Clinical Diagnosis 2014: Improvements in imaging, corneal biomechanics take center stage

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The acquisition of corneal topographic values saw an advancement this year via Scheimpflug imaging.

By Lynda Charters; Reviewed by Peter S. Hersh, MD, and Eric D. Donnenfeld, MD

Advances in Scheimpflug imaging have improved the acquisition of corneal topographic values, notably with the Galilei Dual Scheimpflug Analyzer (Ziemer Group).

Clinicians also are depending more and more on optical coherence tomography (OCT) in refractive surgery.

“Besides the ability of OCT to be used for evaluating the corneal thickness and analyzing the thickness of LASIK flaps in patients who may develop postoperative complications, the ability to measure the thickness of the epithelium is very useful in patient screening and postoperative care, said Peter Hersh, MD, professor of ophthalmology at Rutgers New Jersey Medical School, Newark, and Director, Cornea and Laser Eye Institute-Hersh Vision Group, Teaneck, NJ.

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In patients in whom the cornea has thicker and thinner areas, this clinical scenario seen during a LASIK screening may be an early indicator of potential keratoconus. He explained that the area over the cone tends to have a thinner epithelial layer and the area that is lower ends to be thicker, which can mask a cone.

“Evaluating the corneal epithelial thickness profile provides us with another diagnostic tool,” he emphasized.

Following surgery, OCT can help with retreatments because any apparent regression could be caused by stromal or epithelial etiologies, Dr. Hersh said.

Eric Donnenfeld, MD, likes the Cassini Corneal Shape Analyzer (i-Optics).

“This topographer is a new, very accurate instrument for measuring cylinder prior to surgery. It provides very accurate measurements of the anterior cornea and a new software upgrade will allow surgeons to view the posterior cornea to more accurately treat the total cornea cylinder and not just the anterior topography. Measuring the posterior cornea and creating a vector analysis of the entire cylinder helps reduce the postoperative astigmatism more accurately,” he explained.

Dr. Donnenfeld is clinical professor of ophthalmology, New York University Medical Center, trustee, Dartmouth Medical School, and founding partner, Ophthalmic Consultants of Long Island, Rockville Centre, NY.

Ophthalmic Surgical Microscopes with TrueVision 3-dimentional technology (Leica Microsystems) allows surgeons to have 3D visualization of eyes during cataract and refractive surgeries. This system is a toolbox of technologies that is comprised of an image capture module, image processing unit, and an image display system.

“This system allows us to overlay the location of the pupil and the templates for limbal relaxing incisions. The system is a nice advance in diagnostics that will allow us to improve our therapeutics as well,” Dr. Donnenfeld said.

Corneal Biomechanics

Corneal biomechanics remain a hot topic in the refractive arena.

The Reichert Ocular Response Analyzer previously was the first instrument to measure corneal hysteresis. Another unit-the Oculus system, Corvis ST-is now available commercially, although not widely, and clinicians are talking about the system’s abilities to measure the corneal biomechanics as a potential screening tool for potential LASIK candidates who may be a risk of developing ectasia and then postoperatively to identify developing ectasia and to monitor the corneal biomechanics in patients with keratoconus.

Corneal biomechanics can also be evaluated using Brillouin spectroscopy, a technique that uses a light-scattering approach to look focally at the corneal biomechanics.

“In theory, this technology can make a map of the cornea to show its relative biomechanics in three dimensions. This potentially can be used as a screening tool to determine if the biomechanics are normal and as a postoperative tool to identify any alterations in biomechanics,” Dr. Hersh said.

Other Diagnostic Tools

There have been substantial upgrades in the IOLMaster (Carl Zeiss Meditec) and the Lenstar LS900 (Haag Streit) that make prediction of IOL powers more predictable and accurate with more data points being provided, according to Dr. Donnenfeld.

The IOLMaster now registers iris landmarks and then downloads them into the Callisto eye (Zeiss), which projects the registered landmarks through the OPMI Lumera microscope (Zeiss) to more accurately treat astigmatism with limbal relaxing incisions and toric IOLs. The Verion Image Guided System (Alcon) can be used as well to register landmarks preoperatively and then project them onto the eye at the time of surgery.

“These are very exciting advances,” he said. 

Dr. Donnenfeld also mentioned the launch by Abbott Medical Optics of its iDesign Advanced WaveScan Studio Aberrometer in Europe that will be introduced in the United States in 2015.

“This aberrometer is much more accurate than any other previously available aberrometers.  It will allow us to treat irregular corneas and to diagnose irregularities that could not previously be imaged,” he said.

Dr. Donnenfeld also mentioned the advances achieved yearly by WaveTec, which was purchased by Alcon in August. He pointed out that it would be difficult for him to do surgery every day without their innovations in aligning toric IOLs and predicting IOL powers in patients who had undergone a previous LASIK procedure.

Eric D. Donnenfeld, MD

E: ericdonnenfeld@gmail.com

Dr. Donnenfeld consults with Abbott, Alcon, and Wavetec.

Peter S. Hersh, MD

E: phersh@vision-institute.com

Dr. Hersh has no financial interest in any aspect of this report.