Chapter 2 Flashcards
wave
An oscillation that travels through a medium by transferring energy from one particle or point to another without causing any permanent displacement of the medium.
photon
A quantum of visible light or other form of electromagnetic radiation demonstrating both particle and wave properties.
hue
The perceptual attribute of colors that enables them to be classed as similar to red, green or blue, or something in between.
scatter
To disperse something—such as light—in an irregular fashion.
refract
- To alter the course of a wave of energy that passes into something from another medium, as water does to light entering it from the air. 2. To measure the degree of refraction in a lens or eye.
cornea
The transparent “window” into the eyeball.
transparent
Referring to the characteristic of a material that allows light to pass through it with no interruption such that objects on the other side can be clearly seen.
aqueous humor
The watery fluid in the anterior chamber of the eye.
iris
The colored part of the eye, consisting of a muscular diaphragm surrounding the pupil and regulating the light entering the eye by expanding and contracting the pupil.
vitreous humor
The transparent fluid that fills the vitreous chamber in the posterior part of the eye.
retina
A light-sensitive membrane in the back of the eye that contains photoreceptors and other cell types, that transduce light into electrochemical signals and transmits them to the brain through the optic nerve.
acommodation
The process by which the eye changes its focus (in which the lens gets fatter as gaze is directed toward nearer objects).
focal distance
The distance between the lens (or mirror) and the viewed object, in meters.
diopter (D)
A unit of measurement of the optical power of a lens. It is equal to the reciprocal of the focal length, in meters. A 2-diopter lens will bring parallel rays of light into focus at 1⁄2 meter (50 cm).
presbyopia
Literally “old sight.” The age-related loss of accommodation, which makes it difficult to focus on near objects.
cataract
An opacity of the crystalline lens.
emmetropia
The condition in which there is no refractive error, because the refractive power of the eye is perfectly matched to the length of the eyeball.
refractive error
A very common disorder in which the image of the world is not clearly focused on the retina. The most common refractive errors are myopia, hyperopia, astigmatism, and presbyopia.
myopia
Nearsightedness, a common condition in which light entering the eye is focused in front of the retina and distant objects cannot be seen sharply. Nearsightedness, a common condition in which light entering the eye is focused in front of the retina and distant objects cannot be seen sharply.
hyperopia
Farsightedness, a common condition in which light entering the eye is focused behind the retina and accommodation is required in order to see near objects clearly.
astigmatism
A visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye, usually the cornea.
transduce
To convert from one form of energy to another (e.g., from light to neural electrical energy, or from mechanical movement to neural electrical energy). Neurons use electrical signals in their communication.
fundus
The back layer of the retina: what the eye doctor sees through an ophthalmoscope.
photoreceptor
A light-sensitive receptor in the retina.
macula
The pigmented region with a diameter of about 5.5 mm near the center of the retina. It is sometimes referred to as the macula lutea (from the Latin) because of its yellow appearance.
rod
A photoreceptor specialized for night vision.
cone
A photoreceptor specialized for daylight vision, fine visual acuity, and color.
fovea
A small pit located near the center of the macula and containing the highest concentration of cones and no rods. It is the portion of the retina that produces the highest visual acuity and serves as the point of fixation.
eccentricity
The distance between the retinal image and the fovea.
duplex
In reference to the retina, consisting of two parts: the rods and cones, which operate under different conditions.
visual angle
The angle that an object subtends at the eye.
receptive field
The region on the retina in which visual stimuli influence a neuron’s firing rate.
age-related macular degeneration (AMD)
A disease associated with aging that affects the macula. AMD gradually destroys sharp central vision, making it difficult to read, drive, and recognize faces. There are two forms of AMD: wet and dry.
retinitis pigmentosa (RP)
A progressive degeneration of the retina that affects night vision and peripheral vision. RP commonly runs in families and can be caused by defects in a number of different genes that have recently been identified.
outer segment
The part of a photoreceptor that contains photopigment
molecules.
inner segment
The part of a photoreceptor that lies between the outer segment and the cell nucleus.
synaptic terminal
The location where axons terminate at the synapse for transmission of information by the release of a chemical transmitter.
chromophore
The light-catching part of the visual pigments of the retina.
rhodopsin
The visual pigment found in rods.
melanopsin
A photopigment that is sensitive to ambient light; blue light probably; responsible for day night rhythm and melatonin release
photoactivation
Activation by light.
hyperpolarization
A change in membrane potential such that the inner membrane surface becomes more negative than the outer membrane surface.
graded potential
An electrical potential that can vary continuously in amplitude.
horizontal cell
A specialized retinal cell that contacts both photoreceptor
and bipolar cells.
lateral inhibition
Antagonistic neural interaction between adjacent regions of the retina.
amacrine cell
A retinal cell found in the inner nuclear layer that makes synaptic contacts with bipolar cells, ganglion cells, and other amacrine cells.
bipolar cell
A retinal cell that synapses with either rods or cones (not both) and with horizontal cells and then passes the signals on to ganglion cells.
diffuse bipolar cell
A bipolar retinal cell whose processes are spread out to receive input from multiple cones.
sensitivity
- The ability to perceive via the sense organs. 2. Extreme responsiveness to radiation, especially to light of a specific wavelength. 3. The ability to respond to transmitted signals.
visual acuity
A measure of the finest detail that can be resolved by the eyes.
midget bipolar cell
A small bipolar cell in the central retina that receives input from a single cone.
ON bipolar cell
A bipolar cell that depolarizes in response to an increase in light captured by the cones.
OFF bipolar cell
A bipolar cell
that hyperpolarizes in response to an increase in light captured by the cones.
ganglion cell
A retinal cell that receives visual information from photo- receptors via two intermediate neuron types (bipolar cells and amacrine cells) and transmits information to the brain and midbrain.
P ganglion cell
A small ganglion cell that receives excitatory input from single midget bipolar cells in the central retina and feeds the parvocellular layer of the lateral geniculate nucleus.
M ganglion cell
A ganglion cell resembling a little umbrella that receives excitatory input from diffuse bipolar cells and feeds the magnocellular layer of the lateral geniculate nucleus.
koniocellular cell
A neuron located between the magnocellular and parvocellular layers of the lateral geniculate nucleus. This layer is known as the koniocellular layer.
ON-center cell
A cell that increases firing in response to an increase in light intensity in its receptive-field center.
OFF-center cell
A cell that increases firing in response to a decrease in light intensity in its receptive-field center.
filter
An acoustic, electrical, electronic, or optical device, instrument, computer program, or neuron that allows the passage of some frequencies or digital elements and blocks the passage of others.
contrast
The difference in luminance between an object and the background or between lighter and darker parts of the same object.
