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Institute
Purpose
Automated scanpath comparison metrics should deliver an objective method to
evaluate the similarity of scanpaths. The aim of this thesis is an evaluation of
seven existing scanpath comparison metrics in static and dynamic tasks in order
to provide a guidline that helps to decide which algorithm has to be chosen for a
special kind of task.
Methods
The applicability of the algorithms for a static, visual search task and a dynamic,
interactive video game task as well as their constraints and limitations were tested.
Therefore, binocular gaze data were recorded by using the eye tracking system The
Eye Tribe (The Eye Tribe ApS, Copenhagen/ Denmark). Objective task performance
measures from 21 subjects were used in order to create scanpath groupings
for which a relevant effect of dissimilarity was to be expected. Objective task performance
measures such as task performance time were statistically evaluated and
compared to the results gained by the comparison metrics.
Results
Four of the algorithms being used successfully identified differences for static and
dynamic tasks: MultiMatch, iComp, SubsMatch and the Hidden Markov Model.
ScanMatch was very sensitive for the static task but not applicable to the dynamic
task whereas FuncSim was suitable for dynamic but not for static tasks. Eyenalysis
failed to detect any effect.
Conclusion
The applicability of scanpath comparison metrics depends on the state of the task,
respectively on the kind of experimental set up. In future, the application area for
eye tracking will expand and an improvement of automated scanpath comparison
metrics is therefore required.
Purpose: Although the frequency in which practitioners are fitting scleral
contact lenses is increasing, the recommendation for proper tear layer depth
(thickness) varies amongst experts. The main goal of this paper is to clinically
verify the effect of varying tear layer depths on induced corneal edema during
lens wear.
Methods: Ten subjects with healthy eyes were fitted with scleral lenses on their
right eye. Each of them was fit with two different lenses: one with an apical
clearance of 200 μm and another with an apical clearance of 600 μm. They wore
the lenses for 8 hours on two different days, with at least a one week wash-out
period. Lenses were applied at 8 a.m. on each of the testing days. Pachymetry
measurements were taken one day prior to lens wear at 4 p.m., on the day of
wear prior to lens application, and after removal of the lenses at 4 p.m.
Measurements were collected using both the Pentacam® HR Corneal
Tomographer, as well as the Visante Anterior Segment Optical Coherence
Tomographer (OCT). The apical clearance was measured using the
Visante OCT at two intervals during the test day: immediately after application of
the lens and immediately prior to the removal of the lens.
Results: In this study, there was found to be no significant difference in corneal
edematous response during lens wear between the two test groups. The study
shows that the eyes with the lenses have a statistically significantly thicker
cornea compared to the non-lens-wearing eye after wearing either lens for 8
hours, lying within clinically and physiologically acceptable limits.
Conclusion: Our clinical results do not correlate with current theoretical
calculations, which predict a greater amount of corneal swelling with increasing
tear layer thickness. It has to be evaluated if the effect on corneal edema
changes with longer wearing periods, larger samples or other influences.
Key words: scleral (contact) lens, corneal edema, pachymetry, tear layer
thickness, vaulting, apical clearance