Ophthalmic Optics 2 Lab Midterm

Front 1

Know where the permanent markings are inscribed.

Back 1

1. logo found on nasal side of a lens
2. add power found on temporal side of lens

Front 2

Know the distance between the permanent markings and their distance from the prism reference point.

Back 2

1. 34mm separates logo and add power
2. 17mm each side of the prism reference point

Front 3

Know the significance of the symbols found above the permanent markings.

Back 3

used for the construction of the temporary markings

Front 4

Know how to locate the permanent markings.

Back 4

1. under intense incandescent or fluorescent light while rotating the lens at different angles
2. special light with magnifier (Essilor PAL ID)

Front 5

Know the purpose of each of the temporary markings.

Back 5

verification of distance prescription, add power, prism, far PD, and FCH

Front 6

Know the purpose of the Progressive Identifier and any disadvantages it may have.

Back 6

1. annual publication from Optical Laboratories Assoc.
2. most comprehensive sources of PAL verification info.
3. provides manufacturers design logo, available materials, and minimum FCH for each design
4. contains diagrams that look like verification chart, but they are NOT TO SCALE

Front 7

Know how distance vertex power is verified.

Back 7

neutralized in BACK VERTEX POWER at the distance power arc (DPA)

Front 8

Know how add power is verified by lensometry.

Back 8

1. neutralized in FRONT VERTEX POWER
2. its the difference between the sphere or the cylinder power read at the DPA, and the same power read at the near power circle

Front 9

Know how prism power is verified.

Back 9

1. neutralized at prism reference point
2. target may be slightly blurry because the progressive corridor begins there

Front 10

Know how far PD is verified with a ruler and a verification chart.

Back 10

1. ruler: distance between the center of the fitting cross and the center of the bridge
2. v. chart: place front part side of frames on chart, align it in middle of pyramids, and read the monocular PD on horizontal line

Front 11

Know how FCH is verified with a ruler and a verification chart.

Back 11

1. ruler: distance between fitting cross and deepest part of the inside eyewire (add 1 for plastic and 0.5 for metal)
2. v. chart: same procedure as the far PD but instead of looking that the horizontal line, look at the stacks of horizontal lines at the bottom of the frame

Front 12

Know when a vertical imbalance problem is likely to occur.

Back 12

1. whenever there is a difference in vertex power at 90 between the right and left lenses
2. some vertical prism will be induced anytime a person looks above or below the optical centers

Front 13

Know the purpose of single vision spectacles in vertical imbalance.

Back 13

1. avoid vertical imbalance by switching MF wearers to two pairs of spectacles (distance and reading)
2. if optical centers are lowered approx. 5mm from their customary position, wearers wont have to tilt their chins down as much (COMFORT)
3. half eyes will also fix the problem

Front 14

Know the disadvantages of lowering the distance optical centers in segmented MFs to correct vertical imbalance.

Back 14

1. this will induce same amount of vertical imbalance at distance
2. not a problem because people spend little time looking above their distance optical centers

Front 15

Know where the optical centers of RD, FT, and Executive bifocal segments are located, and the types of prism they create.

Back 15

1. RD: OC @ middle of segment (upper half is BD and lower half is BU)
2. FT: OC @ 5mm below segment line (first 5mm of segment creates BD and remainder creates BU)
3. Exe: OC @ segment line (BASE UP PRISM)

Front 16

Know the advantages and disadvantages of using dissimilar segments to correct vertical imbalance.

Back 16

CHEAP but UGLY

Front 17

Know the disadvantages of compensated ribbon segments for correcting vertical imbalance.

Back 17

1. alters normal shape of segment
2. limited by the amount of vertical imbalance they can correct (1.50PD max)
3. their small size (14x22mm)
4. only available in glass
5. EXPENSIVE

Front 18

Know the purpose and uses of Fresnel Press-On Prisms.

Back 18

1. series of equally powered mini prisms that lie parallel and adj to each other
2. have the deviating power of conventional prisms but thinner (1mm)
3. made of PVC (n=1.525)
4. one side ridged with prism the other side is flat
5. greater number of ridges and channels, the higher the prism power
6. ONLY TEMPORARY SOLUTION
7. can be applied horizontally to relieve convergence disorders

Front 19

Know which method of correcting vertical imbalance can correct the greatest amount.

Back 19

1. fresnel press on prism
2. 1PD to 14PD in steps of 1PD
3. 15PD to 40PD in steps of 5PD

Front 20

Know the advantages and disadvantages of using Fresnel Press-On Prisms to correct vertical imbalance.

Back 20

1. adv: can be used with all types of lenses, easily removable, inexpensive
2. disadv: decrease acuity and contrast sensitivity, unattractive, difficult to clean

Front 21

Know the advantage and disadvantage of using contact lenses to correct vertical imbalance.

Back 21

1. adv: OC moves with the eyes, theres no vertical imbalance hen the eyes are lowered for reading (best solution for correcting vertical imbalanace)
2. disadv: not all patients are good candidates to wear contact lenses, especially mature ones

Front 22

Know what the most common permanent method for correcting vertical imbalance is.

Back 22

SLAB OFF PRISM

Front 23

Know which types of lenses slab-off can be used on.

Back 23

1. can be used on all types of lenses to counteract the vertical imbalance in one lens
2. Single vision, segmented MF, and even PALs

Front 24

Know where the slab-off line is found on FT MFs.

Back 24

the slab off line coincides with the bifocal segment lines

Front 25

Know what type of prism ground slab-off introduces, and which lens it’s applied to.

Back 25

introduces BU prism into the lens that has the least amount of BU prism or the greatest amount of BD prism

Front 26

Know which types of lenses and materials ground slab-off can be used with.

Back 26

1. can be ground on any type of lens and material
2. used with segmented MF, FLAT TOPS are preferred because they off the BEST COSMESIS

Front 27

Know which segmented MF style is preferred with ground slab-off.

Back 27

FLAT TOPS

Front 28

Know which segmented MF styles molded slab-off is currently available in.

Back 28

1. single vision
2. RD25
3. FT28
4. FT35

Front 29

Know which material molded slab-off is available in.

Back 29

ONLY AVAILABLE IN CR-39

Front 30

Know what type of prism molded slab-off introduces, and which lens it’s applied to.

Back 30

1. introduces BD prism into the lens that has the least amount of BD prism or the greatest amount of BU prism
2. thus its used on the lens that has the greatest plus or least minus power @ 90

Front 31

Know my recommendation about switching patients between the two types of slab-off.

Back 31

1. Dr.P says patients who were switched from one type to the other reject the new one because the change in direction of the prism caused an alteration in perception that couldn't be overcome
2. PATIENTS SHOULD RAMIN IN THE SAME TYPE OF SLAB OFF THEY’RE CURRENTLY WEARING