4. Prisms Flashcards
light is
deviated towards the bases in prismsan
angle of deviation
angle of incidence, refracting angle, refractive index
image formed by a prisms
erect
virtual
displaced towards the apex
primary lens position
pretenice position
position of minimum deviation
plastic lens primary positione
minimum deivation
glass lens primary position
prentice position
prism dioptre
: 1 dioptre produces liner displacement of 1cm at 1m
angle of apparent deviation
1 dioptre produces angle of ½ degrees at 1m
centrad
arcuate apparent images displacement of 1cm at 1m
risley prism
may be used with Maddox rod to measure phoriasc
correction for convergence insufficiency
base out prism for exercise periods only
angle of squint
- Synotophore: expressed in degrees
- Prism and cover test: prisms of increasing strength until movement eliminated
diagnostic prisms
- Objective: prism cover test
- Subjective: Maddox rod
- Measurement of fusional reserve
- Four dioptre test: small degrees of esotorpia
corrective prisms
- Correction split between eyes
- Apex of prism is always placed in the direction of deviation (points to where deviation)
esotropia correction
- Convergence (esotropia) base out prisms
right angle prism
image inverted by 90 degrees
porro prism
image inverted 180 degrees (not transposed)
dove prism
image inverted 180 degrees (not transposed)
