Module 7: Lab Flashcards
- 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
Automated Lensometer
- 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
Manual Lensometer (SV w/ minus cyl)
-sphere and cyl mire lines are too far off screen
-use hand-held or compensating ring
Strong Prism
-record SV readings frist
- raise lens table and find segment
-note sphere mires (take power and (-) sphere power = add power
Manual Lensometer Bifocal
- 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
High distance/Add power lensometer
-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
Trifocal verification
-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)
PAL verification
-verticle prism OU same direction
-thinning PAL lens
-equal prism doesnt effect px vision
- make note to lab when replacing only one lens
Prism thinning
- compensated Rx
- 1/100th diopter accuracy
-exact replica of exam results
-needs to match compensated Rx, not original Rx
-keep lab invoice
Freeform verification
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
Identifying unknown PAL
-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
Base Curves
-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
Center thickness
-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
Visual Inspection
- no national standards in Canada
- check standards of your office
-check Provincial College of Opticianry - z80.1-1995 American National Standards Institute
Acceptable toleranes
-should be within 1mm of ordered
- if nose pads> can easily be fixed
Seg/OC Height allowance
- normally tolerate warpage under 1.00 D
- if specified= should be within 0.75 D
Base Curve Allowance
-when specified should be +0.3mm
Lens thickness Allowance
- 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
Lens fabrication
-edger picks up lens>moves to finishing wheel
- completes edging/ applies bevel
-fullframe = V bevel
-semi-rimless = flat bevel & grooving for nylon
Finishing
-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
Prentices rule/ Prism
-starts round in shape
-Rx already ground into lens
- also called “uncuts”
- only SV orders
Finished Lens Blank
-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
Unfinished Lens Blank
-range in size 60mm-80mm diameter
- to fit properly= 2 caluclations
1) lens decentration
2) MBS
Lens blanks
- 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
Lens Decentration
-measure ED (not longest diagonal)
- works on SV lenses
- (=) ED+ Total decentration +2
Minumum Blank size
- longest radius
ED measurement
- frosting naturally occurs from edging
-change into high gloss (jewel-like appearance) - can increase internal reflections
- AR coating recommended
Edge Polishing
- lens can be square and blunt from edging
- made slightly rounded
- illusion of less thickness
Edge Rolling
-for rimless frames
-outdated fashion wise
- very expensive
-lenses enclosed like precious stones
Edge Faceting
- hand painted
- baked
- matched to frame colour
- best on plastic frames
Edge Coating
- 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
Safety Standards
-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
Sphere/Cyl Maximum tolerance
- 0.12-0.37 = max +3
-0.37-1.00= max +2
-above 1.00 = max +1 - should not exceed 0.25 prism
Axis of Cly tolerance
