Personal A-constant in relation to axial length with various intraocular lenses

PURPOSE: To study the relationship between the axial length and personal A-constant for the 1-piece Tecnis (Abbott ZCB00), AcrySof MA60AC (Alcon) and the Quatrix aspheric preloaded (CROMA) intraocular lenses (IOL). MATERIALS AND METHODS: Patients matching the inclusion criteria were further subdivided according to the implanted IOL in this prospective comparative study. The obtained refractive outcomes were introduced into the formula installed in the biometry machine (Humphrey model 820 ultrasonic biometer) to obtain the personal A-constant for each eye. Polynomial regression analysis was done to study the individualized A-constant for each type of IOL in relation to preoperative axial length measurement. RESULTS: Two hundred and forty five eyes of 186 patients were enrolled into this study, of whom 73 eyes with Tecnis 1-piece, 116 eyes with MA60AC, and 56 eyes with Quatrix. The median of personalized A-constant for Tecnis 1-piece, MA60AC, and Quatrix were 119.21 (SD 1.3, Std. Mean error 0.15), 119 (SD 1.2, Std. Mean error 0.11) and 120.4 (SD 1.2, Std. Mean error 0.16) respectively. Regression plots for the same range of axial length among all the groups showed that the Tecnis1 group followed the same pattern of the Quatrix group in which there was a linear relationship of a trend towards myopia when the axial length had increased and a hyperopic shift when decreased. This relationship changed into a plateau when the axial length became in the range of 23.5 mm to 27 mm in the MA60AC group. CONCLUSIONS: Personal A-constant follows different trends with different IOLs even for the same range of axial length.