Module 5: Visual Pathway Flashcards
Examination of visual system
Visual acuity, Visual field, Pupillary light reflex, Extraocular muscles & Fundoscopy “VV PEF”
Anatomy of the visual pathway
Eye-optic nerve-chiasm-optic tract-lateral geniculate-optic radiation-occipital
To assess for macular degeneration
Retina
The optic nerve: etiology of dysfunction
Compression, inflammation, Infarction & Alterations in blood supply “CIAA”
Decussation of visual and pupil fibers. Multiple neighboring influences: ______, ______, ______ & ______.
Optic chiasm. CSF, Vascular, Skull & Pituitary.
In __________, the defects become homonymous, on the same side as the visual space. A ___________ localizes only to the retrochiasmal area.
Retrochiasmal lesions. Complete homonymous hemianopsia.
In retrochiasmal lesions, ________ are identical in size, shape and depth: applies only to _________. Imply a more _______: cortical anatomy.
Congruous lesions. Incomplete hemianopsia. Posterior lesion.
Lesion in congruous homonymous hemianopsia
Optic radiation
Lesion in incongruous homonymous hemianopsia
Optic tract
Retrochiasmal field defects: occipital lobe
Homonymous quadrant, Temporal crescent & Macular sparing “HTM”
Retrochiasmal field defects: lateral geniculate
Homonymous sectoranopia
Retrochiasmal field defects: temporal lobe
Homonymous “pie in the sky”
Carry fibers to the LGB. Carry pupil fibers to the midbrain enlage of _________ via the brachium of the superior colliculus. ________ field defects.
Edinger Westphal. Incongruous.
Located in the posterolateral thalamus. Retinotopic organization: layer _____ from contralateral eye. Layer ____ from ipsilateral eye. The _____ projects to 50% of the LGB.
Lateral geniculate. 1, 4 & 6. 2, 3 & 5. Fovea.
Meyer’s loop: temporal lobe. Parietal lobe path direct. Majority of fibers from other thalamic nuclei.
Optic radiations
Striate cortex V1. Caudal 50% encode central __ degrees. Middle 40% encodes ___ degrees. Rostral 10% encodes __ degrees. (The temporal crescent)
Occipital cortex. 10. 10-60. 60-90.
The where pathway
Occipitoparietal
The what pathway
Occipitotemporal
Testing techniques
Confrontation, Patient drawing & Bowl perimetry “CPB”
Bowl perimetry. Kinetic: ________.
Goldman perimeter
Bowl perimetry. Static: ________.
Humphrey perimeter
May occur unilateral or bilateral. Poor vision with small nerve. May occur in isolation or with ocular or forebrain abnormalities. When bilateral and accompanied by poor vision and nystagmus, usually other developmental abnormalities observed.
Optic nerve hypoplasia
Disturbance of axonal metabolism in the presence of a small scleral canal. Increase in size with time, more visible with time due to calcium deposition. Associated visual defect at times not noticed by the patients.
Optic disc drunsen
Possible association with increased abuse of alcohol and drugs. Phenytoin, quinine, alcohol, LSD and cocaine. Maternal diabetes. Perimetry: irregular borders, stable overtime.
Optic nerve hypoplasia
Central cup absent, anomalous vascular branching, vessels arising from the apex of the nerve, retention of vascular detail. Transillumination and irregular disc margin. No hemorrhage or cotton wool spots.
Disc drunsen (ophthalmoscope)
Causes are protean. Papilledema: elevated ICP and disc edema. Space occupying lesion. Disruption of axoplasmic flow at the level of the lamina cribrosa: fast and slow. Subsequent hypoxia and vascular changes on the disc. May take hours to resolve.
Swollen optic nerve
Elevated ICP: headache,nausea,TOV & tinnitus. Normal neurologic exam. Elevated CSF pressure with normal parameters & normal imaging to exclude mass lesion or dural sinus thrombosis. Transient obscurations of vision. Neck stiffness. Neck, shoulder or arm pain. Diplopia (CN VI palsy)
Idiopathic intracranial hypertension
Acquired optic nerve disease without disc edema. Painless progressive loss of vision over first week. Predominantly monocular. Preceding viral illness & sinus symptoms. Loss of acuity, abnormal visual field, color vision & afferent pupil defect.
Optic neuritis
Most common cause for disc swelling over age of 50.
Ischemic optic neuropathy.
Brings the target to the fovea
Saccades
Looking from far to near
Vergence
Moving objects are kept still on retina
Pursuit
When we move our head eyes stay locked on target
Vestibular ocular reflex
When image slips on a large portion of the retina
Optokinetic reflex
Adduction
Medial rectus
Elevation & small intorsion
Superior rectus
Intorsion & small depression
Superior oblique
Abduction
Lateral rectus
Depression & small extorsion
Inferior rectus
Extorsion & small elevation
Inferior oblique
Along the medial aspect of the eyeball, inserts at a point of 5.5mm of the limbus. It is controlled by oculomotor nerve. Contraction of this muscle causes adduction of the eye.
Medial rectus
Along the inferior aspect of the eyeball, inserts at a point of 6.5mm of the limbus. It is controlled by oculomotor nerve. When the eyeball is positioned 23 degrees ouward in the orbit with respect to primary gaze, contraction of this muscle causes depression of the eye. When the eyeball is postioned 67 degrees inward, causes excycloduction of the eye.
Inferior rectus
Contraction causes depression, excycloduction & adduction of eye
Inferior rectus
Along the lateral aspect of the eyeball, inserts at a point of 7mm of the limbus. It is controlled by abducens nerve. Contraction of this muscle causes abduction of the eye.
Lateral rectus
Along the superior aspect of the eyeball, inserts at a point of 7.5mm of the limbus. It is controlled by oculomotor nerve. Contraction of this muscle causes elevation, incycloduction & adduction of the eye.
Superior rectus
Passes through the trochlea and its insertion on the eyeball below the superior rectus muscle is at 51degrees with respect to primary gaze. Controlled by trochlear nerve. Contraction of this muscle causes incycloduction, depression and abduction of the eye.
Superior oblique
The insertion of the is on the eyeball below the lateral rectus muscle at 51degrees with respect to primary gaze. It is controlled by oculomotor nerve. Contraction of this muscle causes excycloduction, elevation and abduction of the eye.
Inferior oblique
Describes movement of one eye
Duction
Describes movement of two eyes in the same direction
Version
Describes movement of two eyes in opposite direction
Vergence
Point of intersection of line of sight when eyes are maximally converged. Theoretically, should be measured from center of rotation of eyes. Clinically, measured from the facial plane.
Near point of convergence
Maximun convergence ability or NPC is measured by
Confrontational testing
NPC breakpoint, target becomes double.
Greater than 7cm
Average NPC
5cm
The recovery point, target becomes single.
10cm
Fast, step-like eye movement that places image of the target on the fovea.
Saccade
Slow, smooth-following movement that maintains image of the target of fovea
Pursuit
The most common test for extraocular motility
Broad H test
Is also a part of confrontational testing
EOM testing
To investigate the integrity of EO muscles and their nerves. To assess the patient’s ability to perform version eye movements. And to determine if strabismus is comitant.
Extraocular motility testing
A pursuit test done bonocularly with penlight at a test distance of 30-40cm. It tests 9 position of action, starting with primary position. It tests fields of action of the 6 extraocular muscles.
Broad H test
Direction where a particular muscle has the greatest action
Field of action
Look for lags or overshoots at various diagnostic position of gaze. Look for smooth and accurate pursuit movements. Look for any gaze restrictions or overactions of muscle in 9 position.
Broad H Test
When deviation of the visual axes remains constant in all fields of gaze, there is
Comitancy
When deviation of the visual axes changes with field of gaze, there is
Noncomitancy
Check by moving the target to diff. positions of gaze, while keeping the patient steady.
Comitancy
Expected findings for saccade testing
Smooth, Accurate, Full & Extensive. “SAFE”
Drugs, fatigue, basal ganglia syndromes, cerebellar syndromes, peripheral oculomotor weakness, white matter diseases and miscellaneous disorders.
Slow saccades
Calibration errors. Opsoclonus. Restriction syndromes.
Fast saccades
Ocular restriction syndromes. Cranial nerve, muscle palsies. Nuclear lesions.
Assymetrical saccidic velocity
