There are currently many different types of contacts ranging from material type, manufacturer, wear schedule, and more.
What contact lenses have in common is that they require yearly examinations to get updated prescriptions—whether the prescription has changed or not. This means insurances require another co-pay, which can be quite frustrating to patients.
As optometrists, we often hear questions such as why are yearly exams so important? Is it all about money? My prescription has not changed, why am I getting charged more?
These questions are valid and completely understandable. This article is aimed at helping you to understand the higher risks associated with contact lenses and why yearly examinations are so important for contact lens wearers.
Risks Associated with Contact Lens Wear
Anytime we put something into the eyes, we increase the risk for damage and infection. While contact lenses are generally safe with proper wear and care, there are several risks associated with wear including decreased oxygen transmissibility, dryness, and accumulation of debris.
The eye, especially the cornea (outermost layer of the eye), is the only part of the body directly exposed to the elements without a protective layer such as the skin.
The eyelids and lashes are the skin protective coat for the eyes, but in order to see the lids must be open. This makes the eye a little more susceptible to risks that may be miniscule in terms of the rest of the body.
Decreased Oxygen Transmissibility
Contact lenses are made from specialized plastics—most commonly hydrogel or silicone hydrogel.
The material contact lenses are made of determines how much oxygen is transmitted through them. It also determines how thick or thin the lens itself is.
A deceased amount of oxygen reaching the cornea can cause irritation and vascular changes within the eye itself. The front most structure of the eye, the cornea, obtains almost all of its oxygen from the atmosphere when the eye is open.
Therefore, placing a plastic lens on top of the cornea will limit how much oxygen actually reaches the cornea. Oxygen is needed for proper nutrition and tissue survival.
When a patient’s eye does not receive enough oxygen, it can undergo hypoxic (lack of oxygen) conditions resulting in growth of new abnormal blood vessels or death of corneal tissue.
Anytime we have abnormal blood vessel growth in the eye, we run the risk of it obstructing vision. These changes are often permanent, meaning once blood vessels grow and decrease vision they cannot be removed.
Oxygen transmissibility is determined by a value called the “Dk” value. A higher Dk value means more oxygen can pass through the contact lens to reach the cornea.
Hydrogel lenses tend to have a lower Dk value in comparison to silicone hydrogel lenses. However, hypoxia can occur with any contact lens if it is worn too much.
Generally speaking, hydrogel lenses tend to be a little thinner and are a great option for individuals with a silicone allergy. Many hydrogel lenses are 1-day disposable lenses. Popular brands include 1-Day Acuvue Moist lenses, Dailies AquaComfort Plus lenses, BioTrue ONEday lenses, and Proclear lenses.
Silicone hydrogel lenses tend to be a little more comfortable and allow for longer wear periods before getting dried out. Therefore, most 2-week or 1 month lenses are made from silicone hydrogel. Popular brands include Biofinity 1 month lenses, Acuvue Oasys 2 week lenses, Air Optix 1 month lenses, and Precision 1 and Dailies Total One 1-day disposable contact lenses.
Contact Lenses Can Cause Dryness
When the eye is dry it can cause feelings of dryness, burning, itching, excess tearing, light sensitivity, grittiness, irritation, etc. as well as create blurry vision. This is quite uncomfortable and is actually one of the top reasons people stop wearing contact lenses.
There are two major factors that play into contact lens induced dry eye, also known as evaporative dry eye.
The first of the two findings is a decreased blink rate–it is a very common finding that individuals who wear contact lenses tend to blink less frequently than individuals who do not wear contacts.
We need to blink to refresh our tears and smooth out our tear film to create clear stable vision.
Decreased blink rate can lead to the surface of the cornea drying out—resulting in the symptoms noted above.
This leads to the second major player in contact lens induced dry eye: contact lenses need to be kept moist in order to maintain their shape and stay properly “floating” on the cornea.
If the cornea is dry, the contact lens will be dry. The contact lens will need to be re-wetted and therefore when you blink or more tears are made, the lens will absorb most of them for itself. This leads to further drying of the cornea and a continuation of dry eye symptoms.
Dry eye disease is a problem that needs to be treated as soon as it starts, as it is often a progressive disease. While it may start as simple contact lens induced dry eye, it can progress into meibomian gland dysfunction in which the glands of the eye that produce tears become damaged.
Therefore, if a wearer is experiencing chronic dryness with their lenses, it is important to tell your eye doctor so he or she can switch lens type or help find another solution to decrease dryness with lens wear.
Accumulation of Debris
Contact lenses trap debris such as dust, dirt, lint, bacteria, and even natural proteins being expelled from the eye.
This occurs because the contact lens is placed on the eye so that it is exposed in two directions—it catches things trying to enter the eye as well as things exiting the eye.
The tear film of the eye rests in front of the cornea. It keeps the eye lubricated as well as catches debris.
The eyelids then close (via blinking) to push debris-laden tears down into the systemic drainage system where the body breaks down the rest.
Contact lenses can interfere with this process, as debris is more likely to be stuck onto the plastic contact lens rather than be pushed out through the normal system.
Debris is uncomfortable, can interfere with vision if large amounts accumulate, and can even cause infections if left to fester over time.
Depending on the type of debris and how large it is, it can scratch or scrape up the cornea. This can be a pinpoint spot of irregular corneal tissue, or it can be a significantly sized corneal defect often referred to as a corneal ulcer.
In contact lens wearers, these little scrapes and cuts may go unnoticed or cause pain or irritation ranging from mild to severe.
A little scrape is not of significant concern, however a scape or any defect to the cornea’s structural integrity opens up a pathway for bacteria to enter and cause more serious infections.
Any time an eye infection occurs, especially a corneal ulcer, there is a risk of permanent vision loss as any scarring that may occur in the eye can interfere with vision.
Common Culprits of Contact Lens Issues
There are several conditions that further amplify the risk of infection, neovascularization, and dryness in contact lenses wearers. Any of the following situations significantly increase the risk of problems.
Sleeping in Contact Lenses
When we sleep, our eyes are closed. As mentioned previously, the eye gets most of its oxygen from the air, therefore when the eyes are closed there is a natural decrease in oxygen to the cornea.
When there is less oxygen available, the cornea swells slightly. You may have noticed in the morning upon first waking that your vision may appear a little hazy for 5-15 minutes—this is from mild cornea swelling.
When the cornea swells, it alters its shape. If you sleep in your lenses, not only will the lenses be extremely dry upon waking (due to the decreased amount of oxygen), but they will also “stick” to the eye, as they have contoured to the new shape of the swelled cornea and are no longer “floating” above the cornea.
This causes irritation, excessive drying, and decreased vision through the lenses. If you try to remove the lenses without re-wetting them and giving the eye proper time to un-swell, you will note that it feels like the lens is “sticking” to the eye. If you continue to pull at the lens to remove it, you run the risk of causing a corneal defect.
Sleeping in lenses also increases the risk of an infection festering. It is recommended that contact lenses be removed at a maximum of 16 hours—unless you are wearing one of the few brands approved for overnight wear.
Lenses that have been worn 16 or more hours have trapped a lot of debris within them. If bacteria are harboring on the front of the lens and you sleep in the lenses overnight, you are giving the bacteria the opportunity to invade the cornea and cause infections.
This is especially dangerous in contact lens wearers because contact lens wearers often have very small, unnoticed corneal scratches that give bacteria access to a proliferation site and hence encourage infections.
Swimming in Contact Lenses
Swimming on contact lenses offers similar risks to sleeping in lenses. The main difference is that there are more dangerous bacteria lurking in swimming pools, lakes, hot tubs, etc.
If these bacteria latch on to your lenses and find an opportunity to invade the cornea they can cause serious infections such as acanthamoeba—a parasite that causes an extremely painful infection that often requires corneal transplants or even surgical eye removal.
If you swim in your lenses, it is crucial that you do not open your eyes under water, and dispose of the lenses as soon as possible to start refresh with a new pair upon the next day.
Reusing Solutions & Improper Cleaning of Lenses
Contact lenses go in your eyes, therefore it is extremely important that they are properly cleaned at the end of each day.
Daily disposable contact lenses should only be worn once and then thrown away. Therefore, they do not necessarily need to be cleaned.
Contact lenses that are worn for 2 weeks or 1 month at a time, however, do need to be properly cleaned and stored each day.
Contact lens cases are one of the most over-looked culprits for contact lens infections. Cases need to be cleaned with soap and water and then properly dried between each use.
If not, we are providing a dark, damp location for bacteria to proliferate upon during the day. Then, when lenses are removed and placed back into the case, they are being stored in a dirty environment, running the risk of soaking your lenses in bacteria-laden solution all night.
Contact lens solutions have anti-microbial properties within them to kill bacteria. However, this only works when the solution is un-tampered.
This means contact lens solution cannot be re-used. Once used, it loses some of its anti-microbial properties and may no longer be sufficient at killing bacteria.
If the solution sits in the case all day, attracting more bacteria, it can become overrun with bacteria, and similar to a dirty case, you do not want to leave your lenses to soak in a contaminated solution over night!
Contact Lens Overwear
Wearing contact lenses beyond 16 hours is dangerous, as it can cause hypoxic conditions discussed with decreased oxygen transmissibility. Contact lenses are generally safe to wear as long as you give your eyes a break and take care of the lenses properly.
Sleeping in lenses, overwearing lenses, and wearing lenses longer than their intended for (for example 3 months on a 1 month lens), is dangerous.
The day you open the foil packet containing the contact lens is when its “life counter” starts. If you have a 1-month lens, that means the lens is good for 30 days—regardless as to whether you wore the lens all 30 days, or just for 1 day.
This is because lenses structural integrity and ability to ward of bacteria have only been proven to last for so long.
Wearing lenses more than the manufacturer recommended time greatly increases your risk for infection.
Not only does overwearing lenses increase risk for infection, but they can actually change the shape of your cornea, and therefore alter your prescription. This process is called “Corneal Warpage”.
This occurs because the eyes are never given enough time to breathe on their own. They are always being condensed by a contact lens. This can change the shape of the tissue and lead to decreased vision and ocular health problems down the road.
Why Are Yearly Contact Lens Exams So Important?
As you can see, there are many risks associated with wearing contact lenses!
You may not think about it, especially if you have been wearing lenses for a long time, but your eye doctor wants to watch for subtle changes and ensure your eyes are still healthy.
Perhaps the type of lens you are currently in is no longer suitable for your lifestyle. Perhaps your eyes are begging for a lens that allows for better hydration and oxygenation. Perhaps you have an infection festering. There are endless possibilities.
Ultimately, your eye doctor just wants to take a look to make sure your eyes are doing alright. Technology is always improving, what might have been the best lens for your eyes 10 years ago may be different from what is best today.
We only get 2 eyes, it is always best to take care of them and monitor for any subtle changes so that we can intervene and initiate treatment early if necessary.