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MODULE 1: EYEBALL - ANATOMY AND
PHYSIOLOGY
Introduction The Eye
- an organ that reacts with light and allows light perception, color vision, and depth perception
- The eye is a very delicate complex organ consisting of many tissues which protect the optic nerve and photoreceptor cells
- Lids and lashes protect the eye from the external environment (infections and bright lights)
- Light rays focus on the retina = continuous images that are spontaneously transmitted to the brain
- located in the skull cavity
- surrounded by fibrous muscle and lipoidal tissues
- Human eye can see about 10 million different colors
- continuous tear production removes foreign objects from the eye
- anterior segment = refractive system - posterior segment = visual light perceptive mechanism
- human eye is NOT a perfect sphere - made up of two differently shaped pieces: CORNEA and SCLERA
- Cornea (transparent) covers the iris (colored part of the eye) and the pupil (changes size)
- Fundus is on the opposite of the pupil (on the inside of the eye; cannot be seen without special instruments)
- RETINA (most posterior part of the eye) = basically part/ connected to the CNS (central nervous system) Connected to the pupil:
- Optic nerve = conveys the signals of the eye to the brain
- Aqueous humour (AH) = clear fluid in the anterior and posterior chamber
- Vitreous humour (VH) = clear jelly that is bigger than the AH The eye is divided into 3 main layers or tunics (coatings) :
- Outer Fibrous Tunic
- Middle Vascular Tunic
- Inner Nervous Tunic (innermost; part of the eye connected to the brain/ CNS) Lesson 1: Fibrous Tunic Pre-Corneal Tear Film
- Located anterior to/ infront of the cornea
- Outermost part of the cornea
- Exposed to the outside environment - Covers the exposed part of the eyeball
- Protects the eye from trauma and foreign bodies
- Conjunctivitis (sore eyes) = the blood vessels of the conjunctiva that turns red
- Oil/ Lipid Layer (Meibomian gland) ● Made up of oily/ lipid substance Function:
- Retard the evaporation of the aqueous layer
- Prevents the evaporation of water to prevent the surface of the cornea to be dry
- Lubricates your eyelid
- Produced by 3 different glands: meibomian gland (main), zeis gland, moll gland
- Aqueous layer (Lacrimal gland) = tears ● Posterior to the oil/ lipid layer ● Thickest layer among the 3 pre-corneal tear film ● Made up of water ● Water is high in oxygen Function:
- To nourish the cornea with oxygen (water/ aqueous is high in oxygen) - It has an antibacterial effect/ function because, in the aqueous layer, we have an enzyme called lysozyme (destroys bacterial cells)
- It washes away debris/ foreign bodies
- It allows the passage of cells (leukocytes - responsible for phagocytosis) *Phagocytic leukocytes are white blood cells that help fight foreign material such as bacteria and viruses
- Mucoid/ Mucin layer (Goblet cell) ● Closest to the cornea (innermost layer) ● Thinnest layer ● Slippery (made up of mucid) Function:
- lubricate the surface of the cornea - It would cover/ coat the foreign body with a slippery coating to protect the cornea/ conjunctiva against abrasion - It converts hydrophilic into hydrophobic surface
- It causes the tears to adhere to the surface of the eye CORNEA ● It is the transparent film anterior to the iris and the pupil ● Elliptical shape ○ Anterior ○ viewing from the outside ● Circular shape ○ Internal ○ viewing from the inside ● Prolate shape: curvature of the cornea is ○ steeper at the center ○ flatter towards the periphery
the limbus (limbal area) ○ 5-7 layers of cells regenerate every 7 days (prevent scar formation) ● Micorvilli on the surface (velcro) - to adhere the pre-corneal tear film to the anterior epithelium ○ Attaches completely ○ To prevent water from entering the layers of the cornea (to maintain the state of deturgescence) ○ It allows sufficient amount of water to supply oxygen to the corneal tissue ○ Cornea is avascular (no nourishment) and it obtains its nourishment from the environment and corneal epithelium ○ Purpose: increases the absoptive power of the cell ○ water in cornea = opacity ● Hydrophobic Cells present in the Anterior Epithelium: ✤ Epithelial cells
- Outer 2-3 cell layers
- Flat with many microvilli and horizontal nuclei
- Joined with desmosomes (junctions) to prevent tears from penetrating the cornea *Cells are very intact and close to one another because of the presence of junctions/ desmosomes
- Swept away by the eyelids during blinking *when we blink, our epithelial cells are being washed out and napapalitan ng bagong epithelial tissues
- The corneal epithelium is devoid of melanocyte (cell that produces melanin pigment) except in the area of the limbus *excessive pigment in the limbus (in some cases) Langerhans cells (LC) = present in the epithelial cells (anterior epithelium) - macrophages are in the epithelial tissue of the cornea *macrophages change their name as it transfer from one anatomical site to another
- Macrophages phagocytize microorganisms
- If there is an accidental bacterial cells in the peripheral cornea, it would be acted upon by the langerhans cells (LH) to prevent or phagocytize the bacterial cell
- Macrophages = WBC
- Brain = microglia
- Lungs = dust cell
- Liver = kupffer cell ✤ Wing cell layer ● Middle 3-4 cell layer ● Composed of polyhedral cells ● Deep cells have round nuclei, becomes flatter as cells approach the surface of the cornea ● Joined together from the base to apex by desmosomes and zonula occludens ✤ Basal cell layer
● Tall and columnar cells that often show mitosis ● Lateral cell borders are joined by demosomes ● Joined together with the basement membrane by hemidesmosomes Basement Membrane ⇾ Firmly attached to the underlying Bowman zone by irregular filaments (after injury, these attachments may take as long as 6 weeks to be reestablished/ regenerated ) ⇾ Attaches anterior epithelium to the next layer
- Long regeneration process
- Secreted by the basal cells ⇾ Function: It attaches the anterior epithelium to the next layer ⍣ Composed of Type IV collagen and laminin
- Under the anterior epithelium - NOT included in the anterior epithelium layer
- Found in the end of the basal cell Lymph Spaces ⇾ Minute spaces in between basal cells and disappear gradually towards the surface ⇾ May be distended pathologically (glaucoma)
- Increase in volume of aqueous humour = glaucoma (increase in intraocular pressure of the eye) *glaucoma - pathological condition wherein there is an increase in intraocular pressure of the eye ⇾ There is NO lymph fluid that pass through passing through lymph spaces - Aqueous humour (eye) Cell Junctions
- Zonula occludens (tight junctions) - Situated between the wing cells and encircles the cell forming a seal and prevents the small molecules to pass through
- Zonula adherence (desmosomes) 3. Hemidesmosomes
- Situated in between the basal cell and basement membrane Ⓑowman’s Membrane ● 12 μm in thickness ● Structureless & acellular hyaline stroma ○ NOT a true membrane (no collagen fobers/ fibroblasts to help in the repair of damaged cells) ● Made up of randomly oriented collagen fibers ○ There are no fibroblasts ● Resistant to trauma and infection ●
● Thickest region of sclera = area of the optic nerve ● Thinnest region of sclera = insertions of the recti muscles ● Forms the white of the eye *yung pinaka white part lang ang sclera ● Covered with episclera, fascia bulbi (tendon’s capsule) , and conjunctiva ● Characteristics: it has a high water content (65% to 70%) *When it is reduced to less than 40% or increased to more than 80%, the sclera would become transparent ● Conjunctiva - the white part of the eye where the blood vessels are visible; located anterior to the sclera *conjunctiva NEVER reaches the cornea; it is only until the sclare and eyelids Conjunctivitis (sore eyes) ● BACTERIAL conjunctivitis = presence of mucus (greenish/ yellowish) ● VIRAL conjunctivitis = red, no secretion, painful ● ALLERGIC conjunctivitis = teary eyes, itchy Color of Sclera ⇾ Opaque White ⇾ Bluish - children and in scleral thinning *discoloration of sclera if the refractive error/ condition reached -10.00D and beyond (high myope) due to the continuous elongation of the sclera *children (below 8 years old) - scelra is not yet fully developed, the choroid (pigmented tunic of the eye) can be seen ⇾ Yellowish - elderly and jaundice (due to liver disease) *elderly - presence of fat deposits (cholesterol) Functions of the Sclera
- Protects the intraocular contents (crystalline lens, iris, aqueous and vitreous humour) from trauma and mechanical displacement
- Maintains the shape of the eyeball as well as the exact position of the different parts of the optic system - Provides rigid insertion for extraocular muscles (EOM) *EOM are the muscles which cause the movement of our eyeball STRUCTURE and LAYERS of the SCLERA Ⓔpisclera ● 1st layer of the sclera ● Moderately dense, vascular CT that merges with the scleral stroma ● The anterior portion has a rich blood supply from blood vessels *both cornea and sclera are both avascular, but SCLERA is less avascular *SCLERA - has blood vessels ONLY in the EPISCLERA ● The blood vessels are inconspicuous (not visible) except when inflamed *SCLERITIS - when blood vessels become inflamed
● Becomes thinner posteriorly (at the back) Ⓢcleral Stroma ● With bundles of typical collagen fibers (Type I and III) ● Thickest layer in the sclera Ⓛamina Fusca ● Innermost layer ● Formed mainly of elastic fibers and fine collagen fibers ● Brown in color due to the melanocyte pigment of the choroid that is situated next to it Cornea Sclera ⇾ Avascular ⇾ transparent ⇾ deturgescence (dehydration) ⇾ Avascular (less avascular than cornea) ⇾ Opaque white ⇾ rich in water content (65% to 70%) Lesson 2: Vascular Tunic (Uveal Tract) Introduction
- The Uveal Tract is highly vascularised (nourishment coming from the blood vessels in the vascular tunic nourishes the avascular tunic of the eye) *avascular tunic (fibrous tunic) - obtain its nourishment from the outside (pre-corneal tear film, from the oxygen outside environment, vascular tunic)
- Pigmented layer of the eyeball - Comprises the iris , ciliary body , and choroid Functions:
- Blood supply to structures within the eye particularly supplying the fibrous tunic
- Formation of aqueous humour *aqueous humour is situated within the eye - Accommodation = the ability of our eye to look at near print/ targets
- Control of the amount of light entering the eye and in depth of focus *the light entering the eye should be sufficient enough so as not to destroy the photoreceptor cells *too much light striking the inside of the eye will cause death of the rods (scotopic) and cones (photopic)
- The Choroid, Iris, and Ciliary Body ALL have blood vessels and it provides nourishment to the eye CHOROID (Choroidea) ● The blood vessels in the vascular tunic arises from the choroid ● Richly vascular layer ● Contains connective tissues ● Lies between the sclera and retina ● Provides oxygen and nourishment to the fibrous and nervous tunics of the eye ● Dark in color because it absorbs excess light so that it would not immediately reach/penetrate the retina *because rods and cones lie within the retina ● Choroid = heat exchange to prevent the retina from overheating *because rods and cones lie within the retina ● Since choroid contains blood vessels = maintains/ regulate
● The ciliary body is divided into two sections: ○ PARS PLICATA contains the small finger-like projections called ciliary processes ○ PARS PLANA is a flatter region that extends to the ora serrata ■ Where you can see the ciliary muscle *pars plana is the area terminating (kadugtong) with the ora serrata ○ ZONULES extend from between the ciliary processes and lens ● ORA SERRATA - connects the retina and ciliary body *ciliary body Characteristics of Ciliary Body ● Continuous posteriorly with the choroid and anteriorly with the peripheral margin of the iris *posterior = choroid *anterior = iris (peripheral margin of the iris) ● Extends from th posterior limit of the limbus (scleral spur and iris root) to ora serrara ● Triangular shape in cross section (base facing the anterior chamber and apex are ora serrata) ● Dimension ○ 7mm wide temporally ○ 6mm nasally *crystalline lens = central axis ● Color black ○ melanocytes are larger and darker than those of the choroid ● Pars plana - posterior ⅔ (smooth and flattened) ● Pars plicata - anterior ⅓ (ciliary processes) *chororid is pigmented and ciliary body is situated near the choroid, therefore, the melanocytes (pigments) found in the choroid is also present in the ciliary body Functions of the Ciliary Body ● Aqueous humour production ○ Non-pigmented epithelium is responsible for the production of the aqueous humour
● Lens accommodation ○ move of the lens anteriorly to see at near ● Facilitates aqueous drainage ○ to prevent intraocular pressure STRUCTURE and LAYERS of the CILIARY BODY Ⓒiliary Epithelium 2 layers: ➀ Pigmented Epithelium (outermost layer of the ciliary epithelium)
- Continuous with anterior iris epithelium
- Posteriorly continuous wih Retinal Pigmented Epithelium (1st layer of the Retina) ② Non-Pigmented Epithelium (inner) - columnar cells in pars plana - cuboidal cells in pars plicata (flat) - The anterior part is continuous with posterior iris epithelium
- Produces aqueous humour and glycoprotein of the vitreous humour *generally, the ciliary body is responsible for the production of the aqueous humour *to be specific, the non-pigmented epithelium of the ciliary body that is responsible for the release/ production of the aqueous humour
- Blood aqueous barrier = does NOT allow the content of the blood to enter the aqueous humour and vice versa Ⓢtroma/ Vessel Layer ● Supplied by the anterior ciliary arteries and long posterior ciliary arteries *Contains all the blood vessels ● Blood vessels (anterior ciliary arteries and long posterior ciliary arteries) forms the major arterial circle where from branches supply the iris, ciliary body, and anterior choroid *when the anterior ciliary arteries and long posterior ciliary arteries CONNECT, they form the MAJOR ARTERIAL CIRCLE Ⓜuscular Layer Ciliary Process *Ciliary Process is like a microvilli, different name due to different location and function ● 70-80 finger-like projection with
- Helps the aqueous outflow ③ Circular muscle (inner)
- Attached to the ciliary body and iris stroma
- When these muscles contract, the zonule relaxes, increasing the lens axial diameter and its convexity *Once it contracts, zonules relax/ loosen = crystalline lens will increase its diameter/ convexity
- Helps in accommodation of the crystalline lens *Curved crystalline lens = accommodation *Flatten crystalline lens = relaxed and looking at far
- 40 years old and above: zonules and muscles are no longer functioning properly
- Moving the target away since they cannot accommodate (see at near) IRIS ● A thin circular structure located anterior to the lens ● It divides the eyeball into the anterior and posterior chambers ● The central aperture called the PUPIL varies in diameter from approximately 1mm to 9mm depending on the level of light ○ The pupil is the main route of flow of aqueous humour from the ciliary body to the anterior chamber ● It bears the 2 muscles responsible for the changes in the size of the pupil: ○ Sphincter pupilae/ iridae muscle ○ Dilator pupilae/ iridae muscle
- The pupil appears black because - NO PIGMENT because you are seeing the inside of the eye (no light)
- Pupil size depends on the contraction of the iris muscles (Sphincter pupillae and Dilator pupilae)
- Depends on how much light on the eye
- Too much light = constriction
- Low light = dilation 2 zones: ● The central pupillary zone occupies the region immediately adjacent to the pupil ● Thickest part of the iris = COLLARETTE (the edge of the pupillary zone) ● The pupilary margin forms the border of the pupil ● The ciliary zone is that part of the iris from the collarette to the iris root ● Iris color is determined by the stromal melamocytes ↳ Less pigment can be observed in the blue-colored iris (selectively black-scatters the shorter wavelengths of light, leading to the blue appearance)
↳ Brown is the dominant inherited color ↳ Blue is the recessive inherited color
- Light colored iris: lesser melanocytes present
- Dark colored iris: more melanin pigment/ melanocytes *constriction of pupil is difficult to observe *difficult to differentiate the iris from the pupil STRUCTURE and LAYERS of the CHOROID ➢ Two layers of epithelium are located on the posterior aspect of the stroma ➢ The basal part of these cells contains elongated contactile smooth muscle processes ➢ These cells form the “dilator muscle” ○ Externs from the iris root to about the mid-point of the sphiincter muscle in the pupillary zone Ⓐnterior Border Ⓢtroma/ Sphincter Muscle Ⓐnterior Epithelium/ Dilator Muscle
Ⓟosterior Epithelium
MODULE 2: NERVOUS TUNIC
Introduction RETINA ● The structure forming the nervous tunic (innermost) ● It is a continuation of the anterior part of the brain ● It is considered part of the CNS (central nervous system) *The eye is the only organ directly connected to the brain Characteristics of the Retina *viewed using fundus camera ➔ The retina is the area where the image is cast ➔ Covers the posterior ⅚ of the eye *both sclera and retina covers the posterior ⅚ of the eye *retina is posterior to the sclera; sclera is anterior to the retina
● Yellow pigmented area surrounding the fovea centralis Fovea Centralis ● Located within the macula lutea ● Contains only cones and is the site of highest visual acuity (keenest vision) ● Avascular and receives nutrients by diffusion via the choriocapillaries *yung buntot ng artery ay medyo nakapasok sa macula lutea, however, it never reaches the fovea centralis because it is avascular *choroid supplies almost all the nutrients needed by the different structures within the eye ● Subserves color or day (photopic) ● UMBO is the tiny depression at the center of the foveola Foveola ● Approximate diameter = 0.35mm ○ Central floor of fovea Macula → Fovea Centralis → Foveola → Umbo 3. Peripheral retina
4. Ora serrata ● Serrated junction between the retina and the ciliary body STRUCTURE and LAYERS of the RETINA Ⓡetinal Pigmented Epithelium *after the choroid (bruch’s membrane) going to the internal limiting membrane that forms the boundary between the retina and the vitreous humour ● Outermost layer adjacent to the choroid ● Made up of single later of hexagonal epithelial cells ● Outer portion of the has nucleus and moderate number of round pigment granules ● Inner portion has pigment granules - melanin ( FUSCIN ) ○ Continuous with the ciliary epithelium *because it is beside the choroid, which is highly pigmented, it is pigmented as well Functions: ● Stores Vitamin A ● Remove the debris from rods and cones by phagocytic action *meron talagang mamamatay na photoreceptos, minsan may nakakapasok na too much light/ worn
out na yung photoreceptors
Ⓟhotoreceptor Cell Layer (Layer of
the Rods and Cones) ● Contains the light sensitive receptor cell ○ RODS - help in night vision (scotopic vision) ○ CONES - day light and color vision (photopic vision) ● Absorbing scattered light *absorbs excessive light = improvement in the quality of the optical system and reduce radiation inside the retina ● Prevents reflection of light rays back from retina *ayaw natin pabalikin/ bounce back yung light reflection doon sa retina because it will further contribute to the heating the surface *heating of retina = death of photoreceptor cells ● Dendrites formed by: ● Outer Segment - contain visual pigment molecules ↳ Rhodopsin (rods) ↳ Iodopsin (cones) ● Inner Segment - contains organelles (mitochondria, endoplasmic reticulum, and golgi apparatus) ● Cell Body - contains nucleus and photoreceptors ● Axon - synapses with dendrites of bipolar neurons ◦ synaptic ending of the rods and cones ◦ attaches/ synapses with another neuron within the retina Ⓔxternal Limiting Membrane ● A thin layer formed by the chief
● It form the boundary ○ The vitreous humour is bounded by the vitreous chamber ○ The internal limiting membrane forms the basement membrane or the basal lamina of the muller cell - to separate the vitreous from the layers of the retina ● Formed by the basal laminae of Muller Cells ● Forms the innermost boundary of the retina ● Axon of the ganglion cell ● Inside the eyeball unmyelinated ● It will pierce the sclera it will become myelinated fiber (called the optic nerve) ● Transmission from optic nerve to the brain is very fast because it is myelinated CELLS in the RETINA
- 2 different types of cells in the retina: - pigmented epithelium
Pigmented Epithelium (Epithelial Tissue) ● Single layer of hexagonal cells ● Columnar in the area of the posterior pole ● Longer, narrower and densely pigmented in the macular area ● Larger and cuboidal on the ora serrata ● Apex consists of microvilli extending in the layer of the rods and cones ● No intercellular junction ● Connect the Retinal Pigmented Epithelium and phtoreceptor cells
- Microvilli is present because the RPE enhances the absorptive power - Microvilli is extend to the rods and cones
- Microvilli connects the RPE and photoreceptors without junctions
- No tight junctions in the area of the microvilli of pigmented epithelium and photoreceptor cells NERVE CELLS
- The target is the central retina - Nerve cells cannot regenerate, but good at transmitting nerve impulses *Once it is damaged, you will not be able to see anymore Photoreceptor Cells ● 1st order neuron for the visual pathway *Snell: photoreceptor cell and not considered as neuron *Snell: 1st order neuron = bipolar cell ∅ ● Special sense contain pigments that absorb photons of light
*synaptic terminal/ axon terminal = dugungan *there are MORE RODS than cones Bipolar Cell ● 2nd order neuron ● Neulceus is large with minimal cell body cytoplasm ● Dendrite synapses with: ○ Axons of photoreceptor cells ○ Horizontal cell ● Axon synapses: ○ Dendrited ganglion cell ○ Processes of amacrine cell ● Releases a neurotransmitter glutamate ○ essential for the visual pathway Ganglion Cell ● 3rd order neuron ● Multipolar neuron = several dendrites, single axon ● Dendrite synapses with: ○ Axons of bipolar cells ○ Amacrine cells
- Straight ahead = central retina - When your hand is at the periphery = you can see all the structures you can see at the side (horizontal and amacrine cells) so that it would reach the peripheral retina ● Axons ○ Transmit visual impulses synapse in the LGB ○ Transmit afferent impulses to control pupilary respons to light impulse in the midbrain ● Ganglion cell layer is ABSENT in the fovea Q: Why is the ganglion cell absent in the fovea centralis? A: The exit of the ganglion cell is in the optic nerve, and it will not pass through the fovea Amacrine Cell and Horizontal Cell ● Cell bodies lie at the inner nuclear layer ● Processes are directed inward towards the ganglion cell layer in the inner plexiform layer ● Oriented against the direction of light impulse transmission ● Horizontal and Amacrine Cell transmit electrical signals towards the periphery of the retina NEUROGLIAL CELLS
- Neurons cannot regenerate but good at transmitting nerve impulses
- Once damaged, neuroglial cells can regenerate but it cannot transmit electrical impulses Muller Cells ● Provide structural support by enclosing the dendrite processes Microglial Cells
