Refractive Surgery | Apr 2011

Intraoperative Measurement Devices: Optimizing Surgical Results With Callisto Eye and Z Align

Video overlay supports toric IOL alignment.

Premium IOLs are a wonderful way of achieving better visual results after cataract surgery or clear lens exchange. Toric IOLs, which are commonly used to correct astigmatism, do not require a perfect macula or perfect optic nerve function preoperatively, and therefore these lenses are a viable option for a larger portion of the population compared with other premium IOLs. But to achieve adequate astigmatism correction and excellent visual outcomes in these patients, surgeons are faced with the challenge of accomplishing perfect toric IOL alignment.


I have experience with the Callisto eye and Z Align (Carl Zeiss Meditec, Jena, Germany; Figure 1), which uses video overlay to support the alignment of toric IOLs. Callisto eye is part of a larger system that includes collecting and displaying patient, administrative, and diagnostic data. It was first used for customization of the continuous curvilinear capsulorrhexis. Z Align, the latest advancement, uses a competitive eye tracker based on a live video image to mark and project parallel lines for toric IOL alignment. This step enhances my surgical technique and provides more accurate outcomes because it helps me to mark the necessary axes and align the IOL during surgery (Figure 2; for videos of the procedure, visit and The versatility of the system means that I can customize parameters including the shapes, colors, and projections used within the software.

Toric IOLs must be aligned within 3° of intended placement to accurately correct astigmatism and achieve good postoperative results. As little as 10° of misalignment reduces astigmatic correction by approximately 30°. Therefore, an accurate and reproducible surgical process is not just suggested—it is mandatory. Additionally, cyclotorsion is important in astigmatic patients. Because the astigmatic axis is evaluated and marked in a vertical position and the eye operated in a horizontal position, variation in a rotational position can occur. Intraoperative toric IOL alignment tools provide a solution for such variations.

Once the eye tracker is activated, the angle of alignment is programmed and the prealignment process is performed. After removal of the ophthalmic viscosurgical device, the toric IOL can then be aligned using the Callisto eye system, which takes images and relays them to the Z Align module. The surgeon, looking at the touchscreen, uses these images to achieve IOL placement on the target axis. The surgeon is able to continually visualize the target axis and compare this with the position of the toric IOL. The instruments and movements of the eye within the operating field do not interfere with the tracker because it automatically adapts to changes including zoom and focus during surgery.


The advantages of the Z Align module include its ease of use, the fact that no extra time is required, and its customizable surgical interface. Additionally, intraoperative toric IOL alignment, which is highly surgeon dependent, is easier to teach with Z Align because it is not time-consuming.

A future version of Zeiss’ toric solution workflow has been presented at recent congresses. One of the next developments is that surgeons will no longer need to look outside the microscope field when aligning the IOL with Callisto eye and Z Align, as the intraoperative measurements will be incorporated into the opticals of the operating microscope. The surgeon will simply press the footpedal to launch the eye tracker and alignment software. Additionally, data can be projected across both optics or in just one optic of the microscope. For instance, I prefer its display in the optic of my dominant eye.


The biggest advantage of the Callisto eye and Z Align is that I no longer need to mark the patient preoperatively. This device collects data from the IOLMaster (Carl Zeiss Meditec), and matches images of the limbus and scleral and/or conjunctival vessels with the operating field, providing automated anatomic recognition.

Toric IOLs will enjoy incremental progress in the next few years, and intraoperative alignment of these lenses will continue to be a mandatory target for improving surgical outcomes. With a very short learning curve, Callisto eye and Z Align is an easy, accurate, and reproducible process allowing refractive cataract surgeons to optimize surgical results and expand their indications for premium IOLs.

Michel Perez, MD, practices in Dijon, France. Dr. Perez states that he has a patent ownership or a part ownership of the Z Align. He may be reached at tel: +33 380673033; cell: +33 613237631; e-mail: