Lab Procedures Flashcards
PD Tolerance
In NJ and for lab projects, PD’s can only be off 2 mm total
Three purposes of hand edging
- Safety or pin beveling2. Crowning 3. Reducing the lense size or shape
Ceramic hand edging best for
Safety beveling and crowning Very smooth results
Diamond hand edging best for
Reducing lense size/shape Cuts at a faster rate then ceramics
MRP
Point on the lens that equals the amount of prism prescribed Major reference point
When are the MRP and OC the same?
If there is no prism prescribed
FPD > PPD
Decenter inward
FPD < PPD
Decenter outward
Why do we decenter?
To place the MRP in front of the patient’s visual axis
Where do you mark the prism triangle on the lens?
On the same side as the target
If the prism triangle is nasal, you have
Base In
If the prism triangle is temporal, you have …
Base Out
How is horizontal prism usually prescribed?
Horizontal prism is usually prescribed in both eyes in the same direction The OS will always be on the other side of the reticle scale
Projects 1, 2, and 3
Either horizontal or vertical prism in each lens not both 90 or 180
Prentice’s Rule Formula
Prism = power of lens x distance lens is moved
Reason for using Prentice’s Rule
- If lens blank is too small, and you force it, it’s called pushing the PD 2. Amount of prism induced can be figured out by this formula
Base In prism forces the eye to…
Turn outward To keep from seeing double
Negative effects of inducing prism
Could cause outward deviation of the eyes Could cause the suppression of one eye losing visual acuity
When oblique cylinder is present, pushing the PD horizontally will result in
Some degree of vertical prism 1. Cylinder Power increases 2. The cylinder axis approaches the 45 135 degree position
American National Standards Institute (ANSI)
More than 2/3 of a prism diopter is undesirable for horizontal prism
Lens > +- 2.75, PD has to be within
2.5 mm of what was ordered
Vertical Prism Tolerance
No more than 1/3 Prism Diopter should be induced by any differences between R and L
Lens > +- 3.375 D, keep MRP within
1mm of vertical difference
Prism Scale
0.5, 1, 1.5, 2, 3, 4, 5
Auxiliary Prism Cage
A holder for auxiliary prism which is located in front of the telescopic object. Auxiliary prisms come in 3, 6, 9 sets
Definition of Prism
A wedge shaped piece of glass An optical system that deviates the path of light
Prism Diopter
The unit of measurement of prism powerA prism whose power is one prism diopter produces deviation of one centimeter at a distance of one meter
Which part of the prism is at the center of a plus lens?
Base of the prism is at the center Thickest part
Which part of prism is at the center for a minus lens?
Apex of the prism is at the center of a minus lens The thinnest part
How do we create prism?
Decentration of the optical center
Four types of prism uses in Vision Care
- Relieving Prism 2. Adverse Prism 3. Measuring Prism 4. Dissociating Prism
Relieving Prism
Prism prescribed to relieve or aid a patient who has a deficient eye muscle Base positioned over the paralyzed or deficient muscle Apex positioned opposite to the direction in which the muscle would normally turn the eye
Adverse Prism
Prescribed to stimulate a muscle It is placed over the muscle to be stimulated
Measuring Prism
Prism applied to ascertain the abducting or adducting strength Positioned same as relieving prism
Dissociating Prism
Prism applied to effect a temporary destruction of fusion Prism is positioned the same as an adverse prism
Patient reactions to excessive prism
Excessive Base Down Excessive Base Up Excessive Base Out or Base In
Rxn to Excessive Base Down
Causes the floor or other horizontal expanse to seem concave Patient feels as tho he were standing in the bottom of a bowl or trough
Excessive Base Up
- Causes the floor or other horizontal expanse to seem convex. Patient feels as if he were standing on a mound or ridge 2. Makes people and vertical objects seem shorter than they are 3. Makes the patient feel as though he were walking downhill
Excessive Base Out or Base In
Causes the patient to see horizontal objects, such as a table, as too high on one end and too low on the other The too high side is toward the base of the prism
Three different Pattern Makers
WECO - 1st generation Kapper - 40k Cobern - gives 3D image where to put bevel cut, bevel, polish, groove
Optronics / Horizon
Pattern Maker 1. Find dead center with diagonal, put demo lens on top 2. Mark plus sign on demo lens at diagonal Pad on back of lens 3. Your plus sign on top of block plus sign 4. Use Demo Lens as pattern, white plastic with black holder 5. Set machine to 38.5 6. Set to rimless on Keypad
Dry edger, no demo
- Center frame on gray grid 2. Count boxes on R and L 3. Brace frame on bottom last 4. If pattern is off center, PD off center 5. Place grid on matching machine 6. Put on pattern blank 7. Cut
Novamatic Dry Edger
More Automatic 1. Center the frame on grid 2. Set vertical first 3. For horizontal measure FPD - if measurement off by a mm, the pattern will be way off 4. Trace and cut pattern
