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Reducing Surgically Induced Astigmatism by Using a Scleral Tunnel
REDUCING SURGICALLY INDUCED ASTIGMATISM BY USING A SCLERAL TUNNEL LOUIS
J.
GIRARD, M. D., JORGE RODRIGUEZ, M. D., AND MARY L. MAILMAN, PH. D. Houston, Texas
We conducted a prospective study of 36 eyes undergoing pars plana lensectomy, vitrectomy, and implantation of an intraocular lens. We used a scleral tunnel begun 3 mm posterior to the corneosclerallimbus and entered the anterior chamber through clear cornea. We found that this technique produced minimal postoperative astigmatism. After follow-up periods ranging from three to 15 months, the average change in the flatter meridian was -0.07 diopter and that in the steeper meridian was +0.26 diopter. The mean induced astigmatism was -0.33 diopter. A group of nine eyes undergoing pars plana lensectomy and vitrectomy alone showed no significant changes in the postoperative astigmatism. Statistical comparisons established that there was no significant difference between eyes undergoing intraocular lens implantation in addition to pars plana lensectomy and vitrectomy and those not undergoing intraocular lens implantation. Surgically induced astigmatism after cataract extraction, with or without implantation of an intraocular lens, is still a problem despite variations in the type of suture, the technique of suturing, and the use of a surgical keratometer.r" Apparently, the type of incision is an important factor in induced astigmatism. We perform cataract extraction using pars plana lensectomy and vitrectomy by ultrasonic fragmentation." a technique that requires no limbal incision. For implantation of an intraocular lens, we use a scleral tunnel'? to enter the anterior chamber because it minimizes the severity of postoperative astigmatism. Accepted for publication Dec. 19, 1983. From Twelve Oaks Hospital (Drs. Girard and Rodriguez); and the Department of Biochemistry, University of Texas Dental Branch (Dr. Mailman), Houston, Texas. Reprint requests to Louis J. Girard, M.D .. Twelve Oaks Tower, Suite 500, 4126 Southwest Freeway, Houston, TX 77027. 450
SUBJECTS AND METHODS
A total of 36 eyes underwent pars plana lensectomy and vitrectomy by ultrasonic fragmentation.l" In each case, after routine completion of a pars plana lensectomy and vitrectomy, we used a scleral tunnel to enter the anterior chamber to insert an intraocular lens. The incisions were closed by various surgeons with interrupted 7-0 polyglactin sutures. Preoperative keratometric measurements at the visual axis were performed by a technician who had no knowledge of the patient's name or diagnosis. Because polyglactin is absorbed, on the average, after 28 days, we established a minimum follow-up period of three months before repeating the keratometric readings. The technician had no knowledge of the previous measurements. The follow-up periods ranged from the three-month minimum to as much as 15 months (mean, 6.6 months).
© AMERICAN JOURNAL OF OPHTHALMOLOGY 97:450-456, 1984
VOL. 97, NO. 4
SCLERAL TUNNEL TO REDUCE ASTIGMATISM
Surgical technique of scleral tunnelAfter a pars plana lensectomy that leaves the anterior capsule intact except for a central capsulectomy, the sclerotomy incision at the 10 o'clock position is closed with a 6-0 polyglactin suture. The surgeon then inserts a Drews irrigator connected to an overhead irrigation bottle into the sclerotomy incision at the 2 o'clock position to keep the globe inflated (Fig. 1). A 7-mm incision, 3 mm posterior to the corneoscleral limbus, is made through
Fig. 1 (Girard, Rodriguez, and Mailman). Photographic (top) and diagrammatic (bottom) representations of the pars plana lensectomy completed, the sclerotomy at the 10 o'clock position sutured, the Drews irrigator inserted at the 2 o'clock position, and the 7-mm incision 3 mm posterior to the comeosclerallimbus.
451
50% of the scleral thickness (Fig. 2) and then extended anteriorly 2 mm into clear cornea (much like a trabeculectomy incision). The ends of the incision are left intact, making a tunnel rather than a flap (Fig. 3). After checking the length of the incision and controlling bleeding, the surgeon makes an incision into the anterior chamber through clear cornea with a razor blade and scissors (Fig. 4). A posterior chamber intraocular lens (Simcoe) is inserted between the iris and the anterior lens capsule and centered (Fig. 5) and the 7-mm scleral tunnel incision is closed with five or six interrupted 7-0 polyglactin sutures (Fig. 6). The surgeon then withdraws the Drews irrigator and closes the sclerotomy at the 2 o'clock position with u single interrupted polyglactin suture. The fornix-based conjunc-
Fig. 2 (Girard, Rodriguez, and Mailman). Photographic (top) and diagrammatic (bottom) representations of sclera incised through 50% of its thickness.
Fig. 3 (Girard, Rodriguez, and Mailman). Photographic (left) and diagrammatic (right) representations of incision extended anterior into clear cornea.
Fig. 4 (Girard, Rodriguez, and Mailman). Photographic (top left) and diagrammatic (bottom left) representations of anterior chamber entered through clear cornea with razor blade and scissors. Bottom right, Position of incision in anterior chamber.
452
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SCLERAL TUNNEL TO REDUCE ASTIGMATISM
453
Fig. 6 (Girard, Rodriguez, and Mailman). Incision closed with interrupted 7-0 polyglactin sutures.
Fig. 5 (Girard, Rodriguez, and Mailman). Posterior chamber intraocular lens inserted through scleral tunnel.
tival Hap is drawn together but not sutured. Finally, a subtenon's injection of corticosteroid-antibiotic is administered. Three months postoperatively, it is difficult to visualize the internal incision of the scleral tunnel. RESULTS
The mean value for preoperative astigmatism was 1.11 diopters and that for postoperative astigmatism was 1.43 diopters (Table 1). Although the postoperative astigmatism was larger in magnitude and showed a wider variation than the corresponding presurgical astigmatism in these eyes, Student's t-test established that postsurgical astigmatism was not statistically different from presurgical astigmatism (P> .10). The mean induced change in astigmatism was -0.33 diopter (Table 1). Only
two eyes of the 36 exhibited postoperative changes in astigmatism of more than 1.9 diopters. The Hat curvature of astigmatism decreased slightly to a mean value of -0.07 diopter, and the steep curvature of astigmatism increased slightly to a mean value of +0.26 diopter. A t-test comparing the postoperative change in Hat vs steep curvature of astigmatism showed that neither curvature was affected significantly more than the other by the scleral tunnel procedure (P>.05). The mean induced change in the meridian was 65.0 ± 54.3 degrees (mean ± S.D.). Table 2 lists the mean values for induced astigmatism at incremental intervals beginning three months after intraocular lens insertion via scleral tunnel. Analysis of variance showed that no significant changes in postoperative astigmatism occurred as a function of time between three and 15 months. Table 3 shows changes in astigmatism after pars plana lensectomy and vitrectomy without (control) and with (experimental) intraocular lens insertion via
454
AMERICAN JOURNAL OF OPHTHALMOLOGY
APRIL, 1984
TABLE 1 CHANGES IN KERATOMETRIC MEASUREMENTS AFTER ANTERIOR CHA.\1BER INTRAOCULAR LENS IMPLANTATION VIA A SCLERAL TUNNEL Astigmatism (Diopters) Length of Patient Follow-up PrePostNo. (mos) operative operative
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
35 36 Mean S.D. Range
15 11 3 7 13 13 13 6 4 4 3 12 4 8 4 3 3 6 6 9 11 4 3 3 12 6 6 7 3 5 4 5 5 7 4 5 6.6 ±3.6 3 to 15
Surgically Induced Changes Total Astigmatism (Diopters)
Flat Curve (Diopters)
Steep Curve (Diopters)
Meridian (Degrees)
1.12 1.50 +0.38 0.00 +0.38 169 0.63 1.37 +0.74 -0.12 +0.62 90 0.67 1.87 -0.75 +1.20 +0.45 22 0.00 0.13 +0.13 0.00 +0.13 100 1.25 -0.50 2.13 +0.88 +0.38 5 -0.13 1.25 1.12 +0.13 0.00 5 0.50 1.37 +0.87 -0.25 +0.62 154 0.37 1.13 +0.76 -0.13 +0.63 120 0.50 1.37 -0.50 -0.37 +0.87 170 0.88 -0.13 0.75 -0.37 -0.50 90 -0.50 -0.25 1.00 0.50 +0.25 20 0.25 0.87 +0.62 0.00 +0.62 90 1.25 1.25 0.00 +0.12 +0.13 132 0.75 -0.88 -0.13 1.50 +0.75 75 1.13 +0.12 1.25 +0.38 +0.50 35 0.62 0.87 +0.25 +0.75 +1.00 13 -0.55 1.67 1.12 +1.25 +0.70 18 -1.25 -0.25 0.25 1.25 +1.00 83 1.50 1.87 +0.37 +0.25 +0.62 5 0.00 0.38 +0.38 +0.37 +0.75 121 -0.13 0.62 0.75 +0.13 0.00 85 1.88 3.00 -0.62 +0.50 +1.12 115 1.13 1.75 +0.62 +0.63 +1.25 44 -0.75 -0.50 1.75 1.00 +0.25 88 0.27 +0.23 -0.12 0.50 +0.11 10 -0.50 0.25 2.13 +1.88 +1.38 72 1.88 +0.37 +0.50 +0.87 78 2.25 -0.75 +0.13 6 3.37 +0.88 4.25 -0.12 0.63 0.87 +0.24 +0.12 5 -0.50 +0.80 +0.25 170 2.88 2.33 2.00 +0.38 +0.12 +0.50 2.38 10 -0.13 -0.25 -0.12 2 1.13 1.00 -0.25 +0.75 9 1.25 2.25 +1.00 -0.37 -0.37 55 0.25 0.25 0.00 -0.25 -0.12 8 1.87 2.00 +0.13 3.12 -1.87 -0.25 -2.12 67 1.25 -0.33 -0.07 +0.26 65 1.11 1.43 ±0.82 ±0.51 ±0.62 ±54.3 ±0.84 ±0.67 o to 3.37 +0.25 to 4.25 -1.87 to + 1.88 - 1.25 to + 1.25 -2.12 to + 1.38 2 to 170
scleral tunnel. In the control group, the mean values for preoperative and postoperative astigmatism were small and were not significantly different from each other, indicating that pars plana lensectomy and vitrectomy alone do not affect astigmatism, which is to be expected since the incisions for this procedure are
two Lrnm incisions made at the 10 and 2 o'clock positions, 3 mm from the corneoscleral limbus. 9 Eyes in the control group were from patients who elected not to have implants. The postsurgical change in astigmatism in the experimental eyes was larger than that in the control group (1.43 diopters vs
455
SCLERAL TUNNEL TO REDUCE ASTIGMATISM
VOL. 97, NO. 4
SURGICALLY INDUCED ASTIGMATISM IN EYES THAT UNDERWENT PARS PLANA LENSECTOMY AND INTRAOCULAR LENS IMPLANTATION VIA THE SCLERAL TUNNEL
Time After Surgery (mos)
No. of Cases
3 4 5 to 6 7 to 11 12 to 15
7 7 9 7 6
Change in Astigmatism (Mean Diopters ± S.D.)
0.01 0.36 0.31 0.43 0.48
0.60 0.47 1.08 0.36 ± 0.39
± ± ± ±
0.79 diopter) and showed a wider variation. However, t-tests indicated that the surgically induced changes in astigmatism and flat or steep curvatures in the experimental and control groups did not differ significantly (P> .10). The only statistically significant change (P<.001) observed after the scleral tunnel procedure was in the axis of curvature. DISCUSSION
Many factors influence the amount of postoperative astigmatism: the suture technique, the use of a surgical keratome-
ter, the type of incision, surgical and postoperative complications, the general health of the patient, and the health of the eye. In determining the amount of postoperative astigmatism, it is essential to make the evaluation after all the sutures have been removed or absorbed. Evaluation before this time gives erroneous measurements because some suture materials (for example, nylon) continue to act for as long as 12 months postoperatively before being absorbed. Colvard and associates! found that using a surgical keratometer did not influence postoperative astigmatism. The type of suture and the technique used can produce variable results according to Jaffe and Clayman." The most important factor in the degree of postoperative astigmatism appears to be the type of incision. Iliff and Khodadoust!' reported a reduction in surgically induced astigmatism after cataract extraction using a scleral flap, made 0.5 mm posterior to the comeoscleral limbus. Jaffe and Clayman? showed the importance of incisions made posterior to
TABLE 3 PREOPERATIVE AND POSTOPERATIVE ASTIGMATISM LlIi/ EYES THAT DID (EXPERIMENTAL GROUP) AND DID NOT (CONTROL GROUP) UNDERGO INTRAOCULAR LENS IMPLANTATION
Astigmatism
Experimental Group
Control Group
No. of eyes Preoperative astigmatism (diopters) Mean ± S.D. Range Postoperative astigmatism (diopters) Mean ± S.D. Range Flat curve (diopters) Mean ± S.D. Range Steep curve (diopters) Mean ± S.D. Range Meridian (diopters) Mean ± S.D. Range
36
9
1.11 ± 0.84 o to 3.37
0.91 ± 0.51 0.25 to 1.75
1.43 ± 0.82 o to 4.25
0.79 ± 0.63 o to 1.88
-0.07 ± 0.51 -1.25 to + 1.25
-0.01 ± 0.32 -0.12 to +0.75
+0.26 ± 0.62 -2.12 to + 1.38
-0.02 ± 0.17 -0.25 to +0.25
65.03 ± 54.28 2 to 170
1.3 ± 2.18 o to 5
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AMERICAN JOURNAL OF OPHTHALMOLOGY
the corneosclerallimbus. Scleral flaps are now advocated by R. Kratz, H. Hirshman, and L. L. Hyde (personal communication, Sept. 9, 1982), Davis, 12 and Fenzl. 13 Our results indicated that a scleral tunnel is more effective than a scleral flap in reducing postoperative astigmatism. The length of the tunnel (5 mm) heals well with simple interrupted, absorbable 7-0 polyglactin sutures, which can be placed in the sclera by various surgeons with the same results. Hyphema is a potential problem if the technique is not followed correctly. Careful hemostasis is essential before the anterior chamber is entered. The anterior chamber should be entered in clear cornea to avoid the angle vessels. REFERENCES 1. Stainer, G. A., Binder, P. S., Parker, W. T., and Perl, T.: The natural and modified course of post-cataract astigmatism. Ophthalmic Surg, 13:822, 1982. 2. Lieberman, D.: Suture induced astigmatism, letter. J. Am. Intraocul. Implant Soc. 7:65, 1981. Kratz, R. P., Mazzocco, 3. Colvard, D. ~1., T. R., and Davidson, B.: The Terry surgical keratom-
APRIL, 1984
eter. A 12 month follow-up report. J. Am. Intraocul, Implant Soc. 7:248, 1981. 4. Moore, J. G.: Intraocular implants. The postoperative astigmatism. Br. J. Ophthalmol. 64:318, 1980. 5. Troutman, R. C., Kelly, S., Kaye, D., and Clahane, A. c.: The use and preliminary results of the Troutman surgical keratometer in cataract and corneal surgery. Trans. Am. Acad. Ophthalmol. Otolaryngol. 83:232, 1977. 6: Luntz, M. H., and Livingston, D. G.: Astigmatism in cataract surgery. Br. J. Ophthalmol. 61:360, 1977. 7. Jaffe, x. S., and Clayman, H. N.: The pathophysiology of corneal astigmatism after cataract surgery. Trans. Am. Acad. Ophthalmol. Otolaryngol. 79:615, 1975. 8. Meredith, T. A., and Maumenee, A. E.: A review of one thousand cases of intracapsular cataract extraction. II. Visual results and astigmatic analysis. Ophthalmic Surg. 10:42, 1979. 9. Girard, L. J.: Advanced Techniques in Ophthalmic Microsurgery. Volume 1. St. Louis, C. V. Mosby, 1979, pp. 66-88. 10. Girard, L. J., and Hofmann, R. F.: Prevention of induced astigmatism by the use of a scleral tunnel. In Emery, J. M. (ed.): Current Concepts in Cataract Surgery. New York, Appleton-CenturyCrofts. In press. II. Iliff, C. E., and Khodadoust, A.: Control of astigmatism in cataract surgery. Am. J. Ophthalmol. 65:378, 1968. 12. Davis, D. V.: Scleral incisions with cataract surgery, letter. J. Am. Intraocul. Implant Soc. 9:192, 1983. 13. Fenzl, R. F.: Closure of cataract wound, letter. J. Am. Intraocul. Implant Soc. 9:2II, 1983.
J.
GIRARD, M. D., JORGE RODRIGUEZ, M. D., AND MARY L. MAILMAN, PH. D. Houston, Texas
We conducted a prospective study of 36 eyes undergoing pars plana lensectomy, vitrectomy, and implantation of an intraocular lens. We used a scleral tunnel begun 3 mm posterior to the corneosclerallimbus and entered the anterior chamber through clear cornea. We found that this technique produced minimal postoperative astigmatism. After follow-up periods ranging from three to 15 months, the average change in the flatter meridian was -0.07 diopter and that in the steeper meridian was +0.26 diopter. The mean induced astigmatism was -0.33 diopter. A group of nine eyes undergoing pars plana lensectomy and vitrectomy alone showed no significant changes in the postoperative astigmatism. Statistical comparisons established that there was no significant difference between eyes undergoing intraocular lens implantation in addition to pars plana lensectomy and vitrectomy and those not undergoing intraocular lens implantation. Surgically induced astigmatism after cataract extraction, with or without implantation of an intraocular lens, is still a problem despite variations in the type of suture, the technique of suturing, and the use of a surgical keratometer.r" Apparently, the type of incision is an important factor in induced astigmatism. We perform cataract extraction using pars plana lensectomy and vitrectomy by ultrasonic fragmentation." a technique that requires no limbal incision. For implantation of an intraocular lens, we use a scleral tunnel'? to enter the anterior chamber because it minimizes the severity of postoperative astigmatism. Accepted for publication Dec. 19, 1983. From Twelve Oaks Hospital (Drs. Girard and Rodriguez); and the Department of Biochemistry, University of Texas Dental Branch (Dr. Mailman), Houston, Texas. Reprint requests to Louis J. Girard, M.D .. Twelve Oaks Tower, Suite 500, 4126 Southwest Freeway, Houston, TX 77027. 450
SUBJECTS AND METHODS
A total of 36 eyes underwent pars plana lensectomy and vitrectomy by ultrasonic fragmentation.l" In each case, after routine completion of a pars plana lensectomy and vitrectomy, we used a scleral tunnel to enter the anterior chamber to insert an intraocular lens. The incisions were closed by various surgeons with interrupted 7-0 polyglactin sutures. Preoperative keratometric measurements at the visual axis were performed by a technician who had no knowledge of the patient's name or diagnosis. Because polyglactin is absorbed, on the average, after 28 days, we established a minimum follow-up period of three months before repeating the keratometric readings. The technician had no knowledge of the previous measurements. The follow-up periods ranged from the three-month minimum to as much as 15 months (mean, 6.6 months).
© AMERICAN JOURNAL OF OPHTHALMOLOGY 97:450-456, 1984
VOL. 97, NO. 4
SCLERAL TUNNEL TO REDUCE ASTIGMATISM
Surgical technique of scleral tunnelAfter a pars plana lensectomy that leaves the anterior capsule intact except for a central capsulectomy, the sclerotomy incision at the 10 o'clock position is closed with a 6-0 polyglactin suture. The surgeon then inserts a Drews irrigator connected to an overhead irrigation bottle into the sclerotomy incision at the 2 o'clock position to keep the globe inflated (Fig. 1). A 7-mm incision, 3 mm posterior to the corneoscleral limbus, is made through
Fig. 1 (Girard, Rodriguez, and Mailman). Photographic (top) and diagrammatic (bottom) representations of the pars plana lensectomy completed, the sclerotomy at the 10 o'clock position sutured, the Drews irrigator inserted at the 2 o'clock position, and the 7-mm incision 3 mm posterior to the comeosclerallimbus.
451
50% of the scleral thickness (Fig. 2) and then extended anteriorly 2 mm into clear cornea (much like a trabeculectomy incision). The ends of the incision are left intact, making a tunnel rather than a flap (Fig. 3). After checking the length of the incision and controlling bleeding, the surgeon makes an incision into the anterior chamber through clear cornea with a razor blade and scissors (Fig. 4). A posterior chamber intraocular lens (Simcoe) is inserted between the iris and the anterior lens capsule and centered (Fig. 5) and the 7-mm scleral tunnel incision is closed with five or six interrupted 7-0 polyglactin sutures (Fig. 6). The surgeon then withdraws the Drews irrigator and closes the sclerotomy at the 2 o'clock position with u single interrupted polyglactin suture. The fornix-based conjunc-
Fig. 2 (Girard, Rodriguez, and Mailman). Photographic (top) and diagrammatic (bottom) representations of sclera incised through 50% of its thickness.
Fig. 3 (Girard, Rodriguez, and Mailman). Photographic (left) and diagrammatic (right) representations of incision extended anterior into clear cornea.
Fig. 4 (Girard, Rodriguez, and Mailman). Photographic (top left) and diagrammatic (bottom left) representations of anterior chamber entered through clear cornea with razor blade and scissors. Bottom right, Position of incision in anterior chamber.
452
VOL. 97, NO.4
SCLERAL TUNNEL TO REDUCE ASTIGMATISM
453
Fig. 6 (Girard, Rodriguez, and Mailman). Incision closed with interrupted 7-0 polyglactin sutures.
Fig. 5 (Girard, Rodriguez, and Mailman). Posterior chamber intraocular lens inserted through scleral tunnel.
tival Hap is drawn together but not sutured. Finally, a subtenon's injection of corticosteroid-antibiotic is administered. Three months postoperatively, it is difficult to visualize the internal incision of the scleral tunnel. RESULTS
The mean value for preoperative astigmatism was 1.11 diopters and that for postoperative astigmatism was 1.43 diopters (Table 1). Although the postoperative astigmatism was larger in magnitude and showed a wider variation than the corresponding presurgical astigmatism in these eyes, Student's t-test established that postsurgical astigmatism was not statistically different from presurgical astigmatism (P> .10). The mean induced change in astigmatism was -0.33 diopter (Table 1). Only
two eyes of the 36 exhibited postoperative changes in astigmatism of more than 1.9 diopters. The Hat curvature of astigmatism decreased slightly to a mean value of -0.07 diopter, and the steep curvature of astigmatism increased slightly to a mean value of +0.26 diopter. A t-test comparing the postoperative change in Hat vs steep curvature of astigmatism showed that neither curvature was affected significantly more than the other by the scleral tunnel procedure (P>.05). The mean induced change in the meridian was 65.0 ± 54.3 degrees (mean ± S.D.). Table 2 lists the mean values for induced astigmatism at incremental intervals beginning three months after intraocular lens insertion via scleral tunnel. Analysis of variance showed that no significant changes in postoperative astigmatism occurred as a function of time between three and 15 months. Table 3 shows changes in astigmatism after pars plana lensectomy and vitrectomy without (control) and with (experimental) intraocular lens insertion via
454
AMERICAN JOURNAL OF OPHTHALMOLOGY
APRIL, 1984
TABLE 1 CHANGES IN KERATOMETRIC MEASUREMENTS AFTER ANTERIOR CHA.\1BER INTRAOCULAR LENS IMPLANTATION VIA A SCLERAL TUNNEL Astigmatism (Diopters) Length of Patient Follow-up PrePostNo. (mos) operative operative
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
35 36 Mean S.D. Range
15 11 3 7 13 13 13 6 4 4 3 12 4 8 4 3 3 6 6 9 11 4 3 3 12 6 6 7 3 5 4 5 5 7 4 5 6.6 ±3.6 3 to 15
Surgically Induced Changes Total Astigmatism (Diopters)
Flat Curve (Diopters)
Steep Curve (Diopters)
Meridian (Degrees)
1.12 1.50 +0.38 0.00 +0.38 169 0.63 1.37 +0.74 -0.12 +0.62 90 0.67 1.87 -0.75 +1.20 +0.45 22 0.00 0.13 +0.13 0.00 +0.13 100 1.25 -0.50 2.13 +0.88 +0.38 5 -0.13 1.25 1.12 +0.13 0.00 5 0.50 1.37 +0.87 -0.25 +0.62 154 0.37 1.13 +0.76 -0.13 +0.63 120 0.50 1.37 -0.50 -0.37 +0.87 170 0.88 -0.13 0.75 -0.37 -0.50 90 -0.50 -0.25 1.00 0.50 +0.25 20 0.25 0.87 +0.62 0.00 +0.62 90 1.25 1.25 0.00 +0.12 +0.13 132 0.75 -0.88 -0.13 1.50 +0.75 75 1.13 +0.12 1.25 +0.38 +0.50 35 0.62 0.87 +0.25 +0.75 +1.00 13 -0.55 1.67 1.12 +1.25 +0.70 18 -1.25 -0.25 0.25 1.25 +1.00 83 1.50 1.87 +0.37 +0.25 +0.62 5 0.00 0.38 +0.38 +0.37 +0.75 121 -0.13 0.62 0.75 +0.13 0.00 85 1.88 3.00 -0.62 +0.50 +1.12 115 1.13 1.75 +0.62 +0.63 +1.25 44 -0.75 -0.50 1.75 1.00 +0.25 88 0.27 +0.23 -0.12 0.50 +0.11 10 -0.50 0.25 2.13 +1.88 +1.38 72 1.88 +0.37 +0.50 +0.87 78 2.25 -0.75 +0.13 6 3.37 +0.88 4.25 -0.12 0.63 0.87 +0.24 +0.12 5 -0.50 +0.80 +0.25 170 2.88 2.33 2.00 +0.38 +0.12 +0.50 2.38 10 -0.13 -0.25 -0.12 2 1.13 1.00 -0.25 +0.75 9 1.25 2.25 +1.00 -0.37 -0.37 55 0.25 0.25 0.00 -0.25 -0.12 8 1.87 2.00 +0.13 3.12 -1.87 -0.25 -2.12 67 1.25 -0.33 -0.07 +0.26 65 1.11 1.43 ±0.82 ±0.51 ±0.62 ±54.3 ±0.84 ±0.67 o to 3.37 +0.25 to 4.25 -1.87 to + 1.88 - 1.25 to + 1.25 -2.12 to + 1.38 2 to 170
scleral tunnel. In the control group, the mean values for preoperative and postoperative astigmatism were small and were not significantly different from each other, indicating that pars plana lensectomy and vitrectomy alone do not affect astigmatism, which is to be expected since the incisions for this procedure are
two Lrnm incisions made at the 10 and 2 o'clock positions, 3 mm from the corneoscleral limbus. 9 Eyes in the control group were from patients who elected not to have implants. The postsurgical change in astigmatism in the experimental eyes was larger than that in the control group (1.43 diopters vs
455
SCLERAL TUNNEL TO REDUCE ASTIGMATISM
VOL. 97, NO. 4
SURGICALLY INDUCED ASTIGMATISM IN EYES THAT UNDERWENT PARS PLANA LENSECTOMY AND INTRAOCULAR LENS IMPLANTATION VIA THE SCLERAL TUNNEL
Time After Surgery (mos)
No. of Cases
3 4 5 to 6 7 to 11 12 to 15
7 7 9 7 6
Change in Astigmatism (Mean Diopters ± S.D.)
0.01 0.36 0.31 0.43 0.48
0.60 0.47 1.08 0.36 ± 0.39
± ± ± ±
0.79 diopter) and showed a wider variation. However, t-tests indicated that the surgically induced changes in astigmatism and flat or steep curvatures in the experimental and control groups did not differ significantly (P> .10). The only statistically significant change (P<.001) observed after the scleral tunnel procedure was in the axis of curvature. DISCUSSION
Many factors influence the amount of postoperative astigmatism: the suture technique, the use of a surgical keratome-
ter, the type of incision, surgical and postoperative complications, the general health of the patient, and the health of the eye. In determining the amount of postoperative astigmatism, it is essential to make the evaluation after all the sutures have been removed or absorbed. Evaluation before this time gives erroneous measurements because some suture materials (for example, nylon) continue to act for as long as 12 months postoperatively before being absorbed. Colvard and associates! found that using a surgical keratometer did not influence postoperative astigmatism. The type of suture and the technique used can produce variable results according to Jaffe and Clayman." The most important factor in the degree of postoperative astigmatism appears to be the type of incision. Iliff and Khodadoust!' reported a reduction in surgically induced astigmatism after cataract extraction using a scleral flap, made 0.5 mm posterior to the comeoscleral limbus. Jaffe and Clayman? showed the importance of incisions made posterior to
TABLE 3 PREOPERATIVE AND POSTOPERATIVE ASTIGMATISM LlIi/ EYES THAT DID (EXPERIMENTAL GROUP) AND DID NOT (CONTROL GROUP) UNDERGO INTRAOCULAR LENS IMPLANTATION
Astigmatism
Experimental Group
Control Group
No. of eyes Preoperative astigmatism (diopters) Mean ± S.D. Range Postoperative astigmatism (diopters) Mean ± S.D. Range Flat curve (diopters) Mean ± S.D. Range Steep curve (diopters) Mean ± S.D. Range Meridian (diopters) Mean ± S.D. Range
36
9
1.11 ± 0.84 o to 3.37
0.91 ± 0.51 0.25 to 1.75
1.43 ± 0.82 o to 4.25
0.79 ± 0.63 o to 1.88
-0.07 ± 0.51 -1.25 to + 1.25
-0.01 ± 0.32 -0.12 to +0.75
+0.26 ± 0.62 -2.12 to + 1.38
-0.02 ± 0.17 -0.25 to +0.25
65.03 ± 54.28 2 to 170
1.3 ± 2.18 o to 5
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the corneosclerallimbus. Scleral flaps are now advocated by R. Kratz, H. Hirshman, and L. L. Hyde (personal communication, Sept. 9, 1982), Davis, 12 and Fenzl. 13 Our results indicated that a scleral tunnel is more effective than a scleral flap in reducing postoperative astigmatism. The length of the tunnel (5 mm) heals well with simple interrupted, absorbable 7-0 polyglactin sutures, which can be placed in the sclera by various surgeons with the same results. Hyphema is a potential problem if the technique is not followed correctly. Careful hemostasis is essential before the anterior chamber is entered. The anterior chamber should be entered in clear cornea to avoid the angle vessels. REFERENCES 1. Stainer, G. A., Binder, P. S., Parker, W. T., and Perl, T.: The natural and modified course of post-cataract astigmatism. Ophthalmic Surg, 13:822, 1982. 2. Lieberman, D.: Suture induced astigmatism, letter. J. Am. Intraocul. Implant Soc. 7:65, 1981. Kratz, R. P., Mazzocco, 3. Colvard, D. ~1., T. R., and Davidson, B.: The Terry surgical keratom-
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eter. A 12 month follow-up report. J. Am. Intraocul, Implant Soc. 7:248, 1981. 4. Moore, J. G.: Intraocular implants. The postoperative astigmatism. Br. J. Ophthalmol. 64:318, 1980. 5. Troutman, R. C., Kelly, S., Kaye, D., and Clahane, A. c.: The use and preliminary results of the Troutman surgical keratometer in cataract and corneal surgery. Trans. Am. Acad. Ophthalmol. Otolaryngol. 83:232, 1977. 6: Luntz, M. H., and Livingston, D. G.: Astigmatism in cataract surgery. Br. J. Ophthalmol. 61:360, 1977. 7. Jaffe, x. S., and Clayman, H. N.: The pathophysiology of corneal astigmatism after cataract surgery. Trans. Am. Acad. Ophthalmol. Otolaryngol. 79:615, 1975. 8. Meredith, T. A., and Maumenee, A. E.: A review of one thousand cases of intracapsular cataract extraction. II. Visual results and astigmatic analysis. Ophthalmic Surg. 10:42, 1979. 9. Girard, L. J.: Advanced Techniques in Ophthalmic Microsurgery. Volume 1. St. Louis, C. V. Mosby, 1979, pp. 66-88. 10. Girard, L. J., and Hofmann, R. F.: Prevention of induced astigmatism by the use of a scleral tunnel. In Emery, J. M. (ed.): Current Concepts in Cataract Surgery. New York, Appleton-CenturyCrofts. In press. II. Iliff, C. E., and Khodadoust, A.: Control of astigmatism in cataract surgery. Am. J. Ophthalmol. 65:378, 1968. 12. Davis, D. V.: Scleral incisions with cataract surgery, letter. J. Am. Intraocul. Implant Soc. 9:192, 1983. 13. Fenzl, R. F.: Closure of cataract wound, letter. J. Am. Intraocul. Implant Soc. 9:2II, 1983.