13 - Vision 1 Flashcards
How does feature detection differ from adaptation?
feature detection is detecting specific features with specific neurons in your vision such as edges
and adaptation is the ability to focus on changes in your environment and damped down neural signals for constant feature
Why is feature detection important? and for survival?
because brain cant construct a neural model for everything in visual field thus feature detection highlights important things (dangerous objects -> survival)
Function of iris?
What is pupillary dilation/constriction triggered by? What is this ^ process called?
-control amount of light entering eye
-constriction by increasing levels of light vice versa
-reflex
Where is image focussed on?
retina
As the iris contracts, what happens to light levels entering the eye and VISUAL ACUITY?
light levels decrease and visual acuity increases
Whys is there less visual acuity in the dark/pupil dilation?
more light is able to enter the eye but each (and every) point projects to a LARGER area on the retina and these areas overlap, creating BLURRING
What happens to change in pupil diameter as you get older?
ability to dilate decreases thus accommodation dynamics slow down
What function do the lens and cornea have in common?
What is the difference between cornea and lens ability to do this function?
What is accomodation?
-work together to focus the image on the retina by refraction light entering eye
-cornea refractive index stays constant whereas lens changes AND cornea contributes to 75%
-the ability of the lens to change shape to adjust the focal distance and focus the image on the retina
Function of zonules?
For close objects, what is the required shape of the lens?
-suspensory ligaments that hold lens in place
-thicker when closer
Where are the fovea and macula located?
What happens to vision during macular degeneration?
-fovea at the centre of the macula (macula located at very centre of retina)
-black spots in central vision
What cells are present in fovea?
What does this allow fovea to be?
-only a very high density cones (no rods)
-point of highest visual acuity
How can you explain physiologically why stars disappear when you focus directly on one?
when you fixate on something/star, you position image on fovea and fovea has no rods and high density of cones
What is optic disc aka?
What is the process of completion?
blind spot
how the bran compensates for the absence of photoreceptor at the blind spot by filling in the gap with information from neighbouring photoreceptors
What is sclera and function?
What is choroid and function?
-the white of the eye and is a protective layer of tissue
-tissue between retina and sclera to hold all the blood vessels i
Why do you get a red eye in a camera flash ?
-flash is reflects the blood vessel in choroid
Where are photoreceptors and retinal ganglion cells located in retinal layering?
Why is the order of cells in the retinal layers the ‘wrong’ way around in vertebrates?
-photoreceptor at back and retinal ganglion cells at front
- would need larger eyeball to get correct focal distance for accomodation
What are three main layers of cells in retina?
What are the additional cells?
- retinal ganglion cells
- bipolar cells
- photoreceptors
-interneurons: amacrine and horizontal cells
Which cells in retina perform visual transduction? What is visual transduction?
-photoreceptors
-converting sensory light information to neural signals
What is the function of rhodopsin in rods when there are high levels of light?
-what cell is rhodopsin found in
-what is relationship between Na+ channels and cyclic GMP
rhodopsin is a protein found in rods (and cones) which is active in light conditions and breaks down cyclic GMP, causing Na+ channel closing. Rod is hyperpolarised and and glutamate release is reduced
Which photoreceptor works for scotopic and photopic vision?
How does rods have high convergence and cones have low convergence? what effect does this have on visual acuity and sensitivity?
rod - scotopic and cone - photopic
- MANY rods connect to one bipolar cell (low acuity, good sensitivity
cones vice versa (one to one connectivity)
Are rods or cones responsible for central or perihperal vision?
rods peripheral
cones central (fovea)
What are the three colour that cones detect?
red green blue
If you have 2+ photoreceptors, what can you differentiate?
can differentiate wavelength of light from light intensity
What is colour blindness caused by?
What is the most common colour blindness?
-altered sensitivity of cone or complete absence of cone
-deuteranomaly red-green colourblind
