By Michael J. Lyons, OD, FAAO
A visual evoked potential (VEP) instrument, which can be used to manage conditions such as glaucoma and macular degeneration, has been a beneficial addition to my practice. Here are the most important points to consider when purchasing this instrument including the return on investment you can expect.
If the practice median age is 60, and you have many glaucoma suspects, this instrument is a worthwhile investment. VEP is an objective test, and, therefore, measures without a patient response giving you information that you can’t get any other way. VEP allows for an objective detection of defects found in the visual system, often before traditional subjective testing can pick them up. It gives me additional confidence with visual analysis when paired with the OCT and visual field.
Information on Dr. Lyon’s web site about the Visual Evoked Potential (VEP) instrument. Dr. Lyons says it is especially helpful in diagnosing abnormalities of the retina, optic nerve or visual cortex.
What is a VEP?
A visual evoked potential (VEP) instrument, measures the electrical response of the visual system to a stimulus that usually consists of a black and white alternating checkerboard pattern. By placing electrodes on predetermined areas of the scalp, the VEP can measure the strength and duration of the electrical activity as the visual response is generated in the retina and sent to the occipital cortex. Abnormalities that involve the retina, optic nerve or visual cortex will produce a delayed VEP. This allows me to treat and monitor glaucoma patients.
A delayed VEP, along with other clinical data, such as history, exam findings, or other tests such as an OCT and field, allows me to fully analyze the function of the visual system. I most commonly use a VEP in my glaucoma suspect population. When I detect suspicious cupping, I run an OCT, visual field and a VEP. An article, by Banitt et al., showed that an abnormal VEP precedes RNFL loss by several years. If I have an abnormal VEP and the other tests are normal, I will watch these patients more closely for glaucoma progression than I would have in the past.
Set Goals Prior to Acquiring VEP
I have a strong interest in glaucoma and macular degeneration. I was really interested in obtaining this technology to measure how conditions like these affect the visual system. The traditional method of measurement has historically been the visual field, but we know that the reliability of the field is solely dependent on the patient and how they perform on the test. I wanted a test that was objective, and the VEP delivered.
Crunch Cost & How to Acquire
Depending on features and add-ons, expect to pay around $50,000. I purchased the instrument with the help of a five-year loan from a credit union that specializes in optometry. At my current interest rate, my “cost-neutral” point is about seven tests per month. I currently run about three to four tests per week (and the number of tests increase every month), so I expect to have the instrument paid off in just over two years.
Calculate Revenue-Generating Potential
The VEP test costs very little to perform–about $2 per tests when taking into account the disposable electrodes, the prepping gel and the conductive paste. The VEP takes approximately 10 minutes to get the patient set up and to perform the test on both eyes, much better than some of the field tests. The device is primarily a vertical unit on wheels that has a 2 x 2’ footprint. About a 6’ path is needed when the patient is taking the test. As mentioned above, my “cost-neutral” point is about seven VEP tests per month. The bonus: it has a high reimbursement (average nationwide reimbursement is ~$140).
This technology is also not for everyone, so fewer offices will have one, making your practice a potential referral center for the specific device. All of my patients with glaucoma, a macular condition like macular degeneration, diabetic retinopathy, or any other possible post-retinal issue (like amblyopia, optic neuritis, etc), receive a VEP.
Click HERE for information about the billing codes that should be used with this instrument.
VEP Is Practice Differentiator
Very few practices in my area have this instrument and patients have responded. Many of the patients I test have already sat through a visual field and understand how frustrating they can be. They love the fact that they are required to do nothing but stare at a computer monitor as it evaluates their visual system.
Educate Patients About Use of VEP
I tell patients that this is a test “that takes you, the patient, out of the equation as we measure the electrical activity of your visual system.” I usually contrast it with a visual field, which is so dependent on the patent. I tell them that we will place three electrodes on their scalp and have them watch a pattern on the computer monitor for about one minute. I stress that it is important to try to clear their mind and relax while staying focused on the pattern.
Case Study: VEP in Action
During the writing of this article, a young lady was referred to my practice from the local children’s hospital with sudden onset headaches and diplopia. She was correctable to 20/20 OU with refraction, but she displayed a constant left esotropia that was reportedly not there the week prior. I ordered a visual field that showed a non-specific central defect in both eyes.
I then ordered a VEP that showed a mild delay in just the right eye. Sure enough, when I did the dilated exam, I saw that she had papilledema, so I sent her off for an MRI to rule-out an intracranial mass.
In this case, I didn’t necessarily need the VF or VEP to confirm the diagnosis of papilledema with possible intracranial mass or increased CS fluid, but what would I have done if there was no papilledema? With an abnormal VEP and VF, I would have certainly still ordered the MRI.
Ready Technicians to Perform Test
Our technicians perform the test. It takes a total of about 10 minutes to set the patient up and to perform the test.The vendor is very receptive to providing complimentary training and to address any follow-up questions or refresher courses that we’ve required. The hardest part of the training is instructing the technicians on the prep. It is critical that the electrodes are adhered to the scalp. The two on the forehead are usually easy, but the one that overlies the occipital cortex can be challenging if the patient has a lot of hair. Because of this challenge, I have proven to be the perfect test subject.
Make Use of Test Results
This test fits right in the technology stream of other diagnostic instruments, such as digital imaging, visual fields, OCT and MPOD. Especially with my glaucoma population, it is one more test that I can use to confirm the presence or absence of a visual abnormality.