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.