Lectures 25-27: Eye Flashcards
Elevation mediated by…
Sup rectus and inf oblique
Depression mediated by…
Inf rectus and sup oblique
Pulling directions of eye muscles are in same plane as…
Semicircular canals
Torsional eye movements: which muscle groups control which directions?
When eye is abducted, the oblique muscles control torsion; when eye is adducted, the rectus muscles control torsion
Torsion (definintion)
Rotating eye movement within the globe
Two causes of IIIrd nerve palsy
Uncal herniation or PCOM aneurysm
Describe IIIrd nerve palsy
Impaired elevation, depression and adduction (Down and Out); ptosis; enlarged pupil
IVth nerve palsy
Gaze of affected eye is up and medial w/ head tilt to unaffected side
VIth nerve palsy
Gaze of affected eye cannot abduct
Where does binocular coordination occur in LMNs?
Fiber connections in medial longitudinal fasiculus (MLF)
MLF interconnects…
The vestibular nuclei, VI, IV, and III
Lesion of abducens nerve
Impaired abduction of ipsilateral eye
Lesion of abducens nucleus or PPRF also…
Destroys internuclear neurons (which cross and ascend to medial rectus motor neurons in oculomotor nucleus via MLF) –> ipsilateral lateral gaze palsy (inability of patient to look to side of lesion with EITHER eye)
Lesion of MLF…
Internuclear opthalmoplegia (INO) (ipsilateral eye cannot adduct, contralateral nystagmus [because brainstem is attempting to maintain conjugate gaze])
Paramedian pontine reticular formation (PPRF)
Receives connections from contralateral frontal eye fields and innervates abducens nucleus (so, causes same effect as damage of abducens)
What disease often impacts MLF? Talk about age/diagnosis
MS: 1/3 of cases of INO are attributable to MS; 45 yo = unilateral, stroke
Locations of cortical and subcortical control eye movement mechanisms
Cortical eye fields: frontal (supplemental eye field and frontal eye field), parietal (parietal and parieto-occipital eye fields); Subcotical regions: superior colliculus, pretectum, RF
Saccadic eye movements (definition and description). For all saccades, cortical outflow is directed to neurons in the…
Conjugate eye movements intended to foveate a point of interest, fast and ballistic; superior colliculus
How to make a horizontal saccadic eye movement?
PPRF –> abducens –> MLF pathway we learned before PLUS reciprocal inhibitory projections arising from the other abducens nucleus
What is the saccadic gaze center for vertical eye movements? What muscles/nerves?
Rostral interstitial nucleus of the MLF (riMLF); IV and III: io, sr, ir
Smooth pursuit eye movements (definition and stimulus)
Slow conjugate eye movements used to maintain stable retinal image, stimulus is retinal slip
Pathway for smooth pursuit involves…(network name)
Cortico-ponto-cerebellar network
Optokineti nystagmus (phases)
Slow component: smooth pursuit (large moving visual targets); Fast component: saccadic eye movement (reflexively resets the eye; DIRECTION NAMED FOR THIS PHASE)
Vestibulo-ocular reflex (VOR) (definition and neuron arc)
A compensatory eye movement that maintains visual fixation during head movements; head rotation to the right –> activates the right horizontal canal and inhibits the left horizonal canal –> conjugate gaze to the left (involves excitatory [contralateral to activated canal] and inhibitory [ipsilateral to activated canal] pathway of abducens nucleus)
Caloric testing (theory and pneumonic)
Assesses cerebral cortex and brainstem function in unconscious patients, solution different from body temperature will set up convection currents in the fluid w/in the ear, the horizontal (lateral) semicircular canal is tested, then record eye movements; COWS: cold opposite, warm same
Caloric testing (colder)
Cold saline in left ear, nystagmus is to the right (opposite direction of the ear)
Caloric testing (warmer)
Warm saline in left ear, nystagmus is to the left (same direction of ear)
Vergence eye movements (definition, function, what your eye does)
Disconjugate eye movements; maintains fused fixation of a target as viewing distance changes; accommodation and miosis
What fibers interconnect the ciliary muscles and iris muscles?
Zonule fibers
Cornea responsible for how much refraction? And what structure does the remaining fraction?
2/3; lens
Describe the eye chambers
Anterior chamber: b/t cornea and lens filled w/ aqueous humor; Posterior chamber: between zonule fibers and ciliary body, aqueous humor made here by ciliary body; Vitreous body: between retina and lens, filled with vitreous humor
Bipolar cells
Link photoreceptors with retinal ganglion cells
Ganglion cells
First neuron cell in chain of light transduction
Horizontal cells
Horizontal interactions b/t photoreceptor cells (processes in outer plexiform layer)
Amacrine cells
Horizontal interactions b/t ganglion cells (processes in inner plexiform layer)
Layers of retina (10) and locations of cell bodies
Pigment epithelium, next three layers: photoreceptor cells (outer segment, inner segment, outer nuclear layer [cell bodies]), outer plexiform layer, inner nuclear layer (cell bodies of horizontal cells, bipolar cells, amacrine cells), inner plexiform layer, ganglion cell layer, optic fiber layer, internal limiting membrane
Rods
Detect light: low spatial resolution, night/peripheral vision
Cones (and the types w/ colors)
Detect color/acuity: high spatial resolution, day/foveal vision; L = red, M = green, S = blue
Relate convergence to acuity
HIGH degree of convergence of rods and rod bipolar cells onto retinal ganglion cells; LOW degree of convergence of cones and cone bipolar cells onto retinal ganglion
Fovea
Retinal layers become thinner at fovea, reducing barriers to light passage, cone-only region
What’s cool about the structure of the optic nerve?
It’s CNS, so it’s covered with dura right up to the retina w/ central retina vessels running through
Blind spot is located in the _________ portion of the visual field
Temporal
Binocular visual field (definition) is flanked by the ________ _________
Area of the world seen by both eyes; monocular crescents
What happens at the optic chiasm? Which ones cross? So what happens?
Some of the fibers of the optic nerve cross; nasal retinal fibers (NOT temporal retinal fibers); right optic tract carries left visual field, left optic tract carries right visual field
Cut optic nerve…
Monocular blindness
Damage optic chiasm (in saggital plane)…why?
BiTEMPORAL hemianopia (while the nasal retinal fibers are cut, they carry the temporal visual field)
Where does optic tract travel to? How many cell layers and information? Does mixing of information from different eyes happen?
Lateral geniculate nucleus; 6; parvocellular layers (4) = cones, magoncellular layers (2) = rods; NO
Cut optic tract or LGN…
Homonymous hemianopia
What visual field quadrant is carried by Meyer’s loops? Damage (optic radiations temporal lobe)?
Upper quadrant = homonynous superior quadrant hemianopia
Cut optic radiations (parietal lobe)
Homonymous inferior quadrant hemianopia
Superior visual field where in respect to calcarine fissure?
Inferior
Foveal vision maps to where in respect to occipital cortex?
Occipital pole
Damage to primary visual cortex…
Homonymous hemianopia
Damage to primary visual cortex further back…Why?
Homonymous hemianopia with macular sparing; due to magnificant factor (must damage a lot of occipital pole) and to blood supply
What two muscles control pupillary light reflexes and function
Sphincter pupillae: constricts, para; Dilator pupillae: widens, sympa
Steps of direct pupillary light reflex
Afferent: 1. Light to eye; 2. Optic nerve, chiasm, tract; 3. Midbrain pretectum. Efferent: 4. Edinger-Westphal nucleus, 5. CN III to ciliary ganglion; 6. IPSILATERAL sphincter muscle contracts
Steps of consensual pupillary light reflex
Afferent: 1. Light to eye; 2. Optic nerve, chiasm, tract; 3. Midbrain pretectum. Efferent: 4. CONTRALTERAL Edinger-Westphal nucleus via posterior commissure, 5. CN III to ciliary ganglion; 6. CONTRALTERAL sphincter muscle contracts
What cells project to which brain structures (3) to control light-dependent biological clock. Name function of each structure.
Photosensitive retinal ganglion cells project to the hypothalamus (suprachiasmatic nucleus = circadian rhythm), pineal gland = melatonin, and pretectal nucleus = pupillary light reflexes
What determines absorption in eye
Length of time drug stays in cul-de-sac
What are the two themes of distribution for the eye?
Systemic distribution: via nasal mucosa; Ocular distribution: via transcorneal/transconjunctival route
What determines eye metabolism? What does the metabolism?
Tear and tissue proteins, diffusion across cornea/conjunctiva; enzymes in eye and hepatic
Elimination in the eye
Nasolacrimal drainage –> bloodstream –> liver (note: avoids first pass metabolism that you have for oral meds)
Miosis
Constriction of pupils
Mydriasis
Dilation of pupils
Describe iris muscles
Sphincter/inner circular muscle = para; Outer radial muscle = sympa
What characterizes glaucoma
Elevated intraocular pressure (presses backward damaging optic nerve –> progressive retinal ganglion cell axon loss)
Types of glaucoma and presentation. What makes the angle?
Open-angle glaucoma (allows aqueous humor to circulate that is usually found on exam) and closed-angle glaucoma (emergency, no fluid can circulate to cornea, major increase in intraocular pressure that presents with pain, acute visual loss, erythema/edema); lens and iris makes angle
How do we treat closed angle glaucoma?
Lasor irodotomy: drills hole between iris and ciliary body to allow for drainage
Glaucoma is diagnosed with…(3)
Fundoscopic exam: cupping (enlarged, hollowed out appearance of optic nerve), visual field testing, intraocular pressure
Ciliary body consists of…
Ciliary muscles (2) and ciliary epithelium
Accommodation is mediated by __________ stimulation causing which muscle to contract? Define cyclospasm and cycloplegia
Parasympathetic; ciliary muscle; cyclospasm = severe muscle contraction and cycloplegia = no accommodation
What allows the aqueous humor to flow out? (2 methods)
- Para stimulation –> tension of trabecular meshwork –> opening of pres allowing flow through Canal of Schlemm and trabecular meshwork; 2. Uveoscleral outflow pathway: aqueous humor can also flow through ciliary muscles into suprachoroidal space
What promotes aqueous humor secretion
Sympathetic stimulation via beta receptors
How to treat glaucoma?
- Increase outflow (uveoscleral/canal of Schlemm) or 2. Decrease production
What is the first line therapy (example) for treatment of glaucoma, SEs.
Prostaglandin agonists (Latanoprost) which increase aqueous humor outflow via uveoscleral pathway; SEs: blurred vision, irritation, iris color change, keratitis
What receptor antagonist can be used to treat glaucoma (example)? Mechanism, SEs and special considerations (2)
Beta receptor antagonist (Timolol); decrease aqueous humor production; SEs: eye-related AND cardiovascular (bradycardia, hypotension), respiratory (cough, dyspnea); don’t give to patients w/ respiratory disease and CYP2D6 metabolism
What receptor agonist can be used to treat glaucoma (example)? Mechanism, SEs
Alpha2 agonist (Brimonidine); decrease aqueous humor production via pre (less NE) and post synaptic (less cAMP) alpha2 receptors; SEs: eye-related AND cardio: hypotension
Carbonic anhydrase inhibitors example? Mechanism, SEs
Dorzolamide; HCO3- is secreted from blood into aqueous humor, inhibited by CA inhibitor, decreasing aqueous humor production, SEs: eye-related AND metabolic acidosis via CA inhibition in the kidney (HCO3- in lumen not changed into CO2, H2O to be reabsorbed)
Cholinergic agonist: 2 examples? Mechanism, SEs
Carbachol, Pilocarpine; muscarinic agonist: ciliary muscle contraction helps outflow; SEs: eye-related
Name two corneal disorders
Corneal abrasion (visualized with flourescent dye) and corneal ulcer (infection from an abrasion)
What is presbyopia?
Loss of accomodation of the eye due to weakening of the zonules.
A cataract is the most common disorder of the…what happens?
Lens; becomes cloudy and obstruct vision
During cataract surgery, what is put in the eye?
Intraocular lens (lens implant)
What is the second most common cause of visual loss in elderly?
Glaucoma
What is glaucoma?
Optic nerve damage associated with visual field defects usally associated with high intraocular pressure
What kind of vision loss happens with glaucoma?
Loss of peripheral vision
Glaucoma risk factors (6)
Elderly, African/Hispanic Americans, elevated with IOP, family history, diabetics, high myopia
What to check for when looking for glaucoma (3)
Eye pressure, visual field test, optic nerve damage
How do we test for optic nerve damage?
Enlarged cup in optic disc
Treatment for open angle glaucoma
Medications
Treatment for closed angle glaucoma and risk groups
Laser iridotomy; small eyes: Asians, females
What is the most common cause of elderly visual loss?
Age-related macular degeneration
What kind of vision loss happens with ARMD?
Central vision loss
ARMD risk factors (5)
Advanced age, fair skin/eyes, family history, smoking and heart disease
What causes dry ARMD?
Yellow deposits scattered throughout retina with gradual visual loss
What is the difference between dry and wet ARMD?
Fluid/bleeding beneath retina with sudden loss of vision; permanent damage
T/F: Diet has been shown to prevent ARMD
True! A diet rich in fruit and vegetables
Diabetic retinopathy is the __th leading cause of blindness in elderly Americans. How about working-age Americans?
4th; leading cause
What kind of vision loss happens with diabetic retinopathy?
Blurry vision with missing patches
T/F: Diabetic retinopathy cannot be prevented
False! Important for patient to work with doctors to screen for diabetic retinopathy
Increased blood glucose damages what in the eye?
Retinal capillaries
What are four pathological fundoscopic finding in diabetic retinopathy?
Microaneurysms (like little red dots), hemorrhages, cotton wool spots (ischemia), and hard exudates (later stage)
Three stages of diabetic retinopathy
Non-proliferative, pre-proliferatie, proliferative (neovascularization that causes vision loss)
What causes neovascularizastion? What is the reatment?
VEGF, lazer damaging of retina to regress neovascularization
Where does the optic nerve become myelinated? Is it covered by meninges?
After it exits the optic disc; yes
What is optic neuritis (ON)? Pathogenesis
Inflammation of the optic nerve; demyelination of nerve
If optic neuritis occurs alone it’s called ________
Idiopathic
What is the most common optic neuritis association? What are some others (2)
MS (first clinical sign); sarcoidosis and infections
Symptom onset of ON and symptoms (4). Recovery?
Acute, loss of visual acuity, color, field and afferent pupillary defect; vast majority
T/F: ON always presents with a swollen nerve
False! Hard to detect with a fundoscopic exam
If someone has ON, what should be done?
Get an MRI to assess for MS
What is the difference between bilateral optic disc edema (two swollen discs) and papilledema?
Papilledema requires increased ICP (so, not all bilateral disc edemas cause papilledema)
What should you do if you find papilledema?
Scan them!
Reflexes of sphincter muscle
Light and near reflex
Difference in pupil size called? Can be…
Anisocoria; pathologic and physiologic
If one eye sees less light than the other, this is called…
Relative Afferent Pupillary Defect (RAPD)
RAPD can be caused by…(4)
Optic neuropathy, chiasmal/tract lesion, retinal damage, blindness
What is (Holmes-Adie) Tonic Pupil? Who tends to get this and how does it present? What is damaged?
Idiopathic disorder where one pupil (the abnormal one) is larger and reacts poorly to light/accommodation; young women often complain of difficulty reading; parasympathetic fibers to pupil
Argyll Robertson Pupils and number one and two cause
Miotic pupils w/ absence of pupillary light response but retention of near response; neurosyphilis and diabetes
IIIrd nerve palsy tends to effect which fibers first? What does this look like? What can cause this?
Pupillary fibers; affected pupil is mydriatic; uncal herniation/PCOM aneurysm
What is Horner syndrome? It causes…
Oculosympathetic paralysis; miosis of affected pupil and ptosis
