To the Editor:
Coaxial microincision cataract surgery (MICS) can now be performed through similar incision sizes to those previously achieved using sleeveless biaxial MICS, ie, <2 mm. However, measurement variation of corneal astigmatism either by keratometers or topographers may mask the astigmatic effect of such small incisions, necessitating the use of a control sample when studying their effect.1 Knowing that biaxial MICS is astigmatically neutral, we set out to assess the astigmatic effect of coaxial MICS in a sufficiently powered study, controlling for observer variation of keratometry readings.1,2
In a single center, observational, nonrandomized, controlled trial, 35 eyes from 31 patients underwent coaxial MICS using the Bausch & Lomb Stellaris phacoemulsification machine (Bausch & Lomb, Rochester, New York). An Akreos MI60 intraocular lens (IOL; Bausch & Lomb) (27 eyes) or an Acri.Smart IOL (Carl Zeiss Meditec, Jena, Germany) (8 eyes) was inserted using a wound-assisted technique via an unenlarged 1.8-mm incision. The internal dimension of both incisions was measured using an internal incision gauge (Incision Gauge 0.7 to 2.4 mm, code 2000–05; Capital Instruments Ltd, Bellevue, Washington) after insertion of the IOL and the meridian placement of both incisions was confirmed at the end of the procedure. The main phacoemulsification incision mean width was 1.92±0.08 mm. To aid incision closure, both incisions were hydrated. No incisions were sutured. On the first postoperative day, the meridian incision placement was confirmed at the slit-lamp. Pre- and postoperative keratometry readings after 6 weeks were used for vector analysis according to the Alpins method.3 Vector analysis of the alteration of the keratometric cylinder was compared to 74 control eyes not undergoing surgery that underwent keratometry using the same keratometric device over a similar time frame.
Preoperative exclusion criteria for the control and intervention groups were previous anterior segment surgery, corneal pathologies, and irregular astigmatism. Postoperative exclusion criteria were complications such as failure to place the IOL in the capsular bag, suturing of the incisions, and any complication necessitating enlargement of the main incision. Pre-operative clinical assessment included automated keratometric readings, refraction where possible, visual acuity, intraocular pressure, and anterior and posterior segment evaluation. These assessments were repeated at follow-up 1 day, 1 week, and 6 weeks postoperatively.
No statistically significant difference in surgically induced astigmatism (0.53±0.36 surgical group, 0.52±0.54 control group, P=.906) or degree of flattening at the site of the phacoemulsification incision (0.14±0.51 surgical group, −0.07±0.57 control group, P=.073) was detected between surgical cases and routine variability of control keratometry (Table). Surgically induced astigmatism of this magnitude, being indistinguishable from keratometry variation in control, nonsurgical eyes, leads to the conclusion that microincision coaxial phacoemulsification using a 1.9-mm incision is astigmatically neutral, similar to a previously published report on 1.8-mm coaxial MICS.4 An astigmatically neutral coaxial technique removes the necessity for physicians to acquire the new skills of biaxial techniques and allows a more accurate selection of methods of astigmatism control for use during the primary cataract procedure.
Table: Vector Analysis of Astigmatic Change: Coaxial Microincisional Phacoemulsification Versus Nonsurgical Controls
Michael Goggin, FRCSI(Ophth), FRANZCO, MS
Woodville South, South Australia
Sacha Moore, FRCOphth
Katherine Zamora-Alejo, MD
Adrian Esterman, PhD
- Goggin M, Patel I, Billing K, Esterman A. Variation in surgically induced astigmatism estimation due to test-to-test variations in keratometry. J Cataract Refract Surg. 2010;36(10):1792–1793. doi:10.1016/j.jcrs.2010.07.005 [CrossRef]
- Kaufmann C, Krishnan A, Landers J, Esterman A, Thiel MA, Goggin M. Astigmatic neutrality in biaxial microincisional cataract surgery. J Cataract Refract Surg. 2009;35(9):1555–1562. doi:10.1016/j.jcrs.2009.03.048 [CrossRef]
- Alpins NA. Vector analysis of astigmatism changes by flattening, steepening, and torque. J Cataract Refract Surg. 1997;23(10):1503–1514.
- Wilczynski M, Supady E, Piotr L, Synder A, Palenga-Pydyn D, Omulecki W. Comparison of surgically induced astigmatism after coaxial phacoemulsification through 1.8 mm micro-incision and bimanual phacoemulsification through 1.7 mm microincision. J Cataract Refract Surg. 2009;35(9):1563–1569. doi:10.1016/j.jcrs.2009.04.037 [CrossRef]
Vector Analysis of Astigmatic Change: Coaxial Microincisional Phacoemulsification Versus Nonsurgical Controls
|Surgical Group (n=33)||Control Group (n=74)||PValue|
|SIA (D) in surgical cases and the equivalent AMV (D) in controls||0.53±0.36||0.52±0.54||.906|
|Angular separation of SIA or AMV and main phacoemulsification incision (°)||1.01±48.5||12.1±57.3||.344|
|Flattening effect at main phacoemulsification incision (D)||0.14±0.51||−0.07±0.57||.073|
|Torque at main phacoemulsification incision (D)||−0.008±0.37||−0.026±0.49||.857|
|Angular separation of SIA/AMV and “side port” incision (°)||11.15±50.41||−0.23±44.62||.249|
|Flattening effect at “side port” incision (D)||−0.05±0.45||0.06±0.42||.240|
|Torque at “side port” incision (D)||0.12±0.45||−0.04±0.62||.187|
|Torque effect at preoperative steep K axis (D)||−0.11±0.46||0.02±0.39||.157|