VISUAL ACUITY AND AMBLYOPIA

Amblyopia Treatment Study (ATS) Protocol

Download at Apple Store Download at Google Play

We recommend using the App in an iPad Retina because this has been the device used during the studies of clinical validation. Although the App is available for Android, the users who use tablets with this operating system should take special attention to the correct retrieval the pixels per inch from their devices. On the other hand, the visual acuity measure could be erroneous. 

Click on any of the options in the navigation menu below for accessing to all the details of the App

VISUAL ACUITY AND AMBLYOPIA

Amblyopia Treatment Study (ATS) Protocol

Download at Apple Store Download at Google Play

We recommend using the App in an iPad Retina because this has been the device used during the studies of clinical validation. Although the App is available for Android, the users who use tablets with this operating system should take special attention to the correct retrieval the pixels per inch from their devices. On the other hand, the visual acuity measure could be erroneous. 

Click on any of the options in the navigation menu below for accessing to all the details of the App

Introduction

DESCRIPTION

The AmblyopiaVA is a test based on the Amblyopia Treatment Study Protocol for measuring visual acuity in children with Amblyopia.

CLINICAL APPLICATIONS

This test is recommended for using especially in the follow-up of treatments for which a very good inter-session reproducibility is required. For instance, in the treatment of Amblyopia we can obtain a visual acuity variation not due to the treatment but to the test variability in the visual acuity measurement, either in favor or opposite to the desired results. With an automated test, you avoid the inter and the intra experimenter variability improving the reliability of the results

BASIS

Studies performed with this test have demonstrated a better reproducibility that the standard ETDRS procedure with charts. The most interesting findings include: 

  • Fewer difference inter-eyes than the ETDRS. This is very important considering the definition of Amblyopia which establishes that should be at least a difference of one line of visual acuity between eyes with the best correction for the diagnosis.
  • Over-estimation of the visual acuity in comparison to ETDRS chart. Patients can achieve a mean visual acuity difference of 0.06 logMAR (three letters) better with AmblyopiaVA than with ETDRS. This is due to the psychophysical method of measurement and to the existence of only four letters (HOTV).
  • Less difference in the measurement of visual acuity inter-days. No significant differences were found for the same healthy subjects measured in three different days with the AmblyopiaVA. On the other hand, significant differences were found with the ETDRS chart. This means that the AmblyopiaVA can be considered preferable for controlling the evolution of a treatment. 

The AmblyopiaVA is a test based on the Amblyopia Treatment Study Protocol for children with Amblyopia. The details about this protocol are detailed below:

Binocular Screening (Optional)

This step should be performed binocularly with the best compensation of the patient and the main aim is to determine if the Monocular Screening can be later performed. It is directed to patients that have never performed the procedure and the visual acuity value on which the posterior Monocular Screening should start is calculated. 

Six random letters are presented to the patient for a visual acuity of 0.8 logMAR, if patient fails 2/6 (2 from 6), automatically the procedure is repeated for the visual acuity value of 1.3 logMAR. In the case that the patient fails less than 1 of the 6 presented letters, we can proceed with the monocular screening at 0.8 logMAR or 1.3 logMAR depending on the visual acuity level on which we had less than 1/6 mistakes. The binocular screening can be skipped if we previously knew that the visual acuity is better than 0.8 logMAR.

Monocular Screening

Before starting the monocular screening (one eye occluded) the visual acuity value for starting should be selected depending on the binocular screening result, either 0.8 logMAR or 1.3 logMAR. The monocular screening has different stages in order to optimize the time of the trial but without loosing reliability:

  1. Screening stage. The optotype reduces its size in -0.1 logMAR steps for each correct answer until the subject fails, a moment on which the Stage 1 starts. 
  2. Stage 1. This stage starts presenting 4 optotypes of equal size, corresponding to two lines above the visual acuity value on which the screening stage finished. In logMAR scale would be +0.2 logMAR considering that 0 logMAR is 1.0 in decimal visual acuity. If the patient gives a correct answer for 3/4, the optotype size is reduced -0.1 logMAR and the procedure is repeated until the ratio is under 3/4, a moment on which the Stage 2 starts. 
  3. Reinforcement. This stage has no influence in the final visual acuity value therefore has not been included in our test. 
  4. Stage 2. The procedure is the same than in Stage 1, except that if the success ratio is less than 3/4 the procedure ends, being the threshold the last one for which the ratio was 3/4. The ATS procedure has been summarized considering the main characteristics. During the procedure, the steps can change depending on the level of visual acuity on which the mistakes happen. For a complete description of the ATS procedure we recommend to read the original paper. 
REFERENCES

1. Rodríguez-Vallejo M, Llorens-Quintana C, Furlan WD, Monsoriu JA. Visual acuity and contrast sensitivity screening with a new iPad application. Displays 2016;44:15–20.

Instructions

01 Configure test settings

You can go to the settings layout by means of pressing the corresponding button at the button bar. In this screen you can select one of the next options:

You can go to the settings layout by means of pressing the corresponding button at the button bar. In this screen you can select one of the next options:

      1. Start visual acuity level (logMAR). This test includes a binocular screening that determines if it is possible to conduct the Monocular Screening and if so at which level we have to start. The binocular screening is not a required process in order to get the visual acuity threshold and it has been included in the application for clinicians who want to perform the procedure exactly as the ATS describes. We recommend to conduct the Monocular Screening starting in the 0.8 logMAR value.
      2. Optotype. The ATS standard uses a HOTV optotype, you can notice that the default settings of the test are selected according to the standard however you have the possibility to select other two optotypes, the Landolt C or the Snellen E. 
      3. Presentation Distance. The possible distances are 4, 3, 2, 1 and 0.40 m. At 0.40m the visual acuity is measured in 0.2 logMAR steps until new screens appear in the future with higher points per inch (PPI).
      4. Points per inch of your tablet. This is a very important setting that you have to check the first time that you are going to use the test. Please, check that the value corresponds to the PPI described by the manufacturer of your tablet. If the value is retrieved in a wrong way for your device, please insert the correct value in this field. 

02 Go back to home layout.

Once you have selected the test settings come back to the home layout to start the test and press monocular button in order to measure the visual acuity threshold. The binocular procedure is only to be conducted for clinicians who want to perform the test exactly as the ATS procedure describes. 

03 Monocular Visual Acuity Measurement.

Even though this procedure is called "Monocular" because the ATS uses this terminology, this does not mean that the test can only be performed in monocular vision. The monocular screening can be also performed with both eyes (Binocular). The clinician only has to press the letter corresponding to the answer given by the observer even though it is wrong. If the patient refers not recognizing the letter the clinician can press the empty field located at the bottom bar. This corresponds to a fail anwser. The clinician should continue the procedure until the Results page appears on the screen.

04 Visual Acuity Results Screen

The last screen shows the visual acuity threshold in logMAR units in the center and Decimal or Snellen notation at the bottom. 

 

Smartphone Instructions

DESCRIPTION

Bottom image shows the main screen of the App installed in a Smartphone. By pressing in the right button you will access to the setting for configuring the remote control. The remote control only runs when the Smartphone and the Tablet are conected in the same wifi network. Once, the remote control is configured you will able to select if the answer has been right or wrong sliding the finger over the screen as it is shown in the bottom right image. 

 

Updates

Version 3.2
        • The app has been completely reprogrammed.

Android

      • Please, if you are going to use the App in an Android device, ensure that the App retrieves properly the pixels per inch from your device. Uf this value is not properly retrieved, change it for the proper value. 
      • You can find a field for introducing this value in the setting layout. 
      • We recommend you to use the following webpage for computing the points per inch of your device (http://dpi.lv/). For any doubt, please contact us.