Optics 1 - Lecture 3A

what is myopia

• refractive error at plane of cornea

• corrected with minus power

• light image formed in front of the retina

what is hyperopia?

• refractive error at the plane of the cornea is a minus power

• corrected with plus power

• light imaged from behind the retina

how many degrees away are two principal meridians?

90 degrees

what are the meridians in a spherical cornea? in the lens used to correct it?

refractive error is the same in all meridians

• lens used to correct will also be same in all meridians

in an emmetrope, what is the corneal power and axial length relationship?

corneal power is appropriate for axial length

in refractive error, what is the corneal power and axial length relationship?

corneal power is not appropriate for their axial length → refractive error

what is happening in an astigmatism optical cross?

• cornea has 2 meridians

  • one flattest

  • ones steepest

• different power in each direction

• different refractive error in each meridian

• 2 meridians are 90 degrees apart

• two line images on retina

  • Simple Myopia - one in front and one on the retina

  • Simple Hyperopia - one on the retina and one behind

  • Compound Hyperopia - Both behind the retina

  • Compound Myopia - Both in front of retina

  • Mixed Astigmatism - One in front and one behind the retina

where are the 0 degrees, 90 degrees, 180 degrees on the optical cross?

0 to 180 go counterclockwise

• powers on the principal meridian written above the horizontal

• degrees of principal meridian written below horizontal

what are the degrees of the vertical meridian?

090

what are the degrees of the horizontal meridian?

180

what are the oblique angles

45, 135

what is 0 written as?

pl

what is married to what?

sphere is married to axis

what is transposition?

making rx written in plus cylinder into minus cylinder

what are steps of transposition?

1. determine sphere

   1. add cyl power to the sphere, this is the sph power

2. determine cyl

   1. change the sign of cyl

3. determine axis

   1. change by 90 degrees