This case study is an example of how meticulously and elegantly we can identify structural and functional defects by incorporating more than one imaging modality when diagnosing glaucoma patients. Although nerve fiber layer OCT imaging is often 
the most useful to detect early glaucoma, in some instances, the defect can be so localized that it is easy to miss when surrounded by healthy nerve fiber layer (NFL).

In this case study, however, the lesson is two-fold. Not only are images of the macula useful for clinical knowledge and decision making for individual patient management, but there is also considerable value in imaging the NFL and macula connected to patient 
education. A large part of the challenge associated with managing glaucoma patients is convincing them to comply with their treatment regimens. This case study also serves as an example of how imaging allows me to educate patients about their condition and progression. These visuals are easily understood by patients and encourage them to adhere to their treatment and, ultimately, improve their disease.

Case Study

A 66-year-old female presented to my clinic for glaucoma consultation. The highest IOP that had been recorded throughout her prior history was 22 mmHg. Her risk factors were minimal. She had normal central corneal thickness, no significant familial risk factors, an angle open, and an unremarkable slit-lamp examination with OCT (Cirrus HD-OCT, Carl Zeiss Meditec) showed that she had a robust nerve fiber layer, which is typically reassuring (Figure 1).

However, upon completing visual field testing (Humphrey Visual Field Analyzer, Carl Zeiss Meditec), I was surprised that the patient had a definite localized paracentral scotoma (Figure 2).When I compared the visual field results with the OCT result, there was a disconnect. On OCT, the NFL appeared to be quite healthy, thus, the definite and reproducible visual field defect was unexpected.

Next, I administered a macular cube scan, which showed that the right eye was normal, but the left was quite abnormal and consistent with the visual field imaging. The very pronounced defect inferiorly on the macular cube correlated perfectly with the visual field images. I then reviewed the nerve fiber layer again on the OCT images, and I could see the defect on the left NFL at the 4 o’clock position on the optic nerve (Figure 3). If I had only relied on OCT imaging, it would have been very easy to overlook the abnormality in the left eye. I used the images and the visual fields to demonstrate the well-defined structural and functional defects to the patient. The study results had a clear impact on the patient, so her resolve to follow the suggested treatment regimen was enhanced significantly.

An Important Lesson

This case confirms that we should not rely only on just one parameter. It would have been easy to analyze the OCT NFL image and deem it to be a normal scan, but, by also taking a macular scan, in addition to a visual field, the abnormality was clearly apparent. This is a rare example in which the NFL OCT misses glaucoma and the visual field picks it up. It was only when I imaged the macula that it became obvious that there was an abnormality in the NFL as well.

In many similar cases, I might only take images of the NFL and not request a visual field if the images of the NFL looked normal, because in such cases, the likelihood of finding a field defect is small, but we also know from the Ocular Hypertension Treatment Study (OHTS) trial¹ and others that abnormalities don’t always show up on the first attempt at diagnostic testing. In the OHTS trial, 
2,304 patients underwent at least two visual field examinations in both eyes to determine whether they were at risk for developing open-angle glaucoma to be deemed eligible for the trial. The study was designed to evaluate the safety and efficacy of a topical ocular hypotensive medication. On patients whose prior test was abnormal, questionable, or unreliable, researchers performed a third test.

Seventy-nine percent of the patients were eligible based on their initial visual field tests. The third eligibility test was required for 11% of the patients. Researchers reported that by repeating the test one time after an initial unreliable test, they could identify an additional 560 patients as being at risk for developing primary open-angle glaucoma. The practical implications of the OHTS trial’s findings are that there are many instances in our clinics every day where we may be missing an opportunity to properly diagnose a patient by failing to incorporate additional testing.

As a result, many patients benefit from imaging of the macula and NFL in my practice. I perform both types of imaging routinely for patients who have early-to-moderate glaucoma. In some instances, I also image patients with more advanced glaucoma because they’re often far advanced in one eye and only moderate or mild in their fellow eye.

In addition to diagnosis, I use macula and NFL imaging in glaucoma patients to determine if they’re stable or progressing. When progression is identified, it presets an opportunity to review compliance to be certain that patients comprehend the potential severity of their disease. I’ve found that many poorly compliant patients become more compliant when their imaging studies are shared with them and they can clearly see the structural changes.

Furthermore, I’ve found that imaging of the NFL and macula as an educational tool is useful for patients who are at a crossroads in their treatment. When I have patients who need surgery, have had a change in their treatment regimen, or are not complying, I show them their imaging results, because glaucoma is relatively asymptomatic — until it isn’t. Once it’s symptomatic and the patient becomes aware of his visual deficit, he can never turn back the clock.

When I show images, I can point out the structural defect and how it correlates to the visual field to show patients their defects in terrific detail. I also find it useful for family members caring for loved ones who have glaucoma. Imaging helps them better understand the physiology and the seriousness of the disease.

IT TAKES TWO

In this example, the macular scan in conjunction with the visual field and NFL was more useful than the visual field or NFL alone. As a bonus, demonstrating the patient’s abnormality to them, visually and graphically, improves disease education and compliance, especially in patients who need to improve their compliance with recommended therapies.

Reference

1. Kass MA, Heuer DK, Higginbotham EJ, et al. The Ocular Hypertension Treatment Study: a randomized trial determines that topical ocular hypotensive medication delays or prevents the onset of primary open-angle glaucoma. Arch Ophthalmol. 2002;120(6):701-713;discussion 829-830.

Dr. Samuelson is an attending surgeon at Minnesota Eye Consultants in Minneapolis and an adjunct professor at the University of Minnesota in Minneapolis. Dr. Samuelson may be reached at (612) 813-3628; twsamuelson@mneye.com. He is a consultant to Carl Zeiss Meditec, Inc.