Applied optics of prism Flashcards
What is the top point of a prism called?
The apex
What is the bottom of a prism called?
The base
3 reasons a prism may be prescribed
strabismus, convergence problems, hemianopia
What is the purpose of a prism?
To deviate the path of incident light so that it corresponds with the visual axes of the eyes
Where is light always deviated in a prism?
Towards the base of the prism
A one dioptre prism will deviate a ray of light by what distance?
A one dioptre prism will deviate a ray of light by 1cm at a distance of 1m
Why are prisms induced in an optical lens?
The customer is not looking through the optical centre of the lens.
Where will the base direction be in a lens?
The base direction will always be at the thickest part of a lens
A notable difference in prismatic effect between the two eyes, this is called what?
Differential or relative prismatic effect
Where is prismatic effect zero?
At the optical centre of a lens
What is prism by decentration?
Prism by decentration is where the eye stays still but the optical centre of the lens is moved to provide a specific amount of prism.
How is prism affected with an aspheric lens?
When fitting aspheric lenses, any ordered prism must be ground on the lens, no matter how small;
i.e. you must not decentre the lens to obtain the prism.
What can happen with unwanted prismatic effects?
Can cause visual strain
What causes unwanted prismatic effect?
This can occur if the centration
of the lens is different from the PD
What is a temporary prism that is stuck onto a lens called?
A fresnel prism
