rate increases, the viscosity drops as the molecules align in the direction of the flow. In other words, greater force is required to initiate the flow ofHealon than to maintain the flow. 7 With Healon as the lubricant, there could be initial resistance that could raise the lateral stress imposed on the cartridge walls, leading to the extension of stress lines into a full-thickness crack. Viscoat, which has chondroitin sulfate as a component, possesses a constant viscosity. The sodium hyaluronate in Vitrax has a lower molecular weight and a higher concentration than that in Healon. Vitrax is similar to Viscoat in
Table 1. Distribution of cartridge cracks with the 3 viscoelastic agents.
Viscoelastic Agent
Number of Cases
Cases with Cracks 51*
Healon
150
Viscoat
150
Vitrax
50
0
*Associated with IOL shearing, necessitating IOL exchange, in 2 cases
Figure 2. (Singh) Extension of stress lines into a full-thickness crack in the cartridge wall.
J CATARACT REFRACT SURG-VOL 24, SEPTEMBER 1998
1221
CARTRIDGE CRACKS WITH FOLDABLE IOLs
Figure 3. (Singh) Override of the Softip sheath (large arrow) and the trailing edge of the optic with anticipated cartridge crack and IOL shear (small arrow). In this case, the crack was anticipated and the IOL was not inserted. However, the insertion maneuver was completed extraocularly to document the occurrence of the crack.
Figure 4. (Singh) Cartridge crack associated with intraocular shearing of the IOL (arrow).
properties; it is a dispersive viscoelastic material rather than a cohesive one. Surface interaction between silicone and the components of various viscoelastic agents may also play a role in generating lateral stress. We observed that in each case of a cracked cartridge, there was evidence of the plunger overriding the trailing optic edge. The override of the Softip sheath on the optic led to increasing lateral stress on the tube wall and, eventually, to a full-thickness crack. If the plunger advanced over one third of the optic diameter (about 2.0 mm) past the trailing optic edge, the cartridge was likely to crack. The override is probably secondary to increased initial resistance because of Healon and also the rounded anterior surface of the Softip sheath. The complication of intraocular cartridge crack can be anticipated if undue resistance to the forward movement of the IOL is detected or if the override of the sheath and the trailing edge of the optic is noted. When this occurs, further maneuvers should be stopped and the IOL reloaded (after examining the IOL under the microscope for damage) into a fresh cartridge. After insertion, the foldable IOL should be examined carefully for damage caused during the insertion. Healon and the foldable injectable SI-40 IOL are commonly used in small incision cataract surgery. Combining them, there is the possibility of a cartridge crack, with resulting IOL damage. The use of a viscoelastic material that is viscoretentive (i.e., Viscoat and Vitrax) at the outset of surgery yet easily extractable
(i.e., Healon) at the close of surgery without associated intraocular spikes would be ideal. We think the override of the Softip sheath and the trailing edge of the optic can be minimized by using a chondroitin-sulfate-based viscoelastic material. Improvements in the design of the IOL inserter are also needed to eliminate the problem of cartridge cracks.
1222
References 1. Learning DV. Practice styles and preferences of ASCRS members-1997 survey. J Cataract Refract Surg 1998; 24:552-561 2. Brim SF, Ostrick DM, Bryan JE. Keratometric cylinder and visual performance following phacoemulsification and implantation with silicone small-incision or poly(methyl methacrylate) intraocular lenses. J Cataract Refract Surg 1991; 17:32-36 3. Oshika T, Tsuboi S, Yaguchi S, et al. Comparative study of intraocular lens implantation through 3.2- and 5.5mm incisions. Ophthalmology 1994; 101: 1183-1190 4. Kohnen T, Lambert RJ, Koch DD. Incision sizes for foldable intraocular lenses. Ophthalmology 1997; 104: 1277-1286 5. Apple DJ, Mamalis N, Loftfield K, et al. Complications of intraocular lenses. A historical and histopathological review. Surv Ophthalmol1984; 29:1-54 6. Habib NE, Singh J, Adams AD, Bartholomew RS. Cracked cartridges during foldable intraocular lens implantation. J Cataract Refract Surg 1996; 22:630-632 7. Liesegang TJ. Viscoelastic substances in ophthalmology. Surv Ophthalmol 1990; 34:268-293
J CATARACT REFRACT SURG-VOL 24, SEPTEMBER 1998