Module 8: Contact Lenses Flashcards
Surrounding eye structures
Adnexa
-transparent tissue
-forms anterior refracting surface
- no blood vessels
- light not absorbed or diffused
-with the crystalline lens creates optical power
- has 5 layers (thinner in the center)
Cornea
-outermost layer
-5 cell layers thick (10% of thickness)
- 2 surface layers = squamous cells
- middle layers = wing cells
- last layer =basal cells
- water/aqueous do not pass easily
- cells are lipid material
-small attachments= desmosomes> repel water
- adjacent cells interwoven
-heals quickly/ does not scar
- total rejuvination in 7 days
Epithelium Layer
- first two layers of epithelium
-large & thin cells - project microvilli
- continuosly dying/ sloughed into tear film
-not as metabolically active as deeper layers
Squamous Cells
- middle 2 layers of epithelium
-migrate up from deeper layers - metabolically active
Wing Cells
-deepest layer of epithelium
- made of columnar-shaped cells
-most active cells
-secrete thin membrane lies between bowmans layer
-holds tightly attached to Bowman’s layer
Basal Cells
- modification of stroma
- made of collagen fibres
- mucopolysaccharide ground substances
- does not heal when injured
- injuries affect visual aquity
Bowman’s Membrane
- 90% of corneal thickness
-200-250 cell layers (lamellae) - lamellae lay parallel to corneal surface
- has fibroblasts> produce collagen
- damaged= longterm swelling/infection> invading blood vessels
-blood vessels supply oxygen but obscure vision
Stroma
- 200-250 cell layers
- lay parallel to corneal surface
- made of collagen fibrils
- surrounded by viscous substance
Lamellae Cells
- produces collagen
- located inside the Stroma
Fibroblast Cells
- caused by injury/infection in Stroma
- blood vessels invade but supply nutrients/oxygen
- can obscure vision
Neovascularization
- Attached to Stroma & Endothelium
- very resistant to damage
- thickens with age
- elastic
Descement’s Membrane
- bottom layer
- 1 single layer w/ large cells
- bathed in aqeuous humour
-maintaines normal water content in stroma - very metabolically active
- light damage = sourronding cells spread out and cover area
- severe damage = corneal swelling & loss of corneal transparency
Endothelium Layer
- carries dissolved oxygen to epithelium
-oxygen diffuses through Stroma to endothelium - BUT aqueous humour primary supplier of oxygen
- CL sits on top of/ not touching cornea
- spreads with each blink
- 3 layers thick
Tear Film
- important in protecting the eye
- keeps out foreign bodies
- keeps eyes moist
- spreads tear film over cornea/conjuctiva
- outside = skin
-inside = conjunctiva - fibrous tarsal plates
- muscles & sebaceous glands
Eyelids
-inside layer of the eyelids
-thin/transparent tissue
- rich in blood vessels
Conjunctiva/ Eyelids
-almond-shaped opening between eyelids
Palpebral Fissure
- eyelids joined nasally
Medial Canthus
- eyelids joined temporally
Lateral Canthus
- Near inner canthus
-small hole - raised portion on lower lid
-beginning of drainage system
Lacrimal Punctum
- divided into anterior and posterior by grey line
- eyelashes (cilia) anterior to grey line
-meibomian gland ducts @ posterior grey line (mucocutaneous junction)
Lid Margin
- located posterior grey line
- mucocutaneous juncture
- tarsus = 30 modified sebaceous glands> secrete sebum oil
Meibomian Glands
- modified sebaceous glands
- assocaited with lash follicles
- works with meibomian glands
- prevents overflow of tears
Glands of Zeis
- pre-corneal fluid
-thin/liquid layer - essential in maintaining cornea optical quality
- health of cornea & conjuntiva
- bad flow= dry/rough/opaque
- 3 layers
Tear Film