Use of OCT and FA for Initial Diagnosis and Follow-up of Exudative AMD
COORDINATED BY ABDHISH R. BHAVSAR, MD
Welcome to Face Off, a column that explores controversial topics in the diagnosis and management of retinal diseases. Our typical format has involved covering several topics in each issue with 1 retina specialist voicing 1 line of thought in favor of the treatment or surgery and another retina specialist voicing an opposing line of thought. This column should be held in the spirit of a debate society. We do not advocate that you adopt these specific lines of thought, rather we hope this provides you with insight into how some retina specialists view these issues, with the desire that this will engage your thought process.
ABDHISH BHAVSAR, MD
In this issue, we explore the use of optical coherence tomography (OCT) and fluorescein angiography (FA) for initial diagnosis and follow-up of exudative AMD. For many decades, FA has been the gold standard for imaging and managing exudative AMD. Other imaging modalities, such as OCT, have often been termed "unproved" because there has been no large-scale randomized clinical trial to demonstrate the validity of using other imaging modalities. However, with the commonplace use of OCT, is this changing?
PRO USE OF OCT FOR INITIAL DIAGNOSIS OF EXUDATIVE AMD
PETER KAISER, MD
While OCT can never replace FA in the diagnosis of AMD, it does play a crucial role in the management of AMD, especially in the era of anti-VEGF agents. FA is still the gold standard and necessary for the initial diagnosis of the disease and more importantly to differentiate from similar presentations. The initial OCT provides several pieces of information that are very valuable. Thus, while I continue to use FA upon initial diagnosis, I find OCT to be a valuable addition to my armamentarium.
The initial OCT gives me baseline values for comparison at future follow-up examinations, a histopathologic view of the location of leakage that is useful to guide therapy, and it is easy to show patients to illustrate their pathology. While exceedingly safe, FA is not a benign procedure, especially in comparison to OCT, which is rapid, painless, and non-contact. Thus, at follow-up examinations I generally do not obtain FA and only get OCT. My patients prefer this and often interpret their scans before I enter the room.
With the dramatic increase in patient visits for anti-vascular endothelial growth factor (VEGF) injections, using OCT is a huge time saver. Although we only have an uncontrolled case series to guide AMD management by OCT, ongoing randomized clinical trails are using OCT to guide treatment decisions. Thus, we will have a better idea how OCT increases efficacy and hopefully decreases the number of treatments required in the near future.
PRO USE OF FA FOR INITIAL DIAGNOSIS OF EXUDATIVE AMD
STEVE CHARLES, MD
Although I primarily utilize an OCT-driven, treat (prn)-and-extend strategy for wet AMD management as advocated by Philip J. Rosenfeld, MD, PhD, I find FA useful when the patient has a visual complaint but no subretinal fluid or retinal edema on the OCT. I find FA to be of minimal value for subgroup analysis (occult, classic, retinal angiomatous proliferation [RAP], and polypoidal choroidal vasculopathy [PCV]). Younger patients seem to have a better retinal pigment epithelium (RPE) pump and can present with an obvious leak on angiography, no subretinal fluid or retinal edema on OCT and have an excellent treatment response to Lucentis (Genentech) or Avastin (Genentech). This is more often the case with histo or idiopathic choroidal neovascular membranes but is also seen with observant AMD patients. Higher resolution, spectral-domain OCT may ultimately find these early, minimal leak cases and further reduce the need for angiography.
|Abdhish R. Bhavsar, MD, is an attending retina surgeon at the Phillips Eye Institute, director of clinical research at the Retina Center, PA, in Minneapolis, and adjunct assistant professor at the University of Minnesota. E-mail him about Face Off at firstname.lastname@example.org.|
THE IDEAS AND OPINIONS EXPRESSED IN FACE OFF DO NOT NECESSARILY REFLECT THOSE OF THE EDITOR, THE EDITORIAL BOARD, OR THE PUBLISHER, AND IN NO WAY IMPLY ENDORSEMENT BY THE EDITOR, THE EDITORIAL BOARD, OR THE PUBLISHER.
PRO USE OF OCT FOR FOLLOW-UP OF EXUDATIVE AMD
JAY DUKER, MD
At the present time, exudative, or wet, AMD is largely treated with intravitreal injections of anti-VEGF medications. These medications (bevacizumab and ranibizumab) have 3 mechanisms of action in vitro:
From a clinical perspective, it is not confirmed which of these 3 mechanisms is most important for the documented success of these anti-VEGF agents in treating wet AMD over the long term, but clinical experience strongly suggests that the anti-permeability effect is the most important in the short term.
The increased permeability that is the hallmark of choroidal neovascularization (CNV) manifests itself clinically as intraretinal, subretinal, and/or RPE fluid resulting in increased retinal thickening. There is no better way to document the presence of fluid in these various locations and to quantitatively measure changes in the degree of retinal thickening than OCT.
While FA is indispensable for diagnosing, classifying, and locating CNV, it is in essence a qualitative test whose interpretations will vary with differing observers. In addition, the results of FA can only be used to monitor the anti-neovascular effects of the anti-VEGF compounds over the long term (months to years). OCT, on the other hand, can document the anti-permeability effects of the anti-VEGFs on a much shorter time scale.
PRO USE OF FA FOR FOLLOW-UP OF EXUDATIVE AMD
THOMAS FRIBERG, MD
While OCT is certainly valuable in monitoring the response of wet AMD to treatment, I believe it is a mistake to use it to the exclusion of FA. Typically, one uses OCT to measure the thickness of the macula, using the measurement as a rough surrogate for VEGF activity, as thickening is a sequela of vascular leakage. Some inaccuracies in this measurement are not uncommon, however, because the identical region (presumed fovea) might not be consistently sampled from test to test despite all efforts. This problem will be reduced with the adoption of newer spectral OCT systems. On the other hand, FA identifies contemporaneous leakage in the x-y plane (in an "aerial view" of the lesion), with the borders of the lesion often expanding throughout the transit. The FA thus delineates the extent of the lesion and is particularly valuable in the presence of modest subretinal blood, and in revealing choroidal neovascular activity under RPE detachments. For those using photodynamic therapy, the type of membrane may be important in deciding which lesions are likely to respond, and angiography determines this.
I consider the visual acuity, OCT findings, as well as the fluorescein angiogram when assessing an eye initially. I then use the OCT to assess the response to the first course of therapy. However, to confirm a lack of neovascular activity when a treatment hiatus is being considered, FA often reveals continued activity not necessarily reflected by OCT or acuity measurements. If leakage is present, retreatment is typically mandated. RP