Mechanisms mediating avian eye growth

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Near-sightedness (myopia) develops when eyes grow too long for their optics.  In addition to certain visual cues, accommodation, the act of focussing on nearby objects has been implicated  as a driving force for myopia development in humans.  The lens is the structure in the eye that controls focussing and the retina is the structure that controls eye growth.  The long-term aim is to determine how the lens and retina interact to control eye growth.  The short term goals are to first determine the cellular mechanisms underlying how the retina and lens function.  The work will be carried out on two fronts, 1) by examining how eyes with altered retinas respond to environmental growth signals and 2) by examining how the cells of the lens control, or are controlled by focussing.  Chicks will be used for these studies because, like humans, they are diurnal, have colour vision and focus by deforming the lens.  1) CELLULAR CHANGES TO THE RETINA - Disconnecting the eye from the brain by severing the opitc nerve not only removes the drive to focus but also results in a shorter than normal eye, indicating altered eye growth.  Optic nerve-section also results in loss of some cells in the retina therefore optic nerve-sectioned eyes will be used to probe how and which cells of the retina control eye growth in response to visual signals.  2) CELLULAR CHANGES TO THE ACCOMMODATING LENS - Studies suggest that subcellular structrual proteins within the lens might impart contractile activity to the lens.  In addition, mechanical stress has been shown to induce biochemical activity within other cells, yet studies of the cellular changes that affect and are affected by a deforming (mechanically stressed) lens have been neglected.  An accommodation model, which allows direct measurement of the lens during nerve-stimulated focussing, will be used to investigate how the subcellular structures of the lens are affected by naturally-induced mechanical stress and other growth-related changes to the eye.