Materials and Methods: The study included patients whose cataract stage was determined prior to surgery and who had no additional ocular disease. The same physician measured contact A-scan axial length and corneal strength using an A-scan ultrasonic biometry device (HiScan, Optikon, Italy) and a keratometry device (Ophthalmometer, CSO, Italy), respectively.

Results: Of the 52 patients with complete medical files accepted to the study, 32 were women and 20 were men. The average cataract grade was 2.66±0.52 (1 to 4); mean target spheric equivalent was -0.70±0.24 diopter (D) and mean final refraction was -1.28±0.66 D at the 2 month post-operative examination. Mean absolute deviation from target refraction was found to be 0.65±0.45 D (0.04 to 2.51), mean net deviation was -0.58±0.54 D (+0.85 to -2.51). Using standard A-constant, 38.4% (21/52) of the eyes were within ±0.50 D of the target refraction and 82.7% (43/52) of eyes were within ±1.00 D. When the customized A-constants based on mean net deviation were used, these levels increased to 69.2% (36/52) for within ±0.50 D of the target refraction and 96.2% (50/52 eyes) for within ±1.00 D.

Conclusion: Contact with the eye during contact ultrasonic biometry results in a short axial length measurement and causes deviation in the final refraction toward myopia. Through the use of customized A-constant, this habitual measurement error can be corrected effectively. Keywords : Biometry, refraction, intraocular lens