Programm                 "Degeneration und Regeneration– Grundlagen, Diagnostik und Therapie"

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Retinal Image Processing for the Control of Axial Eye Growth and Refractive Development

Seidemann A.
Section of Neurobiology of the Eye, University Eye Hospital, Dept. II, Tübingen

Purpose: Experiments in animal models for myopia have shown that refractive development is under visual control. It is a fundamental question for the understanding of myopia how the underlying neural image processing looks like and where it takes place.
Method: The animal model of the chicken was used. Retinal images were low pass filtered either with frosted eye occluders or by presenting low pass filter video sequences. Spectacle lenses were used to impose different amounts of defocus which could be even better defined if the animals were individually placed in a drum with only one viewing distance. Contrast sensitivity and contrast adaptation were measured by automated recording of the optokinetic nystagmus.
Results: It is sufficient to low pass filter the retinal image to induce "deprivation myopia". However, only 30 min interruption of deprivation per day reduces myopia by 50% and several short intervalls of interruption are even more effective than one longer period. Imposed defocus produces compensatory axial eye growth, even if only one viewing distance is available and if accommodation is abolished. Both deprivation and defocus confined to local retinal areas cause local changes in eye growth, even with the optic nerve cut. Defocus imposed by positive lenses has much faster and stronger effects on eye growth than by negative lenses (ratio 5:1). Defocus produces contrast

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