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52 Cards in this Set

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The optic nerve is myelinated by what type of cells?
oligodendrocytes; this is why multiple sclerosis involves the eye in optic neuritis - MS affects CNS myelin.
Between the choroid and the rods and cones of the outer nuclear layer lies the pigment epithelium. What is its role?
the pigmented epithelium delivers Vitamin A and glucose to the retina; without dietary Vit A, person would have night blindness
Name the three layers of the retina from closest to the vitreous humor (incoming light).
Ganglion layer (contains ganglion that form the optic nerve) --> Inner Nuclear Layer (contain bipolar Cells) --> Outer Nuclear Layer (contain rods and cones).
After the optic nerve turns into the optic tracts at the optic chiasm, where does it go?
optic tracts project to the lateral geniculate nucleus of the thalamus where they then turn into radiations and project to the primary visual cortex.
Which visual fields would be affected if there was a lesion in the middle of the optic chiasm and generally why would this happen?
since the nasal retinal nerve fibers cross and are responsible for temporal visual fields, the pt would experience bilateral heteronymous hemianopsia. generally caused by a pituitary tumor or craniopharyngioma.
Which visual fields would be affected if there was a lesion across the right optic nerve and generally why would this happen?
anopsia (blindness) of the right eye (complete loss of the right visual fields.) generally occurs because of optic neuritis in multiple sclerosis or occlusion of the central artery of the retina.
Which visual fields would be affected if there was an occlusion of the MCA at Meyer's loop on the left side?
since meyer's loop is behind the optic chiasm and is located in the temporal lobe, there would be a "pie in the sky" loss on the right upper quadrant. aka right homonymous superior quadrantanopia.
why is there macular sparing?
the intracortical primary visual cortex contains blood supply from the posterior cerebral artery and the middle cerebral artery, so if there was a lesion in the primary visual cortex (macula is in the most posterior portion) most likely the macula would be okay since there is collateral supply
why do most right nasal hemianopsias occur?
aneurysm of the internal carotid artery
what would produce left homonymous inferior quadrantanopia?
lesion of the right parietal optic radiation to the cuneus - creates "pie on the floor"
all lesions behind the optic chiasm produce what type of visual field defects?
in regard to the eyes, what cranial nerves are involved?
II-VII; II (vision), III (eye movement and pupil constriction), IV (trochlear-superior oblique), V (Trigeminal-corneal reflex), VI (abducens-lateral rectus abducts the eye), VII (facial-eyelid closure and tears)
clinically, what does papilledema look like and why does it occur?
fuzzy disc margins, bilateral swelling of the optic disc (may be asymmetric), absent venous pulsations, splinter hemorrhages (late sign), exudates/cotton wool spots, and haziness of the retinal vessels. - no single sign should be replied upon to diagnose papilledema; it occurs because of increased ICP
what are the 3 layers of tissue that enclose the eye?
outermost- sclera (white part), middle- choroid (highly vascularized and continuous with iris/color and ciliary body), innermost - retina.
what controls the size of the pupil?
pupil is neurally controlled by the circular and radial muscles of the iris
what is unique about the optic disc?
this is where the blood vessels enter. also, there are NO photoreceptors, aka it is the blind spot
what is the yellowish circular portion that lies lateral to the optic disc? what is significant about it?
the macula lutea is responsible for central vision(vs peripheral). It's center contains only cones - called the fovea. there is a small region at the center of the fovea called the foveola that is devoid of blood vessels. the fovea + foveola represent the area of highest visual acuity. thus, macula lutea = visual acuity
what produces the nutritious aqueous humor?
the epithelial cells of the ciliary processes produce the aqueous humor. it flows through the pupil into the anterior chamber and is reabsorbed through the canal of Schlemm.
what causes glaucoma?
an accumulation of aqueous humor increases the intraocular pressure thus reducing blood supply to the eye causing damage to the retina and may cause blindness
What are the two types of glaucoma? explain the difference.
1. OPEN-ANGLE glaucoma - removal of aqeuous humor is decreased due to reduced permeability through the canal of schlemm; 2. CLOSED-ANGLE glaucoma - the anterior chamber angle is obstructed; open is the more chronic form
what are the most popular drugs used to treat open angle glaucoma?
PROSTAGLANDIN analogs - increase outflow from the anterior chamber; BETA-ADRENERGIC receptor BLOCKERS - decrease the secretion of aqueous humor
Explain the retina's blood supply.
ophthalmic artery --> 2 branches: 1. central retinal artery (supplies inside of the neural retina) and 2. Ciliary artery (penetrates the sclera and supplies a part of teh choroid called the choriocapillaris - supplies rods and cones)
Is glaucoma an emergency?
closed angle glaucoma is an emergency - needs surgery or meds to relieve painful increase in intraocular pressure
in regard to visual fields, the left optic tract gives rise to what visual fields?
left optic tract gives rise to the right half of visual fields; the right optic tract gives rise to the left half - homonymous
The lateral geniculate nucleus contains 6 layers, name them and their major function.
layers 1&2: MAGNOCELLULAR aka VENTRAL layers - responsible for detecting fast moving stimuli (location and movement), projections are more superficial in the primary visual cortex; layers 3-6: PARVOCELLULAR aka. DORSAL- responsible for color and visual acuity (color and detail); projections go ventral (deep) into primary visual cortex
What is another name for optic radiations?
geniculocalcarine tracts
if the visual field loss is a pie on the floor, what part of the lateral geniculate nucleus do the axons arise?
pie on the floor means it goes through the parietal lobe; the geniculocalcarine tracts arise from the DORSOMEDIAL REGION of the LGN and use a superior(dorsal) trajectory to synapse on the SUPERIOR BANK of the calcarine fissure of the visual cortex
if the visual field loss is a pie in the sky aka homonymous superior quadrantanopia, what part of the lateral geniculate do the axons arise?
axons from the superior quadrant of the contralateral visual hemifield(via the inferior retina) arise from the VENTROLATERAL REGION of the LGN and use a more inferior trajectory toward the TEMPORAL HORN, looping caudally (MEYER's LOOP) and terminates in the INFERIOR BANK of the Calcarine Fissure of the visual cortex
axons conveying infor from the macula arise from the ________ lateral geniculate nucleus and synapse on the _______ pole occipital cortex.
central; caudal
The Primary visual cortex is also know as ________.
Broadmann's area 17
which (R or L) controls the left visual fields?
right visual cortex
the macular part of the retina is in what portion of the visual cortex?
most posterior portion of the visual cortex
what does the superior colliculus control?
saccadic (high velocity) movements - coordinates with eye and neck movements (through descending fibers of the tectospinal tract) to respond to a stimulus; receives input from sensory and auditory systems
there are 2 types of receptors in the outer layer of the retina: RODS and CONES. explain the difference.
CONES: 7M, central vision, visual acuity, color, bright light, small receptive field, little convergence onto ganglion cells; RODS: 125M, peripheral visual field and movement, grey, dim light, large receptive field and large convergence onto ganglion cells
A collection of these axons make up optic nerves, chiasm, and tracts and terminate in the lateral geniculate nucleus.
ganglion cells (inner layer)
explain the differences in a lesion in front of vs. behind the optic chiasm.
lesion in FRONT: uniocular field defect (possibly complete ipsilateral blindness in eye) ABNORMAL VISUAL ACUITY; lesion behind: binocular (both eyes) hemi-field defects of contralateral eyes, but with NORMAL VISUAL ACUITY
Name the nucleus that is responsible for pupillary constriction.
What are the questions to ask yourself when trying to figure out where the lesion to the visual pathway is located?
1.Is the field loss unilateral or bilateral? 2.Does the field defect respect the vertical meridian? 3.Does the field show a pattern? 4.If bilateral, is the defect homonymous? 5.If the defect is bilateral and homonymous which side of the field is affected? 6.Is the defect congruous?
if a field defect is unilateral, what is damaged?
either optic nerve anterior to chiasm or damage to the eye itself
if a field defect is bilateral, generally where is it located?
behind the chiasm.
what is the first thing one should think of before looking for a lesion?
look for a pathology such as glaucoma or macular degeneration (the can simultaneously affect the optic nerve or retina in both eyes)
what does it mean to "respect" the vertical meridian?
the lesion is chiasmal or retrochiasmal- "one-sided or hemianopia"
if the fixation point is affected with vision loss, what is this called?
central scotoma - usually damage to macular photoreceptors or papillomacular nerve fibers at or within the optic nerve
what is the technical term for a "pie like" field loss? if its in the sky, where is it?
quadrantanopsia; pie in the sky: temporal lobe - Meyer's loop
if the defect is homonymous, where is the lesion?
ALWAYS post-chiasmal; if it is non-homonymous: at chiasm or anterior in the nerve
what does a bi-nasal defect generally indicate?
almost always bilateral optic nerve disease (glaucoma, chronic papilledema)
if there is a lesion above the calcarine fissure, what is the field loss?
inferior quadrantanopsia - since that is the location of where the axons end up from the upper retina (upper retina --> Dorsomedial region of the LGN (through the parietal lobe)--> optic radiations or geniculocalcarine tracts end up on the superior bank of the calcarine fissure)
explain why lesions that are more posterior, generally demonstrate greater congruity?
the visual pathway becomes more organized as it proceeds toward the cortex; the more congrous the lesion, the further back in the pathway
while your doing an ophthalamic exam, you notice a pale fundus with cotton-wool spots, what do you suspect?
while you're doing an ophthalmic exam, you notice a cherry red spot. what do you suspect?
central retinal artery occlusion
while your doing an ophthalamic exam, you notice a fundus that resembles a pizza. what do you suspect?
central retinal vein occlusion