The Eye and Retina Flashcards
What is retinitis pigmentosa?
A genetic disorder that results in total blindness
What is the stimulus for vision?
Light
What is wavelength?
The distance between peaks of the electromagnetic waves
What is visible light?
The energy within the electromagnetic spectrum that humans can perceive
What are the range of wavelengths that humans can perceive?
400-700 nm
Where does light pass through?
The pupil and the aqueous humor
What focuses light?
The cornea and the lens
Why does light need to be focused?
To form sharp images of objects on the retina
What are the two types of photoreceptors?
Rods and cones
What are visual pigments?
Light-sensitive chemicals in the outer segments of the receptors that react to light and trigger electrical signals
What is the optic nerve?
Nerve fibre that conducts signals from the retina to the brain
When do pupils dilate?
To allow more light to enter the eye in dark conditions
When do pupils constrict?
To allow less light to enter the eye in bright conditions to protect the eyes
What is accommodation?
Ciliary muscles change shape of the lens, altering its focal length which keeps the image focused on the retina
What is presbyopia?
Elasticity in the eye decreases as we age, making near point further away
What is the fovea?
An area in the centre of the retina that only contains cones
What is the peripheral retina?
Includes all of the retina outside of the fovea
Contains rods and cones
What is macular degeneration?
Destruction of the cone-rich fovea and a small area that surrounds it
Creates a blind region in central vision
What is retinitis pigmentosa?
A degeneration of the retina that is passed from one generation to the next
First attacks the peripheral rod receptors and results in poor vision in the peripheral field
What is the blind spot?
An area on the retina with no photoreceptors
Where the nerve fibres that make up the optic nerve leave the eye
Why aren’t we aware of our blind spot?
The blind spot is located off to the side of our visual field where objects are not in sharp focus anyways
Our brain fills in the place where the image disappears
What is the cornea?
Transparent covering the front of the eye
Cannot move
80% of eye’s focusing power
What is the lens?
Remaining 20% of eye’s focusing power
Can change its shape to adjust the eye’s focus
What are refractive errors?
Errors that can affect the ability of the cornea and/or lens to focus the visual input onto the retina
What is myopia?
An inability to see distant objects clearly
Occurs when light is focused in front of the retina
What is refractive myopia?
The cornea and/or the lens bends the light too much
What is axial myopia?
The eyeball is too long
What is hyperopia?
When light is focused behind the retina
Eyeball is too short
What is visual transduction?
Photoreceptors transforms light into electricity
What are the two parts of visual pigments?
Opsin and retinal
Both of these together absorb visible light
How is transduction in the eye initiated?
The visual pigment absorbs light which makes the retinal change shape from bent to straight and this creates a chemical chain reaction
What is dark adaptation?
The process of increasing sensitivity in the dark
What is the dark adaptation curve?
The function relating sensitivity to light to time in the dark, beginning when the lights are extinguished
How do we measure the dark adaptation curve?
The participant adjusts a flashing light to be just barely visible and as the eyes adapt to the dark they keep adjusting the light to be just barely visible
What is the cone adaptation experiment?
Repeat original experiment but with light shined just on the fovea
What is the rod adaptation experiment?
Measured with rod monochromats because they have no cones
What is visual pigment bleaching?
When the retinal changes shape and separates from the opsin, the molecule becomes lighter in colour
Pigments in their bleached state are no longer useful for vision
What is visual pigment regeneration?
When retinal returns to its bent shape and becomes reattached to the opsin
What is retina deattachment?
When a person’s eyes become detached from the pigment epithelium which causes blindness in the area where the separation occured
What is spectral sensitivity?
The eye’s sensitivity to light as a function of the light’s wavelength
Measured by determining the spectral sensitivity curve (relationship between wavelength and sensitivity)
What is the Purkinje shift?
Enhanced perception of short wavelengths during dark adaptation
-better at seeing blues/greens
What does the rod pigment absorb best at?
500 nm
What do photoreceptors synapse to?
Bipolar cells
What do bipolar cells connect to?
Ganglion cells
What are the 2 types of ganglion cells?
P and M
What are horizontal cells?
Make lateral connection among receptors and bipolar cells
What are amacrine cells?
Laterally connect among bipolar and ganglion cells
What is neural convergence?
Occurs when a number of neurons synapse onto a single neuron
Compare rods and convergence?
Rods converge more than cones do
Results in better sensitivity than cones
Compare cones and convergence?
Cones have better detail vision than rods due to less neuron convergence
What is visual acuity?
The ability to see details
What is the receptive field?
The region of the retina that must receive illumination in order to obtain a response in any given fibre
What are center-surround receptive fields?
The area in the center of the receptive field responds differently to light than the area in the surround of the receptive field
What are excitatory-center, inhibitory-surround receptive fields?
Stimulation in the center = increases firing
Stimulation in the surround = decreases firing
What are inhibitory-center, excitatory-surround receptive fields?
Stimulation in the center = inhibitory
Stimulation in the surround = excitatory
What is the center-surround antagonism effect?
When light covers both the excitatory and inhibitory fields, the effects will counteract each other
What size of light do neurons respond best to?
Light that is the size of the excitatory center of the receptive field
What is lateral inhibition?
Inhibition that is transmitted across the retina
How does lateral inhibition underlie center-surround antagonism?
Lateral plexus transmits signals laterally in the limulus and the horizontal and amacrine cells transmit inhibitory signals laterally across the retina
Center-surround receptive fields are created by the interplay of excitation and lateral inhibition
What is edge enhancement?
An increase in perceived contrast at borders between region of the visual field
-make edges look more distinct
What is the preferential looking technique?
Two stimuli are presented and experimenter watches to determine where the participant (often an infant) is looking
