This is a summary of the relevant information I have collected, and any suggestions from MFA will be welcomed and added to the guide accordingly.

If you wear glasses, the frames you choose can make or break your appearance. The fact that they are actually worn on your face, and thus are conspicuously visible to all those with whom you interact, means that your glasses are arguably the single most important item in your wardrobe. That being said, don’t skimp on your frames – you should be perfectly satisfied with the pair your choose, as they will define your look.

Shape: The first thing you should consider when buying a new pair of glasses is the shape of your face. Just about every face will fall into one of the following categories: oval, square, circle, and heart 

Instead of matching your face 

, the shape of your frames should actually contrast your face shape. I tried my best to avoid quoting directly, but Harrison Fjord(written by a fellow redditor), says it much better than I possibly can:

• Oval 
  An oval face is longer than it is wide – so a good pair of glasses will help broaden the face. Oval faces look best with rectangular frames, as they make the face appear wider. A modern, half-rimmed pair will do this most effectively. People with oval face should avoid circular glasses, as they will diminish facial definition.

• Square 
  People with square faces already have a strongly-defined facial shape, so their glasses should be either oval or round. Thicker frames work well for this face shape as it helps to give shape to the cheekbones.

• Circle 
  People with round faces should choose glasses that give their face structure and definition. Avoid thick-framed glasses, as well as glasses with a circular shape – these will make your face look large and undefined. Instead, opt for either angular or rectangular glasses with narrow wire frames.

• Heart 
  Heart-shaped faces already have a lot of natural definition, so glasses should be chosen to help bring out the jaw line and cheekbones. This can be achieved by using oval or square-shaped glasses with thick, geometric frames.

Fit: Once you’ve determined which frame shapes complement your face, take a look at how the glasses fit on your head. In general, the best policy is to try a bunch of glasses on in person at a local optician to get a feel for which measurements are right for you, but some online glasses retailers like Warby Parker provide free home try-ons. (Virtual mirror try-ons can be helpful in determining which shapes you like, but are inaccurate with regard to sizing.)

• Your pupils should be centered as much as possible within each lens. This is important not only for aesthetic purposes, but for vision considerations as well; additionally, a centered pupil reduces the necessary overall thickness of the lens. (Important: make sure you ask your optometrist for your pupillary distance (PD) measurement when you get your prescription, as it is often left out!)
• The frames should be approximately as wide as your face. More specifically, the outer edges of the frames should fall somewhere in between your cheekbones and the very sides of your face, looking straight on.

With a measurement like 52-18-140, the numbers refer to lens width, bridge width, and temple length, respectively. Diagram 

(Correction: the temple is actually measured from hinge to tip, not front of frame to tip.)Color: If you search the Interwebs, you will find a lot of conflicting information on how to choose the right color frames for your complexion, so here is my opinion: The color of your frames should bring out your best facial feature. For some people this is their hair, and for others it may be their eyes. Black frames look good if you have black hair, and shades of tortoise similar to your hair color if you are on the brown to blond spectrum also work well. If you have blue eyes, you might consider midnight blue frames to bring out their color. When in doubt though, black and tortoise are classic and timeless colors with which you can’t go wrong.

Lenses: I recommend getting anti-reflective/anti-glare coating on your lenses. This will prevent your eyes from being obscured by reflected light (especially when flash photography is involved) and assist with night driving. If you spend a lot of time looking at a computer screen (and I know you do, fellow redditors) the coating will also help to reduce eye strain.

When you buy glasses, you have the option of choosing conventional (1.50 refractive index) or high-index (1.60+) lenses. For our purposes, these numbers mostly affect the thickness of the lens relative to its power, with higher-index lenses being thinner. Your prescription (sum of sphere + cylinder) will usually determine the type of lens you require, as follows:

• CR-39 (standard plastic): 0.00 to -2.00
• Polycarbonate: -2.00 to -4.00
• Trivex: -2.00 to -4.00 (to be used with rimless glasses)
• Hi Index 1.60: -4.00 to -5.00
• Hi Index 1.67: -6.00 to -8.00
• Hi Index 1.74: -8.00+

Please, just say no to transition lenses (that goes for clip-on sunglasses as well)! Regardless of whether they are useful or not, they will make you look dorky. Invest in a good pair of prescription sunglasses instead.

Sunglasses: Aviators and Wayfarers are classic styles that should work for most people. Other classics that are less overplayed include Clubmasters (modeled after Shuron Escapades) and Persol 649/714. Save sportier styles like Oakley wraparounds for running/biking/beach volleyball, etc. Avoid mirrored 

and light smoke gradient 

lenses (note: this seems to be a controversial opinion so take it with a grain of salt, but they don’t appeal to me). Polarized lenses are recommended whenever possible (more on that here reply from optician).Most frames can have prescription sunglasses lenses put into them, but if I were in the market for prescription sunglasses (and I am!) I would wait for Warby Parker’s Rx Sunwear to be released in late August 2011 (Rx lenses will bring the cost to ~$140). Websites I’ve seen mentioned on MFA as sources of decent cheap sunglasses include 80’s Purple and Knockaround.

Brands:

A non-comprehensive list of quality brands to consider, taken mostly from the Basic Wardrobe guide:

• Oliver Peoples
• Cutler & Gross
• Persol
• Barton Perreira
• Ray-Ban
• Mosley Tribes
• Paul Smith
• SALT Optics
• Selima Optique
• Robert Marc
• 2.5 Eyephorics
• Alain Mikli
• Mykita
• IC! Berlin
• Kio Yamato
• Shuron
• Moscot

Some online retailers:

• Warby Parker – MFA’s darling, as they sell decent quality glasses for $95, provide great customer service, donate one pair for every pair they sell, and offer the aforementioned free home try-ons. Unfortunately their sizes are limited and favor wider faces.
• Spex Club
• Classic Specs
• Eyefly
• Zenni Optical – Seriously cheap glasses. I’d probably only buy these as a secondary beater pair at best.

source: http://www.reddit.com/r/malefashionadvice/comments/ilst4/a_guide_to_glasses_and_a_word_on_sunglasses/