middle layer of eye

Anterior Epithial Layer

1 cell layer thick- living and produces cells for the lens

index of refraction of crystalline lens

1.42

5 layers of choroid

3 blood vessel layers with a support layer on each side, inner layer (bruch's membrane), choriocapillaris, vessel layers of sattler, vessel layer of haller, suprachoroid

Cataract

any opacity of the lens, large or small, causes : not enough nutrition, radiation, old age treatment: removal

Blood Vessels

arteries, veins, capillaries

Lamina Vitria

basement membrane of pigmented epithelium, continuation of bruch's membrane

Basement membrane of non pigmented epithelium

called the Internal Limiting membrane which continues into retina

Choriocapillaris

capillary layer, contains all choroidal capillaries, EXTREMELY LARGE, can handle 2 to 3 times as many cells as regular capillaries, about 20 microns in diameter, all nourishment of choroid from this layer

arteries

carry blood away from heart

veins

carry blood to the heart

5 parts of middle layer

choroid, iris, ciliary body, crystalline lens, blood vessels

Ciliary Body

circular band of tissue, 6mm wide, extends from the ora serrata to the root of the iris

pigment epithelium

continuous with the pigment epithelium of ciliary body and the choroid, except in the iris it has 2 cell layers, numerous melanocytes; extends on to anterior surface a little, pupillary frill

Iris

divides anterior and posterior chamber, about 12mm in diameter with an opening of variable size (pupil)

Caprule (zonule)

elastic protein layer thickens at equator, non living non cellular no fibers just smooth elastic tissue

Crystaline Lens

front radius of curvature of the lens is 9mm, back radius is 5.5mm

what happens when muscle contracts in opening of ciliary body

gets smaller, ciliary body moves closer to the lens, releasing tension of zonule fibers (suspensory ligaments) allowing crystalline lens to become more biconvex (rounder) which shortens focal length for near vision

crypts

holes in the iris, dents go way into stroma

Smooth Muscle (Ciliary Body) 3 layers

horizontal fibers, radial (tangental) fibers, circular fibers

Vessel layer of Haller

large veins, lead to vortex veins (these vortex veins exit the eye through the sclera)

consensual reflex

light causes constriction of contralateral eye; the other non lit eye

direct reflex

light causes constriction of pupil on ipsilateral eye (same side) shine light on the right eye, right pupil constricts

capillaries

little blood vessels, thin walled, deliver nutrients, pick up waste

Vessel layers of Sattler

made up of medium size veins, has some arterioles (smallest arteries, just a little layer than capillaries), a stroma(ground substance) of collagen and elastic fibers around the blood vessels and many melanocytes

6 layers of ciliary body

muscle layer, vessel layer (blood, arteries & veins), pigmented epithelium, non pigmented epithelium, basement membrane, pigmented and non pigmented epithelium

Aging of lens

nucleus becomes larger and yellowish, fills a greater portion of lens, gets more compact and harder which makes it less flexible and so can't accommodate as well, grows throughout your life, 1/3 larger at 65 than at 20

Root

outer edge of iris, which attaches to ciliary body

Suprachoroid

outermost (top) supporting layer, blends with inner layer of sclera, contains choroidal arteries (ciliary arteries) and arterioles, not many vessels, arterioles pass directly into the choricapillaries, has stroma (ground substance) with melanocytes

pupillary frill

part of pigment epithelium which comes to edge of iris

stroma

part you see from the front, contains fibers and blood vessels, melanocytes, (chroma to phores)

functions of ciliary body

pigmented epithelium of pars plicata section makes aqueous honor and secretes it into posterior chamber controls accommodation

sphincter muscle

pupillae muscle, contracts pupil-makes smaller, 1mm wide (about twice is big when pupil is dilated than when contracted), circles pupil at posterior stroma, can change pupil size from 1.5mm to 8.5mm diameter

dilator muscle

pupillae muscle, very thin layer of muscle on top of pigment epithelium; from root of iris to sphincter muscle poorly developed in young children

As cell age they

shrink, lose nucleus, move toward center of lens, become compressed

when pupil constricts

sleep, convergence, sharpens vision, and increases depth of field

muscles in iris

smooth muscles (involuntary); sphincter, dilator

Middle Layer

vascular layer; uveal tract

Choroid

vascular, dark brown tissue, from about .2mm at back of eye to about .1mm at front of eye, nourishes outer layer half of nervous coat; has 5 layers

inner layer - Bruch's membrane

very thin - 2 microns, 3 parts: basement membrane of the pigment epithelium, middle collagen layer for strength, elastic layer which supports all capillaries of choroid