I’m sitting in the waiting room with a patient as the doctor reviews the results of her previous visual field examinations, a crucial tool in diagnosing glaucoma. “The left eye is fine,” the doctor says, “but the right eye exam is not reliable, there’s a 45% false positive score. We’re going to have to do it again.”
The VF exam relies on the patient to stare straight ahead and click a button whenever they perceive a dot of light on the edge of their visual field—unsurprisingly it can lead to a number of false positives or negatives, especially if the patient doesn’t understand the instructions.
The patient doesn’t look too happy, but goes into the exam room and comes out a few minutes later. By now the doctor has gone back to the office. “How’d it go?” I ask. She hands me the exam results and says, “I don’t think it worked this time either, the nurses kept telling me I clicked multiple times, and I tried to keep my eyes straight forward as the doctor said but sometimes it’s hard not to follow the dot of light…”
I look down and indeed there’s a 37% false positive rate, far beyond the acceptable level of 15%. The nurse walks out and starts explaining all the problems to me in a conspicuously frustrated tone. She leaves and I sit down next to the patient, who I notice is now slightly shaking.
“It’s tough, I want to do well too, but I’m really nervous, and failing for the third time makes me even less confident…look at me…” she trails off and blinks furiously a few times. I sit down next to her, and begin to explain in my not-so-perfect Chinese. I tell her that this is nothing to get nervous about, that it’s not a test but simply a check-up procedure. I tell her that it’s simply her nervousness that’s stopping her from getting a good result, and that I was confident she could do it if she relaxed. I do this with all that an undergraduate, not-yet-in-med-school student with mediocre Chinese can offer—a hand on the shoulder and a lot of smiling. Finally, I tell her she’s free to go home if she wants, but if she’s up for it, we can give it one more try.
I speak with the nurses and she’s back in, with me standing in a corner of the room thinking I’m feeling much more emotionally vested in this than is probably warranted. Part of me knows that despite what I said, it doesn’t make much sense that a patient who has failed to get a reliable result her first three times somehow vastly improves on the fourth. But she’s standing up, the nurses are squinting at the monitor, and as the results print out I take a quick look and my eyes widen. 11% false positives, 4% false negatives.
I feel like I’m smiling more than the patient as we walk out of the room together. I sit down with her and tell her, “I’ve got two great pieces of news. The first is that this exam was perfectly reliable. The second is that you don’t have glaucoma.”