Prediction of pseudophakic capsular bag diameter based on biometric variables

Purpose:To measure the capsular bag diameter (CBDm) in vivo and calculate a regression formula for future preoperative prediction of capsular bag diam eter (CBDp) Setting: Department of Ophthalmology, University of Vienna, Austria., Methods: This prospective study comprised 70 eyes having cataract surgery w ith implantation of an open capsular tension ring (CTR) (Morcher Type 14). Within the first post-operative days, the distance between the ends of the CTR were measured through a gonioscopy lens by adjusting the slit height. T his distance was added to the known length of the CTR to calculate the caps ular bag circumference and from this, the CBDm. The CBDm was correlated wit h axial eye length (AL), corneal power (P), preoperative anterior chamber d epth and lens thickness, corneal diameter, and age. A stepwise multiple reg ression analysis was computed with CBDm as the dependent. variable. Results: The mean CBDm was 10.37 mm +/- 0.25 (SD). A statistically signific ant negative correlation was found between CBDm and P (P <.0004; r(2) = 0.1 6) and a positive correlation between CBDm and AL (P <.0226, r(2) = 0.07). Stepwise multiple regression resulted in the following regression formula: CBDp = 3.44 to 0.056 x P + 0.713 x AL -0.0135 x AL(2) (P <.0001; r(2) = 0.3 145). Using this formula with the individual Ps and ALs, all 6 eyes with a large capsular bag diameter (CBDm > 10.7 mm) and 10 of 13 eyes with a small one (CBDm < 10.1 mm) were correctly classified. Conclusion: The capsular bag diameter in vivo correlated negatively with co rneal power (P) and positively with AL. The regression formula used may ser ve as a tool for preoperative identification of eyes with a very large or v ery small CBDm. (C) 1999 ASCRS and ESCRS.