By Andrew Bruce, ABOM
In their effort to provide patients with the best
frame and lens technology, opticians sometimes
lose sight of the fact that the eyewear they dispense
is only as good as the way it fits the patient.
The patient’s satisfaction with their new eyewear
depends upon the optician’s ability to pre-fit it
prior to taking measurements and then adjust the
eyewear to maximize the patient’s vision, comfort
and appearance.
PRE-FIT TECHNIQUES
Pre-fitting a frame prior to taking measurements has
a major bearing on how well the finished product
performs for the patient. The pre-fit also provides the
patient with their first impression of the optician’s
skill level.
THERE ARE SEVERAL STEPS INVOLVED IN THE PREFIT:
• Adjust the nose pads, if present.
• If a zyl frame without nose pads is selected, make
sure the frame sits well on the bridge.
• Make sure the size of frame selected is actually going
to work for the lens style prescribed.
• Apply the appropriate pantoscopic tilt (usually 5
to 15 degrees). Note that for every two degrees of
pantoscopic tilt added to the frame front, the optical
center (O.C.) of the lens is effectively lowered 1mm.
To make sure the visual axis of the eye coincides with
the visual axis of the lens it is imperative that the necessary
pantoscopic tilt be applied prior to measurements
being taken. If the
frame is not pre-fit, it opens the door for patients’
complaints of visual discomfort with their new lenses
(Figure 1).
FINAL DISPENSE AND NOSE PAD ADJUSTMENT
When performing the final fit, place the glasses on the
patient in case substantial adjustments are needed. If
that’s the case, you can remove the eyewear quickly
to avoid a negative impression for the patient.
If the frame has nose pads, fine-tune them so the
frontal/spread angle, the splay angle and the vertical
angle are all correct for the patient. Slim pad arm adjusting pliers (Figure 2) work well for this. The frontal/
spread angle is how far apart the pads are.
The splay angle is their angle to the nose, which
should complement the angle of the nose at the
point at which the nose pad is sitting. The vertical
angle is controlled by the size of the loop of the pad
arm. The standard position requires the bottom edges
of the pads be closer to the eye wires than the top
edges of the pads. The objective is to make all three
angles sit flush with the skin to achieve superior comfort
(Figure 3).
The loop of the pad arm should be small in order to
keep the vertex distance to a minimum. When fitting
patients with very flat bridges, such as those of
Asian ethnicity, frames with nose pads are usually
the best option. In these cases, the splay angle has
to be changed so the pads are sitting almost parallel
to the face.
Also, the loop of the pad arm may need
to be made larger than standard to keep the frame
off the patient’s lower cheeks by changing the vertical
angle. Bent snipe pliers are good tools for this
purpose (Figure 4).
ADJUSTING THE FRAME TILT
In order to achieve premium vision, the optical centers
of the lenses should be horizontally level with
the pupils. However, if the eyes are vertically uneven,
the patient is not going to be happy with a crooked
frame. In a situation like this, try to achieve a compromise.
If the frame front is tilted, always correct it
in the direction of the error. Use a pair of wide jaw
angling pliers for this task to secure the temple and
end piece together so as not to put excessive strain
on the hinge (Figure 5A and 5B). Example: If the right
side of the frame front is tilted down, either increase
the pantoscopic tilt of the right side down, or reduce
it on the left. After leveling, verify the amount of pantoscopic
tilt is between five and 15 degrees. Have the
patient rotate 90 degrees so the angle of tilt can be
evaluated from the side. The need to precisely measure
the pantoscopic angle is becoming increasingly
necessary due to the increased use of freeform lenses.
There are PD rulers that display protractor markings,
making this possible when necessary.
The correct frame tilt is especially important with
multifocals, making sure the segment is in the correct
position when looking down to read. If there is an insufficient
amount, the patient may be looking under
the frame, or at least, the field-of-view for near work
will be narrowed due to the increased vertex distance
between the eye and the segment. As the eyeball
rotates around the horizontal axis to look down
to read, having the pantoscopic tilt of the frame set
at the recommended angle maintains equidistance
between the lens and eye maximizing field-of-view
and visual comfort.
CHECK FOR EQUIDISTANCE
When checking if the lenses are equidistant to each
eye, with the patient seated and tilting their chin
down, observe the frame front from above by standing
and looking down on it. If one lens appears closer
to the eye than the other, the patient’s eyes may
simply be more inset on one side than the other.
Another reason may be due to the temples being at
unequal angles to the frame front when extending
backwards.
Whichever lens is closer to the eye, the same side
temple needs to be brought closer to the head by reducing
the horizontal angle between the frame front
and the temple— using a pair of flat/round metal pliers
at the end piece (Figure 6). Conversely, increasing
the angle between the frame front and the temple of
the opposite side is also an option, effectively moving
the temple away from the head.
The same way pantoscopic tilt affects the vertical
placement of the lens optical center, face form—
positive or negative—will also affect the horizontal
placement of the lens optical center. However, it is
not recommended to compensate for this since lateral
prism would be induced. Applying positive face form so the frame follows the natural horizontal curve of the face is a good
rule of thumb.
THE FITTING TRIANGLE AND TEMPLE ADJUSTMENT
The frame should be touching the head at only three points which form “The
Fitting Triangle”—the nose and the top of each ear. When adjusting behind
the ears, the temple should curve just above the ears and follow the line of the
back of the ear. Temple bending pliers can be used to aid in this process (Figure
7). It should be at an angle of approximately
45 degrees from the temple and it should not
put excessive pressure on the back, or top,
of the ear (Figure 8). If the bend begins too
soon before the top of the ear, it will rub and
irritate the top of the ear. If the bend begins
after the top of the ear, the temple will either
not conform to the curve of the ear, or it will
need to be bent at a greater angle than 45
degrees and the tip will rub and irritate the
back of the ear. Regardless of the optician’s
skill level, a visual inspection of the temples
behind the ears should always be done to
ensure optimum comfort for the patient. The
temple
bend should follow the line of the side of
the head. In order to do this the tip will need
some angling in towards the head. In addition,
the temple tip should not just be touching
the head at the top of the ear leaving a
space between the head and temple tip at
the bottom. Conversely, it should not just be
touching the head with the lower tip of the
temple creating a space between the head
and the temple at the top of the ear. In the
first scenario, if the temple is in contact with
the head only at the top of the ear, adjust
the temple tip so that it angles in towards
the head just enough to gently touch. In the
second scenario, if there is a space between
the temple and head at the bend, adjust the
temple tip so that it is not bending in quite so
much. Occasionally, in this case, the temple
itself may need angling in a little at the end
piece, again using flat/ round metal pliers
to reduce the horizontal angle between the
temple and frame-front, in order to provide
a snug fit.
Regardless of the technology available to
opticians, all is lost if the optician does not
possess the necessary fitting knowledge
and skills to put the final piece of the puzzle
in place. Eyewear fitting is the optician’s specialty and area of expertise and
such a crucial part of the entire process.
The steps outlined here may appear time consuming, but with practice and
perseverance, they will become second nature and help raise the bar for the
standard of care provided.
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