Contact Lenses Flashcards
What are the benefits of a tricurve?
Final peripheral curve much flatter than the first peripheral radius, improves comfort and tear exchange -> better oxygen transmission
What materials are rigid lenses available in?
PMMA
Fluorosiluconeacrylate
Silicone acrylate
What are the specs of a quantum lens?
Polynomial aspheric (fit 0.05 to 0.10mm flatter than flattest K), lathed back.
Made of fluorosiliconeacrylate
dK 97
What are your two goals when fitting an RGP
1) distribution of lens mass over widest possible surface area
2) adequate peripheral clearance
How do you choose TD for an RGP?
Smaller than HVID by 2mm
Ideally lid attached from upper lid
How do you select BOZD?
Usually no choice except in tribute/multicurve
1mm larger than pupil in average illumination
What is the relationship between BOZD and BOZR?
Steeper lens has a smaller BOZD
If you change BOZD what do you do to BOZR?
Every 0.5mm in BOZD you flatten BOZR by 0.05mm
What are the 4 types of corneal astigmatism?
Irregular - not at 90 degrees to each other
With-the-rule steeper vertically
Against the rule - steeper horizontally
Oblique - more than 30 degrees from h or c
What are the two types of toric stabilisation?
Prism ballast and dynamic stabilisation
What do you need to consider for an aphakic CL wearer? X4
1) variable refraction
2) high + rx more likely to decentre
3) need for over specs
4) binocular vision/ aniseikonia
What might be physiological problems when fitting aphakes with CLs?
Corneal topography, pupil shape size and position
Eyelid tonus and resting position
What are common aphake complications in RGP wear?
3&9 staining, deposits, edge chips and lens fracture, decentration, displacement, lens loss
What are common complications of soft lenses?
Deposits, dehydration, inflammation, infections, hypoxia
When can you fit a corneal transplant eye?
Only when epithelium intact. DALK 6 months, PK 12 months
What does a post corneal graft lens need?
High DK, avoid bearing on surface, corneal topography and astigmatism
What are piggyback lenses?
RGP centre with soft skirt- need to ensure smooth junction between two. RGP centre needs to be larger than donor graft
How do cornea-scleral lenses help?
Donor cornea steeper than host cornea, good for steep or tilted grafts
What are the principals of three point touch?
Aims to distribute weight across come and peripheral cornea Divided support 2-3mm apical touch Mid peripheral ring of touch Usual edge clearance Most common accepted fitting philosophy
