Ocular Anatomy 2 Exam 1
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Questions and Answers

During embryological development, what day does the lens develop?

  • 25th day
  • 28th day
  • 27th day (correct)
  • 23rd day

    • Where does most of the metabolic activity occur in the lens?

  • Equatorial region
  • Anterior epithelium (correct)
  • Posterior fibers near the poles
  • Nuclear fibers

    • What is the source of energy required for cellular metabolism and replication in the lens?

  • Citric acid cycle
  • Anaerobic glycolysis (correct)
  • Krebs cycle
  • Aerobic glycolysis

    • Which type of cataract is characterized by a center opacification and susceptibility to oxidative damage due to decreased glutathione?

    <p>Nuclear cataract</p> Signup and view all the answers

    What is the primary protector against oxidative damage in the lens?

    <p>Glutathione</p> Signup and view all the answers

    Which region of the lens experiences higher ATP activity?

    <p>Anterior epithelium</p> Signup and view all the answers

    What is the metabolic consequence if hexokinase is not present in the lens?

    <p>Conversion of glucose to sorbitol</p> Signup and view all the answers

    What is responsible for maintaining a dehydrated lens by pumping out water?

    <p>Active Na/K pump</p> Signup and view all the answers

    What does excess sorbitol production in the lens lead to?

    <p>Cataract formation</p> Signup and view all the answers

    What is the primary component of the lens fibers?

    <p>Crystallins</p> Signup and view all the answers

    Which layer is the center of the nucleus?

    <p>Embryonic nucleus</p> Signup and view all the answers

    Which part of the lens contains a higher concentration of protein?

    <p>Embryonic nucleus</p> Signup and view all the answers

    What provides the barrier function of the lens capsule?

    <p>Basement membrane</p> Signup and view all the answers

    Which type of fibers is primarily responsible for forming the fetal nucleus?

    <p>Secondary lens fibers</p> Signup and view all the answers

    What attaches the posterior lens surface to the anterior vitreous face?

    <p>Wieger's ligaments</p> Signup and view all the answers

    Which suture forms by joining of apical aspects of fibers and forms an upright Y?

    <p>Anterior suture</p> Signup and view all the answers

    What percent of the lens composition is water and protein?

    <p>2/3 and 1/3</p> Signup and view all the answers

    What shape do individual lens fibers take as they mature and lose their interdigitations?

    <p>(Hexagonal)</p> Signup and view all the answers

    What happens to fibers as they age in relation to their connection with the capsule?

    <p>They lose attachment over time.</p> Signup and view all the answers

    What is the correct order of nuclei growth?

    <p>Fetal, juvenile, adult, lens cortex</p> Signup and view all the answers

    The anterior epithelium of lens has two layers of cuboidal cells.

    <p>False</p> Signup and view all the answers

    The lens capsule allows smaller molecules to pass and prevents larger molecules to enter.

    <p>True</p> Signup and view all the answers

    The Zonules of Zinn arise from the basement membrane of the pigmented ciliary epithelium in pars plana.

    <p>False</p> Signup and view all the answers

    There is no metabolic activity found inside of the lens nucleus.

    <p>True</p> Signup and view all the answers

    Which is NOT correct regarding the age changes in lens?

    <p>Increase in alpha crystallin</p> Signup and view all the answers

    During what month of development and from where does the dilator muscle develop?

    <p>Neuro ectodermal cells during 6th month</p> Signup and view all the answers

    Which structure provides tight adhesion between the choroid and the outer pigmented layer of the retina?

    <p>Bruch's membrane</p> Signup and view all the answers

    When does the stroma and ciliary muscle develop?

    <p>4th month</p> Signup and view all the answers

    What are the correct structures that the OUTER layer of the optic cup become?

    <p>RPE and outer pigmented ciliary body epithelium</p> Signup and view all the answers

    Where does Bruch's membrane run from in relation to the eye anatomy?

    <p>Optic nerve to ora serrata</p> Signup and view all the answers

    What type of cells compose the anterior iris epithelium?

    <p>Pigmented cuboidal cells</p> Signup and view all the answers

    What two arteries make up the major circle of the iris?

    <p>Long posterior ciliary arteries and anterior ciliary arteries</p> Signup and view all the answers

    Where can you find fenestrated vessels in the eye?

    <p>Choroid and ciliary body</p> Signup and view all the answers

    Which layer of the choroid contains collagen bands, fibroblasts, and melanocytes and allows accumulation of fluid between the layers?

    <p>Suprachoroid Lamina</p> Signup and view all the answers

    Where is the choroid located in the eye?

    <p>Between the sclera and the retina</p> Signup and view all the answers

    Which layer of the eye is continuous with the choroidal stroma anteriorly?

    <p>Iris stroma</p> Signup and view all the answers

    What provides nutrients to the outer layers of the retina?

    <p>Choriocapillaris</p> Signup and view all the answers

    What layer of the iris is composed of fibroblasts, pigmented melanocytes, and is absent in the iris crypts?

    <p>Anterior border layer</p> Signup and view all the answers

    What is the thickest region of the iris and the site for attachment of the pupillary membrane?

    <p>Collarette</p> Signup and view all the answers

    The minor circle of the iris is fenestrated.

    <p>False</p> Signup and view all the answers

    The sphincter muscle is made of smooth muscle fibers and innervated by the sympathetic system.

    <p>False</p> Signup and view all the answers

    The parasympathetic nervous system stimulates the ciliary muscle.

    <p>True</p> Signup and view all the answers

    The inner pigmented ciliary epithelium actively secretes aqueous humor.

    <p>False</p> Signup and view all the answers

    Which layer of the choroid stroma contains vessels with larger lumens?

    <p>Haller's layer</p> Signup and view all the answers

    Chorio capillaries are densest in the macular region.

    <p>True</p> Signup and view all the answers

    What is the process where substances leave the blood through passive movement from a higher concentration to a lower concentration?

    <p>Diffusion</p> Signup and view all the answers

    In the production of aqueous humor, which mechanism involves molecules being transported across a membrane against a concentration gradient in an energy-utilizing process?

    <p>Active secretion</p> Signup and view all the answers

    Which is NOT a mechanism of aqueous humor production?

    <p>Osmosis</p> Signup and view all the answers

    Which of the following is true regarding ultrafiltration compared to dialysis?

    <p>Ultrafiltration increases the rate of net movement with added hydrostatic pressure.</p> Signup and view all the answers

    What percentage of aqueous humor production is accounted for by active secretion?

    <p>80-90%</p> Signup and view all the answers

    What is the function of the ciliary body in relation to the accommodation of the eye?

    <p>Contraction of circular fibers draws the ciliary body closer to the lens, decreasing the lens power.</p> Signup and view all the answers

    Which is NOT a function of the aqueous humor?

    <p>Provides nutrients to the retina</p> Signup and view all the answers

    What occurs when the longitudinal fibers of the ciliary muscle contract during accommodation?

    <p>The choroid is pulled forward.</p> Signup and view all the answers

    What acts as an antioxidant to protect the cornea and lens against oxidative damage?

    <p>Ascorbate (vitamin C)</p> Signup and view all the answers

    What is the production rate of aqueous humor?

    <p>2.5 microliters/min</p> Signup and view all the answers

    What is the sensory innervation of the uvea?

    <p>Nasociliary branch of trigeminal nerve</p> Signup and view all the answers

    In which condition would one observe sector paralysis of the iris muscles due to blunt trauma?

    <p>Iridodialysis</p> Signup and view all the answers

    Aqueous humor has 200 times more protein than plasma.

    <p>False</p> Signup and view all the answers

    Iris capillaries are non fenestrated to allow larger molecules to leak out into iris blood vessels.

    <p>False</p> Signup and view all the answers

    As we age, aqueous formation increases due to over stimulated ciliary muscle.

    <p>False</p> Signup and view all the answers

    Hypopion is the presence of red blood cells in the anterior chamber.

    <p>False</p> Signup and view all the answers

    ARMD is the accumulation of phospholipids in Bruch's membrane.

    <p>True</p> Signup and view all the answers

    Which cells lining the inner wall of the canal of Schlemm have been found to contain giant vacuoles that act as channels of transport for aqueous humor?

    <p>Endothelial cells</p> Signup and view all the answers

    Which anatomical division of the trabecular meshwork is the inner sheets and attaches to the ciliary stroma and longitudinal muscle fibers?

    <p>Uveal meshwork</p> Signup and view all the answers

    Where is the aqueous humor produced?

    <p>In the pars plicata of the ciliary body</p> Signup and view all the answers

    How does the aqueous humor move in the anterior chamber?

    <p>Up along the cooler cornea</p> Signup and view all the answers

    Where does the aqueous humor exit from the anterior chamber through?

    <p>The pupil</p> Signup and view all the answers

    Through which mechanism does a portion of the aqueous humor leave the eye?

    <p>Passing through uveal meshwork spaces</p> Signup and view all the answers

    What happens to a portion of the aqueous humor that doesn't pass through uveal meshwork spaces?

    <p>It moves into the suprachoroidal space</p> Signup and view all the answers

    Where is the location of higher resistance to aqueous movement in the eye?

    <p>Juxtacanalicular tissue</p> Signup and view all the answers

    Which structure provides little to no resistance to aqueous outflow?

    <p>Schlemm's canal</p> Signup and view all the answers

    What is the primary cause of increased intraocular pressure (IOP) in most cases?

    <p>Decreased aqueous outflow</p> Signup and view all the answers

    What percentage of outflow resistance is attributed to the juxtacanalicular tissue (JCT)?

    <p>75%</p> Signup and view all the answers

    In which location are external collector channels distributed around that eventually empty into the deep scleral plexus?

    <p>Juxtacanalicular tissue</p> Signup and view all the answers

    Which clinical application is associated with the breakdown in blood aqueous barrier?

    <p>Uveitis</p> Signup and view all the answers

    What structure receives blood from the anterior conjunctiva and anterior episcleral veins?

    <p>Episcleral collecting veins</p> Signup and view all the answers

    Zonules are located in the canal of Hannover.

    <p>True</p> Signup and view all the answers

    Aqueous humor flow is more during the night than in the morning.

    <p>False</p> Signup and view all the answers

    Study Notes

    Lens Anatomy and Physiology

    • The lens is a transparent, avascular, and elliptic structure located in the posterior chamber of the eye.
    • It comprises three parts: capsule, lens epithelium, and lens fibers.
    • The lens is suspended from the ciliary body by zonular fibers and is malleable, allowing it to change shape during accommodation.

    Lens Development

    • Lens development begins on the 27th day of embryonic development, when the optic vesicles form and the adjacent surface ectoderm thickens to form the lens placode.
    • The lens placode invaginates, forming the lens pit, which then becomes the lens vesicle as it separates from the surface ectoderm.
    • The posterior lens epithelium differentiates into primary lens cells, which elongate anteriorly as fibers, filling the lumen and forming the embryonic nucleus.
    • All lens growth after the development of the embryonic nucleus is attributed to secondary lens fibers.

    Lens Composition and Structure

    • The lens is composed of 1/3 protein and 2/3 water, with a pH of 6.9.
    • The protein content varies among the lens, with a higher refractive index in the nucleus (1.50) and less in the outer cortical surface (1.37).
    • The lens capsule is an elastic, acellular envelope that allows passage of small molecules and prevents large molecules from entering the lens.
    • The lens epithelium is a single layer of cuboidal cells that secrete the anterior capsule throughout life and facilitate metabolic transport mechanisms.

    Lens Fibers

    • Lens fibers are formed from mitosis in the germinative zone and are initially nucleated and contain organelles.
    • As they elongate, they lose their nuclei and organelles, and their cell membranes become compacted as insoluble protein in the nucleus.
    • Fibers are hexagonal in shape and arranged in concentric rings, with a crescent-shaped cross-section (3 x 9 μm).
    • Lens fiber cytoplasm contains a high concentration of crystallins (90%), which contribute to the gradient refractive index.

    Divisions of the Lens

    • The lens is divided into the embryonic nucleus, fetal nucleus, adult nucleus, and lens cortex.
    • The embryonic nucleus is the center of the lens, formed by the elongating posterior epithelium of primary lens fibers.
    • The fetal nucleus includes the embryonic nucleus and fibers surrounding it that are formed before birth.
    • The adult nucleus includes the embryonic and fetal nuclei and fibers formed from birth to sexual maturation.
    • The lens cortex contains fibers formed after sexual maturation, divided into superficial, internal, and deep zones.

    Lens Sutures

    • Lens sutures are formed by the lens fibers when they reach the poles and meet with other fibers in their layer.
    • The anterior suture is formed by the joining of apical aspects of the fibers, forming an upright Y shape.
    • The posterior suture is formed by the joining of the basal aspects of the fibers, forming an inverted Y shape.

    Zonules of Zinn

    • Zonules of Zinn are thread-like fibers that attach the lens to the ciliary body, also known as the suspensory ligament of the lens.
    • They arise from the basement membrane of the nonpigmented ciliary epithelium in the pars plana and form two column-like structures on both sides of a ciliary process.
    • Primary zonules attach to the lens, while secondary zonules attach to the primary zonules.

    Accommodation

    • Accommodation is the increase in refractive power of the eye when viewing a near object.
    • It is achieved by the contraction of the ciliary muscle, which relaxes the zonules and increases the lens's curvature.
    • The lens changes shape, increasing its refractive power, and the eye is able to focus on the near object.### Lens Physiology
    • The primary function of the lens is refraction of light and transparency, which is achieved by the absence of blood vessels, few cellular organelles, and an orderly arrangement of fibers with short distances between components.
    • The lens obtains nutrients from the surrounding aqueous humor and a small contribution from the vitreous.
    • Metabolic activity in the lens is mostly anaerobic, with 70% of ATP production via anaerobic glycolysis, while aerobic glycolysis and the Krebs cycle are limited to the epithelium or superficial fibers with mitochondria.

    Lens Metabolism

    • The lens constantly pumps out water to maintain the correct constituents for optics, using an active Na/K pump that requires ATP.
    • Both aerobic and anaerobic pathways require hexokinase to convert glucose to glucose-6-phosphate.
    • If hexokinase is not present, glucose is converted into sorbitol (via aldose reductase), leading to an osmotic gradient that favors water movement into the lens, causing swelling, damage, and cataract formation.

    Regulation of Lens Proteins

    • Glutathione is the primary protector against oxidative damage and is transported into the lens by the aqueous humor or synthesized from lens epithelial cells.
    • Ascorbic acid prevents oxidative damage (anti-cataract effect) and is present in the lens at a concentration of 3.5 mmol/liter or higher.

    Oxidative Stress of the Lens

    • Free radicals are a normal product of metabolic processes, and UV light absorption can also produce oxidative changes, causing the formation of free radicals.
    • Glutathione is a reducing agent that detoxifies free radicals, preventing damage.
    • Ascorbic acid also prevents oxidative damage.

    Age Changes in the Lens

    • There is a decrease in soluble lens proteins (alpha crystallins), ATP content, K ions, amino acids, and inositol with age.
    • Glutathione activity decreases with age, leading to less detoxification of free radicals and cell damage.
    • There is an increase in Ca, Na, and H2O with age, causing more permeability and disruption of ion balance.

    Clinical Manifestations of Aging

    • Presbyopia is a loss in accommodative ability, characterized by the inability to focus at near distances.
    • Cataracts are any lens opacity, and the greatest cause of blindness, influenced by multiple factors affecting lens metabolism.

    Choroid Anatomy

    • The choroid is composed of the lamina fuscha (suprachoroidal lamina), choroidal stroma, choriocapillaris, and Bruch's membrane.
    • The choroidal stroma contains melanocytes, fibroblasts, macrophages, lymphocytes, and mast cells, with collagen fibrils arranged circularly around the vessels.

    Choroid Function

    • The choroid is responsible for providing nutrients to the outer retinal layers.
    • The choroidal vessels are innervated by the autonomic nervous system, with sympathetic stimulation causing vasoconstriction and decreased choroidal blood flow, while parasympathetic stimulation causes vasodilation and increased choroidal blood flow.

    Ciliary Body Anatomy

    • The ciliary body is composed of the supraciliaris (supraciliary lamina), ciliary muscle, ciliary stroma, and ciliary epithelium.
    • The ciliary epithelium consists of two layers: the pigmented ciliary epithelium and the non-pigmented ciliary epithelium.

    Ciliary Body Function

    • The ciliary body is responsible for producing and secreting aqueous humor, with the non-pigmented ciliary epithelium being the site of active secretion.
    • The ciliary muscle is responsible for accommodation, with contraction of the longitudinal fibers causing the lens to become more spherical and increasing its power.

    Iris Anatomy

    • The iris is composed of four layers: the anterior border layer, stroma and sphincter muscle, anterior epithelium and dilator muscle, and posterior epithelium.

    Iris Function

    • The iris acts as a diaphragm to regulate the amount of light entering the eye.

    • The iris muscles are innervated separately, with the sphincter muscle being parasympathetically innervated and the dilator muscle being sympathetically innervated.### Functions of the Ciliary Body

    • Aqueous humor maintains the pressure and shape of the eye

    • Provides a transparent and colorless refractive index

    • Provides nutrition for the avascular cornea, lens, anterior vitreous, and trabecular meshwork (TM)

    • Serves as a collection bin for metabolic waste products of surrounding tissues and clears out inflammatory products and blood from the globe

    Aqueous Humor Composition

    • Aqueous humor has 20 times greater ascorbate (Vitamin C) concentrations than plasma
    • Ascorbate acts as an antioxidant to protect the cornea and lens against oxidative damage
    • Aqueous humor has 200 times less protein than plasma
    • Consequence of the tight junctional barrier
    • Low concentration of proteins causes minimal light scatter and thus maximum light transmission

    Waste Products in Aqueous Humor

    • Waste products from the cornea and lens, including Cl-, amino acids, and lactate
    • High concentration of lactate, a metabolic waste product of the anaerobic glycolysis of the lens and cornea

    Aqueous Humor Production

    • 2.5 μl of aqueous humor is produced per minute
    • Aqueous humor production follows the circadian rhythm, with a higher rate during the day and a 50% decrease at night
    • The osmolarity of aqueous humor is slightly hyperosmotic to plasma
    • Aqueous humor viscosity is relative to water (1.025-1.040)

    Blood-Aqueous Barrier

    • Controls the secreted aqueous humor
    • Fenestrated capillaries permit large molecules to exit the blood
    • Tight zonular junctions of the non-pigmented epithelium (NPE) prevent molecules from passing between the cells
    • Forcing molecules to pass through the cell to enter the posterior chamber
    • Protein is well-controlled, with a small content in the aqueous humor

    Iris

    • Iris is freely permeated by the aqueous humor
    • Iris capillaries are not fenestrated, preventing large molecules from leaking out of the iris blood vessels
    • The zonula occludens junction in the endothelial cell maintains the barrier function

    Choroid

    • Provides nutrients to the outer retina
    • Is an egress for catabolites from the retina, passing through Bruch's membrane into the choriocapillaris
    • Dark pigmented to absorb excess light (as in the RPE layer)
    • Suprachoroidal space provides a pathway for the posterior vessels and nerves that supply the anterior segment

    Blood Supply to the Uvea

    • Short posterior ciliary arteries enter around the optic nerve and form the choroidal vessels
    • Long posterior ciliary arteries and anterior ciliary arteries join to form the major circle of the iris, supplying the iris and ciliary body
    • Venous return for most of the uvea is through the vortex veins

    Uveal Innervation

    • Sensory innervation is provided by the nasociliary branch of the trigeminal nerve
    • Sympathetic fibers from the superior cervical ganglion via the ophthalmic and short ciliary nerves innervate the choroidal blood vessels (vasoconstriction), iris dilator (contraction), and ciliary muscle (relaxation)
    • Parasympathetic fibers from the ciliary ganglion innervate the ciliary muscle (contraction), iris sphincter muscle (contraction), and choroidal vessels (vasodilatation)

    Aging Changes

    • Iris: loss of pigment from the epithelium, pigment deposition, and dilator muscle atrophy
    • Ciliary body: connective tissue increase within the layers of the ciliary muscle, ciliary muscle contraction diminution with age, and aqueous humor formation decrease
    • Choroid: drusen, decreased choroidal blood flow, and decreased choroidal thickness

    Clinical Applications

    • Iridodialysis: blunt trauma to the eye or head, resulting in a thin iris root tear away from the ciliary body
    • Iris synechiae: abnormal attachment between the iris surface and another structure
    • Pigmentary dispersion syndrome: pigment granules are shed from the posterior iris surface, dispersed into the anterior chamber, and deposited on the iris, lens, corneal endothelium, and TM
    • Presbyopia: loss of the ability to accommodate due to normal age-related change
    • Thyndall phenomenon: usually, the beam of light in the anterior chamber is dark, but with the presence of particles, it will be visible due to uveal inflammation, flare, and cells

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    Description

    Test your knowledge on the development of the crystalline lens in the human eye, focusing on the formation of the lens placode, lens pit, and lens vesicle. Explore key events that occur during the 27th day of lens development.

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