About six months ago, I was asked to speak at the ASCRS glaucoma subspecialty day on the topic of imaging and detection of progression in severe or advanced glaucoma. During the past six months, some interesting developments on this topic took place that could affect how we practice.
To begin with, a useful rule of thumb: In early glaucoma, optic nerve (ON) imaging (including OCT) tends to be more sensitive, whereas in advanced glaucoma, visual field (VF) testing is most likely to reveal progression. It is said that the ON has a “floor effect” in terms of how much damage imaging can detect; however, there are many caveats and exceptions.
Unfortunately, this rule of thumb made its way into the world of reimbursement, and several insurance carriers recently proclaimed that they will no longer reimburse for ON imaging in patients with advanced glaucoma. Simply put: This reimbursement proposal is ill advised. On a practical level, denying reimbursement for OCT in advanced disease would likely do more harm than good and could increase overall costs in the care of patients with glaucoma.
In this article, I will review glaucoma severity staging, how ON imaging fits into staging and how this affects practice management.
ADVANCED GLAUCOMA BILLING
With the arrival of ICD-10 came a new set of staging rules for glaucoma. Glaucoma is now defined as mild, moderate or severe, and definitions provided for each stage are based upon VF testing. Note that staging may be different for the left and right eyes.
Mild glaucoma, essentially preperimetric glaucoma, is defined as an ON appearance that demonstrates characteristic ON damage, including neuroretinal rim narrowing and retinal nerve fiber layer (RNFL) defects in the presence of a full VF test. Moderate glaucoma is defined as ON damage with a VF defect confined to just one hemifield and more than 5° from fixation. Advanced or severe glaucoma is the presence of ON damage with VF defects that are either in both the superior and inferior hemifields or with visual field defects in either hemifield that exist within 5° of central fixation.
This definition of advanced glaucoma is entirely appropriate, because it defines glaucoma as a disease that threatens the central vision of the patient and therefore may have a significant functional impact on the patient’s quality of life. But, in this definition, the location of the defect defines glaucoma, not the total number of dead fibers. With a definition of severe glaucoma tied to location and not the totality of the loss, it reduces the likelihood of hitting the OCT floor effect. And, when damage occurs close to fixation, protecting the remaining vision becomes more important.
In fact, a patient can have advanced glaucoma while the ON testing or VF is very close to normal. In Figure 1, the patient presented with 20/50 vision and a smudge in her central vision. The VF was essentially normal, except for a reduced foveal sensitivity (0 db). On careful examination of her central VF using a 10-2 paradigm, the offending VF defect was demonstrated, and an abnormal ON examination revealed a structure-function correlation, indicating advanced glaucoma with a VF defect within 5° of fixation. ON imaging was absolutely critical and indispensable for the diagnosis.
Figure 2 shows a patient with a double arcuate scotoma, including two superior arcuate scotomas that are within 5° of fixation. This defines advanced glaucoma, yet the corresponding OCT image shows that although he has two corresponding inferior RNFL focal defects, the average RNFL thickness is normal, indicating the absence of a floor effect — plenty of ON to follow, including the superior nerve, which is normal in all respects.
AN ASYMMETRIC NATURE
Glaucoma is a notoriously asymmetric disease. This asymmetry occurs between the left and right eye and between the inferior and superior VF. So while the superior VF may have enough damage to constitute advanced glaucoma, the inferior field is full, and the corresponding superior ON and RNFL can be normal as well. In this case, monitoring for damage in the healthy half of the ON is more important than any other type of monitoring, because with half of the field gone, we need more attention on the remaining half of the ON, not less. To deny the physician the ability to image the remaining ON is to punish glaucoma patients who have lost half of their vision by dramatically increasing the chances of them losing the second half. It is the exact opposite of what one would want to do.
Also, physicians can follow OCT to detect RNFL progression in advanced glaucoma. Figure 3 shows a patient with advanced glaucoma in both eyes indicated by a pair of superior arcuate scotomas (Figure 3A). Over time, the OCT demonstrated a progressive loss of average RNFL thickness (Figure 3B).
Even with these examples detailing reasons to perform ON imaging in patients with advanced glaucoma, there are other reasons. For instance, glaucoma is not the only condition that can lead to RNFL changes. Sanjay G. Asrani, MD, at Duke University demonstrated that diabetic retinopathy, uveitis and tractional membranes can influence the RNFL.1
Since retinal vein occlusions are more common in patients with glaucoma, it is common to find RNFL changes caused by retinal edema and detecting these changes can be very important for the patient’s eye health.
Finally, physicians can detect ON damage in the macula with ganglion cell analysis and other techniques. In advanced glaucoma, detecting loss of ganglion cells in the macula can help to monitor whether fixation is threatened. In my practice, we monitor the macula in patients with severe glaucoma during each ON assessment to detect changes related to glaucoma and related to other comorbidities. Glaucoma occurs in older patients, and it is common for a patient who is monitored for glaucoma to develop wet macular degeneration, epiretinal membranes, diabetic macular edema and other findings. We may be testing the macula and nerve for glaucoma, but when we discover other sight-threatening conditions, we act and treat our patients to protect their vision.
ON imaging is critical for advanced glaucoma to confirm the correct diagnosis and to detect progression. Any proposed changes to withdrawal reimbursement for ON imaging in patients with advanced glaucoma would likely be harmful and could increase health-care costs by allowing advanced cases to progress and other comorbidities to go undetected. These changes seek to withdraw much-needed resources from vulnerable populations that are at a higher risk for blindness and severe functional visual loss. Due to the complexity of caring for eye diseases such as glaucoma in high-risk patients, ON imaging remains a critical tool for protecting what remains of the ON in individuals who have already lost too much vision. OM
- Moore DB, Jaffe GJ, Asrani S. Retinal nerve fiber layer thickness measurements: uveitis, a major confounding factor. Ophthalmology. 2015 Mar;122(3):511-517. Epub 2014 Nov 4.