Optonet Vision Unit Documentation

Please note that this User Guide is being currently updated; new sections will be added shortly.

  1. QuickStart Guide (in 5 steps)
    1. Step 1. Choosing Hardware
    2. Step 2. Installation and Calibration
    3. Step 3. Menus
    4. Step 4. Control of Menus and Charts
    5. Step 5. Customise Sequences of Charts
    6. How to check if my charts are well calibrated?
  2. Home-based Vision Training (Orthoptics)
    1. Patient Selection
    2. Calendar
    3. Daily Exercise Program
    4. Parameters
    5. Comments
    6. Login Credentials for the patient
    7. Attaching documents
    8. Save Therapy
    9. Access as Patient
    10. Remote monitoring of patient progress
    11. Management of Patient’s Access
  3. Virtual Eye Clinic
  4. Visual Acuity
    1. logMAR VA
    2. Logarithmic Notation
    3. VA Rating (VAR) or VA Score (VAS)
    4. VA Tools Menu
      1. Selecting Rows and VA Values.
      2. Visual Acuity Range
      3. Bi-Chrome Function
      4. Isolated Optotypes (Rows, Columns and Letters)
      5. Contrast
      6. Randomizing the order of optotypes
      7. Vanishing Optotypes
      8. Intermediate Steps
      9. Tablet as a remote controller for VA
    5. VA Optotypes
      1. Sloan letters
      2. British Letters
      3. Numbers
      4. Landolt Optotype "C"
      5. E of Snellen
    6. References Visual Acuity
    7. Paediatric Visual Acuity
      1. Test of “Broken Glasses”
      2. Symmetrical Optotype
      3. References Paediatric Visual Acuity
    8. Automated Visual Acuity Testing
      1. ETDRS, Bailey-Lovie, Snellen E, Numbers and Landolt C
      2. Symmetrical Letter Chart
      3. Broken Glasses Chart
      4. References Automated VA Testing
      5. VA Testing Protocol > 8 years old (printable document)
      6. VA Testing Protocol ≤ 8 years old (printable document)
  5. Setup
    1. Colour Calibration

4.3.Visual Acuity Rating (VAR) or Visual Acuity Score (VAS) #

One problem with logarithmic notation is that it is not intuitive, because the better the vision the lower the acuity value. Thus, the very best acuity values are negative. To solve this problem, Bailey proposed an alternative notation method based on the following formula: 2

Visual Acuity Rating (VAR) = 100 – 50 x logMAR

Which consists of subtracting from 100 the value obtained by multiplying the VA log by 50.

With this notation a value of “1” is assigned to each letter, and we add the value of all letters that the patient has successfully identified. Each line has five letters, so 5 points are added if all letters are seen. A VA of 6/6 (20/20, or 1.0 in decimal notation) corresponds to a logarithmic value of 0 (not very intuitive) whereas the VAR notation assigns a value of 100 (much more intuitive). If the patient reads a letter incorrectly, the value of his VA would be 99, two incorrect letters yields a score of 98, and so on. On the other hand, the patient gets an additional point for reading any letter smaller than 6/6 (20/20, or 1.0 in decimal notation). For example, 6/6 +2 becomes 102 VAR, a value that is sensitive, standardized, and intuitively understood as “better”.

Thus, this system maintains the advantages of logarithmic notation, but avoids negative values, is very easy to calculate and offers a more intuitive number, which the patient can easily understand (higher values indicate better acuity).

For example, the letters that a patient has identified correctly are shown below:

Using the method described above, the logarithmic VA in this example is 0.88 log units, while the Visual Acuity Rating is 56 VAR.

« Logarithmic NotationVA Tools Menu »
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