Preface

During the preparation of a congress in Switzerland inm 2008 the article presented here was written in German language. Most of the data included here are still unpublished. Under natural viewing conditions and in certain situations it is neccesarry to maintain fixation at a certain point of interest and to stopp fixation, when another saccade must be generated. Fixation therefore is an active process in the brain. Its role in the diagnosis of vision has been neglected for a long time not only in neurosciences of eye movements and vision, but also in Optometry and Ophthalmology.

The article refers only to the most important and closely related literature and is far from complete. Comments are welcome anytime.

An English version of the full article is being prepared and will be available here.

Contents

• Introduction
• Methods
• Results
• Binocular instability
• Eye dominance of the binocular instability
• Simple instability (involuntary saccades)
• Monocular optomotor training
• Poor reflex control (express saccades)
• Training of reflex control by training fixation
• The optomotor cycle
• Discussion
• References

Summary

While eye movements as a neccessary prerequisite for natural viewing become more and more important in the diagnostic, fixation is not as established. This article deals with 3 different and independent types of instability of fixation, which can only be recognized by recording and analysing eye movements: (i) the binocular instability, (ii) simple instability = involuntary saccades during periods of fixating a stationary fixation point, (iii) excessive optomotor reflexes (express saccades) among goal directed saccades in the presence of a fixation point. The diagnostic data from children suffering from dyslexia are compared with those of age matched controls. The third almost unknown typ of fixation instability is demonstrated by the data of two "express makers". They produce reaction times shorter than those of age matched controls. In an antisaccade task they exhibit enhanced percent numbers of errors. A special optomotor training with one eye covered improves the binocular instability, an exclusive fixation training reduces the chances of express saccades, but both trainings hardly reduced the number of involuntary saccades. The results indicate that the types of fixation instability are independent from each other.