Prediction of intraocular lens power using the lens haptic plane concept

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Abstract
Purpose: To test algorithms for the preoperative estimation of the lens haptic plane (LHP) and to assess these in terms of predictability of postoperative refraction. Setting: SA Erik's Eye Hospital, Stockholm, Sweden. Methods: Preoperative axial length, anterior chamber depth (ACID), and cataractous lens thickness were measured in consecutive cases scheduled for phacoemulsification and posterior chamber intraocular lens (IOL) implantation. The algorithms tested used ACID and cataractous lens thickness to estimate LHP. The exact geometry of the IOL was used to calculate postoperative ACID from LHP. Thick lens theory and paraxial ray tracing were used to calculate predicted postoperative refraction. The calculated value was compared with actual refraction 3 to 6 months postoperatively. Results: Mean absolute average error in predicted refraction was 0.38 diopters (D), with 78% of eyes within 0.50 D and 97% within 1.00 D for the best algorithm. Conclusions: The predictability in postoperative refraction found by applying the LHP concept and paraxial ray tracing was excellent. However, the small sample, with its unusually slight variation in axial lengths, did not allow statistically significant differences between different postoperative refraction prediction methods to be demonstrated.

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