Optonet Vision Unit Documentation

Please note that this User Guide is being translated into English; 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. Remote Control
    5. Step 5. Personalized test’s sequences
    6. How to check if my charts are well calibrated?
  2. Tele-Consultation
  3. Home-based Vision Therapy (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
  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

4.5.1.Sloan letters #

This is the recommended optotype for VA measurement and clinical refraction. It consists of 10 letters designed in 1959 by Louise Sloan: (C, D, H, K, N, O, R, S, V and Z).

The Sloan letters have the same height to width ratio, similar to the structure of the Snellen letters, drawn on 5×5 matrix.

The Sloan letters are used in the ETDRS charts, which also employ the logMAR design proposed by Bailey-Lovie.1,6 The ETDRS charts are so named because they were used in the “Early Treatment of Diabetic Retinopathy Study)6 funded by the National Eye Institute in the United states. The ETDRS employed the logMAR design to measure VA in the most reliable, standardized and reproducible way. Today, the ETDRS chart is preferred to the traditional Snellen chart (in use since 1862) whenever precise measurement of visual acuity is necessary in research or clinical settings.

The Sloan letters are equally discriminable, similar to Landolt “Cs”. Each row of the ETDRS chart uses a combination of letters with a global difficulty similar to the other rows. In total, 28 combinations of letters of equal difficulty are used.6 This distribution of letters was based on a study carried out by the designers of the optotypes using data from 234 eyes. This study gave rise to the original ETDRS optotypes that are currently used internationally.6

Subsequently, the authors themselves reviewed the difficulty of the Sloan letters and used the results from 7,420 eyes to slightly adjust the combinations of Sloan letters in each row, resulting in “revised” ETDRS letters 7. In theory, these new combinations are slightly more balanced in difficulty. The vision unit allows you to choose between “original” or “revised” Sloan letters (using the configuration menu).

Original

Revised

 

This Sloan letters were selected by the International Council of Ophthalmology8 as the reference optotype for VA measurement, and have since been used as a standard in research studies.

« VA OptotypesBritish Letters »
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