Prediction of pseudophakic capsular bag diameter based on biometric variables

To measure the capsular bag diameter (CBDm) in vivo and calculate a regression formula for future preoperative prediction of capsular bag diameter (CBDp).

Department of Ophthalmology, University of Vienna, Austria.

This prospective study comprised 70 eyes having cataract surgery with implantation of an open capsular tension ring (CTR) (Morcher Type 14). Within the first postoperative days, the distance between the ends of the CTR were measured through a gonioscopy lens by adjusting the slit height. This distance was added to the known length of the CTR to calculate the capsular bag circumference and from this, the CBDm. The CBDm was correlated with axial eye length (AL), corneal power (P), preoperative anterior chamber depth and lens thickness, corneal diameter, and age. A stepwise multiple regression analysis was computed with CBDm as the dependent variable.

The mean CBDm was 10.37 mm +/- 0.25 (SD). A statistically significant negative correlation was found between CBDm and P (P < .0004; r2 = 0.16) and a positive correlation between CBDm and AL (P < .0226, r2 = 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 AL2 (P < .0001; r2 = 0.3145). 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.

The capsular bag diameter in vivo correlated negatively with corneal power (P) and positively with AL. The regression formula used may serve as a tool for preoperative identification of eyes with a very large or very small CBDm.