When it comes to diagnosis, Dr. Majcher reminds practitioners, “When making a diagnosis of glaucoma we can't rely on just one single test, it's putting together pieces of a puzzle. We're looking at structural and functional tests, we're [asking] do they correlate and fit with each other." This allows you to correctly identify those glaucoma masquerades.
Case #1: Fool me once . . .
A 59 year-old American Indian male presented who had been diagnosed with primary open angle glaucoma and started on topical medication 7 years ago. In February 2017, he received SLT in both eyes due to poor drop compliance. His highest untreated IOP was 23/20 and had post laser pressures of 15/13.
He suffered two ischemic strokes (2006 & 2019). The 2019 stroke involved the left anterior pontine & left frontal lobe. Afterward, he received a CT angiogram which revealed some occlusion and possible severe stenosis of the left posterior cerebral artery behind the P2 segment. His other risk factors for stroke included hypertension, DM type 2 and hypercholesterolemia.
In this case, there was poor correlation between the structure and function. There was such dense superior visual field loss, substantial loss in the inferior nerve fiber layer is expected, which can't be seen on this patient's OCT.
When there is a disagreement between structural and functional tests, the suspension arises that maybe one of the tests is not reliable or there is a non-glaucomatous cause to the observed neuropathy.
The visual field, repeated a month later with lids tapped, showed right-sided field loss in both eyes. A right incongruous homonymous hemianopia, denser superiorly with perhaps some vertical respect here in both eyes as well.
The red flags in this case that should raise suspicion for a non-glaucomatous etiology are:
- The vertical respect and heminopic pattern of both of our visual field loss and the GCC loss.
- The nasal and temporal aspect to the nerve fiber layer loss, as opposed to a more vertically oriented as typically expected with glaucoma.
- The disc pallor on the optic nerve of the right eye temporally.
It was concluded that the patient's nerve fiber layer and GCC loss can be attributed solely to a retrochiasmal visual pathway lesion.
Case #2: Every cause has at least one effect
A 63 year-old Han Chinese woman was referred for suspicion of glaucoma. She was highly myopic, good central visual acuity, systemically well, no afferent defects of the eyes and normal color vision. Color vision was not impacted in early or moderate stages of glaucoma.
Her surface corneal thickness was very thin, which is a significant risk for glaucoma, at about 500 microns in each eye. Light based technology, like OCT, allows you to get context as to where these corneal thickness measurements originate from.
The patient had a challenge with her first VF. In the results of the right eye, we see a clover leaf pattern with generalized depression in both eyes. After adjusting the phobial threshold sensitivity and switching to the 24-2C SITA Faster testing strategy, the observed inferior visual field loss in the right eye did not correlate with what was seen clinically in the left eye with possibly an enlarged blind spot in the left eye.
Dr. Steen states: “When we are thinking about diagnosing glaucoma, we've got to take intraocular pressure really out of the equation. While elevated intraocular pressure is a significant risk factor for the development of glaucoma, we know that individuals can develop glaucoma and do develop glaucoma with a wide range of intraocular pressures."
This patient's highest repeat IOP was 21 mm mercury with a thin central corneal thickness.
This case doesn't have the typical structural and functional correlation that's expected, so this patient is now being monitored without treatment. Dr. Steen's practice periodically (currently every 6 months) reevaluates her testing, looking for any progressive change over time that is characteristic of glaucoma.
Case #3: Expect the unexpected
A 50 year-old American Indian male presented as a follow-up for pigmentary glaucoma OU diagnosed 20 years ago. The patient had SLT in 2009 and was taking Latanoprost. His highest IOPs were 18 OD/19 OS while on Latanoprost.
The patient was also in a severe car accident resulting in facial reconstruction surgery 20 years ago. Currently, the patient has a VA of 20/20 OD and 20/30 OS with IOP 14 mmHg OU. Confrontation VF testing showed temporal VF loss. There was a little bit of endothelial pigmentation OU in the anterior segment. Corneal thickness was average. Gonioscopy revealed open angles, no angle recession and 2+ pigmentation.
Dr. Majcher mentions it is assumed that less pigment is being released now due to aging anatomical changes.
Optical nerve head photographs showed some fairly large cups in both eyes about 5 or 6 cup to disk ratio but otherwise it looked pretty symmetrical.
The red flags in this case that should raise suspicion for a non-glaucomatous etiology are:
- The huge degree of asymmetry, much more damage in the left eye
- Has a decreased acuity in the left eye of 20/30
- The visual field defect in the left eye was denser on the temporal hemifield versus the nasal hemifield
A subsequent CT scan found normal parasellar findings however "chronic medical blowout deformity" was noted in the left orbit. This ultimately led Dr. Majcher to diagnose the patient with traumatic optic neuropathy, but also to recommend that the patient's IOPs be monitored without glaucoma treatment at this time.
Takeaways: take your time
In conclusion, Dr. Steen reiterates the importance of taking the time to differentiate between glaucoma and those other possible pathologies. "We need to take the time that we truly need to establish that appropriate diagnosis and to never rely on that first test or an individual test alone . . . we really do have to rely on and understand that while our technology is excellent, it's really about how it's utilized in the hands of ourselves as clinicians."
