Precision Vision Introduces the BRVT Testing Chart – Precision Vision

PV News™ October 2010

The fields of science and sports, different as they are, have long held fascination with one another. The science of sports medicine, for example, aims for the optimal combination of athlete health, safety, and performance. The science of vision care is no different. But would you have guessed that one of the most significant developments in low vision testing in decades is intimately tied to the international game of cricket? Absolutely. To see how, check out our featured article below.

CONTENTS


Precision Vision Offers Breakthrough Low Vision Test: The BRVT Test

From “Counting Fingers” and “Hand Motion” to Evaluating Low Vision Practically Anywhere,
the Journey in Low-Vision Testing Takes a Big Leap Forward

It all started over a game of cricket: blind cricket that is. The most significant development in the field of low vision testing in decades is a direct result of observing an international competition for blind cricketers. In October 2008, one of the world’s leading pioneers in the field of vision testing and research was invited to a meeting in England to discuss the vision standards being applied by the World Blind Cricket Council (WBCC). Dr. Ian L. Bailey accepted the invitation, which opened the door to this breakthrough in low vision testing.

“It’s taken a while to get to this point,” said Ian L. Bailey, O.D., Professor of Optometry and Vision Science at the University of California in Berkeley, Calif., who has a notable resume of significant accomplishments, including the development of the Bailey-Lovie and ETDRS charts (Early Treatment Diabetic Retinopathy Study), recognized as the gold standard in testing visual acuity across the globe today.

BRVT_500

Dr. Bailey felt compelled to change the process for which to measure and evaluate levels of low vision after listening to complaints from members of the WBCC. Because each blind cricket team is comprised of an assigned number of players that are categorized into three levels of vision impairment, the very first step – the measurement of the individual participants’ low vision – is a critical one to ensure that each team’s composition is balanced.

The WBCC was concerned that the participants were not being placed in the proper category of vision impairment due to inaccurate testing. It appeared that the teams that were performing best in the competition were all thought to have too many players that were mis-categorized to their advantage. Everyone believed the winning teams had an advantage that was directly related to the measurement of the players’ low vision levels.

As an expert in low vision and visual acuity measurement, Dr. Bailey has been a long-time critic of the antiquated and inadequate way of testing utilized around the world.

“I don’t blame the council members for complaining. After all, everyone wants a fair shot at winning in sports, don’t they?” said Bailey. “Until now, we didn’t have good standard tests for very low vision. For example, some of the criteria the WBCC used in its set of rules were things like ‘cannot recognize a human hand at any distance.’ It became very obvious that we needed better ways of assessing low levels of vision.”

As an expert in low vision and visual acuity measurement, Dr. Bailey has been a long-time critic of the antiquated and inadequate way of testing utilized around the world.

“I don’t blame the council members for complaining. After all, everyone wants a fair shot at winning in sports, don’t they?” said Bailey. “Until now, we didn’t have good standard tests for very low vision. For example, some of the criteria the WBCC used in its set of rules were things like ‘cannot recognize a human hand at any distance.’ It became very obvious that we needed better ways of assessing low levels of vision.”

Standard visual acuity letter charts become inappropriate or impractical for testing people with very poor vision (at about 20/400 or poorer). If they can read the row with the largest optotype on a standard vision chart, the common practice by most clinicians – and still popular today – is to ask: “Can you count my fingers (CF)?” And if they cannot count the fingers, patients are asked: “Can you see my hand moving (HM)?”

The CF and HM technique of measuring low vision is used all over the world. Dr. Bailey has long been critical of this primitive method, often arguing that the practitioner could always bring a chart close enough or make letters large enough so the patient could read at least some of them. Nevertheless, this makes testing for low vision haphazard.

Another case reinforces this point. Just after he returned to the United States following the WBCC meeting, Dr. Bailey attended an invitational gathering at the Smith-Kettlewell Eye Research Institute in San Francisco, Calif. The topic at hand was how to evaluate vision in persons with sight loss who are receiving retinal implants.

All of the patients discussed were either blind or nearly blind, but their optic nerve fibers were still operational (i.e.: viable). The practitioners and researches in attendance were excited to be on the cusp of new technologies that allow a small array of artificial stimulators to be placed against the retina. A video image is then transmitted to these stimulators that, in turn, stimulate the optic nerve fibers, leading to the fibers sending messages to the brain. The participants in the study may have some visual abilities established. The new variable introduced recently is the revolutionary way of stimulating the optic nerve fibers through the retinal implants. When discussing the experimentation with these devices, the attendees often defaulted to finger-counting and hand-motion to assess vision.

“The point was driven home to me that we desperately needed better systems for measuring visual acuity or visual resolution ability at the poor end of the scale,” said Dr. Bailey. He began work right away on developing a new set of low vision tests that enabled the measurement of vision over a much greater range.

“I experimented with this quite a bit and tried to make the procedures as simple as I could. I decided that having a computerized test wasn’t the best way to go since it would be more convenient to have some easily portable tests that can be administered nearly anywhere in the world,” he continued.

After exploring several different strategies, Dr. Bailey, together with his colleagues Doctors Jonathan Jackson (Northern Ireland) and Hasan Minto (Pakistan), and his Berkeley colleague Dr. Robert Greer, created the Berkeley Rudimentary Vision Test (BRVT). The BRVT test is a simple low vision test that can be appropriate in almost any clinical or quasi-clinical environment, and one that is suitable for application across all cultures and age groups. Its portability is key: it’s available in a card or chart format making it very convenient.

The innovative BRVT low vision test takes but a minute or two to administer and obtain reasonably precise measurements of the patient’s visual resolution abilities. This has application for testing patients with letter-chart visual acuities poorer than 20/500, and represents a substantial improvement over the common but obviously inadequate methods involving “count fingers” (CF) and hand-motion (HM).

The BRVT low vision test charts and cards are currently available through Precision Vision. According to Dr. Bailey, in their experimentations with prototypes, the test has been very well received around the world, including: the University of California Low Vision Clinic, the California School for the Blind, the Orientation Center for the Blind, the San Francisco Lighthouse and in overseas locations in Northern Ireland and Pakistan.

“This is extremely important for people with poor vision to have their vision capabilities properly measured because it is critical to monitor changes in the vision and to modify medical interventions and treatments in response. For example, if a patient with poor vision has a steady decline in their retinal health, their practitioners can make appropriate decisions to help their patients,” said Dr. Bailey.

As new technologies are developed to restore sight or improve sight in severely impaired individuals, a more precise measuring system is essential to the identification and quantification of any improvements or failures. Having more precise measurements of visual resolution abilities enables professionals involved in rehabilitation to better predict functional abilities and customize their rehabilitation programs. For epidemiological purposes, it can be useful to obtain more details about the range of visual acuity within severely impaired populations.

BRVT Test: Extending Vision Testing up to 20/16000

The BRVT low vision test consists of three card pairs. Each pair of cards is hinged together and presents four test targets. These cards are 25 cm square (10 inches).

The first card pair is called the “Single Tumbling E” card pair that uses the single tumbling E as the optotype.

There are four “Single Tumbling E” targets the patient may be asked to identify. Their sizes are: 100 M, 63M, 40M, 25M (the letter heights are about 15 cm, 9.5 cm, 6 cm and 3.8 cm).

In the recommended procedures, the “Single Tumbling E” card pair may be presented at a viewing distance of either 1 meter or 25 cm (this corresponds to the width of the cards).

With the “Single Tumbling E” card pair, it is possible to measure visual acuities to 20/2000 when the viewing distance is 1 meter, and to 20/8000 when the viewing distance is 25 centimeters. The task for the patient is to indicate in which direction the legs of the E are pointing.

The second card pair is called the “Grating Acuity” card pair, which measures grating acuity. The sizes of the black-and-white gratings are 200 M, 125M, 80M and 50M (with stripe widths equaling 60 mm, 38mm, 24 mm, and 15 mm). The task for the patient is to identify whether the stripes run horizontally or vertically.

In the recommended procedures, the “Grating Acuity” card pair is only presented at 25 cm. This allows the measurement of grating acuity to 20/16000.

The third card pair is called the “Basic Vision Function” (BVF) card pair. This pair does not establish a visual resolution limit but rather categorizes basic vision function. On this card pair, two of the test targets test White Field Projection (WFP). On one target, half of the square is black and the other half is white. On the other target, one-quarter of the card area is white. The patient’s task is to identify whether the white area is located up, down, right or left.

The other two targets on the “Basic Vision Function” card pair are simply one black card and one white card. The patient’s task is to indicate whether the card before them is black or white. This Black-White-Discrimination test (BWD) is conducted at 25 cm so the angular size of the field is 53 degrees (1:1 ratio).

There’s a standard recommended sequence with the BRVT test that begins with the “Single Tumbling E” card pair and – when indicated – the “Grating Acuity” card pair or the “Basic Vision Function” card pair is utilized.

“At very poor visual acuities, we needed to make the task progressively simpler, as well as systematically shortening the viewing distance to enable very large angular sizes to be included as part of the results. We have developed our test based on these underlying principals,” said Dr. Bailey.

For standard letter charts, there is a limit to the visual acuity that can be measured. On a letter chart, the patient should be at least able to read all the letters at the largest size when the chart is presented at a reasonable distance. The upper limit for testing visual acuity on a letter chart is about 20/800.”

The remarkable step forward the BRVT test provides is that it substantially extends the range of visual acuity measurement in relatively small increments providing better assessment and monitoring of vision for the severely visually impaired population.

“It’s so important that clinicians know about the vision of these patients. Their practitioners need to know whether one eye is getting better or worse, for example, so they can treat the problem each individual faces,” said Dr. Bailey. “Instead of stopping at 20/800 with standard visual acuity letter charts, the BRVT has just extended measurement to 20/16000. Instead of two steps, we now have more than 10 increments of measurement.”

To view the BRVT low vision testing charts offered by Precision Vision, please click here.


Featured Products

BRVT

The Berkely Rudimentary Vision Test (BRVT) was developed to enable efficient and easy measurement of visual acuity beyond the limits of the letter chart. Patients with low vision have been asked by clinicians to count fingers or detect hand motion. BRVT allows effective measurement with very close viewing distances.

Click Here to learn more about the BRVT Test.

Okolux plus Mobil Display

The Low Vision Magnifier POP Display from Schweizer can be placed in your office to easily show patients how these magnifiers work. Products can be sold directly from the display. All products sold individually as well.

All products are battery operated handheld illuminated magnifiers which come in three light temperatures (2700K, 4500K, and 6000K) for improved reading acuity and customization for each indivdual’s unique visual needs.

Click Here to learn more about the Okolux plus Mobil Display.


Upcoming Tradeshows

Visit Precision Vision at the following tradeshows. If you are attending one of these tradeshows and want to avoid unnecessary shipping costs and delays, we’d be happy to bring small portable products to the meeting. Place your order online or call us at 800-772-9211. Just be sure to tell us which tradeshow to hold the products for

AAOptometry San Francisco, CA 17-20 November

Share Your Stories With Us!

Precision Vision® wants to hear your stories. Tell us how you are impacting the industry. Do you have an interesting story to share about a Precision Vision® product? Contact us and we may use it in a future newsletter.