Flashcards in 6.2 Histology of the eye Deck (59)
What are the 3 layers of the eye?
What is the conjunctiva
mucous membrane which covers the exposed part of the eye (sclera and inner surface of the eyelids)
What is the function of the conjunctiva
Mucinous secretions add to the protective layer covering the eye
Allow eyelids to move freely over the eye
What is the histology of the conjunctiva?
non keratinzing stratified squamous epithelium with goblet cells and scattered melanocytes
What is the common presentation of conjunctiva pathology?
Inflammation bilaterally with a red appearance and hyperaemic vesses
What divides the eye into chambers?
The lens and iris
What do teh anterior and posterior chamber contain?
How does the aqueous humour circulate?
Produced by the ciliary processes, secreted into the posterior chamber by the ciliary body, circulates through the pupil and drains into the canal of schlemm into the anterior chamber
What is the function of the cornea?
Allow entry of light and the principle mechanism for focusing images on the retina
What is the junction of the cornea and sclera?
What are the 5 layers of the cornea?
What kind of epithelium is the cornea?
Where does the cornea get its nutrients from?
The aqueous humour and environmental oxygen
What is ulcerative keratitis?
Inflammation of the cornea from a break in the epithelium
Does the cornea have blood vessels?
What is keratoconus and what causes it?
Bulging of the eyeball due to weak mesenchymal collagen
What is the role of the sclera?
Insertion of the extraocular eye muscles, protection and support
What is the histology of the sclera?
Dense fibrous avascular tissue which is continuous with the dura surrounding the optic nerve
What conditions have a thinning of the sclera?
connective tissue disorders such as marfans, Ehlers danlos and osteogenesis imperfecta
What will you see histologically in thinning of the sclera?
Underlying choroidal pigment shows through which will result in a blue colour (normal in newborns)
What is the role of the iris?
Regulates the amount of light coming in (aperture control), esures light enters through the pupil
What innervates the iris?
What is the iris made of and what are teh surfaces composed of?
Pigmented stromal cells
Anterior: irregular with fibroblasts and melanocytes
Posterior: Smooth pigmented epithelium
What determines eye colour
The amount of pigment in the stroma
What are the iris muscles?
Dilator pupillae and Constrictor pupillae
What orientation are the dilator and constrctor pupillae, what are the made of and what is their innervation?
Dilator: radially oriented made of myoepithelial cells extending from the ciliary body SYMPATHETIC
Constrictor: Circumferentially oriented, smooth muscle PARA
What is a coloboma?
defect in one of teh structures of the eye
What is CHARGE syndrome?
Atresia of the choanae,
Retarded growth and development
What is aniridia and what causes it?
Absence if the iris - congenital or due to penetrating eye injury
What is WAGR syndrome?
What is Mydriasis and what causes it?
Dilation of the pupil - darkness, autonomic neuropathy, trauma, drugs, raised ICP
What is the ciliary body?
A continuous thickened ring on the inner surface of the anterior sclera that is a continuation of the choroid
What is the function of the ciliary body?
Contains ciliary muscle
Permits fine focusing of images on the retina
Attaches lens via the zonules
Secrete aqueous humour
What is the ciliary muscle and what does it do?
smooth muscle which inserts onto the sclera and ciliary body
controls the shape of the lens
What is the role of the ciliary process?
Anchor the lens into place and form aqueous humour
What are the two layers of epithelium of the ciliary processes?
Outer: non pigmented, actively transports aqueous humour
Inner: continuous with retina pigmented epithelium
What are the zonules?
Fibrillin that attaches the lens to the ciliary process
What are the layers of the lens?
What is the function of the lens?
Permits focussing on near and far objects
Accommodation in conjunction with ciliary muscles
what happens when you focus on a near object?
Ciliary muscles contract causing forwards displacement of the choroid and ciliary body reliving tension on the zonules - lens will round up keeping object in focus
What is a cataract and what does it cause?
Opacity of the lens causing light to be scattered and only a small amount transmitted
What is glaucoma?
Raised intra-ocular pressure due to obstruction of the flow of aqueous humour
What causes open angle glaucoma?
Obstruction of the drainage structures in the angle of the anterior chamber
What causes closed angle glaucoma?
Narrow anterior chamber which leads to the peripheral part of the iris compressing the trabecular meshwork
What is the function of the choroid?
Supplies nutrients and oxygen to all layers of the eye and absorbs light to prevent light scattering within the eye
Where does the choroid lie?
Between the retina and the sclera
Where is the vitreous and what is its function
Transmits light, supports the lens, holds the retina in place, contributes to intraocular pressure
What is the function of the retina?
conversion of photons into action potential
What are the 3 types of cells in the retina?
Neurons (ganglion, bipolar, horizontal, amacrine, photoreceptors)
Pigmented epithelial cells
Neuronal support cells (Muller cells)
How many and what are the layers of the retina?
Internal limiting membrane
Inner nuclear (Muller cells)
External limiting membrane
Retinal pigmented epithelium
Where are rods concentrated
outer edge of the retina
What is the inner and outer segments of rods made of?
Inner: golgi and mitochondria
Outer: flattened membranous discs with rhodopsin
What happens with rod loss?
Night blindness and loss of peripheral vision
What are cones sensitive to?
blue red and green light
What kind of epithelium is the retinal pigmented?
Columnar with basal nucleus
What is the function of retinal pigmented epithelium?
Synthesis of melanin that absorbs stray light
Phagocytose shed rod discs
Support for photoreceptors
What fibres form the optic disc?
non myelinated afferent fibres converge medial to the fovea
How does the optic nerve form?
Non myelinated afferent fibres converge at the optic disc, penetrate the sclera through the lamina cribrosa to become the optic nerve - become myleinated fibres from the optic disc