Journal of Cataract & Refractive Surgery
Volume 32, Issue 9 , Pages 1432-1437, September 2006

Corneal astigmatism correction with opposite clear corneal incisions or single clear corneal incision: Comparative analysis

From the Rajendra Prasad Center for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India

Accepted 7 April 2006.

Article Outline

Purpose

To compare the astigmatic correcting effect of paired opposite clear corneal incisions (OCCIs) on the steep axis with that of single clear corneal incisions (CCIs) in cataract patients having phacoemulsification.

Setting

Rajendra Prasad Centre for Ophthalmic Sciences, AIIMS, New Delhi, India.

Methods

This randomized prospective clinical study comprised 40 eyes of 40 patients with topographic astigmatism of more than 1.50 diopters (D). Paired 3.2 mm OCCIs were made in the steep axis in Group 1 and single CCIs in Group 2. Preoperative evaluation included uncorrected visual acuity, refraction, applanation tonometry, dilated fundoscopy, biomicroscopic examination, keratometry, and topography. The steep axis was marked before sub-Tenon's anesthesia was given and routine phacoemulsification was performed through a 3.2 mm CCI on the steep axis. An additional opposite 3-step self-sealing CCI was made in Group 1. Patients were examined 1, 4, and 12 weeks postoperatively. Visual acuity, refraction, keratometry, and topography were evaluated.

Results

The mean preoperative and postoperative topographic corneal astigmatism was 2.51 D ± 0.92 (SD) and 0.91 ± 0.54 D, respectively, in Group 1 and 2.16 ± 0.80 D and 1.57 ± 0.70 D, respectively, in Group 2. Mean astigmatic correction was 1.66 ± 0.5 D and 0.85 ± 0.75 D in Group 1 and Group 2, respectively. Mean surgically induced astigmatism, measured by a vector-corrected method, was 1.66 ± 0.50 D and 0.85 ± 0.75 D in Group 1 and Group 2, respectively (P = .00). The coupling ratio was −0.96 in Group 1 and −0.87 in Group 2. The spherical equivalent was +0.23 ± 0.41 D in Group 1 and +0.11 ± 0.17 D in Group 2 at 12 weeks. Uncorrected visual acuity was better in Group 1 than in Group 2 (P = .032). There was no difference in best corrected visual acuity between the groups. There were no incision-related complications.

Conclusion

Paired OCCIs were predictable and effective in providing an enhanced effect for correcting preexisting corneal astigmatism in cataract surgery.

 

Emmetropia and no surgically induced astigmatism (SIA) are the main objectives of modern small-incision cataract surgery.1, 2 Arcuate keratotomy,3 limbal relaxing incisions,4 toric intraocular lenses (IOLs),5 excimer laser treatment,6, 7, 8 and varied incision types9, 10, 11, 12, 13, 14, 15, 16 have been widely described in the literature to control astigmatism after cataract surgery. The astigmatic effect of clear corneal incisions (CCIs) has been put to effective use in modern cataract surgery for controlling preexisting astigmatism with the incision on the steepest meridian.17, 18

Performing an additional CCI opposite the first CCI to enhance the flattening effect has been reported.19, 20, 21, 22 This method is called paired opposite clear corneal incisions (OCCIs). We performed a comparative evaluation of surgically induced astigmatism between 3.2 mm OCCI and CCI in cataract patients.

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Patients and Methods 

This prospective study comprised 40 eyes of 40 patients who had cataract surgery between October 2003 and January 2004. The patients were randomized into 2 groups. Inclusion criteria were age greater than 21 years and topographic astigmatism of more than 1.50 diopters (D). Patients who had refractive surgery or corneal pathology were excluded. The preoperative evaluation included uncorrected visual acuity (UCVA), refraction, applanation tonometry, dilated fundoscopy, biomicroscopy, keratometry, and topography (Orbscan II, Bausch & Lomb).

The steep axis was marked on the conjunctiva before surgery with the patient in an upright position. All surgery was performed by 1 surgeon (S.K.) on an inpatient basis using topical anesthesia and strict aseptic precautions. A self-sealing 3.2 mm CCI was made and routine phacoemulsification performed, after which a foldable IOL was inserted. Just before irrigation/aspiration (I/A) of the ophthalmic viscosurgical device, a second CCI was made 180 degrees from the first incision in Group 1. Bimanual I/A was used in all cases. Only the phacoemulsification incision was hydrated at the end of the surgery. All patients received routine postoperative topical steroids and antibiotic eyedrops for 4 weeks.

Postoperative evaluations were performed at 1, 4, and 12 weeks and included UCVA, best corrected visual acuity (BCVA), refraction, keratometry, corneal topography, and biomicroscopy.

Astigmatic change was calculated as the difference between the mean preoperative and postoperative topographic readings. The change in SIA was calculated by the Holladay-Cravy-Koch (HCK) method.23, 24 Statistical analysis was performed with SPSS software using paired and unpaired t tests.

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Results 

Of the 40 eyes meeting the inclusion criteria, 20 were randomly allocated to Group 1 (OCCI) and 20 to Group 2 (CCI). The mean age was 61.05 years ± 8.40 (SD) and 58.70 ± 8.20 years in Group 1 and Group 2, respectively. There were 14 men and 6 women in each group. The mean intraocular pressure was 15.12 ± 1.27 mm Hg and 14.87 ± 1.12 mm Hg in Group 1 and Group 2, respectively. The mean axial length was 23.6 ± 1.9 mm in Group 1 and 23.43 ± 1.16 mm in Group 2. There were no statistically significant differences in these parameters.

Central Corneal Power 

Mean preoperative and postoperative (12 weeks) central corneal power was 44.46 ± 1.94 D and 44.23 ± 1.96 D, respectively, in Group 1 and 44.23 ± 1.96 D and 43.97 ± 1.62 D, respectively, in Group 2 (Table 1).

Table 1. Central corneal power.
Mean Power (D) ± SD
Follow-up PeriodOCCI GroupCCI Group
Preoperative44.46 ± 1.9444.04 ± 1.70
Postoperative
1 week44.04 ± 1.9544.10 ± 1.73
4 weeks44.26 ± 1.9243.98 ± 1.64
12 weeks44.23 ± 1.9643.97 ± 1.62

CCI = clear corneal incision; OCCI = opposite clear corneal incision

Corneal Astigmatism and Change in Astigmatism 

Twelve weeks postoperatively, the mean preoperative and postoperative corneal astigmatism was 2.51 ± 0.92 D and 0.91 ± 0.54 D, respectively, in Group 1 and 2.17 ± 0.81 D and 1.57 ± 0.70 D, respectively, in Group 2 (both P = .0000) (Figure 1 and Table 2). The mean change in corneal astigmatism was 1.60 ± 0.45 D and 0.59 ± 0.43 D in Group 1 and Group 2, respectively (P = .00) (Figure 2).

Table 2. Corneal astigmatism.
Mean Astigmatism (D) ± SD
Follow-up PeriodOCCI GroupCCI Group
Preoperative2.51 ± 0.922.17 ± 0.81
Postoperative
1 week1.13 ± 0.751.45 ± 0.76
4 weeks1.00 ± 0.601.54 ± 0.69
12 weeks0.91 ± 0.541.57 ± 0.70

CCI = clear corneal incision; OCCI = opposite clear corneal incision

Surgically Induced Astigmatic Reduction 

The mean reduction in SIA 12 weeks postoperatively was 1.66 ± 0.50 D in Group 1 and 0.58 ± 0.75 D in Group 2. There was a statistically significant reduction in SIA in both groups (P = .00) (Table 3).

Table 3. Surgically induced astigmatism.
Mean SIA (D)
Follow-up PeriodOCCI GroupCCI GroupP value
Preoperative2.512.17.57
Postoperative
1 week2.411.33.05
4 weeks2.341.02.01
12 weeks2.260.85.00

CCI = clear corneal incision; OCCI = opposite clear corneal incision; SIA = surgically induced astigmatism

Spherical Equivalent and Axis Deviation 

Spherical equivalent by the HCK formula was +0.23 ± 0.41 D in Group 1 and +0.11 ± 0.17 D in Group 2. There was no statistically significant difference in the spherical equivalent change between the 2 groups.

The mean preoperative axis was 135.8 ± 59.28 degrees in Group 1 and 115.8 ± 66.56 degrees in Group 2. The absolute axis deviation at 12 weeks was 16.40 degrees and 17.50 degrees, respectively. There was no statistically significant difference in the mean absolute axis change between the groups.

Coupling Ratio 

The coupling ratio (amount of flattening or steepening along the incisional meridian divided by the amount of flattening or steepening 90 degrees from the incisional meridian) was −0.96 and −0.87 in Group 1 and Group 2, respectively.

Refractive Stability and Visual Acuity 

Table 4 shows the postoperative cylinder correction. In Group 1, 20% of patients required no correction and in Group 2, 5%.

Table 4. Postoperative cylinder prescription.
Number (%)
Cylinder (D)OCCI Group 1CCI Group 2
Plano4 (20)1 (5)
<0.506 (30)3 (15)
>0.50 to 1.005 (25)3 (15)
>1.00 to 1.502 (10)6 (30)
>1.50 to 2.002 (10)4 (20)
>2.001 (5)3 (15)

CCI = clear corneal incision; OCCI = opposite clear corneal incision

The UCVA was better in the OCCI group, although no difference in BCVA was seen between the groups (Table 5).

Table 5. Postoperative visual acuity.
Number of Patients
OCCI GroupCCI Group
VAUCVABCVAUCVABCVA
6/6515213
6/98455
6/123091
6/183021
6/241120

BCVA = best corrected visual acuity; CCI = clear corneal incision; OCCI = opposite clear corneal incision; UCVA = uncorrected visual acuity; VA = visual acuity

There were no incision-related complications.

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Discussion 

Recommendations to reduce preexisting astigmatism include making the incision on the steepest meridian in eyes with preexisting astigmatism of 0.50 D or more. However, astigmatism higher than 1.20 D cannot be corrected by a 3.2 mm incision at the limbus; therefore, wider incisions16, 18 or an additional incision2, 19 have been advocated in these cases. An identical CCI opposite the first CCI (OCCI) enhances the flattening effect on the cornea, providing another method to modulate preexisting astigmatism in cataract surgery. As Lever and Dahan observed,19 OCCIs are self-sealing, pose no added risk, require no extra surgical equipment, and are effective in treating preexisting astigmatism. Clear corneal incisions are invasive and produce a stable flattening effect over the long term,17 and OCCIs have an enhanced effect.19

In earlier studies of OCCIs,19, 20, 21, 22 the mean reduction in corneal astigmatism ranged from 0.50 to 2.06 D. Our study concurs with these observations. We saw a mean corneal astigmatic change of 1.60 D in patients with OCCIs. A mean SIA of 2.25 D was reported by Lever and Dahan,19 1.75 D by Tadros et al.,22 1.66 D by Ben Simon and Desatnik,21 and 2.10 D by Qammar and Mullaney.20 The mean SIA was 1.66 D in our OCCI group. Varying incision lengths and the amount and type of preexisting astigmatism preclude accurate comparisons of these series.

In a nonrandomized series, Ben Simon and Desatnik21 compared paired OCCIs with a single CCI for correction of astigmatism. They found an enhanced effect of astigmatic correction of OCCIs on keratometric data analysis. The corneal topographic change analysis in our study concurs with their findings. Changes in spherical equivalent, axis deviation, coupling ratio, and BCVA between the groups showed no statistical difference; the change in spherical power was negligible and hence can be ignored in IOL power calculation in cases of OCCI. Uncorrected visual acuity in the OCCI group was better than in the CCI group, although BCVA was comparable.

Clear corneal incisions have inherent disadvantages including endophthalmitis and early wound-related complications. However, it is a relatively easier procedure that does not require extra expertise or expensive surgical instruments. In addition, given their predictable stability, CCIs are useful in managing mild to moderate preexisting astigmatism. Opposite clear corneal incisions achieve an enhanced effect over CCIs in treating preexisting astigmatism in cataract patients. Long-term outcomes and a larger sample are necessary.

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References 

  1. Nordan LT, Lusby FW. Refractive aspects of cataract surgery. Curr Opin Ophthalmol. 1995;6(1):36–40
  2. Kershner RM. Clear corneal cataract surgery and the correction of myopia, hyperopia, and astigmatism. Ophthalmology. 1997;104:381–389
  3. Inoue T, Maeda N, Sasaki K, et al. Factors that influence the surgical effects of astigmatic keratotomy after cataract surgery. Ophthalmology. 2001;108:1269–1274
  4. Müller-Jenson K, Fischer P, Siepe U. Limbal relaxing incisions to correct astigmatism in clear corneal cataract surgery. J Refract Surg. 1999;15:586–589
  5. Till JS, Yoder PR, Wilcox TK, Spielman JL. Toric intraocular lens implantation: 100 consecutive cases. J Cataract Refract Surg. 2002;28:295–301
  6. Norouzi H, Rahmati-Kamel M. Laser in situ keratomileusis for correction of induced astigmatism from cataract surgery. J Refract Surg. 2003;19:416–424
  7. Choi DM, Thompson RW, Price FW. Incisional refractive surgery. Curr Opin Ophthalmol. 2002;13:237–241
  8. Ayala MJ, Pérez-Santonja JJ, Artola A, et al. Laser in situ keratomileusis to correct residual myopia after cataract surgery. J Refract Surg. 2001;17:12–16
  9. Kawano K. Modified corneoscleral incision to reduce postoperative astigmatism after 6 mm diameter intraocular lens implantation. J Cataract Refract Surg. 1993;19:387–392
  10. Kohnen T, Dick B, Jacobi KW. Comparison of the induced astigmatism after temporal clear corneal tunnel incisions of different sizes. J Cataract Refract Surg. 1995;21:417–424
  11. Neumann AC, McCarty GR, Sanders DR, Raanan MG. Small incisions to control astigmatism during cataract surgery. J Cataract Refract Surg. 1989;15:78–84
  12. Koch DD, Lindstrom RL. Controlling astigmatism in cataract surgery. Semin Ophthalmol. 1992;7:224–233
  13. Kohnen T, Koch DD. Methods to control astigmatism in cataract surgery. Curr Opin Ophthalmol. 1996;7(1):75–80
  14. Müller-Jenson K, Buchholz A, Barlinn B. Stability of astigmatism over 3 years after corneal stretch incision. J Refract Surg. 1998;14:455–459
  15. Roman SJ, Auclin FX, Chong-Sit DA, Ullern J. Surgically induced astigmatism with superior and temporal incisions in cases of with-the-rule preoperative astigmatism. J Cataract Refract Surg. 1998;24:1636–1641
  16. Akura J, Keneda S, Hatta S, Matsuura K. Controlling astigmatism in cataract surgery requiring relatively large self-sealing incisions. J Cataract Refract Surg. 2000;26:1650–1659
  17. 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
  18. Hayashi K, Hayashi H, Nakao F, Hayashi F. The correlation between incision size and corneal shape changes in sutureless cataract surgery. Ophthalmology. 1995;102:550–556
  19. Lever J, Dahan E. Opposite clear corneal incisions to correct preexisting astigmatism in cataract surgery. J Cataract Refract Surg. 2000;26:803–805
  20. Qammar A, Mullaney P. Paired opposite clear corneal incisions to correct pre-existing astigmatism in cataract patients. J Cataract Refract Surg. 2005;31:1167–1170
  21. Ben Simon GJ, Desatnik H. Correction of pre-existing astigmatism during cataract surgery: comparison between the effects of opposite clear corneal incisions and a single clear corneal incision. Graefes Arch Clin Exp Ophthalmol. 2005;243:321–326
  22. Tadros A, Habib M, Tejwani D, et al. Opposite clear corneal incisions on the steep meridian in phacoemulsification: early effects on the cornea. J Cataract Refract Surg. 2004;30:414–417
  23. Holladay JT, Cravy TV, Koch DD. Calculating the surgically induced refractive change following ocular surgery. J Cataract Refract Surg. 1992;18:429–443
  24. Holladay JT, Dudeja DR, Koch DD. Evaluating and reporting astigmatism for individual and aggregate data. J Cataract Refract Surg. 1998;24:57–65

 No author has a proprietary or financial interest in the materials or methods mentioned.

PII: S0886-3350(06)00658-4

doi:10.1016/j.jcrs.2006.04.010

Journal of Cataract & Refractive Surgery
Volume 32, Issue 9 , Pages 1432-1437, September 2006

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