Orbit/Glaucoma (Week 1--Melega)

Question 1

What goes through the optic canal?

Answer 1

Optic Nerve (CN II)

Ophthalmic artery

Question 2

What goes through the superior orbital fissure?

Answer 2

Occulomotor nerve (CN III)

Trochlear nerve (CN IV)

Ophthalmic nerve (CN V1)

Abducent nerve (CN VI)

Superior ophthalmic vein

Inferior ophthalmic vein (one part)

Question 3

What goes through the inferior orbital fissure?

Answer 3

Maxillary nerve branches (CN V2)

Maxillary artery branches

Inferior ophthalmic vein (one part)

Question 4

Walls of orbit shared with paranasal sinuses

Answer 4

Orbital plate of frontal bone with frontal sinus

Thin plate of ethmoid bone with ethmoid sinus

Orbital plate of maxillary bone with maxillary sinus (infraorbital nerve in wall)

Question 5

Fascial sheath

Answer 5

Forms socket for eyeball

Pierced by tendons of extraocular muscles

Forms check ligaments (medial check ligament, lateral check ligament, suspensory ligament) that make sure you can’t turn your eyeballs too far in one direction

Orbital fat provides cushion

Periosteum is called periorbita (lines bone of the orbit)

Question 6

7 extraocular muscles

Answer 6

1) Levator palpebrae superioris (CN III superior): elevate upper eyelid
2) Superior oblique muscle (CN IV): rotate in/intortion
3) Inferior oblique muscle (CN III inferior): rotate out/extortion
4) Superior rectus muscle (CN III superior): look up/elevation
5) Inferior rectus muscle (CN III inferior): look down/depression
6) Medial rectus muscle (CN III inferior): look in/adduction
7) Lateral rectus muscle (CN VI): look out/abduction

Question 7

3 somatic motor nerves

Answer 7

1) Occulomotor nerve (CN III)
2) Trochlear nerve (CN IV)
3) Abducent nerve (CN VI)

Question 8

Occulomotor nerve (CN III)

Answer 8

Superior division: innervates levator palpebrae superioris muscle, superior rectus muscle

Inferior division: innervates medial rectus muscle, inferior rectus muscle, inferior oblique muscle

Question 9

Trochlear nerve (CN IV)

Answer 9

Innervates superior oblique muscle

Question 10

Abducent nerve (CN VI)

Answer 10

Innervates lateral rectus muscle

Question 11

3 coats of wall of eyeball

Answer 11

Fibrous coat

Uvea

Retina

Question 12

Fibrous coat

Answer 12

Cornea: anterior 1/6; avascular; somatic sensory (CN V1)

Sclera: posterior 5/6; pierced by optic nerve and ophthalmic vessels; attachment point for extraocular muscles

Limbus: corneoscleral junction

Question 13

Uvea

Answer 13

Vascular pigmented coat

Choroid: highly vascular

Ciliary body: ciliary muscle (smooth muscle, parasympathetic), ciliary processes become zonules that attach to lens, capillaries (vitreous humor production)

Iris: sphincter pupillae muscle (smooth muscle, paraympathetic, circular muscle?), dilator pupillae muscle (smooth muscle, sympathetic)

Pupil

Question 14

Retina

Answer 14

Retinal pigment epithelium

Neurosensory retina

Optic disc forms optic nerve that penetrates lamina cribrosa of sclera; central retinal artery/vein also passes through

Optic chiasm

Question 15

Eyeball interior

Answer 15

Lens (elastic qualities)

Vitreous chamber with vitreous body (proteoglycans/hyaluronan)

Aqueous humor fills anterior part, which has 2 chambers (posterior chamber and anterior chamber)

Question 16

What happens to the vitreous chamber at 40 - 70 years of age?

Answer 16

Vitreous becomes more liquid and can detach from retina (vitreous detachment) which causes flaskes of light/floaters

If fluid gets into retina get retinal detachment (serious visual problem)

Question 17

What is the flow of aqueous humor?

Answer 17

Aqueous humor produced by epithelium lining ciliary process of ciliary body –> into posterior chamber –> through pupil –> into anterior chamber –> into trabecular meshwork –> into canal of Schlemm –> scleral veins

Question 18

What is aqueous humor?

Answer 18

Produced by epithelium lining ciliary processes of ciliary body

Protein-free ultrafiltrate of blood plasma

Maintains shape of anterior eyeball

Nourishes cornea and lens

Question 19

Ophthalmic nerve (CN V1)

Answer 19

Lacrimal nerve to lacrimal gland

Frontal nerve to upper eyelid and forehead (supraorbital nerve and supratrochlear nerve)

Nasociliary nerve (ciliary ganglion branches pass through ciliary ganglion and become short ciliary branches for sensory to iris and cornea; long ciliary branches are to iris and cornea; ethmoid branches to nasal cavity; infratrochlear branches to medial eyelid)

Question 20

Ciliary ganglion roots

Answer 20

Parasymp pre fibers from oculomotor nerve (CN III) symapse in ganglion

Somatic sensory fibers from ophthalmic nerve (CN V1) pass through

Sympathetic fibers from surface of internal carotid artery (superior cervical ganglion) pass through

Question 21

Short ciliary nerves

Answer 21

Branches off ciliary ganglion

Parasymp post fibers to ciliary muscle and to sphincter pupillae muscle

Somatic sensory fibers from ophthalmic nerve (CN V1) FROM cornea and iris

Sympathetic fibers to blood vessels in choroid

Question 22

Sympathetic fibers of the orbit

Answer 22

Symp pre cell bodies in T1 - 4 –> symp post cell bodies in superior cervical ganglion –> symp post fibers course on surface of internal carotid artery

Question 23

2 courses of sympathetic fibers

Answer 23

Ciliary ganglion (no synapse) –> short ciliary nerves –> blood vessels in choroid

Long ciliary nerves (branches of ophthalmic nerve-nasociliary) –> dilator pupillae muscle in iris

Question 24

Ophthalmic artery

Answer 24

Central artery of retina

Ciliary arteries supply choroid

Lacrimal artery

Supraorbital and supratrochlear arteries

Anterior and posterior ethmoid arteries

Muscular branches

Question 25

Ophthalmic veins

Answer 25

Superior ophthalmic vein --\> superior orbital fissure --\> cavernous sinus Inferior ophthalmic vein branch --\> superior orbital fissure --\> cavernous sinus Inferior ophthalmic vein branch --\> inferior orbital fissure --\> pterygoid venous plexus

Question 26

Optic disc

Answer 26

Small white area where there are no photoreceptors Optic nerve (CN II) passes through Entrance of ventral artery of retina (branches don't anastomose with each other = end artery) Exit of central vein of retina

Question 27

Sympathetic innervation of the eye

Answer 27

NE --\> alpha 1 receptors --\> contract **radial smooth muscle** of iris **(dilator pupillae)** --\> mydriasis (bigger pupil)

Question 28

Parasympathetic innervation of the eye

Answer 28

1) ACh --\> muscarinic receptor --\> **contract sphincter smooth muscle** of iris **(constrictor pupillae)** --\> miosis (smaller pupil) 2) ACh --\> muscarinic receptor --\> **contract ciliary body** --\> accommodation

Question 29

Accommodation

Answer 29

Light from single point of distant object and light from single point of near object being brought to a focus by changing curvature of the lens Ciliary body muscle contracts and moves anteriorly --\> relaxes tension on suspensory ligaments that support lens --\> lens becomes more convex (rounds up in shape) --\> eye focuses on nearby object

Question 30

Accommodation development and age-dependence

Answer 30

Effective by age 4 months Remains adequate until onset of presbyopia at 40 years old

Question 31

Presbyopia

Answer 31

Condition in which lens of eye loses some ability to focus which makes it difficult to see objects up close Also continuing appositional growth of lens fibers and age-related changes in lens capsule causes elasticity of lens to diminsh ??

Question 32

Cycloplegia

Answer 32

Paralysis of ciliary muscle of eye results in loss of accommodation Due to devervation or pharmacologic action (ACh antagonist like atropine)

Question 33

Relationship between mydriasis and accommodation

Answer 33

Mydriasis can occur without loss of accommodation (alpha 1 agonist) If have loss of accommodation, then will have mydriasis (muscarinic antagonist) Alpha 1 only at pupillary dilator smooth muscle ACh at both ciliary muscle and pupillary sphincter smooth muscle

Question 34

Mydriatic agents (increase pupil size)

Answer 34

Sympathomimetics (alpha 1 agonists): phenylephrine Parasympatholytics (muscarinic antagonists): atropine

Question 35

Miotic agents (decrease pupil size)

Answer 35

Parasympathomimetics (cholinergic agonists) Sympatholytics (alpha 1 antagonists) Opioids

Question 36

How do opioids cause miosis?

Answer 36

**Opioid inhibitory interneurons** maintain inhibitory tone on **Edinger-Westphal cell bodies** (**para** **pre** that regulate para contraction of pupillary sphincter smooth muscle of iris) --\> opiods bind receptors on these interneurons and cause them to have **less inhibition of E-W pre neurons** so they fire more rapidly and lead to more activation of para post neurons --\> **contraction of pupillary sphincter smooth muscle** of the iris --\> **miosis**

Question 37

Aqueous humor production and outflow

Answer 37

Produced by **ciliary body** and derived from plasma **capillary network** Secretion of **Na+** and **HCO3-** into aqueous humor draws **water** in osmotically Drained mostly through **trabecular meshwork** to **Canal of Schlemm**; also via **uveoscleral** **pathway** (\<10% of total)

Question 38

Glaucoma

Answer 38

Group of diseases that can **damage optic nerve** and cause vision loss/blindness **Obstruction** of **aqueous** **drainage** --\> **elevated intraocular pressure** --\> damage to optic nerve (more than 1 million fibers connecting retina to brain)

Question 39

Open-angle glaucoma

Answer 39

Angle between peripheral **iris** and **cornea** is normal Drainage of aqueous humor affected due to **clogging** of **trabecular meshwork** Increased IOP, degeneration of optic head, restricted visual field all typify primary open-angle glaucoma Symptoms: generally field of vision **narrowed** so cannot see clearly

Question 40

Closed-angle glaucoma

Answer 40

Angle between **iris** and **cornea** narrows which **blocks** drainage of aqueous humor Rarer, but severe, acute form of disease can cause **blindness** if not treated in **24 - 48 hours** Sudden increase in pressure inside eye causes **intense** **pain** and **blurred vision** Symptoms: **nausea**, **vomiting**, **headaches**, intense pain in eyes, bloodshot eyes and increased sensitivity, medium dilatation of pupil, blurred vision, coloured circles surrounded by light

Question 41

What is the aim of pharmacotherapy for glaucoma?

Answer 41

Reduce intraocular pressure (IOP) to prevent damage to nerve fibers and prevent visual defects 1) **Decrease aqueous production** by ciliary body 2) **Increase aqueous outflow** through trabecular meshwork and uveal outflow paths

Question 42

Drugs used to manage chronic glaucoma

Answer 42

Beta blockers Alpha 2 agonists Carbonic anhydrase inhibitors Prostaglandin agonists Parasympathomimetics

Question 43

Drugs for emergency condition--closed angle glaucoma

Answer 43

Hyperosmotics Note: can also use laser to puncture iris and allow outflow of aqueous humor from posterior chamber!

Question 44

Drugs that inhibit aqueous humor inflow

Answer 44

**Beta blockers** (**timolol** (topical administraction)): block beta receptors on ciliary epithelium so Na/K ATPase can't let Na+ into aqueous humor and thus no water osmotically moves in either **Alpha 2 agonists** (**brimonidine**, apraclonidine (topical administration)): act presynaptically at alpha 2 receptors to inhibit NE release and also block Na/K ATPase from letting Na+ into aqueous humor and thus no water osmotically moves in either **Carbonic anhydrase inhibitors** (**acetazolamide** (systemic) and **dorzolamide** (topical)): reduce HCO3- production (enzymatic process) and secretion into aqueous humor and thus no water osmotically moves in either

Question 45

Drugs that increase aqueous humor outflow

Answer 45

**Parasympathomimetics** (pilocarpine, AChE inhibitors): contract ciliary muscle to increase tone and alignment of trabecular network and facilitate aqueous humor outflow via trabecular meshwork **F2alpha prostaglandin agonists** (**lantanoprost**): increase uveoscleral outflow (aqueous humor goes between ciliary bundles and into episcleral tissues to be reabsorbed into orbital blood vessels and drained via conjunctival vessels)

Question 46

Hyperosmotics

Answer 46

**Mannitol** (20% IV solution) or glycerol (50% oral solution) Increase serum osmolarity to reduce intraocular water content by drawing water out of the eye Use caution in congestive heart failure; avoid glycerol in diabetics Used only in management of **acute** elevations of IOP as seen in closed angle glaucoma and occasionally after surgery

Question 47

Optic cupping

Answer 47

Cuppng of optic nerve is appearance of optic nerve viewed through pupil--**empty space in middle** of optic nerve **surrounded by nerve fibers** Glaucoma causes loss of nerve fibers and cup becomes larger (larger C/D ratio means more damage) because less space occupied by remaining nerve fibers