Table 1. Refraction factors in lens exchanges. Patient Age
Implant Power Change (D)
Refraction Change (D Sph Eq)
Refraction Factor
EG,66
-6.5
+7.25
RH,70
+2.0
-1.63
1.23
EN,72
+3 .0
-6.63
0.45
0.90
JT,65
+2 .5
-2.88
0.87
AM,70
-4 .5
+6.00
0.75
FS,40
-17.0
+ 14.50
1.17
HB,66
- 8.0
+8.00
1.00
EF,66
+4.0
-4.00
1.00
GB,61
-6.5
+5.75
1.13
Mean refraction factor
0.94
Standard deviation
0.24
First eight cases from Salz And Reader,l last case from Parker and Clorfeine.
With a larger number of cases, regression analysis could be use d to correlate refraction factor (or refraction constant) with other factors such as axial length . These data could be used to estimate refraction factor even more accurately for various eyes. Again, congratulations to Dr. Cravy on a fine study. William T. Parker, M. D. Gary S. Clorfeine, M.D.
San Diego, California
REFERENCE 1. Salz Reader AL III : Lens implant exchanges for incorrect power: Results of an informal survey. J Cataract Refract Surg 14:221-224, 1988
n,
OPEN LOOP SOFT INTRAOCULAR LENS To the Editor: In the article entitled "Physical Fixation of Soft Intraocular Lenses" (J Cataract Refract Surg 15:580583, 1989), Shimizu and Komatsu perpetuate a misunderstanding that has arisen about the nature of soft intraocular lenses. The authors point out correctly that one piece "plate" intraocular lenses should only be used in the presence of an intact posterior capsule and a small circular capsulorhexis opening in the anterior capsule. Howeve r, the concluding sentence of their article states, "If a circular capsulotomycannot be done well or if another complication occurs, soft lens implantation should be abandoned and an open loop poly (methyl methacrylate) (PMMA) lens used instead." There is a soft intraocular lens that does have an open loop configuration. This is the SI-18 (manufactured by Allergan Medical Optics). This lens can be used in any
situation in which one would use an open loop PMMA lens . I have used it in over 600 operations without bene fit of a circular capsulorhexis capsulotomy, including several instances in which the posterior lens capsule is not intact. The lens has proven to be as satisfactorv as the PMMA lens. Since then , I have adopted the circular capsulorhexis technique as my standard operation. I wish to assure the readers that that is not necessary for successful use of the AMO SI-18 lens. Ronald W. Barnet, M.D. Phoenix , Arizona
EARLY CAPSULAR FIBROSIS WITH POSTERIOR CONVEX SURFACE POSTERIOR CHAMBER INTRAOCULAR LENSES To the Editor: The incidence of posterior capsular opacification following cataract extraction is dependent upon a number of variables, including the degree of cortical cleanup, the presence or absence of an intraocular lens (IOL), the type (anterior, iris fixation , posterior chamber) and the posterior surface design (convex, plano , laser ridge) of the lens implanted. Posterior capsular opacification occurs by two mechanisms: Elschnig pearl formation and capsular fibrosis. In vitro studies have shown that poly(methyl methacrylate) (PMMA) is actually toxic to lens epithelial cells and inhibits the growth of Elschnig pearls when it is in contact with the posterior capsule. 1 Corroborative clinical studies have shown that the incidence ofElschnig pearl formation is less with a posterior convex surface IOL that is in intimate contact with the posterior capsule. 2 Fibrosis of the posterior capsule, however, does not occur by lens epithelial cell proliferation and apparently is not inhibited by PMMA contact with the posterior capsule. 2 . 3 Few authors have reported the early posterior capsular opacification rate secondary to posterior capsule fibrosis alone and compared its incidence in posterior convex versus posterior plano surface IOL designs. We studied the secondary neodymium:YAG laser capsulotomy rate of one surgeon (H. W.F.) during two consecutive series of phacoemulsification at the Mobile Eye Center. Group I represents 803 patients who had a convex-plano posterior chamber lens implanted following phacoemulsification. Group II represents 450 patients who had a one-piece biconvex posterior chamber lens implanted. All surgical techniques and indications for posterior caps ulotomy were otherwise the same in both groups. At three months, Group I required nine capsulotomies (1.1%) and Group II required 14 capsulotomies (3.1%). All 23 posterior
J CATARACT REFRACT SURC-VOL 16, MARCH 1990
271
capsulotomies were performed for early capsular fibrosis. This difference is statistically significant (P< .012). By six months, there was no statistical difference in the capsulotomy rates in Group I and Group II patients (2.6% versus 4.2% , respectively). These data suggest that the incidence of early capsular fibrosis requiring posterior caps ulotomy in the first three months is almost three times greater with posterior convex IOLs than with posterior plano surface IOLs. An almost two times greater rate of early capsular fibrosis was noted by Sellman and Lindstrom, 2 but was determined statistically insignificant. It has been suggested that YAG caps ulotomies carry a decreased risk of cystoid macular edema, retinal tears, and retinal detachments if performed more than six to 12 months after cataract extraction. 3 Thus, early capsular fibrosis requiring early capsulotomy could lead to an increased incidence of these vitreoretinal complications. In our series, no vitreoretinal complications were encountered , probably because of the short follow-up time and the limited number of capsulotomies performed. In conclusion, despite the fact that posterior convex IOLs lead to a decreased need for posterior capsulotomies in the long run, the possible increased need for posterior capsulotomies in the first three months secondary to early capsular fibrosis might offset the long-term advantage of the posterior convex surface posterior chamber IOL design. H. Wade Faulkner, M.D. Richard J. Duffey, M.D. Mobile, Alabama
REFERENCES 1. Santos BA , Pastora R, DelMonte MA , O'Donne ll FE Jr: Lens
epithelial inhibition by PMMA optic: Implications for lens design . J Cataract Refract Surg 12:23-26, 1986 2. Sellman TR, Lindstrom RL: Effect of plano-convex posterior chamber lens on capsular opacification from Elschnig pearl formation. J Cataract Refract Surg 14:68-72, 1988 3. Lindstrom RL, Harris WS: Management of the posterior capsule following poste rior chamber lens implantation. Am Intra-Ocular Implant Soc J 6:255-258, 1980
ANESTHETIC AGENTS USED IN CATARACT SURGERY To the Editor: Review of recent reports describing the anesthetic agents used in cataract surgery indicates consistent use of a combination of bupivacaine and lidocaine. Apparently this is done with the expectation that the bupivacaine will provide prolonged anesthesia, as well as postoperative analgesia. Lidocaine is included to ensure more rapid onset and more complete akinesia. We are writing to question the routine use of this combination of agents for cataract surgery. Two percent 272
(2%) lidocaine with 1/200,000 epinephrine provides approximately 21/2 hours of anesthesia and akinesiamore than enough time to complete cataract extraction and lens implantation. Furthermore, today's advanced microsurgical procedures and fine suture closure produce little or no postoperative discomfort; therefore, the use of an anesthetic (such as bupivacaine) that gives prolonged anesthesia is unnecessary. The mixture of 0.75% bupivacaine and 2.0% lidocaine results in an effective concentration of 0.375% and 1.0%, respectively. The resultant combination will have a slower onset and be a less effective producer of anesthesia and akinesia than 2.0% lidocaine alone. Subdural injection occurs approximately once in every 2,000 retrobulbar anesthetic injections. If bupivacaine has been injected, the central nervous system effects are more intense and oflonger duration than those which occur when lidocaine is used. Apnea and unconsciousness may persist for up to 30 minutes with bupivacaine following this type of inadvertent high spinal anesthesia. One of us (M.W.L.) is a member of a group of anesthesiologists which provides anesthetic management for six ophthalmic ambulatory surgery centers. In this capacity, we administer approximately 3,000 retrobulbar anesthetic injections each year. At five of the six ambulatory surgery centers, the ophthalmologists have abandoned the routine use of the bupivacaine/lidocaine mixtures, and use only 2.0% lidocaine with 1/200,000 epinephrine. Our experience continues to be extremely favorable - the onset of anesthesia and akinesia is rapid and their duration is adequate . Of course, in situations in which surgeons require more than two hours of anesthesia and akinesia, use of bupivacaine would be appropriate. Martin W. Livingston, M.D. Richard J. Mackool, M.D. Harold Schneider, M . D.
New York New York
THE "THORNTON RING PLUS" FOR KERATOTOMIES To the Editor: Having used the Thornton ring in combination with various lid speculas for three years, I prefer it to fixation forceps in most situations . In some patients, however, pressure exerted on the globe with the Thornton ring leads to a bulging Or even a prolapse of the conjunctiva from the superior fornix (sometimes from the inferior fornix as well) which can interfere with the planned surgical procedure or, at least, make it more difficult. For this reason, I have added lid retractors/retainers, similar to those of the Goldmann-McNeil ring, to the
J CATARACT REFRACT SURG-VOL 16, MARCH 1990
Implant Power Change (D)
Refraction Change (D Sph Eq)
Refraction Factor
EG,66
-6.5
+7.25
RH,70
+2.0
-1.63
1.23
EN,72
+3 .0
-6.63
0.45
0.90
JT,65
+2 .5
-2.88
0.87
AM,70
-4 .5
+6.00
0.75
FS,40
-17.0
+ 14.50
1.17
HB,66
- 8.0
+8.00
1.00
EF,66
+4.0
-4.00
1.00
GB,61
-6.5
+5.75
1.13
Mean refraction factor
0.94
Standard deviation
0.24
First eight cases from Salz And Reader,l last case from Parker and Clorfeine.
With a larger number of cases, regression analysis could be use d to correlate refraction factor (or refraction constant) with other factors such as axial length . These data could be used to estimate refraction factor even more accurately for various eyes. Again, congratulations to Dr. Cravy on a fine study. William T. Parker, M. D. Gary S. Clorfeine, M.D.
San Diego, California
REFERENCE 1. Salz Reader AL III : Lens implant exchanges for incorrect power: Results of an informal survey. J Cataract Refract Surg 14:221-224, 1988
n,
OPEN LOOP SOFT INTRAOCULAR LENS To the Editor: In the article entitled "Physical Fixation of Soft Intraocular Lenses" (J Cataract Refract Surg 15:580583, 1989), Shimizu and Komatsu perpetuate a misunderstanding that has arisen about the nature of soft intraocular lenses. The authors point out correctly that one piece "plate" intraocular lenses should only be used in the presence of an intact posterior capsule and a small circular capsulorhexis opening in the anterior capsule. Howeve r, the concluding sentence of their article states, "If a circular capsulotomycannot be done well or if another complication occurs, soft lens implantation should be abandoned and an open loop poly (methyl methacrylate) (PMMA) lens used instead." There is a soft intraocular lens that does have an open loop configuration. This is the SI-18 (manufactured by Allergan Medical Optics). This lens can be used in any
situation in which one would use an open loop PMMA lens . I have used it in over 600 operations without bene fit of a circular capsulorhexis capsulotomy, including several instances in which the posterior lens capsule is not intact. The lens has proven to be as satisfactorv as the PMMA lens. Since then , I have adopted the circular capsulorhexis technique as my standard operation. I wish to assure the readers that that is not necessary for successful use of the AMO SI-18 lens. Ronald W. Barnet, M.D. Phoenix , Arizona
EARLY CAPSULAR FIBROSIS WITH POSTERIOR CONVEX SURFACE POSTERIOR CHAMBER INTRAOCULAR LENSES To the Editor: The incidence of posterior capsular opacification following cataract extraction is dependent upon a number of variables, including the degree of cortical cleanup, the presence or absence of an intraocular lens (IOL), the type (anterior, iris fixation , posterior chamber) and the posterior surface design (convex, plano , laser ridge) of the lens implanted. Posterior capsular opacification occurs by two mechanisms: Elschnig pearl formation and capsular fibrosis. In vitro studies have shown that poly(methyl methacrylate) (PMMA) is actually toxic to lens epithelial cells and inhibits the growth of Elschnig pearls when it is in contact with the posterior capsule. 1 Corroborative clinical studies have shown that the incidence ofElschnig pearl formation is less with a posterior convex surface IOL that is in intimate contact with the posterior capsule. 2 Fibrosis of the posterior capsule, however, does not occur by lens epithelial cell proliferation and apparently is not inhibited by PMMA contact with the posterior capsule. 2 . 3 Few authors have reported the early posterior capsular opacification rate secondary to posterior capsule fibrosis alone and compared its incidence in posterior convex versus posterior plano surface IOL designs. We studied the secondary neodymium:YAG laser capsulotomy rate of one surgeon (H. W.F.) during two consecutive series of phacoemulsification at the Mobile Eye Center. Group I represents 803 patients who had a convex-plano posterior chamber lens implanted following phacoemulsification. Group II represents 450 patients who had a one-piece biconvex posterior chamber lens implanted. All surgical techniques and indications for posterior caps ulotomy were otherwise the same in both groups. At three months, Group I required nine capsulotomies (1.1%) and Group II required 14 capsulotomies (3.1%). All 23 posterior
J CATARACT REFRACT SURC-VOL 16, MARCH 1990
271
capsulotomies were performed for early capsular fibrosis. This difference is statistically significant (P< .012). By six months, there was no statistical difference in the capsulotomy rates in Group I and Group II patients (2.6% versus 4.2% , respectively). These data suggest that the incidence of early capsular fibrosis requiring posterior caps ulotomy in the first three months is almost three times greater with posterior convex IOLs than with posterior plano surface IOLs. An almost two times greater rate of early capsular fibrosis was noted by Sellman and Lindstrom, 2 but was determined statistically insignificant. It has been suggested that YAG caps ulotomies carry a decreased risk of cystoid macular edema, retinal tears, and retinal detachments if performed more than six to 12 months after cataract extraction. 3 Thus, early capsular fibrosis requiring early capsulotomy could lead to an increased incidence of these vitreoretinal complications. In our series, no vitreoretinal complications were encountered , probably because of the short follow-up time and the limited number of capsulotomies performed. In conclusion, despite the fact that posterior convex IOLs lead to a decreased need for posterior capsulotomies in the long run, the possible increased need for posterior capsulotomies in the first three months secondary to early capsular fibrosis might offset the long-term advantage of the posterior convex surface posterior chamber IOL design. H. Wade Faulkner, M.D. Richard J. Duffey, M.D. Mobile, Alabama
REFERENCES 1. Santos BA , Pastora R, DelMonte MA , O'Donne ll FE Jr: Lens
epithelial inhibition by PMMA optic: Implications for lens design . J Cataract Refract Surg 12:23-26, 1986 2. Sellman TR, Lindstrom RL: Effect of plano-convex posterior chamber lens on capsular opacification from Elschnig pearl formation. J Cataract Refract Surg 14:68-72, 1988 3. Lindstrom RL, Harris WS: Management of the posterior capsule following poste rior chamber lens implantation. Am Intra-Ocular Implant Soc J 6:255-258, 1980
ANESTHETIC AGENTS USED IN CATARACT SURGERY To the Editor: Review of recent reports describing the anesthetic agents used in cataract surgery indicates consistent use of a combination of bupivacaine and lidocaine. Apparently this is done with the expectation that the bupivacaine will provide prolonged anesthesia, as well as postoperative analgesia. Lidocaine is included to ensure more rapid onset and more complete akinesia. We are writing to question the routine use of this combination of agents for cataract surgery. Two percent 272
(2%) lidocaine with 1/200,000 epinephrine provides approximately 21/2 hours of anesthesia and akinesiamore than enough time to complete cataract extraction and lens implantation. Furthermore, today's advanced microsurgical procedures and fine suture closure produce little or no postoperative discomfort; therefore, the use of an anesthetic (such as bupivacaine) that gives prolonged anesthesia is unnecessary. The mixture of 0.75% bupivacaine and 2.0% lidocaine results in an effective concentration of 0.375% and 1.0%, respectively. The resultant combination will have a slower onset and be a less effective producer of anesthesia and akinesia than 2.0% lidocaine alone. Subdural injection occurs approximately once in every 2,000 retrobulbar anesthetic injections. If bupivacaine has been injected, the central nervous system effects are more intense and oflonger duration than those which occur when lidocaine is used. Apnea and unconsciousness may persist for up to 30 minutes with bupivacaine following this type of inadvertent high spinal anesthesia. One of us (M.W.L.) is a member of a group of anesthesiologists which provides anesthetic management for six ophthalmic ambulatory surgery centers. In this capacity, we administer approximately 3,000 retrobulbar anesthetic injections each year. At five of the six ambulatory surgery centers, the ophthalmologists have abandoned the routine use of the bupivacaine/lidocaine mixtures, and use only 2.0% lidocaine with 1/200,000 epinephrine. Our experience continues to be extremely favorable - the onset of anesthesia and akinesia is rapid and their duration is adequate . Of course, in situations in which surgeons require more than two hours of anesthesia and akinesia, use of bupivacaine would be appropriate. Martin W. Livingston, M.D. Richard J. Mackool, M.D. Harold Schneider, M . D.
New York New York
THE "THORNTON RING PLUS" FOR KERATOTOMIES To the Editor: Having used the Thornton ring in combination with various lid speculas for three years, I prefer it to fixation forceps in most situations . In some patients, however, pressure exerted on the globe with the Thornton ring leads to a bulging Or even a prolapse of the conjunctiva from the superior fornix (sometimes from the inferior fornix as well) which can interfere with the planned surgical procedure or, at least, make it more difficult. For this reason, I have added lid retractors/retainers, similar to those of the Goldmann-McNeil ring, to the
J CATARACT REFRACT SURG-VOL 16, MARCH 1990
