Surgically induced astigmatism after phacoemulsification in eyes with mild to moderate corneal astigmatism: Temporal versus on-axis clear corneal incisions
Accepted 21 August 2005.
Purpose
To determine whether there is a difference in surgically induced astigmatism (SIA) and postoperative uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA) between 2 types of clear corneal incisions used in phacoemulsification: the temporal and the on-axis (ie, on the steeper corneal meridian) clear corneal incision (CCTI and CCOI, respectively).
Setting
Moorfields Eye Hospital, London, United Kingdom.
Methods
In a prospective randomized controlled trial (pilot study), 61 eyes with cataract and mild to moderate corneal astigmatism (<2.58 diopters [D] on corneal topography) having phacoemulsification (single surgeon, 3.2 mm incision) were randomized to receive CCTI or CCOI. Main outcome measures included postoperative BCVA and corneal astigmatism and SIA (calculated using the Holladay vector analysis formula). Measurements were repeated postoperatively at 3 weeks in all eyes, whereas only 46 eyes made it to the final assessment at 8 weeks. Continuous variables between groups were compared by Student t test. The power of the study was calculated.
Results
At the first follow-up, the difference in SIA between the 2 incision types was 0.15 D and it was not statistically significant (0.65 D in CCOI; 0.50 D in CCTI). At the second follow-up, the difference was 0.29 D and it was statistically significant (0.63 D in CCOI; 0.34 D in CCTI; P = .0004). There was no statistically significant difference in the final postoperative visual acuity. The power of the pilot study was 72%.
Conclusion
Seven weeks after small-incision phacoemulsification, the CCTI induced less SIA than the CCOI; however, there were no significant differences in the final UCVA and BCVA.
From the Cataract Service, Moorfields Eye Hospital, London, United Kingdom
Reprint requests to Mr. Edmondo Borasio, Moorfields Eye Hospital, 162 City Road, EC1V 2PD, London, United Kingdom.
Presented as a poster at the XXIInd Congress of the European Society of Cataract & Refractive Surgeons, Paris, France, September 2004.
No author has a financial or proprietary interest in any material or method mentioned.
W. Dupont and W. Plummer provided the shareware program PS Power and Sample Size Calculations V 2.13, with which the power of the study was calculated.
ABSTRACT