The newest offerings in glaucoma diagnostic technology include a wide variety of upgrades to optical coherence tomography software packages, more precise measurements of the optic nerve and its specific components, a test that measures glaucoma through visual pathways of the brain and a disposable contact lens that measures intraocular pressure.

This OCT thickness map indicates primary open-angle glaucoma. Image: Fingeret M

These products, which are aimed at addressing the various mechanisms of this condition, hold promise in detecting glaucoma earlier and with greater specificity.

“Knowing that we can reliably identify glaucomatous damage and that we can reliably identify early change consistent with glaucoma brings us confidence that we are providing our patients the best care we can to help preserve their vision,” Robert Dunphy, OD, of the Veteran’s Administration in Boston, told Primary Care Optometry News in an interview.

“You’re going to be seeing instruments that are available in other parts of the world become available here,” Murray Fingeret, OD, a PCON Editorial Board member practicing in St. Albans, New York, said in an interview. “So there will be different instruments available. The more companies with OCTs available for sale, the more pressure there will be on companies already in the market to improve their instruments, to stay competitive.”

Murray Fingeret

Nidek (Gamagori, Japan) is one such company seeking U.S. approval for an OCT currently available in other countries.

The Cirrus HD-OCT

The Cirrus HD-OCT, manufactured by Carl Zeiss Meditec (Dublin, Calif.) is one currently available OCT device that has undergone significant updates over the past year. In late January, Carl Zeiss Meditec received U.S. Food and Drug Administration approval for a new software version 6.0, the company said in a press release. The new application package expands Cirrus diagnostic tools to include Ganglion Cell Analysis and Optic Nerve Head Progression Analysis. The new application package also features Guided Progression Analysis, which tracks progression of average cup-to-disc ratio as well as other retinal nerve fiber layer (RNFL) parameters.

“This is relatively new because for several years, the only thing that OCTs evaluated over time was the RNFL thickness,” Dr. Fingeret said. “Now the Cirrus includes an optic nerve parameter as well as nerve fiber layer measurements to track over time. That’s new and it’s important.” Dr. Fingeret said the Cirrus’ new progression software will be a valuable tool in following changes over time.

“This allows us to follow someone over time, to tell if there is any trend or loss of tissue that is greater than what would happen through the normal variability,” he said, “With the Cirrus, we can look at both RNFL as well as the cup-to-disc ratio for change.”

This ganglion cell map from the Cirrus OCT shows loss on the left side.

The Cirrus OCT 6.0 printout shows RNFL loss in the right and left eyes. Image: Fingeret M

Progressive thinning of the inferotemporal aspect of the RNFL over about a 2-year period flagged on classification with the Spectralis.

More extensive damage showing progressive loss overall over the same time period with the Spectralis. Note follow-up #1 and #2 have areas of black bordering on the left side of the cSLO image, which indicate rotational alignment of the data to maintain consistent placement of the circle scan relative to disc structures, thereby maintaining reliability of TSNIT relationships and increasing confidence in measured change. Image: Dunphy R

Dr. Fingeret said the Ganglion Cell Analysis is also an important development in the Cirrus technology. This is a test that was developed for the Optovue OCT and its importance is slowly being recognized.

“Originally, when we evaluated the eye for glaucomatous damage, we looked at retinal nerve fiber layer thickness. The next software update included optic nerve parameters such as the cup-to-disc ratio and the thickness of the neuroretinal rim. These were evaluated against a normative database. The third area to evaluate for glaucomatous loss is to look at the ganglion cell complex in the macula area,” he said. “So when looking at the image of the back of the eye, we can look at three areas: the nerve, the nerve fiber layer thickness and now the macula, to see if there’s any thinning or reduction or loss of tissue related to glaucoma.”

Heidelberg Spectralis

The Spectralis from Heidelberg Engineering (Vista, Calif.) has also added a new software package called Posterior Pole Asymmetry Analysis. According to the company’s website, this new technology maps retinal thickness across the posterior pole and charts asymmetry, both between hemispheres and between eyes.

“Early glaucomatous damage often preferentially affects one pole of the nerve head to a greater degree than the other,” Dr. Dunphy, who is a Spectralis user, told PCON. “That means that there is often asymmetric loss of corresponding ganglion cells and, therefore, asymmetric loss of retinal thickness across the anatomic horizontal meridian of the posterior pole.

Robert Dunphy

Dr. Dunphy said the Posterior Pole Asymmetry Analysis builds upon the strengths of Spectralis’ existing TruTrak tracking laser system and the Noise Reduction OCT signal processing. He said the Spectralis RNFL circle scan employs TruTrak tracking of the eye during scanning and Noise Reduction OCT signal processing for consistent measurement accuracy and repeatability.

“Because Spectralis can make such precise, repeatable and reliable measurements of retinal thickness, the software can perform regional thickness measurements in a grid pattern aligned across the anatomic horizontal meridian,” he said.

“It can also flag those areas that are relatively thinner in one hemiretina than corresponding regions of the hemiretina across the horizontal meridian. This hemifield thickness comparison is analogous to the hemifield analysis we’re familiar with in visual field testing protocols for glaucoma,” he said.

The system also uses FoDI Fovea to Disc Alignment and Auto Rescan to maintain reliable repeat measurements of scan position on the retina.

“The result is more reliable and repeatable measurement across time,” Dr. Dunphy said. “When OCT devices do not use alignment strategies, rotational movements of the patient’s head causes shifts in the positioning of the circle scan start and end points that result in variation in the measured TSNIT curves for a patient. When this happens, it becomes difficult to reliably identify regions of change in the peripapillary RNFL.”

Dr. Dunphy said that the various updates to the Spectralis software are likely to provide a new level of certainty in glaucoma detection.

“The new software developments in Spectralis scanning technique and analysis protocols give us confidence in our ability to reliably identify early change and subtle features in a patient’s structural profile that alert us to the possibility of early glaucoma damage,” he said.

Diopsys CORDA

Diopsys Inc. (Pine Brook, N.J.) has developed a software program that is designed to improve the analysis of OCT images, according to Alberto Gonzalez Garcia, MD, research director for Diopsys.

Alberto Gonzalez

“CORDA works with all major OCT devices, including Cirrus, RTVue, Spectralis and Topcon 3D OCT-1000,” he told PCON. “CORDA will also improve the sensitivity of time domain OCTs. Optometrists and ophthalmologists who choose not to purchase a new spectral domain OCT can use CORDA to improve the sensitivity of their current OCT device and get better results.”

Dr. Gonzalez said until now, existing OCTs measure only the thickness or volume of the retina and/or optic nerve.

“OCTs measure RNFL thickness, but inside the RNFL there are several primary structures, for example, axons and blood vessels,” he said. “Blood vessels are very different from person to person, and that makes it difficult to normalize the RNFL thickness.”

According to a press release from Diopsys, professional publications state that current OCT algorithms may overestimate sectors with focal defects in the RNFL, causing this layer to incorrectly look more substantial.

“When you have a narrow sectorial defect of the RNFL, OCTs might fail to detect it,” Dr. Gonzalez said. “The CORDA solves this problem.”

What distinguishes CORDA from a typical OCT analysis, he said, is its ability to analyze the internal structure of the RNFL and recognize its different components, focusing only on the structure damaged by glaucoma.

“CORDA analyzes the internal structure of the RNFL – not just the thickness,” he said. “It is able to differentiate and isolate those components (axons) that are damaged because of glaucoma from those not affected by the disease.”

Dr. Gonzalez said he and his colleagues are completing the research phase of CORDA’s development, which they will present in a poster at this year’s Association for Research in Vision and Ophthalmology meeting.

Diopsys NOVA-VEP

Another technology currently available from Diopsys is the NOVA-LX VEP testing system. This test utilizes a short duration transient visual evoked potential (SD-tVEP) technique to screen for functional damage in the eyes of patients with glaucoma. Dr. Gonzalez said the NOVA-LX uses the SD-tVEP to record the electrical responses of a patient’s entire visual system.

“VEP is the activity of the brain in response to visual stimulation,” he said. “The eye converts light into electricity, and this electrical signal is conveyed to the brain through the visual pathway. When the electrical signal arrives at the brain, we’re able to record it using sensors placed on the scalp. We then look at different measurements, such as how fast and how powerful the signal is.”

Dr. Gonzalez said a delay detected in this signaling could suggest a defect in the visual pathway. He said the NOVA-LX can be used to detect and localize such defects.

“Almost all diagnostic tests available today study the structure of the eye, but there is strong evidence that the damage in glaucoma is happening in the mid-brain,” he said.

Optovue updates

Optovue Inc. (Fremont, Calif.) has introduced a real-time eye tracking upgrade for its RTVue Fourier-domain OCT system, according to a company press release. This upgrade, known as the VTRAC, uses hardware already included with the RTVue System. The upgraded software utilizes real-time video image processing to follow patient eye movement during the OCT scanning process.

“The SD-OCT tracking feature affords imaging with increased clarity and exquisite detail,” Larry J. Alexander, OD, FAAO, senior director of clinical education for Optovue Inc., said in an interview. “While usually considered to be of more benefit in retinal imaging, imaging of structures of the optic nerve will also be enhanced.”

Larry J. Alexander

Dr. Alexander said this enhanced imaging will be particularly useful in providing higher resolution of the lamina cribrosa.

“When considering the mechanical component of the genesis of glaucoma, involving the interplay of cerebrospinal fluid pressure and IOP, the status of the lamina cribrosa becomes critical.”

Dr. Alexander said possibly the most important innovation to Optovue’s glaucoma diagnostic technology was the introduction of the ganglion cell complex (GCC) analysis.”

“This allows for another measure of the damage created by optic neuropathies,” he said. “A statistical analysis of the GCC, focal loss volume (FLV) and global loss volume (GLV) adds even more power to the differential.”

The GLV is a measure of overall depression of the GCC, Dr. Alexander said, while the FLV represents focal depressions.

The Optos Daytona

Optos (Marlborough, Mass.) launched the Daytona at Academy 2011 last fall and, according to Leslie Amodei, director of global marketing for Optos, shipments were scheduled to begin at the end of March 2012.

The instrument offers a 200· view of the retina in a single capture through the company’s Virtual Point technology. It has been scaled to fit smaller office spaces while offering ultra high-resolution imaging and ultra-widefield autofluorescence capabilities.

“Daytona is the culmination of intensive design and development activities that stem from our experience in the marketplace and the requirements of our customers,” Roy Davis, chief executive officer of Optos, said in the press release.

Topcon 3D OCT-2000

The Topcon 3D OCT-2000 System uses a high-resolution fundus camera and a color touch screen display in a compact, ergonomic design, according to company literature. It features FastMap software, which provides 3-D, 2-D and fundus images simultaneously. Its Pin-Point Registration indicates the location of the OCT image within the fundus image, and its compare function allows users to compare and analyze serial exams.

The Triggerfish Contact Lens Sensor

Although it is not yet approved for use in the U.S., the Triggerfish Contact Lens Sensor from Sensimed (Lausanne, Switzerland) represents a promising innovation in the area of glaucoma detection and monitoring.

“Previous studies have shown that changes in corneal curvature indicate IOP changes,” John H.K. Liu, PhD, director of the Glaucoma Molecular Pharmacology La- boratory at the Shiley Eye Center and as an investigator in two clinical trials of the device, said in an interview. “This is a contact lens-based IOP sensor that measures the curvature change of the cornea for at least 24 hours. You put it on the patient’s eye, and it takes a home recording. The patient comes back and the data is downloaded to the computer.”

John H.K. Liu

Dr. Liu said the Triggerfish device operates on principles consistent with his findings in his sleep lab study of IOP, which determined that the peak IOP in most glaucoma patients occurs outside office hours.

“Our consensus was that if we have a technology that won’t disturb the patient’s sleep, that will tell you even more.”

Dr. Liu said the Triggerfish, which is currently approved in Europe, Canada and Australia, is not yet able to measure IOP in milligrams of mercury (mm/Hg) but instead detects IOP fluctuations based on corneal curvature changes.

“We’re still trying to figure out how to correlate the pattern to the actual reading,” he said.

Dr. Fingeret said although U.S. commercialization of the Triggerfish may still be a few years off, he thinks it could be a pivotal development in glaucoma diagnostic technology.

“It’s going to lead to a whole new level of personalized diagnostic information,” he said. “Right now, we get IOP readings just a few times a year, and at best, we make guesses. When this comes out, we’re going to have a very good snapshot of what the eye pressure is.”

Dr. Fingeret said the Triggerfish could also be useful in helping monitor patients on glaucoma treatment.

“If we’re seeing somebody on therapy who is getting worse, we can use this lens to see how the eyes are responding to therapy and if they’re getting spikes breaking through,” he said. “So it’s a new level of care that we’ve never had before.” – by Jennifer Byrne

For more information:

• Larry J. Alexander, OD, FAAO, can be reached at 4500 Knightsbridge Drive, McKinney, TX 75070-5299; (502) 228-7231; larryalexander@tx.rr.com.
• Leslie Amodei is director of global marketing for Optos. She can be reached at 67 Forest St., Marlborough, MA 01752; (508) 787-1414;lamodei@optos.com.
• Robert Dunphy, OD, practices at the Veterans Administration Boston Healthcare System, 150 South Huntington Avenue, Jamaica Plain, MA 02120; (857) 364-6669; Robert.Dunphy@va.gov.
• Murray Fingeret, OD, FAAO, is a Primary Care Optometry News Editorial Board member who practices at St. Albans VA Hospital, Linden Blvd. and 179th St., St. Albans, NY 11425; (718) 298-8498; murrayf@optonline.net.
• Alberto Gonzalez Garcia, MD, is research director for Diopsys. He can be reached at Diopsys Corporate Headquarters, 16 Chapin Road, Suite 912, P.O. Box 672, Pine Brook, NJ 07058; (973) 244-0622; agonzalez@diopsys.com.
• John H.K. Liu, PhD, is director of Glaucoma Molecular Pharmacology at University of California San Diego’s Shiley Eye Center. He can be reached at 9415 Campus Point Drive, La Jolla, CA 92093; (858) 534-7056; joliu@ucsd.edu.
• Disclosure: Dr. Alexander is senior director of clinical education for Optovue. Dr. Dunphy has been loaned equipment by Heidelberg, Optovue and Optos for research purposes, he receives speakers honoraria from Heidelberg and Optos and he is a member of the Optovue advisory panel. Dr. Fingeret is a consultant for Carl Zeiss Meditec and sits on the advisory board for Topcon, Optovue and Heidelberg. He also receives research support from Zeiss, Heidelberg and Topcon. Dr. Liu performs clinical tests trials supported by Sensimed. Dr. Fingeret consulted for Carl Zeiss Meditec and sat on the advisory board for Topcon, Optovue and Heidelberg Engineering. He also received research support from Carl Zeiss, Heidelberg, and Topcon.