Visual Systems Flashcards
What is white light?
All the wavelengths of the visible light spectrum together
What are Purkinje images?
Reflections of objects off the structure of the eye. Can be used in eye tracking.
In what part of the eye do axons leave and blood vessels enter?
The optic disk, also known as the blind spot
What are zonule fibres?
They are fibres that are extended around the eyeballs. Connected to ciliary muscles.
What are the ciliary muscles?
Donut shaped muscles that are connected to zonule fibres. It can change the shape of the lens by contracting and relaxing, for viewing objects at different differences. They also regulates the flow of aqueous humour into Schlemm’s canal.
What are the sphincter pupillae?
The iris of the eye. It can contract and dilate the pupils.
What is refraction power and what are its units and equation?
is the degree to which a lens, mirror, or other optical system converges or diverges light. It is in diopters and can be calculated by the reciprocal (1/x) of focal distance in inverse metre m−1, which is the diopter unit.
What is the far point?
The distance where the lens (flattened) begins to have a role in focussing.
What is the near point?
The distance within which accommodation of lens begins to not be good enough. It is as round as it can get. Aging degenerates the ability to make the lens ‘fat.’
What is emmetropia?
The normal healthy state of refraction in the eye.
What is hyperopia? How can it be corrected?
A developmental problem where eyeball is too short. The cornea is shape for normal eye, which means it focuses light beyond the retina. It can be fixed with convex lenses. and is common. (farsightedness)
What is myopia?
Nearsightedness. The eyeball is too long, refraction of cornea is too strong, focuses picture in front of the retina.
What is the binocular visual field? Which type of animals have a wide field and which have a narrow one?
An area of overlap between two fields. ANimals with frontal facing eyes (like humans) have narrow fields, animals with side facing eyes have a wider field (like rabbits). An advantage to having a narrow binocular field of view is the ability of stereopsis (being able to see depth)
Which cells send action potentials in the retina (the only ones)?
Ganglion cells.
What type of potentials do non-ganglion cells in the retina make?
Gradient potentials
What are the inner and outer nuclear layer?
They contain all the nuclei of the photoreceptors (in outer) and the nuclei of bipolar, horizontal and amazcrine cells in the inner nuclear layer
How much more sensitive to light are rods than cones? Why?
About 1000 times, because they have many more disks and photopigment
What is the ratio between photoreceptors and ganglion cells in the fovea and in the periphery?
About 1:1 in the fovea, many photoreceptors to 1 ganglion in the periphery (leading to greater sensitivity to light in the periphery.
Where is the greatest number of rods found?
Just outside the fovea, tapers off in numbers to the edge of the periphery
How are does rod to ganglion information about light become ambiguous?
Multiple rods triggering one ganglion creates ambiguity.
Where is there the greatest absolute density of photoreceptors on the retina? What is the consequence of this?
The fovea. Good two point accuity.
What 3 structural features of the fovea increase two point accuity?
1:1 ratio of photoreceptor to ganglion cells
Absolute density of photoreceptors
Fovea ‘pit’ that provides a less obstructed path for light
When does a rod photoreceptor secrete neurotransmitter? From what? What is the rods response to light? What is its membrane potential in light?
In the dark. From an influx of sodium causing a receptor potential from depolarization. A rod hyperpolarizes in the presence of light to about -60 mV.
The shifting concentration of _____ in light/dark are responsible for the depolarization and hyperpolarization of rods.
cGMP
What are the components of rhodopsin?
opsin protein and retinal vitamin (retinal)
What happens to rhodopsin in light?
The retinal molecule changes shape. Its tail straightens out and bleaches from purple to yellow. This conformational change activates the opsin, which causes cGMP to be converted to the inactive GMP, leading to closed sodium channels.
What is the first molecule that rhodopsin interacts with in light/dark conditions? What activates this molecule and what does this molecule activate?
A transducin G protein. The G protein is activated when rhodopsin is activated, and then the G protein activates phosphodiesterase. Phosphodiesterase convertes cGMP to GMP. The decrease in cGMP concentration results in sodium channels closing.
What is the molecule that directly opens the sodium channels in photoreceptors? What converts this molecule to its inactive form?
cGMP. Converted to GMP by phosphodiesterase.
What wavelength of light do red cones absorb?
560 nm
What wavelength of light do green cones absorb?
530 nm
What wavelength of light do blue cones absorb?
430 nm.
What wavelength of light are rods most sensitive to?
498 nm and around
How long does it take to switch from photopic to scotopic vision?
About 25 minutes
How long does it take to switch between scotopic to photopic vision?
5 minutes
Why are you colour blind at night?
Because there is not enough light to activate cones.
What type of cell is responsible for the surround receptive field being different from centre?
Horizontal cells reverse ON/OFF signal