Redefining Cystoid Macular Edema
Seenu M. Hariprasad, MD (moderator): In the past 3 decades, numerous advances in surgical technique, instrumentation, intraocular lens (IOL) technology and pharmacology have led to dramatic improvements in visual outcomes following cataract surgery. However, cystoid macular edema (CME) continues to compromise postoperative visual acuity in certain patients.
In this discussion, we will examine current and evolving strategies for managing and treating CME. Our retinal specialists are joined by anterior segment surgeon Richard L. Lindstrom, MD, an internationally recognized cataract surgeon. His presence and expertise will give this discussion a multidisciplinary perspective. We will share information and explore how retinal specialists can help cataract surgeons maximize outcomes in their patients.
HIGHER EXPECTATIONS FOR PROMPT REEVALUATION OF CME
Dr. Hariprasad: The definition of CME has evolved as the nature of cataract surgery and macular imaging techniques have evolved. What are your thoughts about the definition of CME?
Michael D. Ober, MD: Before the advent of optical coherence tomography (OCT), CME was diagnosed following cataract surgery when vision measured 20/40 or worse, macular edema was noted on contact lens examination and petaloid leakage with a hot nerve was observed on fluorescein angiography (FA). This traditional definition of CME has changed with new techniques for cataract surgery where attainment of 20/20 vision or better is the expectation and the increasing use of OCT allows detection of subclinical increases in retinal thickness.
Matthew S. Benz, MD: OCT has made a tremendous difference in our ability to diagnose, treat and follow patients. Also, it is potentially helpful in some patients prior to cataract surgery. We can identify pathologies in the macula that lend themselves to a higher incidence of postoperative CME. We need to be aware of conditions such as diabetic macular edema, macular pucker and vitreomacular traction when cataract surgery is being considered.
Richard L. Lindstrom, MD: More anterior segment surgeons have access to OCT now, and we are using it preoperatively. Today, we have a much tighter definition of CME. In the past, we thought 2% to 3% of pseudophakic patients had clinically significant CME, meaning 20/40 or worse visual acuity. Our group began to perform FA and photometry studies and we found that 50% or more of our patients had CME. If we are purist about it, based on OCT, almost 100% have some thickening of the macula.
We have shifted to a position where we believe we should prevent CME instead of treating it only when it is severe. That has led to screening preoperatively for diseases that are likely to contribute to postoperative CME.
ADVANCED IMAGING REVEALS NEW INFORMATION
Dr. Hariprasad: In my practice, I have noticed that many patients who have pseudophakic CME do not have distinct cystoid changes on OCT but rather generalized thickening of the macula. I wonder if this indicates that the definition of CME is outdated. With high-definition OCT, we may be able to tell where the edema is located, whether it is in the inner retina or outer retina. Have you seen thickening on OCT that lacks the distinct cystoid pattern or intraretinal cystic changes that we traditionally talk about in CME?
Dr. Ober: Yes, I have. In most patients, when generalized thickening occurs, we do not find specific cystic spaces inside the retina. We have seen the same pattern in patients with edema from other etiologies, such as epiretinal membranes. Sometimes cystic spaces are present; sometimes the inner retina is more edematous than the outer retina or vice versa; and sometimes there is diffuse thickening without cystic spaces. But the meaning of this is unknown at this time.
Dr. Hariprasad: I believe FA continues to play the distinct role of ruling out other non-CME causes of vision loss after cataract surgery, such as choroidal neovascularization or diabetic macular edema. Dr. Warren, do you have any comments on OCT patterns in CME or the role of FA in the era of OCT?
Keith A. Warren, MD: We have focused on CME related to pseudophakia; however, we know CME can have many other causes, especially in patients who have retinal vascular disease. Our ability to diagnose those patients today has improved tremendously, partly because of our new instrumentation. As we continue to develop our use of the new instrumentation, our diagnoses will improve.
The newer-generation OCT instruments give us more information than we were able to obtain previously. It was possible to see retinal thickening without cystic changes, but now we can do a more thorough screening of the entire macula and perhaps find cystic areas we could not see in the past.
I think the technology we have today has driven us to diagnose patients earlier, which provides us with a better chance to improve their vision. Outcomes may not have been as good in the past because patients were diagnosed at a later stage in the disease process. As Dr. Lindstrom said, with the information we have now we can take preventive measures.
Dr. Lindstrom: To affirm what has been said, our definition of a quality outcome following cataract surgery is definitely changing. We are looking at customizing IOLs in an attempt to reduce root, mean-squared higher-order aberrations or spherical aberrations in 0.10 increments, which is less than 1 letter on a line. We are discussing whether that is a clinically significant outcome. It does not take much macular edema to affect vision by 1 letter.
I use the analogy of a rug getting wet. You can dry it out, but it never looks or feels the same again. If the macula gets meaningfully wet, even if it changes contrast sensitivity only subtly, it still would be better if it had not gotten wet at all.
Dr. Benz: OCT is wonderful, but it is still a complementary test to FA, particularly when used to diagnose a new patient. We may not see cystic changes on OCT in a pseudophakic patient who has 20/30 or 20/40 vision and is unhappy. We may not see cysts on clinical exam. However, FA probably will reveal some leakage.
Dr. Warren: I have seen patients in whom I suspected CME, but OCT showed an epiretinal membrane, which I did not recognize at the slit lamp or on FA. So it is important to use OCT and FA in tandem to verify and define the diagnosis in certain situations.
THE CHALLENGE OF DEFINING MEANINGFUL CHANGES IN MACULAR THICKNESS
Dr. Lindstrom: If you were to perform OCT prior to cataract surgery, what would you consider a meaningful increase in thickness postoperatively?
Dr. Benz: That is an excellent question, but it is not one that can be answered definitively. Perhaps it would be a percentage increase in thickness. "Normal" spans a wide range among patients. A patient with longstanding, dry, age-related macular degeneration may have significant macular thinning and a 140-μm macular thickness that is normal. A younger patient may have a 210-μm or 220-μm macular thickness that is normal. It would be an interesting study to compare preoperative and postoperative OCTs in cataract patients to determine if significant thickening occurs, so that we can better define "normal."
|It does not take much macular edema to affect vision by one letter. I use the analogy of a rug getting wet. You can dry it out, but it never looks or feels the same again. If the macula gets meaningfully wet, even if it changes contrast sensitivity only subtly, it still would be better if it had not gotten wet at all.|
— Richard L. Lindstrom, MD
Dr. Hariprasad: When evaluating the macular thickness number, I also would encourage cataract surgeons to consider the contour, because the foveal contour is extremely important. In the planning of upcoming diabetic macular edema clinical trials, we are struggling to define what constitutes significant thickening or thinning after treatment. Patients who are enrolled in these studies have thicknesses all over the board. To say success is 250 μm may be a bad idea. If a patient is 700 μm at baseline and they improve to 300 μm, that would be a huge success. As a community, we need to define what level of thickening and decrease in thickening is significant. A concept that has been discussed is a 30% decrease, however, in patients with subtle thickening, this may be difficult to achieve.
Dr. Ober: I think a 30% change is a better parameter for patients with retinal pathology. Following cataract surgery, however, a less significant change still may be important. When the visual potential is better, smaller changes become clinically significant.
Dr. Hariprasad: Based on the availability of high-resolution macular imaging devices and high expectations of cataract surgery patients and anterior segment surgeons, it is reasonable to conclude that the time has come to update our definition of CME. RP