Once the calibration stages are complete, the patient is ready to start visual acuity measurements. The system tests distance vision first, followed by near vision. When ‘Finish and Save’ is selected, this will end each vision assessment and move to the next part. Within each assessment the ECP can determine which order they conduct the laterality and correction.
The default measurement output can be selected to be logMAR or number of ETDRS letters and either UK Snellen, US Snellen or Decimal Snellen. The default letter set can also be set from Sloan and Landolt-C, and crowding bars can be switched on or off.
Each measurement follows the same sequence: range finding followed by thresholding. Range finding presents in descending or ascending 2 logMAR line steps a single crowded letter or picture starting at logMAR .60 or 6/24 (20/80 in the US) size. Thresholding then follows where sequential rows of crowded letters are presented starting with a size 2 logMAR lines larger than the last incorrect range finding result. Each letter is scored and the test continues until the pass fail criteria have been satisfied.
Prior to each vision assessment, the ECP will choose the following settings:
Optotype: Sloan letter, Landolt-C
Scoring by: Single, line
Termination criteria: 1,2,3,4,5 out of 5
Crowding box: yes, no
Then select ‘Start’ to move to the next stage (figure 1).
If during a measurement, the ECP tries to change any of these settings, that measurement will be abandoned and the results will not be saved.
Selecting a vision measurement
Select the laterality and correction and then select ‘Start’ to begin the measurement (figure 2).
At this stage, ensure that the settings you have chosen are correct and ensure the patient is at the correct distance for the assessment:
Distance vision: 3m/10ft
Near vision: 40cm/16inch
Completing a vision measurement
Each measurement follows the same sequence: range finding followed by thresholding. A correct response is recorded by selecting the ‘tick’ icon. An incorrect response is recorded by selecting the ‘cross‘ icon. The following should be noted whilst scoring a measurement:
During range finding, the next letter/word will show as soon as the previous is marked as correct or incorrect
During thresholding, the letters/words are marked as correct or incorrect and then the ‘Next’ button must be selected to move on
The ‘Mark remaining results’ button will record any unmarked letter/word as correct or incorrect
Results can be overridden before the ‘Next’ button is selected
The ECP can highlight (underline) a specific letter/word for the patient by clicking on it
At the end of each measurements, results are visible in the table before a new measurement is started. Once all the desired measurements within each vision assessment have been completed, select the ‘Finish and save’ button.
During a distance vision assessment, this will end the distance vision stage and move to the near vision assessment (figure 6).
During a near vision assessment, this will take the ECP to the ‘Session completed’ screen (figure 7).
Before saving results, you will get the option to print the results at this stage. Reports of the whole assessment can be generated and printed via the AOS patient summary page after the VA session has ended.