October 2014

 

CATARACT

 

Device focus

Marking and alignment keys to toric lens placement


by Michelle Dalton EyeWorld Contributing Writer

 
   

Toric markers may not be perfect, but they are integral in identifying axes for lens placement

Proper toric lens alignment starts with properly identifying the axis. Traditional markers use ink, but experts note that is not enough.

When toric lenses were introduced in 2005, we had incredible diagnostics for choosing the IOL, we had fabulous phaco technology for lens removal, we had these sophisticated IOLs and we were using a $1 ink pen, said Robert H. Osher, MD, professor of ophthalmology, University of Cincinnati, and medical director emeritus, Cincinnati Eye Institute, Ohio. The patient is paying out-of-pocket for a better, more precise result, yet we use imprecise marking devices. Numerous variables play a part in ensuring astigmatism correction after toric lens implantation, said John Berdahl, MD, in private practice, Vance Thompson Vision, Sioux Falls, S.D. Its not just getting the ink mark in the right spot to start to compensate for cyclotorsion, but also includes understanding surgically induced astigmatism, posterior corneal astigmatism, and lens alignment, he said.

Ink is by far the least accurate method of marking, Dr. Osher said. Regardless of the device used, ink would diffuse 5 degrees, 10 degrees, 15 degrees, or in the worst cases, entirely disappear, he said. Ophthalmology needed to develop more precise marking and alignment devices, Dr. Osher said. While Dr. Osher has developed several marking devices, the Wet-Field Osher ThermoDot Marker (Beaver-Visitec International, BVI, Waltham, Mass.) uses a tiny point cautery that marks the toric meridian beautifully, he said. The first generation marks intraoperatively, but a second generation that should be introduced early in 2015 will be able to mark preoperatively, he said.

You press a button, and it will leave a tiny dot on the conjunctiva, he said. He thinks preop and intraoperative determination of the target meridian are challenging and remain a deterrent for many surgeons who are not yet implanting toric lenses. Toric marking will become obsolete, Dr. Berdahl said. But its not days away, its a couple of years away from mainstream acceptance.

Belt and suspenders approach

Dr. Osher developed other intraocular approaches by creating a qualitative keratometer with 5 aspherical circles at different dioptric ranges that could offer guidance by corneal reflection, he said. By rotating his hand a few degrees in either direction, the circular light reflex would turn into an oval, he said. While I could guesstimate the amount and axis of the astigmatism, the accuracy was imprecise. Intraoperative aberrometry is gaining momentum as a viable method of aligning a toric lens, and as a result, some physicians are shying away from marking.

Its very helpful, but I dont have enough confidence that every single time aberrometry is going to tell me the right spot to place my toric lenses, Dr. Berdahl said. Dr. Osher recommends using a belt and suspenders approach that works for surgeons, as it eliminates the potential to get disoriented during the surgery itself. I mark the cornea, and I use aberrometry with the VerifEye [WaveTec Vision, Aliso Viejo, Calif.], and the Verion [Alcon, Fort Worth, Texas] for intraoperative alignment. Any single approach is not perfect, and I prefer some redundancy, Dr. Berdahl said.

Misaligning a toric lens by as little as 10 degrees results in a 30% loss of efficacy in the astigmatic correction. That may not be visually disturbing if its a small-powered toric lens, but in a high-powered toric lens, thats more than 1 D of astigmatism correction thats not occurring, Dr. Berdahl said.

Imaging iris landmarks (pigment, nevi, stromal patterns, vessels, Brushfield spots, etc.) and adding software to determine the exact degree can be reliable because the vascular landmarks change after dilating drops, Dr. Osher said, adding when he uses iris fingerprinting, its also in conjunction with the ThermaDot to mark the target meridian.

There are numerous ways of arriving at the target meridian, but surgeons still need to mark because many of the newer marker-less techniques depend on the limbal vascular anatomy, which can change during surgery, Dr. Osher said.

Personal preferences

Dr. Berdahl uses the Davis Plumb-Bob Pre-Marker (Mastel, Rapid City, S.D.) in conjunction with the LenSx femtosecond laser (Alcon). Before we began using the Verion, wed see where the mark is. The LenSx has software designed to compensate for cyclotorsion, he said. Then I make a couple of 50 μm deep incisions, what I call surface AK. I use that as my alignment mark in the OR. Dr. Osher uses iris fingerprinting in conjunction with the ThermoDot to mark the target meridian, which is facilitated by a Geuder hemi-circle (Heidelberg, Germany) or a Mastel ring. I also use the new Verion, he said. Both physicians recommend using multiple methods, and said that no single method is perfect.

I like comparing one technology against another, Dr. Osher said. One of my personal goals is to contribute to the development of evolving marking and alignment technology.

Becoming obsolete?

The Verion in combination with aberrometry may make other methods obsolete, but it is too soon to tell, Dr. Berdahl said. The technology measures a patients corneal curvature and images the iris and scleral vessels. Once the patient reclines, it can detect where those same vessels are, and it superimposes the 2 images so theyre perfectly matched, he said. We know exactly how much the eye cyclorotated. The Verion will place a virtual line over the cornea, so when implanting a toric lens, you can line it up exactly with the axis you need, Dr. Berdahl said.

The inaccuracy of using ink marking is better than nothing, but its far from ideal, Dr. Osher said. My nurses still place a 6 oclock mark prior to surgery, and they are quite good. Marking will never disappear, but ink is going to fall by the wayside, he predicted.

For the time being, however, the standard of care for the majority of surgeons is still using an ink pen in the preoperative area, Dr. Osher said.

Editors note: Dr. Berdahl has financial interests with Alcon, Abbott Medical Optics (Santa Ana, Calif.), and Bausch + Lomb (Bridgewater, N.J.). Dr. Osher has financial interests with Alcon and BVI.

Contact information

Berdahl
: john.berdahl@vancethompsonvision.com
Osher: rhosher@cincinnatieye.com

Quick reference list

Companies that manufacture traditional marking instruments

Accutome (Malvern, Pa.) www.accutome.com
Ambler Surgical Instruments (Exton, Pa.) www.amblersurgical.com
Asico (Westmont, Ill.) www.asico.com
Aurora Surgical (St. Petersburg, Fla.) www.aurorasurgical.com
Beaver-Visitec International (Waltham, Mass.) www.beaver-vistec.com
Duckworth & Kent (Baldock, U.K.) www.duckworth-and-kent.com
Katalyst Surgical (Chesterfield, Mo.) www.katalystsurgical.com
Katena Eye Instruments (Denville, N.J.) www.katena.com
Mastel Precision Ophthalmic Surgical Instruments (Rapid City, S.D.) www.mastel.com
Rhein Medical (St. Petersburg, Fla.) www.rheinmedical.com
Rumex International (Clearwater, Fla.) www.rumex.net
Storz Ophthalmics (Bridgewater, N.J.) www.storzeye.com

 

Marking and alignment keys to toric lens placement Marking and alignment keys to toric lens placement
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