SCL for Astigmatism

Question 1

Types of lens design

Answer 1

1. toric back surface + spherical front surface
2. topic front surface + spherical back surface
3. wraps on cornea so reduce tear lens

Question 2

Method of stabilisation

Answer 2

1. prism ballast
2. peri ballast
3. topic SCL stabilisation : double slab off
4. accelerated stabilisation design

Question 3

1. Prism Ballast

Answer 3

• 1-1.5D base down
• reduced CL O2 transmissibility
• discomfort with lid interaction
• stabilised by prism - CL thickness difference

Question 4

2. Peri Ballast

Answer 4

• thickness differences as stabilising component - creates a base down component
• can cause discomfort with CL - lid interaction at thicker portion
• reduced CL O2 transmissibility in thicker regions
• thinner superiorly, thicker inferiorly

Question 5

3. Topic SCL stabilisation - double slab off

Answer 5

• thin zone inferiorly + superiorly
• overall thinner lens
• lid forces maintain orientation
• CL is symmetrical
• can exhibit reduced rotational stability of low sphere

Question 6

4. Accelerated stabilisation design

Answer 6

• thin zone inferiorly + superiorly
• 4 active zone of added thickness in mid-periphery of the lens
• designed to be actively rotated into place upon blinking

Question 7

When to use a soft topic lens

Answer 7

• refractive astigmatism
• spherical SCLs
• GPs leave residual astigmatism
• GPs cause discomfort

Question 8

Factors affecting SCL location

Answer 8

• lid tension/location/action/blink force
• water content
• lens thickness
• vertical palpebral aperture
• gravity
• tailor made vs soft topic
• total diameter

Question 9

Fitting procedure

Answer 9

• measure rx + vertical distance
• select topic CL design
• select CL power to match both meridians
• select BOZR +/ TD
• complete final Rx
• clockwise ADD
• anticlockwise subtract

Question 10

Limitations of soft topic lenses

Answer 10

• oblique cyls
• large cyls
• irregular astigmatism
• lens thickness