PPLs

Question 1

What are the peripheral distortions caused by?

Answer 1

Surface astigmatism caused by the change in rx through the lens
Curvature of the lens increases and the plus increases

Question 2

What variables can affect the size/power of the peripheral distortions?

Answer 2

Size of rx
Add power
Corridor length
Type of varifocal (hard, soft or supersoft)

Question 3

What are the consequences of having a shorter corridor length?

Answer 3

Increase in plus is more rapid, so a smaller area for intermediate tasks.
Eye movements need to be more precise.
Increased surface astigmatism due to smaller area to fit it into.

Question 4

What are the consequences of having a wider distance area?

Answer 4

Increased surface astigmatism
Wider FOV

Question 5

What are the consequences of having a higher add power?

Answer 5

Reduced FOV at near

Question 6

What are the features of a hard PPL?

Answer 6

Large distance area
Short, narrow corridor
Wide near area
No distortions in distance area, but noticeable in intermediate and near portions due to large power differences

Question 7

What are the features of a soft PPL?

Answer 7

Narrow distance area
Wide, long corridor
Narrow reading area
Distortions encroach into distance portion, but more tolerable as difference in power is more gradual

Question 8

What are the features of a supersoft (firm) PPL?

Answer 8

Very large distance area
Wide corridor
Very wide near area