Using the lens haptic plane concept and thick-lens ray tracing to calculate intraocular lens power.

PURPOSE: To develop a methodology for intraocular lens (IOL) power calculation in which the task of predicting the postoperative position of the IOL is separated from the calculation itself.
SETTING: Pharmacia, Groningen, The Netherlands.
METHODS: The minimum biometry input needed for IOL power calculation is the mean anterior corneal radius and axial length of the eye. The lens haptic plane (LHP) is the plane where the IOL haptics make contact with eye tissue. It is an anatomical site (eg, the equator of the capsular bag) and is independent of the IOL model. The position of the IOL optic in relation to the LHP is determined from the exact design of the IOL. Gullstrand's eye model is adopted to obtain the posterior corneal radius, thickness of the cornea, and refractive indices of the eye media. Thick-lens ray tracing in the paraxial limit is used for the optical calculation.
RESULTS: A spreadsheet is given for the calculation.
CONCLUSIONS: The methodology developed allows for IOL power calculation from first principles (ie, using true physical distances, radii, and refractive indices as input for the optical calculation).