Flashcards in Lecture 7: vision I Deck (86)
bending of light waves at an angulated surface of transient material
What can alter the degree of refraction?
- ratio of two reflective indices
- degree of angle between interface and entering wave light
What is refractive index?
- ratio of velocity of light in air: velocity of light traveling in substance
What is refractive Power?
- measure of how much a lens bends light waves. measure in diopters
What is focal Point?
- point where all parallel rays converge after passing through the lens
What is focal length?
- distance from center of lens to the focal point
Describe how the depth of focus of the lens changes?
The depth of focus is inversely related to the size of the pupil diameter
What is Emmetropia?
- eye has normal depth of focus
-when ciliary muscles relax distant object light rays sharply focus on the retina
What is hyperopia?
-distant objects seen clearly
- caused by eyeball that is too short
What is Myopia?
What causes light rays to converge in from of the retina?
- caused by eyeball that is too long
What is the maximum visual acuity for two-point sources?
1.5 to 2 mm
What is visual acuity?
measures the resolving power of eye
- eye chart test
Where does the aqueous humor come from?
In order to pull the aqueous humor into the anterior chamber, what is the environment like?
it would be high osmolarity. High concentration of ions to draw fluid through via osmosis
What is glaucoma?
Increased intraocular pressure that will lead to damage of the optic nerve and potentially vision loss, if not corrected
What is the photosenstivie pigment of rods?
What is the photosensitive pigment in cones?
contain three different pigments
What two components join together to form rhodopsin?
scotopsin and 11-cis retinal
What happens when rhodopsin is exposed to light waves?
the cis is converted to trans and does not have the proper orientation to bind with scotopsin
- forms bathorhodopsin
What is activated rhodopsin and what does it do?
- metarhodopsin II
- excites electrical charges in rods that signal to optic nerve potential
Degradation of metarhodopsin II produces what compounds?
- all trans retinal and scotopsin
- isomerize with isomerase to the cis form
How can increased levels of Vitamin A be helpful with vision?
Vitamin A is isomerized to 11-cis retinol and converted to 11-cis retinal
What is the resulting receptor potential when the rods are exposed to light?
increasing negativity. hyperpolarizing
Why does activation of rhodopsin cause hyperpolarization?
- the decompensation of rhodopsin decreases the rod membrane conductance for Na ions, in the outer segment of the rod.
- and the rod is continually pumping Na ions out of the membrane
Explain how a -40 mV potential is generated in the rod in a normal dark condition?
- cGMP gated channels are open and allow leaking of Na ions back inside the rod membrane
In what conditions are you likely to find a hyperpolarized rod, and a less polarized rod?
- hyperpolarized: in light conditions
- non polarized: in dark conditions
What is light adaptation?
- results in the reduction of rhodopsin and photosensitive chemicals
- reduces the sensitivity of the eye to light
What is dark adaptation?
- results in low light and the accumulation of rhodopsin and other light sensitive pigments
- increases the sensitivity of the eye to light