OPTOMETRY · SEMESTER 1
Types Of Ophthalmic Lenses Lecture 3
Ophthalmic Dispensing Theory
TYPES OF OPHTHALMIC LENSES AND MATERIALS.
There are two main types of ophthalmic lenses these are]
- Convex lens ( converging lens).
- Concave lens (diverging lens).
OPHTHALMIC LENSES
Types Of Ophthalmic Lenses Lecture 3
Is thicker at the centre and thinner at the edges. It converges (brings together) parallel rays of light to a point called principal focus.
Convex lens
Optical properties of converging lens]
- Has positive (+) power
- Focal length is positive
- Converges light rays
‘light is diplaced towards the base when pass through the prism.
Object beyond 2f – real, inverted , diminished image( btn f and 2f)
- Object at 2f – real, inverted , same size. (at 2f)
- Object btn f and 2f – real, inverted , magnified (beyond 2f)
- Object at f – image at infinity
- Object btn f and optical center – virtual , erect , magnified.
Image formation on convex lens.
Correction of hypermetropia
- Near vision correction in presbyopia.
- Used in magnifiers, reading glasses, and optical instruments.
Uses of convex lenses
Types Of Ophthalmic Lenses Lecture 3
Is the thinner at the center and thicker at the edges. It diverges (spreads out) parallel rays of light, making them appear to come from virtual focus.
Concave lens
Has negative (-) power
- Focal length is negative
- Diverges light rays
Optical properties
Always forms a virtual , erect , and diminished image , regardless of object position.
Image formation on concave lens
Correction of myopia
Uses of concave lens
Key differences
