RAY-TRACING SIMULATIONS WITH AN ASTIGMATIC PSEUDOPHAKIC EYE MODEL AND A GENERIC SIMULATED TORIC IOL

Evaluation of ray-tracing intraocular lens (IOL) power calculation with a developed astigmatic pseudophakic eye model and generic simulated toric IOL.

Group for Lasers and Plasmas, Institute for Plasmas and Nuclear Fusion, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal; Hospital da Luz Lisbon, Lisbon, Portugal; Studio Oculistico D’Azeglio, Bologna, Italy.

An astigmatic pseudophakic eye model suitable to incorporate patient-specific data was developed based on the Personalized Pseudophakic Eye (PPE) model from Ribeiro and the Liou-Brennan eye model, and implemented in the Zemax®. A generic simulated toric IOL was created, and, assuming a target refraction of zero, the correspondent spherical and cylindrical powers calculated via ray-tracing were compared to the implanted toric IOL powers for 19 eyes and for three models: two pre-operative models, one combined with a PPE based formula for the estimation of the post-operatively lens position, and the other one with the C-Constant by Olsen; and a post-operative model where the lens position was known. Considering the implanted IOL power the difference between the refraction obtained with the post-operative model and the refraction with each of the pre-operative models was determined. The cylindrical power variation was assessed for the scenario where the posterior corneal surface is considered as in the Liou-Brennan eye model, with the keratometric index. 

The mean (and standard deviation (SD)) for the spherical and the cylindrical dioptric powers of the known implanted IOL were 19.24 D (3.53 D) and 2.00 D (1.31 D), respectively. For the pre-operative model with the PPE based formula, these were 20.44 D (4.35 D) and 2.04 D (1.82 D), and for the one with the C-Constant formula these were 20.33 D (4.30 D) and 2.04 D (1.80 D). The mean and SD values for the post-operative model were 19.01 D (4.08 D) and 2.06 D (1.86 D).  Considering the implanted IOL powers, the mean (and SD) difference between the refraction obtained with the post-operative model and the pre-operative model combined with the PPE based formula was -0.83 D (0.47) for the spherical power and 0.17 D (0.05 D) for the cylindrical power, while combined with the C-Constant formula these were -0.80 D (0.41 D) and 0.16 D (0.05 D). Not considering the posterior corneal measurements led to an increase of the cylindrical IOL power for with-the-rule (WTR) eyes and a decrease for against-the-rule (ATR) eyes.

The created astigmatic pseudophakic eye model with the generic simulated toric IOL showed similar ray-tracing calculated powers to the implanted IOL powers, highlighting the spherical power tenderness to the post-operative IOL position estimations and the cylindrical power relation to the posterior corneal encountering. The implemented model enables simulations of several scenarios encountering patient-specific data.