Glossary of Sports Vision Terms

Glossary

Work In Progress!

(click the back button on your browser to return)

Snellen Test

A Snellen test uses a chart with different sizes of letters or forms to evaluate your visual acuity-that is, the sharpness of your vision. The test shows how accurately you can see from a distance

More about Snellen test, test yourself

Para-central visual field

The visual field is the total area in which objects can be seen in the peripheral vision while the eye is focused on a central point.

Dynamic Sensory Perception

Dynamic Acuity

Peripheral Vision

Spatial Perception

Contrast Sensitivity

Colour Definition

Visual Stamina

Stereopsis

3D vision, binocular vision and stereopsis all mean the same thing: The power of the visual sense to give an immediate perception of depth on the basis of the difference in points of view of the two eyes. It exists in those animals with overlapping optical fields, acting as a range finder for objects within reach. There are many clues to depth, but stereopsis is the most reliable and overrides all others. The sensation can be excited by presenting a different, properly prepared, view to each eye. The pair of views is called a stereopair or stereogram, and many different ways have been devised to present them to the eye. The appearance of depth in miniature views has fascinated the public since the 1840's, and still appears now and then at the present time. There was a brief, but strong, revival in the 1990's with the invention of the autostereogram. Stereopsis also has technical applications, having been used in aerial photograph interpretation and the study of earth movements, where it makes small or slow changes visible.

Visualisation Strategies

Visual Recognition and

Sequencing

Ocular health

Visual acuity

The sharpness of your vision -how accurately you can see from a distance

See Snellen Test

Depth perception

Fusional abilities including Phorias and fixation disparity

Neuro-muscular action

Accommodative abilities

Foveal system

It is a small pale spot, about the size of a pinhead in the retina - the back of the eye. All the cone sensors of the retina are concentrated in this area . and, on our big picture, is in the darkened area just to the right of the optic disc - it has been electronically enhanced in this image. It is totally responsible for our colour vision and our critical vision.

Cone cells

Cone cells, or cones, are cells in the retina of the eye which only function in relatively bright light. There are about 6 million in the human eye, concentrated at the fovea. They gradually become more sparse towards the outside of the retina.

Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of colour. They are also able to perceive finer detail and more rapid changes in images, because their response times to stimuli are faster than those of rods. Because humans (normally) have three kinds of cones, with different photopsins, which respond to variation in colour in different ways, we have three colour (trichromatic) vision.

Rod Cells

Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of photoreceptor, cone cells. Since they are more light-sensitive, rods are responsible for night vision. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina (see peripheral vision). There are about 100 million rod cells in the human retina.

A rod cell is sensitive enough to respond to a single photon of light. Since rods require less light to function than cones, they are therefore the primary source of visual information at night. Cone cells, on the other hand, require tens to hundreds of photons to become activated. Additionally, multiple rod cells converge on a single interneuron, collecting and amplifying the signals. This convergence comes at a cost to visual acuity, however, since the pooled information from multiple cells is less distinct than if the visual system received information from each rod cell individually. The convergence of rod cells also tends to make peripheral vision very sensitive to movement.
Rod cells also respond more slowly to light than do cones, so stimuli they receive are added over about a hundred milliseconds. While this makes rods more sensitive to smaller amounts of light, it also means that their ability to sense temporal changes (such as quickly changing images) is less accurate than that of cones.

Magnocellular Pathway

Paramacular

(click the back button on your browser to return)