Topic 2- The Eye and the Retina Flashcards
What does the ability to see an object depend on?
The ability to see an object depends on visible light being reflected from that object into the eye
The light within the electromagnetic spectrum that we can see
What is this?
Visible spectrum
Shorter wavelengths we tend to see as BLANK, longer wavelengths are perceived as BLANK
blues, reds
The eyes contain BLANK BLANK for vision and BLANK light into perceptual information
sensory receptors, transform
What is the pupil of the eye?
Opening of the eye through which light from the environment enters
What is the sclera of the eye?
2 points
-The “whites” of the eyes
- Tough membrane; provides a protective coating
What is the cornea?
2 points
-Clear, transparent, outermost surface of the sclera that allows light to pass
- Begins the process of focusing light on to the back of the eye
What is the lens
2 points
- Adjustable focusing element of the eye
- Flexible; muscles change the shape of the lens to focus objects at different distances
What is the iris? Where is it located? What is a pupillary reflex?
5 points
- “Eye colour”
- Located just behind the cornea
- Controls the size and diameter of the pupil
- Controls the amount of light reaching the back
–> Pupillary reflex: Iris relaxes in bright light and contracts in dim light
What is the retina?
Light-sensitive surface at the back of the eye that contains the sensory receptors for vision - the photoreceptors
What are the two photoreceptors?
3 points each
Rods: cylinder shaped, vision at dim light levels, night vision
Cones: Cone-shaped, vision at bright light, colour vision, & fine detail
Outer segments contain….
light sensitive visual pigment molecules
What are optic nerves?
Bundles of millions of nerve fibers that carry signals from the retina into the brain
What is the peripheral retina? What does it contain?
3 points
- Retinal area “away from the center”
- Contains both photoreceptors types
- Many more rods though
What is the fovea?
3 points
- Region at the center of the retina that only contains cones
- Specialized for high visual acuity
- Vision is “sharpest” in the center of the visual field than in the periphery
Area at the back of the eye where axons forming the optic nerve leave the eye, and blood vessels enter/leave
What is this?
Blind spot
What two part system helps light focus on the retina and what percent is it divided into?
80% of the work is done by the cornea
20% of the work is done by the lens
How do lens accomplish changing its shape, increase curvature what muscle help do this?
Through ciliary muscles
What is the process of visual accommodation
2 points
- The ciliary muscles increase the curvature of the lens, this changes the lens shape
- This increase in curvature pulls the focus point forward, so things no longer look blurry
What are refractive errors?
Issues with the cornea or lens ability to focus incoming light onto the retina
- Often occurs in normal aging
- The ability to BLANK decreases; lens hardens and is less flexible
- In addition, the BLANK muscles weaken
What is this?
-accommodate
-ciliary
Presbyopia
Inability to see distant objects clearly
What is this?
Myopia
Since focusing on an image on the retina is the initial step in process of vision, where does vision actually occur?
In the brain
What is transduction? Where does it occur?
transformation of environmental energy into electrical energy
- Occurs in the photoreceptors
What are the two parts of photopigments that are contained in the outer segments?
When combined, what can the resulting molecule do?
3 points
Opsin- a long protein
Retinal- a smaller -light sensitive component
- When combined, the resulting molecule can absorb visible light
BLANK and BLANK control how the visual system adjusts to the dark and to dim level of light
Rods and cones
In dark adaptation, what increases over time and what is it associated with?
Sensitivity to light increases over time, which is associated with regeneration of the rod and cone visual pigments
Explain the dark adaptation curve in terms of what happens for rods and cones separately? What is a rod-cone break?
5 points
- The cones are much more sensitive to light at the beginning of dark adaptation
- Controls most of our vision during the first 5 mins and reaches max sensitivity rapidly
- The rods are much less sensitive to light at the beginning
- Controls most of vision later on
- Takes about 25-30 mins to reach max sensitivity
rod-cone break: The point at which vision in the dark shifts from cone vision to rod vision
Our BLANK to light at any point depends on the concentration of the BLANK visual BLANK that is present
sensitivity, unbleached, pigment
What is the rate of pigment regeneration in cones and rods during dark adaptation?
2 points
Cones pigments regenerate extremely fast in approx 5-6 min
Rods pigments regenerate much slower approx 25 mins
Why do object in dimmed light/dark lighting appear to be more blueish/green?
A tendency for sensitivity of the eye to shift towards the blue-green end of the colour spectrum at low levels of illumination/dimmed lighting.
Purkinje shift –> which is basically when rods are more sensitive to shorter wavelengths than cones
What happens as the signals travel through the retina?
Signals from the photoreceptors travel to BLANK cells and then to BLANK cells
bipolar, ganglion
How many rods vs cones are in the retina? (1 point)
What is the ratio of signals sent to ganglion? (2 points)
Do rods or cones converge more? (1 point)
What are the two differences in perception? (2 points)
- There are 120 million rods vs 6 million cones in the retina
- Means 120 million rods send their signal to a single ganglion cell (120:1) vs 6 million cones to a single ganglion cell (6:1)
- Rods converge far more than cones do
-Rods result in more sensitivity to light (better vision in low light) as it takes less light to generate a response from a rod than from a cone
- Cones result in better visual acuity (seeing fine details)
Signals from BLANK travel through the retina and eventually reach the BLANK cells
photoreceptors, ganglion
They are the final layer of cells in the retina before the optic nerve
Ganglion cells
