American Family Vision Clinic Logo
Kim, Sang-Yeob PhD; Cho, Hyun Gug PhD; Moon, Byeong-Yeon PhD; Yu, Dong-Sik PhD

Fusional Single Vision with Prism-induced Vergence Has More Influence than Diplopia on Postural Stability

publication date
October 21, 2019
see more



Prism-induced convergence and vertical vergence for maintaining binocular fusion induced postural instability to a greater extent than diplopic conditions. This finding has important implication in relation to postural control of patients with large exophoria or vertical phoria in optometric clinic.



The purpose of this study was to examine whether binocular single vision with prism-induced horizontal and vertical vergence and diplopia might affect the static postural stability.



Forty-two subjects with a mean ± standard deviation age of 23.79 ± 2.81 years were enrolled in this study. To simulate convergence and divergence, base-in and base-out (BO) prisms of 4 and 8 Δ were added, respectively. To simulate vertical vergence, vertical prism of 2 Δ was added in a trial frame that corrected for the subject's refractive error during far distance (6 m) gaze. The prism power necessary to break fusion in each subject was detected and applied to induce diplopia in horizontal and vertical directions. Indices of general instability and sway power were measured under visual conditions using Tetrax and compared with normal viewing without the prism. Correlations between general instability indices and the ranges of break point in convergence and divergence were analyzed.



Postural instability was increased significantly when convergence induced by BO 4 and 8 Δ and vertical vergence induced by 2 Δ were stimulated. The correlation coefficient between ranges of BO break point and indices of general instability was −0.308 in the BO 4 Δ and −0.306 in the BO 8 Δ condition.



Although binocular input is recognized as an important factor in postural stability, binocular input with excessively stimulated convergence and vertical vergence during a far distance gaze is a latent factor affecting postural stability. On the other hand, diplopia did not influence postural stability.


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



Understanding Foggy vision

Is foggy vision troubling you? Let our experienced optometrist restore your sight – book an appointment today and see the difference! The term foggy vision often refers to a visual disturbance characterized by blurred, cloudy, or hazy vision, which can make seeing clearly challenging. As your local optometrist, we recognize the significance of maintaining optimal […]

Read More

Vision Therapy for Nystagmus: Improving Visual Function and Quality of Life

According to the National Eye Institute, nystagmus affects approximately 0.24% of the general population in the United States. This means a whopping 720,000 individuals in the US face the challenges of nystagmus. How does Nystagmus Impact Vision?  Nystagmus is a condition that affects the eyes, causing involuntary and rapid movements that can make it difficult to […]

Read More

Cleaning Your Eyelids With Hypochlorous Acid: The Ultimate Solution for Eyelid Infections and Inflammation From Blepharitis

Are you tired of dealing with eyelid inflammation? Well, there's good news for you! Hypochlorous acid, a natural bactericidal compound, has been clinically shown to help fight against various eyelid conditions such as blepharitis, and it's even effective at preventing the development of styes and other eyelid infections. In this blog, we'll be exploring the […]

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