Session 11 Flashcards
Where is the principal point of focus?
The principal point of focus is always the same distance from the lens when the power stays the same.
What happens to the if the lens position has to change but the focal point must stay in the same place?
A new lens power is required.
Practice finding Power/focal distance formula (See questions in the workbook). F=1/fâ fâ=1/F
What is the relationship between plus powered lenses and moving the distance (closer/further)?
Plus lens moved closer to the eye become weaker (effective) so stronger rx is needed (compensated).
Plus lens moved further away from the eye is stronger(effective) so weaker rx is needed (compensated).
What is the relationship between Minus powered lenses and moving the distance (closer/further)?
Minus lens moved closer to the eye become stronger(effective) so weaker rx is needed (compensated).
Minus lens moved further away from the eye is weaker(effective) so stronger rx is needed (compensated).
Right of the Lens =
Plus Powered Lens
Left of the Lens=
Minus Powered Lens
What is the standard Back Vertex distance Doctors conduct an eye exam at?
Vertex Distance (VD) = 12mm
Practice 5 examples of Effective/ Compensated Power Formula for Plus + Minus Rx, with moving further and closer away.
What is effective rx?
This is the effective rx in lenses when the distance is changed.
What is compensated rx?
This is the rx needed to compensated when the distance is changed.
When is - used in the Eff/comp formula?
When the final power needs to be larger (stronger) than orginal rx
When is + used in the Eff/comp formula?
When the final power needs to be smaller (weaker) than orginal rx
DO NOT use a SIGN for power in the eff/comp formula
Practice questions with full rx (sph+cyl) into Eff/Comp rx with +/- and moving closer and further away
