American Family Vision Clinic Logo
Dawn K. DeCarlo, Mark Swanson, Gerald McGwin, Kristina Visscher, and Cynthia Owsley

Visual-Evoked Response, Pattern Electroretinogram, and Psychophysical Magnocellular Thresholds in Glaucoma, Optic Atrophy, and Dyslexia

publication date
April 4, 2006
see more



The purpose of this study is to compare visual-evoked response (VEP) pattern electroretinogram (PERG) and psychophysical thresholds to the same stimulus, designed to be optimal for the magnocellular system, in suspects and patients with early glaucoma, patients with optic nerve disease, dyslexic children, and age-matched controls.



Stimuli were low spatial frequency sinusoidal luminance profile gratings abruptly phase reversing at 7.14 Hz. Electrophysiological recordings were made at 50%, 30%, 20%, 10%, and 5% contrast. Threshold was the lowest contrast evoking a clear response at the stimulus frequency. Three independent judges scored the traces. Psychophysical thresholds were obtained by ascending and descending method of limits. VEPs and PERGs to International Society for Clinical Electrophysiology of Vision (ISCEV) standards and to increasing spatial frequencies were obtained as parvocellular specific controls. Patients were diagnosed independently by the referring professionals.



Parvocellular-specific responses were normal, except in cases with explicable visual acuity loss. The judges scores correlated highly (>0.9). VEPs and PERGs correlated highly and each correlated less well with psychophysics in normals, glaucoma, and dyslexia but the opposite occurred in optic nerve disease. VEPs had the lowest normal values and least variance (all adults <5%, children <10%, PERGs <20%). In glaucoma, VEP magnocellular deficits occurred in 85% of recently diagnosed positive cases, 48% of high-risk suspects, 39% of low-risk suspects, and ocular hypertensives. Approximately 28% of dyslexics had VEP magnocellular deficits. PERG losses were less frequent. There was a clear dichotomy and low correlations between psychophysics and electrophysiology both within and between groups. Psychophysical threshold elevations were absent in all glaucoma groups, often large in optic atrophy and small (2.5%) but highly significant in dyslexia.



Contrast thresholds to magnocellular-specific stimuli are consistent in cortex and retina. VEPs are more reliable. Psychophysics seems to tap different mechanisms. VEPs are very sensitive to early glaucoma. The lack of VEP loss in dyslexia suggests the other losses are artifactual. Further research is needed to see if stimuli even more like the frequency-doubling technology are more useful clinically.


Such a nice optician. My grandson is only 4 and needs glasses. We were so sad, but he explained the issues, and we will follow up as he suggested.

Anna P.

I had such a good experience with the clinic. Very friendly staff and doctor, did not have to wait for long to be called, and was treated respectfully. Thanks, American Family.

June S.

Dr. Zurcher has gone above and beyond what any other eye doctor has ever done to figure out what is going on with my eyes. Very happy with American Family Vision.

Christine R.

Family Vision Clinic changed our lives! My daughter was frequently car sick, and she was getting headaches every day, often painful enough that they brought her to tears. We saw a string of doctors and therapists, but we made no progress. Finally, we found Dr. Levi Zurcher and his eye therapist Rain. After ten weeks of eye therapy my daughter no longer gets headaches, and she no longer gets car sick. Daily tears are a thing of the past. I really can’t say enough about this clinic. It was fascinating to watch Dr. Zurcher work. For the first time, someone who knew what they were doing was intently studying my daughter, really trying to figure out all of her eye issues, and his therapist Rain is one of the most patient and lovely people that I’ve ever had the good fortune to meet. We’re finished with eye therapy—yay!—and I have switched to American Family Vision Clinic for all of my family’s other eye health needs.

Lars Wulff

Very professional, yet kind and helpful. They do what they can to make the appointment comfortable. I was running a bit late, I made sure ti call. They were able to switch me with a patient who was already there, they treated me with respect, and helped my son have confidence by getting him the eye care he needed that day. Thank you so much! Would recommend to anyone. It's a blessing that they care enough to work with people who have all different types of insurance from work to state coverage.

Justin E.

The staff is friendly. The Doc is very knowledgeable. The office is family friendly and everyone is so patient with the little ones.

Amy Fagerness
1 2 3



What Causes Bloodshot Eyes? Understanding the Causes and Treatments

Bloodshot eyes can be alarming, but they are not always a cause for concern. In this blog, we will discuss […]

Read More

Ocular Rosacea: Understanding the Symptoms and Best Treatment Options

Rosacea is a skin condition that affects many people. While it is commonly found on the face, rosacea can also […]

Read More

Can Vision Therapy and Neuro Optometry Help with Motion Sickness?

Motion sickness can be debilitating and affect people's daily activities. Symptoms such as dizziness, nausea, car sickness, and balance problems […]

Read More
see all blogs

Contact Us To Amplify Your EyeCare

Working Hours

Monday - Thursday
8:00 am - 5:15pm
400 Yauger Way SW. Bldg 1, Ste A Olympia, WA 98502
Website Accessibility Policy
Safety protocols page
phone-handsetarrow-uparrow-right linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram