Ocular Anatomy and Physiology

Bony socket containing the eye. Formed from several fused bones
Serves to:
Protects delicate eye +provides mounting point for the 6 striatal muscles that control ocular movement.

white of eye thats tough. Outer protective layer maintains eye shape. Muscles attached to sclera control eye movements.

Located behind pupil + between anterior + posterior chambers. Transparent biconvex structure, that bends/ refracts light rays - focus on nerve cells retina. Suspended by lens zonules.

Filled with a watery fluid that gives shape to the eye and helps refract the light rays.

Provides attachment for lens zonules. Changes the focusing power of the lens.

Coloured smooth muscle surrounding pupil, adjusts opening size according to light brightness. Attached by ciliary body.

Middle vascular layer - maintains eye's blood supply + contains blood vessels.

The circular opening at the front of the choroid.

Inner layer that contains the nerve cells, Photoreceptors (rods, cones), + bipolar cells. Lines back of eye on the inside.

Photoreceptors activation causes action potential generation in optic nerve (bundle of ~1.25´108 nerves)
Pass into skull interior via optic canal to meet at optic chiasma.
Nerves project to visual cortex in occipital lobes.
Carries impulses + transmits images from retina (photoreceptors) to brain.

Lachrymal Gland produces:
Basic tears:
Maintains tear film on corneal surface for optical, metabolic and lubricant.
Reflex tears
Induced in response to chemical or mechanical irritation, cold, light)
Emotional tears from crying.

Precorneal tear film consists of superficial lipid layer, central aqueous layer + inner mucus layer.

Consists mainly of sterol esters, triacylglycerols, phospholipids, free sterols + free fatty acids
Spreads over aqueous layer during eye opening
Lipids reduce evaporation rate - maintains normal tear osmolality

· Inorganic salts
· Glucose
· Urea
· Retinol
· Ascorbic acid
· Various proteins
· Lipocalins (tear-specific pre-albumins)
· Immunoglobulins
· Lysozyme
· Lactoferrin
· Glycoproteins

Prevents corneal drying
Transports oxygen + nutrients to cornea
Maintenance of keeping cornea clean + smooth. Protects against infection

normal tears pH -7.3 - 7.7 (mean : 7.4);
pH lowest on awakening
pH varies between 5.2- 9.3 depending on age + diseases;
Buffer capacity of tears based on bicarbonate ions, proteins and mucins.
Tears more acid in contact-lens wearers - impediment of CO2 efflux.
Tears more alkaline in diseases; dry eye, severe ocular rosacea and lacrimal stenosis.

Under normal conditions human tear volume is ~ 7-9 mL, relatively constant.
Max fluid amount held in lower eyelid sack - 25-30 mL, only 3 mL of solution is incorporated in precorneal film without destabilisation.
With eye-drops, tear volume suddenly increased causing rapid reflex blinking
Tear flow: 1.51±0.58 μL/min

Important defence mechanism of eye.
Brisk blinking reflex fast enough to precede high-speed foreign bodies approaching eye;
Essential for periodic reforming of tear film;
Blinking activates pumping mechanism for tear drainage through lacrimal drainage apparatus. Blink rate is 15-20/ min.

Clear circular area in sclera where light enters eye. Functions are: Passage and refraction of light, and protection.

Anterior fluid. A transparent viscous fluid located in the anterior chamber of the eye.

· 98% water
· amino acids
· electrolytes
· ascorbic acid
· glutathione
· immunoglobulins

Maintains intraocular pressure + inflates eye globe
Provides nutrition for avascular ocular tissues (posterior cornea, trabecular meshwork, lens, and anterior vitreous);
Can transport ascorbate in anterior segment to act antioxidant agent;
Potential immune response to defend against pathogens (immunoglobulins);
Light refraction

Refract light to be focused on retina;
Elastic + can change shape; thicker = focus close objects, thinner = distant objects;
Lens consists of lens capsule, the lens epithelium, and lens fibers.

Posterior fluid. The clear gel that fills the space between the lens and the retina.

Maintains normal anatomic expansion of eye globe.
Impedes diffusion of substances between retina + anterior segments of eye.
Small water-soluble substances in retina may diffuse into vitreous , across the blood-retina barrier.
Acts as reservoir of substances such as oxygen, glucose and ascorbic acid (also metabolic waste products) - supports metabolism of adjacent structures.

· water (99%);
· a network of collagen fibrils;
· large molecules of hyaluronic acid;
· peripheral cells (hyalocytes);
· inorganic salts;
· glucose;
· ascorbic acid

Type of receptor (rods and cones) located on retinal surface. Responds to light to allow vision.
Rods act in low light levels, don't provide colour and has little spatial resolution
Cones act in higher light levels, perceive colour and allow good spatial resolution.
Rods and cones synapse with bipolar cells, which then synapse with ganglia cells, whose axons form the optic nerves.