Purpose: To compare axial length and intraocular lens power calculated from three biometry methods, then to study refractive postoperative results to assess the predictive value of each method.
Material and methods: This prospective study included 40 eyes planned for cataract surgery. Two skilled operators participated in this study: One for the surgery and the other for the biometry and measurement of intraocular lens power. For intraocular lens power, we used the optic biometer from Zeiss and the echograph B Ultrascan from Alcon. IOL power calculation was performed using the usual mathematical formulas based on 3 biometry methods. 1--keratometry measurement, anterior chamber depth (ACD), and axial length using optical biometry; 2--keratometry measurement using the Javal keratometer and biometry using the B mode ultrasonography; 3--keratometry measurement using the Javal keratometer and biometry using A mode ultrasonography.
Results: The average age of our patients was 69.5 years old, ranging from 52 to 81 years old. The average axial length was 23.46 mm with, ranging from 20 to 32.73 mm. The average keratometry with optic biometry was 43.97 diopters +/- 1.44 versus 43.84 diopters +/- 1.45 with the Javal keratometer. 40 eyes were examined and there were 4 failures (10%) for axial length measurement by optic biometry because the cataract was very dense. Biometric preoperative results with the 3 methods show that there was a statistically significant difference between the A mode and the B mode optic biometry (P < 0.006). On the other and, there was no statistical difference between optic biometry and the B mode.
Conclusion: Optic biometry has a number of advantages. This is new method, is non invasive, easy to use, with no contact, and it is reliable. Results with this method are more precise than with ultrasonic biometry. For high myopia, optic biometry is a very valuable method. Its limits are total cataract and intraocular opacities; in these cases ultrasonic biometry is the best method.