OCT: It’s all about the image

Take-home

Innovations in imaging and refractive laser-assisted cataract surgery are among the technologic advancements noted by surgeons in 2013.

Dr. Hersh

By Lynda Charters; Reviewed by Peter S. Hersh, MD, and Jonathan Talamo, MD

Advances in technologies enabling the imaging of the cornea using optical coherence tomography (OCT) and laser-assisted cataract surgery have captured the attention of refractive surgeons during the past year.

Imaging

Use of corneal OCT is generally on the upswing, with the newer generations providing better imaging and a better ability to analyze the corneal epithelial thickness.

However, the newer systems cannot provide a limbus-to-limbus picture of the cornea as the older systems could do, according to Peter S. Hersh, MD, director, Cornea and Laser Eye Institute, Hersh Vision Group, Teaneck, and clinical professor of ophthalmology, and chief, Cornea and Refractive Surgery, Rutgers-New Jersey Medical School, Newark, NJ.

The technology is being used to measure corneal power more accurately by assessing both anterior and posterior corneal curvature measurements, Dr. Hersh noted.

This is of particular importance before cataract surgery in patients who underwent a previous LASIK procedure.

OCT is being used more to measure the corneal epithelial thickness, which guides surgeons’ selections of treatments for a number of corneal problems, he added.

“We can see, for example, if corneal irregularities are secondary to the epithelium or secondary to the stroma,” Dr. Hersh said. “This can guide us in selection of either superficial keratectomy or excimer laser phototherapeutic keratectomy.”

The technology will tell the depth at which surgeons either want to perform superficial keratectomy (in the case of a relatively smooth stromal surface), convert to excimer laser to reach the right level (in the case where the epithelium is masking underlying stromal irregularity), or perform a deeper lamellar procedure, he noted.

The ability to image the depth of stromal scars has been very helpful for anterior lamellar procedures in order to determine the depth of lamellar dissection, he added.

It is also helpful for diagnosing and following patients with keratoconus and refractive regression after LASIK.

“If we can see that there has been a change in the epithelial thickness in association with refractive regression after LASIK, this might suggest an epithelial treatment, such as debridement, and if there is no change that might suggest changes in the stroma that are leading to refractive changes,” Dr. Hersh explained.

Refractive laser-assisted cataract surgery

Dr. Talamo

Jonathan Talamo, MD, commented on the rapid advancement of refractive laser-assisted cataract surgery (ReLACS as he refers to the procedure) over the past year.

“While these systems have been available for the past few years, a full suite of capabilities has only been approved by the FDA for multiple devices during the last year,” said Dr. Talamo, associate clinical professor of ophthalmology, Harvard Medical School, Boston.

These systems include the LenSx Laser (Alcon Laboratories), Catalys Precision Laser System (Abbott Medical Optics/OptiMedica), Victus femtosecond laser platform (Bausch +Lomb), and the LensAR Laser System (LensAR Inc.). With these units, surgeons can perform peripheral and astigmatic corneal incisions, arcuate capsulotomies, and lens softening and fragmentation.

“The ability to leverage the various capabilities is improving as we understand what they do to the cornea and the lens during surgery and IOL placement after surgery,” Dr. Talamo said.

During development of the Catalys Precision Laser System, with which Dr. Talamo was involved, it became clear that when the distance is reduced between the posterior capsule and the point at which the laser begins lens softening and fragmentation-as well as when the space between the laser spots is reduced during lens softening-the amount of ultrasound energy applied during phacoemulsification can be radically reduced.

Dr. Talamo cited recent studies by Abell et al. (Ophthalmology. 2013;120:942-948. doi: 10.1016/j.ophtha.2012.11.045. Epub 2013 Mar 7) and Mayer et al. (Am J Ophthalmol. 2013;Nov 7. doi:pii: S0002-9394(13)00639-9. 10.1016/j.ajo.2013.09.017), both of which reported up to a dramatic reduction, especially in dense cataracts.

“The implications are faster visual recovery, because of less corneal edema, cellular loss, and inflammation,” he said.

Greater understanding of arcuate incisions

Another important advance of the past year is in the understanding of how to use femtosecond laser for cataract surgery to correct astigmatism with arcuate incisions.

A number of investigators are trying to develop nomograms, and online calculators are available. Dr. Talamo said that he uses the AMO LRI Calculator with the Donnenfeld nomogram, which is available online, with the Catalyst laser to correct corneal astigmatism with arcuate incisions. Using this nomogram, he multiplies by 85% after having determined that multiplying by 68% was insufficient.

“I am seeing an improvement in my results without an overcorrection,” he said. “This area is rapidly evolving.”

Much work continues with intrastromal incisions using the femtosecond laser, with which the anterior cornea is not cut.

Generally speaking, Dr. Talamo believes that incisions created with a femtosecond laser are more accurate than the incisions that are created manually.

He also has observed that imaging for femtosecond laser is continuing to improve rapidly with high-resolution OCT, making it possible to do very precise adjustments on the fly after the laser is docked on the eye. The patient interfaces are also improving.

“There seems to be a trend away from using an interface that presses firmly on the corneal toward one with a fluid-filled interface such as that on the AMO/OptiMedica Catalys Precision Laser System and LensAR Laser System or a soft contact lens attachment as employed by the Alcon/LenSx Softfit.

Peter S. Hersh, MD

Hersh E: phersh@vision-institute.com

Dr. Hersh has no proprietary interest in the subject matter.

Jonathan Talamo, MD

E: jtalamo@lasikofboston.com

Dr. Talamo is a consultant to Abbott Medical Optics and OptiMedica.

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