Introduction The slides for this lab are located in the “Special Senses: Eye” folder on the Virtual Microscope. This guide provides you with a short description of the slides that you will be examining and a short conceptual framework for studying them.
The eye is composed of three layers: fibrous, vascular and neural. During this lab you will examine the components of each of these layers. In addition you will examine the histological features of the eyelid.
Learning objectives and activities Using the Virtual Slidebox:
A Use your knowledge of basic tissues to identify the major features of an eyelid.
B Review the basic anatomy of the eye before examining it in more detail.
C Identify the fibrous layer of the eye and examine its major components: the sclera and cornea.
D Identify the vascular (uvea) layer of the eye and examine its major components: iris, choroid and ciliary body.
E Identify the neural layer of the eye and examine each layer of the retina.
F Complete the self-quiz to test your understanding and master your learning
Use your knowledge of basic tissues to identify the major features of an eyelid.
Examine Slide 1 and identify the following basic structural components
The eyelids are folds of skin that cover the anterior surface of the eye. The upper and lower lids create the palpebral fissure and when sealed (eyes closed tightly) create the enclosed conjunctival sac that is lined by palpebral conjunctiva (covering the inner surface of the eyelid) and bulbar conjunctiva (covering the eyeball). i. General organization
a. Skin Identify skin of the The outer eyelid is covered in, thin, hairy skin. You should be able outer eyelid in to identify the major features of and basic tissues associated with Slide 1a skin including the layers of the epidermis and dermis.
b. Palpebral conjunctiva (inner eyelid) The conjunctiva covers the inner aspect of the eyelid and the Identify palpebral bulbar surface of the eyeball. It is a mucosa composed of a thin conjunctiva in stratified squamous epithelium that contains goblet cells. The Slide 1b mucous secretions of the goblet cells contribute to the protective tear film that covers the eye.
c. Tarsal plate and Meibomian glands A dense irregular connective tissue core to the eyelid that Find CT of the tarsal plate supports it and gives it its shape while providing attachment for and embedded Meibomian glands in the palpebral part of orbicularis oculi. Note that the meibomian glands are embedded in the tarsal plate. Slide 1c
d. Accessory lacrimal gland This serous gland produces tears that wash across the surface of Identify accessory the eye. This section contains the smaller accessory palpebral lacrimal gland in portion of the gland. The major lacrimal gland is located in the Slide 1d superior aspect of the orbit.
e. Glands of Moll These are modified sweat glands that form a spiral before opening Identify glands of Moll into the follicles of the eyelashes. As a result they are only in Slide 1e observed in the free edge of the eyelid.
Review the basic anatomy of the eye before examining it in more detail
Use the overviews in Slide 2 and Slide 3 to gain an understanding of the anatomy of the eye by finding the following components.
lens ANTERIOR CHAMBER iris and (contains aqueous humor) FIBROUS LAYER pupil cornea POSTERIOR CHAMBER (contains aqueous humor) sclera
retina (non-visual part of NEURAL LAYER) VITREOUS BODY uvea (contains vitreous VASCULAR LAYER humor)
macula (fovea centralis) fovea
optic nerve
Identify the fibrous layer of the eye and examine its major components: the sclera and cornea.
Slide 4 shows only the anterior part of the eye again. Identify the cornea and its components.
i. GENERAL b. Tear layer c. Corneal epithelium
ORGANIZATION - a transparent layer of tears - nk. strat. squ. epithelium
OF THE CORNEA - keeps corneal epithelium moist - continuous with conjunctiva
Identify the tear layer in Identify the corneal Slide 4b epithelium in Slide 4c
d. Bowman’s membrane - type I collagen - acts as basement membrane a. Cornea Identify the Bowman’s - transparent and avascular membrane in Slide 4d - refracts light toward the midline focusing it on retina e. Corneal stroma - contains sensitive - thick and transparent unmyelinated nerves that - lamellar type I coll. fibers trigger blink reflex Identify the corneal Identify the cornea in stroma in Slide 4e Slide 4a f. Dua’s layer - new layer discovered in 2013
Identify Dua’s layer in
Slide 4f
g. Descemet’s membrane - a thin acellular layer - the endothelial basement membrane
Identify Descemet’s membrane in
Slide 4g
h. Endothelium - the inner simple squamous lining - pumps fluid and ions out of the stroma - keeps it dehydrated which assists refractive quality
Identify endothelium in Slide 4h
Slide 4 shows only the anterior part of the eye. Identify the sclera and its components
ii. GENERAL iii. GENERAL ORGANIZATION ORGANIZATION OF THE SCLERA OF THE LIMBUS
i. Sclera l. Limbus - white part of eye - junction between cornea - dense irregular CT and sclera - maintains eye shape/size
- site of attachment of ocular Identify the limbus in
muscles Slide 4l
Identify the sclera in Slide 4i m. Trabecular meshwork and Canal of Schlemm - aqueous humor (secreted by ciliary j. Lamina cribrosa processes in posterior - where optic nerve passes chamber) drains out of through sclera anterior chamber via trabecular meshwork Identify the lamina into the canal of cribrosa in Slide 4j Schlemm where it enters venous system) k. Angle - if blocked leads to OPEN
- where the iris meets the sclera ANGLE glaucoma due to
- if angle is decreased the iris can increased pressure in
block the entrance to the canal of eye due to build up of
Schlemm impeding drainage of aqueous humor
aqueous humor and resulting in
CLOSED ANGLE glaucoma due to Identify the trabecular
increased build up of pressure in meshwork and canal
the eye. of Schlemm
in Slide 4m Identify the angle in Slide 4k
Identify the vascular (uvea) layer of the eye and examine its major components: iris, choroid and ciliary body.
Slide 5 shows only the anterior part of the eye again. Identify the uvea layer and components.
i. GENERAL ORGANIZATION OF THE CHOROID
a. Choroid Identify the choroid in Pigmented layer lining the eye posterior to ciliary body. It is Slide 5a attached to the sclera and separated from the retina by Brusch’s membrane.
b. Choriocapillary layer Identify the A highly vascular region of the choroid containing many capillaries. choriocapillary layer in Slide 5b c.Brusch’s membrane A thin elastic membrane sandwiched between two layers of Identify Brusch’s collagen fibers. membrane in The collagen layers are basement membranes of capillaries in the Slide 5c choriocapillary layer on one side and retinal pigmented epithelium on the other.
visual retina (see later)
retinal pigmented epithelium (RPE)
Brusch’s membrane choroid choriocapillary layer
pigmented layer
sclera ii. GENERAL ORGANIZATION OF THE IRIS d. Iris - anterior extension of the choroid - forms a contractile diaphragm e. Stroma - controls size of pupil - contains pigmented fibroblasts and melanocytes - loose irregular connective tissue Identify the iris in - less pigmentation = blue iris Slide 5d - more pigmentation = brown iris
Identify the stroma in
Slide 5e h. Retinal pigmented epithelium - pigmented epithelium that is an anterior extension of the retina - it is therefore neural layer NOT vascular layer
- continuous with the RPE covering the ciliary body
Identify the RPE in f. Sphincter pupillae muscle
Slide 5h - smooth muscle cells arranged
into a circular sphincter hence
cells are cut in xs
- innervated by the g. Dilator pupillae muscle parasympathetics of CNIII - thin layer of myoepithelial - contract to constrict pupil and cells let less light in during bright - run radially like spokes of conditions a wheel - innervated by sympathetics Identify the sphincter - contract to dilate the pupil and pupillae in Slide 5f let more light in during low light conditions Identify the dilator pupillae in Slide 5g
iii. GENERAL ORGANIZATION OF THE CILIARY BODY
i. Ciliary body j. Ciliary processes - wedge shaped portion of choroid - short finger-like projections - located between iris and vitreous body - contain abundant capillaries - produces aqueous humor - zonule fibers extend from the - is responsible for accommodation reflex process to insert in the lens
Identify the ciliary body in Identify the ciliary processes
Slide 5i in Slide 5j
k. Zonule fibers
- thin CT fibers that run from
the ciliary processes to the
lens
lens - they are taught when the
ciliary muscle is relaxed and
loose when it is contracted
which affects lens shape
Identify the zonule fibers in Slide 5k
l. Non-pigmented retinal epithelium
- thin layer of retinal epithelium
- is therefore neural not vascular
layer
- stains pale (hence non-
pigmented)
- is responsible for secretion of
aqueous humor
Identify the NPRE in Slide 5l n. Ciliary muscle
- smooth muscle in the ciliary body running in a circular organization m. Pigmented retinal epithelium
- contraction is mediated by parasympathetics in CNIII - thin layer of retinal epithelium
- contraction decreases tension on zonule fibers and lens thickens and is - is therefore neural not vascular
more more convex during focusing on close objects layer
- relaxation puts tension on the zonule fibers and lens stretches and is less - contains melanin (hence
convex during focusing on distant objects. pigmented) - this process is called ACCOMMODATION. Identify the PRE in Identify the ciliary muscle in Slide 5n Slide 5m
Identify the neural layer of the eye and examine each layer of the retina.
Examine Slide 6 and identify the different layers of the retina
The retina is the innermost tunic of the eye and is composed of 10 layers. i. Layers of the retina
a. Retinal pigmented epithelium (RPE) - contains melanin granules (hence pigmented) Identify the RPE in - absorb light that has passed through all 9 previous layers Slide 6a - this prevents light reflecting in eye which would impair focus
b. Rod and Cone cell layer Identify rod/cone layer - contains the outer segments of the photoreceptor cells. in Slide 6b
c. Outer limiting membrane Identify the external - is not a membrane limiting membrane in - is the site of interaction between Muller cells (glial cells) and Slide 6c photoreceptor cells
d. Outer nuclear layer Find the outer nuclear - contains the cell bodies of photoreceptor cells. layer in Slide 6d
e. Outer plexiform layer Identify the outer - contains synapses between photoreceptor cells and dendrites of plexiform layer in bipolar neurons and horizontal cells Slide 6e
f. Inner nuclear layer Identify inner nuclear - contains the cell bodies of bipolar neurons, amacrine cells Muller layer in Slide 6f cells and horizontal cells.
g. Inner plexiform layer Identify inner - contains processes of amacrine cells, bipolar cells, ganglion cells. plexiform layer in Slide 6g h. Ganglion cell layer - contains cell bodies of ganglion cells Identify ganglion cell - these cells generate the action potential that travels along their layer in axons which run in the optic nerve. Slide 6h
i. Nerve fiber layer Identify nerve fiber - the unmyelinated axons of ganglion cells layer in Slide 6i
j. Inner limiting membrane Identify inner limiting - the basal laminae and feet of the Muller cells membrane in Slide 6j Identify the inner limiting
membrane in Slide 6j
Identify the nerve fiber layer
in Slide 6i
Identify the ganglion cell layer ganglion cell
in Slide 6h - fibers in optic nerve
amacrine cell Identify the inner plexiform - provides feedback layer in Slide 6g from ganglion cells to bipolar cells
horizontal cell Identify the inner nuclear - modulates signal layer in Slide 6f from rods/cones
Identify the outer plexiform bipolar cell
layer in Slide 6e - summates signal from multiple rods/cones
Identify the outer nuclear layer in Slide 6d
Identify the external limiting membrane in Slide 6c
Muller cell - supportive glial cell Identify the rod/cone cell layer in Slide 6b rods/cones - photoreceptor cells
Identify the retinal pigmented epithelium layer in Slide 6a Slide 5l
In addition to all the basic tissues in slides and all previously covered items from MOHD1 that are relevant to interpreting tissue structure you must be able to identify the following structures and their features:
Eyelid Vascular layer (uvea) Skin (outer eyelid) Choroid Palpebral conjunctiva Choriocapillary layer Tarsal plate Brusch’s membrane Meibomian gland Iris Accessory lacrimal glands Stroma of iris Glands of Moll Sphincter pupillae m. Dilator pupillae m. Retinal pigmented General features of eye epithelium Lens Ciliary body Pupil Ciliary processes Anterior chamber Zonule fibers Posterior chamber Ciliary muscle Vitreous body Retinal pigmented Optic nerve and Optic disc epithelium Macula (fovea centralis) Retinal non-pigmented epithelium Fibrous layer Neural layer (retina) Cornea Visual retina Tear layer Non-visual retina Corneal epithelium Retinal pigmented epithelium Bowman’s membrane Rod and cone cell layer Corneal stroma Outer limiting membrane Dua’s membrane Outer nuclear membrane Descemet’s membrane Outer plexiform layer Endothelium Inner nuclear layer Sclera Inner plexiform layer Lamina cribrosa Ganglion cells layer Limbus Nerve fiber layer Trabecular meshwork Inner limiting membrane Canal of Schlemm