Vision video Flashcards
What are the visual receptors?
- Visual stimuli
- Help us form specific detailed visual images of objects
- Photoreceptors
- Used to detect light, color, and movement
Describe how light interacts with eyes?
- Our eyes respond to visible light, a small portion of the electromagnetic spectrum
- Light: packets of energy called photons (quanta) that travel in a wavelike fashion
- Rods and cones respond to different wavelengths of the visible spectrum
What is refraction?
Refraction
- Bending of a light ray due to change in speed when light passes from one transparent medium to another
- Occurs when light meets the surface of a different medium at an oblique angle
- Light passing through a convex lens (as in the eye) is bent so that the rays converge at a focal point
What is pathway of light?
Light is refracted
- At the cornea
- Entering the lens
- Leaving the lens
* Change in lens curvature allows for fine focusing of an image
What can problems of refraction cause?
Astigmatism-caused by unequal curvatures in different parts of the cornea or lens
- Corrected with cylindrically ground lenses, corneal implants, or laser procedures
- Myopia
(nearsightedness)-foc point is in front of the retina, e.g. in a longer than normal eyeball - Corrected with a concave lens
Hyperopia (farsightedness)-focal point is behind the retina, e.g. in a shorter than normal eyeball
- Corrected with a convex lens
How is the lens able to change shape?
When the ciliary muscles relax, the ciliary body moves posteriorly, and tension on the suspensory ligaments increases. This causes the lens to flatten to view distant objects. Lens accommodation to see near objects is accomplished by ciliary muscle contraction and rounding of the lens.
What is porpose Rods and cones?
- Outer segment of each contains visual pigments ( Photopigments) - molecules that change shape as they absorb light
- Inner segment of each joins the cell body
What are Rod charachteristic?
Rods
- More numerous than cones
- Longer and narrower than cones
- Primarily located in peripheral regions of neural layer
- Especially important in dim light
- Detect movement well but have poor sharpnes
- cannot distinguish color
What are characteristic cones?
Cones
- Less numerous than rods
- Activated by high-intensity light
- Provide precise visual sharpness and color recognition
- Primarily located in fovea centralis
- Subdivided into three types of cones
* each best detecting different wavelengths
What is Photopigment?
Photopigments
- Contain protein, opsin
* several types, each transducing different wavelengths
* each photoreceptor with only one opsin type
- Contain light-absorbing molecule, retinal
* formed from vitamin A
What are Rhodopsin and photosin?
Rhodopsin
* opsin in rods
* involved in transduction of dim light
Photopsin
* specific opsin associated with retinal in cone cells
* three different proteins providing for different absorption in cones
What is light Adaptation?
- Occurs when moving from darkness into bright light
- Large amounts of pigments are broken down instantaneously, producing glare
- Pupils constrict
- Dramatic changes in retinal sensitivity: rod function ceases
- Cones and neurons rapidly adapt
- Visual acuity improves over 5-10 minutes
What is Dark adaption?
- The reverse of light adaptation
- Cones stop functioning in low-intensity light
— Pupils dilate - Rhodopsin accumulates in the dark and retinal sensitivity increases within 20-30 minutes
What are the differences between rods and cones with respect to their anatomy, photopigments, and kind of light processed?
Cones are shorter and wider than rods and primarily within the fovea. Each cone is associated with one of three different photopsins. They respond to bright light.
Rods are longer and narrower than rods and primarily in the periphery. Each cone is associated with rhodopsin.
They respond to dim light.
Pathway of optic nerve
- formed from converged ganglionic axons
- project from each eye
- converge at the optic chiasm anterior to pituitary gland
- medial axons crossing to opposite side of brain
- lateral regions remaining on same side
