Lec 6 Torics

Question 1

Why are toric RGP fitted

Answer 1

Improve fitting on astigmatic cornea with mod to high cyl

Correct significant residual astig that occurs when fitting a spherical RGP

Question 2

What’s residual astigmatism

Answer 2

Uncorrected astigmatism found by over refraction when a spherical RGP is fitted on cornea

SPEC CYL - CORNEAL CYL

Question 3

Why is flexible important in RGP

Answer 3

You can have more or less residual astigmatism than predicted

Can be measured by keratometer over CL as a cyl result

Question 4

How much astig warrants a bitoric or back surface toric

Answer 4

2D of regular astig

Question 5

How to fit a back toric (?)

Answer 5

Fit a BC near K for each meridian but go for one where vertical is slightly flatter so there’s a better tear fluid pump for movement

Question 6

Why are Front surface toric less prescribed

Answer 6

Because soft torics are successful so they can fit over the cornea well and get rid of remaining astigmatism

Question 7

What’s main disadvantage of front surface toric

Answer 7

Prism is used to stabilise the lens but thick increases thickness (decreases 02) and lens awareness

Question 8

What’s good for low corneal cyl that’s equal to spectacle cyl

Answer 8

Spherical RGP as it fits well and TLP corrects for it

Question 9

What’s good for low corneal cyl that matches a significant non matching refractive cyl

Answer 9

Front toric as it fits well and then gives extra correction for cyl from lens

Question 10

What’s good for medium corneal cyl that matches spectacle cyl

Answer 10

Spherical RGP as fits Ok and TLP corrects

Toric periphery as same as spherical RGP but better fit

SPE Bitoric as fits well and not affected by rotation so is same as spherical RGP

Question 11

What’s good for medium corneal cyl with a non matching refractive cyl

Answer 11

Front surface toric as fits ok and gives extra correction from lens

Bitoric as fits well and gives extra correction for lens

Question 12

What’s good for high corneal cyl that mace he’s the spectacle cyl

Answer 12

SPE Bitoric as fits well and has spherical effect so doesn’t matter if rotates and corrects all corneal cyl

Question 13

What’s good for high corneal cyl with a non Matching refractive cyl

Answer 13

CPE Bitoric as fits well and gives extra correction for lens

Back surface toric as fits well and ….

Question 14

What is a TSP

Answer 14

Spherical back optic and toric periphery (Toric Secondary and Peripheral curves)

Used if normal spherical RGP is good vision but uneven edge lift on a toric cornea

1.5-2.5DC

Question 15

What does TSP 0.8 mean?

Answer 15

Difference between the peripheral curves is 0.8

Eg SC curve be 9.0 in one meridian and the flatter meridian will be 9.8

Question 16

What is the bi-sym and quad-sym lens

Answer 16

Bi- Lower mid periphery of lens steepens independent of upper mid periphery = top and bot diff while middle used as blending zone

Quad - 4 independent curves

Question 17

What’s induced astigmatism

Answer 17

An over correction that’s pretty much a Minus cyl at the axis of flatter meridian

Proportional to CL toric it’s and refractive index of material (hi RI =hi cyl)

Question 18

Why do we care about how much induced astigmatism there is

Answer 18

Because if BC toricity plus the induced over correction equals the refractive astigmatism then it causes the front surface to become spherical so u get back surface toric

Question 19

Advantage of back surface toric

Answer 19

Easy to manufacture as one side is just sphere so better lens quality

Allows front surface modifications e.g plus power or polishing

Costs less as only one curve is larger in front

Question 20

What’s a Bitoric RGP

Answer 20

Lenses with 2 central BC in back 90deg apart and 2 front surface curves which produce a BVP for each meridian

Question 21

Advantages of SPE Bitoric

Answer 21

Works for refractive astigmatism that matches corneal cyl

Rotation doesn’t produced IA as tears and front surface neutralises itself (as curves rotate together)

Good as trial lenses to easily over refract to get final rx to check if there’s any residual astig