L1 Introduction

Question 1

Spherical Lenses

Answer 1

• Power is the same all around the lens, in all directions

- Used to correct myopic/hypermetropic patients only

Question 2

Toric Lenses

Answer 2

Power of cylindrical lens = no power along the axis, has 2 principal meridians at perpendicular meridians to one another
- axis direction of cylinder is always 90 to meridian where the power is positioned - axis always 90 to cyl power
-still has a max and min power but min power is not zero as it is in a spherical lens
toric is a spherical and cyl lens combined to neutralise both meridians

Question 3

Prisms

Answer 3

• Transparent block of material, has an apex and a base at the bottom which is the thickest part of the lens
• Light deviates towards the base of prism and its because it slows down as it passes through the lens
• Because light is deviated towards the base, vision and so image is deviated towards the apex

Question 4

Why is a prism used?

Answer 4

• Used for patients with muscle imbalance
• there are some pathologies which cause frequent change in vision, so surgery isnt an option
• some people are born with muscle imabalances - EOM can be too long/short so pull eye in a certain direction
• can still get px to see one image, even if both eyes see diff images

Question 5

Surfaces of a lens?

Answer 5

Front surface = away from eye

Back Surface = closest to eye

Question 6

Plano concave/ Plano convex

Answer 6

No power

Question 7

Bi concave/Bi convex

Answer 7

• same curve on front and back surface. but not necessarily of equal power
• when power is same = equi convex/equi concave

Question 8

Meniscus

Answer 8

Most common lens type = gives best optics so ensures image quality
- has one convex and one concave curve