Eye-Cup. A patch of light-sensitive receptor cells sunk into the skin present in some species.
Ocular Dominance Columns
The primary visual cortex (V1) is organized into alternating columns sensitive to input from the left and right eyes.
(See also Hypercolumn
and Orientation Columns).
On-Center Cells
Increase their activity when light increments are presented in their receptive files. Surrounded by an antagonistic region which responds with the opposite polarity. Both ganglion and bipolar cells are separated into two classes, on-center and off-center. The on-center cells have dendrites that branch in the inner portion of the inner plexiform layer.
(See also Off-Center Cells).
Off-Center Cells
Decrease their activity when light increments are presented in their receptive fields. Surrounded by an antagonistic region which responds with the opposite polarity. Both ganglion and bipolar cells are separated into two classes, on-center and off-center. The off-center cells have dendrites that branch in the outer portion of the inner plexiform layer.
(See also On-Center Cells).
Opsin
Protein portion of rhodopsin.
Opthalmoscope
Device for seeing light reflected from the interior of the eye. First built by Hermann von Helmholtz.
Optic Chiasm
Location where the optic nerve axons from the two retinae join and are reorganized into two separate groups (the optic tracts) that encode information about the right and left visual fields.
Optic Disk
Where the ganglion cell axon fibers leave the retina. Contains no photoreceptors and therefore creates a blind spot in the visual field.
(See Figure).
Optic Nerves
Myelinated axons from the optic disk of each eye which join at the optic chiasm.
(See Figure).
Optic Radiations
Projections from LGN to primary visual cortex (V1).
Optic Tectum
Structure in the mid-brain of cold-blooded vertebrate that receives input from the optic nerve (homologous to the superior colliculi)
Optic Tract
Retinal fibers leaving the optic chiasm separated by visual hemi-field (i.e. not by eye). Projects to three areas, the pretectum, the superior colliculus and the LGN.
(See Figure).
Optical Power (of a lens)
Measure of how strongly a lens bends incoming rays. Measured in
diopters and equal to the reciprocal of focal length. Human eye has
an optical power of about 58.8 diopters.
(See also Diopter).
Optokinetic Reflex
Elicited by coherent movement of a large region of the visual field.
Helps stabilize the visual scene on the retina.
(See Optokinetic Nystagmus).
Optokinetic Nystagmus
Eye movements characterized by a series of smooth movements in the
same direction of a moving visual scence interspersed with rapid
movements in the opposite direction.
(See also Optokinetic Reflex).
Optomotor Response
The turning response of an animal presented with uniform flow of optic texture in the direction which minimizes rate of flow relative to the animal.
Orientation Columns
The primary visual cortex (V1) is organized into narrow columns (from pial surface to white matter) containing cells with almost identically the same orientation preferences.
(See also Hypercolumn
and Ocular Dominance Columns).
Oreintation Selectivity
Cells which have oriented receptive fields, responding more for some orientations than others.
