Eye Flashcards
90% of optic tract axons from the eye retina target the lateral geniculate nucleus (thalamus). What are 3 roles that the 10% remaining play?
1) to hypothalamus (suprachiastamtic): influence of light over neuroendocrine function and over sleep/wake cycle through pineal gland
2) to Pretectum - pupillary light and accommodation relfexes
3) to superior colliculus - coordinate vision with other sensory inputs, allows us to follow visual subjects clearly, visual motor reflexes
What does it mean if a lesion somewhere along the visual system has abnormal pupillary reflex or normal pupillary reflex.
abnormal: before the LGN
Normal: after the LGN, optic radiation, visual cortex, because axons reaching pretectum will leave before synapsing
what is a likely cause of a left contralateral homonymous superior quadrantanopia?
Right temporal lobe tumor, compressing the right Meyer loop
Describe the autonomic control of the eye
Ciliary muscle: Contraction (M3)
for near vision or relaxation (β2) for distant vision
• Sphincter pupillae muscle: Contraction (M3) to decrease the diameter of the iris to reduce the amount of light
entering the eye.
• Dilator pupillae muscle: Contraction (alpha1) to increase the diameter of the pupil to allow more light to enter
the eye.
• Ciliary epithelium. ↑ production (β2) of aqueous humor- decrease (alpha2)
How do beta blockers, and muscarinic agonists/cholinesterase inhibitors affect intraocular pressure
Beta blockers reduce production of aqueous humor to lower intraocular pressure. (beta receptors - ciliary body)
Muscarinic agonists or cholinesterase inhibitors facilitate outflow to reduce IOP.
(muscarinic receptors on ciliary body causes tension of trabecular meshwork to increase outflow of Canal of Schlemn)
What are classes of drugs to treat glaucoma?
- Prostaglandin analogs - increase outflow
- Beta blocker - decrease aqueous humor production
- Carbonic anhydrase inhibitors: decrease aqueous humor production
- Alpha2-agonists - do both, decrease aqueous humor production, increase outflow
- Cholinergic agonist/ cholinesterase inhibitors: contract muscle fibers in ciliary body, increase in AH outflow
- Osmotic agents, increase the osmotic agents leading to fluid going into blood.
What are some eye disorders that can be treated with pharmacology.
- age related macular degeneration
- dry eyes
- allergic conjunctivitis
- bacterial conjunctivitis
The eye is relatively secluded from systemic access, so how come drugs applied topically to the eye can influence the systemic circulation?
lacrimal drainage goes to the nose, lined by highly vascular mucosal epithelium
What are the three muscarinic receptor antagonists and how may they be used
- tropicamide - duration of effect - 4 hours
- this short duration is important for mydriasis on optic exam
- (muscarinic activation cause contraction of pupillary constrictor muscle) - Scopolamine - 3-7 days
- formulated as a patch for motion sickness, - Atropine - 7-10 days
- target is the ciliary muscle because half life is too long, control accommodation.
- effect is cycloplegia (blocking of accommodation important for the treatment of lazy eye amblyopia
Antimuscarinic excess effect (too little acetylcholine effect, opposite of cholinergic excess.
Dry as a bone, blind as a bat, mad as a hatter, hot as hell, red as a beet, full as a flask.
- decrease secretion and salivation because exocrine glands feature M3 muscarinic receptors
- cycloplegia - ciliary muscle paralysis, can’t focus on close objects
- CNS excitation, restlessness, irritability
- decreased ability to sweat
- cutaneous vasodilation
- urinary retention
What are the muscles of the eye under autonomic control
- Sphincter pupillae - pupillary constrictor (parasympathetic, muscarinic)
- Dilator pupillae: (sympathetic, alpha receptor)
- Ciliary epithelium (sympathetic, beta)
- Ciliary muscle (parasympathetic, muscarinic)
What layer of V1 receives input.
M cells - gross stimulus features and movement
P cells - color, visual detail
M cells > magnocellular layers (first two) in LGN > layer 4Calpha > Layer 4B > V5
P cells > parvocellular > layer 4Cbeta > layer 2,3 blobs > V2,3,4
Where are V2,3,4,5 located?
V1,2,3 are medial and travel upwards (form/shape)
V4 is occipital, ventral medial (color)
V5 is temporal. (motion)
- painless vision loss
- hemmorrhages in all 4 quadrants
- dilated tortuous veins
- optic nerve head swelling
- cotton wool spots
- macular edema
- optociliary shunt vessels
Central Retinal Branch Occlusion.
*if found in a young person - prompt inflammatory/hypercoaguability workup.
Generalized breakdown of
blood-retinal barrier with
leakage
Treatment?
Diffuse macular edema
-laser, steroids, anti VEGF
inflammation of: iris (iritis) ciliary body (cyclitis) choroid (choroiditis) Encompasses a large group of diverse diseases This has many potential causes: infectious traumatic neoplastic *AUTOIMMUNE
Symptoms Treatments?
Uveitis:
Redness • Pain • Photophobia - it hurts when the iris moves back and forth so they get photophobia.
Treatments:
Medications
• Topical steroids - Durezol, prednisolone
Mydriatic and
Cycloplegic Agents
• Atropine Sulfate 1%
-the thought process is to keep the pupils dilated so as to keep the iris away from the lens capsule which inflammatory mediators can get the two stuck.
Oral prednisone • Quick onset of action. Less risk of
increase IOP and cataract.
Systemic side effects.
Immunomodulators • Humira, MTX, cyclosporin
Regional depot triamcinolone (4mg) • Periocular • Intraocular
Optic nerve damage
• Ocular hypertension
• Visual field loss (peripheral>central)
Condition, diagnostics and treatment
Glaucoma.
Hypertension arises from the ciliary body and the Canal of Schlemn.
Most people with glaucoma are managed by topical
anti-hypertensive drops
• Beta blockers - decrease production of aqueous humor.
Put a valve connected to the anterior chamber which is equalized to a pressure. When pressure rises in the eye, the fluid will leave into the valve and take residence under the conjunctiva.
The corneal blink reflex
Touch the side of the cornea > afferent (opthalmic division of trigeminal) > spinal trigeminal nucleus >efferent limb - orbital part squinting, palpebral part (blinking) - facial nerve.
What is the role of the endothelium in the cornea?
deturgenscence - pumping ions out of the cornea to keep it transparent.
Where do sty’s form?
sebaceous glands of eyelashes and apocrine glands of eyelids.
Papilledema
Papilledema is swelling of the optic disk (papilla) due to
increased intracranial pressure (ICP) and is almost always
bilateral.
It may develop acutely (ruptured cerebral aneurysm)
or over the course of several weeks or months (tumor).
Patients may have symptoms of increased intracranial
pressure, such as headache or nausea and vomiting.
Papilledema requires an immediate search for the cause.
Diagnosis is by ophthalmoscopy with further tests, usually
brain imaging and sometimes subsequent lumbar puncture,
to determine cause. Treatment is directed at the underlying
condition.
How would each of these look (VF)
occlusion of the right opthalmic artery
aneurysm of right internal carotid
left middle cerebral artery
left parietal lobe lesion
Monocular inferior scotoma
Right nasal hemianopia.
Contralateral homonymous superior quadrantanopsia.
Contralateral homonymous inferior quadrantanopsia
How would optic tract lesion differ from a right PCA infarct?
They would both be contralateral homonymous hemianopia but the one in the primary visual cortex would have macular sparing.
Because macular representation is very large in primary visual cortex Also can receive blood supply from PCA and MCA
Left homonymous superior quadrantanopia with macular sparing
Infarct of posterior cerebral artery branches supplying lingual gyri causing lesion to right occipital lobe and preserving the right occipital pole.
Glaucoma vs macular degeneration loss of vision.
peripheral vision goes first in glaucoma.
In AMD (age related macular degeneration), it is characterized by progressive loss of central vision due to deposition of fatty tissue (drusen) behind the retina (dry) or neovascularization of retina (wet). First to go is central visual field.
