20/20 vision, which represents normal visual acuity using the standard
"E" letter chart, means that a person is able to identify
a line of small sized letters at a distance of 20 feet.
Commonly called lazy eye, amblyopia refers to a reduction or dimness
of vision that occurs with no apparent pathology.
Macular Degeneration (ARM)
See Macular Degeneration.
Cloudiness or opacity in the eye's lens or capsule.
The Channel Model equates visual cells to filters, or channels, that
pass a certain range of information to the human visual system for processing.
Refers to the ability of the visual system to distinguish between an
object and its background.
Refers to a testing methodology that involves the measurement and analysis
of the human visual system's ability to detect variances in the size
and contrast of objects. Contrast sensitivity testing is a qualitative
test, that is, it tests the functional vision, or how well individuals
see everyday visual objects or scenes.
known as 20/20 letter chart)
A standard visual acuity tool used in testing the optics of the eye
by measuring how well the eye is able to focus an image at a specific
distance. Also known as the Snellen eye chart, the E-chart uses black
letters on a white chart background. The E-chart test measures the quantity
of an individual's vision and scoring is based on the distance at which
an individual can accurately identify the tiniest set of black letters
(e.g., 20/20 vision). Also see Snellen eye chart.
Refers to the interaction of visual perception and the environment,
or how well individuals see in their everyday lives (e.g., while driving
or at work and play).
An eye disease characterized by changes in the optic nerve, head and
visual field. If left untreated, it may cause further damage to the
optic nerve and result in permanent vision loss.
An area of scholarly study and research that deals with functional vision,
or the interaction of visual perception and the environment. Human factors
experts focus on determining the functional significance of refractive
error or eye disease on a normally healthy visual system.
- Age Related (ARM)
Refers to the degeneration of the central area of the retina of the
eye leading to a loss of central vision.
A science that deals with ocular diseases. An ophthalmologist is a medical
doctor or eye surgeon who specializes in the treatment of eye diseases
A doctor of optometry is a primary eye care practitioner who evaluates
all aspects of a patient's vision including the diagnosis, management
and treatment of refractive errors and eye diseases.
Sine wave gratings are special test patterns for contrast sensitivity
testing. Sine-wave grating contrast sensitivity testing uses varying
sizes and contrasts of gray bars set up in circular patterns to test
an individual's ability to detect different gratings to identify the
individual's visual contrast threshold.
Snellen eye chart
Hermann Snellen, a Dutch doctor, invented the Snellen eye chart in 1862.
The Snellen eye chart tests an individual's visual acuity. Scoring is
based on the distance at which an individual can correctly identify
a tiny set of black letters on a white background. An average normal
vision score (20/20) is based on correctly identifying the smallest
set of black letters at a viewing distance of 20 feet.
Visual forensics deals with the use of functional vision as a standard
for the analysis of legal issues and visually based demonstrative evidence.
A field of study that deals with the mechanisms of the optics and retina/brain
system which transform an image received by the eye into neural code
for visual system processing. A vision scientist defines, measures and
assesses these mechanisms regarding visual perception and functional
Visual acuity refers to the measurement of the power of the eye and
is a quantitative measure of the eye's ability to see an in-focus image
at a certain distance. It is usually determined by having an individual
read letters of various sizes at a standard distance from a chart.