Unit 5: Rgp Review

Question 1

Up to what amount of a stigmatism should we consider a spherical lens?

Answer 1

2.50D

Question 2

How do we know if astigmatism is corneal?

Answer 2

Find RA (Rx cyl)-(K cyl). If it’s within half a diopter, it can probably be neutralized by the tear layer

Question 3

When is a front surface toric lens used?

Answer 3

There is over 1.25 of Rx cylinder correction with a spherical or near spherical cornea.

Question 4

When is a back surface toric lens used?

Answer 4

When corneal astigmatism is approximately 2/3 of the refractive astigmatism
(=0.666 of Rx power or lower)

Question 5

What are two designs of bitoric lenses?

Answer 5

Spherical power effect
Cylindrical power effect

Question 6

What is an SPE bitoric?

Answer 6

Spherical power effect
-optics of a sphere when combined with tear lens

Question 7

What does an SPE bitoric correct?

Answer 7

Corrects only induced cylinder. Does not correct residual astigmatism.

Question 8

How does an SPE bitoric work?

Answer 8

Plus cylinder is ground on the front surface, which cancels out the induced cylinder power created by the tear lens and the posterior curve.

Question 9

What is a CPE bitoric?

Answer 9

Cylindrical power effect toric

Question 10

When do we use a CPE bitoric?

Answer 10

When a spherical power effect bitoric results in significant cylindrical over refraction.

Question 11

SPE or CPE: which one needs to be rotationally stable?

Answer 11

CPE, To prevent inducing further astigmatism

Question 12

What is a saddle fit?

Answer 12

-on k in each meridian
-allows for better alignment with overall toric corneal shape
-tighter fit, more centered
-not used often

Question 13

What is a low toric simulation?

Answer 13

-Fit flat Meridian on K and steep Meridian 0.75 flatter than steep k
-More common fitting philosophy
-Provides stability

Question 14

How to solve a prescription for low toric simulation?

Answer 14

-Flat k is unchanged
-Vertex meridians
-Add 0.75 to the steepest Meridian

Question 15

What is the name of the fit factor guide?

Answer 15

Mandell-Moore

Question 16

Why would you choose GP multifocals over soft multifocals

Answer 16

-Better optical correction.
– corrects corneal astigmatism.
– resists deposits better than soft contacts.
– more stable with blink
– often more comfortable for dry eye patients

Question 17

What are two kinds of simultaneous multifocals?

Answer 17

Aspheric
-gradual change in power from distance to near
Concentric
-Individual rings of distance and near

Question 18

How does a translating GP work?

Answer 18

There is an area for near at the bottom of the lens, and when the patient looks down, the lower eyelid holds the lens in place so the pupil looks through the near zone

Question 19

When to not prescribe translating GPs

Answer 19

When they don’t rest on or about the lower lid

Question 20

When to prescribe Concentrics and aspherics

Answer 20

There is some degree of upper lid attachment

Question 21

How to find residual astigmatism

Answer 21

Rx cyl-K cyl

Question 22

How to find spherical overrefraction

Answer 22

Sph-trial lens