EYE HISTOLOGY I 2023_Starla Meighan.pptx

EYE HISTOLOGY I Michael Steadman with help from Dr. Starla Meighan, Ph.D. [email protected] 👀 Chapter 23 Chapter 8 Chapter 24 LEARNING OBJECTIVES  Label basic anatomy of the eye.  Understand the cellular and tissue level organization of 2 of the 3 tunics (fibrous, vascular, nervous) of t...

EYE HISTOLOGY I Michael Steadman with help from Dr. Starla Meighan, Ph.D. [email protected] 👀 Chapter 23 Chapter 8 Chapter 24 LEARNING OBJECTIVES  Label basic anatomy of the eye.  Understand the cellular and tissue level organization of 2 of the 3 tunics (fibrous, vascular, nervous) of the eye, and be able to recognize and label various aspects of the tunics histologically.  Understand lens cellular morphology and functional anatomical characteristics.  Understand specific functional aspects of the eye:  Adaptation  Accommodation  Production and flow of aqueous humor  Integrate eye anatomy/histology knowledge with medical application scenarios. LEARNING OBJECTIVES  Label basic anatomy of the eye.  Understand the cellular and tissue level organization of 2 of the 3 tunics (fibrous, vascular, nervous) of the eye, and be able to recognize and label various aspects of the tunics histologically.  Understand lens cellular morphology and functional anatomical characteristics.  Understand specific functional aspects of the eye:  Adaptation  Accommodation  Production and flow of aqueous humor  Integrate eye anatomy/histology knowledge with medical application scenarios. BASIC EYE ANATOMY LENS IRIS CORNEA SUSPENSORY LIGAMENTS (zonule fibers or Zonule of Zinn!) CILIARY BODY IRIS SCLERA PUPIL CHOROID RETINA HYALOID CANAL OPTIC DISC CENTRAL ARTERY OF THE RETINA OPTIC NERVE BASIC EYE ANATOMY Other Important Terminology BULBAR Areas of FORNIX CONJUNCTIVA Thin mucous membrane PALPEBRAL CORNEA BASIC EYE ANATOMY Humor-filled spaces ANTERIOR SEGMENT filled with aqueous humor NUTRIENTS TO ANTERIOR CHAMBER POSTERIOR CHAMBER AVASCULAR LENS AND CORNEA POSTERIOR SEGMENT filled with vitreous humor PROTECTS RETINA, HOLDS LENS AND RETINA IN PLACE, MAINTAINS SHAPE OF EYE VITREOUS CHAMBER LEARNING OBJECTIVES  Label basic anatomy of the eye.  Understand the cellular and tissue level organization of 2 of the 3 tunics (fibrous, vascular, nervous) of the eye, and be able to recognize and label various aspects of the tunics histologically.  Understand lens cellular morphology and functional anatomical characteristics.  Understand specific functional aspects of the eye:  Adaptation  Accommodation  Production and flow of aqueous humor  Integrate eye anatomy/histology knowledge with medical application scenarios. SUMMARY of TUNICS OF THE EYE FIBROUS TUNIC VASCULAR TUNIC NERVOUS TUNIC FIBROUS TUNIC OVERVIEW 1 SCLERA  The “white” of the eye  The sclera should be white (other colors are possible…)  A thin sclera appears blue (newborns)  Can be yellow in liver failure  Pierced by blood vessels and nerves  Extends onto the optic nerve  Dense fibrous connective tissue w/microvasculature  Attachment for extrinsic eye muscles 1 1 SCLERA HISTOLOGY SC EPISCLERA   External layer of loose connective tissue Adjacent to periorbital fat C SUBSTANTIA PROPRIA (SCLERA PROPER)      Investing fascia of the eye Dense network of thick collagen fibers Some elastic fibers and ground substance Scattered fibroblasts Tendons of extraocular muscles attach here SUPRACHOROID LAMINA   Superficial to the choroid Thinner collagen plus elastic fibers, fibroblasts, melanocytes, macrophages R ET IN A H O R of O ID of ne rv ou s LE va sc ul ar tu ni c R A of fi br ou s tu EP IS CL ER A L ni SU c B ST A N tu n ic SU P R A CH O R O ID LA M TI A IN A P R O PR IA SP A EP IS CL ER CE A FIBROUS TUNIC OVERVIEW 1 SCLERA  The “white” of the eye  The sclera should be white (other colors are possible…)  A thin sclera appears blue (newborns)  Can be yellow in liver failure  Pierced by blood vessels and nerves  Extends onto the optic nerve  Dense fibrous connective tissue w/microvasculature  Attachment for extrinsic eye muscles CORNEA 2 Transparent “window” of the eye  Primary refractive surface of the eye  No blood or lymph vessels  5 layers 1 2 2 CORNEA HISTOLOGY CORNEAL EPITHELIUM (superficial)  TYPE: Nonkeratinized stratified squamous epith  At the base, low columnar with round nuclei  Becomes squamous (w/flat nuclei) at the surface  Turnover time 7 days  Microvilli on surface cells help retain tear film  Numerous free nerve endings make it highly sensitive 3 Layers with 2 Membranes OUTER BOWMAN’S MEMBRANE  Basal lamina of randomly oriented collagen  Provides Strength and barrier to infection  Ends abruptly at the sclera x280 x140 INNER CORNEAL STROMA  90% of corneal thickness  Parallel bundles of collagen fibrils (highly ordered)  Sheets of flattened fibroblasts  Special arrangement of components gives transparency (next slide) DESCEMET’S MEMBRANE  “Unusually thick basal lamina” of collagen  Extends beneath sclera to form pectinate ligament and help maintain curvature of CORNEAL ENDOTHELIUM (deep)  cornea Single layer of squamous cells  Metabolic exchange between cornea and aqueous humor occurs here  Corneal edema occurs if this is CORNEAL STROMA ARRANGEMENT and corneal transparency STROMA x2 80 LA ME A LL 60 thin lamellae (layers) of parallel collagen fibril bundles alternating with fibroblasts (keratocytes) Collagen bundles in adjacent lamellae are at right angles to each other – imparts TRANSPARENCY Flattened corneal fibroblast (keratocyte) in between lamellae LA ME A LL LA ME A LL x16,7 00 CORNEA MEDICAL APPLICATION LASIK Surgery for Vision Correction FIBROUS TUNIC OVERVIEW 1 3 SCLERA  The “white” of the eye  The sclera should be white (other colors are possible…)  A thin sclera appears blue (newborns)  Can be yellow in liver failure  Pierced by blood vessels and nerves  Extends onto the optic nerve  Dense fibrous connective tissue w/microvasculature  Attachment for extrinsic eye muscles CORNEA 2 Transparent “window” of the eye  Primary refractive surface of the eye  No blood or lymph vessels  5 layers CORNEOSCLERAL LIMBUS (JUNCTION) 3  Transition zone between cornea and sclera  Corneal stem cells are found here 1 2 3 LIMBUS HISTOLOGY SCLERA CORNEA OUTER SURFACE OF EYE CEp Bulbar CONJUNCTIVA (Cj) CONJUNCTIVAL EPITHELIUM (CjEp)  Irregular in thickness compared to corneal epithelium (CEp) LOOSE VASCULAR CONNECTIVE TISSUE replaces Bowman’s membrane  Unlike the orderly Bowman’s membrane of cornea STROMA (S)     Flat collagen bundles irregularly arranged Interspersed with fine networks of elastic fibers and ground substance Scattered fibroblasts Highly vascularized (BV = blood vessels) TRABECULAR MESHWORK (MW)  Decemet’s membrane and endothelium disappear  These are replaced by the trabecular meshwork – reabsorbs aqueous humor from the anterior chamber of the eye into the Canal of Schlemm (CS) ansition zone of LIMBUS (approximately at arrow) Corneolimbal stem cells – maintain corneal epithelium  Here, they proliferate, differentiate, and migrate to cornea Cells here prevent conjunctival epithelium from migrating to cornea If injured, conjunctivalization of the cornea can occur  Vascularization  Irregular, unstable corneal epithelium  Ocular discomfort and reduced vision MW x130 ANTERIOR CHAMBER OF EYE REVIEW Comparison of regions of fibrous tunic SCLERA exterior interior LIMBUS CORNEA VASCULAR TUNIC OVERVIEW 1 CHOROID of uvea  Dark brown (melanin) vascular sheet between sclera and retina  Vascular = nutrients to retina Vascular tunic = Uvea 1 1 CHOROID HISTOLOGY  Highly vascularized and pigmented (melanin)  Melanocytes produce pigment that absorbs scattered and reflected light to reduce “glare”  Choriocapillaris is bed of highly fenestrated capillaries providing nutrients to retina  Bruch’s membrane (elastin and collagen hyaline membrane between the choriocapillaris and RPE of the retina) acts as a molecular sieve for molecules between blood and retina The choroid is engorged with blood in life (it has the highest perfusion rate per gram of tissue of all vascular beds of the body)! SCLERA RETINA CHOROID VASCULAR TUNIC OVERVIEW 1 CHOROID of uvea  Dark brown (melanin) vascular sheet between sclera and retina  Vascular = nutrients to retina CILIARY BODY of uvea 2  Thickened anterior aspect of vascular tunic Vascular tunic = uvea 2 1 2 CILIARY BODY HISTOLOGY  CILIARY MUSCLE: mostly smooth muscle  CILIARY PROCESS: Inner, vascular region (continuous with vascular choroid) LIMBUS CILIARY MUSCLE  ATPases drive the production of aqueous humor  Lined on the inner surface by DOUBLE LAYER ciliary epithelium  Layer next to stroma = highly pigmented continuation of pigment epithelium of the retina  Surface layer = contiguous with the sensory layer of the retina (non-pigmented) FUNCTIONS of the CILIARY BODY  ZONULAR FIBERS: Suspensory  Changes in the contractile state of ciliary muscle ligaments of the lens determines the flatness of the lens (see Accommodation slides)  Production of aqueous humor by ciliary process (see Aqueous Humor slides) ANTERIOR CHAMBER IRIS POSTERIOR CHAMBER CILIARY PROCESS VASCULAR TUNIC OVERVIEW3 1 CHOROID of uvea  Dark brown (melanin) vascular sheet between sclera and retina  Vascular = nutrients to retina CILIARY BODY of uvea 2  Thickened anterior aspect of vascular tunic of uvea 3IRIS  Thin anterior aspect of vascular tunic  Contractile diaphragm in front of lens  Arises from anterior border of ciliary body  Attached to sclera Vascular tunic = uvea 2 1 3   IRIS HISTOLOGY Posterior Side of the Iris  Melanin-containing cells (posterior pigment epithelium (PE)) – a continuation of the retinal pigment epithelium (see retina section)  Just anterior to PE is the anterior pigment myoepithelium with anterior contractile elements that constitute the dilator pupillae muscle (DPM, responsible for PUPIL DILATION)  Around the pupillary margin are smooth muscle cells of the sphincter pupillae muscle (SPM, responsible for PUPIL CONSTRICTION) Anterior Side of the Iris  Mostly stroma (S) of highly vascularized connective tissue w/ FUNCTIONS scattered melanocytes.  Pigmentation limits light that  The surface next to the AC and transmits through tissue aqueous humor is airis dense layer of  Musculature increases or fibroblasts and melanocytes (not decreases the size of the pupil to epithelium!) change light entry ANTERIOR IRIS LENS POSTERIOR 3 A Note about Eye Color… LEARNING OBJECTIVES  Label basic anatomy of the eye.  Understand the cellular and tissue level organization of 2 of the 3 tunics (fibrous, vascular, nervous) of the eye, and be able to recognize and label various aspects of the tunics histologically.  Understand lens cellular morphology and functional anatomical characteristics.  Understand specific functional aspects of the eye:  Adaptation  Accommodation  Production and flow of aqueous humor  Integrate eye anatomy/histology knowledge with medical application scenarios. LENS Just hangin’ out 3 PRINCIPAL COMPONENTS OF THE LENS LENS CAPSULE (LC)  Thick basal lamina surrounding lens  Type IV collagen and proteoglycans  Point of attachment for zonule fibers SUBCAPSULAR LENS EPITHELIUM (LE)  Single layer of cuboidal lens epithelial cells  Only on the anterior lens surface  At the equator in germinal zone, these multiply to form LENS FIBERS (DLF and new lens fibers (slows as MLF) age)  you Highly elongated, thin, flattened cells  Lack organelles  Filled with crystallin protein LC = LENS CAPSULE LE = LENS EPITHELIUM DLF = DIFFERENTIATING LENS FIBERS Cataracts… Intraocular Lens used in Cataract Surgery LEARNING OBJECTIVES  Label basic anatomy of the eye.  Understand the cellular and tissue level organization of 2 of the 3 tunics (fibrous, vascular, nervous) of the eye, and be able to recognize and label various aspects of the tunics histologically.  Understand lens cellular morphology and functional anatomical characteristics.  Understand specific functional aspects of the eye:  Adaptation  Accommodation  Production and flow of aqueous humor  Integrate eye anatomy/histology knowledge with medical application scenarios. THE FUNCTION OF THE EYEBALL Light Management ADAPTATI ON Changing the size of the pupil with changes in light intensity Determines how much light gets in Cornea OF IRIS ACCOMMODAT ION OF IRIS OF CILIARY BODY Changing the thickness of the lens when viewing something near vs distant Standardizes angle of light rays ADAPTATION to variations in light intensity PUPIL SIZE CHANGES Abnormal sustained pupillary dilation (mydriasis) may occur in certain diseases or as a result of trauma or the use of certain drugs. CAN TAKE UP TO 20 MIN Pupil dilating = MYDRIASIS Pupil shrinking = MIOSIS Note: We will see the sympathetic and parasympathetic nerve pathways to these muscles in the adnexa lecture next week. INSTANTANEOUS ACCOMMODATION for focusing light from near and far LENS THICKNESS CHANGES STANDARDIZING THE ANGLE OF LIGHT Due to the set length from the cornea to the retina, light must be at a specific angle after refraction to focus precisely on the retina. Ciliary muscle tight and lens pulled flat Because light rays coming from a point at a distance “achieve parallel” before interacting with cornea, the refractive power of the cornea alone will be enough to focus them onto the retina. Ciliary muscle relaxed and lens fattens Because light rays coming from a near point (closer than 6 meters) do not achieve parallel before interacting with cornea, the refractive power of the cornea alone it NOT enough to focus them on retina, so lens fattens up to give a little extra refraction. A     DETAILED VIEW OF CILIARY MUSCLE AND ZONULE FIBERS – VIEWING OBJECTS AT DISTANCE Ciliary muscle relaxed Pulls zonules with it holding them taut Pulls on lens and flattens Very little refraction by lens for distance viewing A B – VIEWING OBJECTS AT NEAR Ciliary muscle contracted (PARASYMPATHETIC) Zonules become relaxed Allows lens to fatten/thicken Increased refractive power by lens for close viewing Presbyopia As we age, the lens slowly loses elasticity, and accommodation for near vision decreases B Myopic (aka near-sighted) = good near vision Vs Hyperopic (aka far-sighted) = good AQUEOUS HUMOR WHAT IS IT? • Derived from blood plasma, but with less protein WHAT DOES IT DO? • Provides nutrients/Removes metabolites from the lens and cornea • Maintains the intraocular pressure WHERE DOES IT COME FROM? • Posterior chamber by epithelial cells of the ciliary WHERE DOES IT GO? processes • Ciliary process ➡️posterior chamber ➡️anterior chamber ➡️iridocorneal angle ➡️ trabecular meshwork (aka Spaces of Fontana) ➡️scleral venous sinus (aka Canal of Schlemm) • Turns over every 1.5 – 2 hours • Angle-closure glaucoma CORNEA LIMBUS Canal of Schlemm (scleral venous sinus leads to “aqueous veins” Spaces of Fontana (trabecular mesh in stroma at limbus) AQUEOUS HUMOR Iridocorneal angle SC LE IRIS INN OF Z E L U ZON LENS CILIARY PROCESS VITREOUS CHAMBER Intra-ocular pressure (IOP) is a balance between production and outflow of aqueous humor. RA NEXT HOUR – PICKS UP WITH 3RD TUNIC FIBROUS TUNIC VASCULAR TUNIC NERVOUS TUNIC QUESTIONS? Michael Steadman with help from Dr. Starla Meighan, Ph.D. [email protected] 👀