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Comparative study of corneal topographic changes after 3.0 mm beveled and hinged clear corneal incisions
Comparative study of corneal topographic changes after 3.0 mm beveled and hinged clear corneal incisions Clemens Vass, MD, Rupert Menilpace, MD, Georg Rainer, MD, Oliver Findl, MD, Iris Steineck, MD
C
lear corneal incisions (CCls) have become popular because they are easy to construct and are convenient for the patient and relatively astigmatically neutral. However, the lack of conjunctival covering of
Reprint requests to Clemens Vass, MD, University of Vienna, Department of Ophthalmology, Wiihringer Gurtel 18-20, A-1090 Vienna,
Austria. 1498
the incision can lead to postoperative leakage or endophthalmitis in the case of improper wound construction. 1 To improve wound stability, the hinged CCI was introduced. 2 This 0.75 mm deep incision has a perpendicular precut and a corneal tunnel starting from the precut at a depth of 0.50 mm. In a cadaver eye study, Ernest and coauthors3 found hinged CCls were more stable than beveled CCIs of the
J CATARACf REFRACT SURG-VOL 24, NOVEMBER 1998
TOPOGRAPHIC CHANGES AFTER BEVELED AND HINGED CCls
same width. The degree of surgically induced astigmatism (SIA) with this better wound stability is still unknown. This study compared the induced corneal shape changes after beveled and hinged CCls using topographic batch-by-batch analysis. 4
Patients and Methods This prospective study included 89 eyes of 79 patients scheduled for phacoemulsification with implantation of a foldable intraocular lens (IOL). Patients were assigned to a beveled-incision or hinged-incision group. Exclusion criteria were previous ocular surgery, corneal pathology, or pathology of the anterior segment other than cataract. Postoperative exclusion criteria were a follow-up of less than 3 months or poor-quality topographic readings. Topographic readings in 64 eyes of 56 patients were evaluated: 29 in the beveledincision group and 35 in the hinged-incision group. In both incision groups, a temporal CCI of3.00 mm width and 1.75 to 2.00 mm length was made. The incision entry point was 0.50 mm into clear cornea. In both groups, the incision was self-sealing and sutureless. In the beveled-incision group, a stab incision was made with a 3.0 mm keratome blade (Alcon). In the hingedincision group, a 3.0 mm long, 0.7 mm deep perpendicular precut was done first with a calibrated diamond RK-T knife (Katena). Then, the CCI was made with the 3.0 mm keratome blade, starting at about half of corneal thickness. Except for the CCI construction, the surgical procedure was identical in all patients and performed by the same surgeon (R.M.). In all patients, 2 side-port incisions were made at the 7 and 11 o'clock positions (right eye) or the 1 and 5 o'clock positions (left eye). A continuous curvilinear capsulorhexis was performed through the 7 o'clock (right eye) or 1 o'clock (left eye) paracentesis. Bimanual phacoemulsification and aspiration of cortex followed. After the injection of viscoelastic material, a silicone 10L (Allergan, AMO SI-30) was implanted in the capsular bag with a Fine II forceps (Rhein Medical Inc.) and the viscoelastic material was removed. The wound was tested for watertightness and hydrated if necessary. No corneal sutures were used in any case. Corneal topography was recorded 5 times using a
computer-assisted videokeratoscope (TMS-l, Computed Anatomy, Inc.): preoperatively, and 1 week, 1 and 3 months, and 1 year postoperatively. All topographic readings were taken unmasked by 1 of 2 experienced investigators (CY., G.R.). For every patient, the localization of the incision was postoperatively estimated at the slitlamp with an accuracy of 1/2 o'clock position. At the 1 week and 1 month postoperative slitlamp examination, wound-related localized keratopathy and the external CCI gape were graded (Table 1). The data of the topographic readings were exported to a personal computer. The evaluation was done with the help of a topographic batch-by-batch analysis program. 4 The records were corrected for small local artifacts. If necessary, the data were rotated according to localization of the incision to simulate an exact temporal position. Then, the data were reduced to 225 corneal areas and corrected for defocus artifacts. On the basis of these data, the differences were statistically evaluated preoperatively to 1 week, 1 and 3 months, and 1 year postoperatively; 1 week to 1 month postoperatively; 1 month to 1 year postoperatively. Color-coded averaged difference maps were made to depict the differences for the whole group. Paired Wilcoxon signedrank tests were calculated for the same periods and then transformed into color-coded Wilcoxon-test maps. Group comparisons of the above paired differences of the 2 incision groups were calculated and transformed into color-coded maps. The changes in the spherical power (apparent spherical shifts) of the corneal topographic maps were calculated for the different time periods. If there appeared to be a statistical significance in the paired t tests, the apparent spherical shifts were called true spherical shifts. Otherwise, they were called defocus artifacts. The true spherical shifts (or defocus artifacts) were also subjected to group comparisons. Table 1. Grades of wound-related keratopathy and incisional gapes.
o
Absent
Absent
Trace
Trace
2
Moderate
Present
3
Marked
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TOPOGRAPHIC CHANGES AFTER BEVELED AND HINGED CCls -o.a.
-0.8. -0.7· -0", -0,5. -0.4. -0,3. -G.2.
-0.71 -0,,1 -0,51 -0.41 -0,31 -0.21 -0.11 -o~1 - -0.01 E!a.~ O· O. 0.1· 0.1 11.2. 0
-0.7· -0.8. -0.5 -G.4 -
-0.71 -0.81 -0,51 -0.41
-0.31
-Q,3 - -0.21 -0,2. -0.11 . -0.1 - -0',01 iifi'
0-
0.1· 0,2 -
CI.3 •
0,3 -
0.4 0,5 • 0.8 • 0.7·
o.a •
0.
0
0.1 0
0
D.4 -
0
0.8· 0.7 -
0.
Figure 1. (Vass) Averaged difference maps of reduced data
Figure 2. (Vass) Averaged difference maps of reduced data
1 week postoperatively. Left: Beveled-incision group. Right: Hingedincision group.
1 month postoperatively. Left: Beveled-incision group. Right: Hinged-incision group.
In addition, a vector analysis of the topographic data of the zone 1.5 mm from the center was done. 5- 8 The significance of group comparisons was calculated using t tests.
Throughout the follow-up, the semi meridians of steepening were not truly vertical but were bent toward the incision at an angle decreasing from the center (169 to 180 degrees) toward the periphery (102 to 147 degrees) (1 area = 11.25 degrees). The lower semimeridian of steepening seemed to be more distorted toward the incision in the hinged-incision (Figures 1 to 4, right) than in the beveled-incision (Figures 1 to 4, left) group. The corneal areas with significant surgically induced changes at 1 week postoperatively by paired Wilcoxon tests are shown in Figure 5 (P < .01). Temporal corneal flattening as well as lower and upper corneal steepening were statistically significant in both groups. One month postoperatively (Figure 6), there was significant surgically induced temporal flattening and lower corneal steepening in both groups. 'three months postoperatively, temporal flattening was still statistically significant in both groups (Figure 7), while lower corneal steepening was statistically significant only in the hinged-incision group. One year postoperatively in both groups, the only major region of significant surgically induced change was temporal flattening (Figure 8). This region was greater and extended to
Results One week postoperatively (Figure 1), both groups had a similar amount of temporal corneal flattening and upper and lower corneal steepening compared with preoperatively. The most pronounced effect was a peripheral temporal flattening of - 0.7 D (beveled incision; Figure 1, left) or -0.8 D (hinged incision; Figure 1, right), which decreased to -0.4 D in both groups at a distance of 1.5 mm from the center (1 ring = 0.5 mm). One month postoperatively (Figure 2), the peripheral temporal flattening slightly regressed in the beveledincision (-0.5 D) and hinged-incision (-0.7 D) groups (Figure 2, left and right, respectively). There was still some upper and lower corneal steepening in both groups. After 3 months (Figure 3) and 1 year (Figure 4), there was continued regression of surgically induced corneal shape changes. The 2 groups appeared to be similar.
-0. . . -0,7· -0", -0.11 -0.4. -003· -0.1. -0.1.
O· 0,1·
o.a.
o.a •
-o.e -
-0.71 -0.81 -0.111 -0.41 -0031 -0.11 -0.11 -0.01
-0.71 -0.7· -0.. ' -0.8 - -0.111 -0.11 - -0.41 -0.4. -003' -Q,3. -0..' -0.1. -0.11 -0.1· -0.0, D· D
0 D.1
D.1·
D
D,2·
o.a -
D.4 • D.II·
o.a • 0.7 -
D.4 • D.II •
o.a •
D.
D.7·
Figure 3. (Vass) Averaged difference maps of reduced data 3 months postoperatively. Left: Beveled-incision group. Right: Hinged-incision group. 1500
D,'
D
Figure 4. (Vass) Averaged difference maps of reduced data 1 year postoperatively. Left: Beveled-incision group. Right: Hingedincision group.
J CATARACT REFRACT SURG-VOL 24, NOVEMBER 1998
TOPOGRAPHIC CHANGES AFTER BEVELED AND HINGED CCIs -4.11 -4.7 -4,,-4.8-4.4 -
-4.71 ...., _1 ...... -o.a1 -o.a - -4.21 -o,a- -4.11 -4.1 - -4.D1
.-4.7 . . -- -0,71 _, -GA- -0.51
-4.5 - -4.41 00,4 -
-o.a -
a- a 0.1 a o.a - a OA- a
0-
0.1 -
0.1 -
0.2 -
D.II D.II 0.7 -
11,2 -
o.a -
CI.4 0.5 -
o.e -
0.
data 1 week postoperatively. Only significantly changed areas are shown (P < .01). Left: Beveled-incision group. Right: Hingedincision group.
Figure 6. (Vass) Paired Wilcoxon signed-rank tests of reduced data 1 month postoperatively. Only significantly changed areas are shown (P < .01). Left: Beveled-incision group. Right: Hingedincision group.
_ -0,7 -- ..0.71 _,
00,4 -
-4.. - -4.71
::::
-0,"1- ....,
-4" - -o,In -4,8 - ......., -4,.& - -4,:11 -o.a - -o,Z1 -4~ - 411 41- -4.111
-o,a1
. . . - -4.21 _ - -0,11
-0,'- -4.111 00.1 -
o.a -
0. 0.1
II -
0.1 -
0.2 -
o.a -
CI.4 D.II D.II -
q;, -
a
0.7 -
Figure 5. (Vass) Paired Wilcoxon signed-rank tests of reduced
~:
-4~1
-4.21 411 .cj~1 - -4.D1
-o,a-
a
0.1
o.a -
CI.4 D.II -
o.e -
0.
0.7 -
0,
Figure 7. (Vass) Paired Wilcoxon signed-rank tests of reduced data 3 months postoperatively. Only significantly changed areas are shown (P < .01). Left: Beveled-incision group. Right: Hingedincision group.
data 1 year postoperatively. Only significantly changed areas are shown (P < .01). Left: Beveled-incision group. Right: Hingedincision group.
more central areas in the hinged-incision than in the beveled-incision group (18 versus 4 areas). The regression in surgically induced changes was not statistically significant by Wilcoxon tests between 1 week and 1 month in all 225 areas (not shown). Between 1 month and 1 year postoperatively, only 2 areas showed a statistically significant regression in the beveled-incision group (Figure 9, left). In contrast, there were 2 large regions (43 areas) with statistically significant regression of temporal flattening and lower
corneal steepening in the hinged-incision group (Figure 9, right). Group comparisons of surgically induced corneal shape changes are shown in Figure 10. The only region with consistently significant between-group differences was a radial sector at 237 to 248 degrees 1 week postoperatively (Figure 10, left) and 214 to 259 degrees 3 months postoperatively (Figure 10, right). In this sector, the hinged-incision group exhibited 0.1 to 0.3 D more steepening than the beveled-
--
Figure 8. (Vass) Paired Wilcoxon signed-rank tests of reduced
-4.1147-4.11-4.11 -
-4.11 - -0,71 -0,7 - -0,.' _ - -4'"
00,4_- _ 00,41 ,
-4.4 - -4..,
....,
-o.a_ - ...., -0,,'
-4" - -0,11 41- _ 1 00.1 •
-4.1 - -4.D1 00.1 -
o.a • o.a •
....
0.2 • 0.2 -
OA· D.II •
0."1.
471 ...., _, -4.111
OA· 0 .. •
o.e •
0:
0,7 -
Figure 9. (Vass) Paired Wilcoxon signed-rank tests of reduced data from 1 month to 1 year postoperatively. Only significantly changed areas are shown (P < .01). Left: Beveled-incision group. Right: Hinged-incision group.
a 0.,
Figure 10. (Vass) Group comparison of reduced data of the beveled-incision and the hinged-incision groups (Wilcoxon signedrank tests). Only significantly different areas are shown (P < .05). Left: 1 week postoperatively. Right: 3 months postoperatively.
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Table 2. Spherical shifts of corneal topography from preoperatively to postoperatively.
Preop
2:
1 week
-0.09::': 0.32
NS
0.03::': 0.38
0.631 0.096
NS
NS
Preop
2:
1 month
0.01 ::': 0.31
NS
0.09::': 0.30
Preop
2:
3 months
0.01 ::': 0.31
NS
0.03::': 0.27
0.471
NS
Preop
2:
1 year
-0.07::': 0.31
NS
-0.09::': 0.30
0.078
NS
NS = not significant
the beveled-incision group 1 week (chi-square < .001) and 1 month (chi-square = .001) postoperatively (Table 5). In all 89 eyes, there were no serious complications, including postoperative wound leaking, endophthalmitis, or wound-gape infection.
incision group. This was also present 1 month postoperatively (not shown). Table 2 shows the apparent spherical shifts in both groups for different periods. There were no statistically significant spherical corneal topography changes in either group, nor were there differences between groups. The spherical changes were attributed to defocus artifacts. Tables 3 and 4 show the mean induced changes in topographic cylinder calculated on the basis of the Cravy, Naeser, Jaffe, and vector decomposition methods. There was a small with-the-rule shift in both groups immediately postoperatively. This shift was significantly larger in the hinged-incision than in the beveled-incision group when calculated using Cravy's method. In the hinged-incision group, there was a statistically significant decrease in SIA 3 months and 1 year postoperatively compared with 1 week postoperatively. In the beveled-incision group, SIA was stable after 1 week postoperatively. Wound-related keratopathy was not statistically significantly different between the groups 1 week and 1 month postoperatively. An external wound gape was observed more frequently in the hinged-incision than
III
Discussion Both the beveled and hinged incisions resulted in a similar typical pattern of temporal flattening and a nonorthogonal vertical steepening. In the group comparison, the only region of consistently different surgically induced shape changes was in the lower temporal sector. In this sector, there was a statistically significant enhancement of steepening in the hinged-incision group compared with the beveled-incision group 1 week and 1 and 3 months postoperatively. This corresponds to the finding that the semimeridian of lower corneal steepening was more bent toward the incision in the hinged-incision group. However, the difference between the groups was small: 0.1 versus 0.3 D. The amount of temporal flattening and vertical steepening was similar in both groups.
Table 3. Postoperative change in topographic cylinder, mean::': SO.
1 week
0.29::': 0.22
OA1 ::': 0.33
0.040
0.29::': 0.26
OA6 ::': 0.37
NS
0.36::': 0.32
OAO ::': 0.34
NS
1 month
0.36::': 0.29
0.38::': 0.32
NS
3 months
0.22::': 0.27
0.21 ::': 0.30*
NS
0.23::': 0.30
0.22::': 0.33*
NS
1 year
0.22::': 0.32
0.18::': 0.27*
NS
0.20::': 0.36
0.20::': 0.29*
NS
NS = not significant *Statistically significant difference compared with 1 week postoperative values
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Table 4. Postoperative change in topographic cylinder, mean ± SO.
1 week
0.47 ± 0.25
0.63 ± 0.42
NS
0.39 ± 0.23
0.56 ± 0.38
NS
0.09 ± 0.10
0.07 ± 0.10
NS
1 month
0.54 ± 0.28
0.54 ± 0.30
NS
0.45 ::!: 0.28
0.48 ± 0.31
NS
0.09 ± 0.11
0.06 ± 0.09
NS
3 months
0.43 ± 0.25
0.37 ± 0.32*
NS
0.33 ::!: 0.25
0.30 ± 0.31'
NS
0.10 ± 0.11
0.07 ± 0.11
NS
1 year
0.42 ± 0.72
0.40 ± 0.30*
NS
0.31 ::!: 0.29
0.30 ± 0.27'
NS
0.11 ± 0.13
0.10 ± 0.14
NS
NS = not significant; WTR = with the rule; ATR = against the rule *Statistically significant difference compared to 1 week postoperative
In all types of vector analysis, the beveled-incision group showed very low and stable SIA. This agrees with published results of vector analysis of 3.0 to 3.5 mm temporal CCls.9-16 The corneal topographic changes in both groups also agree with existing reports of corneal topographic changes after CCI. In an earlier paper,17 we reported a peripheral temporal flattening of 0.9 0 after a 3.0 mm CCI with a 300 J.Un groove. This is slightly more than in the present study (beveled incision 0.5 0; hinged incision 0.7 D). The difference might be the result of different wound construction because in the previous study, we used a diamond blade for CCIs. Joo and coauthors l8 report results of a videokeratographic analysis of surgically induced corneal shape changes after oblique and superior 3.1 mm beveled CCls. Similar to our results, they found a decreasing amount of wound-related flattening from the periphery toward the center. The oblique beveled CCI exhibited more wound-related flattening than our temporal beveled CCI, but their results were similar to ours with the temporal hinged CCI. This may be explained by the oblique position of the incision. It has been reported that superior incisions induce higher astigmatism than temporal incisions of the same size and construc-
Table 5. Postoperative wound gape.
o
25
2
2
26
5
15
2
5
16
10
tion. 13,15,19 This was also confirmed in a study by Joo and coauthors l8 in which the changes were more pronounced after a superior 3.1 mm beveled CCI than after an oblique incision. In contrast, Nielsen and Neuhann 10 found that only the direction of astigmatism, not the amount, was changed by moving the CCI from a superior to a temporal position. Langerman2 described the hinged incision with the idea of making the CCI safer. This concept has been tested in a cadaver eye model by Ernest and coauthors, 3 who proved the resistance to external pressure was greater with a hinged CCI than a beveled CCI. A limbal beveled incision, however, was as stable as a corneal hinged incision. The clinical implications of these findings are unknown. There is evidence that sutureless 5.0 mm CCls can lead to postoperative leaks in wounds that were watertight at the end of surgery.20 There is also evidence of an increased risk of endophthalmitis after sutureless 5.0 to 7.0 mm CCIs,I,21 perhaps because of postoperative inoculation of bacteria. It is unclear whether the incidence of postoperative endophthalmitis is greater after 3.0 mm sutureless CCls than after sclerocorneal incisions and whether the incidence might be the result of a postoperative intercurrent wound leak. Because of our study size, we cannot draw conclusions about the incidence of endophthalmitis in the 2 groups; there were no cases in either group. The question of whether a hinged CCI is safer than a beveled CCI can only be addressed by evaluating a larger sample. On the other hand, we did not observe clinically significant 'problems caused by the hinged incision. This incision induced a similar, although slightly in-
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creased, amount of astigmatism as the beveled incision. We frequently observed wound gape in the early postoperative period in the hinged-incision group. Although this gape might act as a reservoir for bacteria, we observed no cases of wound-gape infection. Assuming that cadaver eye studies give valid information about the stability of incisions, a transient intercurrent wound leak might also occur after a 3.0 mm CCI when the patient presses down hard on his or her eye. According to Ernest and coauthors,3 there are 2 ways to avoid this: placing the incision as near to the limbus as possible (not clear corneal) or making a hinged incision. In conclusion, our study indicates that the price for possibly increased safety of the hinged incision is only minimally additional induced astigmatism. The safety of the hinged incision must be evaluated in a larger study.
10.
11. 12.
13.
14.
15.
References 1. Davis PL. PMMA implants via temporal clear corneal incisions: concern replaces confidence. Eur J Implant Refract Surg 1994; 6:205-210 2. Langerman DW Architectural design of a self-sealing corneal tunnel, single-hinge incision. J Cataract Refract Surg 1994; 20:84-88 3. Ernest PH, Fenzl R, Lavery KT, Sensoli A. Relative stabiliry of clear corneal incisions in a cadaver eye model. J Cataract Refractive Surg 1995; 21:39-42 4. Vass C, Menapace R, Rainer G, Schulz H. Improved algorithm for statistical batch-by-batch analysis of corneal topographic data. J Cataract Refract Surg 1997; 23:903-912 5. Cravy Tv. Calculation of the change in corneal astigmatism following cataract extraction. Ophthalmic Surg 1979; 10:38-49 6. Naeser K. Conversion of keratometer readings to polar values. J Cataract Refract Surg 1990; 16:741-745 7. Jaffe NS, Clayman HM. The pathophysiology of corneal astigmatism after cataract extraction. Trans Am Acad Ophthalmol Otolaryngol1975; 79:0P615-0P630 8. Seiler T, Wollensak J. Uber die mathematische Darstellung des postoperativen regularen Hornhautastigmatismus. Klin Monatsbl Augenheilkd 1993; 203:7076 9. Kohnen T, Dick B, Jacobi KW Comparison of the induced astigmatism after temporal clear corneal tunnel
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16.
17.
18.
19.
20.
21.
incisions of different sizes. J Cataract Refract Surg 1995; 21:417-424 Nielsen pJ, Neuhann T. Prospective evaluation of surgically induced astigmatism and astigmatic keratotomy effects of various self-sealing small incisions. J Cataract Refract Surg 1995; 21:43-48 Ernest PH. Posterior limbal incision. J Cataract Refract Surg 1996; 22:78-84 Pfleger T, Skorpik C, Menapace R, et al. Long-term course of induced astigmatism after clear corneal incision cataract surgery. J Cataract Refract Surg 1996; 22:72-77 Masket S, Tennen DG. Astigmatic stabilization of 3. 0 mm temporal clear corneal cataract incisions. J Cataract Refract Surg 1996; 22:1451-1455 Long DA, Monica ML. A prospective evaluation of corneal curvature changes with 3.0- to 3.5-mm corneal tunnel phacoemulsification. Ophthalmology 1996; 103: 226-232 Oshima Y, Tsujikawa K, Oh A, Harino S. Comparative study of intraocular lens implantation through 3.0 mm temporal clear corneal and superior scleral tunnel selfsealing incisions. J Cataract Refract Surg 1997; 23:347353 Muller-Jensen K, Barlinn B. Long-term astigmatic changes after clear corneal cataract surgery. J Cataract Refract Surg 1997; 23:354-357 Vass C, Menapace R. Computerized statistical analysis of corneal topography for the evaluation of changes in corneal shape after surgery. Am J Ophthalmol 1994; 118:177-184 Joo C-K, Han H-K, KimJ-H. Computer-assisted videokeratography to measure changes in astigmatisn;J. induced by sutureless cataract surgery. J Cataract Refract Surg 1997; 23:555-561 Hayashi K, Nakao F, Hayashi F. Corneal topographic analysis of superolateral incision cataract surgery. J Cataract Refract Surg 1994; 20:392-399 Menapace R. Delayed iris prolapse with unsutured 5.1 mm clear corneal incisions. J Cataract Refract Surg 1995; 21:353-357 Pham DT, Liekfeld A, Anders N, et al. 7-mmTunnelschnitt mit lateralem Zugang als Routineeingriff in der Kataraktchirurgie. Ophthalmologe 1997; 94:3-5
From the Department ofOphthalmology, University of Vienna, Vienna, Austria. None ofthe authors has a proprietary interest in any material or method mentioned.
] CATARACT REFRACT SURG-VOL 24, NOVEMBER 1998
C
lear corneal incisions (CCls) have become popular because they are easy to construct and are convenient for the patient and relatively astigmatically neutral. However, the lack of conjunctival covering of
Reprint requests to Clemens Vass, MD, University of Vienna, Department of Ophthalmology, Wiihringer Gurtel 18-20, A-1090 Vienna,
Austria. 1498
the incision can lead to postoperative leakage or endophthalmitis in the case of improper wound construction. 1 To improve wound stability, the hinged CCI was introduced. 2 This 0.75 mm deep incision has a perpendicular precut and a corneal tunnel starting from the precut at a depth of 0.50 mm. In a cadaver eye study, Ernest and coauthors3 found hinged CCls were more stable than beveled CCIs of the
J CATARACf REFRACT SURG-VOL 24, NOVEMBER 1998
TOPOGRAPHIC CHANGES AFTER BEVELED AND HINGED CCls
same width. The degree of surgically induced astigmatism (SIA) with this better wound stability is still unknown. This study compared the induced corneal shape changes after beveled and hinged CCls using topographic batch-by-batch analysis. 4
Patients and Methods This prospective study included 89 eyes of 79 patients scheduled for phacoemulsification with implantation of a foldable intraocular lens (IOL). Patients were assigned to a beveled-incision or hinged-incision group. Exclusion criteria were previous ocular surgery, corneal pathology, or pathology of the anterior segment other than cataract. Postoperative exclusion criteria were a follow-up of less than 3 months or poor-quality topographic readings. Topographic readings in 64 eyes of 56 patients were evaluated: 29 in the beveledincision group and 35 in the hinged-incision group. In both incision groups, a temporal CCI of3.00 mm width and 1.75 to 2.00 mm length was made. The incision entry point was 0.50 mm into clear cornea. In both groups, the incision was self-sealing and sutureless. In the beveled-incision group, a stab incision was made with a 3.0 mm keratome blade (Alcon). In the hingedincision group, a 3.0 mm long, 0.7 mm deep perpendicular precut was done first with a calibrated diamond RK-T knife (Katena). Then, the CCI was made with the 3.0 mm keratome blade, starting at about half of corneal thickness. Except for the CCI construction, the surgical procedure was identical in all patients and performed by the same surgeon (R.M.). In all patients, 2 side-port incisions were made at the 7 and 11 o'clock positions (right eye) or the 1 and 5 o'clock positions (left eye). A continuous curvilinear capsulorhexis was performed through the 7 o'clock (right eye) or 1 o'clock (left eye) paracentesis. Bimanual phacoemulsification and aspiration of cortex followed. After the injection of viscoelastic material, a silicone 10L (Allergan, AMO SI-30) was implanted in the capsular bag with a Fine II forceps (Rhein Medical Inc.) and the viscoelastic material was removed. The wound was tested for watertightness and hydrated if necessary. No corneal sutures were used in any case. Corneal topography was recorded 5 times using a
computer-assisted videokeratoscope (TMS-l, Computed Anatomy, Inc.): preoperatively, and 1 week, 1 and 3 months, and 1 year postoperatively. All topographic readings were taken unmasked by 1 of 2 experienced investigators (CY., G.R.). For every patient, the localization of the incision was postoperatively estimated at the slitlamp with an accuracy of 1/2 o'clock position. At the 1 week and 1 month postoperative slitlamp examination, wound-related localized keratopathy and the external CCI gape were graded (Table 1). The data of the topographic readings were exported to a personal computer. The evaluation was done with the help of a topographic batch-by-batch analysis program. 4 The records were corrected for small local artifacts. If necessary, the data were rotated according to localization of the incision to simulate an exact temporal position. Then, the data were reduced to 225 corneal areas and corrected for defocus artifacts. On the basis of these data, the differences were statistically evaluated preoperatively to 1 week, 1 and 3 months, and 1 year postoperatively; 1 week to 1 month postoperatively; 1 month to 1 year postoperatively. Color-coded averaged difference maps were made to depict the differences for the whole group. Paired Wilcoxon signedrank tests were calculated for the same periods and then transformed into color-coded Wilcoxon-test maps. Group comparisons of the above paired differences of the 2 incision groups were calculated and transformed into color-coded maps. The changes in the spherical power (apparent spherical shifts) of the corneal topographic maps were calculated for the different time periods. If there appeared to be a statistical significance in the paired t tests, the apparent spherical shifts were called true spherical shifts. Otherwise, they were called defocus artifacts. The true spherical shifts (or defocus artifacts) were also subjected to group comparisons. Table 1. Grades of wound-related keratopathy and incisional gapes.
o
Absent
Absent
Trace
Trace
2
Moderate
Present
3
Marked
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TOPOGRAPHIC CHANGES AFTER BEVELED AND HINGED CCls -o.a.
-0.8. -0.7· -0", -0,5. -0.4. -0,3. -G.2.
-0.71 -0,,1 -0,51 -0.41 -0,31 -0.21 -0.11 -o~1 - -0.01 E!a.~ O· O. 0.1· 0.1 11.2. 0
-0.7· -0.8. -0.5 -G.4 -
-0.71 -0.81 -0,51 -0.41
-0.31
-Q,3 - -0.21 -0,2. -0.11 . -0.1 - -0',01 iifi'
0-
0.1· 0,2 -
CI.3 •
0,3 -
0.4 0,5 • 0.8 • 0.7·
o.a •
0.
0
0.1 0
0
D.4 -
0
0.8· 0.7 -
0.
Figure 1. (Vass) Averaged difference maps of reduced data
Figure 2. (Vass) Averaged difference maps of reduced data
1 week postoperatively. Left: Beveled-incision group. Right: Hingedincision group.
1 month postoperatively. Left: Beveled-incision group. Right: Hinged-incision group.
In addition, a vector analysis of the topographic data of the zone 1.5 mm from the center was done. 5- 8 The significance of group comparisons was calculated using t tests.
Throughout the follow-up, the semi meridians of steepening were not truly vertical but were bent toward the incision at an angle decreasing from the center (169 to 180 degrees) toward the periphery (102 to 147 degrees) (1 area = 11.25 degrees). The lower semimeridian of steepening seemed to be more distorted toward the incision in the hinged-incision (Figures 1 to 4, right) than in the beveled-incision (Figures 1 to 4, left) group. The corneal areas with significant surgically induced changes at 1 week postoperatively by paired Wilcoxon tests are shown in Figure 5 (P < .01). Temporal corneal flattening as well as lower and upper corneal steepening were statistically significant in both groups. One month postoperatively (Figure 6), there was significant surgically induced temporal flattening and lower corneal steepening in both groups. 'three months postoperatively, temporal flattening was still statistically significant in both groups (Figure 7), while lower corneal steepening was statistically significant only in the hinged-incision group. One year postoperatively in both groups, the only major region of significant surgically induced change was temporal flattening (Figure 8). This region was greater and extended to
Results One week postoperatively (Figure 1), both groups had a similar amount of temporal corneal flattening and upper and lower corneal steepening compared with preoperatively. The most pronounced effect was a peripheral temporal flattening of - 0.7 D (beveled incision; Figure 1, left) or -0.8 D (hinged incision; Figure 1, right), which decreased to -0.4 D in both groups at a distance of 1.5 mm from the center (1 ring = 0.5 mm). One month postoperatively (Figure 2), the peripheral temporal flattening slightly regressed in the beveledincision (-0.5 D) and hinged-incision (-0.7 D) groups (Figure 2, left and right, respectively). There was still some upper and lower corneal steepening in both groups. After 3 months (Figure 3) and 1 year (Figure 4), there was continued regression of surgically induced corneal shape changes. The 2 groups appeared to be similar.
-0. . . -0,7· -0", -0.11 -0.4. -003· -0.1. -0.1.
O· 0,1·
o.a.
o.a •
-o.e -
-0.71 -0.81 -0.111 -0.41 -0031 -0.11 -0.11 -0.01
-0.71 -0.7· -0.. ' -0.8 - -0.111 -0.11 - -0.41 -0.4. -003' -Q,3. -0..' -0.1. -0.11 -0.1· -0.0, D· D
0 D.1
D.1·
D
D,2·
o.a -
D.4 • D.II·
o.a • 0.7 -
D.4 • D.II •
o.a •
D.
D.7·
Figure 3. (Vass) Averaged difference maps of reduced data 3 months postoperatively. Left: Beveled-incision group. Right: Hinged-incision group. 1500
D,'
D
Figure 4. (Vass) Averaged difference maps of reduced data 1 year postoperatively. Left: Beveled-incision group. Right: Hingedincision group.
J CATARACT REFRACT SURG-VOL 24, NOVEMBER 1998
TOPOGRAPHIC CHANGES AFTER BEVELED AND HINGED CCIs -4.11 -4.7 -4,,-4.8-4.4 -
-4.71 ...., _1 ...... -o.a1 -o.a - -4.21 -o,a- -4.11 -4.1 - -4.D1
.-4.7 . . -- -0,71 _, -GA- -0.51
-4.5 - -4.41 00,4 -
-o.a -
a- a 0.1 a o.a - a OA- a
0-
0.1 -
0.1 -
0.2 -
D.II D.II 0.7 -
11,2 -
o.a -
CI.4 0.5 -
o.e -
0.
data 1 week postoperatively. Only significantly changed areas are shown (P < .01). Left: Beveled-incision group. Right: Hingedincision group.
Figure 6. (Vass) Paired Wilcoxon signed-rank tests of reduced data 1 month postoperatively. Only significantly changed areas are shown (P < .01). Left: Beveled-incision group. Right: Hingedincision group.
_ -0,7 -- ..0.71 _,
00,4 -
-4.. - -4.71
::::
-0,"1- ....,
-4" - -o,In -4,8 - ......., -4,.& - -4,:11 -o.a - -o,Z1 -4~ - 411 41- -4.111
-o,a1
. . . - -4.21 _ - -0,11
-0,'- -4.111 00.1 -
o.a -
0. 0.1
II -
0.1 -
0.2 -
o.a -
CI.4 D.II D.II -
q;, -
a
0.7 -
Figure 5. (Vass) Paired Wilcoxon signed-rank tests of reduced
~:
-4~1
-4.21 411 .cj~1 - -4.D1
-o,a-
a
0.1
o.a -
CI.4 D.II -
o.e -
0.
0.7 -
0,
Figure 7. (Vass) Paired Wilcoxon signed-rank tests of reduced data 3 months postoperatively. Only significantly changed areas are shown (P < .01). Left: Beveled-incision group. Right: Hingedincision group.
data 1 year postoperatively. Only significantly changed areas are shown (P < .01). Left: Beveled-incision group. Right: Hingedincision group.
more central areas in the hinged-incision than in the beveled-incision group (18 versus 4 areas). The regression in surgically induced changes was not statistically significant by Wilcoxon tests between 1 week and 1 month in all 225 areas (not shown). Between 1 month and 1 year postoperatively, only 2 areas showed a statistically significant regression in the beveled-incision group (Figure 9, left). In contrast, there were 2 large regions (43 areas) with statistically significant regression of temporal flattening and lower
corneal steepening in the hinged-incision group (Figure 9, right). Group comparisons of surgically induced corneal shape changes are shown in Figure 10. The only region with consistently significant between-group differences was a radial sector at 237 to 248 degrees 1 week postoperatively (Figure 10, left) and 214 to 259 degrees 3 months postoperatively (Figure 10, right). In this sector, the hinged-incision group exhibited 0.1 to 0.3 D more steepening than the beveled-
--
Figure 8. (Vass) Paired Wilcoxon signed-rank tests of reduced
-4.1147-4.11-4.11 -
-4.11 - -0,71 -0,7 - -0,.' _ - -4'"
00,4_- _ 00,41 ,
-4.4 - -4..,
....,
-o.a_ - ...., -0,,'
-4" - -0,11 41- _ 1 00.1 •
-4.1 - -4.D1 00.1 -
o.a • o.a •
....
0.2 • 0.2 -
OA· D.II •
0."1.
471 ...., _, -4.111
OA· 0 .. •
o.e •
0:
0,7 -
Figure 9. (Vass) Paired Wilcoxon signed-rank tests of reduced data from 1 month to 1 year postoperatively. Only significantly changed areas are shown (P < .01). Left: Beveled-incision group. Right: Hinged-incision group.
a 0.,
Figure 10. (Vass) Group comparison of reduced data of the beveled-incision and the hinged-incision groups (Wilcoxon signedrank tests). Only significantly different areas are shown (P < .05). Left: 1 week postoperatively. Right: 3 months postoperatively.
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TOPOGRAPHIC CHANGES AFTER BEVELED AND HINGED CCls
Table 2. Spherical shifts of corneal topography from preoperatively to postoperatively.
Preop
2:
1 week
-0.09::': 0.32
NS
0.03::': 0.38
0.631 0.096
NS
NS
Preop
2:
1 month
0.01 ::': 0.31
NS
0.09::': 0.30
Preop
2:
3 months
0.01 ::': 0.31
NS
0.03::': 0.27
0.471
NS
Preop
2:
1 year
-0.07::': 0.31
NS
-0.09::': 0.30
0.078
NS
NS = not significant
the beveled-incision group 1 week (chi-square < .001) and 1 month (chi-square = .001) postoperatively (Table 5). In all 89 eyes, there were no serious complications, including postoperative wound leaking, endophthalmitis, or wound-gape infection.
incision group. This was also present 1 month postoperatively (not shown). Table 2 shows the apparent spherical shifts in both groups for different periods. There were no statistically significant spherical corneal topography changes in either group, nor were there differences between groups. The spherical changes were attributed to defocus artifacts. Tables 3 and 4 show the mean induced changes in topographic cylinder calculated on the basis of the Cravy, Naeser, Jaffe, and vector decomposition methods. There was a small with-the-rule shift in both groups immediately postoperatively. This shift was significantly larger in the hinged-incision than in the beveled-incision group when calculated using Cravy's method. In the hinged-incision group, there was a statistically significant decrease in SIA 3 months and 1 year postoperatively compared with 1 week postoperatively. In the beveled-incision group, SIA was stable after 1 week postoperatively. Wound-related keratopathy was not statistically significantly different between the groups 1 week and 1 month postoperatively. An external wound gape was observed more frequently in the hinged-incision than
III
Discussion Both the beveled and hinged incisions resulted in a similar typical pattern of temporal flattening and a nonorthogonal vertical steepening. In the group comparison, the only region of consistently different surgically induced shape changes was in the lower temporal sector. In this sector, there was a statistically significant enhancement of steepening in the hinged-incision group compared with the beveled-incision group 1 week and 1 and 3 months postoperatively. This corresponds to the finding that the semimeridian of lower corneal steepening was more bent toward the incision in the hinged-incision group. However, the difference between the groups was small: 0.1 versus 0.3 D. The amount of temporal flattening and vertical steepening was similar in both groups.
Table 3. Postoperative change in topographic cylinder, mean::': SO.
1 week
0.29::': 0.22
OA1 ::': 0.33
0.040
0.29::': 0.26
OA6 ::': 0.37
NS
0.36::': 0.32
OAO ::': 0.34
NS
1 month
0.36::': 0.29
0.38::': 0.32
NS
3 months
0.22::': 0.27
0.21 ::': 0.30*
NS
0.23::': 0.30
0.22::': 0.33*
NS
1 year
0.22::': 0.32
0.18::': 0.27*
NS
0.20::': 0.36
0.20::': 0.29*
NS
NS = not significant *Statistically significant difference compared with 1 week postoperative values
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TOPOGRAPHIC CHANGES AFTER BEVELED AND HINGED CCls
Table 4. Postoperative change in topographic cylinder, mean ± SO.
1 week
0.47 ± 0.25
0.63 ± 0.42
NS
0.39 ± 0.23
0.56 ± 0.38
NS
0.09 ± 0.10
0.07 ± 0.10
NS
1 month
0.54 ± 0.28
0.54 ± 0.30
NS
0.45 ::!: 0.28
0.48 ± 0.31
NS
0.09 ± 0.11
0.06 ± 0.09
NS
3 months
0.43 ± 0.25
0.37 ± 0.32*
NS
0.33 ::!: 0.25
0.30 ± 0.31'
NS
0.10 ± 0.11
0.07 ± 0.11
NS
1 year
0.42 ± 0.72
0.40 ± 0.30*
NS
0.31 ::!: 0.29
0.30 ± 0.27'
NS
0.11 ± 0.13
0.10 ± 0.14
NS
NS = not significant; WTR = with the rule; ATR = against the rule *Statistically significant difference compared to 1 week postoperative
In all types of vector analysis, the beveled-incision group showed very low and stable SIA. This agrees with published results of vector analysis of 3.0 to 3.5 mm temporal CCls.9-16 The corneal topographic changes in both groups also agree with existing reports of corneal topographic changes after CCI. In an earlier paper,17 we reported a peripheral temporal flattening of 0.9 0 after a 3.0 mm CCI with a 300 J.Un groove. This is slightly more than in the present study (beveled incision 0.5 0; hinged incision 0.7 D). The difference might be the result of different wound construction because in the previous study, we used a diamond blade for CCIs. Joo and coauthors l8 report results of a videokeratographic analysis of surgically induced corneal shape changes after oblique and superior 3.1 mm beveled CCls. Similar to our results, they found a decreasing amount of wound-related flattening from the periphery toward the center. The oblique beveled CCI exhibited more wound-related flattening than our temporal beveled CCI, but their results were similar to ours with the temporal hinged CCI. This may be explained by the oblique position of the incision. It has been reported that superior incisions induce higher astigmatism than temporal incisions of the same size and construc-
Table 5. Postoperative wound gape.
o
25
2
2
26
5
15
2
5
16
10
tion. 13,15,19 This was also confirmed in a study by Joo and coauthors l8 in which the changes were more pronounced after a superior 3.1 mm beveled CCI than after an oblique incision. In contrast, Nielsen and Neuhann 10 found that only the direction of astigmatism, not the amount, was changed by moving the CCI from a superior to a temporal position. Langerman2 described the hinged incision with the idea of making the CCI safer. This concept has been tested in a cadaver eye model by Ernest and coauthors, 3 who proved the resistance to external pressure was greater with a hinged CCI than a beveled CCI. A limbal beveled incision, however, was as stable as a corneal hinged incision. The clinical implications of these findings are unknown. There is evidence that sutureless 5.0 mm CCls can lead to postoperative leaks in wounds that were watertight at the end of surgery.20 There is also evidence of an increased risk of endophthalmitis after sutureless 5.0 to 7.0 mm CCIs,I,21 perhaps because of postoperative inoculation of bacteria. It is unclear whether the incidence of postoperative endophthalmitis is greater after 3.0 mm sutureless CCls than after sclerocorneal incisions and whether the incidence might be the result of a postoperative intercurrent wound leak. Because of our study size, we cannot draw conclusions about the incidence of endophthalmitis in the 2 groups; there were no cases in either group. The question of whether a hinged CCI is safer than a beveled CCI can only be addressed by evaluating a larger sample. On the other hand, we did not observe clinically significant 'problems caused by the hinged incision. This incision induced a similar, although slightly in-
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TOPOGRAPHIC CHANGES AFTER BEVELED AND HINGED CCIs
creased, amount of astigmatism as the beveled incision. We frequently observed wound gape in the early postoperative period in the hinged-incision group. Although this gape might act as a reservoir for bacteria, we observed no cases of wound-gape infection. Assuming that cadaver eye studies give valid information about the stability of incisions, a transient intercurrent wound leak might also occur after a 3.0 mm CCI when the patient presses down hard on his or her eye. According to Ernest and coauthors,3 there are 2 ways to avoid this: placing the incision as near to the limbus as possible (not clear corneal) or making a hinged incision. In conclusion, our study indicates that the price for possibly increased safety of the hinged incision is only minimally additional induced astigmatism. The safety of the hinged incision must be evaluated in a larger study.
10.
11. 12.
13.
14.
15.
References 1. Davis PL. PMMA implants via temporal clear corneal incisions: concern replaces confidence. Eur J Implant Refract Surg 1994; 6:205-210 2. Langerman DW Architectural design of a self-sealing corneal tunnel, single-hinge incision. J Cataract Refract Surg 1994; 20:84-88 3. Ernest PH, Fenzl R, Lavery KT, Sensoli A. Relative stabiliry of clear corneal incisions in a cadaver eye model. J Cataract Refractive Surg 1995; 21:39-42 4. Vass C, Menapace R, Rainer G, Schulz H. Improved algorithm for statistical batch-by-batch analysis of corneal topographic data. J Cataract Refract Surg 1997; 23:903-912 5. Cravy Tv. Calculation of the change in corneal astigmatism following cataract extraction. Ophthalmic Surg 1979; 10:38-49 6. Naeser K. Conversion of keratometer readings to polar values. J Cataract Refract Surg 1990; 16:741-745 7. Jaffe NS, Clayman HM. The pathophysiology of corneal astigmatism after cataract extraction. Trans Am Acad Ophthalmol Otolaryngol1975; 79:0P615-0P630 8. Seiler T, Wollensak J. Uber die mathematische Darstellung des postoperativen regularen Hornhautastigmatismus. Klin Monatsbl Augenheilkd 1993; 203:7076 9. Kohnen T, Dick B, Jacobi KW Comparison of the induced astigmatism after temporal clear corneal tunnel
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21.
incisions of different sizes. J Cataract Refract Surg 1995; 21:417-424 Nielsen pJ, Neuhann T. Prospective evaluation of surgically induced astigmatism and astigmatic keratotomy effects of various self-sealing small incisions. J Cataract Refract Surg 1995; 21:43-48 Ernest PH. Posterior limbal incision. J Cataract Refract Surg 1996; 22:78-84 Pfleger T, Skorpik C, Menapace R, et al. Long-term course of induced astigmatism after clear corneal incision cataract surgery. J Cataract Refract Surg 1996; 22:72-77 Masket S, Tennen DG. Astigmatic stabilization of 3. 0 mm temporal clear corneal cataract incisions. J Cataract Refract Surg 1996; 22:1451-1455 Long DA, Monica ML. A prospective evaluation of corneal curvature changes with 3.0- to 3.5-mm corneal tunnel phacoemulsification. Ophthalmology 1996; 103: 226-232 Oshima Y, Tsujikawa K, Oh A, Harino S. Comparative study of intraocular lens implantation through 3.0 mm temporal clear corneal and superior scleral tunnel selfsealing incisions. J Cataract Refract Surg 1997; 23:347353 Muller-Jensen K, Barlinn B. Long-term astigmatic changes after clear corneal cataract surgery. J Cataract Refract Surg 1997; 23:354-357 Vass C, Menapace R. Computerized statistical analysis of corneal topography for the evaluation of changes in corneal shape after surgery. Am J Ophthalmol 1994; 118:177-184 Joo C-K, Han H-K, KimJ-H. Computer-assisted videokeratography to measure changes in astigmatisn;J. induced by sutureless cataract surgery. J Cataract Refract Surg 1997; 23:555-561 Hayashi K, Nakao F, Hayashi F. Corneal topographic analysis of superolateral incision cataract surgery. J Cataract Refract Surg 1994; 20:392-399 Menapace R. Delayed iris prolapse with unsutured 5.1 mm clear corneal incisions. J Cataract Refract Surg 1995; 21:353-357 Pham DT, Liekfeld A, Anders N, et al. 7-mmTunnelschnitt mit lateralem Zugang als Routineeingriff in der Kataraktchirurgie. Ophthalmologe 1997; 94:3-5
From the Department ofOphthalmology, University of Vienna, Vienna, Austria. None ofthe authors has a proprietary interest in any material or method mentioned.
] CATARACT REFRACT SURG-VOL 24, NOVEMBER 1998