different methods for keratometric measurement and corneal power formulas following photorefractive keratectomy

purpose: to measure corneal power using different methods to assess agreement between these methods among patients who underwent photorefractive keratotomy. methods: in this prospective comparative study, keratometry was measured in 66 eyes of 33 refractive surgery candidates using manual keratometry (kr), conventional topography average central corneal power (accp), galilei total corneal power (tcp), orbscan ii and eye sys (effrp). corneal power was also calculated using clinical history method (chm) and two corneal power formula (adjusted accp and adjusted effrp). the readings by these instruments and methods were compared using t-test. agreement among the measurements by three devices was assessed using pearson (r) and intraclass correlation coefficients (icc). linear regression analysis was used to quantify this correlation. results: the values for chm were correlated with all keratometric methods and corneal power formulas. however, postoperative kr, accp, orbscan ii and effrp were higher than chm. (-0.58±0.63, -0.55±0.66, -0.51±0.62, -0.36±0.62, respectively, p<0.001). chm demonstrated the least mean difference with tcp, adjusted accp and adjusted effrp (0.17±0.77, -0.14±0.63, 0.07±0.63, respectively). chm had narrowest limit of agreement with adjusted effrp and adjusted accp (-1.16 to 1.3, -1.37 to 1.09, respectively). conclusion: chm has the least mean difference with tcp, adjusted accp and adjusted effrp. however, the narrowest limits of agreement were between chm and adjusted effrp; and chm and adjusted accp.