Imaging for Glaucoma Diagnosis

American Academy of Ophthalmology (AAO) 2015

Douglas J. Rhee, MD; Shuchi B. Patel, MD


December 18, 2015

Editor's Note:
Douglas J. Rhee, MD, and Shuchi B. Patel, MD, convened after Glaucoma Subspecialty Day 2015, Winning Strategies—Glaucoma in the 21st Century, held during this year's American Academy of Ophthalmology (AAO) meeting, to discuss some of the session's highlights for Medscape readers. An edited transcript of their discussion is below.

Dr Rhee: Dr Patel, thank you for joining us. Kicking off this year's Glaucoma Subspecialty Day was a session[1] that covered existing optical coherence tomography (OCT) technology, with a look at what the future may hold. How are you using OCT in your practice now, both for the diagnosis of new glaucoma and for following progression in patients with existing glaucoma?

Dr Patel: OCT has definitely improved the diagnosis and treatment of glaucoma in patients. For early monitoring or early detection of glaucoma, OCT tends to show changes before functional changes are noted on visual field testing. For all patients who are glaucoma-suspect or even those with known glaucoma, I will perform a baseline OCT to be able to measure their retinal nerve fiber layer. Depending on the severity or the rate of progression, these patients will undergo yearly or perhaps even twice-yearly OCT to monitor any changes.

That being said, the changes that are seen on OCT are reportedly more reliable in patients with early glaucoma, before significant thinning of the retinal nerve fiber layer has occurred. After thinning of the retinal nerve fiber layer reaches less than 50 microns, because of the variabilities seen with even spectral-domain OCT, it becomes more difficult to use OCT to monitor progression. In those patients, I typically rely on functional testing, such as visual field examination.

Dr Rhee: So, it sounds as though you are using OCT to establish the diagnosis of glaucoma in someone who has otherwise suspicious findings, and also to detect progression in early-stage glaucoma. Is that correct?

Dr Patel: Yes, that is correct.

Dr Rhee: Suppose you have established a diagnosis of early glaucoma, and the patient has both visual field and OCT changes that corroborate the diagnosis. If you see a change on OCT, but the pressure remains stable, would that lead you to change your management plan?

Dr Patel: That is a great question. For this type of patient, I would have to look at the OCT and see how much change has occurred. The presentations[1] at the meeting (which reflected other data) indicate that a change of at least 5 microns is considered significant. If I detected a change greater than 5 microns, I would take my OCT findings very seriously. It is possible that the pressure is stable and just not at adequate control for the patient. It is also possible that the patient is not adhering to the treatment regimen and is only using the medications before visits with the physician, which should at least inspire a renewed conversation about medication adherence.

When there are significant fluctuations in the intraocular pressure, the patient will need further management, like laser therapy, to help reduce those fluctuations.

Dr Rhee: Could the changes warrant testing of a more sensitive nature, even assuming that their visual field test, white-on-white, is the same? Is there a role for frequency-doubling perimetry or SITA SWAP [Swedish interactive threshold algorithm short-wavelength automated perimetry] testing to further interrogate that dip in the OCT to ascertain whether or not it is real progression?

Dr Patel: I believe that either of those would be great modalities to look for a correlation in the structural and functional tests, given that the data show the early to moderate stages of glaucoma. Now, if these are patients with low-tension or normal-tension glaucoma, or where I noticed that the pressures are low and I am still seeing progression, another option would be to change to a 10-2 visual field test, to focus in on where I may be seeing more visual field defects in these patients to pick up on them as well.

Dr Rhee: In patients whose OCT values fall within the green—that is, the normal for the normative database—but have a classic nerve fiber layer-localizing lesion and perhaps a corresponding subtle optic nerve change, would you still define that as glaucoma, or is OCT the only way to establish a diagnosis of glaucoma in its early stages?

Dr Patel: Obviously, OCT is a very useful modality to help us with diagnosis, but as in any field of medicine, there has to be a clinical correlation, patient history, and other factors taken into account before a final diagnosis can be made.

Dr Rhee: I agree. The Ocular Hypertension Treatment Study[2] and the European Glaucoma Prevention Study[3] found that in 50% of the cases, the structural changes were picked up first, but in the other 50%, the visual field changes came first. The OCT does not have to be abnormal to establish the diagnosis. It seems that ophthalmologists' understanding has shifted to thinking that if the patient's visual fields show a classic localizing defect, but this is not seen on OCT, then the patient does not have glaucoma. I believe that is incorrect, and that the pendulum has swung too far.

Dr Patel: I agree with that. I would add that the converse is also true. A significant number of patients are overtreated and have what we call "red disease": Practitioners are getting an OCT, seeing an area that is abnormal or red on the OCT, and treating patients without considering the entire picture or analyzing the OCT very critically to look for artifacts or other reasons than true thinning for that area to be red.

Dr Rhee: This is particularly interesting, because one of the sessions[4] at Glaucoma Subspecialty Day comprised a series of case presentations, followed by asking the expert panel and the audience, "Is this a convincing enough case to justify the initiation of therapy?" In essentially every case that was presented, roughly one half would say, "Yes, treat," and the other half would say, "No, do not treat." Even with all the literature we have thus far, what are your insights as to why that has not resulted in more concrete and discrete answers?

Dr Patel: This is a perfect example of the complexities of glaucoma, and glaucoma treatment and care. Many factors go into our decisions about whether a patient has glaucoma and whether there is progression of that glaucoma. There is no single formula for us to establish that. There will always be differences of opinion. There will be different treatments that could be offered the patient, and that is clearly supported by the fact that so many physicians could not agree on whether to treat or not treat in those scenarios. Until we come up with even more evidence, we are left with the continuing need to individualize treatment for our patients.

Dr Rhee: Thus, taking into account the individual patient's specific situation is still very important. Glaucoma management is not quite formulaic yet.

Dr Patel: Correct. However, some of the presentations during Glaucoma Subspecialty Day were helpful in providing more evidence-based guidelines and data that may help to guide our care in the future and to assist us with our decision-making processes.

Dr Rhee: Let's go back to OCT for a minute. What about macular OCT? Will that help with these decisions? Is this technology ready for prime time?

Dr Patel: Macular OCT will provide us with a lot of information in the future. Even currently, it has been shown to correlate very well with the optic nerve head structurally, but it is probably not ready for use in monitoring for progression, especially given that the different machines and modalities are using different areas to measure thickness. They are including the inner plexiform layer and, therefore, do not consistently measure the same thickness. Moreover, the different machines are not interchangeable for measuring retinal nerve fiber thickness.

Until we have more data on this, I do not believe it is ready to use for making clinical decisions. The technology itself shows promise, but more work needs to be done on the technology platform.

Dr Rhee: Before we conclude our discussion, which of the surgical complications presentations did you find to be the most interesting?

Dr Patel: The presentation[5] about the iStent® (Glaukos; Laguna Hills, California) by Dr Steven Sarkisian of the Dean McGee Eye Institute in Oklahoma City was very interesting to me. During the last year, I have begun to routinely incorporate the iStent into my surgical practice. I believe that many physicians, even comprehensive ophthalmologists, are adding the iStent to their surgical armamentarium.

Watching this video presentation was quite informative, because it showed that there is definitely a learning curve to the iStent. It is very reassuring for those who are learning to do the iStent that there can be some challenges even with experienced practitioners; one of the most common ones is having the heme obscure the view. I think the tips on how to overcome those challenges were very useful for people to incorporate into their practice.