Diagnose glaucoma earlier and detect progression sooner using these VF-testing tips

The World Glaucoma Association (WGA) has said that, “Functional testing is essential for the evaluation, staging, and monitoring of glaucoma…[and that]…the likelihood of the diagnosis of glaucoma is increased through corroboration of abnormal structural and functional tests.”¹ So, when in doubt, “play the field.”

Cover three bases

Diagnosing glaucoma, and detecting glaucomatous progression directly depends on a reliable baseline data set of both structural and functional testing. Specific for VF testing, and while always being mindful of other non-glaucomatous causes of VF progression, ODs should remember to cover these three bases, provided by the WGA,² to diagnose and manage glaucoma early:

• “A good baseline of reliable VFs is essential to be able to monitor for progression.”
• “Decisions on progression should not be made by comparing only the most recent [visual] field with the one before.”
• “Suspected progression should be confirmed by repeating the [visual] field.”

Such additional, reliable, and correlating testing increases certainty and accuracy,³ and doing testing more frequently (two to three within the first year) on the front end of care may help optometrists detect glaucoma progression sooner.⁴

For example, consider this: Patients in the Ocular Hypertension Treatment Study, displayed “…partial arcuate (21.7%), paracentral (15.6%), and nasal step (10.6%) VF defects.”⁵ Interestingly, variability of these defects was usually lower among ocular hypertension patients vs. early glaucoma patients. Furthermore, the following phases in their proposed three-phase process may show “…shallow VF defects [which] are often transient and are barely detectable…” followed by “… VF defects [which] progress at an uneven pace to become dense.”⁶ Thus, confirmation “… of VF abnormalities through retesting is essential for distinguishing the development or progression of glaucomatous VF loss from long-term variability.”⁶

When trying to detect this progression sooner, ODs should look for one (or all three) of these potential problems:

1. Deepening of current VF defects (worse pattern standard deviation).
2. Enlargement of current VF defects (worse mean deviation).
3. New VF defects.

Having said that, and importantly, we do not have to wait for functional progression to confirm our diagnosis and/or start treatment if there are reliable, supportive, structural findings, such as localized neuroretinal rim thinning — even in the context of borderline VF results.⁷

Step up to the plate

Because glaucoma follows a very particular and preferential pattern of structural loss, optometrists should always put the VF in the context of the clinical exam/structural findings and then look for associated correlating VF defects.

For example, the correlating associated VF defects in early glaucoma often start in the superior nasal quadrant,⁸ then the inferior nasal quadrant, followed by Bjerrum defects connecting these defects to the blind spot,⁹ with any remaining islands of VF present in the central/inferior temporal quadrant with advanced glaucoma.¹⁰

Additionally, there is an observed faster rate of VF loss in the superior hemifield compared to corresponding points in the inferior hemifield in primary open-angle glaucoma patients (POAG).¹¹

Also, and regarding the subset of POAG patients who have nor-mal tension glaucoma (NTG), such NTG patients have scotomas that are, “more likely to be deeper, steeper, more localized, and closer to the fixation, whereas the VF loss in POAG eyes is more diffuse and symmetric than that in NTG…”¹⁰ Importantly, any central defects observed on 10-2 VF testing are shown as an effective predictor of subsequent 24-2 VF glaucomatous progression.¹²

Furthermore, any VF damage is usually denser in the superior hemifield relative to the inferior hemifield among primary angle-closure glaucoma patients (PACG) and POAG patients but more so in POAG eyes, whereas the VF defects were more diffuse among PACG patients.¹³

Importantly, and regardless of the location, a recent study shows that if glaucoma patients have a reliable VF defect present in both hemifields on initial testing, these patients’ glaucoma progressed faster than those patients with superior or inferior defects alone. Therefore, for these patients, “…more aggressive therapy should be considered…”¹⁴ while always monitoring the central vision carefully.¹⁴

In summary, “…when visual field loss already is present, perimetry will find progression more frequently…”¹⁵ and this may be true regardless of the stage of the disease.¹⁶

Issue connection

As this is Optometric Management’s annual dry eye disease (DED) issue, it’s important to note that DED can affect the reliability of structural and functional glaucoma tests. A small study shows the importance (and improvement) of a single drop of an artificial tear prior to VF testing among DED patients who had glaucoma.¹⁷ OM

References are available in the online version of this article.

DR. LIFFERTH practices at Center for Sight. He is a member of the Optometric Glaucoma Society and a Glaucoma Diplomate of the American Academy of Optometry. For additional glaucoma cases, you can also follow Dr. Lifferth on his Instagram account: glaucomaqd. Disclosures: None. Email him at glaucomaqd@yahoo.com.