RGP Fitting 2

Question 1

How big should the back optic zone diameter be?

Answer 1

• Should be 1.50mm larger than pupil size

– Small: < 7.30mm

– Medium: 7.30-7.90mm

– Large: > 7.90mm

Question 2

What will px experience if they are not looking through the back optic zone of the contact lens?

Answer 2

They will experience flares/halos (especially in mesopic light conditons).

[This is why we measure pupil size in both ambient and mesopic conditions]

Question 3

True or false- Chnaging the BOZD alters the fluorescein pattern?

Answer 3

True

Question 4

What is the difference between the back optic zone radius and the back optic zone diameter?

Answer 4

The red arrow represents the back optic zone diameter

The blue arrow represents the back optic zone radius.

Question 5

In order to change the back optic zone diameter and still keep the same fluorescein pattern, how must you change the back optic zone radius?

Answer 5

0.5mm change in BOZD needs a 0.05mm change in BOZR to keep the same fluorescein pattern

– This means that if you are not happy with BOZD AND BOZR, you need to change the BOZR twice.

Question 6

If you had a px with a BOZR:BOZD ratio of 7.50:7.50 and wnated to adjust the lens so that the BOZD was 8.00 what BOZR would you order?

Answer 6

Question 7

What is edge lift also called?

Answer 7

Edge clearance

Question 8

What is the difference between axial edge lift and radial edge lift?

Answer 8

It depends on whether you view the distance from the base curve ( i.e. if the back optic zone radius was continued) to the contact lens from side on or front on.

Question 9

What is the difference between edge lift and edge clearance?

Answer 9

Edge lift is the distance from the tip of the contact lens to where the continuation of the back optic zone radius would be.

Edge clearance is the diatnce between the tip of the lens and the cornea.

Question 10

Which measurement will always be greater axial edge clearance or radial edge clearance?

Answer 10

Axial edge clearance

(any axial measurement will always be greater than a radial measurement)

[The larger the diameter of the lens, the greater the difference]

Question 11

What is the optimum tear meniscus at lens edge ( i.e. how thick do we want the flourescin line around the CL to be)?

Answer 11

80um

Question 12

Is BOZR more related to vision or fluorescein pattern?

Answer 12

BOZR is related to fit (i.e. the fluorescein pattern)

[BOZD- is related to vision]

Question 13

When assessing the fit of the lens on the cornea what are we looking at bar fluorescein?

Answer 13

Position of the lens

Movement after blink - ideally we wnt 1-1.5mm vertically

Question 14

If a lens is flat, are we expecting more or less movement after blinking?

Answer 14

We are expecting more movement after blinking (>2.5 mm).

Question 15

If a lens is steep are we expecting more or less movement after blinking?

Answer 15

Less movement after blinking (<0.5mm).

Question 16

If after blinking a px’s contact lens moves in a curved direction, has the lens been fitted correctly?

Answer 16

No it is too flat

Question 17

How does a toric with the rule lens look under fluorescein?

Answer 17

Question 18

How does a toric against the rule lens look under fluorescein?

Answer 18

Question 19

If you are not seeing a symmetrical fluorescein pattern with spherical lenses what can you assume?

Answer 19

Lens is not centered and if that’s not the case then there is perhaps scarring or even keratoconus.