deck_635614 Flashcards
Emmetropia
match b/w focal length and length of eyeball
Myopia
“near-sighted” light from objects far away are refracted to much –> focus object in front of retina concave lens to correct (diverge light a little)
Hyperopia
“far-sighted” objects (particulary close) are focused behind the retina –> to little convergence convex lens to correct –> aids in convergence
astigmatism
focal planes are not the same in all meridians –> blurred visionregular - toric eyeballirregular - cornea irregularity
lens formula
1/f = N-1 (1/R1 - 1/R2)1/f = refractive power (diopters) convex lens = + diopter (convergent) concave lens = - diopters (divergent)
Site of greatest refractory power?
anterior corneairregularity can cause astigmatism
accomodation
cilliary muscles relax –> lens balls up –> decrease radius of curvature –> increase refractory poweroccurs when object close up
The Near response
- accomodation2. pupil constriction3. convergence of the eyes
presbyopia
loss of accommodation w/ agenear point continually increases w/ ageConvex lens/ increased refractory power -> treatment
Pupil constriction: effect and mechanism
increases depth of field but loses peripheralsANS controls: sympathetic = mydriasis (dilation) via papillary dilators; parasymp = miosis (constriction) via papillary sphincters
Retina layers
PREPhotoreceptor layerouter nuclear layerouterplexiform layerinner nuclear layerinnerplexiform layerganglion cell layeroptic nerve layer
region of highest accuity
fovea - center of optical axis - all cones w/ 1:1 cone to bipolar cell ratio; no blood vessels or ganglia so little light scattering
cones
High acuity and low sensitivity a few photoreceptors per bipolar cellfunction in high light and have color vision quickly “bleach” in dim light3 different opsin types –> color vision
rods
Low acuity and high sensitivity many photoreceptors per bipolar cellfunction in low light and only have black and white visiononly 1 opsin type
Critical Fusion Frequency
frequency at which continuous flashes of light appear to be continuous rather than flickeringin normal light - CFF greatest in foveain dim light - CFF greater in peripheral retina (b/c more rods)
Spectral Sensitivity
bright light - see longer wavelengths better (Photopic) see red betterdim light - see lower wavelengths better (scotopic) don’t see red wellknown as purkinje shift
Absolute sensitivity
threshold to light sensitivity is much lower in dim light but takes time for threshold to fall (dark adaptation) - more sensitive due to rods high sensitivity to lightrod photopigment must regenerate and recycle upon entering dark environment rods act fast to light, but recycle very slowly
Light Reaction
Light hits rhodopsin –> transducin g protein –> Phosophodiesterase –> decrease cGMP –> close Na channels –> hyerpolarization –> decrease inhibitory neurotransmitter release from photoreceptors –> increase ganglion firing to brain
