Dallas, Texas – (August 2009) – Visual testing is one of the primary focuses at the Retina Foundation of the Southwest. Along with ongoing studies to understand the complexity and potential treatments for a number of eye diseases, our researchers develop advanced testing techniques that can be used to more effectively evaluate the eyesight of our patients. Testing equipment is equally vital for monitoring the progression of disease, which allows our researchers to make better recommendations regarding the timing of treatment.

Timing is particularly critical for the 1,776 infants and children who walk through the doors of the Retina Foundation annually. Many suffer from developmental disorders that not only disrupt their vision, but greatly impact their quality of life. Some congenital and early onset eye disorders make it impossible for the visual area of the brain to develop properly, leaving the child with a permanent visual impairment uncorrectable by glasses.

Therefore, when the researchers of the Pediatric Eye Research Laboratory sought to develop a new tool to monitor exotropia in patients, it addressed an important need for this area of study. Exotropia is defined as an outward misalignment of the eyes. Stereopsis, the ability to detect differences in distance by using the two eyes together (as in a 3D movie), may be disrupted when a child suffers from exotropia . Exotropia often starts out as an intermittent misalignment—sometimes the eyes are straight and sometimes an eye drifts out of alignment.

Some children with intermittent exotropia are able to keep their eyes straight most of the time and may not need treatment. Other children have exotropia that gets worse over time. These children are at risk of permanently losing the ability to use their two eyes together. Our pediatric researchers wanted to develop a test that was simple enough for children, but also one that could detect whether the exotropia was worsening.

In 2003, our pediatric researchers collaborated with long-time partners, Stereo Optical Company, Inc., to produce a prototype of a product that could measure the stereoacuity—quality of depth perception—of children with exotropia. In addition, the test was designed to measure stereoacuity at a 3-meter distance because researchers believe that the occurrence of misalignment is more sensitively detected when the child is focusing on a distant object. Studies with the prototype test showed that it provided a reliable and valid way to test stereopsis for exotropic children.

In 2009, the test was further simplified and the Distance Randot Test® is now distributed by Stereo Optical Company, Inc. It has undergone intensive study to determine its effectiveness and safety in monitoring exotropia in patients ages 4 and older. Earlier studies performed at the Retina Foundation prove that the Distance Randot Test is effective in detecting abnormalities in depth perception at a distance and can effectively monitor the progression of extropia in patients over time. The results for the 2009 version of the Distance Randot Test® were presented at the 2009 meeting of the Association for Research in Vision and Ophthalmology and a manuscript describing the most recent data has been submitted for publication.

“Changes in distance stereoacuity over time may signal deterioration and the need for surgical correction of the exotropia to re-align the eyes,” said Dr. Eileen Birch, Director of the Gary C. Morchower Pediatric Lab at the Retina Foundation. “Intermittent exotropia is an outward misalignment of the eyes that is not constant and is mainly present when the child views something off in the distance, so testing of distance stereoacuity may be especially important in this condition.”

This is how the Test works:

• The subject is seated or stands 3 meters from the examiner in a normally lighted room while wearing polarizing glasses over their spectacles if any.
• The testing booklet is a Polaroid vectographic book (3D picture book), presenting 2 geometric shapes at each of 4 disparities (levels of depth): 400, 200, 100, and 60 arcsec.
• Testing begins with the 400 arcsec level, the easiest level, and proceeds until the child makes an error.
• The smallest disparity, most difficult level at which the child identifies or matches both shapes correctly, is recorded as their stereoacuity.

The Distance Randot Test is particularly important because there are no other tests available to monitor distance stereoacuity in exotropic patients, which is critical for recommending treatment on an individual case basis.

“The Test is not intended for diagnosis. It is intended for use in monitoring whether intermittent exotropia is getting worse, perhaps indicating the need for surgery,” explains Jingyun Wang, Ph.D. and researcher in the Pediatric lab.

Over the years, there have been significant modifications to the protocol. “The new test is much quicker to administer and is bound in a single testing book rather than 4,” said Wang.

Our researchers also hope the low cost and simplicity of the final version will allow the Retina Foundation to expand our strabismus studies to multiple testing sites. Dr. Birch remarks, “We wanted to develop an inexpensive, book format…this will allow us the opportunity to conduct multi-center studies of the natural history of intermittent exotropia and of treatments for this condition.”