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J. C. Merriam, L. Zheng, B. Cheng; Effect of Incision Size and Location on Surgically-Induced Astigmatism (SIA). Invest. Ophthalmol. Vis. Sci. 2009;50(13):5567.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the effect of incision size and location on SIA during the initial four years after cataract surgery.
This retrospective study of 1454 eyes from 908 patients with an average age of 77 years was approved by the IRB of Columbia University Medical Center. The study eyes were organized into 7 groups by incision type: ECCE (12 mm superior incision), 6Sup (6 mm superior scleral tunnel), 3Sup (3 mm superior scleral tunnel), 4Cor (4 mm temporal cornea), 3Cor (3 mm temporal cornea), 3Temp (3 mm temporal scleral tunnel), and 2.6Cor (2.6 mm temporal cornea). Corneal astigmatism was measured with a manual keratometer (Bausch & Lomb) during post-operative visits at 1 day, 2 weeks, 1 month, 2 months, 4 months, 6 months and every 6 months thereafter to 48 months. Over 13,100 data points were stored in a database created with FileMaker Pro 8 Advanced. SIA at each follow-up time was calculated with vector analysis using a new online tool, the "Astigmatism Calculator". The calculated SIA was analyzed using a linear mixed effects model with patients as random effects to account for within subject correlations. The main predictors were surgery type (incision size and location) and follow up time (treated as categorical) and their interactions. Analysis was performed with SAS software. A p-value of 0.05 was deemed statistically significant.
SIA is greatest at all times after ECCE. SIA after 6Sup is consistently greater than the other smaller incisions until month 6 when it becomes statistically similar to SIA after 3Sup. SIA after 3Sup is greater than SIA after all the temporal incisions until month 1, when it is statistically similar to the temporal incisions. By 12 months SIA after 3Sup is absolutely greater and generally statistically different than all the temporal incisions. SIA after 4Cor, 3Cor, 2.6Cor and 3Temp were generally greater on day 1 than at any other time point, but they are not significantly different from each other at any time.
SIA after a superior incision depends on incision size, and superior incisions induce more SIA than temporal incisions. This study detected no statistically meaningful difference in SIA after 3Temp, 4Cor, 3Cor and 2.6Cor.
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