Fundamentals of GP Lens Design and Fitting

Question 1

Describe the gradual adaptation schedule for first time wearers of RGP lenses

Answer 1

First Day- 4 hours
Day 2- increase by 2 hours
Day 3- increase by 2 hours
etc….. up to a full day

Question 2

What is a good way to describe the irritability of wearing them before adaptation?

Answer 2

‘You’ll have an awareness of the lens” … better than “It’ll be painful”

Question 3

How do we know what base curve lens to try as a diagnostic lens?

Answer 3

Use HVID (horizontal visible iris diameter)

Question 4

What is the normal range of HVID?

Answer 4

11.4 to 12.1 mm

Question 5

What is a large HVID?

Answer 5

> 12.2mm

Question 6

What is a small HVID?

Answer 6

Less than 11.4 mm

Question 7

If the patient has a HVID of 11.5 or greater, what diameter should you try as a diagnostic lens first?

Answer 7

9.5 mm

Question 8

If the patient has a HVID of less than 11.4, what diameter should you try as a diagnostic lens first?

Answer 8

9.0 mm

Question 9

When dispensing an RGP lens, should you anesthetize the eye?

Answer 9

No

Question 10

What is the term do we use when describing how a lens clears the central cornea?

Answer 10

Vault

Question 11

The lens should rest (land) where on the cornea ideally?

Answer 11

Midperipheral cornea along the horizontal meridian

Question 12

Ideally the lens should have unobstructed movement along what meridian?

Answer 12

Vertical

Question 13

In the mid-periphery, the lens will always ‘land’ at the point of greatest elevation.

Answer 13

Free card

Question 14

There was a second type of topography that we looked at once the lens was on. What do the colors and numbers represent?

Answer 14

Red (+ numbers) higher than the reference sphere

Blue (- numbers) lower than the reference sphere

Question 15

Beyond how many diopters of WTR will a spherical RGP begin to rock vertically?

Answer 15

Beyond 2 Diopters

Question 16

What is corneal eccentricity?

Answer 16

Basically the cornea not being perfectly spherical as it flattens toward the periphery. One of the slides had 3 different examples (i.e. 0.6, 0.4, 0.2; the 0.6 cornea was flatter). This is why we use a diagnostic flat K lens, but then try steeper or flatter lenses.

Question 17

When you have a K reading, how do you round to get your first diagnostic lens

Answer 17

They mentioned rounding up is best (i.e. K is 43.7, use a 44.0D diagnostic lens)

Question 18

What does a lens drifting side to side indicate?

Answer 18

Flatter than K lens

Question 19

What does a lens riding high indicate?

Answer 19

Flatter than K Lens, too flat

Question 20

What does a low riding lens indicate?

Answer 20

Steeper than K lens, too steep

Question 21

A lid can push the lens downward giving a false impression that it’s riding low. Patient’s must keep their eyes wide open as you access this.

Answer 21

Free Card

Question 22

What are 3 GP fitting factors?

Answer 22

1- center of lens should clear central cornea
2- Should be midperiphery contact point along horizontal meridian
3- Lens should maintain unobstructed movement along the vertical merician

Question 23

Where will a RGP lens move on the eye?

Answer 23

In the direction of least mechanical resistance, hopefully vertically

Question 24

What does inferior clearance look like

Answer 24

Fluorescein will be thinner superiorly. May be caused by unequal toricity on cornea or upper lid pressure attributing to this.

Question 25

When doing an overrefraction, if you under X diopters, you do not need to do a vertex calculation. How many diopters is this?

Answer 25

4D

Question 26

How much of the corneal astigmatism will be neutralized by tear film under RGP lens?

Answer 26

Hopefully 100%, this is the main reason why RGP lenses offer superior optics compared to soft lenses.

Question 27

If you have ATR astigmatism, where will you have touch/clearance?

Answer 27

Touch- 12 & 6

Clearance- 3 & 9