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Analysing Astigmatism Following Cataract Surgery

Univariate and bivariate polar values facilitate the analysis of astigmatism arising from cataract surgery.

Researchers from Ålborg Sygehus Syd and other Centres in Denmark, prospectively investigated astigmatism following cataract surgery. The procedures used superior corneal incisions of 9.0 mm in 70 eyes, 5.5 mm in 71 eyes and 4.0 mm in the remainder. Patients were aged, on average, 67 years, although this ranged from 33 to 99 years. Surgeons operated on 130 eyes in women and 70 eyes in men.

Univariate polar value analysis revealed that a year following surgery, flattening averaged 1.02 D for the 9.0 mm incisions. This compared to 0.71 and 0.64 D for 5.5 mm and 4.0 mm incisions respectively. In patients operated on with 9 mm incisions, the induced torque was 0.46 D anticlockwise. However, induced torque was almost zero in eyes managed with 5.5 and 4 mm incisions. These findings suggest that univariate polar value analysis can demonstrate steepening and torque induced by surgery.

However, bivariate polar value analysis revealed statistically significant differences in astigmatism following cataract surgery between the 9.0 mm and the two smaller incisions at all follow-up intervals during the year long study. The authors commented that bivariate analysis demonstrated the joint variation in steepening and torque. As a result, bivariate analysis "always yielded the correct result."
J Refract Surg 2002;18:72-78. "Bivariate Polar Value Analysis of Surgically Induced Astigmatism"

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