Contact Lenses

Question 0

What are the benefits of a tricurve?

Answer 0

Final peripheral curve much flatter than the first peripheral radius, improves comfort and tear exchange -> better oxygen transmission

Question 1

What materials are rigid lenses available in?

Answer 1

PMMA
Fluorosiluconeacrylate
Silicone acrylate

Question 2

What are the specs of a quantum lens?

Answer 2

Polynomial aspheric (fit 0.05 to 0.10mm flatter than flattest K), lathed back.
Made of fluorosiliconeacrylate
dK 97

Question 3

What are your two goals when fitting an RGP

Answer 3

1) distribution of lens mass over widest possible surface area
2) adequate peripheral clearance

Question 4

How do you choose TD for an RGP?

Answer 4

Smaller than HVID by 2mm

Ideally lid attached from upper lid

Question 5

How do you select BOZD?

Answer 5

Usually no choice except in tribute/multicurve

1mm larger than pupil in average illumination

Question 6

What is the relationship between BOZD and BOZR?

Answer 6

Steeper lens has a smaller BOZD

Question 7

If you change BOZD what do you do to BOZR?

Answer 7

Every 0.5mm in BOZD you flatten BOZR by 0.05mm

Question 8

What are the 4 types of corneal astigmatism?

Answer 8

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

Question 9

What are the two types of toric stabilisation?

Answer 9

Prism ballast and dynamic stabilisation

Question 10

What do you need to consider for an aphakic CL wearer? X4

Answer 10

1) variable refraction
2) high + rx more likely to decentre
3) need for over specs
4) binocular vision/ aniseikonia

Question 11

What might be physiological problems when fitting aphakes with CLs?

Answer 11

Corneal topography, pupil shape size and position

Eyelid tonus and resting position

Question 12

What are common aphake complications in RGP wear?

Answer 12

3&9 staining, deposits, edge chips and lens fracture, decentration, displacement, lens loss

Question 13

What are common complications of soft lenses?

Answer 13

Deposits, dehydration, inflammation, infections, hypoxia

Question 14

When can you fit a corneal transplant eye?

Answer 14

Only when epithelium intact. DALK 6 months, PK 12 months

Question 15

What does a post corneal graft lens need?

Answer 15

High DK, avoid bearing on surface, corneal topography and astigmatism

Question 16

What are piggyback lenses?

Answer 16

RGP centre with soft skirt- need to ensure smooth junction between two. RGP centre needs to be larger than donor graft

Question 17

How do cornea-scleral lenses help?

Answer 17

Donor cornea steeper than host cornea, good for steep or tilted grafts

Question 18

What are the principals of three point touch?

Answer 18

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