Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
51 Cards in this Set
- Front
- Back
|
what are the signs and symptoms of PRESBYOPIA
|
1. uncomfortable with near work, using more than 1/2 accommodative ability
2. blurred near vision 3. fatigue at near work 4. holding near work farther away 5. requiring more light for reading |
|
|
what are the factors that influence ADD power
|
1. age
2. occupation/visual demand 3. stature/arm length 4. pupil size |
|
|
relationship between ADD power and ACCOMMODATION
|
must allow patient to use 1/2 of accommodative ability at near
ex: AA= 2.5D Reading Distance= 13in (33mm)=3D ADD=3-1.25= +1.75D |
|
|
relationship between ADD power and AGE TABLES
|
1. may be used for tentative ADD
2. not reliable for prescribing ADDs ex. +0.75D at 40 add +0.1D for each year after 40 |
|
|
relationship between ADD power and BCC
|
1. useful in tentative or working ADD
2. tends to overestimate for early presbyopes |
|
|
relationship between ADD power and PLUS BUILD UP
|
1. increase plus at near to maximum BVA
2. least amount of plus that yields the best vision |
|
|
relationship between ADD power and NRA/PRA
|
1. prescribe the amount of plus that "balances" the NRA/PRA
2. add puts patient in the middle of the NRA/PRA ranges ADD=(NRA+PRA)/2 |
|
|
definition of amplitude of accommodation
|
dioptric difference between the far and near points of accommodation
AA=(1/Fp)-(1/Np) |
|
|
amplitude of accommodation ESTIMATION in relation to myopes?
hyperopes? |
1. uncorrected myope, OVER ESTIMATE amplitude
2. uncorrected hyperope, UNDER ESTIMATE amplitude |
|
|
which optotype suffers the most from not correctly measuring AA.
|
HYPEROPES!!
because they are constantly accommodating. |
|
|
retinal image size with/without spec Rx for AXIAL
|
UNCORRECTED
1. axial myope: INCREASE 2. axial hyperope: DECREASE CORRECTED: 1. axial myope: EQUAL 2. axial hyperope: EQUAL |
|
|
retinal image size with/without spec Rx for REFRACTIVE
|
UNCORRECTED:
1. refractive myope: EQUAL 2. refractive hyperope: EQUAL CORRECTED: 1. refractive myope: DECREASE 2. refractive hyperope: INCREASE |
|
|
spectacle magnification:
definition causes |
DEFINITION:
mag. brought about by a spectacle lens. compares the image size with the correcting lens to the image size without the correcting lens CAUSES: 1. power of lens 2. shape of lens |
|
|
Relative Spectacle Magnification:
definition |
the comparison of the size of the retinal image of the eye, with the correcting lens, to the size of the retinal image of the emmetropic eye.
|
|
|
accommodation in HYPEROPES CORRECTED WITH SPECTACLES
|
1. hyperopes need MORE accommodation than emmetropes
2. hyperopes will require presbyopic correction EARLIER then emmetropes |
|
|
accommodation in MYOPES CORRECTED WITH SPECTACLES
|
1. myopes need LESS accommodation than emmetropes
2. myopes will require presbyopic correction LATER than emmetropes |
|
|
definition of NEAR POWER
|
amount of plus power added to the distance power to get the near power
ex: Distance: -1.25-0.75X180 with ADD: +2.00D Near: +0.75-0.75X180 |
|
|
definition of ADD POWER
|
1. the power on top of the distance refraction
2. usually same ADD is prescribed for each eye, but may be unequal if indicated 3. usually the same segment type is ordered for each eye, but may differ if indicated |
|
|
what do you do to the ADD POWER if you INCREASE the distance PLUS POWER (DECREASE minus)
|
1. increase near plus power
2. MAY KEEP ADD THE SAME |
|
|
what do you do to the ADD POWER if you DECREASE the distance PLUS POWER (INCREASE minus)
|
1. decrease near plus power
2. MAY NEED TO INCREASE ADD POWER |
|
|
ADD POWER in relation to ONE PIECE BIFOCALS
|
ADD POWER is obtained by a change in CURVATURE of the near portion of the lens
use lensometer or lens clock to measure |
|
|
ADD POWER in relation to FUSED BIFOCALS
|
change in INDEX OF REFRACTION
1. front surface radius of curvature is r1 2. back surface of the major lens, radius is r2 3. countersink radius of curvature is r3 |
|
|
THE POWER OF THE SEGMENT OF A FUSED BIFOCAL IN AIR IS NOT EQUAL TO THE POWER OF THE READING ADD
|
THE POWER OF THE SEGMENT OF A FUSED BIFOCAL IN AIR IS NOT EQUAL TO THE POWER OF THE READING ADD
|
|
|
where is the OPTICAL CENTER for a ROUND segment
|
at the geometrical center of the segment
|
|
|
where is the OPTICAL CENTER for a FLAT TOP segment
|
5mm below segment top
|
|
|
where is the OPTICAL CENTER for an ULTEX segment
|
19mm below segment top
|
|
|
where is the OPTICAL CENTER for a EXECUTIVE segment
|
TOP of the segment
|
|
|
what is image jump
|
1. the differential displacement at the TOP of the segment
2. ALWAYS BASE DOWN, if present Image Jump: is the distance of the optical center from the top of the segment MULTIPLE by ADD POWER...ALWAYS BASE DOWN |
|
|
what is differential displacement at the reading level
|
1. change in image position through a lens due solely to ADD POWER
2. comparison of image position through a particular point on the seg to the image position through the distance portion alone 3. prismatic effect measured from the seg optical center |
|
|
what are the prismatic effects of the differential displacement at the reading level
|
1. through OC: NO DD
2. above OC: BD prismatic effect 3. below OC: BU prismatic effect |
|
|
Total displacement at the Reading Level
|
the prismatic effect at a point on the segment is the sum of:
1. the induced prism from the distance lens 2. any induced prism from the seg (DD) 3. use prentice's rule TWICE |
|
|
Blended Bifocals:
width of usable zones varies with... |
1. manufacturer
2. base curve 3. add power -ROUND SEGMENT -fused seg with 3-5mm annular zone surrounding the usable seg |
|
|
Blended Bifocals:
difference between hard and soft |
transition from distance to near portion is more gradual, but NOT USABLE
1. soft transition: wider zone 2. hard transition: narrower zone fit top of blended zone 1-2mm above lower lid margin |
|
|
PROGRESSIVES (PAL):
advantages |
advantages:
1. no visible seg or line demarcation (looks better) 2. clear vision at all distances 3. no unwanted differential image displacement or jump |
|
|
PROGRESSIVES (PAL):
disadvantages |
disadvantages:
The gradual change in curvature over the lens surface results in unwanted surface astigmatism which produces astigmatic error. |
|
|
PROGRESSIVES (PAL):
Unwanted Astigmatism is influenced by... |
1. Add Power
2. Length of Progressive Corridor 3. Width of Distance and Near zones |
|
|
PROGRESSIVES (PAL):
relationship of PALs and ADD POWER |
The amount of astigmatism is proportional to the add power of the lens.
|
|
|
PROGRESSIVES (PAL):
relationship of PALs and Length of Progressive Corridor |
1. Shorter corridors produce more rapid power changes and higher levels of astigmatism
2. Shorter corridors have the advantage of requiring less eye movement |
|
|
PROGRESSIVES (PAL):
relationship of PALs and Width of Distance and Near Zones |
1. Wider distance and near zones have the advantage of wider field of clear vision but produce higher amounts of unwanted astigmatism
2. Narrower distance and near zones produce less unwanted astigmatism |
|
|
PERFORMANCE RATING:
Best for intermediate and low unwanted astigmatism |
J&J Definity
|
|
|
PERFORMANCE RATING:
Best for reducing unwanted astigmatism |
Varilux Panamic
|
|
|
PERFORMANCE RATING:
Best for distance vision |
SOLA Percepta
|
|
|
PERFORMANCE RATING:
Best for near vision |
SOLA VIP
|
|
|
PERFORMANCE RATING:
Best for low seg heights |
Shamir Piccolo
|
|
|
compare HARD PALs to SOFT PALs
|
SOFTER Designs have...
1. Wider distance and near zones 2. Shorter narrower corridors 3. Higher more rapidly increasing levels of astigmatism |
|
|
PALs HARD DESIGN characteristics
|
better fro EYE MOVERS when reading
1. Concentrates the astigmatic error into smaller areas of the lens surface 2. Expands areas of clear vision at the expense of higher levels of blur and distortion |
|
|
PALs SOFT DESIGN characteristics
|
better for HEAD MOVERS when reading
1. Spreads the astigmatic error across larger areas of the lens surface 2. reduced the overall magnitude of blur 3. narrow zones of clear vision |
|
|
what are the advantages and disadvantages of ROUND BIFOCALS
|
advantages:
1. nearly invisible, good cosmesis disadvantages: 1. image jump greater than FT segment 2. narrower reading field at top of segment |
|
|
what are the advantages and disadvantages of FLAT TOP BIFOCALS
|
advantages:
1. less image jump than ROUND or ULTEX 2. wider reading field near top of lens 3. can eliminate most or all of differential displacement at the reading level disadvantages: 1. segment is more visible than round bifocal |
|
|
what are the advantages and disadvantages of EXECUTIVE BIFOCAL
|
advantages
1. no image jump 2. widest reading field possible 3. with minus lens little prismatic effect disadvantages: 1. segment very visible 2. can result in thick, heavy lenses |
|
|
what are the advantages and disadvantages of LARGE ROUND BIFOCAL (ULTEX)
|
advantages:
1. can eliminate or minimize total displacement at the reading level on a plus lens disadvantages: 1. large image jump |
