EYES Flashcards
EYEBALL AND OPTIC NERVE
Components in the eyeball
(light must pass through before reaching the retina)
cornea - aqueous humor - pupil - lens - vitreous humor
EYEBALL AND OPTIC NERVE
Components of the retina
(layers and cells)
Ganglion Layer
(axons = optic nerve)
Inner Nuclear Layer
(bipolar cells)
Outer Nuclear Layer
(nuclei of rods and cones)
EYEBALL AND OPTIC NERVE
How do rods and cones transduce light energy?
rods and cones absorb photons
→
conformational changes in the photopigments
→
sodium channels close
→
hyperpolarization
→
reduction of NT release
EYEBALL AND OPTIC NERVE
True or false: rods and cones release less NT in the light and more NT in the the dark
TRUE
photons stimulates the sodium channels to close, causing hyperpolarization. Thus, in the dark, there is despolarization process, determinating the release of NT
EYEBALL AND OPTIC NERVE
Vitamin A function
Vit A is necessary for retinal transduction
+
cannot be synthesized
=
deficiency causes night blindness
EYEBALL AND OPTIC NERVE
Impulse’s traject in the retina layers
rods and cones (outer nuclei layer)
→
bipolar cells (inner nuclei layer)
→
ganglion cells (axons = optic nerve)
EYEBALL AND OPTIC NERVE
Optic nerve traject
axons of ganglion cells converge at the optic disc
(myelination process from the oligodendrocytes)
→
optic nerve enters the cranial cavity
(optic foramen)
EYEBALL AND OPTIC NERVE
Glaucoma: concept
Increase of intraocular pressure
EYEBALL AND OPTIC NERVE
Glaucoma: open-angle
Chronic, painless and progressive condition
+
Decrease reabsorption of aqueous humor
+
visual loss and blindness
EYEBALL AND OPTIC NERVE
Glaucoma: narrow-angle
Acute (painful) or Chronic (genetic) condition
+
Blockade of Canal of Schlemm
+
Emergency treatment
(surgery + cholinomimetics, carbonic anhydrase inhibitors and/or mannitol)
EYEBALL AND OPTIC NERVE
Photoreceptor rods
(1 kind)
Achromatic
+
Low-light sensitive
+
Night vision
EYEBALL AND OPTIC NERVE
Photoreceptors cones
(3 kinds)
red + green + blue
chromatic
bright light sensitive
object recognition
VISUAL PATHWAY
The eye inverts images like a camera, so …
(nasal vs temporal)
Nasal retina receives information from temporal hemifield
+
Temporal retina receives information from nasal hemifield
VISUAL PATHWAY
At the optic chiasm, from which half do the fibers of retina cross and project into the colateral optic tract ?
(nasal or temporal)
NASAL
almost 60% of the fibers cross
VISUAL PATHWAY
Do the fibers from temporal retina cross ?
NO
only ipsilateral optic tract
VISUAL PATHWAY
components of optic nerve
vs
components of optic tract
OPTIC NERVE
nasal and temporal fibers from the ipsilateral retina
OPTIC TRACT
temporal fibers from ipsilateral retina
+
nasal fibers from contralateral retina
VISUAL PATHAWAY
Fibers from optic tract project to …
(4)
Lateral Geniculate Nucleus
(most fibers)
Superior Colliculi
(reflex gaze)
Pretectal Area
(light reflex)
Suprachiasmatic Nucleus
(circadian rhythms)
VISUAL PATHWAY
Most important pathway
(visual pathway)
optic tract
→
lateral geniculate body
→
primary visual cortex
(Brodmann area 17, in occiptal lobe, via optic radiations)
VISUAL PATHWAY
Components of visual cortex (striate cortex)
(3)
striate cortex is divided by calcarine sulcus
→
cuneus gyrus
(superior in cortex - receives medial fibers)
lingual gyrus
(inferior in cortex - receives lateral fibers)
VISUAL PATHWAY
Axons from lateral geniculate body that project to visual cortex are known as …
optic radiations
or
visual radiations
or
geniculocalcarine tract
VISUAL PATHWAY
Components of visual radiations
(lateral geniculate body → visual cortex)
(2)
LATERAL FIBERS
visual information from lower retina
(upper contralateral visual field)
→
temporal lobe (Meyer Loop) to lingual gyrus
MEDIAL FIBERS
visual information from upper retina
(lower contralateral visual field)
→
parietal lobe to cuneus gyrus
VISUAL REFLEXES
Pupillary Light Reflex
impulse in optic nerve (stimulated by light)
→
pretectal area
→
Edinger-Westphal nucleus
(bilateral)
→
preganglionic parasympathetic fibers to ciliary ganglion
(by oculomotor nerve)
→
pupillary sphincter muscle (miosis)
→
direct light reflex (ipsilateral)
+
consensual light reflex (contralateral)
VISUAL REFLEXES
Accommodation - Convergence Reaction
(components)
Focus on a nearby object
=
Accommodation
+
Convergence
+
Miosis
VISUAL REFLEXES
Accommodation - Convergence Reaction
(accomodation)
Edinger-Westphal send preganglionic parasympathetic fibers by oculomotor nerve to ciliary ganglion
→
Ciliary ganglion send postganglionic parasympathetic fibers suply ciliary muscle
→
ciliary muscle contration = suspensory ligaments of the lens relaxation = increase of convexity = increase of refractive index
VISUAL REFLEXES
Accommodation-Convergence Reaction
(convergence)
both medial rectus muscles contract
→
adducting both eyes
(oculomotor nerve)
VISUAL REFLEXES
Accommodation-Convergence Reaction
(miosis)
Edinger-Westphal nucleus
→
preganglionic parasympathetic fibers to ciliary ganglion
(by oculomotor nerve)
→
pupillary sphincter muscle (miosis)
CLINICAL CORRELATE
What is the predominant innervation in the eye (PANS or SANS)?
Parasympathetic Nervous System
→
muscarinic antagonists + ganglionic blockers
(large pharmacological effect)
CLINICAL CORRELATE
Pupillary Sphincter Muscle (iris)
(predominant receptor + stimulation + blockade)
M3 receptor (PANS)
+
stimulation = miosis
+
blockade = mydriasis
CLINICAL CORRELATE
Radial Dilator Muscle (iris)
(predominant receptor + stimulation + blockade)
Alpha receptor
(SANS)
+
stimulation = mydriasis
+
blockage = miosis
CLINICAL CORRELATE
Ciliary Muscle
(predominant receptor + stimulation + blockade)
M3 receptor (PANS)
+
stimulation = accommodation
+
blockade = focus for far vision
CLINICAL CORRELATE
Ciliary Body Epithelium
(predominant receptor + stimulation + blockade)
Beta receptor (SANS)
+
stimulation = increase of aqueous humor
+
blockade = decrease of aqueous humor
CLINICAL CORRELATE
Pupillary Abnormalities
Argyll Robertson Pupil
NO light reflexes (direct and consensual)
NORMAL accommodation reflex
+
seen in neurosyphilis, diabetes
CLINICAL CORRELATE
Pupillary Abnormalities
Horner Syndrome
Lesion in oculosympathetic pathway
+
PANS > SANS
→
miosis + ptosis + enophthalmos + hemianhidrosis
CLINICAL CORRELATE
Pupillary Abnormalities
Relative Afferent Pupil
(Marcus Gunn)
Lesion in afferent fibers
→
pupil don’t constrict fully
+
when shine light immediately against affected eye, apparent dilation
+
seen in multiple sclerosis
CLINICAL CORRELATE
Pupillary Abnormalities
Adie Pupil
ciliary ganglion lesion
+
accommodation reflex > light reflex
+
women, loss of knee jerk
CLINICAL CORRELATE
Pupillary Abnormalities
Transtentorial (uncal) Herniation
“down-and-out” eye
+
dilated and fixed pupils
+
ptosis
+
increase of intracranial pressure = uncal herniation = compression of III cranial nerve
CLINICAL CORRELATE
Lesions of the retina that includes macula destruction
(3)
macula is sensitive to trauma, intense light, aging and neurotoxins
+
central scotoma
+
common in Multiple Sclerosis
(auto-immune demyelination of the nerve)
CLINICAL CORRELATE
Lesions in the optic nerve
(3)
blindness (anopia)
+
direct light reflex - NO
consensual light reflex - YES
+
optic neuritis and central retinal artery occlusion
CLINICAL CORRELATE
Compression of optic chiasm
(2)
bitemporal heteronymous hemianopia
(peripherical vision)
+
pituitary tumor, meningioma
CLINICAL CORRELATE
Internal carotid artery aneurysm
(2)
temporal retina fibers
+
ipsalteral nasal hemianopia
CLINICAL CORRELATE
Lesions in the optic tract
(3)
vascular causes
+
homonymous hemianopia
+
always contralateral defects
CLINICAL CORRELATE
Lesion of the visual radiations
(3)
contralateral homonymous quadrantanopia
+
Meyer Loop - Lateral fibers - Lower retina = superior quadrantanopia
(middle cerebral artery occlusion)
+
Via parietal lobe - medial fibers - superior retina - inferior quadrantanopia
(posterior cerebral artery occlusion)
CLINICAL CORRELATE
Lesions of the primary visual cortex
contralateral homonymous hemianopia
(macular/central vision spared)
CLINICAL CORRELATE
Lesions of the visual radiations are more common than lesions of optic tract?
TRUE
CLINICAL CORRELATE
Lesions of the visual radiations and primary cortex: are pupillary reflexes present?
YES
cortical blindness
=
blindness
+
pupillary reflexes
