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Neurology Chapter 8
The Visual System
| Term | Definition |
|---|---|
| Refraction | When light comes into eye, it is bent so that it converges at the fovea at bottom part of eye. Responsible for acute vision |
| Optic Nerve | Visual fibers from retina to optic chiasm. Carries info from eye to the optic chiasm- where decussation occurs |
| Optic Tract | Optic fibers between chiasm to lateral geniculate body of thalamus (info you see) or fibers that bypass thalamus to superior colliculus of the mid brain (visual reflexes) |
| geniculocalcarine fibers (aka optic radiation) | When info has entered the thalamus this will relay the info further back to the primary visual cortex of occipital lobe - Goes through the temporal lobe to get to the occipital lobe |
| Visual Field | area you see before you - outside world |
| Retinal Field | -Focused representation of visual field -Reversed (right/left, up/down) -Imaged is reversed in your cortex |
| Monocular Visual Field | Lateral portion perceived in only one eye (peripheral vision) |
| Binocular Visual Field | Common area seen by both eyes |
| Eyeball | -Weighs 7.5 g and 2.4 cm long -What you see when you look at a person is only 1/6 of it -5/6 of it is cased in orbital cavity |
| Anterior Chamber of the eye | -filled with aqueous humor |
| Aqueous humor | -made by choroid plexus of the ciliary processes -drains through canal of Schlemm -Flow needed to maintain pressure and circulation |
| Fovea | Area for acute vision where all all visual info must be centralized |
| Vitreous humor | -located between the lens and retna -jelly like substance that helps to maintain eye pressure and prevents eye from collapsing |
| Macula lutea- | cells underneath the fovea |
| Cones | -receptor cells that perceive photons - about 30 million in human eye - Discriminate color and sharp vision - Mainly located in macula lutea and the fovea centralis |
| Optic disk | -No rods and cones at this location cause a blind spot -Where the optic nerve starts. |
| Retina | -Innermost layer of eye. -Where visual stimulation starts -Houses: Rods& Cones, Bipolar Cells,Ganglion Cells - Light passes through cell layers and then back to the ganglion cells. |
| Choroid layer of the eye | makes up the iris |
| Fibrous Tunic | -makes up hard surface of the eye. -Makes up total outer surface. - Made up of the Sclera and Cornea |
| Sclera | Part of the Fibrous Tunic that makes up the white part of eye |
| Cornea | Nonvascular and transparent fibrous region of eye |
| 3 layers of the eye | -Fibrous Tunic -Vascular Tunic -Retina |
| Vascular Tunic | Includes: -Choroid -Iris -Ciliary Body |
| Lens | Focuses images on the Retina |
| Ciliary Muscle | -Regulates changes by lens (near and far vision) -Responsible for contracting or enlarging the iris |
| Iris | -Controls pupil size -Controls amount of light that gets in to the pupil by contracting. |
| Bipolar Cells and Ganglion Cells | -Responsible for taking info away from the rods and the cones and passing it through the neural projections of the eye to the optic nerve where that neural impulse is carried on to the brain. |
| Rodes | -photon receptor in the eye - about 100 million in human eye - Discriminate in dim light - Sensitive to shape and movement - Lateral peripheral retina |
| Central Visual Mechanism/ path | -Visual pathway from retina to primary visual cortex -Optic nerve fibers exit the optic foramina & move to optic chiasm -Optic tract moves to lateral geniculate bodies in thalamus -Travel to occipital lobe to visual cortex through the optic radiation |
| optic foramina | Hole in skull that allows optic nerve to project from eye into the brain. |
| Nasal visual fields | -project to temporal retinal fields and do not cross at optic chiasm |
| Temporal visual field | Project to nasal retinal fields and do cross at optic chiasm |
| Left optic tract | carries info from right visual field in each eye |
| Right optic tract | carries info from left visual field in each eye |
| Reason people with aphasia have visual spacial problems | Optic radiation is cut off due to lesion in temporal lobe. |
| Brodmann area 17 | -aka Primary visual Cortex -Processes raw info being projected from eyes - Has a point to point representation of the retinal fields |
| Visual association cortex | -Makes sense out of what you are seeing- understanding a bottle is a bottle |
| Pupillary Light Reflex | -auto processes of the eye that never make it to brain but is handled in mid brain at the Edinger-Westphal Nucleus and is carried on by oculomotor cranial nerve III -tells pupil to contract w/ light -Damage due to Horner’s syndrome or CN III lesion |
| Horner’s syndrome | Associated w/ stroke or tumor -Characterized by an always constricted pupil and drooping of one eyelid, and inability to sweat on face |
| Accommodation Reflex aka the Focus Reflex | -Modifies lens curvature when object moves closer to eyes -Lens flexibility important -Lens tends to become less flexible around age 45 |
| Hypermetropia | -aka farsightedness -Can see distant objects but not near -Due to short eyeball & inadequate refractory power of lens -Can correct by keeping pupil elongated by contracting the Ciliary muscles. -Gets worse with age b/c Cilliary muscles get tired |
| Myopia | -Nearsightedness -Can see near objects but not distant -Due to abnormally long eyeball & too strong refractory power of the lens -info comes together before it hits the fovia. -Does not get worse with age. -Easily corrected with glasses) |
| Astigmatism | -Focus disorder of vertical and horizontal rays -Caused by irregular shape of the cornia, lens, or both |
| Monocular blindness | Blindness in one eye due to optic nerve lesion before optic chiasm |
| Bitemporal (heteronymous) hemianopsia | -Loss of temporal visual fields of each eye -Lesion at optic chiasm -Also called tunnel vision -LR |
| Nasal hemianopsia | -Partial lesion in optic nerve -Loss of nasal vision in one eye due to lesion in lateral edge of optic chiasm. -R or L |
| Homonymous hemianopsia | -lesion that cuts off optic tract or optic radiations. -Most common lesion found in stroke victims -Loss of left or right visual fields for both eyes due to lesion in right optic tract -LL |
| Homonymous left Superior quadrantopsia aka Upper Left Quadrantanopsia | -uncommon Loss of vision in left upper quadrant of each eye due to lesion in Meyer’s Loop/ optic radiation |
| Homonymous left Inferior quadrantopsia aka Lower left Quadrantanopsia | -uncommon Loss of vision in lower left quadrant of each eye due to lesion in medial fibers of visual tract |
| Homonymous | -Similar regions affected in each eye -Right visual fields of both eyes |
| Heteronymous | -usually occurs from lesion in optic chiasm -Different regions affected in each eye -i.e. Left visual field of one eye and right visual field in other eye |
| Homonymous Hemianopsia | Loss of left or right visual fields for both eyes due to lesion in right optic tract |
| Presbyopia | decrease in vision with age |
| Cataract | Increase in protein in lens -corrected by surgery |
| Glaucoma | Increased intraocular pressure- usually caused by the blocking of the canal Schlemm. -Parallel to hydrocephalus |
| Infections | Inflammation of the eye |
| Retinitis Pigmentosa | Familial disorder causing loss of rod cells. Includes peripheral visual loss and night blindness |
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aramos139
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