Ординатура / Офтальмология / Английские материалы / Essentials of Ophthalmic Lens Finishing, 2nd edition_Brooks_2003

S E R I E S 1

Single Vision Lenses

Choose the single vision lens from the kit and place three dots on the lens, as would be applied ordinarily with a lensmeter. The center dot should appear at the center of the lens, and the other two dots should be approximately 15 mm to either side of the center dot.

1. (a) Place an R above the three dots on the back surface of your single vision lens to make it a right lens. With the lens front side up, decenter it 3 mm inward. Because inward is toward the nose, you must visualize whether the nose will be to the right or to the left of the lens (Figure CSS-4, p. 441). Which way did you move the lens to decenter it?

Reference: Pages 78, Figure 4-2, and 79, Box 4-1.

(b)Now mark the lens with a cross to indicate the correct position for blocking (Figure CSS-5, p. 441). (This cross indicates what will become the geometrical or boxing center of the lens once it has been edged.) Is the cross you drew to the right or to the left of the center lensmeter spot?

Reference: Page 80.

2.Calculate the decentration required; place an L on the lens, and hand mark this left lens with a cross for blocking. Place the lens convex (front) side up.

Frame A = 50 DBL = 18

Wearer’s PD = 64 mm

How much decentration per lens did you calculate? Was your marked cross to the right or to the left of your center lensmeter spot?

Reference: Pages 76 and 82.

3.Mark the lens with an R, calculate the decentration required, and hand mark the lens for blocking when the wearer has a PD of 67, the frame A dimension = 53, and the DBL = 17.

For each of the following, calculate decentration, place the lenses convex side up and mark the lenses to indicate the location of the center of the block. With the lens still convex side up, is the marked cross to the right or left of your center lensmeter spot?

4.Right lens

A = 52 mm DBL = 16 mm

Wearer’s PD = 65 mm

5.Left lens

A = 49 mm DBL = 17 mm

Wearer’s PD = 62 mm

S E R I E S 2

Single Vision Lenses

CENTRATION FOR MONOCULAR PDS AND PRACTITIONER-

SPECIFIED MAJOR REFERENCE POINT HEIGHT

Reference: Page 96.

When interpupillary distances (PDs) are given monocularly, they must be calculated separately for right and left lenses. For each of the exercises in this section, perform the following steps:

•Dot the single vision lens with the three parallel lensmeter dots using your watersoluble overhead transparency pen.

•Calculate the correct decentration.

•Lay out the lens for the calculated decentration.

•Mark the lens with a cross to show where the center of the block will be.

1.A = 48 mm B = 45 mm

DBL = 15 mm

Monocular PDs: R = 26.5 mm; L = 28.5 mm

2.A = 56 mm B = 49 mm

DBL = 18 mm

Monocular PDs: R = 30 mm; L = 29 mm

3.A = 57 mm B = 49 mm

DBL = 16 mm

Monocular PDs: R = 29.5 mm; L = 31.5 mm

4.A = 54 mm B = 48 mm

DBL = 17 mm

Monocular PDs: R = 32 mm; L = 34 mm

5.A = 55 mm B = 47 mm

DBL = 16 mm

Monocular PDs: R = 31.5 mm; L = 32.5 mm

6.A = 60 mm B = 47 mm

DBL = 14 mm

Monocular PDs: R = 34 mm; L = 31 mm

7.A = 54 mm B = 51.5 mm

DBL = 14 mm

Monocular PDs: R = 31.5 mm; L = 28.5 mm

Reference: Pages 78 through 81.

In most cases, the major reference point (MRP) of a lens is placed along the horizontal midline so that the MRP falls halfway between the highest and lowest points on the edged lens. This corresponds to the horizontal reference line in the centration

device. If the MRP is specified vertically, it is given in terms of its vertical distance from the lowest portion of the inside groove of the lower eyewire. For layout, the vertical decentration above or below the horizontal midline must be known. This is calculated as follows:

Vertical decentration = MRP height –

B

2

For each of the exercises in this section, perform the following steps:

•Dot the single vision lens with the three parallel lensmeter dots.

•Calculate the correct horizontal decentration per lens.

•Calculate the correct vertical decentration per lens.

•Lay out the lens for the calculated horizontal and vertical decentration.

•Mark the lens with a cross to show the location of the lens block using your watersoluble transparency marker.

8.A = 54 mm B = 50 mm

DBL = 14 mm PD = 61 mm

MRP height = 27 mm

9.A = 56 mm B = 54 mm

DBL = 17 mm PD = 64 mm

MRP height = 30 mm

10.A = 54 mm B = 50 mm

DBL = 14 mm PD = 57 mm

MRP height = 26 mm

For the following exercises, calculate the horizontal decentration per lens for the monocularly specified PDs and also vertical decentration. Mark the lens with a cross to show the location of the lens block using a water-soluble transparency marker.

11.A = 50 mm B = 45 mm

DBL = 22 mm

Monocular PDs: R = 32 mm; L = 33 mm MRP height = 26 mm

12.A = 54 mm B = 51.5 mm

DBL = 15 mm

Monocular PDs: R = 27.5 mm; L = 30.5 mm MRP height = 27 mm

13.A = 50 mm B = 41.5 mm

DBL = 17 mm

Monocular PDs: R = 30.5 mm; L = 27.5 mm MRP height = 22 mm

S E R I E S 3

Single Vision Lenses

LENSES WITH PRESCRIBED PRISM

Reference: Pages 20 through 23.

Lenses with prescribed prism are decentered for prism during the spotting process using the lensmeter. This places the three dots off the optical center of the single vision lens. Yet once the lenses have been spotted, the centration process is identical to the centration process for single vision lenses without prism.

HORIZONTAL PRISM

For the following exercises, place the three lensmeter dots 5 mm to the right of center, as viewed from the front. Calculate the correct horizontal decentration and mark the lenses with a cross to show where the center of the block will be located. In addition, tell what the prism base direction would be, assuming the lenses are spheres.

Example

A right lens of minus power, spotted as described, will result in prism base

.

A = 46 mm

DBL = 20 mm

PD = 60 mm

The lens will look like Figure CSS-6, A, (on p. 442) when spotted 5 mm to the right of center and viewed from the front. The prism base direction may be thought through by looking at a cross-section of the lens as shown in Figure CSS-6, B (on p. 442). As seen in Figure CSS-6, B, the prism base direction is base in.

Horizontal (distance) decentration is as follows:

Decentration per lens = A + DBL – PD 2

=46 + 20 – 60

2

=62

=3 mm

In lens layout, the MRP is moved 3 mm to the right. So the center lensmeter dot (where the MRP is) is 3 mm to the right of the marked cross, as in Figure CSS-6, C (on p. 442).

A = 55 mm

DBL = 14 mm

PD = 61 mm

VERTICAL PRISM

For the following exercises, place the three lensmeter dots 5 mm above the center of the lens. This will result in vertical prism. Calculate the correct horizontal decentration and mark the lenses with a cross to show where the center of the block will be located. In addition, tell what the prism base direction will be, assuming the lenses are spheres.

A = 55 mm

DBL = 14 mm

PD = 58 mm

HORIZONTAL AND VERTICAL PRISM

For the following exercises, place three lensmeter dots 5 mm to the left and 5 mm below the geometrical center of the single vision lens, as viewed from the front of the lens. Calculate the correct horizontal decentration and mark the lenses with a cross to show where the center of the block will be located. In addition, tell what the prism base direction will be, assuming the lenses are spheres.

9. A right lens of minus power spotted as described will result in prism base and .

UNDERSTANDING PRISM

For each of the following exercises, look at the lens power, then decide the approximate position the three lensmeter dots would have after being spotted in a lensmeter. Place the dots in this location using your water-soluble overhead transparency marking pen. Calculate the correct horizontal decentration and mark the lenses with a cross to show where the center of the block will be located.

S E R I E S 4

Progressive Addition Lenses: Using the Fitting Cross

Reference: Pages 99 through 102.

Although progressive addition lenses have a near portion that is invisible to the casual observer, they should not be confused with invisible bifocals.

Invisible or blended bifocals are round-style segment lenses with the demarcation line smoothed over to be indistinct.

Progressive addition lenses differ from blended bifocals in that they increase in power gradually, beginning at the major reference point of the lens and gaining power the farther downward into the near area the wearer looks.

LAYOUT USING THE FITTING CROSS

Lay out the following progressive add lenses for edging using the fitting cross system. Carry out the proper layout procedures and mark the lens with a cross to show the location of the block.

1.A = 53 mm B = 50 mm

DBL = 16 mm

Monocular PDs: R = 30 mm; L = 29 mm Fitting cross heights: R = 27 mm; L = 27 mm

2.A = 48 mm B = 41 mm

DBL = 20 mm

Monocular PDs: R = 31 mm; L = 32 mm Fitting cross heights: R = 23 mm; L = 24 mm

3.A = 52 mm B = 49 mm

DBL = 16 mm

Monocular PDs: R = 32 mm; L: = 32 mm Fitting cross heights: R = 28 mm; L = 28 mm

4.A = 50 mm B = 48 mm

DBL = 14 mm

Monocular PDs: R = 31 mm; L: = 29 mm Fitting cross heights: R = 25 mm; L = 26 mm

5.A = 53 mm B = 49 mm

DBL = 14 mm

Monocular PDs: R = 32 mm; L: = 31 mm Fitting cross heights: R = 29 mm; L = 29 mm

6.A = 54 mm B = 49 mm

DBL = 17 mm

Monocular PDs: R = 31 mm; L: = 31 mm Fitting cross heights: R = 28 mm; L = 29 mm

7.A = 56 mm B = 44 mm

DBL = 18 mm

Monocular PDs: R = 32.5 mm; L = 33.5 mm

Fitting cross heights: R = 25 mm; L = 26 mm

8.A = 51 mm B = 42 mm

DBL = 17 mm

Monocular PDs: R = 29 mm; L = 31 mm Fitting cross heights: R = 25 mm; L = 26mm

9.A = 50 mm B = 45 m

DBL = 15 mm

Monocular PDs: R = 28 mm; L = 29 mm Fitting cross heights: R = 24 mm; L = 24 mm