contact lenses Flashcards
Scleral lenses size (diameter) Material comfort vision Rx availability
12 -25mm
PMMA - no reactions can be made RGP material
doesnt touch Cornea - good comfort
good optic Zone held in place by eyelids brilliant vision tear inbetween acts as a lens = correct Astigmatism
RX = Almost anything
Scleral lenses
advantages
Stable VA Easy to handle + maintain unlikely to be dislodged or lost large optic zone - reduces flare Therapeutic uses,cosmetic options fB - unlikely few allergies does not absorb Solution can be modified
Scleral lenses
disadvantages
low oxygen supply as covers entire Cornea Ocular Problems related to corneal hypoxia insertion + removal issues long adaptation long chair time use of fitting sets moulding can be uncomfortable higher cost
Hard rigid contact lenses ( Corneal lenses ) Size materials comfort vision Rx availability
8.10.5 mm Total Diameter 2mm Smaller then HvlD
RGP Sometimes PMMA
feel Something there -wear 30 mins 1st day build up wear as much as can
good VA - tear lens Corrects astigmatism multifocal/ bifocal
Rx = most limited prism 2 Prism down max
Hard / Rigid contact lenses
advantages
good oxygen Supply due to tear exchange tear pump
few deposits
easy to maintain
Robust- long life
Easy I/ & R
many designs and modifications possible
Solution toxicity does not absorb unlikely allergy
Hard/rigid contact lenses
Disadvantages
can be displaced/ lost Slow adaptation long chair time FB a risk flare due to Smaller Optic Zone 3+ 9 O clock Staining lens adherence cleaning regime - more complicated initial cost high
.Soft contact lenses size materials comfort vision Rx availability
12-15mm 2mm bigger than HVID
Silicone Hydrogel /hydrogel
Good initally may decrease throughout the day
Ok, variable- due to movement avoid low Rx high cyl- more awkward
RX -more limited XR toric
soft contact lenses
advantages
Convenient Sporadic wear and disposable options less chair time fast adaptation few FB flare unlikely rarely lost intitally cheaper
Soft lenses
Disadvantages
less oxygen exchange - no tear pump long term ocular problems- get over worn Dehydration Require up keep due to deposits Handling may be difficult Solution allergies Difficult to verify
Rigid Cl material
PMMA (PolynethyImethacrylate)
Advantages - Good wetting,no deposits,mechanically strong optically good
Disadvantages -low Oxygen Supply
Rigid CL material
silicone Acrylates- copolymer containing varying proportions of PMMA + silicone
Advantages- Availability,Good oxygen Supply,Dimensional stability,Good stable vision
Disadvantages -Attracts deposits,3 + 9 o’clock Staining, Poor wetting,Prone to breaks
Rigid C L Materials
floursilicon Acrylates .
Addition of fluarine to Improve wettability,tear film stability desposit resistance
advantages Excellent oxygen supply,Possible in extended wear,Good wettability,deposit resistant
Disadvantages - very prone to breakage,Corneal adhesion careful manufacture required
materials soft
Ionic and non - Ionic ( how easily the lens attracts an electrochemical charge and therefore how it attracts or repels deposits)
I group 1 - low water ( < 50% H20 ) Nanionic Polymers ‘ good for dry eye
II group 2 - High water ( > 50% H20) Nonionic Polymers bad for dry eye
Ill group 3 - low water ( < 50% H2O) Ionic Polymers
lV group 4 - High water ( > 50% H20) Ionic Polymers
V group 5 High 02 - Silicone Hydrogels
Materials Soft
Biomimetic
Mimic human tissue In the form of a contact lens
better interaction with ocular tissues + fewer deposits
( BIOfinity Acuvue oasys, Pro clear
Soft materials
Silicone Hydrogel
increases permeability - IncreasesOxygen supply to the eye
classified as extended wear
clarity 1 Day Air optix Night+ day
Types of Solution Daily Bi -weekly / Monthly non Disposable soft RGP (Corneal and Scleral)
Daily -none
monthly - Peroxide,multipurpose,Saline
non- Dispossible Soft - Peroxide,multipurpose,saline,Daily cleaner,Protien removal
RGP - wetting + Soaking,multipurpose,conditioning,daily cleaner,Protien removal
-
Reason for non compliance
cost convenience apathy - not Caring Ignorance Denial lack of Proper instruction Bad advice
a contact lens Solution must
Disinfect
Decontaminate
Enhance
Disinfect
destroy or inhibit growth of microbes to Prevent Contamination of the lenses or lens case
Decontaminate
to remove Deposits and build up from the lens surface
deposits affect the comfort and visual quality of the lens
they can be organic ( lipids,tear Components ) or Inorganic ( metal lons dust
Enhance
ensure that he lens remains in good condition and maintain optimum Vision for the Patient
Bacteria
conjunctivitis Keratitis Blepharitis Trichiasis Can cause staphylococcus aureus (+ ) stapococcurs Pneumonia ( + ) Pseudomonas aureginosa ( - )
Virus
conjunctivitis
Keratitis
may cause
Haemophilus influenzae
Herpes Simplex
Adenovirus
Fungus
Keraitis Endophthalmicths Can cause canidids albicans fusarium Aspergillus
Protozoa
Keratitis
can cause
Acanthamoeba
Preservatives
keeps Solution sterile Prevents microbial growth Bacteriostati ( Prevent growth) Bactericidal destroy microbe But can cause allergic reaction eg Polyhexanide Chlorhexidine Benzalkonium chloride Polyquads Aldox
chelating Agents
Enhance the action of Preservatives
Bind metal Ions required for bacterial growth
lon + EDTA = chelate
eg
Ethylenediamine tetracetic acid ( EDTA)
Buffers
maintain PH of the Solution at 6 -7 tears have ph of 7.1 - 7.4 eg Sodium phosphate sodium borate Sodium perborate
Tonicity Agents
maintain osmotic potential of the tears ( 0.9 % ) imbalance can cause discomfort eg sodium chloride Potassium Chloride
