Anatomy & Physiology of the Orbit and Eye

lens

to refract (bend) and focus light, enabling clear vision by projecting an image onto the retina, can become less or more convex 

cornea

prevent the entrance of foreign objects or substances

transparency maintained as endothelium layer has a pump that actively keeps aqueous humor out 

sclera

protects the delicate inner parts of the eye from injury

maintaining the eyeball's shape

providing an attachment point for the eye muscles that control movement

preventing off-axis light from entering the eye to maintain a clear image 

iris

to control the amount of light that enters the eye by adjusting the size of the pupil

in bright light constricts to make pupil smaller

in dim light expands to make pupil larger

ciliary body

Production of the aqueous humor, change of eye focus (via the accommodation function) 

choroid

 made up of fenestrated blood vessels of varying diameter which supply outer layers of retina with blood by diffusion

Provide oxygen and nourishment to outer retina

thermoregulation of posterior eye

modulation of intraocular pressure

drainage of aqueous humor from anterior chamber 

retina

capture light that comes through the eye and change that light into an electrical signal that your brain interprets 

conjunctivae

 protection and lubrication of the eye by the production of mucus and tears. 

prevents microbial entrance into the eye and plays a role in immune surveillance.

lines the inside of the eyelids and provides a covering to the sclera.

highly vascularized and home to extensive lymphatic vessels. 

tear film

Tear film keeps cornea moist

prevents drying

washes away any particular foreign bodies

has antibiodies to kill microbes

smooths outer surface of cornea providing smooth surface refraction 

tear film components

mucinous layer (30%) overlying corneal epithelium

aqueous layer (69%) lies over mucinous lauer

oily layer (<1%) most superficial. 

function of aqueous fluid

clear fluid provides nutrients to the lens and cornea. It also helps maintain pressure inside the eye

function of vitreous humor

gel-like substance supports the eye’s shape. It also helps hold the retina in place.

how aqueous fluid circulates through the anterior segment of the eye

Ciliary processes in posterior chamber produce aqeuous humor -> flows through the pupil to the anterior chamber -> exits at drainage angle through trabecular meshwork (filter like system) -> aqueous humor enters blood stream through schlemm's canal (small channel) 

how is transparency of cornea maintained

by regular arrangement of collagen in stroma

no blood vessels and endothelium cell layer with pump that actively keeps aqueous humor out 

what are corneal opacities

nature of healing of wounds of cornea leads to loss of transparency and opacification of cornea, cornea transparency lost = diminished vision

lens opacification

cataract, avascularity predisposes it to become opaque later in life 

blood aqueous barrier

formed by the ciliary body epithelium and the iris capillary endothelium

blood retinal barrier

inner BRB from retinal capillary endothelium

the outer BRB from retinal pigment epithelium (RPE).

Both barriers, which contain tight junctions, are crucial for maintaining a stable internal environment for optimal vision and protecting the eye from pathogens and inflammation 

parasympathetic CN VII secretes..

tears into conjunctival sac

during a blink the…

 sharp lower border of the upper eyelid distributes tear film evenly

when eyelid opens..

aqueous component of tears begin to evaporate, oily layer comes close to the mucin layer

when the aqueous and oily layer touch each other..

the tear film breaks up and stimulates further blinking