Evolving technologies raise bar for anterior segment imaging

Topography and biometry retain a firm foothold, while ongoing innovations make gradual inroads in preop assessment, especially in challenging cases.

Increasingly precise and powerful anterior segment imaging and measurement technologies help surgeons assess various eye diseases, plan treatment, optimize outcomes and reduce risks.

Some surgeons adhere to tried-and-true modalities such as keratometry, corneal topography, pachymetry and non-contact biometry. Others have begun to use anterior segment optical coherence tomography (AS-OCT) and combined technologies to visualize subtle anatomic structures, especially those behind the iris.

Recent innovations augment basic diagnostic information to help surgeons fine-tune treatment strategies, screen for major ocular disorders such as corneal ectasia and link images to electronic medical records.

Some measurement tools help both cataract and refractive surgeons, given the impact of biometry and corneal topography on premium IOL placement and power. Imaging is also critical in assessing LASIK flaps before laser enhancement surgery or the placement and design of corneal incisions in cataract surgery.

“Obviously, the No. 1 imaging technology for a cataract surgeon is the IOL measuring that he has to do,” Roger F. Steinert, MD, OSN Cornea/External Disease Board Member, said. “The other thing that I think that you just can’t live without if you’re going to be a serious cataract surgeon doing premium IOLs is some form of topography.”

Pros and cons of AS-OCT

Richard J. Duffey, MD, OSN Refractive Surgery Board Member, said he was disappointed with the performance of AS-OCT platforms such as the Visante OCT (Carl Zeiss Meditec) in measuring the thickness of LASIK flaps.

Richard J. Duffey

“When comparing how consistent the flap thickness is with one technology vs. another using OCT as the final arbiter, the resolution is not good enough to have a consistent endpoint that the same observer will measure every time or that multiple observers would agree upon,” Dr. Duffey said.

Dr. Duffey said he uses a subtraction technique intraoperatively to measure his flap thicknesses. He resorts to PRK in most enhancements in patients whose original LASIK was performed elsewhere to reduce the risk of ectasia in these cases in which flap thickness cannot be determined with any degree of precision, especially when the original surgery was performed years before and OCT resolution is even worse.

AS-OCT also lacks sufficient resolution to visualize anatomic structures behind the iris, Dr. Duffey said.

In contrast, Dr. Steinert said the Visante OCT is the only viable tool for assessing LASIK flap thickness and determining whether to perform a LASIK enhancement or resort to PRK.

“Not only can you measure your performance and know what your true flap thickness is, which is important in terms of not creating ectasia, but if you’re talking about an enhancement later, even years later, the OCT usually can show you the interface,” Dr. Steinert said. “Then, you know whether you can do a flap lift or whether you need to do surface ablation or whether you don’t have any tissue left to do anything. The only way to do it is OCT.”

Current tools and metrics

Dr. Duffey said he prefers the Orbscan II topographer (Bausch + Lomb) and Atlas corneal topographer (Zeiss).

“I still use manual keratometry when it’s necessary,” Dr. Duffey said.

Dr. Steinert said it is important to assess corneal topography in premium IOL cases.

“The keratometry readings, no matter how accurate they are, don’t tell you the whole story,” he said. “If you’re doing astigmatic keratotomy, if you’re doing toric IOLs and if you’re doing premium IOLs where you want to cut the astigmatism down and orient your incision correctly and all of those issues that impact the uncorrected vision, you are going to need to do topography.”

Dr. Steinert said his practice uses the Atlas and the Pentacam Scheimpflug camera (Oculus). He emphasized the reliability of Placido-based technology (Atlas) in evaluating topography in challenging cases.

“I just feel more comfortable with it and I think I can interpret it better and deal with the strange cases better,” he said.

The IOLMaster (Zeiss) and Lenstar optical biometer (Haag-Streit) have long dominated imaging and measurement in cataract surgery, Dr. Steinert said.

The relatively new IOLMaster 500 offers automatic keratometry and partial coherence interferometry. Dr. Steinert said his practice has achieved positive outcomes with the Lenstar and IOLMaster 500.

“Subjectively, both seem to be functioning at a pretty high level and we’re getting tighter and tighter accuracy on our IOL power predictions,” he said.

Dr. Steinert noted that the Lenstar combines pachymetry, keratometry, lens thickness, pupillometry, axial length and several other measurements. He also noted that the Galilei dual Scheimpflug imaging system (Ziemer) offers a wide depth of focus.

New and desired innovations

Dr. Duffey said his practice is preparing to purchase the latest iteration of the Pentacam, which can be connected to an electronic medical record system.

“It has the ability to be bi-directional so that I can basically scan people in one part of the building and send it immediately to the electronic medical record in whatever room I’m in. I don’t have the ability to do that with the Orbscan II,” Dr. Duffey said.

The Pentacam also has the ability to interface with the Belin/Ambrosio Enhanced Ectasia Display software, developed by Michael W. Belin, MD, FACS, and Renato Ambrosio, MD, PhD. The program combines elevation and pachymetry and enables the surgeon to screen patients for ectatic disease, Dr. Duffey said.

“As a screening software, it is another feature that I’ve liked about the Pentacam that I think will make it a step above what we have with the Orbscan II in addition to the interface capabilities with our electronic medical records,” Dr. Duffey said.

Dr. Steinert noted that the Visante Omni (Zeiss) links the Atlas and Visante OCT.

“Basically, what the software does is integrate the information from the two, so you do pachymetry mapping with the OCT and you do the Atlas,” Dr. Steinert said. “Between the two of them, you get a huge amount of information, including the posterior curvature, the anterior curvature, the Placido-based pachymetry, the works.”

Dr. Steinert envisioned a platform that combines topography, pachymetry and wavefront measurements.

“But if you could combine that with partial coherence interferometry, then you’d really be cooking,” he said. – by Matt Hasson

• Richard J. Duffey, MD, can be reached at 2880 Dauphin St., Mobile, AL 36606; 334-470-8928; fax: 334-470-8924; email: richardduffey@gmail.com.
• Roger F. Steinert, MD, can be reached at The Gavin Herbert Eye Institute at University of California, Irvine, 118 Med Surge I, Irvine, CA 92697-4375; 949-824-8089; fax: 949-824-4015; email: steinert@uci.edu.
• Disclosures: Drs. Duffey and Steinert have no relevant financial disclosures.