Flashcards in Optics Deck (22)
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1
Distance vs. Near Vision
At 20 ft or greater, light travels parallel. So less convergence is needed to focus light on the retina. Inside 20 ft, the rays are divergent
2
Emmetropia
Ideal, rays focused onto retina
3
Myopia
Rays focus in front of retina (maybe bc of larger eyes). Nearsightedness
4
Hyperopia
Rays focus behind retina, farsightedness
5
Astigmatism
Rays focus in 2 different points from rugby-ball shaped cornea w/ 2 curvatures
6
The Near Triad of Accomodation
Pupillary constriction
Convergence of eyes
Crystalline lens increases in plus power
7
3 Corrective Lenses
Myopia: Minus lenses made apex to apex increase divergence
Hyperopia: Plus lenses made base to base to increase convergence
Astigmatism: Toric lenses which are glass w/ two radii of curvature 90 degrees apart
8
Presbyopia
Age Related Farsightedness, decreased ability of lens to accommodate to near object from weakening of ciliary muscle and hardening of lens. Hold things further away and turn on lights to cause pupillary constriction
9
Accommodative Esotropia
Overconvergence in accommodation, one of most common types of strabismus in childhood. Corrected w/ glasses
10
Distribution of Cones and Rods
Cones way highest at fovea and macula, and rods increase outside of that
11
3 Ranges of Luminance
Scotopic - darkest
Mesopic - moonlight
Photopic - good acuity
12
3 Kinds of Dichromats
Protanopia: Red absent
Deuteranopia: Green absent
Tritanopia: Blue absent
13
Phototransduction Mech
Photon stimulates rhodopsin (in rods). Changes conformation to all-trans retinal. Transducin GPCR is activated. Activates PDE. Hydrolyzes cGMP, reducing its concentration. This causes Na channels to close
14
Photopic vs. Scotopic Phototransduction
Photopic - low cGMP - Na channels close - hyperpol - less Ca channel opening and less release of NTs
Scotopic opposite
15
Biphasic Waveform ERG
a wave corresponds to PhotoR signaling in response to stimulus, b wave in response to these + Muller plus pretty much all other cells
16
Retinitis Pigmentosa (symptoms, sign, treatment)
Retinal dystrophy resulting in nyctalopia/tunnel vision that may progress to loss of central vision as well. Mottling of RPE with black-bone spicule pigmentation. Vitamin A may delay progression
17
Receptive Field
On center ganglion cell will respond if center of its visual field activated, off center opposite. Both respond weakly if all is activated. This allows for contrast and resolution
18
Horizontal Cell Function
Communicate through gap junctions and converge signals onto bipolar cells
19
Graded Responses vs. AP
PhotoRs, horizontal, and bipolar cells use graded for fast and continous transmission of info
Amacrine and Ganglion cells convert graded into APs for long distance transmission
20
Big Difference b/w Moderately Dark Adapted and Extremely Adapted Eye
Rods communicate via electrical synapses via cone bipolars vs. cones don't work so communicate via rod bipolars
21
3 Kinds of Retinal Ganglion Cells (RGCs) (& what they do)
Ps respond to changes in color
Ms respond to low contrast stimuli
Ks always on to blue and off to red and green cones. First ones damaged in glaucoma so do tests w/ blue backgrounds to determine
22
