PD or Pupil Distance is the distance between the pupil of each eye. Usually it is not provided by your optometrist and taken by the optician when you place order for eyeglasses. We highly recommend that you get this PD value when you have your eye examination from the Optometrist and keep it safe. 
This value is measured in mm (MILLIMETER) which is used to align the center of the lenses with the pupil. The PD is very important measurement specially for strong prescription. Incorrect PD may result in eye strain or headache.

If you do not have the PD on your prescription, you can measure it as shown below:
Step - 1 Place a simple mm ruler on your nose so that the starting point of the ruler is exactly at your left or right eye pupil. Keep the scale straight 
Step - 2 Make Sure to look straight 
Step - 3 Stand in front of the mirror or ask one of your friend to read the scale to measure the distance between the pupils. 
Step - 4 Repeat this at least three times to be more accurate. 

In most of the cases, PD value ranges between 57 mm to 65 mm with most common 63 mm 
Most optometrists/ophthalmologists do not routinely write this measurement on their prescription because they assume it will be measured by the optician who is making your lenses.
You may ask your or any local optician/optometrist to measure your PD and send it by return e-mail or call us with it.

The material from which a lens is made has little impact on the corrective power of the lens, but it can have a major impact on lifestyle. Learn about the different lens material options and make the best choice for your next pair of eyeglasses.

Materials

CR-39 Plastic

For many years, CR-39 plastic has been the standard lens material for eyeglasses. (The "CR-39" is the name given to the resin formulation by the original manufacturer.) CR-39 plastic lenses are half the weight of glass lenses, have better ultraviolet (UV) light protection, are less prone to shattering, and can be tinted more easily. And with an added scratch-resistant coating, they are nearly as resistant to scratches as glass lenses. CR-39 plastic lenses are about the same thickness as glass lenses. IMPORTANT. CR 39 lenses are not suitable for rimless and semi rimless frames . RANGE SPH +/-4 Cyl +/ -2 ,Cyl over  2  CUSTOM MADE LENSES

Polycarbonate lenses

Polycarbonate was one of the first "thinner, lighter" lens materials. Polycarbonate lenses are both thinner and lighter than CR-39 plastic lenses. But the most important feature of polycarbonate lenses is their impact resistance. Polycarbonate lenses are 10 times more impact-resistant than glass or regular plastic lenses, making them the preferred choice for safety glasses and eyewear for children and adults who desire lightweight, protective lenses.  Polycarbonate lenses are most suitable for semi-rimless and rimless frames. RANGE  SPH +/-6 CYL +/-2 Cyl over  2  CUSTOM MADE LENSES

High index plastic lenses

High index plastic is a term used to describe a variety of plastic lens materials that are thinner and lighter than regular CR-39 plastic. For a given prescription power and lens design, the factor that determines lens thickness is the index of refraction (also called refractive index) of the lens material. Materials with a higher refractive index bend light more efficiently than materials with a lower index of refraction. CR-39 plastic lenses have a refractive index of 1.498. Any lens material that has a refractive index higher than glass (1.523) is considered a high index material.

Today's high index plastic lenses sold in the United States range in refractive index from 1.54 to 1.74. One of the most popular high index lens materials has a refractive index of 1.67. Lenses of this material are about 50% thinner than lenses made of standard CR-39 plastic.

Your professional optician will be able to help you determine which high index lens material is best for your prescription and budget. 

RANGE  High index 1.67   SPH -3 to  -8 Cyl +/-2. All positive power  prescription have to  be CUSTOM MADE. Cyl over  2  CUSTOM MADE LENSES

RANGE  High index 1.74   SPH -3 to  -10 Cyl +/-2. All positive power  prescription have to  be CUSTOM MADE. Cyl over  2  CUSTOM MADE LENSES

Coatings

Anti-reflective Coatings:

Anti-reflective coating is applied to eyeglass lenses to reduce the amount of internal and external reflections on a lens. This increases the amount of light transmitted through the lens, which improves quality of vision. Anti-reflective coating also decreases unwanted glare and halos at nighttime. It also makes the lenses appear somewhat invisible and very thin. While everyone could benefit from an anti-reflective coating, it is especially beneficial for people with high prescriptions, people who have a decrease in vision at night, and professions in which cosmetic appearance is important.

Scratch-Resistant Coatings:

Scratch-resistant coatings are applied to the front and back of lenses in the manufacturing process. Although it is important to realize that no lens is scratch-proof, this special coating does make lenses harder to scratch when dropped or rubbed against a hard surface. While most lenses are made with scratch-resistant coating, sometimes the term scratch-resistant coating indicates a type of “scratch warranty.” These warranties guarantee against scratches, ensuring the lenses will be remade if a scratch does occur. Be sure to clarify any warranty of this nature.

Ultraviolet Treatments:

Ultraviolet treatment is applied to lenses to protect against harmful UV sunrays that can accelerate the development of cataracts and macular degeneration. It is extremely important to protect eyes from the damaging effects of the sun. UV treatment is easy to apply to lenses and is often included with the purchase of eyeglasses.

Polarized Lenses:

Polarized lenses are usually used to make sunglasses. They are available most commonly in grey or brown tint but many other colors are available. Vertically polarized lenses decrease bright glare and reflections by blocking horizontal polarized reflected light. Polarized lenses have been used by fishermen for years to better deal with bright light being reflected off water and to see deeper into the water.

Crizal is the brand name of optical lens coatings manufactured by the French corporation Essilor. Its coatings were created to allow greater transparency in lenses made of certain plastics by repelling rain and being anti-reflective, smudge-resistant, dust-resistant, and scratch-resistant.

Crizal lenses are unlike any other pair because you can:

1. See Better Crizal lenses mean safer, more comfortable nighttime driving by reducing glare from headlights, taillights and street lights. Studies have shown that visual acuity is improved by decreasing glare and scratches on lenses. Contrast is also improved while driving by 20% and recovery time is faster by 5 seconds. Regular uncoated lenses can block up to 18% of light. Crizal coated lenses transmit up to 99%! As a rule of thumb, the lens materials or lenses for higher prescriptions will reflect light more and anti reflection coating is necessary.
   Most Crizal lenses do 3 things to make you see better:
   1. Eliminates Glare by using precise thin coats to cancel out internal reflections within the lens.
   2. Add scratch resistance by fusing silica (glass) and then zirconium (artificial diamond) to the lens for an extra tough finish.
   3. Reduces smudges and static and repel water through additional coatings.
2. Look Better Crizal lenses are clean, clear, and glare-free so they're virtually invisible to those around you. People see you instead of your glasses. They have an extra hard scratch coating made of artificial diamond (zirconium) you don't need to look through scratched lenses.
3. Feel Better Crizal lenses mean fewer headaches and less eye fatigue caused by reflections from computer screens and daytime lights. Studies show computer users are 3 times more satisfied with their lenses with anti-reflection coating when used on a computer.