الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Eighty eyes of 40 normal subjects were selected from the subjects attending the out patient clinic of the Ophthalmology Department of Benha University Hospital during the period from Jan. 2005 to Dec. 2005.
Corneal curvature measurements were taken from all subject using the Bausch and Lomb keratometer and the Orbscan II topographer.
Corneal power was calculated using Bausch and Lomb keratometer reading of anterior curvature with formula:
P=n-1/r
Using two refractive indices 1.3375 and 1.3315 named as Bausch 3375 and Bausch 3315, respectively.
Corneal power was recalculated using thick lens formula:-
P=P1+P2-t/n2(P1P2)
For this study power calculated using slit–scan topography data for r1 ,r2 and corneal thickness (Orbscan Power) or using Bausch and Lomb keratometry for r1 and slit–scan topography for r2 and corneal thickness (Orbscan/ Bausch Power).The Orbscan II also calculates the total corneal power averaged across the central 3mm of cornea (Orbscan Mean Power).
Statistical analysis made comparing the pervious results.
Conclusions
Orbscan II measurement of posterior corneal curvature may be used to calculate corneal power in normal eyes,using the thick lens formula. The same methodology could be applied to corneal power calculation after refractive surgery, comparing the perioperative data method of corneal power calculation with Orbscan II power calculation. If good agreement can again be demonstrated, then the current difficulties in IOL selection in patients with prior refractive surgery may be overcome.
refractive surgeons might consider giving their patients a wallet card indicating their preoperative keratometric reading, preoperative refraction, and postoperative refraction at some stable time point (e.g., after 6 months) to allow for the application of the “clinical history method.