EYE GLASSES:
Eye glases are used to correct vision of people who are short sighted, far sighted or have age related vision problems.Children may need glasses to treat & prevent certain conditions like amblyopia(which means lazy eye) and some eye muscle problems.
The selection of glasses usually follows a comprehensive eye exam by an eye specialist.Eye glasses come in many shapes & sizes to meet the appearance & occupational need of the person.The first step is to choose a suitable frame that is comfortable to wear & sits properly on the face.The general rule is not too large or not too small.The lenses that are fitted into the frame come either of plastic or glass.The lens slab are ground & polished to certain specifications according to your prescription and shaped into lenses to fit your choosen frame style.
Your eye specialist may prescribe 1.Regular or 2.Bifocal glasses.
Regular glasses have one lens on each side that contains a single prescription which may be different in each lens.
Bifocal glasses contain two prescriptions in each lens.The upper portion of the lens corrects the long distance vision while the lower portion helps to clearly see small objects closer to the eye like book etc.
READING GLASSES provide a prescription for small objects held close to the eyes. IT IS IMPORTANT TO INFORM YOUR DOCTOR WHAT OCCUPATION YOU WILL BE USING THE GLASSES FOR, as there are variety of ways in which the lenses may be customised to best fit your needs.
SELECTING FRAMES FOR CHILDREN:
When selecting frames for children appearance should not be the most important factor.Special care should be taken to choose frames that are comfortable, safe & well made.They may benefit from use of straps, or cords & flexible hinges on the side arms (ear pieces) of the frame to keep the glasses from falling off.Specially for children the lens material made of shatter proof plastic materials (polycarbonates) are best.
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 measurment based on how much light rays will bend as they pass through the lens. The goal is to creat 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(+) infront indicates hyperopia or farsightedness.
CYLINDER OR ASTIGMATIC NUMBER:
Refers to amount of astigamatism 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.
CARRING 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.
ABOUT SUN GLASSES
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Sunglasses a immensely popular with people all over the world as they provide eye comfort & also used as fashion accessroy. Sun glasses protects the eyes from long term damage due to harmful effects of ultra violet rays.
FEATURES OF SUN GLASSES
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1) UV Protection
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You should always wear sunglasses that provide ultra violet radiation protection feature. Both plastic & glass lenses absorb some UV light but the absorption can be improved by adding chemicals to the lens material during manufacturing or by applying special lens coatings.
2)Infrared Protection
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Infrared wave lenghts are invisible & produce heat. Sunlight has low levels of infrared rays & the eye tolerates this well.
3) Polarised Sun Glasses
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Polarised lenses cut reflected glare such as sunlight that bounces of smooth sufaces like pavement or water. So they are particularlly usefull for driving & fishing.
4)Blue blocking
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Lenses that block all blue light are amber & make your surrounding look yellow or orange. This tint makes distant objects more distinct specially in snow or haze. Specially used by skeers, hunters, boaters & pilots.
5)Mirror Coated Sunglasses
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Mirror finishes are thin layers of various metalic coating on ordinary lens. But this is not an alternative to UV protection.
6) Wrap Around
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These sunglasses are shaped to keep light entering from around your eyes.
7) Gradiant Sunglasses
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They are shaded from top to bottom so they cut the glare from the sky but allow you to see clear from below. They are usefull specailly for driving as they don't dim the view of the dash board. But they are not good for the beach or the snow.
8)Photochromatic & Transitions
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These lenses automatically darken in bright light & lighten in low light. Most of the darkening takes place in thirty to sixty seconds while the lightening takes upto 4 to 5 minutes.
9) Lens Darkness
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The colour & the degree of darkness do not tell you anything about the ability to block the UV light. People with certain eye diseases need to protect their eye when they go outside irrespective of how briefly.
10)Cataract Surgery Patients
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During cataract surgery procedure the eyes natural lens is removed leaving the eye more vulnerable to UV light. During the surgery the natural lens is usally replaced with intraocular lens. If the IOL or intraocular lens is not UV absorbent type you will need to wear sunglasses & a hat for added protection.
11) How to judge the quality of Non Prescription Sunglasses
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To judge the quality of non prescription sunglasses look at something as a rectangular pattern such as the floor tile . Move the glasses slowly from side to side & then up & down. If the lines stay straight then the lenses are fine & if the lines appear wavy specially in the centre of the lens then the lenses are not perfect.
If you need any further information on speciall types of sunglasses or prescription sunglasses you should visit your opthalmologist.
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