Ocular Anatomy and Physiology Overview

Anatomy

Science of body structures

Physiology

The science of body functions (ocular physiology)

Gross anatomy

Visible to the naked eye

Examples of gross anatomy of the eye

Iris, lens, palpebrae, sclera

Complementarity of structure and function

Function always reflects structure; what a structure can do depends on its form

Cornea

Curved, transparent. Allows to focus light

Iris and pupil

Contains muscle. Allows to adjust pupil size to control amount of light entering the eye

Lens

Lens is flexible and biconvex. Varying size of lens allows control of light being focused on the retina

Retina

Retina layout. Central cones allow that our best vision is focused on them

Optic nerve

Large bundle of optic nerves. Allows for efficient and rapid signal conduction

Microanatomy

Too small to be seen with naked eye

Anatomical position

A reference point. Universal shared method which allows healthcare professionals to pinpoint structures in an organism when communicating

Anatomical terms

Terms: Anterior, posterior, lateral, medial, superior, inferior

Sagittal plane

Divides body into left and right side (line from front to back)

Coronal (frontal) plane

Divides body front and back (side to side line)

Transverse plane

Divides body into superior and inferior

Principle structures of the eye (external features)

Limbus, sclera, iris, pupil, palpebrae, canthus, plica semilunaris, lacrimal caruncle + ocular adnexa

Principle structures of the eye (internal features)

Optic nerve, choroid, macular + fovea, vitreous humor, aqueous humor

Lesions

Can be described as being located inferio - medial, infero nasal. Use time as well e.g. 12 o'clock, size of lesion

Histology

The study of cells and tissues by microscopy

Epithelial tissue

Layers of cells that cover body surfaces. 2 main subtypes: covering or glandular

Role of epithelial tissue

Protection, absorption, secretion, filtration, excretion, sensory perception

Features of epithelial tissue

Good regeneration, sits on basal lamina, avascular, innervated, tightly joined together and polar

Naming epithelia

Based on two factors: Number of layers (simple, stratified, pseudostratified) and shape (squamous, cuboidal, columnar, transitional)

Microvilli

Membrane projections that increase the surface area of plasma membrane (for absorption)

Cilia

Tiny hair-like structures that are motile and sweep debris and mucus

Keratin

A protein that helps protect the skin from heat, microbes and chemicals

Connective tissue

The most abundant and widely distributed tissue in the body. Space filling tissue.

Fibroblasts

Produces extracellular matrix (and cells) which provides support and elasticity to tissues.

Adipocytes

Cells that store fat.

White blood cells

Cells of the immune system that help the body fight infection.

Extracellular matrix

Made up of fibres (collagen, elastic and reticular) and ground substances which binds everything together.

Loose connective tissue

Loose arrangement of fibres (collagen) with lots of ground substances, providing support and flexibility.

Dense connective tissue

Closely packed collagen fibres with little ground substances, providing support and resistance to stretching.

Ground substances

Combination of water, glycosaminoglycans, proteoglycans, and adhesion proteins that fills space between cells and acts as a medium for exchange in nutrients and waste.

Collagen fibres

A protein (most abundant protein in the body) which is very strong but also flexible.

Types of cell junctions

Includes tight junctions, desmosomes, and gap junctions, each with specific functions.

Tight junctions

Integral membrane proteins from neighbouring cells fuse together to form impermeable junctions which prevent molecules from passing.

Desmosomes

Anchoring junctions that prevent adjacent cells from separating but still allow molecules to pass.

Gap junctions

Hollow channels (connexins) from both plasma membranes of adjacent cells connect with each other, allowing molecules to transport from cell to cell.

Bone shapes

Four different bone shapes: long, short, irregular, and flat bones.

Mineral composition of bone

Made up of majority calcium at 39%, phosphate, carbonate, potassium, sodium, magnesium, and organic compounds (cells & extracellular matrix).

Osteogenic progenitor cells

Stem cells that can differentiate into osteoblasts.

Osteoblasts

Cells that secrete collagen.

Osteocytes

Mature bone cells.

Osteoclasts

Created by fusion of many white blood cells and involved in phagocytosis and repair of bone.

Compact bone

Found on external surface, dense, strong, and heavy.

Spongy bone

Found internal to compact bone, light and loose.

Periosteum

A thin dense layer of connective tissue that surrounds compact bone.

Osteons

Arranged units in compact bone.

Lacunae

Empty spaces where osteocytes reside in compact bone.

Trabeculae

An irregular latticework of thin bone found in spongy bone.

Function of bone tissue

Supportive for movement and protection, mineral homeostasis, blood cell production (red bone marrow), and triglyceride storage (yellow bone marrow).

Cranial bones

Include Parietal (x2), Temporal (x2), Occipital, sphenoid, and ethmoid.

Facial bones

Include Nasal (x2), Maxillary (x2), Zygomatic (x2), Mandible, Lacrimal (x2), Palatine (x2), Inferior nasal conchae (x2), and Vomer.

Sutures

Joints that unite the bones of the skull, forming immovable joints except for the mandible.

Cavities

Spaces within the skull, including the orbital cavity, cranial cavity, and nasal cavity.

Paranasal sinuses

Mucosa lined, air-filled cavities located in four orbital bones: frontal sinus, maxillary sinus, ethmoid sinus, and sphenoid sinus.

Articulations

The region where adjacent bones contact each other, forming a joint.

Foramina

A small opening that allows the passage of structures from one region to another.

Fissures

Similar to foramina, these are small openings that allow the passage of structures, shaped more like a crack or cleft.

Fossa

A shallow depression in the bone.

Blowout fracture

A medical condition where high external pressure on the eye causes the maxillary sinus bone to break, leading to immediate swelling, bleeding, and limited ocular movement.

Weak points of the orbit

The floor and medial aspects are the weak points that can lead to fractures.

Osteoporosis

A condition that leads to weak bones, making them prone to breaking, which can increase the risk of orbital cellulitis.

Orbital cellulitis

A bacterial infection of the skin around the eye, common in children under 7, characterized by inflammation, redness, swelling, and fever.

Total volume of the orbit

30ml, which includes 6.5ml for the eyeball and 23.6ml for the optic nerve, connective tissue, muscles, and adipose.

Retina

The innermost layer of the eye, sandwiched between the choroid and the vitreous, with light-sensitive and non-light-sensitive parts.

Optic disc

A pale-colored area that lies medially, where branching blood vessels extend from.

Macula

A central part of the retina that includes the fovea and is crucial for high-acuity vision.

Functions of the retina

Converts light into neural signals and sends these signals to the brain for visual recognition.

Retinal pigment epithelium (RPE)

The outer layer of the retina that supports photoreceptors.

Photoreceptors

Cells in the retina that detect light and convert it into neural signals.

Outer nuclear layer

Layer in the retina containing the cell bodies of photoreceptors.

Inner nuclear layer

Layer in the retina containing the cell bodies of bipolar, horizontal, and amacrine cells.

Outer plexiform layer

Layer in the retina where synapses occur between photoreceptors and ganglion cells.

Inner nuclear layer

Cell bodies of bipolar, horizontal and amacrine cells

Inner plexiform layer

Synapse with ganglion cells

Ganglion cell layer

Layer containing retinal ganglion cells

Nerve fibre layer

Layer made up of axons of ganglion neurons, unmyelinated until they penetrate the sclera at the optic disc

Internal limiting membrane

Basal lamina which forms the boundary between retina and vitreous body

Neuroglial cells

Support cells in the retina that don't transfer neural signals, including Muller cells, microglia, and astrocytes

Muller cells

Cells that extend throughout the retina, enclosing dendritic processes within the synaptic layer and maintaining pH by absorbing waste products and regulating ion concentration

Microglia

Wandering phagocytic cells found in the retina that become active during infection or injury

Astrocytes

Star-shaped fibrous cells found in the inner retina that provide support to nerve fibres and retinal capillaries

Photoreceptor layer

Layer made up of rods and cones segment

External limiting membrane

Made up of tight junctions between Muller and photoreceptor cells

Outer nuclear layer

Layer made up of rod and cone cell bodies

Outer plexiform layer

Layer made up of neural synapses of photoreceptors, horizontal and bipolar cells

Inner plexiform layer

Layer made up of nuclear synapses between bipolar cells and amacrine cells with retinal ganglion cells

Ganglion layer

Layer consisting of retinal ganglion cells and displaced amacrine cells

Optical coherence tomography (OCT)

Non-invasive imaging tool to observe changes in the retina, allowing visualization and evaluation of distinctive layers and nerve fibre layers

Rods

Photoreceptors with discs that are separate from the outer membrane

Cones

Photoreceptors with discs that are continuous with the outer membrane

Outer segment of photoreceptors

Contains discs, functions to contain photopigment and initiates phototransduction cascade

Inner segment of photoreceptors

Contains mitochondria and resides in the photoreceptor layer of the retina, serving as the metabolic centre

Connecting cilium

Joins the inner and outer segments of photoreceptors

Fovea

Region where cones are elongated and longer, providing high acuity vision

Isomerisation

Chemical process where one molecule is transformed into another molecule with the same composition but different order

Hyperpolarisation

Condition where the cell becomes more negative inside