Comparison of Four Methods for Entering the Gap Position of Landolt Cs

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.

Inclusion criteria

• Age: ≥ 18 years
• Informed consent
• (Distance) visual acuity with best correction: ≥ 0.8
• (Distant) ametropia: ≤+8.0 Diopters (spherical equivalent)
• Anisometropia ≤ 3 dpt
• Astigmatism ≤ 2.5 dpt

Exclusion criteria

• Prolonged reaction time caused by drugs (medications)/ drugs/alcohol
• Movement disorders (of hands) such as Parkinson's disease
• Indication of amblyopia (strabismus surgery, occlusion therapy etc.)
• Eye movement disorders/double vision
• Defective stereo vision (according to LANG [I] stereo test)
• Presence of a relative afferent pupil defect ("swinging flashlight test)
• Any hint of visual pathway lesion or other chronic or progressive eye disease