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Prospective evaluation of surgically induced astigmatism and astigmatic keratotomy effects of various self-sealing small incisions
Prospective evaluation of surgically induced astigmatism and astigmatic keratotomy effects of various self-sealing small incisions Per Julius Nielsen, M.D.
ABSTRACT The refractive effects of self-sealing clear corneal and corneoscleral tunnel incisions, 3.5 mm and 5.2 mm, in cataract surgery were studied prospectively by automatic keratometric evaluation at day one postoperatively and weeks one, three, and six. Keratometric readings were converted to polar values. The amount of surgically induced astigmatism was calculated for each incision and mean postoperative keratometric astigmatism was estimated for patients with preoperative against-the-rule and with-the-rule astigmatism to evaluate the astigmatic keratotomy effects of the incisions. The corneoscleral incisions were almost astigmatically neutral, with no major difference between the 3.5 mm and the 5.2 mm incisions after six weeks. The 5.2 mm frown incisions were less stable than the straight corneoscleral incisions. Clear corneal incisions resulted in a considerable amount of induced astigmatism; there was more with the 5.2 mm incisions than with the 3.5 mm incisions. Temporal incisions resulted in a with-therule induced change and superior incisions, an against-the-rule induced change. The refractive effect of the clear corneal incisions did not change significantly from day one to week six. The astigmatic keratotomy effects of these incisions were therefore more useful and predictable. Preoperative against-the-rule astigmatism was reduced significantly by temporally placed clear corneal incisions and preoperative with-the-rule astigmatism, by superiorly placed clear corneal incisions. If one considers the preoperative astigmatism when selecting incision type and location for small incision cataract surgery, one can minimize postoperative keratometric astigmatism. Key Words: astigmatic keratotomy, cataract surgery, clear cornea, corneoscleral, induced astigmatism, keratometric astigmatism, selfsealing incision
The refractive aspect of cataract surgery has received considerable attention with the advent of modern small incision surgery. The amount of surgically induced astigmatism can be controlled, and faster wound stability reduces the time required for visual rehabilitation. 1-3 Recently, preference has shifted from corn eo scleral incisions to clear corneal incisions. 4 ,5 One result of this change has been more induced astigmatism because the corneal incisions are closer to the visual axis.
This result seems to be exaggerated at the superior site where an against-the-rule (ATR) shift in preoperative astigmatism is seen. For that reason, unsutured clear corneal incisions should not be used in cases with preoperative ATR astigmatism unless a temporal incision site is used. Temporally placed incisions induce with-the-rule (WTR) shift in preoperative astigmatism and can reduce pre-existing ATR astigmatism. 4 ,6 Against-the-rule astigmatism yields poorer vision than WTR astigmatism, and WTR astigmatism post-
From the Department of Ophthalmology, Hjr;;rring Hospital, Hjr;;rring, Denmark. Reprint requests to Per Julius Nielsen, M.D., Department of Ophthalmology, Rigshospitalet, University Hospital of Copenhagen, DK-2JOO Copenhagen, Denmark. J CATARACf REFRACf SURG-VOL 21 , JANUARY 1995
43
operatively seems to be better for unaided distance vision and near vision? Therefore, preoperative evaluation of keratometric astigmatism is important, not only for calculating the intraocular lens (IOL) power, but also for planning the incision type, length, and location to control the amount and direction of postoperative astigmatism. 2 The present study was planned prospectively to evaluate the amount of surgically induced astigmatism and its decay with various self-sealing cataract incisions. The effect and stability of the incisions on the preoperative keratometric astigmatism were also evaluated, primarily to determine the astigmatic keratotomy effects of the clear corneal incisions.
MATERIALS AND METHODS This investigation was originally planned as a prospective, randomized study of the amount of surgically induced astigmatism with eight different self-sealing incisions used in cataract surgery performed by phacoemulsification. Twelve patients were assigned to each incision group. In the first few cases, the incision site was randomly selected according to the protocol, but then the preoperative astigmatism was taken into consideration. Patients with significant preoperative ATR astigmatism had temporal clear corneal incisions; patients with small amounts of WTR or no preoperative astigmatism had corneoscleral, frown, or 3.5 mm superior clear corneal incisions, and those with greater WTR astigmatism had 5.2 mm superior clear corneal incisions. This study design change was made to prevent adding a significant amount of induced astigmatism to the preoperative astigmatism, especially when a clear corneal incision was used. Ninety-three consecutive patients were included in the study. Incision lengths of 3.5 mm were used in cases in which a foldable silicone IOL (Allergan SI-30 or Staar 4203) was implanted. Incisions of 5.2 mm were used in cases in which a one-piece poly(methyl methacrylate) (PMMA) IOL (Pharmacia 809P or 809C) was implanted. The clear corneal incisions were placed superiorly or temporally; the corn eo scleral incisions and frown incisions were placed superiorly. Clear corneal incisions were used in 54 patients: 3.5 mm incisions were placed superiorly in 17 patients and temporally in 16; 5.2 mm incisions were placed superiorly in 10 patients and temporally in 11. Corneoscleral and frown incisions were used in 39 patients: 3.5 mm corneoscleral incisions in 13 patients and 3.5 mm frown incisions in 7 patients; 5.2 mm corneoscleral incisions in 12 patients and 5.2 mm frown incisions in 7 patients. A 3 mm diamond blade was used to make the three-step clear corneal incision, and metal blades were used with the three-step corneoscleral and frown 44
J CATARACT REFRACT
incisions. In addition to the primary incision, a stab incision was made for bimanual phacoemulsification. Cautery was used only with corneoscleral and frown incisions. The intraocular technique was the same in all patients: capsulorhexis, viscoelastic agent (sodium hyaluronate, Healon-GV@), and phacoemulsification with nucleus cracking. None of the incisions was sutured. Intrastromal injections were sometimes used with the clear corneal incisions to ensure watertightness. Steroid and antibiotic ointments were used by the patients twice a day for two weeks. Keratometric astigmatism was measured at day one and weeks one, three, and six by a trained nurse using an automatic keratometer (Allergan-Humphrey). Keratometric readings were converted to Naeser's polar values to obtain a single value for the balance between ATR and WTR for any given keratometric astigmatism. 8 Surgically induced astigmatism was calculated for each incision as the difference between preoperative and postoperative keratometric values at each follow-up interval. Stability of the astigmatic decay was evaluated by comparing mean induced astigmatism over the six week follow-up. The astigmatic keratotomy effect of the clear corneal incisions was determined by the reduction in preoperative ATR keratometric astigmatism with the 3.5 or 5.2 mm temporal incision and by the reduction in preoperative WTR keratometric astigmatism with the 3.5 or 5.2 mm superior incision. The astigmatic neutrality and stability of the corn eo scleral and frown incisions were determined by comparing mean keratometric astigmatism over the six-week follow-up. Statistics were evaluated using unpaired or paired, two-tailed t-tests; P < .05 was considered significant.
RESULTS Surgically induced astigmatism is reported in Tables 1 and 2 and shown in Figures 1 and 2. The astigmatic keratotomy effects of the 3.5 mm and the 5.2 mm temporal clear corneal incisions on pre-existing ATR astigmatism are shown in Tables 3 and 4, respectively. The astigmatic keratotomy effects of the 3.5 mm and the 5.2 mm superior clear corneal incisions on pre-existing WTR astigmatism are shown in Tables 5 and 6, respectively. The astigmatic neutrality ofthe 3.5 mm and 5.2 mm corneo scleral and frown incisions are shown in Tables 7 to 10.
DISCUSSION Astigmatic neutrality and rapid stabilization are major goals of small incision cataract surgery. These seem to be achieved with most sutured and
SURG~VOL
21, JANUARY 1995
Table 1. Surgically induced polar astigmatism with clear corneal incisions. Incision
3.5 CCS (n = 17)
Postop Interval
-.93 -.79 -.56 -.55
Day 1 Week 1 Week 3 Week 6
± .89 ± .65 ± .57 ± .57
3.5 CCT (n = 16) +.55 +.37 +.59 +.46
± ± ± ±
5.2 CCS = 10)
5.2 CCT
(n
-1.44 -1.55 -1.47 -1.24
.45 .50 .43 .54
± ± ± ±
(n
.96 .71 .75 .76
= 11)
+1.41 +1.21 +1.20 +.82
± 1.13 ± .78 ± .72 ± .76
CCS = clear corneal superior clear corneal temporal plus (+) = WTR minus (-) = ATR
ccr =
Table 2. Surgically induced polar astigmatism with corneoscleral incisions. Incision
3.5 CSS = 13)
Postop Interval
(n
+.14 +.01 -.05 -.10
Day 1 Week 1 Week 3 Week 6
± .70 ± .59 ± .55 ± .44
3.5 Frown (n = 7) -.01 -.06 -.02 -.20
± ± ± ±
5.2 CSS = 12)
5.2 Frown (n = 7)
(n
.82 .46 .58 .83
-.36 -.20 -.25 -.13
± .50 ± .56 ± .48 ± .46
-.84 -.49 -.50 -.35
± .89 ± .54 ± .63 ± .55
CSS = corneoscleral superior plus (+) = WTR minus (-) = ATR
WTR 0.6- 0 - - - - - - - - . . . . . - - - - - - - - - - - - - - - . ~
~
.Q
c
E rJl
0.4
oDay 1 ~
Week 1
0.2
HE!
O ~==~~~~WW~~~F=~~F=~ Week 3
EJ]
~ E -0.2
Week 6
Cl
+=I
!Q -0.4
~
:::J "U
-0.6
Fig. 1.
(Nielsen) Induced astigmatism with different 3.5 mm self-sealing incisions: clear corneal superior (CCS), clear corneal temporal (CCf), corneoscleral superior (CSS), and frown superior (frown). (Mean values and SDs are in Tables 1 and 2.)
.£ -0.8
ATR
-1+=======~======r=====~======~
unsutured corneoscleral incisions between 3.5 and 6.0 mm.z,3,6,9-11 Visual rehabilitation following cataract surgery may, however, be limited by remaining or exaggerated preoperative astigmatism. The standard approach of placing a self-sealing incision at 12 o'clock increases preoperative ATR astigmatism unless this is balanced by suturing. Suturing, however, delays stabilization by prolonging the
period during which astigmatic decay can occur. 2 The enhanced effect on preoperative astigmatism is even greater when a clear corneal incision is used. 4 Some surgeons have suggested that changing the incision site from a superior to a temporal position reduces the amount of surgically induced astigmatism, especially with clear corneal incisions, and addresses pre-existing ATR astigmatism. 4 ,6 A standard temporal
J CATARACf REFRACf SURG-VOL 21, JANUARY 1995
45
WTR 1,5
Fig. 2.
e! .sl c.
(Nielsen) Induced astigmatism with different 5.2 mm selfsealing incisions: clear corneal superior (CCS), clear corneal temporal (CCT), corneoscleral superior (CSS), and frown superior (frown). (Mean values and SDs are in Tables 1 and 2.)
0
is
E Ul
~
E O)
~
Day 1
~
a -0,5 -1
".£
-1 ,5
Q)
Week 1
0,5
" 0
D
~
Week 3
:." B
{
cct
::i: .--.-.-.-
.
[IT]
.
Week 6
.-".-".-".-----"------""".-..-.-..-.-".-,,.
::J
ATR
-2
Table 3. Astigmatic keratotomy effect of the temporal 3.5 mm unsutured clear corneal incision used to reduce pre-existing ATR astigmatism in 12 patients. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism -.92 - .38 -.18 -.41
± ± ± ±
.58 (ATR) .87 (P = .07) .n(p = .005) .97 (P = .02)
Table 4. Astigmatic effect of the temporal 5.2 mm unsutured clear corneal incision used to reduce preexisting ATR astigmatism in 10 patients. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism -1.41 - .15 -.10 -.59
± ± ± ±
.81 (ATR) 1.12 (P = .0006) 1.06(P = .0001) 1.28 (P = .01)
approach may, however, worsen preoperative WTR astigmatism, although postoperative WTR may be less troublesome than ATR astigmatism. 7 When the amount of surgically induced astigmatism is negligible, refractive cataract surgery can be performed by including astigmatic keratotomy in the cataract extraction procedure. When the amount of induced astigmatism is not negligible, the simultaneous use of astigmatic keratotomy may be less reliable. Although the mean value of induced astigmatism may be favorable, changes in the amount of induced astigmatism with different incisions still occur, as can be seen from the large standard deviations in this study (Tables 1 and 2) and others. This could make a simultaneous astigmatic keratotomy procedure unpredict46
Table 5. Astigmatic keratotomy effect of the superior 3.5 mm unsutured clear corneal incision used in 11 cases with WTR astigmatism preoperatively. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism
+ .69 ± .62 (WTR) -.25 ± .47 (P < .0001) -.19 ± .64(P = .0002) - .04 ± .50 (P = .01)
Table 6. Astigmatic keratotomy effect of the superior 5.2 mm unsutured clear corneal incision used in five cases with WTR astigmatism preoperatively. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism .96 - .82 - .78 -.47
± ± ± ±
.47 (WTR) .67 (P = .002) .64 (P = .0006) .79 (P = .005)
able in some cases. Instead, in cases with some induced astigmatism, incisions can be used to reduce preoperative astigmatism simply by changing the incision site to the steeper meridian. In the present study, we evaluated the amount of surgically induced astigmatism of unsutured self-sealing incisions to look for differences related to incision length and IOL choice (3.5 mm foldable silicone or 5.2 mm PMMA), differences related to wound architecture (corneoscleral straight or frown), and differences related to wound position (scleral/corneal, superior/temporal). Statistical evaluation of these differences has been hampered by the small number of patients in some of the treatment groups (e.g., the frown incision groups) (Tables 1 and 2).
J CATARACT REFRACT SURG-VOL 21, JANUARY 1995
Table 7. Astigmatic neutrality of the superior 3.5 mm unsutured corneoscleral incision used in 13 cases with only minor preoperative astigmatism. Interval
Mean Astigmatism
Preoperative
+.25 ± .77 (WTR)
Week 1
+ .20 ± .99 (P = .80) +.14 ± .98 (P = .56)
Week 3 Week 6
+.10 ± .81 (P
= .35)
Table 8. Astigmatic neutrality of the superior 5.2 mm unsutured corneoscleral incision used in 12 cases with only minor preoperative astigmatism. Interval
Mean Astigmatism
Preoperative Week 1
+ .05 ±
Week 3 Week 6
+ .01 ± .80 (P -.25 ± .85 (P
.87 (WTR)
+ .01 ± 1.05 (P
= .87) = .46) = .21)
Table 9. Astigmatic neutrality of the superior 3.5 mm unsutured frown incision used in seven cases with minor preoperative astigmatism. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism
+ .05 ±
.88 (WTR) -.01 ± .86 (P = .72) - .05 ± 1.30 (P
- .33 ± 1.46 (P
= .93) = .58)
Table 10. Astigmatic neutrality of the superior 5.2 mm unsutured frown incision used in seven cases with minor preoperative astigmatism. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism +.61 +.12 +.31 +.26
± ± ± ±
1.09 (WTR) .94 (P = .05) .60 (P = .43) .73 (P = .15)
The decay and stability of the induced astigmatism, as well as its ability to reduce pre-existing keratometric astigmatism, were followed to determine the astigmatic keratotomy effect of the different incisions. All self-sealing incisions produced a relaxing effect in the incision axis that depended on the incision length (Tables 1 and 2). With superior incisions this effect was ATR and with temporal incisions, WTR (Figures 1 and 2). The steepening (WTR) seen in the
first postoperative week for 3.5 mm corneoscleral incisions was probably an effect of cautery (Table 2). Corneoscleral incisions were more astigmatically neutral than clear corneal incisions, and this was not changed by shifting the latter from the superior to the temporal position (Tables 1 and 2). The corneoscleral incisions were almost astigmatically neutral; there were only minor, insignificant differences between 3.5 and 5.2 mm incisions during the first three weeks and no difference at six weeks after surgery (Table 2). The 5.2 mm frown incisions created more initial induced astigmatism than the 5.2 mm corneoscleral incisions (straight) (Table 2 and Figure 2). This was unexpected because the frown configuration should counteract the sliding or relaxing effect of the incisions?,l0 Only a small number of patients had frown incisions and therefore more cases have to be studied to verify their protective effect against sliding. Mter six weeks when glasses were prescribed, no differences related to variations in architecture (frown versus straight) or length (3.5 versus 5.2 mm) of the corneoscleral incisions were detected (Table 2). This means that although the larger incisions were more unstable during the first few weeks, visual rehabilitation was as fast with the larger, nonfoldable small incision lenses as with the foldable ones. The clear corneal incisions produced significant relaxation in the axis of the incision which was surprisingly stable; only insignificant minor decay occurred during the six week follow-up (Table 1 and Figure 1). Shifting from the superior to the temporal position did not significantly change the amount of induced astigmatism, only the direction (Figure 1). This contradicts the finding of some investigators that temporal clear corneal incisions are more astigmatically neutral than superior clear corneal incisions. 4 Initial astigmatic decay (insignificant) occurred with the superior 3.5 mm clear corneal incisions; otherwise the induced astigmatism was stable and did not change significantly during the six-week follow-up. By changing the position of the clear corneal incision to temporal in cases with preoperative ATR astigmatism (Tables 3 and 4) and superior in cases with preoperative WTR astigmatism (Tables 5 and 6), it was possible to reduce preoperative astigmatism as part of the cataract procedure. As mentioned, some postoperative WTR astigmatism may be beneficial for uncorrected near and distance vision. 7 Therefore one probably should use superior clear corneal incisions only in cases with major WTR astigmatism; overcorrection to ATR postoperatively did occur, especially with 5.2 mm superior clear corneal incisions (Tables 5 and 6). The mean keratometric astigmatism with corneoscleral incisions did not change from preoperatively to the end of the follow-up (Tables 7 to 10). With these incisions, refractive cataract surgery would require a
J CATARACf REFRACf SURG-VOL 21, JANUARY 1995
47
separate astigmatic keratotomy procedure in cases of pre-existing astigmatism. In conclusion, in this study we found that the effect of surgically induced astigmatism on preoperative astigmatism was enhanced by varying the incision site and length, especially when clear corneal incisions were used. Astigmatic neutrality occurred more with corneoscleral than with clear corneal incisions. Only the direction of induced astigmatism, not the amount, was changed by moving the clear corneal incision from a superior to a temporal position. There were no clinically significant differences between 3.5 mm and 5.2 mm self-sealing corneoscleral incisions in the amount of induced astigmatism with the prescription of glasses after six weeks, and there was no difference between foldable and nonfoldable IOLs in visual rehabilitation.
REFERENCES
5. 6. 7.
8. 9.
10.
1. Lindstrom RL. Cataract surgery and lens implantation; editorial overview. CUff Opinion Ophthalmol 1993; 4:1-2 2. Feil HF, Crandall AS, Olson RJ. Astigmatic decay following small incision, self-sealing cataract surgery. J Cataract Refract Surg 1994; 20:40-43 3. Nielsen PJ. Induced astigmatism and its decay with a
48
4.
11.
frown incision. J Cataract Refract Surg 1993; 19:375379 Fine IH, Fichman RA, Grabow HB. Clear-Corneal Cataract Surgery and Topical Anesthesia. Thorofare, NJ, Slack, 1993 Langerman DW. Architectural design of a self-sealing corneal tunnel, single hinge incision. J Cataract Refract Surg 1994; 20:84-88 Axt JC, McCaffery JM. Reduction of postoperative against-the-rule astigmatism by lateral incision technique. J Cataract Refract Surg 1993; 19:380-386 Bradbury JA, Hillman JS, Cassells-Brown A. Optimal postoperative refraction for good unaided near and distance vision with monofocal intraocular lenses. Br J Ophthalmol 1992; 76:300-302 Naeser K. Conversion of keratometer readings to polar values. J Cataract Refract Surg 1990; 16:741-745 Steinert RF, Brint SF, White SM, Fine IH. Astigmatism after small incision cataract surgery. A prospective, randomized, multicenter comparison of 4- and 6.5-mm incisions. Ophthalmology 1991; 98:417-424 Singer JA. Frown incision for minimizing induced astigmatism after small incision cataract surgery with rigid optic intraocular lens implantation. J Cataract Refract Surg 1991; 17:677-688 Martin RG, Sanders DR. Visual, astigmatic, and inflammatory results with the Staar AA-4203 single-piece foldable IOL. A randomized prospective study. Ophthalmic Surg 1992; 23:770-775
J CATARACT REFRACT SURG-VOL 21, JANUARY 1995
ABSTRACT The refractive effects of self-sealing clear corneal and corneoscleral tunnel incisions, 3.5 mm and 5.2 mm, in cataract surgery were studied prospectively by automatic keratometric evaluation at day one postoperatively and weeks one, three, and six. Keratometric readings were converted to polar values. The amount of surgically induced astigmatism was calculated for each incision and mean postoperative keratometric astigmatism was estimated for patients with preoperative against-the-rule and with-the-rule astigmatism to evaluate the astigmatic keratotomy effects of the incisions. The corneoscleral incisions were almost astigmatically neutral, with no major difference between the 3.5 mm and the 5.2 mm incisions after six weeks. The 5.2 mm frown incisions were less stable than the straight corneoscleral incisions. Clear corneal incisions resulted in a considerable amount of induced astigmatism; there was more with the 5.2 mm incisions than with the 3.5 mm incisions. Temporal incisions resulted in a with-therule induced change and superior incisions, an against-the-rule induced change. The refractive effect of the clear corneal incisions did not change significantly from day one to week six. The astigmatic keratotomy effects of these incisions were therefore more useful and predictable. Preoperative against-the-rule astigmatism was reduced significantly by temporally placed clear corneal incisions and preoperative with-the-rule astigmatism, by superiorly placed clear corneal incisions. If one considers the preoperative astigmatism when selecting incision type and location for small incision cataract surgery, one can minimize postoperative keratometric astigmatism. Key Words: astigmatic keratotomy, cataract surgery, clear cornea, corneoscleral, induced astigmatism, keratometric astigmatism, selfsealing incision
The refractive aspect of cataract surgery has received considerable attention with the advent of modern small incision surgery. The amount of surgically induced astigmatism can be controlled, and faster wound stability reduces the time required for visual rehabilitation. 1-3 Recently, preference has shifted from corn eo scleral incisions to clear corneal incisions. 4 ,5 One result of this change has been more induced astigmatism because the corneal incisions are closer to the visual axis.
This result seems to be exaggerated at the superior site where an against-the-rule (ATR) shift in preoperative astigmatism is seen. For that reason, unsutured clear corneal incisions should not be used in cases with preoperative ATR astigmatism unless a temporal incision site is used. Temporally placed incisions induce with-the-rule (WTR) shift in preoperative astigmatism and can reduce pre-existing ATR astigmatism. 4 ,6 Against-the-rule astigmatism yields poorer vision than WTR astigmatism, and WTR astigmatism post-
From the Department of Ophthalmology, Hjr;;rring Hospital, Hjr;;rring, Denmark. Reprint requests to Per Julius Nielsen, M.D., Department of Ophthalmology, Rigshospitalet, University Hospital of Copenhagen, DK-2JOO Copenhagen, Denmark. J CATARACf REFRACf SURG-VOL 21 , JANUARY 1995
43
operatively seems to be better for unaided distance vision and near vision? Therefore, preoperative evaluation of keratometric astigmatism is important, not only for calculating the intraocular lens (IOL) power, but also for planning the incision type, length, and location to control the amount and direction of postoperative astigmatism. 2 The present study was planned prospectively to evaluate the amount of surgically induced astigmatism and its decay with various self-sealing cataract incisions. The effect and stability of the incisions on the preoperative keratometric astigmatism were also evaluated, primarily to determine the astigmatic keratotomy effects of the clear corneal incisions.
MATERIALS AND METHODS This investigation was originally planned as a prospective, randomized study of the amount of surgically induced astigmatism with eight different self-sealing incisions used in cataract surgery performed by phacoemulsification. Twelve patients were assigned to each incision group. In the first few cases, the incision site was randomly selected according to the protocol, but then the preoperative astigmatism was taken into consideration. Patients with significant preoperative ATR astigmatism had temporal clear corneal incisions; patients with small amounts of WTR or no preoperative astigmatism had corneoscleral, frown, or 3.5 mm superior clear corneal incisions, and those with greater WTR astigmatism had 5.2 mm superior clear corneal incisions. This study design change was made to prevent adding a significant amount of induced astigmatism to the preoperative astigmatism, especially when a clear corneal incision was used. Ninety-three consecutive patients were included in the study. Incision lengths of 3.5 mm were used in cases in which a foldable silicone IOL (Allergan SI-30 or Staar 4203) was implanted. Incisions of 5.2 mm were used in cases in which a one-piece poly(methyl methacrylate) (PMMA) IOL (Pharmacia 809P or 809C) was implanted. The clear corneal incisions were placed superiorly or temporally; the corn eo scleral incisions and frown incisions were placed superiorly. Clear corneal incisions were used in 54 patients: 3.5 mm incisions were placed superiorly in 17 patients and temporally in 16; 5.2 mm incisions were placed superiorly in 10 patients and temporally in 11. Corneoscleral and frown incisions were used in 39 patients: 3.5 mm corneoscleral incisions in 13 patients and 3.5 mm frown incisions in 7 patients; 5.2 mm corneoscleral incisions in 12 patients and 5.2 mm frown incisions in 7 patients. A 3 mm diamond blade was used to make the three-step clear corneal incision, and metal blades were used with the three-step corneoscleral and frown 44
J CATARACT REFRACT
incisions. In addition to the primary incision, a stab incision was made for bimanual phacoemulsification. Cautery was used only with corneoscleral and frown incisions. The intraocular technique was the same in all patients: capsulorhexis, viscoelastic agent (sodium hyaluronate, Healon-GV@), and phacoemulsification with nucleus cracking. None of the incisions was sutured. Intrastromal injections were sometimes used with the clear corneal incisions to ensure watertightness. Steroid and antibiotic ointments were used by the patients twice a day for two weeks. Keratometric astigmatism was measured at day one and weeks one, three, and six by a trained nurse using an automatic keratometer (Allergan-Humphrey). Keratometric readings were converted to Naeser's polar values to obtain a single value for the balance between ATR and WTR for any given keratometric astigmatism. 8 Surgically induced astigmatism was calculated for each incision as the difference between preoperative and postoperative keratometric values at each follow-up interval. Stability of the astigmatic decay was evaluated by comparing mean induced astigmatism over the six week follow-up. The astigmatic keratotomy effect of the clear corneal incisions was determined by the reduction in preoperative ATR keratometric astigmatism with the 3.5 or 5.2 mm temporal incision and by the reduction in preoperative WTR keratometric astigmatism with the 3.5 or 5.2 mm superior incision. The astigmatic neutrality and stability of the corn eo scleral and frown incisions were determined by comparing mean keratometric astigmatism over the six-week follow-up. Statistics were evaluated using unpaired or paired, two-tailed t-tests; P < .05 was considered significant.
RESULTS Surgically induced astigmatism is reported in Tables 1 and 2 and shown in Figures 1 and 2. The astigmatic keratotomy effects of the 3.5 mm and the 5.2 mm temporal clear corneal incisions on pre-existing ATR astigmatism are shown in Tables 3 and 4, respectively. The astigmatic keratotomy effects of the 3.5 mm and the 5.2 mm superior clear corneal incisions on pre-existing WTR astigmatism are shown in Tables 5 and 6, respectively. The astigmatic neutrality ofthe 3.5 mm and 5.2 mm corneo scleral and frown incisions are shown in Tables 7 to 10.
DISCUSSION Astigmatic neutrality and rapid stabilization are major goals of small incision cataract surgery. These seem to be achieved with most sutured and
SURG~VOL
21, JANUARY 1995
Table 1. Surgically induced polar astigmatism with clear corneal incisions. Incision
3.5 CCS (n = 17)
Postop Interval
-.93 -.79 -.56 -.55
Day 1 Week 1 Week 3 Week 6
± .89 ± .65 ± .57 ± .57
3.5 CCT (n = 16) +.55 +.37 +.59 +.46
± ± ± ±
5.2 CCS = 10)
5.2 CCT
(n
-1.44 -1.55 -1.47 -1.24
.45 .50 .43 .54
± ± ± ±
(n
.96 .71 .75 .76
= 11)
+1.41 +1.21 +1.20 +.82
± 1.13 ± .78 ± .72 ± .76
CCS = clear corneal superior clear corneal temporal plus (+) = WTR minus (-) = ATR
ccr =
Table 2. Surgically induced polar astigmatism with corneoscleral incisions. Incision
3.5 CSS = 13)
Postop Interval
(n
+.14 +.01 -.05 -.10
Day 1 Week 1 Week 3 Week 6
± .70 ± .59 ± .55 ± .44
3.5 Frown (n = 7) -.01 -.06 -.02 -.20
± ± ± ±
5.2 CSS = 12)
5.2 Frown (n = 7)
(n
.82 .46 .58 .83
-.36 -.20 -.25 -.13
± .50 ± .56 ± .48 ± .46
-.84 -.49 -.50 -.35
± .89 ± .54 ± .63 ± .55
CSS = corneoscleral superior plus (+) = WTR minus (-) = ATR
WTR 0.6- 0 - - - - - - - - . . . . . - - - - - - - - - - - - - - - . ~
~
.Q
c
E rJl
0.4
oDay 1 ~
Week 1
0.2
HE!
O ~==~~~~WW~~~F=~~F=~ Week 3
EJ]
~ E -0.2
Week 6
Cl
+=I
!Q -0.4
~
:::J "U
-0.6
Fig. 1.
(Nielsen) Induced astigmatism with different 3.5 mm self-sealing incisions: clear corneal superior (CCS), clear corneal temporal (CCf), corneoscleral superior (CSS), and frown superior (frown). (Mean values and SDs are in Tables 1 and 2.)
.£ -0.8
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-1+=======~======r=====~======~
unsutured corneoscleral incisions between 3.5 and 6.0 mm.z,3,6,9-11 Visual rehabilitation following cataract surgery may, however, be limited by remaining or exaggerated preoperative astigmatism. The standard approach of placing a self-sealing incision at 12 o'clock increases preoperative ATR astigmatism unless this is balanced by suturing. Suturing, however, delays stabilization by prolonging the
period during which astigmatic decay can occur. 2 The enhanced effect on preoperative astigmatism is even greater when a clear corneal incision is used. 4 Some surgeons have suggested that changing the incision site from a superior to a temporal position reduces the amount of surgically induced astigmatism, especially with clear corneal incisions, and addresses pre-existing ATR astigmatism. 4 ,6 A standard temporal
J CATARACf REFRACf SURG-VOL 21, JANUARY 1995
45
WTR 1,5
Fig. 2.
e! .sl c.
(Nielsen) Induced astigmatism with different 5.2 mm selfsealing incisions: clear corneal superior (CCS), clear corneal temporal (CCT), corneoscleral superior (CSS), and frown superior (frown). (Mean values and SDs are in Tables 1 and 2.)
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Week 3
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Table 3. Astigmatic keratotomy effect of the temporal 3.5 mm unsutured clear corneal incision used to reduce pre-existing ATR astigmatism in 12 patients. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism -.92 - .38 -.18 -.41
± ± ± ±
.58 (ATR) .87 (P = .07) .n(p = .005) .97 (P = .02)
Table 4. Astigmatic effect of the temporal 5.2 mm unsutured clear corneal incision used to reduce preexisting ATR astigmatism in 10 patients. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism -1.41 - .15 -.10 -.59
± ± ± ±
.81 (ATR) 1.12 (P = .0006) 1.06(P = .0001) 1.28 (P = .01)
approach may, however, worsen preoperative WTR astigmatism, although postoperative WTR may be less troublesome than ATR astigmatism. 7 When the amount of surgically induced astigmatism is negligible, refractive cataract surgery can be performed by including astigmatic keratotomy in the cataract extraction procedure. When the amount of induced astigmatism is not negligible, the simultaneous use of astigmatic keratotomy may be less reliable. Although the mean value of induced astigmatism may be favorable, changes in the amount of induced astigmatism with different incisions still occur, as can be seen from the large standard deviations in this study (Tables 1 and 2) and others. This could make a simultaneous astigmatic keratotomy procedure unpredict46
Table 5. Astigmatic keratotomy effect of the superior 3.5 mm unsutured clear corneal incision used in 11 cases with WTR astigmatism preoperatively. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism
+ .69 ± .62 (WTR) -.25 ± .47 (P < .0001) -.19 ± .64(P = .0002) - .04 ± .50 (P = .01)
Table 6. Astigmatic keratotomy effect of the superior 5.2 mm unsutured clear corneal incision used in five cases with WTR astigmatism preoperatively. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism .96 - .82 - .78 -.47
± ± ± ±
.47 (WTR) .67 (P = .002) .64 (P = .0006) .79 (P = .005)
able in some cases. Instead, in cases with some induced astigmatism, incisions can be used to reduce preoperative astigmatism simply by changing the incision site to the steeper meridian. In the present study, we evaluated the amount of surgically induced astigmatism of unsutured self-sealing incisions to look for differences related to incision length and IOL choice (3.5 mm foldable silicone or 5.2 mm PMMA), differences related to wound architecture (corneoscleral straight or frown), and differences related to wound position (scleral/corneal, superior/temporal). Statistical evaluation of these differences has been hampered by the small number of patients in some of the treatment groups (e.g., the frown incision groups) (Tables 1 and 2).
J CATARACT REFRACT SURG-VOL 21, JANUARY 1995
Table 7. Astigmatic neutrality of the superior 3.5 mm unsutured corneoscleral incision used in 13 cases with only minor preoperative astigmatism. Interval
Mean Astigmatism
Preoperative
+.25 ± .77 (WTR)
Week 1
+ .20 ± .99 (P = .80) +.14 ± .98 (P = .56)
Week 3 Week 6
+.10 ± .81 (P
= .35)
Table 8. Astigmatic neutrality of the superior 5.2 mm unsutured corneoscleral incision used in 12 cases with only minor preoperative astigmatism. Interval
Mean Astigmatism
Preoperative Week 1
+ .05 ±
Week 3 Week 6
+ .01 ± .80 (P -.25 ± .85 (P
.87 (WTR)
+ .01 ± 1.05 (P
= .87) = .46) = .21)
Table 9. Astigmatic neutrality of the superior 3.5 mm unsutured frown incision used in seven cases with minor preoperative astigmatism. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism
+ .05 ±
.88 (WTR) -.01 ± .86 (P = .72) - .05 ± 1.30 (P
- .33 ± 1.46 (P
= .93) = .58)
Table 10. Astigmatic neutrality of the superior 5.2 mm unsutured frown incision used in seven cases with minor preoperative astigmatism. Interval Preoperative Week 1 Week 3 Week 6
Mean Astigmatism +.61 +.12 +.31 +.26
± ± ± ±
1.09 (WTR) .94 (P = .05) .60 (P = .43) .73 (P = .15)
The decay and stability of the induced astigmatism, as well as its ability to reduce pre-existing keratometric astigmatism, were followed to determine the astigmatic keratotomy effect of the different incisions. All self-sealing incisions produced a relaxing effect in the incision axis that depended on the incision length (Tables 1 and 2). With superior incisions this effect was ATR and with temporal incisions, WTR (Figures 1 and 2). The steepening (WTR) seen in the
first postoperative week for 3.5 mm corneoscleral incisions was probably an effect of cautery (Table 2). Corneoscleral incisions were more astigmatically neutral than clear corneal incisions, and this was not changed by shifting the latter from the superior to the temporal position (Tables 1 and 2). The corneoscleral incisions were almost astigmatically neutral; there were only minor, insignificant differences between 3.5 and 5.2 mm incisions during the first three weeks and no difference at six weeks after surgery (Table 2). The 5.2 mm frown incisions created more initial induced astigmatism than the 5.2 mm corneoscleral incisions (straight) (Table 2 and Figure 2). This was unexpected because the frown configuration should counteract the sliding or relaxing effect of the incisions?,l0 Only a small number of patients had frown incisions and therefore more cases have to be studied to verify their protective effect against sliding. Mter six weeks when glasses were prescribed, no differences related to variations in architecture (frown versus straight) or length (3.5 versus 5.2 mm) of the corneoscleral incisions were detected (Table 2). This means that although the larger incisions were more unstable during the first few weeks, visual rehabilitation was as fast with the larger, nonfoldable small incision lenses as with the foldable ones. The clear corneal incisions produced significant relaxation in the axis of the incision which was surprisingly stable; only insignificant minor decay occurred during the six week follow-up (Table 1 and Figure 1). Shifting from the superior to the temporal position did not significantly change the amount of induced astigmatism, only the direction (Figure 1). This contradicts the finding of some investigators that temporal clear corneal incisions are more astigmatically neutral than superior clear corneal incisions. 4 Initial astigmatic decay (insignificant) occurred with the superior 3.5 mm clear corneal incisions; otherwise the induced astigmatism was stable and did not change significantly during the six-week follow-up. By changing the position of the clear corneal incision to temporal in cases with preoperative ATR astigmatism (Tables 3 and 4) and superior in cases with preoperative WTR astigmatism (Tables 5 and 6), it was possible to reduce preoperative astigmatism as part of the cataract procedure. As mentioned, some postoperative WTR astigmatism may be beneficial for uncorrected near and distance vision. 7 Therefore one probably should use superior clear corneal incisions only in cases with major WTR astigmatism; overcorrection to ATR postoperatively did occur, especially with 5.2 mm superior clear corneal incisions (Tables 5 and 6). The mean keratometric astigmatism with corneoscleral incisions did not change from preoperatively to the end of the follow-up (Tables 7 to 10). With these incisions, refractive cataract surgery would require a
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separate astigmatic keratotomy procedure in cases of pre-existing astigmatism. In conclusion, in this study we found that the effect of surgically induced astigmatism on preoperative astigmatism was enhanced by varying the incision site and length, especially when clear corneal incisions were used. Astigmatic neutrality occurred more with corneoscleral than with clear corneal incisions. Only the direction of induced astigmatism, not the amount, was changed by moving the clear corneal incision from a superior to a temporal position. There were no clinically significant differences between 3.5 mm and 5.2 mm self-sealing corneoscleral incisions in the amount of induced astigmatism with the prescription of glasses after six weeks, and there was no difference between foldable and nonfoldable IOLs in visual rehabilitation.
REFERENCES
5. 6. 7.
8. 9.
10.
1. Lindstrom RL. Cataract surgery and lens implantation; editorial overview. CUff Opinion Ophthalmol 1993; 4:1-2 2. Feil HF, Crandall AS, Olson RJ. Astigmatic decay following small incision, self-sealing cataract surgery. J Cataract Refract Surg 1994; 20:40-43 3. Nielsen PJ. Induced astigmatism and its decay with a
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frown incision. J Cataract Refract Surg 1993; 19:375379 Fine IH, Fichman RA, Grabow HB. Clear-Corneal Cataract Surgery and Topical Anesthesia. Thorofare, NJ, Slack, 1993 Langerman DW. Architectural design of a self-sealing corneal tunnel, single hinge incision. J Cataract Refract Surg 1994; 20:84-88 Axt JC, McCaffery JM. Reduction of postoperative against-the-rule astigmatism by lateral incision technique. J Cataract Refract Surg 1993; 19:380-386 Bradbury JA, Hillman JS, Cassells-Brown A. Optimal postoperative refraction for good unaided near and distance vision with monofocal intraocular lenses. Br J Ophthalmol 1992; 76:300-302 Naeser K. Conversion of keratometer readings to polar values. J Cataract Refract Surg 1990; 16:741-745 Steinert RF, Brint SF, White SM, Fine IH. Astigmatism after small incision cataract surgery. A prospective, randomized, multicenter comparison of 4- and 6.5-mm incisions. Ophthalmology 1991; 98:417-424 Singer JA. Frown incision for minimizing induced astigmatism after small incision cataract surgery with rigid optic intraocular lens implantation. J Cataract Refract Surg 1991; 17:677-688 Martin RG, Sanders DR. Visual, astigmatic, and inflammatory results with the Staar AA-4203 single-piece foldable IOL. A randomized prospective study. Ophthalmic Surg 1992; 23:770-775
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