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Canadian Certified Optometric Assistant > Module 5: Ophthalmic Lenses > Flashcards

Module 5: Ophthalmic Lenses Flashcards

1
Q

-UVA (400-320 nm)
-UVB (320-290 nm)
-UVC (290-200 nm)
-Violet (400-446 nm)
-Yellow (560-592 nm)
-Blue (446-500 nm)
-Orange (592-650 nm)
- Green (500-560 nm)
-Red (650-750 nm)
-Infrared (750 nm +)

A

Spectrum of light

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2
Q
  • disruptive to px
  • rainbow/shifts of colour @peripheral
  • measured in Abbe/chromatic aberration
  • high abbe = less dispersion> better optics (20-60)
    -very important 4 diopters +
A

Dispersion

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3
Q
  • crown glass (58)
  • CR-39 (58
    -Trivex (43-45)
  • Polycarbonate (31)
A

Abbe lens materials

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4
Q
  • light travels straight line@ object=bent
  • bending = refraction
  • light rays> lenses> slows down> bent/refracted
  • 3 factors of lens bending:
    1) angle of light when hits lens
    2) lens material
    3) shape of lens front/back
A

Refraction

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5
Q
  • exact location of lens passing no bending
  • placed infront of px pupil (unless prism)
A

Optical Center

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6
Q
  • light travels @ diff speeds/depends on material
    -air = 186,000 MSP
  • slower through lenses
  • measured by “index of refraction”
A

Speed

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7
Q

-speed of light in air/ speed of light in lens material
- index of air = 1.00
- each lens has assigned index (1.49-1.9)
- Mid-index (1.54-1.58)
-High index (1.59 +) glass and CR-39
- higher index = thinner lens

A

Index of refraction

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8
Q
  • CR-39 (1.49) = thicker
  • Crown glass (1.523)
    -Polycarbonate (1.59) = thinnest
A

Indices of refraction lens material

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9
Q

-all lenses reflect light
- light not reflected = transmitted thru lens
-% transmittion depends on material/colour
- high index = more reflection
- high index reflect more = transmit less light= decrease VA
- can add anti-reflective coating to help

A

Reflection

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10
Q

-two basic shapes: convex OR concave
- meniscus lenses= combination both
- power depends on curve (front/back)
- two basic forms: sphere & clyinders

A

Ophthalmic Lenses

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11
Q

-thicker center/ thinner edges
-converge light
- real positive
- plus lenses
-high plus power= thicker lens= thicker middle = faster light converges
- against motion (right to left/left to right)
-magnifies images
-hyperopia/ far-sightedness

A

Convex Lenses

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12
Q

-thicker edges/thinner center
-diverges light
-virtual negative
-minus lenses
-higher minus = thicker edges= faster light diverges
with motion (right to left/right to left)
-reduces images
-myopia/ near-sightedness

A

Concave lenses

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13
Q

-same curve over entire lens
- only 1 power cross

A

Sphere lenses

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14
Q
  • multiple power crosses (flattest/steepest)
  • curves 90* apart
    -2 blurred & tilted lines
    -Toric lens
  • treats astigmatism
    -can be lenticular (via crystalline lens)
    -mixed astig = corneal & lenticular astig
  • every cyl has a direction (axis)
A

Clyinder lenses

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15
Q
  • meridian= edge-edge crossing OC of lens
    -axis = between 1-180*
  • 0* is the same as 180* (always write 180)
    -spherocylinder
  • cyl = strongest and weekest meridian (90* apart)
    -also called principal/major meridians (one will become the axis)
    -cyl measured by distance between both meridians
A

Meridians & Axis

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16
Q

-scissors motion (lines rotated criss-cross)
- compound/toric lenses

A

Cylinder lenses

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17
Q
  • 1 major meridian has no power (distance/sphere)
A

Plano Cylinder Lenses

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18
Q

-2 major meridians have diff powers

A

Spherocylinder lenses

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19
Q
  • measured in diopters
    -based on focal length of lens
    -Diopter (D) = 1/f (focal length of lens meters)
    -D=1/2meters (D =0.05) > lens power +0.50
    –2.00 D= 1/f (f=1/2)> virtual focal 0.50 meters
A

Lens power

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20
Q
  • relates to * in cirlce (360*)
  • only uses 0-180 (upper half circle)
  • axis degress increase counter-clockwise
  • OD = 0* @ nose
  • OS = 0* @ temple
  • with-the-rule astig = near 90*
  • against-the-rule astig= near 0/180*
  • oblique astig = between 45-135*
A

Axis

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21
Q

-spherical lens = power @ both meridians match
-Cylinder lens = Power @ meridians different
- sphere power at axis location
- sphere is most + value
- helps determine thickness of a lens

A

Optical/ Power cross

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22
Q

Abbreviations

A
  • OD = oculus dexter (right eye)
  • OS = oculus sinister (left eye)
  • OU = oculi uterque/unitas
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23
Q
  • OMD use this form of plus astig rx
    1) add sphere and cyl together to make new sphere
    2) keeo cyl value and switch to minus power
    3) take axis and change by 90*
A

Transposition

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24
Q

-front/back lens each have power
-power depends on steep/flat curve is
- measured with lens gauge/clock
-middle pin depresses and changes dial
-must known lens refractive index= accuracy
- old clocks work with CR-39 (1.49)
- New clocks have 2 dials 1.49 & 1.6
- read pg 15-18

A

Base/Lens Curve

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25
Q

-critical in Rx over 7.00
- minus closer = stronger rx
- plus closer = weaker rx
- minus out = weaker rx
- plus out = stronger rx

A

Vertex Distance

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26
Q
  • all lenses are composed of prism
  • prism have apex (tip) and base
  • prism = light bend toward base
    -plus Rx prism meets base-base
    -minus rx prism meets apex-apex
  • OC is where all prisms meet (not bending)
  • treatment for strabismus
  • OC in wrong place = unwanted prism (wrong PD)
  • Verticle OC height error= unwanted verticle prism
  • MRP = prism location ( OC without)
A

Optical Prism

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27
Q
  • Base Up
  • appear walking down hill
  • feel shorter than normal
  • objects look shorter
  • top of hill/ sides sloping down
A

Prism Direction BU

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28
Q

-Base Down
- appear walking up hill
- feel taller than normal
- objects look taller
- standing inside bowl/ side sloping up

A

Prism Direction BD

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29
Q
  • Base in/ Base out
    -horizontal objects aren’t level
A

Prism Direction BI/BO

30
Q
  • diplopia occur when OD/OS rx don’t match > px looking down thru reading seg. (more verticle prism in one eye)
  • 2 pairs of SV might be more suitable
  • lenses made “slab-off” prism (bicentric grind)> BU prism put on front of lens (creates line thru lens)
  • reverse slab-off=BD @ back of lens
  • read pg 26/28
A

Verticle Imbalance/ Slab-off

31
Q

-press on prism stickers ranges 1-40 diopters
- used to correct verticle imbalance @ near
-temporary to test various prisms
- high Rx that would create thick lens
- vision loss monocular (stroke px)
- can be cut to a small location on the lens

A

Fresnel Prism

32
Q
  • original lens matieral (OG)
  • must be tempered= impact resistant
    -scratch resistant
  • won’t warp
    -most precise optics
  • heavy
  • unsafe when scratched
A

Crown Glass

33
Q
  • conventional plastic
  • 50% lighter than glass
  • can be tinted
  • can be coated without UV
    -scratches easily
  • thickest material
  • can warp
A

CR-39

34
Q
  • index 1.54-1.58
    -best cosmetically 2.00-3.00 diopters power
  • come scratch coated
  • maybe avail in aspheric for thinning/less heavy
  • more affordable
  • UV protection
  • Lighter weight
  • better Abbe
  • scratches easily
    -can warp
  • better optics with AR coating
  • more expensive than CR-39
  • TRIVEX= strength of poly w/ better optics
A

Mid-Index Plastic

35
Q

-index range 1.59-1.74
- no cosmetic advantage under 3.00 D
- shock-absorbing coating = 1mm thin lens
- highest index= thinnest material
- UV protection up to 380 nm
-scratches easily
-low Abbe = colour aberration
- high cost
- weaker than trivex/poly
- needs AR for best optics

A

High Index Plastic

36
Q
  • first high index plastic
    -best for children
  • very light weight
  • good for high rx
  • UV protection 380nm
  • thinner than CR-39
  • can be surfaced thinner
    -safe- doesn’t shatter
  • scratches easily
  • lower Abbe
    -more expensive than CR-39
  • less precise optics
  • hard time tinting
A

Polycarbonate

37
Q
  • best for rx -10.00 +
  • highest = extra thin
  • scratch resistant
  • 1.6 abbe/ better than plastic
  • best optics
  • heavy
  • high index= high cost
    -higer indices can’t be tempered
A

High index glass

38
Q
  • impact resistant= lens hardened
  • heat OR chemicals
  • CR-39 cannot be tempered
  • Trivex and poly most impact resistant
    -1)Heat = extreme hot> rapid cooling (air blower)
  • if scratched lose impact resistance
  • can’t use with high index glass
    2) chemical = soaking in molten salts
  • takes 16 hours
  • lens stronger than heat method
A

Impact Resistance/Safety

39
Q
  • one power present over entire lens
  • distance
  • reading only
  • intermediate only
A

Single Vision lens

40
Q
  • distorted peripheral in high Rx
  • looks more natural/ better cosmetics
  • flatter curves
  • wider peripheral vision
  • fits better into frames
  • less weight
  • large eyes (plus Rx)/ small eyes (minus Rx)
  • all PAL are aspheric
  • first made for apkakic post-cat px (1960)
A

Aspheric Lenses

41
Q

-gradually flatten toward edge of lens
- lighter weight/ less buldge

A

Plus Aspheric Lenses

42
Q
  • gradually steepen towards edge of lens
  • thinner edges
  • reduces distortion of unwanted astig (off axis)
  • eye look less reduced in size
A

Minus Aspheric Lenses

43
Q
  • great for high cyl Rx
  • Aspheric @ back = optimize meridian powers> thinner edges than @ front of lens
  • even wider peripheral view
  • px eyes appear more normal size/shape
  • PAL available
    -50% thinner & lighter
  • better optics
A

Atoric Lenses

44
Q
  • prism 2 diff methods (OC move & grinding)
  • Aspheric/Atoric = grinding/surfacing only
  • OC must stay @ pupil
A

Prism with Aspheric/Atoric

45
Q

s - check lens countour (flat =Atoric)
- check power (high rx/thin lens= aspheric)
- lens clock (change in curve readings= aspheric)
-amsler grid (curved = sphere),
(flat = atoric/aspheric)

A

Indentifying Aspheric/Atoric len

46
Q
  • adjust frame before measurements
    -MPR height ratio to pantoscopic tilt (1mm lower from pupil every 2* tilt)
    -MRP not lower than 5mm below pupil
  • Small frames should be used
  • pupil should be within 3mm from frame geometric center horizontal/vertical
    -pantoscopic angle not more than 10*
  • use monocular PD
  • no more than 13mm vertex distance
  • short vertex reduces magnified eyes
  • cant decenter OC, prism must be ground in
A

Dispensing tips Atoric/Aspheric

47
Q
  • hyperopes +2.00 ^ (try aspheric)
  • myopes -2.00 ^ ( try atoric)
  • Astig -2.00 (try atoric)
  • within +2.00 to -2.00 (no need for atoric)
    -mix mid/high index with atoric/aspheric= thin lens
A

Lens selection guide

48
Q
  • means power covers full lens surface
  • for +10.00 D and up
    -must be aspheric
  • highest index possible
  • choosing small rounded frames
  • consider lenticular
A

Full Field Lens

49
Q
  • lens has power only in center 40mm
  • rest of lens “carrier” = stays thin/no power
  • reduces weight and thickness in high Rx
  • still used for complications in cat sx left aphakic
  • only available in CR-39
  • 1960s “ welsh 4-drop”
  • 4 diopters of flattening between edge and center
  • lens looks like fried egg
A

Lenticular

50
Q
  • small round frames
  • take PD and match with frame PD (eyesize+bridge)
  • 2.00 to -4.00 (low) = mid index
    -4.00 to -6.00 =mid/high index
    -6.00 above = high index
    -12.00 above try special lens (myodiscs/lenticular myodisc)
A

High minus lens

51
Q
  • very flat front surface (plano/low+/low-)
  • circle minus “scoop” @ back side= power “bowl”
  • outside area = carrier
  • size of bowl= aperture & varies
  • aperature range from 20mm-30mm around
  • not cosmetically attractive
  • solves weight and thickness
A

Myodisc lens

52
Q

-myodisc lens enhanced to look better
- bowl is blended better into carrier space
-thins the edges more
-aperture ranges 28mm-42mm around

A

Lenticular Myodisc

53
Q
  • located 3mm-9mm above line MF seg
  • all same height = no vertical prism
  • horizontally OC is px PD
A

Distance OC

54
Q
  • near OC moved in nasally
  • difference between distance PD & near PD
A

Seg inset

55
Q
  • available multiple sizes
  • always measure widest of seg design (flat top)
A

Multifocal width

56
Q
  • straight top/ D-style
    -28mm width most popular
  • fused design (glass)= line lip not felt
  • one-piece (plastic) = lip ridge felt front lens
A

Flat Top bifocal

57
Q

-kryptok
- less commonly used
- restricted field of vision
- only two diamter choices (22,24mm)
- not available in high index
- seg line less visible
-high plus Rx= reduced image jump

A

Round bifocal

58
Q
  • franklin style
  • widest field of vision
  • line very visible/ extends the width of entire lens
  • no image jump
  • thick and heavy
  • not good for large frames
  • no intermediate
A

Executive bifocal

59
Q
  • straight top trifocal
    -most common type
  • less popular because PALs
    -50% for intermediate power
  • difficult px adaptation
    -intermediate ribbon depth of 8mm= intermediate tasks/jobs
A

Flat top trifocal

60
Q
  • clearer distance areas
  • well-defined intermediate/reading zones
    -more swimming effect periphery
A

Hard PAL

61
Q

-less clear distance zone
-softer edges into intermediate/reading zone
- wider intermediate zone
- less swimming effect periphery
-swimming= unwanted astig

A

Soft PAL

62
Q
  • eqaul amounts astig each lens
A

Symmetric PAL

63
Q
  • pushes astig to nasal lens
  • takes few days to adapt
A

Asymmetric PAL

64
Q
  • narrow space between distance/near when progressing
    -vary in length/width
    -1990 short corridor introduced (12mm)
A

Corridor

65
Q
  • locate 2 etched refernce markings (34mm apart)
  • dot on top of markings
  • below nasal etch = company logo
  • below temporal etch = Add power
  • every PAL has own chart
  • place dots over chart> mark MRP
  • includes MBS options
    -Pupil height/PD can be measured via rulers
A

PAL template/cut out chart

66
Q
  • uses computer design> custom lenses
  • position of wear
  • can compensate frame position on face
  • reduce unwated astig distortion
  • require more measurements(mono distance/near PD,mono height/pupil OC, panto, vertex, frame wrap)
  • 1/100th of a diopter accuracy
A

Freeform/digital lens

67
Q
  • Pink = indoor glare
  • Yellow = enhances contrast (ski goggles)
  • Green = sunglasses
    -Brown = enhances contrast
  • Gray= no colour change/sunglasses
A

Lens tints

68
Q

MASCOT

A

-Material
-Style
-Coating
-Tint

69
Q
  • plastic needs this
  • keep away from heat
A

Scratch resistant (SR)

70
Q
  • 5 layers including more SR
  • adheres better with SR applied first
A

Anti- reflection (AR)

71
Q
  • polycarbonate doesn’t need
  • Glass doesn’t need
  • photochromic doesn’t need
    ** CR-39 needs UV400**
A

UV filter

72
Q

-likely for sports
- mirror
-glare
-blue blocker

A

Anti-fog

Canadian Certified Optometric Assistant (9 decks)

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