How pattern, flicker ERG can impact cataract treatment decisions

Dr. BondRetinal issues can impact cataract surgery outcomes, especially for those with multifocal or other premium lenses. While multifocal lenses may allow the patient to see more clearly across a range of distances, they may also decrease the amount of light that reaches the retina, exacerbating any issues that may already be present.

In addition, cataract surgery will not restore optimal vision if the cataract is not the main issue for the decline of visual acuity. Removing the cataract would only be treating part of the problem.

Knowledge of the posterior segment health is essential prior to moving forward with cataract surgery, whether using a premium lens or not. However, when a cataract is present, it can be difficult to view the macula. As cataracts worsen, they may impinge on the visual field quality and make it more difficult to determine if any other pathology must be addressed.

Even without cataracts, traditional diagnostics only provide valuable information on the structure of the cells but do not objectively reveal how well those cells are functioning. Electrophysiology testing-particularly, pattern electroretinography (PERG)-solves this issue and can be effectively and efficiently performed with an in-office device (Diopsys NOVA Vision Testing System, Diopsys).

While examination with optical coherence tomography (OCT) provides valuable information, it is not always sufficient when cataracts are present. The media opacity can render information gathered unreliable or unobtainable.

Consequently, testing that does not rely on the ability to detect patterns is needed.

Full-field electroretinography (ffERG), including flicker ERG do not rely on refraction or recognition of patterns and can therefore provide the ability to detect disease behind cataracts.

What are PERG and flicker ERG?

What are PERG and flicker ERG?

PERG is ideal for the early detection of glaucoma as it allows surgeons to objectively determine the health of retinal ganglion cells and measure the function of cells that may be struggling but are not yet dead.

The retina is stimulated by an alternating pattern, typically horizontal bars or checks. The response to these stimuli is recorded as a measureable signal that provides valuable information on cell dysfunction. This allows for earlier detection of disease, particularly in glaucoma suspects.

As abnormalities from dysfunctional cells can be detected up to eight years sooner than structural tests,¹ this provides the possibility for earlier and more effective treatments and a greater ability to slow disease progression and improve cell health.

For patients with early nuclear sclerosis, some information can be gathered with PERG testing, however, ffERG-particularly flicker ERG-is even more beneficial.

Flicker ERG tests retinal function by stimulating the entire retina with alternating flashes of light at a rate of 32 Hz. This makes it possible to analyze the coordination between cone cells as the rods do not respond to that frequency of stimulus.

The intensity of the stimulus makes this test useful for tracking disease and treatment efficacy. Preliminary studies² show better responses indicate a better probability for improved functional vision after cataract surgery.

This is true in my practice as well, I have found. Because most premium lenses are not compatible with retinopathy, the ability to determine pertinent information about the responsiveness of the cones, even in the presence of media opacities, is invaluable for diagnostic purposes, treatment projections, and to generate more accurate expectations for patients.

Patient Selection

I routinely see about 9,000 patients a year. I do not perform PERG or flicker ERG on all of my patients, however, I will use PERG for any patient who has glaucoma or is a glaucoma suspect.

PERG will not only detect glaucoma issues much earlier than other diagnostics, it is also excellent for tracking early to moderate disease and treatment efficacy. I still perform visual field testing in conjunction with the PERG.

A good way to think of it is that a visual field tells where the patient has been and the PERG tells where the patient is going. We repeat these tests on a yearly basis in order to track disease progression and treatment efficacy.

Patients with a sufficiently dense cataract that prevents me from adequately viewing the retina are excellent candidates for flicker ERG. About 50 to 65% of my cataract patients fall into this category.

Of these, results of the test determine the necessity to change our planned surgical course in about 20% of cases.

These tests are not only easy to read and interpret, but also very reliable. I have not experienced any false results and to date have not found a comparable test. It is also efficient and convenient.

The disposable electrodes can be used for both tests, so if either test is indicated, both will be performed in a convenient process. This ensures we are detecting any possible glaucoma concerns and testing for other retinal issues that may affect the outcomes of cataract surgery.

I have found the flicker ERG in particular to be reliable where other diagnostics are not. My technicians perform the testing in the office and the results have allowed us to improve outcomes for our patients. At the end of the day, that is what it is all about.

References

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;2346-2352.

2. Mackool RJ and Mackool Jr. RJ. Evaluating macular function before cataract surgery. CRST. June 2016; 56-57.

William Bond, MD

E: wbond666@gmail.com

Dr. Bond is medical director of Bond Eye Associates in Peoria, IL, and is assistant clinical professor at the University of Illinois Medical School in Peoria, IL. Dr. Bond is a consultant and speaker for Diopsys.