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Block 4
The Eye
| Question | Answer |
|---|---|
| What are the three structural layers of the eye? | Corneoscleral coat, vascular coat and retina |
| Corneoscleral coat consist of what? | Sclera and cornea |
| The vascular coat consist of what? | The uvea (choroid and the stroma of the ciliary body and iris) |
| The retina consist of what? | Outer pigment epithelium, inner neural layer and the epithelium of the ciliary body and the iris |
| The anterior chamber is the space between what? | Cornea and the iris |
| The posterior chamber is the space between what? | Posterior surface of the iris and the anterior surface of the lens. |
| The vitreous chamber is the space between what? | The posterior surface of the lens and the neural retina. |
| As the neural tube closes the optic grooves form outpocketings called what? | Optic vesicles |
| As the optic vesicle grows laterally the forebrain becomes constricted forming what? | Optic stalk |
| The overlying ectoderm of the optic vesicle forms what? | Lens placode |
| The lens placode and the optic vesicle invaginates forming what? | Double layered optic cup |
| The inner layer of the optic cup becomes what? | Neural retina |
| The outer layer of the optic cup becomes what? | Retinal pigment epithelium |
| Grooves containing blood vessels develop along the inferior surface. They are called what? | Choroid fissures (enable the hyaloid vessels to reach the inner chamber of the eye) |
| The distal portions of the hyloid vessels degenerate but the proximal portions remain as what? | Central artery and vein of the retina |
| During the third month of gestation, the groth of the optic cup gives rise to what? | The ciliary body and iris |
| The key regulator gene for the eye is what? | PAX6 |
| PAX6 initiates the formation of what? | A ridge of neural plate that forms a single eye field. |
| The signal for separation of the eye field is what? | Sonic hedgehog (SHH) |
| What structures of the eye are derived from ectoderm? | Lens, epithelium of the cornea, conjuctiva, lacrimal gland and its drainage system |
| What stuctures of the eye are derived from neural ectoderm? | Vitreous body, epithelium of the retina, iris, ciliary body, sphincter pupillae, dilator pupillae and the optic nerve |
| A cleft in the iris that may be associated with other congenital defects is called what? | Coloboma |
| When the lens becomes clouded during intrauterine life it is termed what? | Congenital cataracts (may be cause by maternal rubella infection) |
| When the eye is to small it is termed what? | Microphthalmia (caused by infections such as cytomegalovirus and toxoplasmosis) |
| Absence of an eye an eye is termed what? | Anophthalmia (accompanied by severe cranial abnormalities) |
| Absence of the lens is termed what? | Congenital aphakia (caused by mutations in PAX6 gene) |
| Fusion of the eyes is called what? | Cyclopia or synophthalmia (associated with holoprosencephaly) |
| Ansence of the iris is called what? | Aniridia (caused by mutations in the PAX6 gene) |
| WAGR is an acronym for what 4 diseases? | Wilm's tumor (cancer of the kidney), aniridia, genitourinary abnormalities and mental retardation |
| What are the five layers of the cornea? | Corneal epithelium, Bowman's membrane, corneal stroma, Descemet's membrane and corneal endothelium. |
| The corneal epithelium has what diagnostic features? | Nonkeratinized stratified squamous epithelium and it is connected to Bowman's membrane by HEMIDESMOSOMES |
| Bowman's membrane ends abruptly where? | Corneoscleral limbus (acts as a barrier to the spread of infection) |
| Corneal stroma (substantia propria) has what diagnostic feature? | Has layers of parallel bundles of collagen fibrils (normally avascular) |
| Descemet's membrane has what diagnotic feature? | It is an unusually thick basement membrane |
| Corneal endothelium does what for the eye? | Provides metabolic exchange between the cornea and the aqueous humor |
| The corneoscleral limbus is a transition zone between what? | Cornea and sclera |
| The limbus region, the iridocorneal angle, contains what? | The apparatus for the outflow of aqueous humor |
| Endothelium lined channels what merge to form the scleral venous sinus (canal of Schlemm)? | Trabecular network |
| The canal of Schlemm encircles the eyes and performs what function? | Drains aqueous humor from the anterior chamber of the eye |
| The vascular coat of the eye is known as what? | Uvea |
| The most anterior part of the vascular coat is what? | Iris (forms diaphragm of the lens) |
| The central apeture of the eye is known as what? | Pupil |
| The ciliary processes are covered by a double layer of columnar epithelium called what? | Ciliary epithelium |
| What are the three functions of the ciliary epithelium? | SECRETION OF AQUEOUS HUMOR, participation in the blood-aqueous barrier, secretion and anchoring of the zonular fibers that form the suspensory ligaments of the lens |
| Nonpigmented cells have the characteristics of what? | Fluid transporting epithelium (well developed zonula occludens) |
| Cells of the nonpigmented layer has a less developed junctional zone because they are held together by what? | Desmosomes and gap junctions (creates discontinuous spaces called ciliary channels) |
| An obstruction in the drainage of aqueous humor which leads to an increased intraocular pressure is called what? | Glaucoma (can damage the retina and cause blindness if not treated) |
| What are the 2 types of glaucoma? | Open-angle and closed angle glaucoma |
| Open-angle glaucoma is caused by what? | When the trabecular meshwork drains aqueous humor but the canal of Schlemm is blocked (most common type) |
| Closed-angle glaucoma is caused by what? | Results when the aqueous humor is unable to reach the trabecular meashwork because of inflammatory process of the uvea. |
| Surgery that uses a laser to burn holes in the trabecular meshwork (used to treat glaucoma) is called what? | Trabeculoplasty |
| Glaucoma can be treated with eye drops that contain what? | Carbonic anhydrase inhibitor (blocks carbonic anhydrase isoenzyme CA-II which plays impotant role in production of aqueous humor) |
| Photorecepters of the retina are what? | Rods and cones |
| Conducting neurons of the retina are what? | Bipolar and ganglion cells |
| Supporting cells of the retina are what? | Muller cells, microglial cells and astrocytes |
| What are the 10 layers of the retina? | Retinal pigment epithelium, rods and cones, outer limiting membrane, outer nuclear layer, outer plexiform layer, inner nuclear layer, inner plexiform layer, ganglion cell layer, optic nerve fibers, inner limiting membrane |
| A single layer of cuboidal cells connected by junctional complexes which helps form the blood-retina barrier is called what? | The retinal pigment epithelium |
| The blood-retina barrier does what function? | Isolates retinal cells from blood-bourne substances (cells rest on Bruch's membrane of the choroid layer) |
| The retinal pigment performs what function? | Absorption of light passing through the retina to prevent reflection and glare |
| A small shallow depression at the posterior pole of the optical axis of the eye is called what? | Fovea (fovea centralis) composed entirely of cones |
| The area surrounding the fovea is called what? | Macula lutea (yellow due to the presence of xanthophyll) |
| The site where the optic nerve exits the retina is called what? | Optic disc or papilla (potoreceptors are absent, blind spot of the eye) |
| if the potential space between the optic cup expands what can occur? | The neural retina pulls away from the retinal pigment epithelium (retinal detachment) |
| The most common cause of blindness in older individuals is what? | Age related macular degeneration (ARMD) |
| What are the 2 forms of macular degeneration? | Dry (atrophic, nonexudative) and wet (exudative, neovascular) |
| Dry ARMD is caused by what? | Degenerative lesions of the macula lutea (causes blind spots in the visual field) |
| Wet ARMD is caused by what? | Complications of dry ARMD where new blood vessels form (neovascular) in the area of the thickened Bruch's membrane |
| What are 2 diagnostic features of the lens? | Avascular and biconvex |
| The lens capsule is composed primarily of what? | Type IV collagen and proteoglycans (elastic) |
| In the lens, cuboidal cells are connected to subscapular epithelium via what? | GAP JUNCTIONS |
| The lens capsule is what? | Thick basal lamina produced by the anterior lens cells |
| The subcapsular epithelium is what? | Cuboidal cells only present on the anterior surface of the lens |
| Lens fibers are derived from what? | Subcapsular epithelial cells |
| Lens fibers lose their nuclei and other organelles when they become filled with proteins called what? | Crystallins |
| A disease that causes opacity of the lens is called what? | Cataracts (cause by a change in the solubility of lens proteins) |
| In cataract patients, when glucose levels are high what byproduct is produced that leads to this condition? | Sorbitol (decreases the solubility of crystallins) |
| Hyalocytes of the vitreous humor is responsible for what? | Synthesis of collagen fibers and glycosaminoglycans |
Created by:
shuckybean