Lecture 9 and 10 Ocular Anatomy

eye

the organ of sight
-an extension of the central nervous system
-contains all four basic tissue types

anteroposterior diameter

~24mm
from front to back of eye

horizontal diameter

~23.5mm
from lateral to medial sides of the eye

vertical diameter

~23 mm
from top to bottom of the eye

anatomic equator

Divides the globe into two unequal halves
-Approximately 13 to 14 mm behind the limbus

13 years of age

what age does the eye reach normal adult size?

eye position in the orbit

anteriorly and slightly closer to the roof than the floor
-more fat in the floor of the orbit

the lateral orbital rim

protects the posterior 1/2 of the globe from the temporal side

lateral portion of the eye

what portion of the eye is most exposed ad more prone to injury?

visual axis

An imaginary line passing from the midpoint of the visual field to the fovea centralis.

orbital axis

line down the center of the orbit
-in line with optic nerve

ocular tunics

-Fibrous
-Vascular or Uveal
-Neural or Retina

fibrous tunic

composed of the transparent cornea anteriorly and the opaque sclera posteriorly
-both made of collagen but the arrangement contributes to the colors

Corneoscleral limbus

where the cornea and sclera merge

sclera function

provides the attachment sites for intraocular structures and extraocular muscles
-uveoscleral outflow pathway for aqueous humor

scleral aperatures

allow for passage of blood vessels and nerves to enter and exit the eye

scleral thickness

non-uniform
-greatest around the optic nerve 1 mm
-thinnest just posterior to the insertion of the rectus muscles 0.3 mm
-Continues to increase until it reaches the corneoscleral limbus 0.8 mm

where is the sclera most vulnerable to rupture?

just posterior to the insertions of the rectus muscles (where it is thinnest)

spiral of tillaux

The insertion pattern of the rectus muscles

layers of the sclera

-Stroma
-Lamina Fusca

Episclera

fibrovascular layer situated between the sclera and tenon's capsule

-provides nutrients to sclera

-Thickest anteriorly and thins progressively towards the tendinous insertions of the rectus muscles

Tenon's Capsule

connective tissue
-the socket in which the globe is suspended; kept intact for ocular prosthesis

Cornea

The clear tissue that is part of the fibrous tunic.
-Tough, highly innervated
-Avascular
-Major Refractive component of the eye

Where is the cornea thickest?

periphery
~670 um

where is the cornea thinnest?

center
~520-550 um

astigmatism

unequal curvature of the cornea
-prevents light from being focus to a single point on the retina

Corneal tear film

-Lipid Phase (surface)
-Aqueous Mucinous phase
-Glycocalyx

Lipid phase

aggregates of lipid held together by hydrophobic forces

Aqueous Mucinous Phase

-both soluble and gel-forming mucins
-interact with a base layer of epithelial membrane-bound mucins

Glycocalyx

-secreted by epithelial cells
-includes several trans membranous mucins
-directly related to cornea

5 layers of cornea

-Anterior epithelium
-Bowman's Layer
-Stroma
-Descemet's Membrane
-Endothelium

Vascular Tunic

heavily pigmented and highly vascularized
composed of
-Iris
-Ciliary body
-Choroid

Iris

regulates the amount of light reaching the retina via its aperture, the pupil, and has been likened to a diaphragm in an optical system

what divides the aqueous compartment into anterior and posterior chambers?

the iris

Ciliary body

-formation and secretion of aqueous humor

-Synthesis of lens zonules and vitreous during fetal development

-Acts as a fulcrum for the lens zonules

-Major role in accommodation

Parts of the Ciliary Body

Pars plicata and pars plana

Pars Plicata

part with ciliary processes

Pars plana

Smooth, flat part of the ciliary body

irregular oblong spheroid

shape of the globe

ciliary processes

hair-like processes that extend from its inner border to into the posterior chamber

choroid

composed of blood vessels, melanocytes, connective tissue, and a mucinous extracellular fluid

What is the sole source of nutrients for photoreceptors in the retina?

choroidal vasculature

Location of choroid

between sclera and retinal pigment epithelium

why is the choroid brownish in color?

dense melanocyte population

Neural tunic

innermost layer of the eye composed of the retina
-responsible for converting light into a neural signal by the process of phototransduction

retina

contains the first three cells of the visual pathway
-composed of 10 layers

what forms the optic nerve?

axons of the retinal ganglion cells

retinal ganglion cells

the third layer of retinal neurons whose axons leave the eyeball and form the optic nerve.

-the output cells of the retina

Anterior chamber

between cornea and iris, filled with aqueous humor

what is responsible for keeping normal pressure in the eye?

trabecular meshwork

posterior chamber

between iris and lens, filled with aqueous humor

flow of aqueous humor

unidirectional from posterior chamber through pupil to anterior chamber

crystalline lens

biconvex structure that is located posterior the iris and pupil and anterior to the vitreous body.
-Focusing element of the eye's optical system

vitreous chamber (body)

between the lens and the retina
filled with vitreous humor

ocular adnexal structures

-eyelids
-conjunctival sac
-lacrimal apparatus
-orbital contents

eyelids

(palpebrae) two movable flaps of skin which cover and uncover each eyeball.

lacrimal apparatus

the structures that produce, store, and remove tears

conjunctiva

Delicate membrane lining the eyelids and covering the eyeball

extraocular muscles

-Superior rectus
-Inferior Rectus
-Medial Rectus
-Lateral Rectus
-Superior Oblique
-Inferior Oblique

Internal Carotid Artery

artery that branches off to ophthalmic artery

Ophthalmic Artery

main arterial blood supply to orbit and eye

where does the ophthalmic artery enter the orbit?

via optic canal/foramen

cranial nerves associated with eye and orbit

-Optic Nerve CNII
-Oculomotor Nerve CNIII
-Trochlear Nerve CN IV
-Trigeminal Nerve CN V
-Abducent Nerve CN VI
-Facial Nerve CN VII

cranial nerve II

Optic Nerve;
Sensory
Vision

CN 3, 4, 6

oculomotor, trochlear, abducens
responsible or eye movements

Cranial Nerve V

sensory information of eye
e.g. pain, touch

CN VII

motor innervation to orbicularis oculi - a muscle of facial expression