Comparison of Four Methods for Entering the Gap Position of Landolt Cs
Condition: Quality Control; Validation Study
Study type: Observational

Summary: 
      The aim of this study is to investigate and compare the validity of four different input
      methods for Landolt Cs, i.e. the proportion of correct gap positions in relation to the total
      number of performances. The four input methods are a numeric keypad, an eight-positions
      rocker switch, a remote control and voice feedback.
    

Detailed description: 
      The measurement of visual acuity is the most frequent and one of the most important
      ophthalmological functional investigations. Therefore, it is particularly important to find a
      measuring procedure with as little input errors as possible.

      The 8-position Landolt C (LC) is the internationally accepted, well-standardised optotype for
      the determination of visual acuity.

      Usually, the subjects informs the examiner verbally about the perceived position of each LC.
      According to the current literature, about 20 to 30 % of the population suffers from a
      right/left weakness. Furthermore, language barriers are an additional considerable hurdle.

      Therefore, it is important to find an input method for the LC gap positions with minimal
      entry mistakes. In oder to avoid the thresholding procedure and its inherent difficulties,
      highly supra-threshold (10 times above the previously determined individual central visual
      acuity threshold) 8-position LCs are presented.

      The study compares four input methods for entering of the Landolt C gap positions: a modified
      numeric keypad, an 8-position rocker switch, a modified TV remote control and voice/verbal
      feedback.

      Each subject will perform all four input methods, with 2 test runs of 16 Landolt C
      presentations, each. A forced-choice method will be applied, i.e. the test is not continued
      until the test person has responded ot each single presentation. Regardless of whether the
      entry was correct or incorrect, the next Landolt C is displayed.

      The optotypes are presented using modified version of the Freiburg Visual Acuity and Contrast
      Test (FrACT), which allows to present the 8-position Landolt Cs in a standardized way on a
      video display unit (VDU).

      The sequence of the input methods is randomized. This study is carried out in a
      "within-subject design", i.e. all test persons go through all test conditions and serve as
      their own controls.
    

Intervention name(s): Landolt C entry method
Intervention type(s): Diagnostic Test
Intervention description(s): Four different methods for entering the Landolt C gap position are compared
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Healthy, young subjects recruited for the students and or co-workers of the Aalen
        University of Applied Sciences
      
Keywords: psychophysics; visual acuity; response; response entry; validity; retest reliability; reproducibility; evaluation; optotype; Landolt C