Eye Glasses!
POWER OF GLASSES: DIOPTERS
The number that appears on an eyeglass prescription
are written in the form of diopters. A diopter is a unit
of measurement based on how much light rays will bend as
they pass through the lens. The goal is to create the
right amount of bending of the light rays in order for
the image to meet on the retina of the eye.
SPHERE OR SPHERICAL NUMBER:
Refers to how near or far sighted you are. A minus(-) in
front of the number indicates myopia or short sightedness
& plus(+) in front indicates hyperopia or
farsightedness.
CYLINDER OR ASTIGMATIC NUMBER:
Refers to amount of astigmatism in your refractive error
prescription.
AXIS:This is measured in degrees &
only present with cylinder.
ADD: Indicates the power needed for
multifocal or bifocal lenses.
LENS MATERIAL:
PLASTIC or polycarbonate: Highly impact resistant,
thinner, & lighter. Scratch resistance coatings can
be applied on it.
CROWN GLASS: This has been used for longest time. Surface
does not scratch.
HIGH INDEX PLASTIC: Thinner than other materials. Thus
lighter also.
MULTIFOCAL LENSES:
Most people over forty need reading glasses due to
condition called presbyopia, where the eyes ability to
focus near objects weakens. Reading glasses is one
solution but they can be annoying when you want to see
the distance and you have to peer over the top or remove
them all together. To avoid this inconvenience bifocals
are other alternatives.
BIFOCALS: It has top part for distance & has small
segment at bottom for near use. There are different types
of bifocals.
1. FLAT TOP OR STRAIGHT TOP
2. KRYPTOC OR ROUND TOP
3. EXECUTIVE; This lens offres widest reading area.
TRIFOCALS:
This lens has three parts top, intermediate & near.
Recommended for music players, computer users
PROGRESSIVE:
Designed to satisfy the widest possible range of visual
needs without any dividing lines. They are also called
invisible or varifocals.In this lens the optic varies
gradually from distance to near.The advantage is that the
segments are invisible & transition from distance to
near is gradual.
COATINGS & TINTS:
Anti reflective coating:
With this special tint lenses appear invisible allowing
people to see your eyes very clearly behind the glasses.
TINTS:
Reduces glare and adds to eyewear comfort. Also right
selection of tint complements your face & adds more
fashionable look.
TINT SELECTION:
yellow, brown & amber helps depth perception.Good for
target shooters.Rose or pink tint good for people who
work under fluoroscent lighting.
ULTRAVIOLET COATING:
UV is invisible to human eyes.There are two types UV A
& UV B.Guarding against both is best.They both can
affect & cause long term damage to lens & retina.
PHOTOCHROMATIC LENSES:
This lenses contain millions of light sensitive
photochromatic molecules.When exposed to sunlight &
uv rays a chemical reaction transforms these molecules
into coloured light absorbers.Thus changing the lens from
clear indoors to coloured outdoors.
CARING FOR YOUR EYE GLASSES:
1. Keep your lenses clean by washing them daily in warm
water or with special lens cleaner. Dry them with a soft
cotton towel or special eyeglass cleaning cloth.
2. When not wearing them keep them in protective case.
3. Never rest them face down in a way that the lens touch
the surface.
4.Always put on or take off your glasses with both the
hands holding the side arms midway on each side &
sliding them backwards over your ears.Thid will help them
keep the adjustment longer.
5. Dont wipe your lenses while they are dry. Wash or blow
off the dust first.
6. Never use paper or silicon products to wipe the
glasses as they can be scratched.
7. Avoid spraying aerosol hair sprays & perfumes near
the lenses as these can cause the lens coatings to peel.
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