EYEGLASS ADJUSTMENTS
Ophthalmic medical assistants are often asked to make minor adjustments to the frames, such as tightening frame screws, measuring optical centers, and for multi-focals, measuring segment heights to ensure that they are properly placed and not a source of patient complaint.
FRAME SCREWS:
Plastic frames usually have one screw holding each temple piece to the frame front (Fig 1.1). Most non-rimless metal frames have two screws on each side, one to hold the eyewire (the metal that encircles each lens) together and one to keep the temple piece in place.
Loose eyeglass frame screws are a common problem. To adjust or tighten these screws, a jeweler's or optician's screwdriver and a small bottle of clear nail polish are needed. For instructions, see the box "ADJUSTING FRAME SCREWS"
ADJUSTING FRAME SCREWS:
1. Tighten the screws with a jeweler's or optician's screwdriver so that the temple piece moves freely without binding.
2. Apply a small drop of clear nail polish to the screw head. When the nail polish dries, the screw will not loosen easily.
OPTICAL CENTERS:
The ophthalmic medical assistant may need to check the optical centers of the patient's eyeglass lenses to determine whether the placement of the optical centers matches the measured interpupillary distance. Measuring the optical center or distance between centers(DBC) of eyeglass lenses requires using the marking, or dotting, device on a lensmeter. This procedure is described in the box "CHECKING OPTICAL CENTERS."
CHECKING OPTICAL CENTERS:
1. Place the lens against the lens stop of the lensmeter.
2. Make certain the eyeglass frame sits squarely on the spectacle table.
3. Focus the mires and center them within the focused eyepiece target (see the figure). Use the dotting device to mark the lens while it is held in this position. The center mark (usually of three) is the optical center of the lens. If the lensmeter does not have a marking device, use a nonpermanent marker pen to record the approximate center of the lens.
4. Use a millimeter ruler to measure the distance between the center dots; this measurement should correspond to the patient's distance IPD unless a prism has been prescribed.
SEGMENT HEIGHTS:
The segment height is the distance between the lowest part of the rim and the top of the multi-focal lens segment(Fig 1.2). The correct segment height for a multi-focal lens has a direct effect on the patient's satisfaction with the eyeglasses. In determining segment heights, remember that each patient has different vision requirements and must be treated individually with respect to these special requirements. Most opticians recommend fitting the top of a bifocal segment level with the patient's lower lid margin, which is the area where the lid touches the eyeball (Fig 1.3). Some patients prefer the bifocal line at a slightly higher or lower level than at the lower lid margin, but the segment height usually will not vary more than 1 or 2 mm higher or lower. Trifocals are usually fit about 7 mm higher than the lower lid margin.
Most opticians recommend fitting progressive-addition lenses according to the individual lens manufacturer's fitting manual. Each progressive-addition lens has a specific optical design, and fitting characteristics will vary. Fitting progressive-add lenses may be very difficult. Sometimes, despite the fact that patient measurements and laboratory quality control are precise, the patient may remain displeased with the eyeglasses. This may be due to the inability of the patient to ignore the areas of disortion inherent in progressive multifocals. Such patients may need to use conventional bifocals or trifocals.
Ophthalmic medical assistants are often asked to make minor adjustments to the frames, such as tightening frame screws, measuring optical centers, and for multi-focals, measuring segment heights to ensure that they are properly placed and not a source of patient complaint.
FRAME SCREWS:
Plastic frames usually have one screw holding each temple piece to the frame front (Fig 1.1). Most non-rimless metal frames have two screws on each side, one to hold the eyewire (the metal that encircles each lens) together and one to keep the temple piece in place.
Fig 1.1 Typical Frame screw for a plastic frame
Loose eyeglass frame screws are a common problem. To adjust or tighten these screws, a jeweler's or optician's screwdriver and a small bottle of clear nail polish are needed. For instructions, see the box "ADJUSTING FRAME SCREWS"
ADJUSTING FRAME SCREWS:
1. Tighten the screws with a jeweler's or optician's screwdriver so that the temple piece moves freely without binding.
2. Apply a small drop of clear nail polish to the screw head. When the nail polish dries, the screw will not loosen easily.
OPTICAL CENTERS:
The ophthalmic medical assistant may need to check the optical centers of the patient's eyeglass lenses to determine whether the placement of the optical centers matches the measured interpupillary distance. Measuring the optical center or distance between centers(DBC) of eyeglass lenses requires using the marking, or dotting, device on a lensmeter. This procedure is described in the box "CHECKING OPTICAL CENTERS."
CHECKING OPTICAL CENTERS:
1. Place the lens against the lens stop of the lensmeter.
2. Make certain the eyeglass frame sits squarely on the spectacle table.
3. Focus the mires and center them within the focused eyepiece target (see the figure). Use the dotting device to mark the lens while it is held in this position. The center mark (usually of three) is the optical center of the lens. If the lensmeter does not have a marking device, use a nonpermanent marker pen to record the approximate center of the lens.
4. Use a millimeter ruler to measure the distance between the center dots; this measurement should correspond to the patient's distance IPD unless a prism has been prescribed.
The segment height is the distance between the lowest part of the rim and the top of the multi-focal lens segment(Fig 1.2). The correct segment height for a multi-focal lens has a direct effect on the patient's satisfaction with the eyeglasses. In determining segment heights, remember that each patient has different vision requirements and must be treated individually with respect to these special requirements. Most opticians recommend fitting the top of a bifocal segment level with the patient's lower lid margin, which is the area where the lid touches the eyeball (Fig 1.3). Some patients prefer the bifocal line at a slightly higher or lower level than at the lower lid margin, but the segment height usually will not vary more than 1 or 2 mm higher or lower. Trifocals are usually fit about 7 mm higher than the lower lid margin.
Fig 1.2 The segment height is the distance between the lowest part of the rim and the top of the segment. A) Incorrect Measurement B) Correct Measurement
Most opticians recommend fitting progressive-addition lenses according to the individual lens manufacturer's fitting manual. Each progressive-addition lens has a specific optical design, and fitting characteristics will vary. Fitting progressive-add lenses may be very difficult. Sometimes, despite the fact that patient measurements and laboratory quality control are precise, the patient may remain displeased with the eyeglasses. This may be due to the inability of the patient to ignore the areas of disortion inherent in progressive multifocals. Such patients may need to use conventional bifocals or trifocals.
Fig 1.3 Placement of Bifocal Segment
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