Flashcards in Exam 7 Vision Special Senses 73X Deck (88)
In broad terms give the overview of Image formation?
1) Light refracted through refractive structures of eye
2) Receptor potential produced by retinal photoreceptors
3) Neural layer processes visual data, sends nerve impulses to optic nerve
4) Impulses conveyed to thalamus and onto the cerebral cortex for interpretation as images
What is refraction and what causes it?
Light bending as it travels through different transparent substances of different densities
What provides refraction of light rays entering the eye? Which structure provides the majority?
Aqueous Humor (Minor Role)
Vitreous Body (Minor Role)
An images formed on the retina has what orientation?
The variable refraction of light rays reflected form objects further than about 20 feet from the viewer are essentially parallel, what does this mean regarding the ciliary muscle and lens?
Ciliary Muscle is relaxed
Lens is fairly flat
The variable refraction of light rays reflected from objects closer than 20 feet from the viewer are not parallel, what does this mean regarding the ciliary muscle and lens?
Ciliary Muscle Contracts--> reducing tension on suspensory ligaments -->
Lens shape is more spherical (thicker)
The increase in curvature of the lens for near vision is called what?
What shape will the lens have if tension is reduced via the suspensory ligaments (zonular fibers)?
If the ciliary muscles relax and tension is restored to the suspensory ligaments via the choroid (acts like a spring), what shape will the lens take?
Flat (less convex)
How is tension released from the suspensory ligaments allowing the lens to thicken and take on a more convex shape?
Ciliary muscle contracts, stretching choroid and releasing tension
What is the minimum distance from the eye an object can be clearly focused w/maximum accommodation?
Near Point of Vision
What term is used to describe the loss of elasticity of the lens w/aging, and therefore cannot accommodate and focus the light?
The normal eye in which is able to refract light rays from an object 20 ft (6meters) away and form a clear image on the retina is called?
Refraction abnormalities that prevent a clear image to form on the retina are?
Astigmatism (Irregular curvature of cornea)
What occurs when the eyeball is too long relative to the focusing power of the cornea and lens?
Where does the image focus for a person suffering from Myopia?
In Front of the Retina
Myopia may be caused by what and how is it corrected?
Elongated Eyeball or thickened Lens
Corrected: Use of Concave Lens
What refraction abnormality is characterized by an eyeball that is too short relative to the focusing power of the cornea and lens (thin) and in which the image is focused behind the retina?
-Convex lens to correct
What refractive abnormality is caused by irregular curvature of either the cornea or lens and results in parts of the image blurred or distorted, and correction is by a lens that rotates the axis of the light going into the eye?
What is the other part of the overall accommodation mechanism that occurs simultaneously w/changes in thickness of the lens and will allow the light rays to enter the eye in a more parallel orientation for better focus?
Pupil Constriction (circular muscles of the iris constrict)
Since humans are only able to focus on one set of objects at a time this provides what type of vision?
Binocular Vision: Depth perception, three-dimensional perspective
How is Binocular vision created in our human perception?
1) Two retinas see an object from slightly different angles
2) Brain fuses the two slightly different images creating stereoscopic vision (seeing solid)
The eyes must move medially so that both are directed toward the object being viewed as we move closer and rotate medially so light rays strike the same point on both retinas, this is called?
The microscope view of rods and cones consists of what? Term given in the 1830's due to their shape
Rods: Outer Segments cylindrical or rod-shaped
Cones: Tapered or cone-shaped
Where are cones most highly concentrated and in which dramatically decrease in density moving away from this area?
Central Fovea (Cone Peak)
Where are rods most highly concentrated?
Ring around the foveal pit (18 degrees, 4.5mm)
Which photoreceptor tends to be more densely concentrated?
Rods more so than cones
What area of the retina of the eye is receptor free?
Optic Disc (blind Spot)
The outer segment of rods and cones are next to the pigmented layer and is responsible for what?
Transducing light energy into receptor potential