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How ocular non-corneal remaining astigmatism influences the outcome of photorefractive keratectomy (PRK)

Session Details

Session Title: Surface Ablation I

Session Date/Time: Sunday 06/10/2013 | 08:00-09:30

Paper Time: 08:42

Venue: Main Lecture Hall (Ground Floor)

First Author: : A.Peyman IRAN

Co Author(s): :    M. Peyman              

Abstract Details


to determine the effect of pre and post-op non-corneal ocular remaining astigmatism (ORA) on visual and refractive outcome after PRK for correction of myopic astigmatism


Isfahan Ophthalmology Research Center, Isfahan University of Medical Sciences


71 eyes of 36 subjects enrolled in this study. Patients underwent PRK for treatment of myopia and myopic astigmatism. After alcohol assisted corneal epithelium removal, excimer laser ablation performed with Technoals 217z. A soft bandage lens and standard post-op antibiotic and corticosteroid regimen used similarly in all patients. Subjects evaluated regarding their refractive error, keratometry, visual acuity, and slit lamp exam before and six month after surgery. Pre and post-op non-corneal astigmatism defined as ORA calculated by vectorial analysis of difference between corneal plane refractive astigmatism and keratometric astigmatism. Statistical analysis used to determine correlation between ORA and outcome of surgery including efficacy of astigmatic treatment.


Pre-op spherical equivalent (SE) was -6.27 +/- 1.48 with 1.16 +/- 1.02 diopters of corneal plane refractive astigmatism and 1.44 +/- 0.47 diopters keratometric astigmatism. Post-op values were -0.60 +/- 0.85, 0.56 +/- 0.47, and 1.06 +/- 0.57 diopters for SE, refractive corneal plane astigmatism, and keratometric astigmatism respectively. Pre-op and post-op non-corneal ORA was 0.76 +/- 0.41 and 0.76 +/- 0.46 diopters respectively two values were not different statistically (p: 0.976) and had significant correlation (r: 0.37, p: 0.002). Pre-op ORA correlated to pre-op SE (r: -0.25, p: 0.04), but not correlated to pre and post op LogMAR corrected acuity. Pre-op ORA had correlation to keratometric difference vector of astigmatic correction (r: 0369, p: 0.002), but had no significant correlation with refractive difference vector or refractive astigmatism correction index of success. Post-op ORA correlated to keratometric induced astigmatism (r: 0.334, p: 0.006), keratometric index of success (r: 0.571, p< 0.001), and post-op keratometric astigmatism (r: 0.736, p< 0.001).


PRK do not alter non-corneal ORA. Refractive astigmatic correction vectors and indices are not correlated with ORA, but post-op keratometric astigmatism is strongly correlated to ORA. It seems that PRK effectively adjust keratometric astigmatism to correct total refractive astigmatism as well as ORA.

Financial Interest:


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