Week 1 - Exam prep

Question 1

Which system uses Roman numerals to describe the degree of angle closure and also grades angle pigmentation?

A) Shaffer System
B) Spaeth System
C) Scheie System
D) Schlemm’s canal System

Answer 1

Scheie System

The Schaffer System is used to describe the degree of angle that is open and Approximates angle of iris insertion relative to trabecular meshwork

Question 2

Which structure directly contributes to the regulation of pupil size?
A) Cornea
B) Lens
C) Ciliary body
D) Sclera

Answer 2

Ciliary Body

The ciliary body contains the muscles responsible for adjusting the shape of the lens, known as ciliary muscles. These muscles play a crucial role in controlling the size of the pupil by adjusting the tension on the suspensory ligaments attached to the lens, which consequently alters the shape of the lens and influences pupil size.

Question 3

Which neurotransmitter is associated with the parasympathetic innervation of the Sphincter Pupillae muscle?
A) Dopamine
B) Acetylcholine
C) Serotonin
D) Norepinephrine

Answer 3

Acetylcholine

The parasympathetic innervation of the Sphincter Pupillae muscle involves the release of acetylcholine as the neurotransmitter. Acetylcholine acts on cholinergic receptors to stimulate the muscle, leading to pupil constriction (miosis). Pharmacological agents such as pilocarpine, which mimic the action of acetylcholine, are classified as parasympathomimetics and are used to induce pupil constriction in clinical settings.

Question 4

Which cranial nerve is responsible for the pre-ganglionic parasympathetic innervation of the Sphincter Pupillae muscle?

A) Trigeminal nerve (CN V)
B) Facial nerve (CN VII)
C) Oculomotor nerve (CN III)
D) Trochlear nerve (CN IV)

Answer 4

Oculomotor nerve

The pre-ganglionic parasympathetic fibers that innervate the Sphincter Pupillae muscle originate from the Edinger-Westphal nucleus in the midbrain and travel via the oculomotor nerve (CN III). These fibers synapse at the ciliary ganglion before reaching the target muscle, controlling the constriction of the pupil in response to light.

Question 5

Which neurotransmitter is associated with the sympathetic innervation of the Iris Dilator muscle?

A) Dopamine
B) Acetylcholine
C) Epinephrine/Norepinephrine
D) Serotonin

Answer 5

Epinephrine/ Norepinephrine

The sympathetic innervation of the Iris Dilator muscle involves the release of epinephrine (adrenaline) and norepinephrine (noradrenaline) as neurotransmitters. These neurotransmitters act on adrenergic receptors to stimulate the muscle, leading to pupil dilation (mydriasis). Pharmacologic agents such as phenylephrine, which mimic the action of epinephrine and norepinephrine, are classified as sympathomimetics and are used to induce pupil dilation in clinical settings.

Question 6

What is the site of synapse for the sympathetic innervation of the Iris Dilator muscle?
A) Oculomotor nerve
B) Ciliary ganglion
C) Superior cervical ganglion
D) Edinger-Westphal nucleus

Answer 6

Superior cervical ganglion

The sympathetic pre-ganglionic fibers that innervate the Iris Dilator muscle originate from the hypothalamus and travel via cervical sympathetic nerves. These fibers synapse at the superior cervical ganglion before reaching the target muscle. Post-ganglionic fibers then travel via long ciliary nerves, which are branches of the trigeminal nerve (cranial nerve V), to innervate the Iris Dilator muscle and induce pupil dilation.

Question 7

Which class of pharmacologic agents mimics the action of sympathetic neurotransmitters to induce pupil dilation?
A) Cholinergics
B) Anticholinergics
C) Adrenergics
D) Parasympathomimetics

Answer 7

Adrenergics

Adrenergic agents, also known as sympathomimetics, mimic the action of sympathetic neurotransmitters such as epinephrine and norepinephrine. These agents act on adrenergic receptors to stimulate the Iris Dilator muscle, leading to pupil dilation (mydriasis). Phenylephrine is an example of an adrenergic drug used clinically to induce pupil dilation.

Question 8

How does Horners relate to the parasympathetic and sympathetic pathway dysfunction

Answer 8

Horner’s syndrome results from interruption of sympathetic nerve pathways involved in pupil dilation, causing a characteristic triad of symptoms:

1. Ptosis (drooping of the upper eyelid) due to the loss of sympathetic innervation to the Müller’s muscle responsible for eyelid elevation.
2. Miosis (constriction of the pupil) due to unopposed parasympathetic innervation from intact cranial nerve III (oculomotor nerve) to the Iris Sphincter muscle.
3. Anhidrosis (lack of sweating) on the affected side of the face due to interruption of sympathetic innervation to sweat glands.

Horner’s syndrome can result from various causes, including injury, tumors, vascular disorders, or neurological conditions affecting the sympathetic pathway. It can be localized to different parts of the pathway, including the hypothalamus, brainstem, sympathetic chain, or even peripheral nerves.

Question 9

Which structure forms a major arterial circle in the eye?

A) Retina
B) Ciliary body stroma
C) Optic nerve
D) Choroid

Answer 9

Ciliary Body Stroma

The major arterial circle in the eye is located in the ciliary body stroma near the iris root. It is formed by branches derived from both the anterior ciliary arteries and long posterior ciliary arteries. These branches course through the iris stroma in a radial pattern, supplying blood to the iris tissue.

Question 10

Which part of the ciliary body marks the transition between ciliary processes and the retina?

A) Pars plicata
B) Ciliary processes
C) Pars plana
D) Ora serrata

Answer 10

Pars Plana

The pars plana is the posterior zone 4mm of the ciliary body, characterized by its flat region. It serves as the transition zone between the ciliary processes (found in the pars plicata) and the neural retina.

The Ora serrata, on the other hand, represents the junction between the ciliary body and the retina, where the non-pigmented ciliary epithelium transitions into the neural retina with a scalloped edge appearance.

Question 11

What structures provide tension to the lens zonules?

A) Retinal pigmented epithelium
B) Ciliary processes
C) Corneal endothelium
D) Scleral fibers

Answer 11

Ciliary processes

Ciliary processes are villus-like structures composed of a capillary network, loose connective tissue (lamina propria), and a double-layered epithelium. They are responsible for producing aqueous humor and providing tension to the lens zonules. The zonular insertions arise from the ciliary epithelium, approximately 1mm anterior to the ora serrata. These processes pass through the valleys of the pars plicata to insert onto the lens, thereby exerting tension on the zonular fibers and contributing to accommodation.

Question 12

Which layer of the ciliary muscle is attached to the ciliary processes?

A) Longitudinal/meridional
B) Radial/oblique
C) Circular
D) None of the above

Answer 12

Circular

The circular layer of the ciliary muscle is the innermost layer and is closest to the ciliary processes. It is responsible for regulating the tension on the lens zonules and thereby controlling the shape of the lens during accommodation.

Question 13

What forms the major arterial circle of the iris?

A) Long posterior ciliary arteries
B) Anterior ciliary arteries
C) Vascular plexus in the ciliary processes
D) Branches from the major arterial circle

Answer 13

Branches from the major arterial circle

The major arterial circle of the iris is formed by branches derived from both the long posterior ciliary arteries and the anterior ciliary arteries. These branches then form the vascular plexus in the ciliary processes. It’s essential to note that the vascular supply of the ciliary body, including the ciliary processes, differs from that of the iris vessels and the capillaries in the ciliary body.

Question 14

Which component of the ciliary body histology is responsible for uveoscleral outflow?

A) Ciliary muscle
B) Ciliary body stroma
C) Ciliary nerve branches
D) Ciliary body microvasculature

Answer 14

Ciliary Body Stroma

The ciliary body stroma, characterized by loose, vascularized connective tissue, fills the core of ciliary processes and extends between ciliary muscle fibers. The connective tissue spaces in the muscle serve as the pathway for uveoscleral outflow, allowing aqueous humor to exit the eye.

Question 15

Which neurotransmitter pathway leads to the contraction of the constrictor pupillae muscle?

A) Dopaminergic
B) Adrenergic
C) Cholinergic
D) Serotonergic

Answer 15

Cholinergic

Activation of muscarinic acetylcholine receptors by parasympathetic nerves to the eye results in the contraction of the constrictor pupillae muscle. This leads to pupillary constriction, which helps adjust the pupil in response to changes in light intensity and regulates intraocular pressure. Pilocarpine, an example of a muscarinic agonist, activates these receptors and is used clinically to induce pupil constriction and increase trabecular outflow, thereby lowering intraocular pressure.

Question 16

Which of the following mechanisms involved in aqueous humor formation requires active cellular participation?

A) Diffusion
B) Ultrafiltration
C) Active secretion
D) None of the above

Answer 16

Active secretion

Active secretion is the mechanism of aqueous humor formation that involves active cellular participation. This process occurs primarily in the ciliary epithelium, where specialized cells actively transport ions and solutes from the blood into the aqueous humor, contributing to its composition and volume. Diffusion and ultrafiltration, on the other hand, are passive processes responsible for the accumulation of plasma ultrafiltrate in the stroma of the ciliary body.

Question 17

Across which structures do water and water-soluble substances flow into the ciliary stroma?

A) Non-fenestrated ciliary capillary endothelia
B) Ciliary muscle fibers
C) Fenestrated ciliary capillary endothelia
D) Zonular fibers

Answer 17

Fenestrated ciliary capillary endothelia

Water and water-soluble substances flow across fenestrated ciliary capillary endothelia into the ciliary stroma. Fenestrated endothelia have small pores (fenestrations) that allow the passage of small molecules and water. This movement occurs in response to an osmotic gradient or hydrostatic pressure, facilitating the exchange of fluid and solutes between the blood and the ciliary stroma.

Question 18

Which cells serve as the main site for active secretion in the formation of aqueous humor?

A) Pigmented epithelial cells
B) Endothelial cells
C) Non-pigmented epithelial cells
D) Fibroblasts

Answer 18

Non-pigmented epithelial cells

Non-pigmented epithelial cells are the main site for active secretion in the formation of aqueous humor. These cells are part of the ciliary body epithelium and are responsible for actively transporting ions and other molecules across a concentration gradient. This process is mediated by protein transporters and contributes significantly to the overall volume of aqueous humor produced.

Question 19

Which signaling cascade is initiated upon stimulation of β adrenergic receptors localized to the ciliary epithelium?

A) Phospholipase C pathway
B) Adenylate cyclase pathway
C) Tyrosine kinase pathway
D) cGMP pathway

Answer 19

Adenylate Cyclase Pathway

Stimulation of β adrenergic receptors localized to the ciliary epithelium initiates a signaling cascade involving adenylate cyclase. This cascade leads to the stimulation of cyclic AMP (cAMP) production and subsequent activation of protein kinase-A. Protein kinase-A can then affect the rate of the Na⁺/K⁺ pump, thereby modulating aqueous secretion rate. Timolol, an example of a β adrenergic receptor antagonist, such as Timolol, reduces both aqueous inflow and intraocular pressure (IOP) through this mechanism.

Question 20

Which type of adrenergic receptor is primarily targeted by commercially available α-2 adrenergic agonists for reducing intraocular pressure?

A) β adrenergic receptors
B) α-1 adrenergic receptors
C) α-2 adrenergic receptors
D) Dopaminergic receptors

Answer 20

α-2 adrenergic receptors

Activation of these receptors leads to inhibition of the adenylate cyclase pathway, resulting in decreased cyclic AMP (cAMP) levels and prevention of protein kinase-A phosphorylation.
e.g. Brimonidine
Reduces Aq production and increased uveoscleral outflow?

Question 21

What is the rate-limiting step in the conventional (trabecular) outflow pathway of aqueous humor?

A) Flow through the inner wall of Schlemm’s canal
B) Flow through the ciliary muscle
C) Flow through the iris stroma
D) Flow through the ciliary processes

Answer 21

Flow through the inner wall of Schlemm’s Canal

In the conventional (trabecular) outflow pathway of aqueous humor, the rate-limiting step is the flow through the inner wall of Schlemm’s canal. This pathway is pressure-dependent and involves the drainage of aqueous humor through the trabecular meshwork into Schlemm’s canal, ultimately leading to aqueous drainage from the eye.

Question 22

In which pathway of aqueous outflow is the rate-limiting step the flow through the ciliary muscle?

A) Conventional (trabecular) outflow
B) Unconventional (uveoscleral) outflow
C) Schlemm’s canal outflow
D) Aqueous humor production pathway

Answer 22

Unconventional (uveoscleral) outflow

In the unconventional (uveoscleral) outflow pathway of aqueous humor, the rate-limiting step is the flow through the ciliary muscle. This pathway is pressure-independent and involves the drainage of aqueous humor from the eye through the ciliary muscle into the suprachoroidal space and eventually into the sclera, from where it is absorbed into the systemic circulation.

Question 23

What is the mechanism of action of Brimatoprost and what class of drug is it?

Answer 23

Prostaglandin Analogue

Increased Outflow of Aqueous Humor: Bimatoprost increases the outflow of aqueous humor from the eye. It primarily acts on the uveoscleral outflow pathway, facilitating the drainage of aqueous humor through the ciliary muscle into the suprachoroidal space and eventually into the sclera. This results in a decrease in intraocular pressure.