ETDRS acuity testing has become the worldwide standard for visual acuity testing, replacing the Snellen and Sloan acuity tests. ETDRS stands for Early Treatment Diabetic Retinopathy Study. The ETDRS test is designed to eliminate inaccuracies in the Snellen and Sloan tests.
The ESV-3000 ETDRS testing device has patented (Patent # 5,078,486) self-calibrated test lighting. The ESV-3000 device incorporates highly advanced LED light source technology. The auto-calibration circuitry constantly monitors the LED light source and calibrates the test luminance to 85 cd/m2 or 3 cd/m2. Other ETDRS testers are not standardized and have no circuitry to control the test lighting. They use "off-the-shelf" non-standardized fluorescent bulbs that require a bulb "burn-in" period. The bulbs must be constantly replaced and each time a bulb is replaced, there is an additional "burn-in" period. No testing can be accomplished during the "burn-in" period.
The ESV-3000 is the only large-format standardized ETDRS testing device. The ESV-3000 allows testing up to 20/200 ETDRS Acuity at a test distance of 4 meters (The CSV-1000 has a smaller footprint and allows testing up to 20/200 at a test distance of 8 feet.). The device is operated by infrared remote control.
The ESV-3000 is designed specifically for clinical trials where large-format ETDRS testing (up to 20/200) is performed at 4 meters. Unlike other large-format back-lit devices for ETDRS evaluation, the light level is calibrated and held constant, allowing the automatic replication of testing light levels from different clinical trials locations or for evaluating before and after treatment. Other devices are not standardized and cannot provide constant test lighting for ETDRS evaluation between locations or over time. A wide variety of ETDRS LogMAR tests are available, including Chart R, Chart 1, Chart 2, Tumbling E and many others.
The ETDRS acuity test was developed to aid in evaluating the changes in vision following panretinal photocoagulation in patients with diabetic retinopathy. Previous studies had somewhat confusing results due to inadequacies of the acuity tests used in those early studies. For example, the Snellen acuity test has a different number of letters per row, e.g. 10 letters on the 20/20 line, but only 3 letters on the 20/70 line. Therefore, if the results of a study showed that the patients "gained three letters of acuity," the results could indicate the gain of a full acuity line, as in the 20/70 line, or only a portion of an acuity line, as in the 20/20 line. Also, the individual lines on the Snellen acuity test are not equally spaced. For example, the change from the 20/25 line to the 20/20 line is a 20% change, while the change from the 20/30 line to the 20/25 line is a 16% change. Again, referring back to the diabetic studies, if a study demonstrated a two line increase in acuity, it could mean a 33% improvement from 20/30 to 20/20, or a 40% improvement from 20/50 to 20/30. These inadequacies of the Snellen acuity test made it impossible to properly evaluate the acuity data and to compare data from study to study.
Other inadequacies also exist in the Snellen Acuity test. These include the types of letters used on the test and the spacing of the letters. These details are beyond the scope of this website, but if there are questions involving the more detailed design characteristics of the ETDRS chart, please feel free to call us at 800 526 7703 or 937 548 7970.
The ETDRS test incorporates specific design criteria to make it more accurate than the Snellen or Sloan acuity tests. These include:
To prevent memorization, different versions of the ETDRS test chart are available. The three standard versions of the ETDRS chart are R, 1 and 2.
To properly evaluate ETDRS, the test should be conducted under standardized lighting conditions. The CSV-1000 is the only device that self-standardizes the test lighting level to the recommended photopic test level of 85 cd/m2. This light level has been recommended by the National Academy of Sciences and by the American National Standards Institute for ETDRS and contrast sensitivity vision testing.
Scoring the ETDRS Chart
ETDRS scoring can be accomplished in a number of different ways. The two most common methods are described below. Both of these methods provide scores that can be used for statistical analysis, unlike the scores provided by the standard Snellen or Sloan Acuity tests.
ETDRS Scoring Method 1: The patient starts are the top of the chart and begins to read down the chart. The patient reads down the chart until he or she reaches a row where a minimum of three letters on a line cannot be read. The patient is scored by how many letters could be correctly identified.
ETDRS Scoring Method 2: The ETDRS charts were originally used in ETDRS studies where patients had relatively poor vision. For these studies, starting patients at the top of the chart to read down worked well since most patients could read only about half way down the chart. However, the ETDRS charts are now being widely used for many studies, including IOL and refractive surgery studies, where patients have very good vision. For these patients, it makes little sense to start them at the top of the chart and read down. For these patients, a second scoring method is used. The patient starts on the last row where he or she can read all of the letters, and then reads down until he or she reaches a row where a minimum of three lines cannot be read. For these patients, a decimal ETDRS acuity score can be used. To calculate the decimal acuity score, follow the guidelines below. (In reality, scoring method 1 can also be used for statistical analysis, by assuming that the patient could have read all of the letters above where he or she started on the test. Then add that number of letters on to the number of letters actually read by the patient.)
20/30 Row = 0.20
3 letters X 0.02 log/letter = - 0.06
ETDRS Acuity Log Score = 0.14
Are Bailey-Lovie and ETDRS Different?
Bailey-Lovie Charts and ETDRS are different. Bailey-Lovie charts incorporate the European design of LogMAR; i.e. letter sizes are rectangular. For example, for the Bailey-Lovie Chart Design, a 20/20 letter is 4 minutes of arc in height by 5 minutes of arc in width. ETDRS letters are all square, i.e. 5 by 5.
The CSV-1000 offers six test faces to provide contrast sensitivity testing:
the most widely used contrast sensitivity test in the world
used for screening refractive surgery patients
used for in or out of office screenings and for cataract evaluation
provides the same tests as the 1OOOS, except that the acuity test is presented in Landolt C format.
special test face designed specifically for Food and Drug Administration clinical trials