L3 Reflection and refraction at prism surfaces Flashcards
Parts of prism
Base, apex, apical angle, refracting surfaces, internal angles
what happens when light enters through one refracting surface and leaves through another (formula)
Apical = internal angle (1) + internal angle (2)
Define deviation (of a prism)
The angle between the incident and the emergent ray
Prism power proportionate to deviation power
Calculation for deviation
The sum of the external angles minus the apical angle
What is normal incidence and normal emergence
When the incident/ emergent ray is normal to the refractive surface
State the limitations on refraction
An incident ray at the first refracting surface may yield the critical angle at the second refracting surface. Then, no light will emerge from the second refractive surface.
explain limiting incident angle
the incident angle at the first refracting surface that yields a 90 degree emergent angle at the second refracting surface
define ophthalmic prisms and its unit of deviation
- thin, apical angles less than 15°
- either incident/emergent ray leaves normally to a refracting surface
unit of deviation is pd (prism diopter)
how do u calculate prism diopter
1 Pd is a deviation that produces a lateral displacement of 1 Cm at 1m; prism diopter are proportional
1pd=1cm (displacement) ÷ 1m (distance)
explain image displacement through a prism
- eye sees object through prism (eye naturally turns toward apex)
- image of object is displaced towards apex of prism
Terms to define orientation of prism’s base
Base in, out, up, down
Explain Tropia (term to define The Eye)
One eye deviated (in/out) so that the two eyes are not looking at the same position. (double image)
Explain Esotropia
Eye deviated inwards toward nose
Explain exotropia
Eye deviated outwards away from nose
