Diagnostic test results may vary in the same patient on the same day.
Every time I have a physical examination, I am reminded of the importance of reliable and repeat testing. In fact, the physical exam I had a few months ago was no different. Let me preface this by saying that I truly like and trust my primary care physician; he is knowledgeable, patient, and kind, with a wonderful chairside manner. His staff, however, leaves me wanting.
Case in point: I am called back to the pretesting area by a nurse. She weighs me with all my clothes on, including my shoes, and tells me I’ve gained a few pounds since my last visit, which is fair enough. She instructs me to sit down, straps the blood pressure cuff quickly to my right arm, and squeezes so tightly that I almost say something about it. I casually say, “When you guys check my blood pressure, it’s always high, but I check it at home and it’s always normal.” No response is given—not even a smile or eye contact—and she proceeds to check my blood pressure level. Well, guess what? It is high. Without looking at me, she says, “Your pressure’s up.” Then, before I can respond, she tightens the cuff to the point that it hurts significantly. She checks my blood pressure level again and tells me it’s still high. In my head I say, “Ya think?!” She shows me the way to the examination room, and as I sit there waiting for my doctor to come in, I think to myself, “Well, it’s a good thing I don’t have any medical complaints, because she never bothered to ask.”
Enter the doctor. He knows my significant history of white coat syndrome and jokingly says that my pressure level was up because I had to come and spend time with him. I smile and say, “Yeah, I think your nurse was having a bad day.” He then puts the cuff on my arm and starts talking to me about football. We are fans of the same college team and have a great conversation about the current season. He slowly checks my blood pressure level a couple of times during the conversation before saying, “I must bore you.” I ask what he means. He shows me the screen on the sphygmomanometer, showing my systolic blood pressure level has come down significantly from when it was first checked that day. We both have a good chuckle. Never get too excited about the results of a single test.
How am I going to segue this anecdote into the arena of glaucoma? Let’s begin with when I ordered a spectral domain optical coherence tomography (SD-OCT) study on a patient who was taking hydroxychloroquine for systemic lupus erythematosus.
This 31-year-old woman also had a diagnosis of systemic hypertension for which she took a low dose of lisinopril. Her ocular history was remarkable for low myopia and mild dry eye, the symptoms of which were alleviated with lipid-based artificial tears on an as-needed basis. Her best corrected visual acuities that day were 20/20 in each eye; her intraocular pressures by means of rebound tonometry were 14 mm Hg in the right eye and 12 mm Hg in the left eye. Pupil function was unremarkable as was the remainder of her eye examination.
When I asked one of the technicians to run a macular 512 × 128 scan and print out the macula OU analysis, I’m certain I did not misspeak. However, when I came back into the examination room, a retinal nerve fiber layer study result and ganglion cell complex study result were sitting on the countertop. Even though these were the wrong studies, I looked at them anyway. To my surprise, the ganglion cell complex study result lit up like a Christmas tree! There were scattered defects flagged for both maculae. I rechecked her intraocular pressure levels and found no difference. I then looked at her optic nerve/retinal nerve fiber layer study result, and it was essentially clear for both eyes, showing small cup-to-disc ratios and thick and robust nerve fiber layers.
The ganglion cell complex study, which has been commercially available as part of SD-OCT software for several years, allows the clinician to quantify inner retina layers in patients and addresses the condition of glaucoma.1 The inner retina is host to the retinal nerve fiber layer, inner plexiform layer, and the ganglion cell layer. It is the inner layer of the retina which may convey glaucomatous damage, and the average thickness of this ganglion cell complex can serve as a reliable biomarker for early glaucomatous damage. Because this study algorithm is not affected by axial length, it can be especially useful in detecting glaucomatous damage in patients with myopia. Retinopathy from hydroxychloroquine use is typically confined to the outer retina, with thinning and eventual vision changes developing.2 The inner retina does not seem to receive damage from this medication.
To get back to my patient who came in for a macular SD-OCT and may now have early glaucoma due to the wrong study being printed, I did print out her macula OU analysis study result and was delighted to report no outer retinopathy from hydroxychloroquine. However, I now had this ganglion cell complex study result to explain. Because it didn’t make sense to me that her inner retina was flagged, I decided to repeat the SD-OCT study.
We went next door and repeated a macular scan for each eye, and when I saw the result, I was surprised. Her ganglion cell complex study result looked significantly better than the one performed 5 minutes ago. I went back and looked at the reliability of her first study, and the score was 7 out of 10. Her second study had good reliability as well. I told her the good news and invited her back for her next comprehensive eye examination.
It has been ingrained in my mind since optometry school that reliable and repeatable visual field studies are necessary to detect glaucomatous damage. Although I do repeat them over time, I never gave much thought to repeatable SD-OCT studies as I did for visual field studies. Because this patient had markedly different study results in the same day, I am now thinking it would be a good idea to perform a couple of SD-OCT studies during a visit and compare. Would it be overkill? Perhaps. Would it take much time and labor? Not really.