PPVK - Vision1 Flashcards
Light
a narrow band of electromagnetic radiation that can be conceptualized as a wave or a stream of photons
Photon
a quantum of visible light (or other form of electromagnetic radiation) demonstrating both particle and wave properties.
Absorbed energy
energy that is taken up and is not transmitted at all
Scattered energy (raspršena e.)
→energy that is dispersed in an irregular fashion
→Rayleigh scattering
gives the sky its colour
energija koja se raspršuje na nepravilan način
Reflected light
→ energy that is redirected when it strikes a surface, usually back to its point of origin
→ the most informative kind of light for visual perception
Transmitted light
energy that is passed on through a surface (neither reflected nor absorbed by the surface)
Refracted light
→ energy that is altered as it passes into another medium
→ when light passes from air into water or into the eyeball
Cornea
the transparent “window” into the eyeball
Aqueous humor
the watery fluid in the anterior chamber
Crystalline lens
the lens inside the eye, which focuses light onto the back of the eye.
Pupil
→ the dark circular opening at the center of the iris in the eye, where light enters the eye
Iris
the colored part of the eye, a muscle that regulates the amount of light entering the eye by expanding and contracting the pupil
Vitreous humor
the transparent fluid that fills the large chamber in the posterior part of the eye
Where seeing really begins?
Retina
Transduction
light energy is turned into electrical neural signals
Retina (mrežnica)
→a light-sensitive membrane in the back of the eye that contains rods and cones
→ the lens focuses an image on the retina
→ then sends signals to the brain through the optic nerve
→ motion, color, edges, and shape are all processed by specialized groups of cells in the retina
Refraction
focusing light rays on to the retina accomplished by the lens
Accomodation
the process in which the lens changes its shape, thus altering its refractive power; change in focus
Presbyopia “old sight”
the age-related loss of accommodation difficult to focus on near objects
Emmetropia
no refractive error
Myopia (nearsightedness)
when light is focused in front of the retina and distant objects cannot be seen sharply
Hyperopia farsightedness
when light is focused behind the retina and near objects cannot be seen sharply
Astigmatism
unequal curving of one or more of the refractive surfaces of the eye, usually the cornea.
Fundus
back surface of patients’ eyes
Photoreceptors
Cells in the retina that transduce light energy into neural energy
Rods (Štapići)
- photoreceptors specialized for night vision (90mil)
- respond well to low luminance conditions
- do not process colors
Respond well in low luminance conditions
Rods
Cones (Čunjići)
- photoreceptors specialized for daytime vision, fine visual acuity, and color (5 mil)
- respond best in high luminance conditions
Respond best in high luminance conditions
Cones
What is the pathway of light and signal transmission through the retina, from light entry to signal exit?
- Light passes through layers of cells to reach rods and cones (photoreceptors).
- Activated photoreceptors signal horizontal and bipolar cells.
- Bipolar cells connect to amacrine and ganglion cells.
- Ganglion cell axons exit the eye via the optic disc (blind spot)
How is retinal size typically measured, and what factors determine visual angle?
Retinal size is measured in degrees of visual angle.
Visual angle depends on the object’s actual size and its distance from the observer.
Rule of thumb:
If you hold your thumb out at arms length, the width of your thumbnail is about 2 degrees of visual angle
What type of photoreceptors are mostly found in the fovea?
Cones
What type of photoreceptors are mostly found in the periphery?
Mostly rods
How is visual acuity in the fovea?
High
How is visual acuity in the periphery?
Low
How is light sensitivity in the fovea?
Low
How is light sensitivity in the periphery?
High
What type of bipolar cells are in the fovea?
Midget
What type of bipolar cells are in the periphery?
Diffuse
How is neural convergence in the fovea?
Low
How is neural convergence in the periphery?
High
What is the receptive-field size in the periphery?
Large
What is the visual function zone where both rods and cones are active?
Mesopic vision (Twilight vision)
In which visual range is there no color vision and poor acuity?
Scotopic - is the vision of the eye under low-light conditions
In which visual range do we have good color vision and best acuity?
Photopic
At approximately what luminance level does rod saturation begin?
Around 0 log cd/m²
What is the luminance threshold at which cones begin to function?
Cone threshold is around -2 log cd/m²
What happens to the retina at very high luminance levels (around 8 log cd/m²)?
Possible damage
What visual function dominates under moonlight conditions?
Mesopic
Photopigments
Pigments that undergo a chemical change when they absorb light.
What must happen to a photopigment after it detects a photon (is bleached)?
It must be regenerated before it can absorb another photon.
What happens to photopigments when more light enters the retina?
They are used up faster, leaving fewer available to process more light.
What happens to photopigments when less light enters the retina?
They are used up more slowly, so more remain available to process the light.
Photic sneeze reflex
successive sneezing induced by bright light
5 major classes of neurons in retina
photoreceptors, horizontal cells, bipolar cells, amacrine cells, ganglion cells
photoactivation
light hitting a photoreceptor
chemical changes that start a cascade of neural events ending in a visual sensation.
Function of outer, inner and synaptic terminal in photoreceptors
- outer segment (stores visual pigments pigments)
- inner segment (manufactures visual pigments)
- synaptic terminal (connection to other cells)
Cones work best in_________situations
Photopic - high illumination
Rods work best in___________situations
Scotopic - low illumination
What pathway in the retina is responsible for lateral inhibition (bočna inhibicija)?
The retina’s horizontal pathway, involving horizontal and amacrine cells.
Function of horizontal cells in retina
Horizontal cells run perpendicular to photoreceptors and contact both photoreceptors and bipolar cells.
They are responsible for lateral inhibition, which creates the center-surround receptive field structure of retinal ganglion cells.
Role of amacrine cells in retina
Amacrine cells run horizontally between bipolar cells and retinal ganglion cells. They are implicated in contrast enhancement and temporal sensitivity (detecting light patterns that change over time), though their precise function remains unclear.
Retinas vertical pathway:
photoreceptors, bipolar cells, and ganglion cells
Bipolar cell
*connected with one or more rods or cones and with horizontal cells
*passes the signals to ganglion cells
What is the function of a diffuse bipolar cell?
A diffuse bipolar cell receives input from multiple photoreceptors, resulting in convergence. This pooling of signals decreases acuity but increases light sensitivity.
the way your eyes move together and point inward when you look at nearby objects, such as books, tablets or smartphone screens.
What is the role of a midget bipolar cell in the retina?
A midget bipolar cell receives input from a single cone. Each foveal cone contacts two bipolar cells, resulting in divergence.
What happens to an ON bipolar cell in response to an increase in light?
An ON bipolar cell is excited and depolarizes in response to an increase in light captured by the cones.
What happens to an OFF bipolar cell in response to an increase in light?
An OFF bipolar cell is inhibited and hyperpolarizes in response to an increase in light captured by the cones.
How do ON and OFF bipolar cells contribute to retinal processing?
ON and OFF bipolar cells provide information about whether retinal illumination has increased or decreased.
Effect of low convergence in the fovea?
ensures high acuity but poor sensitivity to light
P ganglion cells(~70% of all ganglion cells in retina)
receive input from midget bipolar cells
→connect to the parvocellular pathway of LGN
-> parvocellular(„small cell”) pathway is involved in fine visual acuity, color, and shape processing; poor temporal resolution but good spatial resolution.
M ganglion cells (~10% of all ganglion cells in
receive input from diffuse bipolar cells
connect to the magnocellular pathway of LGN
magnocellular(“large cell”) pathway is involved in motion processing; excellent temporal resolution but poor spatial resolution
ON-center ganglion cells
Excited by light that falls on their center and inhibited by light that falls in their surround.
OFF-center ganglion cells
Inhibited when light falls in their center and excited when light falls in their surround.
Why do retinal ganglion cells (RGCs) have center-surround receptive fields?
Center-surround receptive fields help retinal ganglion cells (RGCs) respond best to spots of a particular size, with reduced response to spots that are too big or too small.
How do retinal ganglion cells (RGCs) act as a filter for information?
by responding best to stimuli that are just the right size and less to stimuli that are either too large or too small.
What are retinal ganglion cells (RGCs) most sensitive to?
differences in light intensity between the center and surround of their receptive field
How do luminance variations affect perception in the retina?
tend to be smooth within objects and sharp between objects, which helps the brain distinguish boundaries.
How do center-surround receptive fields emphasize object boundaries?
enhance object boundaries by emphasizing the contrast between the center and surround, helping to detect edges and transitions
