Optics Flashcards
What is the formula for working out the Power of a lens?
P = M x 4
Power (in Dioptres) = Magnifying power x 4
What is the image like in a Porro Prism? (2 things)
- Rotated (deviated) 180 degrees
- Inverted
What does a Wollaston Prism split the incident beam into?
2 polarised emergent beams
(GCSE physics stuff)
What is the image like in a Dove Prism? (2 things)
- Not deviated
- Inverted
Difference between Myopic and Hyperopic?
Myopic = short sighted (light ray stops short of retina)
Hyperopic = long sighted (light ray is too long for retina)
What is the concept of Chromatic Aberration?
How is concept of chromatic aberration used in duochrome test?
What does a normal eye look like in duochrome test?
What does a Myopic eye look like in duochrome test?
Red clearer than green
What does a Hyperopic eye look like in duochrome test?
Green clearer than red
What happens when you correct a hyperopic eye in duochrome test?
Red and green look the same
What happens if you OVERCORRECT the hyperopic eye in duochrome test?
Red clearer than green
so you basically made them myopic
Does colour blindness invalidate duochrome test?
No, chromatic aberration still applies
How will you remember which myopic vs hyperopic sees which colour more clearly?
Hyperopic is active and go so green
Myopic is sleepy so red led lights
What will happen to the eyes of the OVERCORRECTED myopic patient?
They will try fix the overcorrection by doing accommodation → will cause eye to strain
Overcorrection pushes focal point BEHIND retina, so accommodation will make CB to contract to make lens more curved to bring focal point closer, doing this too much will cause strain
How can we calculate the power of IO lens in cataract surgery?
SRK formula
A is a constant that depends on brand of lens, haptics, and even surgeon doing the surgery
What happens with a Minus (concave) lens in GLASSES when eyes converge inwards?
Lens pushes image outwards, so you don’t need to converge your eyes as much
What happens with a Minus (concave) lens in CONTACT LENSES when eyes converge inwards?
You need to converge your eyes more
Because contact lenses move with the eye
What happens with a PLUS (convex) lens in GLASSES when eyes converge inwards?
Lens pushes image inwards, so you need to converge your eyes MORE
What is Corneal warpage?
When cornea shape changes when you wear contact lenses for a long time
What happens with corneal warpage that is bad?
Glasses that previously worked now no longer work so you get blurry vision
How do you overcome Corneal warpage?
How is this used clinically?
Stop wearing contacts for 2-3 weeks
Before LASIK consultations (post op follow ups) they ask you to stop wearing contacts for 2-3 weeks to allow accurate measurements
What is truncation?
Cutting the contact lens to allow it to fit better or reduce friction
What is Keratoconus?
When cornea bulges out
What contact lens do you need to use in Keratoconus and why>
Rigid
