VISUAL SYSTEMAnatomy of the eyeCorneaAnterior chamberContains aqueous humorPosterior chamberContains vitreous humorIrisPupilLens

VISUAL SYSTEMRetinaComposed of 2 layersNeural retina7 layers of the neural retinaPhotoreceptor cell outer & inner segmentsOuter nuclear layerOuter plexiform layerInner nuclear layerInner plexiform layer with ganglion cell bodiesNerve fiber layer (optic fiber layer)

VISUAL SYSTEM2 Limiting membranesOuter limiting membrane is between layers 2 & 7Photoreceptors in this layer interdigitate with the pigmented cells of the retinaCombine with the iris to contract/dilate which protects the photoreceptor cells from damage from bright lightInner limiting membrane is between the nerve fiber layer & the vitreous humor

VISUAL SYSTEMPigmented retinaContinuous sheet of cuboidal cellsFunctions includeNutritional supply for the neural retina glucose & essential ionsProtects photoreceptors in the retina from potentially damaging levels of lightVital role in maintenance of the photoreceptors by phagocytosis

VISUAL SYSTEM

Connection between neural & pigmented retinaRemnant of the embryologic optic cupLocation of a detached retinaImportant in diabetics

CLINICAL CORRELATIONSRetinal detachmentCommon in diabeticsSecondary to inherent problems in the microcirculatory systemOther etiologiesTraumaBlow to the headIncreased ICPTreatmentSurgical reattachment

VISUAL SYSTEMPhotoreceptor cellsFunction is photoreceptionHumans can detect 1 photon of light2 basic types rods & conesSimilar in designLight is transduced in the outer segmentOriented towards the pigmented epitheliumCilium (stalk) connects the outer segment to the inner segmentCell terminates in the outer plexiform layerSynaptic ribbon

VISUAL SYSTEMRodsLocation of transductionPhoton electrical impulseDependent on rhodopsinHave a limited shelf lifeResponsible for Black white differentiationSecondary to this, humans can detect more shades of gray than colors

VISUAL SYSTEMConesLocation of transductionTip of the coneContinuously decreasing numbers of cellsGives the cone its characteristic shapeDependent on cone opsin

VISUAL SYSTEM3 types of conesAbsorb different wavelengths of lightL cones Referred to as red conesSensitive to long wavelengths of lightM conesReferred to as green conesSensitive to medium wavelengths of lightS cones Referred to as blue conesSensitive to short wavelengths of light

VISUAL SYSTEM

Colors are perceived secondary to different amounts of photoreceptors stimulatedColors are represented by a unique combination of these stimulations in the 3 types of cones

CLINICAL CORRELATIONSColor blindnessNot true blindnessSecondary to a genetic defect1 or more of the cone types are missingIndividual can see colorPerception of the color is differentMost common type is red / greenIndividual is missing the L cones (red)

VISUAL SYSTEMSteps in the interpretation of sightPhotoreceptor cells gather photonsPhotons are transduced into electrical signalsGanglion cells in the retina send axons to locations in DiencephalonMidbrain

VISUAL SYSTEM

Nuclei involved in this interpretation includeSuprachiasmatic nucleusHypothalamic regionResponsible for diurnal rhythms

VISUAL SYSTEMPupillary light reflexEdinger Westphal nucleusAccesory optic nucleusOlivary pretectal nucleiSuperior colliculusAssists in controlling eye movementsProjects to the pulvinar

VISUAL SYSTEMPulvinar receives input fromSuperior colliculusPretectumVisual cortexPulvinar sends output toVisual association areasAccomplished via association neurons

VISUAL SYSTEMOptic nerveExtends from the retina to the optic chiasmEncased in arachnoid materBathed in CSFElevated ICP can be detected through the eyesPapilledemaSwelling of the optic nerve headResult is partial / total loss of vision in that eye

VISUAL SYSTEMOptic chiasmOptic nerves from each eye converge hereSecondary to location, the optic chiasm is susceptible to damage

VISUAL SYSTEM

Optic tractComposed of axonal fibers from the retinal ganglion cellsTerminate in the diencephalonLateral geniculate nucleus

CLINICAL CORRELATIONSVisual field defectsEtiologyLesions / trauma alongOptic nerveOptic chiasmOptic tractOptic radiationsVisual cortexOccipital lobe

VISUAL SYSTEMVisual cortexBrodmanns area 17Located in the occipital lobeSpecifically along the calcarine sulcusCuneus gyrusInput from inferior portion of the contralateral hemifieldsLingual gyrusInput from superior portion of the contralateral hemifields

VISUAL SYSTEMNeocortex of Brodmann area 17Contains all 6 layers of the neocortexLayer VI is extremely thickHighly integrated association neuron arrangementAllows for interpretation of sensory photon receptionOccurs n different regionsHelps preserve vision secondary to damage

VISUAL MOTOR SYSTEMextraocular muscles6 Extraocular muscles4 are innervated by the oculomotor nerve (CN III)Superior rectus muscleMedial rectus muscleInferior oblique muscleInferior recuts muscelSuperior oblique muscle is innervated by the trochlear nerve (CN IV)Lateral rectus muscle is innervated by the abducens nerve (CN VI)

VISUAL MOTOR SYSTEMIntraocular musclesCiliary muscleResponsible for changing the thickness & curvature of the lensFacilitates accomodationSphinctor pupillae muscleControls constriction of the pupilDilator pupillae muscleControls dilation of the pupil

VISUAL MOTOR SYSTEMEyelidControlled by 3 musclesLevator palpebrae muscleInnervated by the oculomotor nerve CN IIIFunction is to hold the eyelid upObicularis oculi muscleInnervated by the facial nerve CN VIIFunctions to close the eyelidTarsal or Muller muscleInnervated by postganglionic sympathetic fibersFunctions to help keep the eyelid up

VISUAL MOTOR SYSTEMMotor nuclei associated with the visual motor systemOculomotor nucleusCoordinates movements of the globe & eyelidEdinger Westphal nucleusControls pupillary reflexes

VISUAL MOTOR SYSTEM

Trochlear nucleusInnervates the contralateral superior oblique extraocular musclesAbducens nucleusInnervates the contralateral lateral rectus muscles

VISUAL MOTOR SYSTEMTargeting movementsSaccadesRapid movements of the eyeFrom 200 700 degrees / secondIncludes fixation points at each pointIncludes both horizontal & vertical gazeSmooth pursuitSlow moving targets30 degrees / second or lessCan pursue a target at 100 degrees / second

VISUAL MOTOR SYSTEMVergence eye movementsResponsible for accomodationFocusing on a target at a distanceChanging to focus on a target that is closerVergence movements are much slower than saccadesVergence & saccades may occur in combinationHand eye coordination

VISUAL MOTOR SYSTEMReflex eye movementsOptokinetic eye movementsPanoramic / wide angle view of the worldPupillary light reflexReflex arc mediated by the Edinger Westphal nucleusLesions here result in a fixed, dilated (blown) pupil & is a grave signBlink reflexCorneal wink reflexAutomatic blink if an object is headed for the eye

CLINICAL CORRELATIONSHorners syndromeTriad of signs / symptoms that includePtosisDroopy eyelidMiosisPupil cannot be dilatedAnhydrosisLack of sweating on the affected sideMay indicate a Pancoast tumorBronchogenic lung cancer

CLINICAL CORRELATIONSArgyll Robertson pupilLoss of light reflex constrictionMay be unilateral or bilateralSometimes called prostitutes eyeAccomodates but does not reactPathognomonic for tertiary syphilisTabels dorsalisCentral nervous system syphilis