SCL For Astigmatism

Question 1

Types of Lens design

Answer 1

• toric back surface and spherical front surface
• toric front surface and spherical back surface
• wraps on cornea so reduce tear lens

Question 2

Method of stabilisation

Answer 2

• prism ballast.
• peri ballast
• toric SCL stabilisation: double slab-off
• accelerated stabilisation design

Question 3

Prism ballast

Answer 3

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

Question 4

Peri ballast

Answer 4

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

Question 5

Toric SCL stabilisation - double slab off

Answer 5

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

Question 6

Accelerated stabilisation design

Answer 6

• thin zone inferiorly and 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 toric 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 toric
• total diameter

Question 9

Fitting procedure

Answer 9

• measure rx and vertex distance
• select toric CL design
• select CL power to match both meridians
• select BOZR &/or TD
• complete final Rx
• clockwise ADD
• anticlockwise subtract

Question 10

Limitations of soft toric lenses

Answer 10

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