BLOG: Let’s forget the ink
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It’s amazing to think of all the science and technology utilized for cataract surgery, from sophisticated biometry and preoperative surgical guidance and planning tools to the latest femtosecond lasers, phaco machines and multifocal IOLs.
And then we have the lowly ink marker — the same surgical marking pen we’ve used for decades. That sure takes the sophistication level down a notch, doesn’t it?
There are several problems with manual ink marking for toric IOL implantation. First, the ink mark starts out at an imprecise 5° to 10° wide, and the ink may run farther or even disappear during surgery. Because of these problems, manual ink marks have been shown to account for up to 10° of axial misalignment. Given that each degree of rotational misalignment reduces the effect of a toric IOL by 3.3%, that could change the astigmatic correction by more than 30%.
Additionally, manual marking is a two-step process that requires leaving the OR to mark the reference axis (90° or 180°) preoperatively, and then (ideally) a second step in the OR to mark the steep axis with an axial marker such as a Mendez gauge. Some surgeons may skip this step or just “eyeball” it. Not only is two-step marking time-consuming, but the eye may have dilated unevenly or cyclorotated in the interim, making the accuracy of the axis questionable. Some surgeons take multiple intraoperative aberrometry measurements. However, aligning the microscope’s reticle to manual ink reference marks still has room for error.
Femtosecond laser marking addresses all these problems. Laser marks are accurate within 0.6° — that’s about five times more precise than a manual ink mark.
Several different laser/phaco platforms now offer the ability to eliminate one or both marking steps. One study found, for example, that eliminating ink marking with the Zeiss Callisto system improved refractive accuracy, reducing the percentage of eyes with more than 0.5 D of residual astigmatism from 6% to 0.6%. Another study found a reduction in IOL misalignment and less deviation from the targeted induced astigmatism with Verion digital marking (Alcon).
The Catalys system (Johnson & Johnson Vision) that I use imports data directly from the Cassini Technologies’ Ambient, a sophisticated corneal diagnostic device that measures total corneal astigmatism. Not only can the laser use this data to mark an accurate steep axis (taking posterior astigmatism into account), but it also compares iris structures between the preoperative and intraoperative images to ensure that it compensates for any tilt or rotation before marking. Radial intrastromal toric marks of 0.75 mm to 1 mm in length are positioned at the 8-mm optical zone by default; I like to move them more centrally, to a 7-mm optical zone, so that the radial marks are more proximal to the toric IOL dots for even greater ease of alignmen.
With all of these developments, it’s time to set yourself free from the marking pen.
- References:
- Black D. Evaluation of markerless alignment system for toric IOLs. Presented at: ASCRS/ASOA meeting; April 20, 2015; San Diego.
- Elhofi AH, et al. Medicine (Baltimore). 2015;doi:10.1097/MD.0000000000001618.
- Ma JJ, et al. J Cataract Refract Surg. 2008;doi:10.1016/j.jcrs.2008.04.041.
- Titiyal JS, et al. Clin Ophthalmol. 2018;doi:10.2147/OPTH.S164175.
- Visser N, et al. J Cataract Refract Surg. 2011;doi:10.1016/j.jcrs.2011.02.024.
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