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Frequently
Asked Questions |
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Q: What do
the numbers on the frames mean? |
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A:
Frames are identified by manufacturer / designer,
model number or name, size, and color information.
Size information contains the horizontal measurement
of each lens in millimeters (i.e. 47) and bridge
size (the distance between the lenses) i.e. 18.
This information can help you in sizing a frame
for your face. To better understand the frame
size, double the first number and add the second.
This will give you the distance across the full
front of the frame. For example, a frame size
of 47/18 means that the frame measures 112 mm
across (47 x 2 + 18 = 112).
Frame size may also contain the temple length
(including the portion going behind the ear) in
millimeters such as 145. Therefore a frame size
would be written 47/18 or 47-18 or 47/18-145.
Color may be noted as a description such as gunmetal,
other manufacturers use a color number. NeoVision’s
opticians will help you in choosing the right
size frame for the best possible fit.
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Q: What do the
numbers on my eyeglass prescription mean? |
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A:
Your eyeglass prescription contains information
regarding the lens power required to correct your
vision problems. It consists of spherical power,
cylindrical power, cylinder axis, bifocal addition,
and prism power. Your prescription will contain
only those numbers that are pertinent for your
vision correction, for example if you do not have
astigmatism,
you would not have a cylindrical power and axis
information in your prescription. Most prescriptions
do not contain prism power.
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| Q: What is sphere
power? |
| A:
This is the main part of your prescription. This
number denotes the strength of the lens as measured
in diopters. |
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| Q: What is a
diopter? |
| A:
A diopter is a unit of measurement that is simply
the inverse of the focal distance of the lens as
measured in meters. For example, if a lens has strength
of 2 diopters, then parallel light rays that pass
through this lens will focus together at a distance
of 1/2 meter (50 cm) away from the lens. |
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| Q: What is cylindrical
power? |
| A:
If there is no value under the cylinder heading,
then you have a simple prescription. If there is
a value under this heading, then you have astigmatism.
Like sphere power, the cylinder power is also measured
in diopters. |
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Q: Is there more
than one way of writing the eyeglass prescription
for astigmatism? |
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A:
Yes, there are two ways of writing a prescription
for astigmatism. Some prescriptions are written
in (-) cylinder and some are written in (+) cylinder.
These prescriptions are equal even though they
may not appear so.
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Q:
What is inter-pupillary distance (PD) and
why is it so important for fabricating glasses?
A: Inter-pupillary distance
(PD) is the distance from the center of
the pupil in one eye to the center of the
pupil in the other eye. A PD measurement
ensures that the center of the lenses line
up with the center of your pupil. Before
your prescription lenses are cut into the
shape of your frame, the pupillary distance
needs to be measured. This measurement is
then used so that the optical center of
each lens can be lined up with your pupils
in order to give optimal visual clarity.
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| PD measurements
for distance and near vision are different,
like 62/59, the first number is your distance
PD and the second is for your near PD (for
reading-only glasses). For people with asymmetric
eyes, PD measurement for each eye is done
separately (called "monocular PD"),
like 30.5/31.5. The first number is for the
right eye (O.D.) and the second number is
for the left eye (O.S.). |
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Q:
What is the relation in anisometropia and double
vision? |
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A:
Anisometropia is a condition where there is a
significant difference in the refractive errors
of the two eyes. If this condition is present
in infancy and is undetected or untreated, it
often results in the development of lazy
eye or amblyopia in the weaker eye.
The greater the amount of the difference, the
more likely the development of lazy eye will be.
A problem can occur when glasses are made for
an anisometropic individual. The difference in
the powers of the lenses induces a prismatic difference
that can cause double vision in off-center areas
of the lens, which can be compensated for by the
use of slab-off prism. |
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Q: How do you measure the bifocal
segment height? |
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A:
Bifocal segment height is measured from the bottom
of the lens to the margin of the lower eyelid. |
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Q: How do you measure the progressive
segment height? |
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A:
Progressive segment height is measured from the
bottom of the lens to the center of the pupil. |
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Q: Is there any relationship
in the height of a person and the segment height? |
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A:
No, there is none. A tall person may need shorter
seg height and a shorter person may need a higher
seg height. |
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Q: Can you raise segment height
by adjusting the frame on my face? |
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A:
Yes, the seg height can be raised either by bringing
the nose pads together or by adding a pantoscopic
tilt. |
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Q: How are the light rays refracted
by different types of lenses? |
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A:
Light rays are diverged by minus (concave) lenses
and converged by plus (convex) lenses. |
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Q: Light rays pass through what
part of a lens without being refracted? |
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A:
Light rays passing through the optical center (OC)
of a lens are not refracted. With proper PD measurements,
your eyes are centered at the optical center of
the lens. |
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Q: For ordering my new glasses,
do I need to be physically present or I can simply
fax in my prescription? |
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A:
For taking your unique fitting measurements, your
physical presence is absolutely necessary. We will
need to pre-adjust the frame on your face before
ordering your glasses. |
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Q: What types of vision problems
are corrected by plus (convex) lenses? |
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A: Plus
(convex) lenses are used for correcting hyperopia
(far-sightedness) and presbyopia (aging eye vision). |
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Q: What part of a plus lens is
thickest, center or the edge? |
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A: Center
is the thickest part of a plus (convex) lens. |
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Q: What part of a minus lens
is thinnest, center or the edge? |
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A:
Center is the thinnest part of a minus (concave)
lens. |
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Q: What is the difference in
a spherical and an aspheric lens? |
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A:
An aspheric lens is flatter than a spherical lens. |
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Q: What has more focusing power,
cornea or optical lens? |
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A:
Cornea has 70-80% of eye’s focusing power. |
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Q: What is a lens called that
has no corrective power? |
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A: A
lens with no corrective power is called plano. |
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Q: What do you call the procedure
used for creating a prescription in a lens? |
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A:
The procedure is called surfacing which involves
grinding the back side of a lens. |
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| Q: What is the
meaning of “axis” in eye glass prescriptions? |
| A:
A special cylindrical
lens is needed in order to correct astigmatism.
Not only does the strength of the cylindrical lens
need to be specified, but the lens itself must be
rotated into a specific position in order to provide
the proper vision correction. The axis represents
the amount of rotation of the cylindrical lens in
degrees ranging from 1 to 180. |
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| Q: What is prismatic
power? |
| A:
When the two eyes are not properly aligned and looking
directly at the same thing, prism can be ground
into the lenses in order to re-align them. This
can occur with strabismus or in situations where
the eyes are properly aligned but are under a tremendous
amount of strain in order to keep them aligned.
The value under the 'prism' heading of your prescription
denotes the strength of the prism. |
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| Q: What is the
meaning of “base” in eye glass prescriptions? |
A:
The base is to the
prism what the axis is to the cylinder. As you
know, a prism is shaped like a triangle. The thicker
the triangle at its base, the stronger is the
power. Much like the axis specifies the direction
of rotation of the cylindrical lens for astigmatism,
the prism must also be rotated into a specific
position. But the rotation of the prism is simply
specified as 'base in' or 'base out' (where 'in'
means towards the nose) or 'base up' or 'base
down'. Only these four positions exist as opposed
to the 180 positions that can be specified for
a cylindrical lens. However, orientations between
these four positions can be specified by using
combinations of horizontal and vertical prisms
in the same lens. |
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Q: What is the
difference in NeoVision and other optical stores? |
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A:
Our highly skilled opticians help you in selecting
the right frame to fit your face comfortably.
People usually do not know what to look for in
a frame
and end up choosing frames that are not appropriate
for their prescription or their facial features.
NeoVision’s opticians will also help you
in selecting the right lens
material (CR-39 plastic, polycarbonate,
Trivex, hi index), lens
design (single vision, bifocal, trifocal,
progressive), and lens
coatings (scratch resistance, UV
protection, anti-reflective, transitions, polarized)
to match your lifestyle.
The optician will measure the precise inter-pupillary
distance (PD) to ensure accurate placement of
lenses in the frame. PD is the distance from the
center of the pupil (black circle) in one eye
to the center of the pupil in the other eye. For
multifocal lenses (progressive, bifocal, or trifocal),
an optician must determine the correct position
for the line that divides the distance vision
lens from the near vision lens. The optician will
mark the demo lenses for the correct position
of this line. The height from the bottom of the
lens up to the correct position of the lens-dividing
line is called “seg-height.” In order
to determine the correct seg-height, the optician
must fit and adjust the eyeglass frames on the
wearer’s face. The seg-height is different
for every pair of glasses, and can only be determined
after the eyeglasses have been fit to your face
by an optician. If your eyeglasses are manufactured
without the appropriate measurement of PD and
seg-height, they may not function properly for
you. Never order eyeglasses without trying the
frame on, optician fitting the frame on your face,
and taking the measurements.
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Q: Once I place
my order, how long will it take for my eyeglasses
to be ready? |
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A:
Eyeglasses ordered under an insurance plan are
usually processed by the insurance labs and we
do not have much control over it. They usually
take 5-10 business days. However, if you order
your glasses privately (i.e. without an insurance
plan) and you need single vision lenses without
any special coatings, your glasses can be made
ready in 1-2 days.
We usually promise 5-10 business days to process
an eyeglass job. The actual time for a particular
pair of eyeglasses depends upon a variety of factors
including your prescription and lens options you
have chosen. Remember, eyeglasses are a custom-product
i.e. they are made to your unique specifications.
Occasionally, during the process of lens edging
and mounting, the frames or the lenses are damaged
and the lab needs to start the order all over
again. This can add to the overall time to finish
a particular job. Eyeglasses with drill mount
lenses (i.e. rimless frames) generally take longer.
 At
NeoVision, we apply stringent quality control
standards on each and every eyeglass order. Our
opticians inspect every job after it has already
been checked and approved by the manufacturing
lab. If we notice any defects in the frame or
lenses, we will not deliver it to you. Instead,
we reorder the frame or the lenses and process
the order all over again. While this could add
time to your order, you can be assured that the
final product you receive from us will be in a
perfect condition. Our emphasis is on the finest
quality of the final product rather than rushing
an order.
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Q: Can I use paper
tissues for cleaning my glasses? |
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A:
No, if you have plastic lenses in your glasses
then dry tissues will scratch them. It is generally
better to dampen the tissue, or even use soapy
water and a soft cloth. Glasses with anti-reflective
coating should be cleaned with a special cloth
and spray.
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Q: What kind of
frame and lenses are recommended for people with
high near-sightedness? |
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A:
We recommend polycarbonate or high-index lenses
in a small frame. Avoid rimless frames.
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Q: What kind of
frame and lenses are recommended for people with
high far-sightedness? |
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A:
We recommend polycarbonate
or high-index aspheric lenses. Avoid
rimless frames.
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Q: What types
of lenses are recommended for people who are more
likely to hurt their eyes? |
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A:
We highly recommend polycarbonate
lenses that are more impact
resistant.
Q: What type of
lenses and frames do you recommend for children?
A:
Polycarbonate
lenses in a flexon frame with
spring hinges.
Q:
What is the difference between plastic (CR-39)
and polycarbonate?
A:
The "standard plastic" lenses
are often called "Hard Resin",
"CR-39 plastic", or just
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"plastic" lenses. CR-39®
is actually a PPG Industries registered trade name
for a DADC (diallyl diglycol carbonate) polymer
that was introduced in 1941. The "CR"
stands for Columbia Resin and CR-39 was the 39th
batch or formula made by Columbia Laboratories in
Ohio. The "hard resin" or "CR-39
plastic" is a thermoset plastic meaning it
cannot be molded or bent when heated. On the other
hand, the polycarbonate polymers are thermoplastic
which means that the lenses can be formed by melting
polycarbonate pellets and injecting them into a
mold. |
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Q:
I very often speak in front of people under
cameras. What do you recommend for me?
A: Lenses
with anti-reflective
coating. These
lenses cut down glare on glasses and improve
appearance of your eyes. |
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Q: Who
is at risk for eye problems related to UV radiations? |
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A:
All people, including children, are at risk. People
who spend long hours in the sun because of work
or recreation, those who have had cataract
surgery, individuals who have certain
retinal disorders, and those who take certain
medications, such as tetracycline, sulfa drugs,
birth control pills, diuretics, tranquilizers
etc. are at even higher risk.
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Q:
What is UV400 and what does it mean?
A:
UV400 means that the lens blocks all lightwaves
400 nanometers and below. 400 nanometers
is typically referred to as the point where
UV light starts. Anything below 400 nanometers
is considered to be in the ultraviolet range.
Q:
My glass frame slides down my nose all the
time. What should I do?
A:
You need frame adjustment. Also consider
lighter lenses such as hi-index or polycarbonate
in a smaller frame. |
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Q:
Which color transition is more effective for sun
protection, brown or gray?
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A:
Both are equally effective. It is your preference.
Generally people match the color of transition lenses
with the color of the frame. |
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Q:
Why are polycarbonate polarized lenses better than
plastic polarized lenses? |
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A:
Polycarbonate lens material
is so tough that you can hit it with a hammer and
it won't shatter. Ordinary polarizing lenses are
made out of plastic (CR-39), and are not shatter
resistant. In addition, polycarbonate lenses absorb
harmful UV radiations. |
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Q: I
have to tilt my head back too much to look at the
computer screen. What should I do? |
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A:
Ask your optician to raise bifocal height or consider
using progressive
lenses.
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Q: I
have a trouble seeing at intermediate distance.
What should I do? |
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A:
You should consider using progressive
or trifocal
lenses.
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Q:
I have to hold material out too far to read.
What could be the problem?
A:
Your bifocal power needs to be adjusted.
Schedule an eye exam with your eye doctor.
Q:
I need glasses for reading only; can I use
over-the-counter glasses?
A:
It all depends upon your
reading prescription and how much you care
about the quality of your reading vision.
If your prescription is SAME for both the
eyes and there is NO |
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astigmatism, you can use reading
glasses off the shelf. Of course, you will be very
limited in choice of frame and you will also compromise
on the optical quality of lenses. |
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Q: What
are my options for the reading glasses at NeoVision? |
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A:
You can order your own custom reading glasses
by choosing any of our eye glass frames and adding
reading lenses in your unique prescription. You
will be able to order glasses with clear prescription
lenses or with tinted prescription sunglass lenses
with anti-scratch, anti-UV, and / or anti-reflective
coating. You will also have a choice of lens materials
such as CR-39 plastic, polycarbonate, Trivex,
or hi-index. |
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Q: Is
it important for me to keep a spare pair of eye
glasses? |
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| A:
Many people underestimate the importance of
backup pair of glasses. Under certain situations,
it may not be possible to repair or replace
glasses within the time you have. Imagine,
you are about to leave for a business / pleasure
trip or you are already on such a trip and
your current glasses break. You will unnecessarily
go through a lot of inconvenience and lose
precious time. You can also imagine what will
happen if a student breaks or misplaces his
glasses during the exam period. Always keep
an extra pair of glasses for unforeseen emergencies.
It is like driving a car with a spare tire. |
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Q: How
should I take care of my eye glasses? |
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A:
Clean your lenses daily either in running warm
water or with a special lens cleaner. For drying,
use a soft cotton cloth or special eyeglass cleaning
cloth. When not in use, always store your glasses
in their protective case. Never place them face
down on their lenses. Always use both hands while
putting on or taking off your glasses. |
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Q:
Do sunglasses provide protection against certain
eye diseases?
A:
There is evidence that sunlight exposure plays
a role in certain eye diseases, such as cataract,
macular degeneration,
pterygium,
and eyelid cancer. It is a good idea to wear
sunglasses with protection against ultraviolet
light. Patients with or at risk for macular
degeneration may also benefit from lenses
which block blue wavelengths, such as yellow
or amber lenses. |
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Q: How
can I find out if my sunglasses are polarized? |
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A:
Find a reflective surface and hold your sunglasses
so that you can see the surface through one lens.
Rotate the glasses to see if the glare increases
or decreases. If the glare decreases, then you
know your sunglasses are polarized. Alternatively,
try to see an object below the surface of water
through your sunglasses. If you can see the object
clearly under water, your sunglasses are polarized.
Another simple way to check the polarization of
a lens is by holding the lens over the top of
a lens that you know is polarized. A liquid crystal
display (LCD) or digital watch is polarized. Hold
the lens over the watch on a horizontal plane
and rotate it. If the lens is polarized, you will
notice the watch display appears darker as you
rotate the lens above it. If the lens is not polarized,
there will be no visual difference as you view
the watch through the lens. |
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Q: How
can I check the optical quality of my sunglasses? |
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A:
Find a repeating pattern, like a tiled floor or
some wild wallpaper. Hold the sunglasses a few
inches from your face, cover one eye, and move
the sunglasses slowly up and down, left and right.
Look through one of the lenses. If the lines stay
straight, you’re holding quality sunglasses.
If lines wiggle or waver, your glasses are not
of high optical quality and will distort your
vision. |
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Q:
Why do children need sunglasses?
A:
Children are at a higher risk from the harmful
effects of UV since they generally spend
more time outside in the sun. Select sunglasses
that suit your child’s active lifestyle.
The lenses should be impact resistant i.e.
made of polycarbonate. |
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| Q:
What should I look for in a good pair of
sunglasses?
A:
Sunglasses are used for three main reasons:
health, performance,
and fashion. A quality
pair of sunglasses should provide all three
functions. Lenses should be of high optical
clarity and protect your eyes from harmful
effects of UV
radiations so that you are
protected from developing early cataracts
or pterygium.
By reducing intense bright light as well
as glare, sunglasses should keep you safe
whether you are driving or participating
in active sports. If you have sensitive
eyes, you may also want your sunglasses
to filter out more light. Your glasses should
also protect your eyes against powerful
damaging
impacts.
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Your
choice in sunglasses will also be influenced
by fashion. Wire frames go well with most
outfits but tend to be more fragile than
plastic frames. Wrap-around frames with
large lenses will protect you from ambient
and direct light and glare from every angle.
Wraparounds stick to your face and are in
fashion with the surfing, skating, and snowboarding
enthusiasts. How your sunglasses look, ultimately,
depends on your face, square and rectilinear
glasses look better on round faces, and
square faces are well suited to oval frames.
Strong, lightweight composite or metal frames
are typically used for brand-name sunglasses.
The higher-quality sunglasses generally
have tension springs connecting the arms
to the face. Brand-name sunglasses with
polarized polycarbonate lenses are comfortable
to wear and do not distort colors. |
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Q: I
want to get my eyes checked and order my eyeglasses,
what is the next step? |
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A:
Schedule an appointment at NeoVision Eye Center
by calling toll free at 1-877-NEOVISION
(1-877-636-8474). |
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