Some prescription spectacle lens extras are:
• Scratch Resistant/Hard Coating
• Anti-Reflective Coating
• Transitions
• Tinting
• Polarisation
• UV Filters

A scratch resistant/hard coating usually comes as standard on most plastic spectacle lenses these days so it isn’t really an add on anymore but in some cases, lenses may still be supplied to the consumer without a scratch resistant/hard coating.  The coating is used to protect plastic lenses from scratches by forming a protective layer on both sides of the lens.  A plastic lens with a scratch resistant/hard coating will still scratch if it is dropped or continuously put down on the desk the wrong way (with the lenses touching the desk) but it will resist more scratches than an uncoated lens and will last much longer.

An anti-reflective coating is used to improve the clarity of an optical lens by substantially reducing reflections and therefore allowing more light to transmit through the lens.  An uncoated lens usually reflect approximately 8%-13% of light depending on the prescription, the shape of the lens and the lens material.  High index lens materials will reflect more light than standard CR39 1.5 lenses so most high index lenses will come with an anti-reflective coating as standard.  An anti-reflective lens may reduce reflections to as little as 0.1% depending on the shape of the lenses and the lens material.  An anti-reflective coating is made of up many layers including a scratch resistant base coating followed by multiple layers of anti-reflective layers which are matched to eliminate one specific wavelength of light and also a hydrophobic water and grease repellant layer.  An anti-reflective coating cuts down reflections from artificial lights so this coating is great for indoor use including working with computers and under fluorescent lighting.  It is also recommended for night time driving to stop annoying reflections interfering with the vision of the wearer.  This type of coating needs to be cleaned with a micro-fibre cloth.  It can also be damaged by heat so lenses with this coating must not be washed with hot water or left in a hot car in the middle of summer!

Transitions (photochromic) lenses are lenses with a variable tint.  When exposed to UV light, transitions lenses will go from clear to dark (from clear glasses to sunglasses).  Transitions lenses are clear indoors and automatically adjust their tint levels to suit changing light conditions.  Transitions block 100% of UVA and UVB harmful light.  Transitions lenses will only work properly when exposed to direct sunlight.  If you are in a car, they won’t work as the car windscreen will absorb the UV light.  Transitions lenses work best when combined with an anti-reflective coating and are available in most types of lenses including single vision in standard, mid and high index and also bifocals and progressive lenses.

Most plastic lens materials can be tinted permanently.  A standard clear lens will be dipped into a dye so that it absorbs the colour.  Lenses can be tinted almost any colour but most commonly sunglasses will be tinted either grey, brown or G15 (Greenish Grey).  Tints cannot be added to lenses with anti-reflective coatings.  If you want to tint a lens and have an anti-reflective coating, this must be done by a lens laboratory as the lenses will need to be tinted before the anti-reflective coating is added.

Polarised lenses look like tinted lenses but they have a special polarised film/filter which is laminated to a lens to stop reflected glare.  Polarised lenses are used to block horizontal glare which is reflected from horizontal surfaces such as water, the pavement or the dash or bonnet of a car.  The laminated film is made of up tiny stripes side by side which are extremely close together and are so small that they won't be visible to the naked eye.  These stripes will be fitted to the sunglass frame vertically and will only allow vertically polarised light to enter the eyes of the wearer.  The horizontal glare/reflections will be eliminated as they cannot enter a lens with a vertically polarised filter.  If the wearer was to tilt their to the side, the lenses won't stop the horizontal glare as they'll be sitting off axis and will allow the bright horizontal glare the pass through the lenses.

A UV (ultra-violet) filter can be added to lenses to block 100% of harmful UV rays to protect the eyes.  Most good quality lenses already have full UV protection but some cheaper lenses don’t offer full protection.  A UV filter is recommended on any lenses that don’t come with it as standard.  It can be added for a small extra cost.