Abstract
Purpose :
Manufacturers of multifocal intraocular lenses (MIOLs) describe the near addition power at the IOL plane. However, the effective addition power at the spectacle plane better describes the actual working distance that a MIOL provides to a patient. The effective addition power is dependent on both the power of the IOL and an individual’s ocular biometry. This study was designed to explore the relationship between the theoretical add power at the spectacle plane and the effective addition power at the spectacle plane. In addition, a simple clinical technique for predicting the post-operative add power was evaluated.
Methods :
This was a prospective study involving twenty subjects who were implanted with a diffractive MIOL. Pre- and post-operative ocular biometry measurements were attained using the LenStar (Haag-Streit). Monocular and binocular defocus curves from +1.5D to -5.0D in 0.5D randomised steps were measured. An 8th order polynomial was fitted to the curve and the distance and near focal points were identified by deriving the inflection points of the polynomial. The effective add power was defined as the dioptric distance between the distance and near inflection points. The post-operative ocular biometry and known IOL power was used to calculate the theoretical add power according to paraxial ray tracing. Pre-operative biometry results were used to predict the add power according to the Hagis, Holladay and SRK/T formulae.
Results :
There was a significant correlation (r=0.502, p=0.029) between the theoretical near addition, as determined through ray tracing, and the effective add power. The effective addition values for the actual near addition (2.763±0.042D) were greater than those theoretically calculated (2.473±0.015D; p<0.0005). The predicted add power according to the SRK/T formulae correlated with the effective add power (r=0.524, p=0.021) however, there was no significant correlation when the Haigis and Holladay formulaes were used.
Conclusions :
The results of this study demonstrates that the effective addition power can be predicted using pre-operative ocular biometry measurements and conventional IOL formula. This research may lead to personalized and reliable selection of addition power in accordance with an individual’s visual needs.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.