Contrast enhancement of the retinal image and image distortion associated with macular degeneration.
An analysis of image distortion in connection with macular degeneration revealed that seeing objects requires brightness contrast enhancement. Thus macular degeneration changes neural interaction controlling bipolar cell responses to light stimulating photoreceptors to reverse spatial brightness contrast enhancement with the consequence that objects cannot be seen. This shows that the contrast of the retinal images is too low for vision without enhancement. However images consisting of randomly arranged small spots of different brightness are seen because of cones enhancing bipolar cell responses to rod input and rods enhancing bipolar cell responses to cone input. This residual vision and the observation that image distortion disappears at low light intensities reveal that macular degeneration is a functional disorder with intact photoreceptor function. The affection may therefore be caused by a reduction of blood flow through the choriocapillaries associated with ageing. The analysis of image distortion associated with the affection led to a simple way to determine the size of the affected retinal area, making it possible to follow the progression of the affection in a direct and simple way. Basic aspects are described of synaptic interaction within the information processing unit that determines the responses of the bipolar cells to photoreceptor input. This unit is the first information processing unit that has been revealed thanks to the extension of the analysis of the nervous system to the nanometer level at which information is processed. The minute size of the information processing unit, the special conditions for synaptic transmission combined with the short distances separating the synapses create special conditions for neural interaction at the nanometer level, establishing conditions for high speed neural communication.
Sjöstrand
F S
FS
Department of Biology, University of California, Los Angeles, CA, USA. fsjostra@ucla.edu
D000818:Animals; D002829:Choroid / Q000098:blood supply / Q000502:physiology; D015350:Contrast Sensitivity; D006801:Humans; D008029:Lighting; D008268:Macular Degeneration / Q000473:pathology / Q000503:physiopathology*; D008564:Membrane Potentials / Q000502:physiology; D010469:Perceptual Distortion; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology; D012160:Retina / Q000503:physiopathology*; D014792:Visual Acuity