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
- oily layer
- outtermost layer (first layer)
- made by meibomian glands
- stops evaporation of aqeuous humour
- increases surface tension/vertical stability
-lubricates the eyelids
Lipid Layer
- made by main lacrimal gland & accessory lacrimal glands
-thickest layer
-keeps eyes wet
-supplies atmospheric oxygen to corneal epithelium
-antibacterial substances (lactoferrin/lysozyme)
-provides smooth optical surface by abolishing little irregularities on cornea - washes away debris from cornea/conjunctiva
- deficiency = keratoconjuctivitis sicca (KCS)
Aqueous Layer
- glycoproteins
- innermost layer
- produced by goblet cells (conjunctiva)
- wetting layer
-smooth surface for light reflection
-convert corneal epithelium from hydrophobic> hydrophilic surface
-makes tears stick to eyes - without it aqueous solution cannot convert> will not be moistened by aqueous tears
Mucin Layer
- hosts enviroment for CL
-optically smooth/clean anterior cornea
-rinsing system/remove debris
-create reservoir/passageway for gasses (oxygen/carbon dioxide)
-wetting
-maintain soft lens hydration - create surface tension & capillarity to hold CL in place
Pre-Corneal fluid & CL
1) starting in the lacrimal glands= tears
2) tears @ superior cul-de-sac
3) upper & lower puncta
4) into tube-like canliculi
5) emptied into lacrimal sac
6) flow through nasolacrimal ducts
7) ending in the nose
Tear Flow
-10-15 times per minute
- provides first 3 layers of eyes with nutrition
- keeps cornea wet
- centering CL
- wiping action = spreads mucin layer> epithelial cells > tear film forms
- without wiping action = epithelium breakdown> transparency of cornea lost
- moves tears & debris > lid margin>puncta> nasal passage
- lower lid = horozontal/transverse/ nasal movement
Blinking
- tear pool collects at lower lid margin
-1/2 pre-corneal fluid volume collects here - each blink moves fluid around
Marginal Meniscus
-oxygen tranmissibility
Diffusivity/Solubility
- most common
- hydrophilic gels (hydrogels)
-plastic/silicon
-silicon increased oxygen
Soft CL
- generally soft lenses
- can be worn during sleep
- increased risk of threatening complications
- oxygen deprivation
- high risk of bacterial infections
- decreased cornea sensitivity= injury risk
Continuous Wear (extended wear/EW)
- previously used
- PMMA material didnt allow flow of oxygen
- risk of corneal edema
Hard (rigid) lenses
- allows oxygen passage 2 ways
1) permeability through CL
2) tear exchange - maintianes shape= good for torics
- good for dry eyes/allergies/ infections/ high Rx
- sharp vision
- less lens deposits
- less comfortable
- long adaptation
- flare at night
Gas Permeable Hard Lenses (GP/RGP)
-hybrid lens
- soft/hard within the lens material
- keratoconus= hard center/soft skirt
- hard GP base w/ soft lens coating
-soft lens underneath GP (piggyback)
Combination Lenses
- specifically designed GP lenses
- worn while sleeping
- re-shapes cornea
- mild/moderate Rx
- no correction needed during daytime
Accelerated Orthokeratology (AOK)
- CL for high powers
- post-cataract surgeries without IOL inserted (10+ D)
- silisoft = babies without IOL
Aphakic CL
- to cover & protect the cornea
- large lenses/ blankets
- retains moisture
- pain relief
Bandage CL
- for presbyopics
1) Annular (concentric)
2) Prism Ballast (translating)
3) Aspheric
4) Diffractive
5) Mono vision
Multifocal CL
- uses opposing rings
- center ring = distance
- outside rings = near
Annular (concentric) CL
- translating
- resembles bifocal
- top 1/2 = distance
- bottom 1/2 = near
Prism Ballast CL
- Rx grandually changes from top to bottom
- top = near
- bottom = distance
-PAL like
Aspheric CL
- circular grooves
- back surface of lens
Diffractive CL
- OD = distance
- OS= near
Monovision CL
- supported by sclera
- vaulted over cornea
- tear-filled pocket (artificial tears)
- bludge outwards
- for sensitive corneas
- irregular corneal shape
Scleral CL
-increase CL visibility (handeling = light blue)
- reduces photophobia
- enhance or change eye colour
- identify OD from OS
- helps px with colour vision defects
Tinted CL
- soft or GP
-corrects astigmatism (corneal/lenticular) - laser marks on soft lens (assesing rotation)
- can be weighted to keep place
Toric CL
- daily use
- preperation for disinfecting solutions
- removes oil/mucous/protiens/debris/makeup
- Has high Ph
-chelating agents (EDTA) remove metal ions - rub lens side-to-side
- rub lens in pie/triangular pattern
- 1-2 drops @ end of day
- ## rinsed in saline
Surfactant Cleaning Solution
- risning agent
- pH varies from brand to brand (may cause stinging)
- most use buffered products (borate/phosphate)= no stinging
- some brands may have preservatives
- no preservatives = not sterile after opening
- yellow = expired
Saline Solutions
-soaking solution
- lens storage
- destroys/limits bacteria growth
- prevents scratching from touching case
- hydrates lens
- prevents dried on tear protiens/mucus
Disinfecting Solutions
- simple care for soft/GP lenses
- first cleaned with surfactant
- use fresh solution
- inside case overnight
- minimal risk of allergy
- doesnt kill fungi/ acanthamoeba
Chemical disinfection
-quick disinfection time
- 2 step system
- not for longterm storage
- converts to saline (where bacteria can grow)
- most organisms killed in 20 mins
- but best soaked 6-8 hours
- must be neutralized before eye contact
- not nuetralizing = damage/pain for days
Hydrogen Peroxide disinfection
- rarely used today (outdated)
- case/lenses/saline heated high temp
- higher heat = less time required
- still most effective
Heat disinfection
- light kills bacteria
- lens inside chamber with special solution
- takes 15 mins
- soft lenses only
- rarely used today
UV disinfection
- used with Gas Permeable lenses
- placed on lens before contact with eyes
- transforms hydrophobic > hydrophillic
- mucoid layer take over after intitial process
- helps clean the lens
- mechanical buffer between lens/cornea/lids
- soft lenses can do this with saline
Wetting Soultions
- comfort drops
- used to rewet the eye after insertion
- not all soultions are compatible with lens types
Lubricating Solutions
- used weekly
-removes protien deposits - reduced risk of Giant Papillary Conjunctivitis
- 1 liquid type, but most are tablets
- usually used for GP lenses
Enzymatic Cleaners
- no substances leach from material used
- clean with cleaning solution (rubbing(
- rinse with saline or disinfectant
- air dry upside down
- can you toothbrush for deeper clean
- can boil the case once a week
- replace every time with new bottle solution
Lens Cases
- gritty/scratchy/sandy
- cornea can be compromised longterm
- blinking problems
- dirty lenses
- environment
- hormonal changes
- medications
-tear chemistry
Dryness complication
- calcium deposits (crystals)
- fungus (hairy/grey/brown/pink/orange)
-Jelly bumps (white) = px tear chemistry - protein deposits (white film)
- rust spots (brown/orange) metal flakes
Deposits/discolorations
- corneal epithelium rubbed off
- caused by ill-fitting lens
- overwearing
- injury by foreign body
- pain and photophobia
Abraisions
-Swelling of cornea
- greater than normal fluid absorption
-overwearing poor fit
- dirty lens
- foggy vision
- damage deeper layers
Edema
- redness
- discomfort
-discharge
-Acanthamoeba - Pseufomonas
Eye infections
- exposed to tap water
- swimming pools
- hot tubs
-distilled water
Acanthamoeba
- wetting lenes inside mouth
Pseudomonas
- not cleaning CL adequately w/ surfactant
- protein builds up
- px develops allergy to proteins
- eyelid = orange/bumpy
- muscous/itching/blurry vision
- topical steroids
- discontinue entirely/ period of time
Giant Papillary Conjunctivitis
- lack of oxygen on cornea
- new blood vessels grow from limbus
- caused by tight-fit
- overwearring
- dirty lenses
-interfere with vision
Neovascularization
- mild discomfort
- vision may be different from glasses
- one eye might have better vision
Expected Soft Lens ajdustmen
-pain
- extreme photophobia
- redness
- halos around lights
- change in vision
- cloudy vision
- flare
- vision blurred after 1 hour removal
Abnormal Soft Lens /GP reactions
- tearing
- awareness sensation
- sensitive to light/wind/smoke/dust
- slightly blurred vision (excess tears)
- slight redness
- mild itching
- mild fatigue
Expected GP adjustments
-manipulate lens with fingers through eyelid
- push lens on centre with fingers on lid margin
- move lens centrally> roated eye> fingers hold
-look in opposite direction> hold lens> pressure at canthus> rotate until slides under lens
Re-Center GP lens
