Trial for new intraocular lens power calculation following phototherapeutic keratectomy

Purpose: To determine an equation to calculate the intraocular lens (IOL) p ower for eyes that have undergone laser phototherapeutic keratectomy (PTK). Methods: The Gullstrand series was used to determine the power and radius o f curvature of a convex-plane IOL, which will alter the focal point from th e cornea to the conjugate point on the retina using the ray tracing method. Results: The radius of curvature of the anterior corneal surface (R), axial length (it,YL), the predicted postoperative anterior chamber depth (ACD), and lens thickness (LT) were used in the following formula to calculate the refractive power of the IOL to be used: K = R/7.7, DC = 337.5/R:VC = 1000/ DC 1.336 where VC is the posterior vertex focal length, Al -(VC - ACD), B-1 = AXL - 0.5 K - ACD - 0.103LT S = 1/A(1) + 1/B-1 k is the proportional exp ression for anterior corneal curvature, DC = anterior corneal refractive po wer, Al = distance from anterior surface of IOL to posterior vertex focal p oint, B1 = distance from the second principal point of IOL to the retina, S = 1/focal length of IOL in air. Using this equation, the power tin diopter s) of the IOL in liquid was determined to be 1000/(I/S) 1.336. Ln eves that have undergone PTK, the keratometric value prior to cataract surgery is no t used. Instead a value, R', is introduced. R' is defined as (R - 376/1376 dT), where R is the radius of corneal curvature prior to PTK; and dT the am ount of corneal tissue removed. The corneal thickness after cataract surger y, CT' was defined as (TT - dT, where CT is the corneal thickness prior to PTK. Conclusion: The new equation appears to be useful for determining the IOL p ower, although it is important to select a lens that has the accurate predi cted anterior chamber depth. (C) 2000 Japanese Ophthalmological Society.