VISION A Flashcards
________
= formation by cornea and lens of a real, reduced, up-side-down image on back of eye
= transmission of visual information to the visual cortex
Seeing
The ______ controls balance, the ________ keeps vision steady as head moves
Vestibular apparatus
Vestibular ocular reflex
What is the pathway of rays through the eye to reach the photoreceptors?
Cornea, anterior camber, pupil, lens, vitreous, inner retinal layers
Visual-based neural signals pass through what structures of the eye to visual cortex ?
Photoreceptors, intermediate retinal neurons, retinal ganglion cells to Lateral Geniculate Nuclei
Axons from the retina exit via the ____
Optic nerve
The choroid layer contains ____
Blood vessels
Pigment epithelium of retina absorbs excess ____
Light
Light rays must be focused on the ____ , a maximally focused image initiates resolution of the finest detail
Fovea
Light strikes the photoreceptors in the fovea directly because overlying ____ are pushed aside
Neurons
During the __________ the lens becomes more powerful to converge divergent rays coming from close objects onto the fovea
Accommodation reflex
Far objects (>20 ft) : parallel/diverging rays? Lens or no lens accommodation ?
Parallel
No lens accommodation
Near objects (<20 ft) : parallel/diverging rays? Lens/no lens accommodation ?
Diverging
Lens accommodation
_____ objects :Parallel Rays, No Lens Accommodation
Far
_______ objects :Diverging Rays, Lens Accommodation
Near
A physiological reflex that permits focusing on near and far objects by changing the curvature of the lens
Accommodation
_______: Relaxation of ciliary body muscles: Tightens
zonule ligaments, stretches lens, is sympathetically controlled.
Far focus
________: Contraction of ciliary body muscles moves ciliary body inward : Loosens zonule ligaments, lens gets fatter (more convex), is parasympathetically controlled.
Near focus
“Normal” eye: “__________”
-Far focused as default
-Near needs lens accomm.
(Lens gets fatter to converge
and move light rays forward onto fovea)
Emmetropic
Eyeball too long: “_______”
-Near focused as default
-Far focused front of retina -Correct w/CONCAVE lenses (To diverge rays and
MOVE IMAGE BACKWARD to fovea)
Myopic
Eyeball too short: “________”
-Far focused by lens accomm.(lens gets fatter)
-Near focused behind retina
-Correct w/CONVEX lenses (To converge rays and MOVE IMAGE FORWARD TO FOVEA)
Hyperopic
Optic nerve afferents driven from each eye lead to _______ controlling both eyes
Binocular efferents
_______ conditions:
Iris dilator pupilae muscles contract
Radial fibres shorten
Pupil diameter increases
Allows more rays to enter eye
Low light
__________ conditions:
Iris constrictor pupilae muscles contract
Concentric fibres shorten
Pupil diameter decreased
Blocks some rays from entering eye
High light
Low light conditions = pupil _____
High light conditions = pupil _____
Dilates
Constricts
________= spatial resolving capacity of the visual system
Ability of eye to see fine detail
Limited by diffraction , aberrations and photoreceptor density in eye
Target recognition tasks, which are most commonly used in clinical visual acuity measurements, require recognition or naming of a target , such as with snellen letters
Visual acuity
List 3 factors that affect visual acuities :
Eye movement
Pupil size
Refractive error
Illumination
Exposure time of target
Area of retina stimulated
State of adaptation of eye
In the ____ fraction 20/20, the 1st number represents test distance, 20 ft
2nd number represents distance that normal eye can see the same letter on eye chart
Snellen
_______- distance away from object a normal subject can be to clearly see detail
Visual acuity
