Eye movements used for the objective assessment of contrast sensitivity

Abstract

Assessment of contrast sensitivity (CS) from eye movements has already been proposed as a possible method to gain objective information about this visual function. The currently submitted dissertation holding the title Eye movements used for the objective assessment of contrast sensitivity improves the currently proposed approaches of the eye-movement-based CS tests and proposes novel ones. The first project of this dissertation extends the applicability of microsaccadic rate signatures, already proposed as the tool for objective CS testing, into the clinical practice by stimulation of microsaccades under monocular conditions, while analyzing the eye movements as binocular events. In this approach an infra-red filter for covering the left eye of the tested subjects and an infrared eye-tracker were used, resulting in the stimulation of just one eye of the participant, however allowing the eye movement detection in both eyes. Because the microsaccadic events were found to be rare in some participants, the second project utilized optokinetic nystagmus in CS testing. In this project, the optokinetic nystagmus was detected in real-time when running the experiment, using a newly-developed life detection method, and along with a one-dimensional adaptive psychometric procedure (QUEST+) for the contrast level management enabled a fully automated CS examination. Furthermore, the examination was conducted for a range of spatial frequencies of a grating as well as a range of defocus conditions, replicating the well-known effects on CS from the clinical trials. The third project aimed to extend the eye-movement-based testing also to the peripheral visual field, and thus replicate the CS perimetry testing procedure in an objective way. In this project CS was tested using reflexive (reactive) saccades, occurring towards a newly presented target, which was located in one of the four cardinal directions in the patient’s visual field. Here the four independent QUEST+ psychometric procedures sought for the contrast threshold in the four directions individually, for each of the three tested eccentricity levels. Moreover, the measurements were conducted for the eye-movement-based and key-board-based measurements to run a rounded validation of this novel procedure, showing its feasibility for future clinical application. In conclusion, this thesis extends an improves the portfolio of eye movements used in CS testing, shows novel approaches to improve the time efficiency, and replicates the well-known effects from the clinical trials.