What Do You Need From OCT?

For the comprehensive ophthalmologist, historical data may trump a more vivid image.

BY LESLIE GOLDBERG, ASSOCIATE EDITOR

While retina specialists are rapidly adopting the new spectral-domain (SD) optical coherence tomography (OCT) technology into their practices, general ophthalmologists have different requirements for tracking the diagnosis and progression of their patients' diseases. The lack of a normative historical database, coupled with the extra cost for SD OCT, are keeping comprehensive ophthalmologists true to their time-domain systems.

"The principal difference between a retina specialist and the general ophthalmologist when it comes to OCT is that a retina doctor typically needs results 'right now' whereas the general ophthalmologist also needs 'change over time' information for his/her glaucoma patients" says Andrew Iwach, M.D., glaucoma specialist, executive director of the Glaucoma Center of San Francisco and on faculty at the University of California at San Francisco. "Thus in managing glaucoma patients there are two objectives for OCT: at the front end for helping to make a diagnosis and the more challenging issue of detecting subtle changes over time," he adds.

"Acknowledging the limitations of imaging technologies some have come to accept the two laws of limitations," says Dr. Iwach. "Number one, the technology progresses quicker than optic nerves do and number two, the only time you know that the machine is working is when it agrees with you."

The Importance of OCT for Glaucoma

Dr. Iwach says that in terms of glaucoma, the most common form of the disease progresses slowly. "You follow patients for a long time, over a long period of time. So OCT is particularly helpful in diagnosis," he says. "OCT gives you the opportunity to measure the thickness of the nerve fiber layer and thus complement what we see when we examine the optic nerve itself. That is where OCT in our practice has been very helpful."

Dr. Iwach says that for follow up, as far as he knows, the only company that has software that overlays the different OCT scans is Zeiss' Stratus OCT unit. "To Zeiss's credit, once you are on the Stratus OCT platform, the new software will allow you to import the data from previous exams for analysis and comparison." (Some of this software has not been released to the public and Dr. Iwach is testing at his practice, which is a Zeiss research site.)

"This shows that they are aware of the need for historical data," says Dr. Iwach.

The Importance of Historical Data

"The issue for a comprehensive ophthalmologist is you now have two types of OCT," says John J. Dagianis, M.D., of Nashua Eye Associates, in Nashua, N.H. "You have the standard OCT and the Fourier-analysis or SD OCT. The Fourier is more expensive and gives a very detailed view of the retina and provides beautiful images. The question is — does it have a normative database to follow glaucoma progression?"

Dr. Dagianis emphasizes the importance of a normative database. "You need to be able to compare normals to other normals and abnormals to abnormals," he says. "You need to be able to tell if the numeric values are statistically significant and to compare the other numbers and to past exams."

Dr. Dagianis explains that when his practice made its first glaucoma diagnostic purchase, there was a choice of the Stratus OCT3 or a GDx (Carl Zeiss Meditec, Inc.), which did not do corneal compensation for nerve fiber layer analysis. "While the GDx is improved, the issue comes down to this — the images are prettier but does it do anything clinically for glaucoma progression? The answer, so far, is no."

Why Fourier is Not an Option Yet

"The barrier to entry with the Fourier is cost," says Dr. Dagianis. "It is a different machine. What will it do for me that my present machine doesn't do? It gives me prettier pictures but is it going to change my thinking as to how I am going to treat my patient? There are subtle things that the Fourier will give me, but not things that I use in the treatment of my patients."

Dr. Dagianis says that if he were starting from scratch, he would only move to the Fourier if it had a normative database. "That's crucial," he says. "Otherwise I cannot track glaucoma progression. You need to have enough historical data to trace and that is what is important." Dr. Dagianis says that it could take 2 to 3 years to create a normative database. "You need to have enough subjects enrolled to have a meaningful database. This is crucial to the system."

Dr. Iwach says that, while the resolution on the Fourier OCT is an improvement over standard OCT, he is not sure if and when it will make a significant impact on how he analyzes the nerve fiber layers in managing glaucoma patients.

"Now that I have had an OCT for over 5 years, with 5 years of data, if I change platforms, do I start all over again?" asks Dr. Iwach. "The question is — what is the trade-off if you do want to switch platforms? It's all about compatibility, unless you are bringing something new to the table. OCT is a very practical tool in diagnosis. It has helped us with clinical management of disease," concludes Dr. Iwach. OM