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

is slanted, the eyewire has been rolled. The practitioner can correct a roll by heating that portion of the eyewire involved and either twisting it with the fingers or pressing the frame against a flat surface with a counterrolling motion. If uncorrectable by this method, removal of the lens and correction of the eyewire without the lens in it is best. Then the lens is reinserted properly after heating the frame. Antireflection-(AR)coated lenses should not be heated and should be removed from the frame during correction for a rolled eyewire.

Checking the Lens for Rotation

The eyewire containing the lens is compared with the empty eyewire adjacent to it. If the lens is rotated (Figure 12-3), lens-twisting pliers are used to correct the problem. The frame may first need to be heated, and

hot air is the recommended method. However, if hot salt is used to prevent scratching on the lens surface, both the lens and the plier surfaces are inspected to ensure that they are free of salt before the lens is rotated.

The practitioner should check to ensure that the top edges of flat-top bifocals are straight by placing a ruler in front of both segments for reference. With progressive addition lenses, the marked 180-degree reference marks should be horizontally straight. This is accomplished also by placing a ruler along the 180-degree line.

NONCELLULOSE ACETATE

For most plastic frames, basic lens insertion technique is fairly standard. However, each frame material has its own peculiarities. Table 12-1 shows what those important

differences are for some plastic frame materials. Of particular importance are the following considerations:

•How (or even if) the frame material is heated

•What it takes to “shrink” the material down around the lens to achieve a tight fit

Inserting Lenses into Metal Frames

Lenses to be inserted into a metal frame must be edged to the exact size. To put a lens in a metal frame, the curves of the top and bottom of the lens are compared with the corresponding curves of the upper and lower frame eyewires. Using eyewire-forming pliers occasionally will be necessary to reshape the frame eyewire. To increase the meniscus curve, the pliers are positioned along the eyewire (Figure 12-4) and squeezed lightly. Then the pliers are repositioned along the upper and possibly lower eyewire until the new curve is evenly formed.

The eyewire screw is removed to place the lens in the eyewire. Use of an eyewire closure pliers (Figure 12-5) may be helpful to aid in seating the lens in the eyewire groove. Closure pliers are especially useful during edging to see if the lens will be the correct size (Figure 12-6).

Standard Alignment of Plastic

Frames

Before a pair of glasses leaves the laboratory it should be adjusted so that it will sit symmetrically when placed on an individual of average head shape and size.

FIGURE 12-5 Eyewire closure pliers are made to fit into the top and bottom of the eyewire barrel. (From Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, Butterworth-Heinemann [Figure 7-16].)

For standard alignment, this procedure begins with the bridge and then follows next with the endpieces. The temples are handled last. Obviously, changes made in one part of a frame may influence the alignment in another part. Bending the bridge, for example, may change the relationship of the temples. Handling the bridge first, and the other parts in order, helps to eliminate the need to go back and realign parts.

In general, plastic frames must be heated for most alignments. Box 12-2 summarizes how frames are heated using forced hot air or a salt bath. Hot air is best for frames that can be adjusted with heat. Salt is fast and appropriate if no danger exists of damaging the type of frame or lenses being used.

BOX 12-2

Points to Remember in Heating Frames

With Hot Air

1.Check the type of frame material. Some materials can stand more heat than others.

2.Heat only the portion of the frame on which work is to be performed.

3.Rotate the frame in the heat. (This step is important for warmers with heat from one direction only.)

With Salt or Beads

1.If in doubt as to whether the frame material or the lenses should be subjected to salt or beads, use hot air.

2.Always stir the salt (or glass beads) before use.

3.Keep the area of the frame being heated parallel to the surface of the salt.

4.Keep the frame moving slowly.

5.Heat only the portion of the frame on which work is to be performed.

BRIDGE

Bridge alignment is judged mainly by the effect it has on the plane of the lenses. If alignment is “off,” the lenses are readjusted to their proper planes by first heating the bridge area, then grasping the frame by the lens areas.

If the lenses deviate from the horizontal plane (one lens appears to be higher or lower than the other), they

are said to be out of horizontal alignment. If the lenses deviate from the vertical plane (one lens appears to be farther forward or backward than the other), they are said to be out of vertical alignment.

Rotated Lens

Two common causes exist for a frame being out of horizontal alignment: rotated lens and skewed bridge. A lens rotated in the frame causes the top of the eyewire to hump up at the nasal bridge or one endpiece to appear somewhat upswept in shape. An example of a rotated lens was shown in Figure 12-3.

Skewed Bridge

When viewed from the front, a skewed bridge causes one lens to appear higher than the other. This should not occur on a new frame unless the frame has been poorly manufactured or mishandled during processing.

Vertical Alignment (Four-Point Touch)

To check for vertical alignment, or four-point touch, a ruler or straight edge is placed so that its edge goes across the inside of the entire front of the spectacles below the nosepad area. Theoretically the frame eyewire should touch at four points on the ruler, that is, at each place where the ruler crosses the eyewire (Figure 12-7). This will be the case only if the frame is small compared with the wearer’s head size; otherwise face form is required. If the lenses are decentered inward because the frame’s A + distance between lenses (DBL) is greater than the wearer’s PD, then face form is appropriate.

Face form or wraparound is when the frame front is just slightly rounded to the form of the face. Frames with face form will not conform to the four-point touch test. But the temporal sides of the eyewires should touch, and the nasal sides should be equidistant from the ruler (Figure 12-8).

‘X-ing’

The frame front may be somewhat twisted. This is called “X-ing” (Figure 12-9). X-ing causes the temples to be out of line with each other.

Variant Planes

Another form of vertical misalignment is when the lens planes are variant, or out of coplanar, alignment. When the lens planes are parallel, but one lens is farther forward than the other, the frame is out of coplanar

FIGURE 12-9 X-ing may be identified by the characteristic “X” the eyewires make with one another when viewed from the side. (From Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, Butterworth-Heinemann [Figure 8-9].)

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alignment. This almost never occurs with a new frame unless it has been stressed during lens insertion.

Open Temple Spread

After horizontal and vertical preadjustments have been made to the bridge and eyewires, the next aspect considered is how far the temples are spread.

To allow a good picture of temple spread, temple shafts must be straight. Any curve to the temple shaft should be eliminated by heating the temple and straightening it with the hands. The open temple spread is the angle that open temples form in relationship to the front of the frame.

Temples Spread Too Far

Temples flaring more than 95 degrees are spread too far for standard alignment. The endpiece must be heated and bent around so that the temple will not be able to open out as far.

The practitioner begins by heating the endpiece. The temple should already be spread to the wide-open position. Then the endpiece is bent inward with use of one of the following methods:

1.Heat the endpiece and press it back with the thumb.

2.Heat the endpiece and press it against the tabletop.

3.Remove the lens and bend the endpiece and eyewire near the endpiece. Reinsert the lens.

4.When the frame is old or does not respond to the above methods, grasp the temple butt with halfpadded pliers and bend the temple as close to the pliers as possible.

5.Sink the hidden hinge deeper into the frame front using a soldering iron or Hot Fingers unit.

Temples Not Spread Enough

Occasionally the temples are not spread enough after the lenses have been inserted. This may happen more if lenses with steep front curves are used. If the temples are not spread enough, the following may be attempted:

1.File the temple where it abuts with the front.

2.Bend the endpiece forward.

Temple Parallelism

In standard alignment (but not necessarily after frame fitting) the two temples must be parallel to one another when viewed from the side. If the “pantoscopic angles” the left and right temples make with the frame front are unequal, the temples will not be parallel.

The following steps are used to test whether the temples are parallel:

C H A P T E R 1 2 L E N S I N S E R T I O N A N D S TA N D A R D A L I G N M E N T

1.Position the glasses upside down on a flat surface with the temples open.

2.Note whether both temples sit flat or whether one temple is not touching the flat surface.

3.Touch first one temple and then the other to see whether the frame wobbles back and forth or sits solidly.

This procedure is known as the flat surface touch test (Figure 12-10). If the frame wobbles, it needs correction. If left uncorrected, the frame will likely sit on the face at an angle.

A common mistake is to check for temple parallelism with the glasses placed on the table right side up instead of upside down. If this mistake is made and either the bent-down portion of one temple is bent down the slightest bit more than the other, or if one temple bend is located even the least bit farther forward than the other bend, then the flat surface touch test for temple parallelism will not work.

Several possible sources exist for incorrect temple parallelism, as follows:

•A bent endpiece

•A broken rivet or loose hidden hinge (the temple will be loose and tightening the screw will not help)

FIGURE 12-10 Testing for parallelism using the flat surface touch test. (From Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, ButterworthHeinemann [Figure 8-21].)

C H A P T E R 1 2 L E N S I N S E R T I O N A N D S TA N D A R D A L I G N M E N T

•A bent temple shaft

•A bent hinge

•A twisted bridge

Aligning the Temple Ends

A good standard alignment is one in which the ends of both temples are bent down equally. They also should be bent inward slightly.

Temple-Fold Angle

The final alignment step is to fold the temples to the closed position and observe the angle formed as the temples cross. The temples should fold so that they are parallel to one another or form slight angles from parallel. The temples should cross each other exactly in the center of the frame. A proper temple fold angle permits the spectacle to easily fit into a standard glasses case.

Changing the temple-fold angle on a plastic frame by simply bending the temple with the hands does not work as successfully as using pliers. Using hands alone may cause the temple to split at the hinge. Instead, angling pliers can be used to grasp the top and bottom of the hinge screw. Because the metal hinge is being bent, heating the frame is not necessary.

The second method of angling the temple fold uses finger-piece pliers. These pliers, sometimes referred to as Fits-U pliers, are made with parallel jaws. With the temple folded, the pliers are held parallel to the endpiece hinge screw so that the hinge is grasped on both sides. While the frame front is held with the other hand, the hinge is angled until it reaches the proper position (Figure 12-11).

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Standard Alignment of Metal

Frames

Metal frames are aligned using the same standards as were used in evaluating plastic frames. Metal frames require heating only in those places where plastic coats the metal. All other bends are done “cold.”

Pliers are used for the majority of adjustments. Because the pressure of the metal jaws may mar or disfigure the finished surface of the frames, to use padded pliers or to cushion one jaw of nonpadded pliers by attaching friction or adhesive tape to it is essential. The order of procedure for aligning metal frames is the same as that used for plastic frames, beginning with the bridge. The frame must be checked for horizontal alignment, a rotated lens, face form, and X-ing.

One of the primary areas in which adjustments are different than those outlined for plastic frames is when the temple angles are adjusted. Adjusting the temple angles encompasses open temple spread, temple parallelism, and temple-fold angles, which are discussed in the following sections.

Metal Temples Spread Too Far

If the temples are spread too far apart, a few selected methods that may be used to correct them, as follows:

1.Use a pair of thin pliers that has a small metal jaw on one side and a nylon-padded jaw on the other as bending pliers. Grip the outside of the endpiece (Figure 12-12) but hold the front firmly near the

FIGURE 12-12 If the temples are spread too far apart, a pair of half-padded pliers may serve as bending pliers and grip the outside of the endpiece. (From Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, Butterworth-Heinemann [Figure 8-41].)

FIGURE 12-13 The hand is used to grasp the frame front firmly at the endpiece. Temple spread is decreased with the pliers. If risk of chipping the lens is possible, the lens is removed first. (From Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, ButterworthHeinemann [Figure 8-42].)

endpiece with the free hand. (When the endpiece is wide enough, a second pair of thin pliers is used to hold the endpiece where it joins the eyewire.) Rotate the bending pliers until the temple has reached and maintains the desired temple-spread angle.

2.Close the temple and grip the hinge from below with the thin pliers. (Because no visible external frame areas are being gripped, the pliers do not have to be padded.) Rotate the pliers and bend the endpiece area inward (Figure 12-13). Because of the risk of

chipping the lens, whenever there is sufficient space available, a second pair of pliers is used to grip the frame near the lens so that the eyewire area is not stressed (Figure 12-14).

3.Bend the endpiece using a method that does not involve pliers but only a smooth flat surface. With both hands, hold the frame by the lens and eyewire just adjacent to the endpiece. (The closer to the endpiece the frame is held, the less danger there is of breaking a lens.) Hold the frame front perpen-

dicular to the table surface and push the endpiece against the surface.

Temples Not Spread Enough

When the temple spread is too small, it can be increased by several methods. The outside section of the endpiece is grasped with padded pliers in the same manner as for decreasing the temple spread. (This was shown in Figure 12-12.) The endpiece is bent outward to the proper spread, while the front is supported at its junction with the endpiece.

The second method listed in the previous section is used to close the temple and grasp the hinge. (This was shown in Figure 12-13.) As noted previously and seen in Figure 12-14, certain kinds of frames allow enough space at the endpiece to permit a second pair of pliers next to the eyewire as holding pliers. This takes any possible strain off the eyewire, which reduces the possibility of chipping a lens.

Temple Parallelism

The glasses are placed upside down on a flat surface and notice taken as to whether one or both temples touch the surface (flat surface touch test). This is done as first one temple and then the other is touched, as shown for plastic frames in Figure 12-10. If the frame wobbles, the angle the frame front makes with the temple must be adjusted until the two temples are parallel and both touch the surface.

Several ways exist for bending the temple of a metal frame up or down, as follow:

1.Using the simplest way, grasp with one hand the eyewire and lens close to the endpiece on the same side of the frame as the temple that needs to be angled and bend the temple up or down with the other hand.

2.Using a pair of bracing pliers with one metal and one nylon jaw, hold the endpiece on the front of the frame if there is room, or just anterior to the hinge if there is not. (The second pliers, used for bending, should be double-padded nylon jaw pliers to grasp the temple close to or directly on the hinge. It may be prudent to remove the lens if the frame is stiff or there appears to be a possibility of chipping the lens.) Grasp the frame as shown in Figure 12-15 and reangle it upward or downward.

3.It may be possible to do the bend just described in the previous method but without using a pair of bracing pliers. This is shown in Figure 12-16. Take care to prevent chipping the lens.

After the temples have been aligned for parallelism, the bend-down end positions of the temples are aligned for symmetry. Both ends must be bent downward equally

FIGURE 12-15 To change the pantoscopic angle, the endpiece is held, the top and bottom of the hinge area are grasped, and the temple reangled. (From Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, Butterworth-Heinemann [Figure 8-46].)

FIGURE 12-16 When the endpiece is too small, the pantoscopic angle can be changed without holding pliers. If the frame does not have enough flexibility, the lens may be removed first. (From Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, ButterworthHeinemann [Figure 8-47].)

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and inward slightly so that they are mirror images of each other.

Temple-Fold Angle

To change the fold angle on the commonly used types of metal frames, hold the front in the hand firmly, with the temples closed, and bend the temple upward or downward.

To accomplish this same adjustment using pliers, with the temples closed, the frame front is held firmly in one hand. The top and bottom of the hinge area is gripped with double-padded pliers similar to the manner pictured in Figure 12-15 but with the double-padded pliers pointing toward the center of the frame along the direction of the closed temple. The pliers are rotated in the direction necessary to line up the temples.

C H A P T E R 1 2 L E N S I N S E R T I O N A N D S TA N D A R D A L I G N M E N T

Nosepads

Nosepads3 already should be properly aligned at the factory. From the laboratory standpoint, the most important thing to keep in mind is symmetry. The nosepads should be aligned to be mirror images of one another, as follows:

•Both pads should be at the same height.

•Both pads should be the same distance from the frame front.

•Both pads should be equally angled so that the tops of the pads are closer together than the bottoms.

•Both pads should be equally angled so that the back edges of the pads are slightly farther from each other than the front edges.

3For more information on standard alignment of nosepads, see Brooks CW, Borish IM: System for ophthalmic dispensing, ed 2, Boston, 1996, Butterworth-Heinemann, pp 171-174.

1.True or False? Eyewire forming pliers are used to reshape the upper and sometimes lower rims of a metal frame so that it conforms to the meniscus curve of the edged lens.

2.True or False? Eyewire closure pliers squeeze the top and bottom rims of a plastic frame together so that there are no gaps between lens and rim.

3.True or False? In general, metal frames are heated for most adjustments.

4.Which of the following items may be helpful in identifying a lens that is rotated from its correct position in the frame? (Note: More than one response may be correct.)

a.Incorrect cylinder power

b.A tilted flat-top segment top

c.Temples that are not parallel with each other

d.Nasal humping of the eyewire

e.An off-axis cylinder

5.To check for temple parallelism, the glasses are placed on the table, with the temples open, so that they are in which of the following positions?

a.Right side up

b.Upside down

c.It makes no difference.

6.Vertical alignment or four-point touch is done using which of the following?

a.Tabletop

b.Lensmeter

c.Ruler

d.Pliers

7.True or False? If the temples are spread to 95 degrees each, they should be re-adjusted so that they are both spread 90 degrees. If this is not done, the frame is not properly standard aligned.

8.True or False? For plastic frames, the temple fold angle should be changed without using heat.

9.Which of the following statements about nosepad alignment is false?

a.Both pads should be at the same height.

b.Both pads should be the same distance from the frame front.

c.Both pads should be equally angled so that the tops of the pads are closer together than the bottoms.

d.Both pads should be equally angled so that the back edges of the pads are slightly farther from each other than the front edges.

e.All of the statements about nosepad alignment are true.