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    Integrating computer-assisted toric IOL implantation

    Surgeon finds image registration technology helps eliminate need for axis marking

    Take-home message: Since making the switch to a markerless toric alignment system, Bryan S. Lee, MD, JD, explains how the technology has eliminated ink marking.

    By Bryan S. Lee, MD, JD; Special to Ophthalmology Times

    Dr. LeeFrom an optical standpoint, toric IOLs are of benefit to patients with astigmatism, but their performance is dependent on proper lens selection and positioning. Surgeons who implant toric IOLs have to consider the concept of “stackable” sources of error.

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    Compared with a standard monofocal IOL, there are several additional steps—identifying the correct axis of astigmatism, marking the reference axis, marking the steep axis, and aligning the IOL—that must all be done correctly. Although the risk of a mistake is low at each step, small errors can add up and contribute to an undesirable outcome.

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    Though traditional marking and alignment techniques can work well, I prefer to eliminate as many potential sources of human error as possible. To that end, I have found that switching to a markerless toric alignment system (Callisto Eye, part of the Zeiss Cataract Suite) has eliminated ink marking altogether. This device is an easy transition for users of other elements of the suite (including the IOLMaster and the OPMI Lumera microscopes).

    The registration process

    Here’s how it works: A reference image is automatically acquired by a camera integrated with optical biometry (IOLMaster) during routine preoperative biometry. That image can be manually transferred via USB drive or sent by a secure connection to the surgery center.

    The markerless alignment system compares the preoperative reference image with the eye during surgery, using limbal blood vessels to register the images in real time.

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    Much like iris registration in laser vision correction, this helps to correct for unpredictable cyclorotation. It also superimposes key information on the surgeon’s view through the microscope, including the reference (0 to 180 degree) axis and the steep axis.

    If desired, the markerless alignment system can show virtual marks for the capsulorhexis and identify the visual axis to aid in multifocal IOL centration. The system continuously tracks the image and adjusts the overlay to maintain accurate registration throughout the case.

    A typical toric case

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