Detecting glaucoma early allows for better treatment strategies and improved outcomes, but traditional visual field testing and optical coherence tomography (OCT) are not always sufficient to determine when disease is present. Often, by the time glaucoma has been detected, ganglion cell death and optic nerve damage have already occurred. Although visual field testing and OCT certainly provide valuable information, they do not detect disease early enough to preserve optimal vision health.
Electrophysiology testing of the retina and neuro-visual pathways is objective and capable of detecting cell distress prior to actual cell death, making possible the treatment and potential restoration of distressed cells. In-office systems such as the Diopsys NOVA ERG and VEP Vision Testing System (Diopsys) allow physicians to efficiently and accurately detect disease while there is still time to prevent and possibly reverse permanent damage.1
AT A GLANCE
- Often, by the time glaucoma has been detected, ganglion cell death and optic nerve damage have already occurred.
- Electrophysiology objectively tests the function of the visual pathway. Pattern electroretinography focuses on retinal ganglion and macular cell function, making it suitable for detecting early glaucoma.
- Such testing allows doctors to practice truly preventive medicine, because they can use the information obtained to prevent and sometimes restore damaged cells.
THE VALUE OF PATTERN ELECTRORETINOGRAPHY
Electrophysiology objectively tests the function of the visual pathway. Pattern electroretinography (PERG) focuses on retinal ganglion and macular cell function, making it suitable for detecting early glaucoma. Such testing allows doctors to practice truly preventive medicine, because they can use the information obtained to prevent and sometimes restore damaged cells. Multiple studies have found that PERG testing can detect differences between healthy and glaucomatous eyes, including identifying dysfunction within inner retinal layers, even in the presence of normal optic disc morphology and visual field analysis.2,3 Additionally, PERG has been found capable of detecting ganglion cell loss up to 8 years earlier than traditional testing.1
Structural damage to the optic nerve is permanent once it occurs. Studies have shown that detecting impending damage prior to actual cell death, in conjunction with lowering IOP, makes it possible not only to slow disease progression but, in many cases, to reverse the dysfunction of the retinal ganglion cells.4,5 The earlier disease is detected, the better the possibility that suffering cells can be restored.
PERG testing can also be used to measure the functionality of the retinal ganglion cell complex and determine the efficacy of treatment. This allows the physician to establish whether therapy is working or if treatment requires adjustment.
HOW IT WORKS
In the past, eletroretinography (ERG) testing was conducted by placing sterilized electrodes on the eye for a long duration. Now, disposable sensors are placed under the eye on the lower eyelid, and information is generated quickly, providing greater comfort and convenience for the patient. The electrodes collect information while a stimulus is presented to the patient.
ERG can be conducted via various modules, including full-field ERG and the previously mentioned PERG. The latter evokes a response from the ganglion and macular retinal cells by using an alternating checkerboard or set of bars as a stimulus. When this stimulus is presented, the system detects the amplitude and phase of the electrical signal that passes through the cells and provides information on which cells are dysfunctional. Clinicians can then use this information to determine how far the disease has progressed and whether or not treatment is working.
INCORPORATING THE TECHNOLOGY INTO PRACTICE
In my experience, ERG testing can fit seamlessly into the flow of a practice. Most glaucoma patients are seen at least twice a year, and incorporating these tests into their treatment routine is typically unproblematic. ERG can easily be used in conjunction with other tests and should serve as a supplement to more structural tests such as OCT. I perform PERG on anyone who has glaucoma or is a glaucoma suspect.
I have found PERG to be a valuable test that allows me to intervene before glaucoma begins damaging the visual system. When used together with OCT and visual field testing, PERG provides valuable information on the patient’s condition and on treatment efficacy.
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(3):2346-2352.
2. Ventura LM, Sorokac N, De Los Santos R, et al. The relationship between retinal ganglion cell function and retinal nerve fiber thickness in early glaucoma. Invest Ophthalmol Vis Sci. 2006;47(9):3904-3911.
3. Parisi V, Miglior S, Manni G, et al. Clinical ability of pattern electroretinograms and visual evoked potentials in detecting visual dysfunction in ocular hypertension and glaucoma. Ophthalmology. 2006;113(2):216-228.
4. Ventura LM, Porciatti V. Restoration of retinal ganglion cell function in early glaucoma after intraocular pressure reduction: a pilot study. Ophthalmology. 2005;112(1):20-27.
5. Sehi M, Grewal DS, Goodkin ML, Greenfield DS. Reversal of retinal ganglion cell dysfunction after surgical reduction of intraocular pressure. Ophthalmology. 2010;117(12):2329-2336.