Vision Flashcards
Presbyopia
- diminished ability to focus on near objects due to old age
- EVERYONE has this when they get old
Focusing the light on the retina
- mostly done by cornea
- lens does fine adjustment
Aqueous humor: synthesis & removal
- synthesized by ciliary epithelium
- removal through trabecular meshwork
Glaucoma
- decreased aqueous humor outflow leading to increased intraocular pressure, which injures the optic nerve
- second most common cause of blindness
Sympathetic nervous system effect on pupil
Dilation via radial dilator muscles
Parasympathetic nervous system effect on pupil
constriction via pupillary sphincter
Efferent nerve defects
- anisocoria: unequal pupils
Afferent nerve defects
- pupils are always EQUAL
Cataract effect on pupil response to light
- none
- media opacities do not affect pupil response to light
Result of injury to sympathetic fibers to eye
Horner syndrome
Horner Syndrome
- anisocoria: small pupil on affected side
- ptosis: droopy eyelid on affected side
- diminished sweating on affected side
Sodium channels during darkness
- open
- depolarized membrane
Sodium channels during light
- closed
- hyperpolarized membrane
Phototransduction
- cascade of reactions that happen in the photoreceptors
* *light–rhodopsin–transducin–phosphodiesterase–less cGMP–sodium channels close–graded HYPERpolarization**
What type of protein is rhodopsin
G-protein-coupled receptor
In oder for rhodopsin to be sensitive to light it needs what
- vitamin A derivative (11-cis retinal)
Result of light hitting rhodopsin
- isomerization of 11-cis retinal to all trans retinal
Visual cycle
- conversion of trans retinal back to 11-cis retinal
- occurs outside photoreceptor cell in retinal pigment epithelium (RPE)
Photoreceptor surface turn over
- RPE allows turnover of entire photoreceptor surface every 10 days
Conversion of light to neurological impulse
- minimum of three neurons: photoreceptor, bipolar cell, ganglion cell
- light stimulus on retina turns into neurological impulse
Graded potential neurons
- photoreceptor and bipolar cell
Action potential neuron
ganglion cells
Retina blood supply
- derived from ophthalmic artery: retinal vessels, choroidal vessels
Age related macular degeneration
- accumulation of extracellular lipids (lipofuscin) and protein deposits (drusen) beneath RPE
- most common cause of blindness
Retinal vasculature injury causes
- diabetic retinopathy
- atherosclerotic disease
Choroidal circulation injury causes
- age related macular degeneration (neovascularization)
Area bounded by temporal vascular arcades
Macula
Fovea
point of fixation in the center of the macula
Altinudal defects
- suggest disease inside the eye
Unilateral field defects
suggest disease anterior to the chiasm
Bitemporal field defects
suggest disease at the chiasm
Homonymous field defects
suggest disease behind the chiasm
Motor control of the eye
- abducens (VI): lateral rectus
- trochlear (IV): superior oblique
- oculomotor (III): all other eye muscles
- **LR6SO4
