From Naysayer to Believer: Using PERG to Diagnose Early Glaucoma

A new tool may help to diagnosis glaucoma.

By Ben Gaddie, OD, FAAO

With new technological advancements and devices constantly being released, it can be difficult to discern which devices will truly make a difference in improving diagnostics. Although pattern electroretinography (PERG) platforms have been sold for many years, the systems were, until recently, only available in hospital settings; because they were unavailable in clinical settings, many eye care providers were unfamiliar with their capabilities.

TO THE POINT

PERG testing could be a useful diagnostic tool to choose when seeking objective data on retinal ganglion cell activity.

Somewhat analogous to optical coherence tomography (OCT), PERG analyzes the retinal ganglion cells (RGCs) but does so by measuring function rather than assessing structure, thus minimizing subjective analysis of RGCs. PERG testing causes no discomfort to patients and is easy to perform; nonverbal, disabled, and pediatric patients can be tested quickly and effectively. During the PERG test, a patient looks at alternating black and white horizontal bars on a screen while a slim, noninvasive electrode placed under the patient’s eye records the amplitude and magnitude of the response of electrically active RGCs. The test can also be repeated after the initiation of glaucoma treatment, and can be used to measure therapeutic results.

Devices such as the Nova ERG (Diopsys) and visual evoked potential (VEP) Vision Testing System (Diopsys) make it possible for these diagnostics to be performed in the office.

Figure 1. Patient presents with normal RNFL and RGC data.

Figure 2. PERG testing indicates glaucoma OS.

Figure 3. A patient with possible RNFL defect and mild RGC defect presents with visual field tests not consistent with structural findings.

Figure 4. PERG testing confirms that this patient has glaucoma OS.

FROM NAYSAYER TO BELIEVER

My initial reservations about using PERG were linked to a lack of clinical trials using such platforms to evaluate glaucoma. Since 2013, however, studies have shown that PERG can detect glaucoma earlier than traditional diagnostics.1-3 Such data, combined with my colleagues’ overall positive impression of the PERG platform, encouraged me to evaluate it for myself.

I typically use PERG when evaluating patients whose clinical findings may indicate the presence of glaucoma. It has joined OCT, RGC analysis, corneal hysteresis, visual field, gonioscopy, and optic nerve exam as my go-to evaluation methods. I have found that PERG is especially useful when other diagnostic tools deliver data that do not result in a definite diagnosis.

I commonly encounter patients who I suspect have glaucoma, but present with normal visual fields borderline damage of the retinal nerve fiber layer (RNFL) on OCT. I have found PERG to be very helpful in these situations, as the objective data it provides can determine if there is RGC damage. These data are good functional correlations to the structural tests that eye care providers use to diagnose glaucoma.

I have also found PERG to be useful after a patient has initiated therapy. I sometimes retest patients after starting treatment to track the improvement in RGC function. However, I do not use PERG in patients who have been managing their glaucoma for several years.

CASE EXAMPLES

A 59-year-old white man presented with no previous diagnosis of glaucoma and a family history of glaucoma. His pressure was somewhat high at 26 mm Hg OU, and pachymetry showed corneal thickness of 541 OD and 529 OS. Mean corneal hysteresis scores were abnormal at 8.9 OD and 6.8 OS. The RNFL had no clear defects and RGC analysis showed nothing unusual (Figure 1). His visual field test was equivocal. I performed PERG testing on this patient and the results showed mild abnormality OD and more defined abnormalities OS, clearly indicating early glaucoma (Figure 2). He initiated prostaglandin therapy.

A 55-year-old black woman presented with normal IOP, 14 mm Hg OD and 17 mm Hg OS. She demonstrated questionable RNFL defect and mild RGC defect, both in her left eye. Her visual field results were not consistent with the structural findings (Figure 3). I performed PERG testing in this patient and confirmed that she had RGC damage and glaucoma in her left eye (Figure 4).

PERG IN MY OFFICE

The addition of PERG to my diagnostic regimen was fairly simple to integrate into my practice. Most importantly, I am able to definitively diagnose or rule out glaucoma in borderline patients, allowing the patient to begin therapy prior to substantial RGC loss and functional visual field damage.

1. Banitt MR, Ventura LM, Feuer WJ, et al. Progressive loss of retinal ganglion cell function precedes structural loss by several years in glaucoma suspects. Invest Ophthalmol Vis Sci. 2013;(54)2346-2352.

2. Porciatti V, Ventura LM. The PERG as a tool for early detection and monitoring of glaucoma. Curr Ophthalmol Reports. 2017;5(1):7-13.

3. Porciatti V. Electrophysiological assessment of retinal ganglion cell function. Exp Eye Res. 2015;(141)164-170.

Ben Gaddie, OD, FAAO
• senior partner and director, Gaddie Eye Centers, Louisville, Kentucky; cochairman, International Vision Expos; executive vice president, Optometric Glaucoma Society
• 502-423-8500; ibgaddie@bellsouth.net
• financial disclosure: consultant, Aerie Pharmaceuticals, Akorn, Alcon, Allergan, Bausch + Lomb, Diopsys