The lens modulus (also simply referred to as modulus) measures the degree of flexibility of a contact lens. As such it has an impact on how well a lens will 'snap back' into its original position when being stretched or when the lens is inside out. A higher modulus value (measured in MPA) stands for higher stiffness compared to a lens with a lower modulus.  As a consumer you might notice a difference in the handling of a lens with a higher modulus as it's less likely that the lens will flip inside out.  It also translates into easier handling when applying or removing the lens. However on the downside you might feel the lens on your eye due to possible edge fluting or standoff.

Most Acuvue lenses either come with an 1-2-3 inside-out mark or an AV inside-out mark.  This helps you to determine whether or not your lens is inside out. How it works:

Put your Acuvue lens on your finger and look at the lens from the side. You should see the 1-2-3 written correctly. If the lens is inside out, the 1-2-3 will appear reversed.

The AV mark works in a similar way: If you place your lens on your finger and look at it from the side, you should be able to see the AV written correctly. If the lens is inside out, the AV will appear reversed.

Hydraclear is a proprietary technology that was developed by Vistakon and has been applied to Acuvue Oasys, Acuvue Advance, Acuvue Advance for Astigmatism and Acuvue Oasys for Astigmatism. Unique Silicone Polymers bind long-chain water loving molecules (also referred to as the wetting agent) resulting in very smooth and more wettable contact lenses.

Replace your lenses as scheduled. Take the hassle out of replacing your contact lenses and write your fresh lens date on each new lens package for an easy and convenient reminder.

Have an eye exam every year: It is the simplest and most important thing you can do for your eyes. Plus, your eye care professional may be able to recommend different solution products or modify your wear schedule to simplify your care routine and maximize your comfort in contact lenses.

Wear the right lenses to fit your needs, like the ultra comfortable Acuvue Oasys, Acuvue Oasys for Astigmatism or - if you prefer a daily-wear lens - try the brand new 1 Day Acuvue TruEye.

The FTC (Federal Trade Commission) has issued clearly defined rules for prescribing contact lenses. This ensures that consumers can shop around for contact lenses and do NOT have to buy from the prescribing eye doctor or eye care practitioner.  This created the foundation for online stores to do business and sell contact lenses over the internet. The prescriber has to give you a copy of the contact lens prescription at the end of the contact lens fitting process – even if you don't ask for it. A valid prescription includes all required prescription parameters as well as a expiration date - latter one has to be one year unless the doctor has a medical reason to shorten the expiration period. In addition prescribers cannot require you to buy contact lenses, pay additional fees (besides the fees for the eye exam and the fitting process) or sign a waiver or release in exchange for a copy of the contact lens prescription.

A prescription should contain the following items:

• Your name

• Date of Examination

• Date patient receives prescription after a contact lens fitting (issue date) and expiration date of prescription

• Name, address, phone number and fax number of prescriber

• Power

• Material and/or manufacturer of the prescribed contact lens

• Base curve or appropriate designation of the prescribed contact lens

• Diameter, when appropriate, of the prescribed contact lens

• For a private label contact lens, the name of the manufacturer, trade name of the private label brand, and if applicable, trade name of equivalent brand name

The rule was issued in July 2004.

For (online) sellers the main requirement is to ensure that the buyer has a valid prescription. This can be done by contacting the prescriber directly and getting prescription parameters and patient name confirmed. If the seller doesn't hear back from the prescriber within 8 business hours, the prescription is considered to be verified.

What does this mean to you, the consumer?  Well, this makes it quite easy for you to buy contact lenses online as you do no have to provide a copy (using fax or mail) of the prescription.  Instead the online store has to check with your eye doctor or your eye care professional directly.  This explains why you usually have to provide your eye doctor's address and/or phone number during the check out process.

LACREON™ is a technology that permanently embeds a water holding ingredient, similar to that found in natural tears. The ingredient is embedded into one of Vistakon's lens materials - etafilcon A - and available with the popular 1-Day Acuvue Moist lenses (by the way: this technology is not present in the standard 1-Day Acuvue lenses). The moisture is permanently kept in the lens, thus resulting in keeping the eyes feeling fresh and more comfortable all day long. In addition to this silky smooth cushion the reduced surface friction allows the eyelid to glide over the lens easily.

OS stands for 'Oculus Sinister' and is the latin phrase for 'Left Eye'. OD stands for 'Oculus Dexter' and means 'Right Eye'.  Your prescription parameters will usually refer to your right and left eye and - when ordering contact lenses - online stores will ask you to enter the prescription parameters accordingly.

In general contact lenses are broken down into high water content and low water content lenses.

High water content lenses are lenses with more than 50% water, whereas low water content lenses have less than 50% water. Contact lenses with a lower water content dehydrate less on the eye than do lenses with a high water content, so they could be better for people with dry eyes.

Contacts with a high water content have a higher oxygen permeability. Therefor they are more suitable for longer wear. However high water content doesn't always translate into a higher oxygen permeability (the Dk value) with hydrogels, except if they are silicone hydrogels. Silicone is responsible for the oxygen permeability, and silicone is water repelling, (also known as hydrophobic).

As a result silicone hydrogels might have a lower percentage of water but can have many times the Dk of traditional hydrogel materials.

High water content lenses come with additional challenges for the manufacturer (and patient): They are less stable and tend to leave more deposits in the lens. 

To summarize: If you have dry eyes, soft contact lenses with high water content can cause problems for you, since these absorb the natural supply of water (film of tears) of the eye like a "sponge". Silicone hydrogels are combining the advantages of lower water content lenses and high oxygen permeability.

The Dk value measures oxygen permeability, the Dk/t value measures oxygen transmissibility of a contact lens. Dk/t is calculated from the oxygen permeability (Dk) of the material and the thickness (t) of the contact lens. Usually the Dk/t value refers to a certain center thickness of a lens with a certain power, therefor making it easier to compare lenses.

In general, the higher these values are, the better is the oxygen permeability/transmissibility of the material. A high level of oxygen flow to the cornea is important as it improves wearing comfort and longer term tolerance (i.e. Acuvue Oasys lenses can be worn up to 6 consecutive days and night).

Base Curve (BC) is one of the main parameters of a contact lens and describes - in general - the shape of the contact lens measuring the radius of the sphere of the back side. The range usually goes from 8mm to 10mm. The Diameter (DIA) describes the size of the lens. During the fitting process your eye doctor will determine the base curve and the diameter that is right for you as it will ensure maximum wearing comfort and optimized vision correction.

Today, most contact lenses are colored with a visibility tint. This improves handling as the lenses are easier to find when you take them out of the container or when you drop them. The tint does not change your natural eye color. All Acuvue lenses are tinted except Acuvue 2 Colours and 1-Day Acuvue Define.

CT stands for 'Central Thickness' and measures the thickness of the contact lens in the center. The thickness depends on the power of the lens. As a consumer you do not need to know the CT value of your contact lenses when ordering or re-ordering your lenses.

Contact lenses with a lower water content might be better for you if you suffer from dye eyes. Lenses with a high water content can act like a 'sponge', causing the eyes to dry out even faster.  Dry eyes can also be a contraindication when wearing contact lenses so you should always consult your eye doctor or eye care professional.

Here are some general guidelines and tips for wearing and handling of your Acuvue contact lenses.

• Always wash and rinse your hands before touching any contact lens.

• Also you should make sure make sure your hands are dry.

• When using a lens care solution, make sure that the solution is fresh and not past it's expiry date.

• Use the recommended system of lens care, chemical (not heat), and carefully follow instructions on solution labeling.

• Different solutions cannot always be used together, and not all solutions are safe for use with all lenses.

• Do not alternate or mix lens care systems unless indicated on solution labeling.

• Always remove, clean, rinse and disinfect your contact lenses according to the schedule prescribed by your Eye Care Professional. The use of any cleaning solution does not substitute for disinfection.

• Do not use saliva or anything other than the recommended solutions for lubricating or re-wetting your lenses.

• Don't put lenses in your mouth!

• Throw away your lenses after the recommended wearing period (as prescribed by your Eye Care Professional)

• Never rinse your lenses in water from the tap. Not only you could loose your lens in the drain but - even more important - tap water contains many impurities that can contaminate or damage your lenses.

• Your Eye Care Professional should recommend a care system that is appropriate for your Contact Lens. Each lens care product contains specific directions for use and important safety information, which you should read and carefully follow.

  Note: Some solutions may have more than one function, which will be indicated on the label. Read the label on the solution bottle and follow instructions.

• Always clean one lens first (we recommend to always start with the same lens first to avoid mix-ups). Rinse the lens thoroughly with recommended saline or disinfecting solution to remove the cleaning solution, mucus and film from the lens surface. Follow the instructions provided in the cleaning solution labeling. Put that lens into the correct chamber of the lens storage case. Then repeat the procedure for the second lens.

• After cleaning, disinfect lenses using the system recommended by your Eye Care Professional and/or the lens manufacturer. Follow the instructions provided in the disinfection solution labeling.

• When you don't wear your lenses, keep them completely immersed in a recommended disinfecting solution.

• To store lenses, leave them in the closed/unopened case until ready to wear. If lenses are not to be used immediately following disinfection, you should consult the Package Insert or your Eye Care Professional for information on storage of your lenses.

Worldwide, there are 125 million contact-lens wearers and annual sales are $4.56 billion.

In the United States, there are 38 million wearers, annual sales of $1.9 billion, and continuing annual growth – 3 million new contact-lens wearers a year.

However, 3 million wearers drop out a year, while 10-15 per cent cease wear within two to three years (with the main problems being comfort or dryness – more than 50 per cent), but 30-50 per cent of drop-outs later return to contact lenses.

Narafilcon A is a new silicone hydrogel material being used in Johnson & Johnson's new daily disposable lens 1-Day Acuvue TruEye. With a Dk of 100 and a Dk/t of 118 it increases oxygen flow and allows the cornea to breathe naturally through the material.  As a result, lenses that are manufactured utilizing this material, promise better wearing comfort and fewer dry eyes.