Re: Long-time contact wearer, suddenly presbyopia is a problem


retinula wrote:
marcia_jay via MedKB.com wrote:
As for 'trying different alternatives"... do they charge you for each
fitting/pair until they get a good match? Or do they charge you just the one
time and keep trying different types till they get a good match but all under
the one initial cost.




The following is based upon my personal "experiences" in wearing
progressive lenses for the last 14 years. It has taken me that long to

be able to quantify how badly made and fitted some of those glasses
have been.

Your observations and criticism of my comments would be very greatly
appreciated in validating my analysis, and possibly having my
experience be of help to others.


--------------------------------------------


A Method for Verifying the Alignment of Progressive Lenses


One of the virtues of progressive lenses is that the wearer is able to
"see clearly" and adjust the focal point for viewing an object by
merely changing the horizontal viewing angle to match the magnification

necessary for clear vision. This essentially gives the wearer the
advantages of bi-focal glasses "without the (bifocal) line" with a
seemingly continuous range of viewing magnification.


Unfortunately, this frequently means reduced peripheral vision, because

the focal point for both eyes is essentially a range in narrow vertical

area in front of each eye. While adjustment to progressive lenses is
usually easy, it requires the wearer to move their head horizontally to

face the object being viewed, and then raise or lower their head to
bring the object into focus. Complications occur, however, if the lens

is too far forward or too close to the eye (usually caused by
misaligned nose pads), or tilted too far forward or backward (usually
caused by a skewed frame), or if the vertical visual areas are not
aligned with the focal point of the eyes (usually caused by an
inaccurate positioning of the lenses).


Vertical misalignment is difficult to verify since it is barley
noticeable and usually subjective, but it can be a major source of
discomfort and dissatisfaction with progressive lenses since only the
dominant eye focuses on the object and causes the recessive eye to
sense a "double vision." While not exactly painful, the resulting
discomfort is mentally exhausting, irritating, and inhibits reading and

reading coherence. Most Optometrists and patients assume that if the
visual areas are close enough to the alignment of the eyes, the muscles

of the eye will make an adjustment. Instead, in many cases the lack of

accurate close vision is NOT noticed but is instead mistaken for
decreased "mental function" by the wearer since most daily
functions do NOT require precise visual coherence. The lens
misalignment also obviates accuracy of the Optometrist's or
Ophthalmologist's prescription.


While a competent Optician can easily and properly adjust the problem
by precisely adjusting the lenses, the diagnosis and verification of
visual accuracy is normally subjective. Accuracy of close vision can
be determined by looking at a point about 2 feet away with the
recessive eye covered, covering the dominant eye, and then un-covering
the recessive eye. The need to move the head either left or right to
bring the point into focus indicates that the progressive visual area
is NOT in alignment. The necessary lens adjustment, however, can be
quantified by the use of two different water-soluble thin-tipped
colored felt markers and a digital display device such as a digital
clock viewed in a somewhat darkened room.


The adjustment measurement involves using a focal point (a digital
clock or a point on computer screen) at distances of 2, 4, 8, and 16
feet away alternately covering the recessive eye and the dominant eye,
and then viewing the focal point with both eyes. With the recessive
eye covered, the wearer uses a thin colored marker to put a dot on the
front of the dominant lens to match the visual focus point. The wearer

then covers the dominant eye, uncovers the recessive eye, and uses the
same marker to put an "identical" dot on the front of the recessive
lens matching the visual focus point. The wearer then views the same
focal point at each successive viewing distance with BOTH eyes
uncovered and uses a DIFFERENT colored marker to place a dot on BOTH
lenses WITHOUT MOVING THE HEAD to matches (cover) the focal point. The

space between the two differently colored dots on the recessive lens at

each viewing distance is the measurement of the vertical focal area's
displacement of the lenses for that viewing distance and quantifies the

lens' vertical misalignment. Accurate alignment should have both
colored dots match at the same point and same viewing distances for
both lenses.


This test is simple, inexpensive, fast, and an objective way of
measuring the visual accuracy of progressive lens alignment.


(There is a graphic of the lens and the colored marks on them resulting

from the trials, but I do not know how to include it in this post, my
first to Google.)


Essentially the graphic looks like:
o = lens allignment points
, = 1st colored dot (comma) with both eyes open (left eye dominant)
. = 2nd colored dot (period) other eye covered and head NOT moved
| = outside of lenses


left lens right lens
| |
16 feet | ,. ,. |
12 ' | o ,. o bridge o , . o |
8 ' | ,. , . |
4 ' | ,. , . |
2 ' | ,. , . |
| |


This attempt at a "graphic" may not be "to scale." The space between
the two differently colored dots (comma versus period above) on the
recessive right lens at each viewing distance is the measurement of the

vertical focal area's displacement of the lenses for that viewing
distance and quantifies the lens' vertical misalignment.

.

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