Ocular physiology

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Which of the following is NOT a function of the eyelids?

Contributing the mucin to the precorneal tear film

What determines the shape and width of the palpebral fissure?

Medial and lateral canthal ligamentous and muscle attachments

Which of the following breeds is likely to have a narrow, almond-shaped palpebral fissure?

Dolichocephalic breeds

Which metabolic pathway is primarily used by keratocytes for glucose metabolism?

Pentose phosphate shunt

What is the main function of nicotinamide adenine dinucleotide phosphate (NADPH) produced by the corneal epithelium?

Free radical scavenging

Which layer of the cornea has the highest glucose needs?

Corneal endothelium

Which muscle is responsible for opening the upper eyelid in animals?

Levator palpebral superioris

Which nerve innervates the levator palpebral superioris muscle?

Oculomotor nerve (CN III)

Which reflexes are primitive reflexes with a purely subcortical course and are elicited by touch?

Corneal and palpebral reflexes

Which reflex is cortically mediated and is initiated by a threatening gesture?

Menace response

Which layer of the tear film is the thickest and performs the primary functions of the tear film?

The middle aqueous layer

What is the primary purpose of the outer lipid layer in the tear film?

To prevent evaporation of the underlying layers

Which gland is responsible for producing the outer lipid layer of the tear film?

Meibomian gland

What is the approximate tear volume turnover rate in horses?

7 minutes

Which of the following animals has been detected to have lysozyme activity in their tears?


Which of the following immunoglobulins is present in greater concentrations in the precorneal tear film (PTF) than immunoglobulins G and M?


Which nerve provides the lacrimal gland with its parasympathetic and sympathetic fibers?

Trigeminal nerve

Which cells in the lacrimal gland are primarily responsible for secretion of proteins in lacrimal gland fluid?

Acinar cells

Which test is primarily used to evaluate the aqueous portion of tears in clinical settings?

Schirmer tear test (STT)

Which layer of tears is composed of tear mucins produced by the apocrine conjunctival goblet cells?

Deep layer

Which of the following is responsible for corneal scarring?

Changes to the light-scattering properties of keratocytes

Which species has the highest density of goblet cells in the fornix?

Guinea pigs

What is the primary role of the corneal endothelium?

To maintain stromal deturgescence

Which type of mucin is associated with the corneal and conjunctival microvilli?

Membrane-bound mucin

What is the function of the corneal epithelium?

To provide a physical barrier against aqueous humor

What is the mechanism that maintains steady-state hydration in the cornea?

Pump-leak mechanism

Which nerve is responsible for the involuntary blinking that occurs upon stimulation of the cornea?

Facial nerve

Which skull type has the lowest corneal sensitivity in dogs?


Which region of the cornea has the highest sensitivity?

Central cornea

What is the function of the sphincter muscle in the iris?

To constrict the pupil

Which nerve innervates the constrictor muscle in the iris?

Oculomotor nerve (CN III)

What is the primary function of the dilator muscle in the iris?

To dilate the pupil

Which nerves primarily innervate the dilator muscle in the iris?

Sympathetic nerves

Which vessels in the eye are under the strong influence of sympathetic stimulation?

Choroidal vessels

What is the primary cause of retinopathy of prematurity?

Exposure to higher oxygen concentrations

Which type of autoregulation is present in the eye?

Metabolic and myogenous

Which vessels have little to no autoregulatory mechanism?

Choroidal vessels

Which blood vessels supply the cornea and lens in the embryo?

Uveal vessels

Which structure is a heavily pigmented and highly vascularized source of nutrients for the inner retina in birds?

Pecten oculi

Which blood vessels supply the iris and ciliary body in most species?

Uveal vessels

Which blood vessels supply the choroid in most species?

Uveal vessels

Which barrier prevents the movement of ions and fluid from the tears into the stroma and protects the cornea from pathogens?

Corneal epithelial barrier

Which route is the most permeable for hydrophilic drugs and macromolecules?

Conjunctival/scleral route

Which barrier prevents nearly all protein movement and is effective against low-molecular-weight solutes?

Blood-retinal barriers

Which barrier is formed by the nonpigmented layer of the ciliary epithelium and the endothelium of the iridial vessels?

Blood aqueous barrier

Which species have been demonstrated to have species differences in the α- and β-receptors?

Nonhuman primates, cats, and dogs

Which receptor is primarily responsible for the constriction of feline pupils with the use of timolol?


Which neurotransmitter is involved in enhancing adrenergic-induced contractions of the iris dilator muscles?

Neuropeptide Y

Which photopigment has peak sensitivity at 480 nm in dogs?


Which layer forms a size-selective barrier for molecules entering the neuroretina?

Bruch’s Membrane

Which cells form the inner blood-retinal barrier?

Endothelial cells

What is the most permeable point of the blood-retinal barrier?

Optic nerve head

What drives the transport of water from the retina to the choroid?

Active transport of chloride

Which layer forms the blood-aqueous barrier in the eye?

Nonpigmented layer of the ciliary epithelium

Which type of junctions are present in the layers forming the blood-aqueous barrier?

Tight junctions of the 'leaky' type

Which part of the eye controls the flow of fluid into the posterior chamber?

Inner, nonpigmented ciliary epithelium

Which pathway is dependent on IOP for outflow?

Traditional pathway

What is the primary factor impacting uveoscleral outflow?

Ciliary body state

Which medication can increase uveoscleral outflow?


What is the main effect of cholinergic agonists on outflow resistance?


Which substance is found in higher concentrations in the aqueous humor (AH) compared to plasma?


Which substance has a lower concentration in the AH compared to plasma in dogs?

Amino acids

Which substance has a concentration in the AH that is increased in diabetic patients?


Which substance is present in lower concentrations in the AH compared to plasma due to the blood-aqueous barrier (BAB)?


Which animal species has the highest percentage of uveoscleral outflow?

Nonhuman primates

What is ocular rigidity?

The resistance offered by the fibrous tunics of the eye to a change in intraocular volume

What is the relationship between IOP and volume of the globe?

logP2 / P1 = k (V2 - V1)

Which enzyme is abundantly present in the non-pigmented ciliary epithelium and plays a critical role in the active secretion of aqueous humor?


What is the primary mechanism by which aqueous humor is formed in the eye?

Active secretion

Which layer of the ciliary epithelium forms a barrier that inhibits paracellular diffusion?

Inner non-pigmented epithelium

Which enzyme catalyzes the reaction of CO2 and H2O to produce bicarbonate, which is essential for the secretion of aqueous humor?

Carbonic anhydrase

Which of the following is the primary route of aqueous humor outflow?

Conventional outflow through the trabecular meshwork

What is the major site of aqueous outflow resistance?

The juxtacanalicular zone

What is the primary cause of primary open angle glaucoma (POAG) in humans and likely dogs with the ADAMTS10 mutation?

Excessive deposition of extracellular matrix (ECM)

What are the two routes of aqueous humor outflow in the iridocorneal angle (ICA)?

Conventional and nonconventional routes

Test your knowledge on Veterinary Medicine and Ophthalmology with this quiz! Covering topics such as small animal clinical sciences, surgical and radiological sciences, and absorption systems. Challenge yourself and see how well you know these important subjects in the field.

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