Module 7: Lab

Question 1

• high index lenses may not read properl
• Dark tinted lenses may not be accurate
• trouble with low axis cyl
  -trouble with high plus power lenses
  -user error can create false prism

Answer 1

Automated Lensometer

Question 2

• turn eyepeice counter clockwise to blur black concentrice rings (recticle)
  -slowly turn eyepeice clockwise until recticle is clear
  -set glasses on lens table (bottom eyewires rested)
• inside OD lens first on lens stop
  -raise or lower table (matched with OC)
  -swing lens holder to secure in place
  rotate power wheel and notice the target lines
  -two lines very close (sphere lines)
• three lines further apart (cyl lines)
• if lens is sphere both set of lines will focus together/same time
• Lines also called “mires”
• rotate wheel for sphere lines in focus (most plus position)
  -then rotate the axis as well
• if cyl lines are in focus most plus position rotate by 90*
• rotates wheel towards minus # (away from yourself) don’t change axis
  -note when the cyl lines come into focus
  -calculate the difference between sphere and cyl # for amount of cyl in minus power
• same concept as optical cross

Answer 2

Manual Lensometer (SV w/ minus cyl)

Question 3

-sphere and cyl mire lines are too far off screen
-use hand-held or compensating ring

Answer 3

Strong Prism

Question 4

-record SV readings frist
- raise lens table and find segment
-note sphere mires (take power and (-) sphere power = add power

Answer 4

Manual Lensometer Bifocal

Question 5

• placing front of lenses away from you against lens stop.
  -check lens power
• turn glasses around
  -re-do the power check
• axis changes like mirror image (80=100)
  -next check sphere power through segment
  -comparing verticle lines in distance helps accuracy

Answer 5

High distance/Add power lensometer

Question 6

-measure top of segment to bottom lens edge
-neutralize and calculate the add in each segment
-check if add is 50% or different
-Verify PD and segment heights

Answer 6

Trifocal verification

Question 7

-leave markings from lab on lenses
-distance power = above + inside curved line (semi-circle)
-Add power marked inset circle from power cross
- can be difficult due to corridor power
-fitting cross = px pupil
- Distance from fitting cross to bottom lens = OC height
- use pyramid-like chart for monocular PD check
- prism power directly under fitting cross (small dot)

Answer 7

PAL verification

Question 8

-verticle prism OU same direction
-thinning PAL lens
-equal prism doesnt effect px vision
- make note to lab when replacing only one lens

Answer 8

Prism thinning

Question 9

• compensated Rx
• 1/100th diopter accuracy
  -exact replica of exam results
  -needs to match compensated Rx, not original Rx
  -keep lab invoice

Answer 9

Freeform verification

Question 10

1) have Progressive Identifier (optical laboratories association OLA)
2) need plently of light (incandescent/pen light)
- hover lens over dark background
- use magnifiers if needed
- some markings fluroescent (use UV lamp)
3) find 1 of 2 small marks (34mm apart) (each 17mm from MRP)
- circles/squares/triangles/diamonds/letters/pluses
/ logo
-mark with felt pen
- check back of lens> symbol marked (under MRP nasal side)
4) match symbols to indentifier book
5) use centration chart
6) check add power
7)neutralize lenses

Answer 10

Identifying unknown PAL

Question 11

-use lens clock perpendicular to lens on front side
-press gently
-middle clock leg lined up with OC
-rotate clock 90*
-front lens read in (+)/ back lens read in (-)
-indicator arm moves = warped lens/old plus cyl
- MF legs stay on distance portion
- cannot use on aspheric/atoric/Freeform/PAL
- for plastic lens lift and reposition to avoid scratching
-non-spherical = back lens arm doesnt move when rotated
-Aspheric =place center lens>move to lens edge>dial changes

Answer 11

Base Curves

Question 12

-lens calipers meausred in (mm)
-pinch arms until 2 finger open
-place the fingers at OC
- read # at bottom
-minimum thickeness specified (+) lens> check thinnest area of lens
- 1mm difference between OS/OD cause visual issues

Answer 12

Center thickness

Question 13

-check material ordered
-check lens design
-check segment alignment
-check tints/coatings
- lenses only> shape and size (box-o-graph A+B)
-check correct frame
-check for scratches/imperfections

Answer 13

Visual Inspection

Question 14

• no national standards in Canada
• check standards of your office
  -check Provincial College of Opticianry
• z80.1-1995 American National Standards Institute

Answer 14

Acceptable toleranes

Question 15

-should be within 1mm of ordered
- if nose pads> can easily be fixed

Answer 15

Seg/OC Height allowance

Question 16

• normally tolerate warpage under 1.00 D
• if specified= should be within 0.75 D

Answer 16

Base Curve Allowance

Question 17

-when specified should be +0.3mm

Answer 17

Lens thickness Allowance

Question 18

• use lens chuck (adherence device)>fits into edger> hold lens secure
  -automated = checks MBS (will reject job)
  -place lens on edging wheel> grind off material to shape (roughing)
• roughing may use water to keep cool
  -polycaronate roughed dry

Answer 18

Lens fabrication

Question 19

-edger picks up lens>moves to finishing wheel
- completes edging/ applies bevel
-fullframe = V bevel
-semi-rimless = flat bevel & grooving for nylon

Answer 19

Finishing

Question 20

-moving OC of lens blank= prism (small amounts)
-calculates amount of movement of OC by dividing amount of prism by dioptre value of lens
- meaured in (cm) = divide by 10 for (mm)
- lens blanks may be too small for this option

Answer 20

Prentices rule/ Prism

Question 21

-starts round in shape
-Rx already ground into lens
- also called “uncuts”
- only SV orders

Answer 21

Finished Lens Blank

Question 22

-starts round in shape
-Rx not gorund in
- front curve (base curve) pre-created
- back surface curves must be created to Rx
- must be surfaced and edged

Answer 22

Unfinished Lens Blank

Question 23

-range in size 60mm-80mm diameter
- to fit properly= 2 caluclations
1) lens decentration
2) MBS

Answer 23

Lens blanks

Question 24

• determine Frame PD (A+DBL)
  -determine px PD
• frame PD- Px PD (divide by 2)
  -OC moved towards nose typically (frame PD wider)
• Frame PD smaller = OC moved toward temples

Answer 24

Lens Decentration

Question 25

-measure ED (not longest diagonal)
- works on SV lenses
- (=) ED+ Total decentration +2

Answer 25

Minumum Blank size

Question 26

• longest radius

Answer 26

ED measurement

Question 27

• frosting naturally occurs from edging
  -change into high gloss (jewel-like appearance)
• can increase internal reflections
• AR coating recommended

Answer 27

Edge Polishing

Question 28

• lens can be square and blunt from edging
• made slightly rounded
• illusion of less thickness

Answer 28

Edge Rolling

Question 29

-for rimless frames
-outdated fashion wise
- very expensive
-lenses enclosed like precious stones

Answer 29

Edge Faceting

Question 30

• hand painted
• baked
• matched to frame colour
• best on plastic frames

Answer 30

Edge Coating

Question 31

• established standards in Canada
  -z94.3-07 edition (CSA) (must be marked on temple)
  -covers not less than 40 mm wide/ 33mm high of each eye while geometric centered
  -must have integrated/permenant side protection
• glass and CR39 dont meet standards

Answer 31

Safety Standards

Question 32

-0.00 = max +0.06
-up to 6.00= max +0.12
- 6-12.00 = max +0.18
- 12.00 above = max +0.25
-bifocal max +0.12 dioptre

Answer 32

Sphere/Cyl Maximum tolerance

Question 33

• 0.12-0.37 = max +3
  -0.37-1.00= max +2
  -above 1.00 = max +1
• should not exceed 0.25 prism

Answer 33

Axis of Cly tolerance