When we get a prescription for refractive correction we start thinking about spectacles. Spectacles have become a very good means of correcting refractive error but sometimes we do want to break free from the glasses and enjoy our coffee without the fog, enjoy the rain without the blur & enjoy the dance floor without worrying about the glasses. There are various other options that we can choose if we are fed up with the spectacles. The very first option that I, as an Optometrist suggest to my patients is Contact Lenses. But before buying Contact Lenses we should always know about these wonderful inventions and the way to handle it.
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Should I Buy Contact Lenses Online?
We find a lot of online stores selling contact Lenses mostly yearly disposable these days but is it a right way to get your contact lenses? If I was an owner of an online store I might have said, “Contact Lenses are just like spectacles you can buy anywhere you want if you have the prescription” but being an Optometrist I know the risk of buying contact lenses without proper fitting and evaluation of your eye health conditions. Buying your contact lenses is fine if the seller can arrange an eye examination from an eye health care practitioner who is authorized to dispense contact lenses but it can lead to serious complications if you buy those contact lenses without consulting with a contact lens practitioner.
How long can I wear a Contact Lens?
If you can understand how long you can stay underwater without oxygen then you will get your answer of how long a contact lens can be worn. This is just an analogy but when the Contact lens sits in front of your eye (the Cornea ), the time that it can be worn depends upon how much oxygen can be passed into the cornea through the contact lens. This is determined by the property of the contact lens material called Oxygen permeability (DK). When contact lenses are made with the material having certain DK the amount of oxygen that will go through that contact lens will now be dependent upon the thickness of the contact lens which will be termed as oxygen transmissibility (Dk/t). So every material with which the contact lens is made has a DK value.
Now the actual question of how long a contact lens can be worn will be dependent upon the Dk/t value of the lens.
For Daily Wear modality lenses (the lens that is worn on the day for 10 to 14 hours ), the Dk/t value according to Holden & Mertz criteria is 24 x 10-9
For Extended Wear Modality lenses (the lens that is worn overnight while sleeping ) the DK/t value according to Holden & Mertz criteria is 87 x 10-9
Another thing to know in order to understand how long you can wear a contact lens is to know the replacement schedule of the contact lens. This means when you should dispose of your lenses.
Types
There is currently four contact lens replacement schedule:
1. Daily Disposable Contact Lens
2. Biweekly Disposable Contact Lens
3. Monthly Disposable Contact Lens
4. Yearly Disposable Contact Lens
1. Daily Disposable (Replacement) Contact Lens
The daily disposable lenses are worn and disposed of every day. So you can wear a fresh pair of lenses every day. This type of contact lens usually come in a 30 or 32 piece lens in a box. Some of the Contact lenses also come in a small eco pack of 4 to 8 piece lens in a box. These lenses are the most recommended contact lens to wear because of very less chance of infections and other complications because every day the lenses are disposed and a new one is worn. Because these lenses are daily disposable you will not need any lens care solution to clean these every day. Simply dispose of it and use a new pair of lens. Do Not wear the same daily disposable lenses for more than 1 day.
2. The biweekly disposable (Replacement) lenses
These are worn and disposed of in every two weeks. That means you store these lenses in a lens storing case for 2 weeks and get a new pair after 2 weeks. The lenses are worn each day for 8 to 14 hours depending upon the contact lens material and removed and stored in a lens case after cleaning. The lenses should be cleaned with a lens care solution every day before wearing and after removing during the 2 weeks period time of wearing. These lenses will come in a 6 piece lens pack. That means when you buy one box of biweekly disposable lens you will have 6 lenses to wear and each lens can be worn for 2 weeks. Do Not wear the same biweekly disposable lenses for more than 2 weeks.
3. The Monthly Disposable (Replacement) Lenses
The monthly disposable lenses are worn and disposed of in every month. Similar to biweekly you should clean these lenses every day with the lens care solution for the period of one month and dispose of it at the end of the month and wear a new one. The lenses are worn each day for 8 to 14 hours depending upon the contact lens material and removed and stored in a lens case after cleaning. These lenses will also come in a 6 piece lens pack and you can wear each lens for 1 month. Do not wear the same monthly disposable lenses for more than 1 month.
4. Yearly wear Contact Lenses
Yearly / Conventional disposable lenses are not prescribed in western and developed countries nowadays because of the high chances of infection and complications than other disposable lenses. They usually come in a pair and the same lens is worn for a long time. Similar to monthly and biweekly these lenses should be cleaned every day with a multi-purpose lens care solution. These lenses are not usually recommended to wear nowadays.
In short, while buying a contact lens you should know which replacement schedule contact lens you need ( daily, biweekly, monthly or yearly) and when to dispose of it. Before buying any lenses make sure you have a detailed eye examination and after buying the lenses make sure you are taught how to correctly insert and remove the lenses with proper maintenance and lens handling.
Summary
Contact Lenses are a great alternative for your spectacles. There are daily disposables, biweekly disposables, monthly disposables and yearly disposables contact lens currently in the market. Make sure to choose the right one with the help of your Optometrist. Don’t buy any contact lens without consulting with an Optometrist or Contact lens practitioners and make sure you are taught the proper way of lens care and maintenance. A good Optometrist will always help you to make you comfortable with your contact lens.
(Only Soft Contact Lens is discussed in this article. There are many other contact lenses which are used as speciality contact lenses )
Author:
Sakar Subedi
Optometrist & OrthoK practitioner
