Ocular anatomy Flashcards
what is orbit?
what is its roles?
bony socket containing the eye
formed from a number of fused bones
serves:
-protect the delicate eye
-provide a mounting point for the six striatal muscles that control the ocular movement.
what are the structures in the internal eye?
their functions?
Sclera
Tough, outer protective coat
Lens
transparent biconvex structure, suspended by lens zonules
Cilliary body
provides attachment for lens zonules. Changes the focusing power of the lens
Iris
regulates light entering eye attached by cilliary body
Choroid
maintains the eye’s blood supply
Retina
inner layer containing visual photoreceptors (rods & cones)
Optic nerve
transmits images from photoreceptors to the brain
tear production by lachrymal glands
what are the different types of tears
Basic tears (to maintain a tear film on the corneal surface for optical, metabolic and lubricant purposes)
Reflex tears are induced in response to chemical or mechanical irritation, cold, light, etc)
Emotional
lipid layer
what does it consist of
where is it found
what is its role
It consists mainly of sterol esters, triacylglycerols and phospholipids, free sterols and free fatty acids
It spreads over the aqueous layer during eye opening
The lipids play an important role in reducing the evaporation rate to maintain the normal tear osmolality
what consists in the aqueous layers in the cornea?
Inorganic salts
Glucose
Urea
Retinol
Ascorbic acid
Various proteins
Lipocalins (tear-specific pre-albumins)
Immunoglobulins
Lysozyme
Lactoferrin
Glycoproteins
what is the function of tear films?
Prevention of corneal drying
Transport of oxygen and nutrients to the cornea
Maintenance of cornea clean and smooth
Protection against infection
what is the pH of tear films?
7.3-7.7
pH lowest on awakening
pH can also vary between 5.2 and 9.3 depending on age and diseases;
why is tears more acidic in contact lens wearer
The tears are more acid in contact-lens wearers due to impediment of the efflux of carbon dioxide, and more alkaline in the case of diseases such as dry eye, severe ocular rosacea and lacrimal stenosis.
what is the buffer capacity of tears determined by?
Buffer capacity of the tears is determined by bicarbonate ions, proteins and mucins;
what is nasolacrimal drainage?
how does it work?
Under normal conditions the human tear volume is about 7-9 L and it is relatively constant
The maximum amount of fluid that can be held in the lower eyelid sack is 25-30 L, but only 3 L of a solution can be incorporated in the precorneal film without causing it to destabilise;
When eye-drops are administered, the tear volume is suddenly increased which can cause rapid reflex blinking
what is blinking and its role?
Blinking is an important defence mechanism of the eye. The brisk blinking reflex is usually fast enough to precede high-speed foreign bodies approaching the eye;
Blinking is also essential for the periodic reforming of the tear film;
Blinking also activates a pumping mechanism for the drainage of tears through the lacrimal drainage apparatus;
The blink rate in humans is 15-20 per min (roughly one blink every 5-7 s. In rabbits it is slower than in humans (roughly 5 per min).
epithelium = lipophilic
stroma - hydrophilic
why is it like this?
protect eye ball
to temper foreign substances getting in to the eyeball
what is the functions of the cornea?
passage of lights
reflection of light
protection
what is aqueous humour
what is it composed of?
The aqueous humour is a transparent viscous fluid located in the anterior chamber of the eye
Composition
98% water
amino acids
electrolytes
ascorbic acid
glutathione
immunoglobulins
what is the function of aqueous humour?
It maintains the intraocular pressure and inflates the globe of the eye
It provides nutrition for the avascular ocular tissues (posterior cornea, trabecular meshwork, lens, and anterior vitreous);
May serve to transport ascorbate in the anterior segment to act as an antioxidant agent;
Potential immune response to defend against pathogens (immunoglobulins);
Light refraction
