EYES Flashcards by Luiz Felipe Blanco

EYEBALL AND OPTIC NERVE

Components in the eyeball

(light must pass through before reaching the retina)

cornea - aqueous humor - pupil - lens - vitreous humor

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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)

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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

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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

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EYEBALL AND OPTIC NERVE

Vitamin A function

Vit A is necessary for retinal transduction

cannot be synthesized

deficiency causes night blindness

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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)

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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)

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EYEBALL AND OPTIC NERVE

Glaucoma: concept

Increase of intraocular pressure

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EYEBALL AND OPTIC NERVE

Glaucoma: open-angle

Chronic, painless and progressive condition

Decrease reabsorption of aqueous humor

visual loss and blindness

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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)

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EYEBALL AND OPTIC NERVE

Photoreceptor rods

(1 kind)

Achromatic

Low-light sensitive

Night vision

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EYEBALL AND OPTIC NERVE

Photoreceptors cones

(3 kinds)

red + green + blue

chromatic

bright light sensitive

object recognition

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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

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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

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VISUAL PATHWAY

Do the fibers from temporal retina cross ?

only ipsilateral optic tract

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VISUAL PATHWAY

components of optic nerve

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

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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)

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VISUAL PATHWAY

Most important pathway

(visual pathway)

optic tract

→

lateral geniculate body

→

primary visual cortex

(Brodmann area 17, in occiptal lobe, via optic radiations)

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VISUAL PATHWAY

Components of visual cortex (striate cortex)

(3)

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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 …

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optic radiations

visual radiations

geniculocalcarine tract

VISUAL PATHWAY

Components of visual radiations

(lateral geniculate body → visual cortex)

(2)

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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

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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)

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Focus on a nearby object

Accommodation

Convergence

Miosis

VISUAL REFLEXES

Accommodation - Convergence Reaction

(accomodation)

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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 **L**oop - **L**ateral fibers - **L**ower 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

EYES Flashcards

(45 cards)