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Li Wang, Douglas D. Koch, Mitchell P. Weikert, Richard Jenkins; Corneal Astigmatism And Its Correction With The Toric Intraocular Lens And Peripheral Corneal Relaxing Incisions. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6639.
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In a previous study investigating the effect of posterior corneal astigmatism on overall corneal astigmatism, we found that the posterior corneal steep meridians were primarily vertical (creating net plus astigmatism along the horizontal meridian) and did not change with age, whereas the anterior corneal steep meridian shifted from vertical to horizontal with age. The purpose of this study was to evaluate the outcome of toric intraocular lens (IOL) implantation and peripheral corneal relaxing incisions (PCRIs) based on corneal astigmatism from anterior corneal measurements only.
A total of 192 consecutive cases of cataract surgery combined with toric IOL (n=77) or PCRIs (n=115) performed by a single surgeon were included. A 2.2- or 2.4-mm horizontal clear corneal incision was used in all cases. Toric IOL and PCRIs were selected based on corneal astigmatism from Atlas and IOLMaster; both devices calculate total corneal astigmatism based on anterior corneal measurements only. Using Alpins’ vector analysis, the correction index (CI) was calculated by the ratio of surgically induced astigmatism and target induced astigmatism. CI > 1 indicates over-correction. Corneal astigmatism was taken as pre-op astigmatism and manifest refractive astigmatism 3 weeks after the surgery, as post-op astigmatism. Eyes were divided into with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism subgroups.
In WTR and ATR groups respectively, in toric IOLs eyes, the mean CI values were 1.20 and 1.04, and the percentages of eyes with over-correction were 83.9% and 57.5% (both P<0.05); in PCRIs eyes, the mean CI values were 0.92 and 0.81, and the percentages of eyes with over-correction were 23.4% and 11.8% (both P>0.05), respectively.
Even though the horizontal clear corneal incision creates a small WTR shift, compared to the ATR group, over-correction occurred in more eyes with WTR astigmatism. This demonstrates that total corneal astigmatism based on anterior corneal measurement only was overestimated in eyes with WTR, presumably due to the vertical steep meridian on posterior corneal surface.
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