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How Imaging Technology Has Improved My Glaucoma Practice
A specialist's personal experiences with the evolution of the technology, and a case study that illustrates its usefulness.
BY E. RANDY CRAVEN, M.D.

Figure 1. This is an example of a patient with healthy RNFL and the OCT illustrates a normal pattern.

Years ago, we relied solely on nerve drawing and disc photography. Personally, I never liked using disk photos to examine the nerve because of the numerous limitations associated with them. There was no instant feedback, often the exposure was a little off and the focus was not sharp. It seemed that it took days or even weeks for the technicians to see their results, and they did not remember what they had done to improve their images.

If we fast forward to today, we now have digital imaging products that create real-time images and lead to a more comprehensive viewpoint of a patient's glaucoma during the actual exam. In this article, I will discuss how one of these contemporary diagnostic technologies has helped me to detect and manage glaucoma patients more effectively.

A Little History

In the late 1980s, computers and imaging devices seemed to offer a possible solution for better images. Because of the problems I was having with standard and red-free photos, I started on a search for computer-assisted imaging technology.

During my fellowship at Wills Eye Hospital, we had the opportunity to work somewhat with the PAR-2000. It was an attempt to image the nerve, but this device fell short of what we wanted. In 1991, I met Andreas Dreher and Gerhard Zinser. They had a background in optics and physics and worked on scanning laser imaging devices. Initially they worked together, then Laser Diagnostic Technologies became Dr. Dreher's company and Heidelberg Engineering became Dr. Zinser's. Both of them were working on scanning laser ophthalmoscopy, but Dr. Dreher had an interest in polarization used with the scanning laser.

Later, I received a grant from the Tarus Foundation for the purchase of the second Heidelberg Retinal Tomography (HRT, Heidelberg Engineering, Germany) in the U.S. This was the original version of the product. Within a year we were also helping Laser Diagnostic Technologies with their first Nerve Fiber Analyzer (NFA and later GDx), and the Topographic imaging device (TopSS), which was very similar to the HRT. Finally, we purchased a Stratus optical coherence tomographer (OCT, Carl Zeiss Meditec, Dublin Calif.) and a Talia retinal thickness analyzer (RTA, Talia Technology, Israel). All of these instruments have gone through establishing a normative database for comparison. We participated in many of these studies.

Since the start of this technology over 15 years ago, there have been many mergers, acquisitions and closures of imaging companies and programs, such as Carl Zeiss acquiring Laser Diagnostic Technologies. What has remained is the significance glaucoma specialists have attached to nerve imaging.

We are able to get assistance with our questions about how visual field changes may or may not be supported by anatomic or structural damage. Structure and function correlation is key when you put scanning laser technology to use.

What has made the biggest difference for me? It would be the fact that now we are given pieces to the puzzle that help to answer our questions. Let us look at an example of how I believe that imaging helped to sort out what was happening with this patient. This case might be a bit controversial, but that is even more reason we need imaging to help us with puzzling cases.

Figure 2 Tilt OD. Upon first viewing, figures appear mislabeled.

Fig 3. Tilt OS. However, the patient presented with tilted disks.

A Case Study

A closer look at one of my patients utilizing the OCT can better illustrate the product's capabilities. This particular patient was a 55-year-old woman who presented for consultation. The referring corneal specialist was not sure what to make of the situation. 

She had visual field defects with significant decreased central sensitivity, yet she did not notice there was a problem. The patient had never seen much better than 20/40. She had recently lost a little vision with 20/50 to 20/60 vision bilaterally. She only noted blurred vision and not a scotoma. She had a normal IOP of 15mm Hg.

I want to first point out a normal OCT pattern. As you can see (Figure 1.) the nerve fiber thickness goes from thin to thick along the temporal retinal nerve fiber layer (RNFL) to superior RNFL to thin on the nasal RNFL then thick back to the inferior RNFL temporal-superior-nasal-inferior-temporal plot (TSNIT).

Most patients maintain a thickness of greater than 100 microns in the superior and inferior nerve fiber peaks, which is where the RNFL bundles are thickest. Most of the time the temporal and nasal thickness is much below 100 microns, so if the RNFL is thicker, something is atypical with the array of the retinal nerve fibers. 

There were very atypical nerves on ophthalmoscopy. At first, looking at figures 2 and 3, you might think the slide is mislabeled. However, the disk is very tilted with the vessels exiting from the opposite side they normally do, or nasally. There was significant elevation of the nasal disk margin by biomicroscopy. The macula was ill defined. This appears to be a left disk in the right eye, or situs inversus, but it is probably a significant tilt.

Figures 4 and 6 show the visual fields were atypical with an inferior arcuate defect and a nasal loss as well, but it was not a typical nasal step. There is a decrease in the central sensitivity for both eyes. Usually, with such scotomata, patients will notice this. The patient was adamant that she had no defect.

As shown in Figure 5, the OCT is able to aid in sorting out this patient's atypical nerves. You will note in the same figure that there is a super high nasal portion of the RNFL and a relative void of the temporal RNFL. There appears to be a shift of the orientation of the RNFL orientation. All of the fibers are entering the optic canal from the nasal side, this is what has led to the scan appearance.

So what is going on? The right optic nerve almost looks like it should be a left. This disc is very atypical, it has a severe tilt and all of the nerve fibers are exiting on the nasal side. What causes the visual field defect? It is my opinion that the abundance of fibers going into the nasal region of the RNFL are causing a lack of NFL supplying the normal macular region. This has led to a central depression in the visual field. This is probably why the patient has not noticed this defect.

We were then able to reassure the patient that this probably was a long-standing problem, and that her recent gradual vision loss was secondary to a cataract. Subsequently, she underwent cataract surgery by her referring ophthalmologist and her vision did improve.

Figure 4. The visual fields were atypical.

Figure 5. OCT is able to show the patient's atypical nerve pattern.

Figure 6. Patient also had bilateral decreased central sensitivity.

Imaging's Benefits

In this particular situation, the OCT has allowed me to answer a question that I would not have been able to without this tool. This instrument, along with others imaging technologies, is changing the ways glaucoma specialists are diagnosing and managing this silent disease. In the process, we are providing better care for patients by identifying the changing pathologies in a timely manner.

E. Randy Craven, M.D., is the principal of Glaucoma Consultants of Colorado, PC, located in Denver, Colo. He can be e-mailed at rcraven@glaucdocs.com.