When you look at your prescription for glasses, you will see numbers listed under the headings of OS and OD. They are Latin abbreviations; OS (oculus sinister) means the left eye and OD (oculus dextrus) means the right eye. Occasionally you will see a notation for OU, which means something involving both eyes. In general, the further away from zero the number on your prescription, the worse your eyesight and the more vision correction you need.

A plus sign in front of the number means you are farsighted (difficulty seeing up close) and a minus sign means you are nearsighted (difficulty seeing far away).

The numbers represent diopters, the unit used to measure the correction, or focusing power, of the lens your eye requires.

For people who have astigmatism (blurring due to an irregularly shaped cornea) there will be three numbers in your prescription. The general form for writing these numbers is S x C x Axis

The S refers to the "spherical" portion of the prescription, which is the degree of nearsightedness or farsightedness discussed above.

The C refers to the "cylinder" or astigmatism, and can be a negative or a positive number. It measures in diopters the degree of astigmatism that you have. The bigger this number, the more astigmatism you have.

The Axis is a number anywhere between 0 and 180 degrees. It reveals the orientation of the astigmatism It is not enough to specify how much astigmatism there is; you have to know where the difference in curvature is taking place.

For those who have a prescription of more than + or - 2.50, we will need the distance in millimeters between the center of your two eyes. It is easy to obtain this, just asks a friend to hold a millimeter rule just above the center of your eyes and measure the distance between the outside edge of one pupil to the inside edge of the other pupil.

Typical adult's Pupillary Distance measurements (PDs) are 58 to 70

Typical children's Pupillary Distance measurements (PDs) are 41 to 58

Both of you should be at the same height approximately, sat opposite each other. The measurer holds the ruler in their left hand across the bridge of your nose and closes their LEFT eye to avoid any parallax error. With their RIGHT eye open, they then first line up the ruler with outside edge of your left pupil. Then without moving the ruler they close their RIGHT eye and with their LEFT eye read off the measurement to the inside edge of RIGHT pupil. (See diagram)

You should fix on an object. E.g. the open eye of the measurer. This should ideally be about 40 centimeters, 16 inch (400mm) away.

This measurement will ensure the accuracy of your spectacle lenses when supplied.

A typical measurement will usually be somewhere between 55mm and 72mm

Most children's school rulers have inches on one side and centimeters on the other. Just multiply by 10 as in the example above.

Certain frame shapes will balance and complement your facial features. But others can result in an unattractive, awkward look. The following guidelines will help you choose the most flattering frame shape for your facial features.

General Frame Selection Guidelines

Though frame styles frequently change, these general guidelines for selecting frames always apply:

Eye position

Regardless of the shape of the frame, your eyes should be centered within the lens openings of the frame.

Width

The frame should be wide enough so there is just slight clearance between the frame temples and the sides of your head.

Brow

The top of the frame Eyewire should follow (but not cross) your brow line, and should not be noticeably higher or lower than the brow line. If you have thick eyebrows, consider a thicker, darker frame for balance.

Proportion

The size and weight of your eyeglasses should be in proportion to your body size and weight. If you have a slim or petite build, choose thinner, more delicate frames for a balanced look.

Lenses

Thinner, lighter, reflection-free lenses are always the best choice. Choose high index plastic lenses with anti-reflective (AR) coating for the most flattering appearance. If you have a bifocal prescription, choose Progressive lenses to avoid old-fashioned bifocal lines.

Determining Your Face Shape

There are seven basic face shapes: oval, diamond, round, square, triangle, inverted triangle, and oblong.

Follow these simple steps to determine your face shape:

1. Have someone take a passport-style photograph of you.

2. Draw six dots on the outline of your face in the picture:

• Two on each side of your forehead

• Two at your cheekbones (near your eyes)

• Two at your jaw line (at the level of your mouth).

3. Analyze the width of each pair of dots to determine your face shape.

Possible Face Shapes

Oval

• Dots on cheekbones are farthest apart.

• Dots on forehead and jaw are about equally spaced, slightly closer together.

• Face is longer than it is wide.

Diamond

• Similar to oval, but dots on forehead and jaw are closer together.

• Face is more angular, with a smaller forehead and chin than an oval face.

Round

• Dots on cheekbones are farthest apart.

• Dots on forehead and jaw are slightly closer together.

• Width and height are nearly equal.

• Face has a full appearance with few angles.

Square

• The distance between all three pairs of dots is roughly equal.

• Width and height of face are nearly equal.

• Jaw line has an angular or square appearance.

Triangle

• Dots on the jaw are farthest apart.

• Dots on forehead are closest together.

• Face has a narrow forehead and is wider at the cheeks and jaw line.

Inverted triangle

• Dots on the forehead are farthest apart.

• Dots on the jaw are closest together.

• Cheekbones are high.

• Face has a broad forehead and gradually narrows to the chin.

Oblong

• Distances between all three pairs of dots are roughly equal.

• Similar to square, but face is noticeably longer than it is wide.

Once you have determined your face shape, continue below to learn which frame shapes will best complement your facial features.

Best Frame Shapes For Your Face

In general, the most attractive frames gently counterbalance your face shape and features.

For example, if you have a round face, frames with angular shapes will counterbalance the roundness of your face for a more attractive look. Round frames will do the opposite - they will exaggerate the roundness of your face (and possibly make your head look like a basketball - sorry).

For an Oval Face

• An oval face gives you the greatest freedom in selecting a frame shape - you can wear nearly any frame style.

• Select a frame that is just slightly wider than the broadest part of your face.

• Keep the size and weight of the frame proportional to your body size and weight.

For a Diamond-Shaped Face

• The goal is to add width to your forehead and jaw, and make your cheekbones appear narrower.

• Choose softly curved frames that are no wider than your cheekbones.

• Square frames or frames with a straight top and rounded bottom are also good choices.

• Avoid decorative temples, which will exaggerate the width of your cheekbones.

For a Round Face

• The goal is to make your face appear longer and thinner.

• Choose low, wide rectangles and other short geometric shapes.

• Frames with hinges located above eye level can help lengthen the face.

• A Bridge located near the top of the frame can also add length.

For a Square Face

• The goal is to make your face appear longer, with softer curves.

• Choose oval or slightly angular frame styles with curved corners.

• Frames with hinges located above eye level can help lengthen the face.

• A bridge located near the top of the frame can also add length.

For a Triangle-Shaped Face

• The goal is to add width to your forehead and make your jaw line appear softer and narrower.

• Choose frame styles that angle up and outward at the top corners.

• For women, cat's-eye shapes are flattering.

• For men, square frames are attractive.

• Frames with rimless bottoms are also good for both men and women.

• Frames with temples and bridge located near the top of the frame are best.

For an Inverted Triangle Face

• The goal is to make your forehead looker narrower and add width to your jaw line.

• Choose frame styles that angle outward at the bottom.

• Aviator and "bow tie" shapes are good choices.

• Rectangular styles are also good.

• Frames with temples and bridge located near the middle of the frame help balance facial features.

For an Oblong-Shaped Face

• The goal is to make your face appear wider and shorter.

• Choose round styles or geometric shapes with generous vertical dimensions.

• Decorative temples or temples with contrasting colors can help add width.

• Frames with temples and bridge located near the middle of the frame are best.

All frames have standardized size measurements to help manufacturers and optical personnel fit them appropriately for consumers.

The first number, represents the size of the lenses.

The second number is the bridge size, which ensures that the frame fits your nose.

The third number, is the temple length — temples are the parts that hook over the ears

Size numbers look something like this

50-19-140

All measurements are in millimeters

If the numbers are worn off your old frame, you can use a ruler to measure end to end,as shown below. Measure across the front of the frame from it's widest points - where the temples attach.

Once you have your prescription, PD and frame size you can really have fun.

PLEASE NOTE IF YOU HAVE A COMPLICATED Rx and BIFOCALS SEEK A PROFESSIONAL.

Frames Direct has a virtual eyeglass try-on that is amazing. Your can upload a photo of yourself and see what you look like in thousands of frames. I used this for my son and he loves his glasses.

Lens Coatings

• Anti-reflective coating. If glare becomes a problem, consider an anti-reflective coating applied to new eyeglasses. Anti-reflective coating will reduce reflections, decrease halos around light, and create a nicer cosmetic appearance.
• Scratch-resistant coating and ultraviolet coating. Most eyeglass lenses today have built-in scratch resistant coatings and ultraviolet protection.
• Tinted lenses. Sometimes a light or dark hint of color on the eyeglass lens can be beneficial to aid in vision. For example, a yellow tint may increase contrast and a gray tint may not alter color perception with sunglasses. A light tint can also hide the signs of aging around the eyes.
• Mirror coatings. If you are looking for a purely cosmetic lens that allows the eyes to be hidden from view, then this is the coating for you. Mirror coatings come in a variety of colors such as silver, gold, and blue.