Image-Guided Cataract Surgery

Why alignment matters

A toric lens corrects astigmatism only when it sits at the right axis. Every degree of misalignment loses about three percent of the correction, and a lens ten degrees off loses a third of it. Traditionally the axis was marked on the cornea with ink while the patient sat upright, because the eye rotates slightly when a patient lies down; the marks were then used as a reference under the microscope. Ink marks are a few degrees wide and can smudge or fade during surgery.

How image guidance works

Before surgery, a diagnostic device photographs the front of your eye in high resolution alongside the measurements of its curvature and astigmatism. The image records the unique pattern of blood vessels on the white of the eye and features of the iris. In the operating room, the microscope's camera recognizes those same features, matches the two images, and projects the surgical plan onto the surgeon's view: the axis for the toric lens, the center and diameter of the capsulotomy, and the position of the incisions. The overlay moves with the eye, so the reference stays accurate even if the eye rotates.

What it improves

• Toric lens alignment, with the largest gain in accuracy for astigmatism correction
• Centration of the capsulotomy and of multifocal and extended depth of focus lenses, whose optics depend on being centered on the visual axis
• Placement of arcuate incisions for astigmatism at the planned axis
• Consistency: the plan the surgeon made from the measurements is the plan executed, without a transcription step in between

Combined with other technology

Image guidance is typically used with the femtosecond laser, which cuts the capsulotomy and incisions the overlay planned, and with intraoperative aberrometry, which confirms the axis after the cataract is removed. Together they address the three sources of error in premium lens surgery: the measurement, the placement and the final position.