PHYSIOLICAL OPTICS

Stimulus-Response Phenomenon

It is the ability of a body or being to adjust itself to changes in the environment.

Receptors

- Organs in which irritability is highly developed

- It responds or is sensitive to stimuli (environmental changes)

- The eye responds to light or photic

Effectors

- Responding organs

- Acquaint the organism with the environmental changes thereby enables the organism to adjust itself to the changes.

- Important effectors: muscles and glands

Physiological Connectors

- Strands of protoplasm that connects the receptor and effector

- Once a disturbance or stimulus is set by the receptors, physiological connectors will carry it out to the effectors

- Commonly known as Neurons

- Disturbance - Nerve Impulse

Nervous System

Divided into two:

1. Central Nervous System

- brain and spinal cord

2. Peripheral Nervous System

- nerves directly springing from CNS; autonomic nervous system

Neuron

- a morphological unit

- also known as nerve cells, that builds the nervous system

- composed of: cell body, axon and dendron

- estimated 14M cell bodies in the brain; and is called a gray matter in the spinal cord

Spinal Cord

- The gray matter is centrally located on a cross-section: capital H shape

- the cell body of the neuron is supplied by three short dendrites and one long axon

- axon is also called nerve fiber because it leaves the spinal cord and connects itself to a skeletal muscle or gland.

Nerve Fiber

Carries impulses and thereby initiate activity in some other part of the body

- types: afferent and efferent nerve

- SAME (Sensory-Afferent; Motor-Efferent)

Afferent Nerve

- carries impulses from the sensory surface towards the spinal cord

- ad means towards

- also called Sensory Nerves

because they send impulse to

the spinal cord then to the brain and

causes an arousal of a sensation

Efferent Nerve

- carries impulses from the spinal cord towards the muscle

- ef or ex means out; fero – to carry

- also called Motor Nerves because they send impulses largely to the muscles

- but if it transmit impulses to glands, it is called Secretory Nerves.

Somatic Nerve

- fibers of the skeletal muscle and this includes the extrinsic ocular muscles.

Optic Foramen

- situated at the apex of the orbit

- passageway for the optic nerve and ophthalmic artery

Sphenoidal Fissure

passageway for: the 3rd, 4th and 6th CN; three branches of the ophthalmic division of the 5th CN a branch of the sympathetic nerve and the ophthalmic vein

 central part is crossed by the Annulus of Zinn

 The ocular globe occupies only a small portion of the orbital space.

 the remaining space is taken up by Extrinsic muscles, nerves, blood vessels and adipose (fat) tissue

Tenon’s Capsule

Forms a protective cushion for the eyeball

 It is a thin membranous sac

 Closely envelops the posterior 2/3 of the eyeball; at the anterior end, the capsule is continued by the conjunctiva

 Other names: tunica vaginalis oculi or fascia bul

Check Ligaments

which limit the extent of the ocular movement.

Lymph Space

Space between the capsule and the eyeball

THE EYEBALL

 Slightly elongated

 Its length (antero-posterior diameter) is about 24 millimeters

 It is composed of 3 coats or tunics and 3 transparent medias

Tunics of the Eyeball

 Sclero-corneal coat (Sclera)

 Uveal Tract (Choroid)

 Retina (Neural Coat)

Transparent Medias

 Aqueous Humor

 Crystalline Lens

 Vitreous Humor

SCLERO-CORNEAL COAT

 Is the outermost and composed of sclera and cornea.

SCLERA

 The sclera is the white coat of the eyeball

 Scleros means hard

 It is a tough layer composed mostly of bundle of white, inelastic fibers, interspersed with a smaller number of elastic connective tissue fiber

Functions:

1. Helps obtain a smooth screen (retina) by maintaining internal pressure and firm, unyielding shape formed

2. Protects the eye against various forms of injury.

3. Furnishes firm surface for the attachment of muscles.

4. Being fairly opaque, it aids in excluding extraneous light.

CORNEA

 It is the anterior portion of the sclera

 Has a diameter of 11-12mm, vertically 10-11mm and a radius of curvature of 8mm

 It is about 0.8mm thick at the margin and thins out in the center, approx. 0.5mm

 It is devoid of blood vessels and is

abundantly supplied with nerves of pain

 Functions:

1. By its rigidity (same of sclera), it gives

the eyeball a constant shape

2. Its transparency permits the light to

reach the interior of the eye

3. By its extreme sensitivity, it aids in

protecting the eye

Schlemm’s Canal

 At the circumference of the cornea and the elastic lamina of Descemet’s membrane breaks up into separate fibers

 This canal is a tube near the sclero corneal junction, encircling the cornea and connecting with the veins of the sclera.

UVEAL COAT

 Also known as Tunica Vasculosa

 It is the middle coat

 Uvea came from the word uva means

grape, because of its dark brown color

 Divided into:

1. Choroid

2. Ciliary Body

3. Iris

CHOROID

 Also known as choriodea

 Covers about 5/6 of the interior of the eyeball

 It is a dense, flat network of blood vessels held together by connective tissue

 It is the nourishing coat of the eye

CILIARY BODY

 It is the prolongation and thickening of the choroid, extending from the Ora Serrata to the base of the Iris.

 Lies as a ring posterior to the sclero-corneal junction

 Ciliary muscles are developed at its anterior end causing the appearance of a long, thin, triangular body in a meridional section

 This fibers held the lens in place, designated as the Suspensory Ligaments of the lens or the Zonule of Zinn

IRIS

 Anterior to the ciliary body the choroid coat modified to form the Iris.

 Its central aperture, the pupil, allows the light to pass freely into the lens

RETINA

 Forms the 3rd and innermost tunic

 It is the coat which the images are cast and in which nerve impulses are generated

 These impulses are conveyed by the optic nerve to the brain

 It is a delicate, almost transparent membrane composed chiefly of neuron held together by a minimum amount of connective tissue

Optic Disk

also known as the nerve head, optic papilla or blind spot: at this point, all fibers turn outward, pass through the 3 tunics of the eye and leave the eyeball as the Optic Nerve

Macula Lutea

Is also known as the yellow spot and found a little temporal side

 Its central depression called the Fovea Centralis. Fovea means a small pit.

 It contains the most number of rods and cones, especially in the fovea.