Visual Tracts Flashcards
Functions of Retinal Pigmented Epithelium
- Absorbs scattered light to supplement choroid (b/c has some melanin granules)
- Forms part of blood-retina barrier (separating photoreceptors from choroid)
- Isomerizes all-trans retinal –> 11-cis retinal –> sends back to photoreceptors
- Phagocytosis & degradation of components/waste from photoreceptors
- Remove free radicals & secretes ATP, polypeptide growth factors & immunomodulatory factors
Function of the superior colliculus
- Important in directing eye movements
- Spatially directs head movements and visual reflexes
- Retinal input bypasses the lateral geniculate nucleus and targets the brachium of the superior colliculus –> terminates retinotopically
- Also receives spinotectal (somatosensory) and auditory inputs
Function of the pretectal/pretectum area
- Important in pupillary light reflex
- Nuclei located near the midbrain/forebrain junction that receives inputs from optic tracts, lateral geniculate nucleus and the suprachiasmatic nucleus
- Responds to varying intensities of illuminance and unconscious behavioral responses (e.g. pupillary light reflex)
Associative visual agnosia
- Infarction of LT occipital lobe + posterior corpus callosum (especially splenium) typically due to posterior cerebral artery damage
- Disconnects the language area from the visual association cortex –> Pt cannot name or describe an object in visual field BUT can recognize and demonstrate its use
- Pts may also be alexic (unable to read) and writing ability may be affected (agraphia)
Name the visual field deficit for lesion: RT optic nerve
Total vision loss in RT eye
Name the visual field deficit for lesion: Optic chiasm (midline)
Bitemporal hemianopsia (heteronymous defect)
Name the visual field deficit for lesion: RT optic tract
Contralateral (LT) homonymous hemianopia
Name the visual field deficit for lesion: RT temporal lobe (Meyer’s loop)
Superior LT homonymous quadrantanopia (pie in the sky disorder)
Name the visual field deficit for lesion: RT parietal lobe
Inferior LT homonymous quadrantanopia (pie in the floor disorder)
Name the visual field deficit for lesion: RT Geniculocalcarine tract
Contralateral (LT) homonymous hemianopia
Name the visual field deficit for lesion: Inferior bank of RT calcarine fissure
Superior LT homonymous quadrantanopia w/ macular sparing
Name the visual field deficit for lesion: Superior bank of RT calcarine fissure
Inferior LT homonymous quadrantanopia w/ macular sparing
Name the visual field deficit for lesion: Both banks of RT calcarine fissure
Contralateral LT homonymous hemianopia w/ macular sparing
Describe the concentric tunics/layers that make up the eye
- Fibrous layer - tough external layer consisting of the sclera & cornea
- Vascular layer - choroid, ciliary body and iris
- Retina - inner sensory layer gives rise to optic nerve (layer II)
Sclera
- Fibrous, external layer of eyeball which protects internal structures
- Dense regular connective tissue w/ flat bundles of type I collage and microvasculature near outer surface
- Extraocular muscles insert anteriorly on sclera
Cornea
- Transparent and avascular structure w/ distinct layers (superficial to deep)
1. Corneal epithelium - nonkeratinized stratified squamous
2. Anterior limiting membrane (Bowman’s membrane)
3. Thick stroma comprised of keratocytes
4. Posterior limiting membrane (Descemet’s membrane) - basement membrane of endothelium
5. Inner endothelium
What is the limbus?
- Transitional area where transparent cornea merges w/ opaque sclera
- Denotes end of Bowman’s membrane and beginning of conjunctiva (covers the anterior sclera and lines the eyelids)
- Epithelial stem cells at its surface give rise to progenitor cells that move into corneal epithelium
Choroid
- Consists of loose, well-vascularized connective tissue and contains numerous melanocytes
- Black layer that prevents light from entering the eye from anywhere besides the pupil
Ciliary body
- includes ciliary muscle, processes & zonula
- Involved in affecting shape of lens (e.g. accomodation)
Iris
- Covers outer boundary of lens and creates the pupil
- Denotes color of our eyes
Name the 9 layers of the neural retina (following path of light travel past the vitrous body)
- Inner limiting membrane - basement membrane covered by processes of Muller cells
- Nerve fiber layer (NFL) - contain ganglionic cell axons and converge @ optic disc to form CN II
- Ganglionic layer (GL) - contains ganglion cell bodies, thicker near retina’s center
- Inner plexiform layer (IPL) - contains fibers/synapses of ganglion cells and bipolar neurons
- Inner nuclear layer (INL) - bipolar cell bodies
- Outer plexiform layer (OPL) - contains fibers/synapses of bipolar neurons and rods/cones
- Outer nuclear layer (ONL) - cell bodies of rods/cones
- Outer limiting layer (OLL) - line of junctional complexes holding photoreceptors to Muller cells
- Rod and cone layer (RCL) - contains outer segments of rods/cones
Fovea centralis
- Highest concentration of cones
- Area where visual acuity is sharpest (20/20)
- Absence of blood vessels, cell bodies and axons of ganglionic & inner nuclear layer
Macula Lutea
- Surrounds fovea and protects cones
- Antioxidant properties and short wave UV filter
Where does the LT half of visual field form an image on the retinas?
- Nasal (RT) half of left retina
- Temporal (RT) half of right retina
Where does the RT half of visual field form an image on the retinas?
- Temporal (LT) half of left retina
- Nasal (LT) half of right retina
Where does the inferior visual field information project in the primary visual cortex?
-Superior bank of the calcarine sulcus –> cuneus
Where does the superior visual field information project in the primary visual cortex?
-Inferior bank of the calcarine sulcus –> lingual gyrus
Where does the macula/fovea information project in the primary visual cortex?
-Represented more posteriorly in region of the occipital pole and peripheral fields more anteriorly
