Ensuring postoperative safe distances between the iris-fixated phakic IOL and crucial tissues (eg, corneal endothelium, crystalline lens) remains one main challenge in phakic IOL implantation. To assure a more precise and accurate preoperative patient selection, we developed—in cooperation with Oculus Optikgeräte GmbH (Wetzlar, Germany)—a phakic IOL simulation software module. This module, applicable to the new high resolution Pentacam HR (Oculus Optikgeräte GmbH), will improve preoperative diagnostic evaluation. After entering the patient's refraction, the software calculates the required refractive power of the phakic IOL that is stored in an integrated lens database. This individual phakic IOL is then projected into the patient's anterior chamber, which has been obtained by regular Scheimpflug measurement. A three-dimensional calculation obtains the values of interest.

The Pentacam images the anterior segment of the eye by a rotating Scheimpflug camera noncontact measurement. Two devices are currently available; the newer is the Pentacam HR, which offers an increased image resolution. The rotating Scheimpflug camera provides a series of 50 Scheimpflug images in 2 seconds. The images capture the anterior corneal surface to the posterior surface of the crystalline lens. Out of these images, the software extracts and obtains 1,380 true elevation points for each surface, including the center of the cornea. The software generates a three-dimensional model of each surface as a basis for corneal topographic and chamber analysis.

The new Pentacam software module simulates the positioning of a phakic IOL into the anterior chamber via a three-dimensional model, creating a visual for the surgeon. The lens is automatically aligned on the iris surface and centered on the pupil after it is selected from a lens database. In every Scheimpflug image, the outlines of the simulated implant are drawn. These outlines include the distortion of the shape typically caused by optical refraction in Scheimpflug imaging. From each surface point of the phakic IOL, the software three-dimensionally calculates the distances to adjacent eye structures, which results in real minimum values. These distances are presented both in color maps, showing every point of the implant in top view and as minimum space values for critical areas of the phakic IOL. Beside the color maps represent the actual simulated position in the x- and y-planes relative to the apex and the pupil.

The surgeon carries out phakic IOL alignment by dragging and dropping the color maps in every direction. With the help of online refreshed distance values and images, the optimum lens position and axis alignment is defined, and the compliance of the minimum distances is supervised. The software assists in moving the phakic IOL in x- and y-direction or changing the axis angle by always aligning the IOL on the iris surface. The surgeon will then perform final corrections in height and tilt to compensate for incorrect positioning caused by irregular iris spots.

Beside projection of the selected IOL power/type in the anterior chamber, the software program gives exact millimeter values for minimal distances (1) between the endothelium to the IOL optic and haptic, (2) from the backside of the IOL to the iris, and (3) between the backside of the IOL and the crystalline lens. Additionally, distances from the IOL to other tissues are read by placing the curser on the specific point of the implant.
We studied 44 eyes (23 patients) at the University of Mainz, in Germany. The average age of patients was 38 years (range, 24 years to 61 years), and the average implanted phakic IOL was -8.70 D (range, -22.00 D to 11.00 D). Seventeen eyes received the foldable Artiflex (Ophtec BV, Groningen, Netherlands), and 13 eyes received a rigid PMMA IOL (VeriFlex; Advanced Medical Optics Inc., Santa Ana, California). Eight eyes received the myopic and five the hyperopic model.

One day before planned surgery, a Pentacam investigation using the novel phakic IOL software module was performed. One month after surgery, a second investigation was performed to compare preoperative simulation values with actual postoperative distance values. A mean deviation from simulation to postoperative values was detected. The distance between central phakic IOL optic to corneal endothelium was 18 µm; 56 µm for the distance between peripheral optic to corneal endothelium; and 25 µm for the distance between posterior phakic IOL optic to anterior surface of crystalline lens. Finally, a mean deviation between simulation and postoperative position of 31 µm for the distance between phakic IOL haptic to corneal endothelium was evaluated (Figure 1).

When developing this simulation module, we also considered the (1) changes in anterior segment dimension through the aging process and (2) annual decrease in anterior chamber depth. The software predicts the decreasing anterior chamber depth for a selected patient's age to avoid future complications. The aging tool can predict the phakic IOL position up to 30 years in advance. Clinical studies are still ongoing (Figure 2).

By providing a three-dimensional image of the anterior segment, the Pentacam can be used to investigate important features for phakic IOL candidate selection, including a protruding iris (ie, excluding a patient from hyperopic implantation), or the anterior chamber dimensions that must be considered in patients receiving a toric phakic IOL. The ability to screen candidates for phakic IOL implantation is enhanced with the availability of the phakic IOL software feature.

Preoperatively, phakic IOL simulation during the patient selection process represents a powerful step toward increasing safety of this surgical option. Patients with irregular iris formation as well as poor central and peripheral anterior chamber dimension, may benefit from these additional features of the Pentacam. Additionally, the image can be shown directly to the patient (Figure 3), illustrating why they may not be a good candidate for iris-fixated IOL implantation. Clinical results of this phakic IOL simulation module are finalizing, and will be presented as an upcoming prospective study with high numbers. Another important feature under development is the option to simulate toric models (ie, Model A and B) where the surgeon can decide what model would fit better in the patient's anterior chamber.

H. Burkhard Dick, MD, is Chairman of the University Eye Hospital, Department of Ophthalmology, in Bochum, Germany. Professor Dick was involved in the development of the phakic IOL Simulation Module. He may be reached at burkhard.dick@kk-bochum.de.

Mana Tehrani, MD, is from the Department of Ophthalmology, Johannes Gutenberg-University, in Mainz, Germany. Dr. Tehrani states that she was involved in the development of the phakic IOL Simulation Module and may receive a royalty agreement. She may be reached at mtehrani@hotmail.de.