Last updated on May 27th, 2017 at 12:24 am
Silicone hydrogel contact lenses are sophisticated soft lenses that enable more oxygen to go through the lens to the cornea than regular soft (“hydrogel”) contacts. In reality, silicone hydrogel lenses enable as much as 5 times more oxygen to reach the cornea than regular hydrogel lenses.
Silicone hydrogel and regular hydrogel lenses both are made of plastics that are hard when dry however easily take in water and become soft and gel-like when hydrated.
If you’ve ever let a soft or silicone hydrogel lens dry out, you know that it ends up being warped, difficult and fragile. However if you soak it for a few minutes in contact lens solution, it becomes soft and flexible again.
In 2014, silicone hydrogel lenses represented 68 percent of contact lens fittings carried out in the United States, compared to 24 percent for regular soft lenses, 6 percent for rigid gas permeable contacts and 1 percent for hybrid contact lenses.
Popular brand names of silicone hydrogel contact lenses consist of Acuvue Oasys (Vistakon), Air Optix Aqua (Alcon), Biofinity (CooperVision) and PureVision2 (Bausch + Lomb).
Silicone Hydrogel Contacts
Silicone hydrogel contact lenses in some cases are incorrectly called silicon hydrogel lenses.
Silicon is a typical mineral. In fact, normal sand is composed mostly of silicon dioxide (silica).
And highly purified silicon is used to produce semiconductors, which is why the southern part of the San Francisco Bay area, home of Apple and numerous other state-of-the-art and computer business, is nicknamed Silicon Valley.
Silicone is the name of a group of flexible, plastic-like products that contain silicon, carbon, oxygen and other chemicals. In addition to its use to increase the oxygen permeability of contact lenses, silicone is used to make breast augmentation, medical tubing and other medical devices.
Silicone hydrogel lenses are soft lenses, however silicone also is used in the production of lots of stiff gas permeable contacts to enhance oxygen permeability of the lenses.
Advantages Of Silicone Hydrogel Lenses
All contact lenses reduce the amount of oxygen that reaches the front surface area of the eye to some degree. When the cornea’s oxygen supply is substantially minimized — a condition called hypoxia — a variety of issues such as red eyes, corneal swelling, blurred vision and eye discomfort can happen. Hypoxia likewise can increase contact lens wearers’ risk for a number of eye infections.
Hypoxia-related eye problems ended up being a considerable problem in the 1990s when extended wear contact lenses first gained popularity. As the number of individuals who used contacts overnight and constantly for several days increased, so did the variety of contact lens-related eye infections.
Silicone hydrogel lenses were introduced in hopes of decreasing hypoxia-related issues and increasing the safety of both daily wear and extended wear of soft contact lenses.
Increasing the oxygen supply to the eye is potentially useful for all contact lens wearers, particularly considering that lots of users are not complying with their optometrists’ instructions concerning proper lens wear and replacement.
According to Alcon, nearly one in 5 soft contact lens users wear their lenses during sleep, and among patients who oversleep their lenses, nearly two out of 3 are wearing lenses that are not approved for overnight wear.
Specialty Silicone Hydrogel Lenses
The enhanced oxygen permeability of silicone hydrogel contacts makes them a fantastic suitable for special contact lens designs that may cause hypoxia issues when made with traditional soft hydrogel materials.
These consist of any designs that require higher lens mass, such as toric contacts for astigmatism, bifocal contacts, contacts for hard-to-fit eyes, and custom contact lenses, including soft contact lenses for keratoconus.
Risk Of Keratitis With Silicone Hydrogel Contacts
Do silicone hydrogel contact lenses decrease the risk of keratitis and eye infections? Yes and no.
A recent study published in the British Journal of Ophthalmology discovered a significantly lower risk of severe keratitis amongst silicone hydrogel users, but a higher risk of non-severe keratitis.
The 12-month, hospital-based study conducted in the U.K. revealed the yearly occurrences of non-severe keratitis (NSK) were low in both groups, impacting 14.1 per 10,000 users (0.14 percent) among hydrogel wearers and 55.9 per 10,000 users (0.56 percent) among silicone hydrogel users.
There were no cases of severe keratitis (SK) among patients utilizing silicone hydrogel contact lenses for daily wear, whereas there were 6.4 cases of SK per 10,000 patients using regular hydrogel lenses for day-to-day wear.
The risk of keratitis was considerably greater for both types of soft contacts amongst patients who used their lenses for over night wear. Hydrogel lenses used continuously caused 48.2 cases of NSK and 96.4 cases of SK per 10,000 wearers; silicone hydrogel lenses used for extended wear triggered 98.8 cases of NSK and 19.8 cases of SK per 10,000 wearers.
The researchers concluded there is a considerably greater incidence of severe keratitis in wearers who sleep in contact lenses compared with those who only use contact lenses during the waking hours. They advised that people who want to wear contact lenses continuously should be recommended to use silicone hydrogel lenses, which seem much safer for overnight wear than regular hydrogel lenses.
Critics of silicone hydrogel contact lenses have actually used this research study as evidence that silicone hydrogels are connected with a higher risk of non-severe keratitis compared with regular hydrogel lenses. It deserves noting, nevertheless, that the study did not assess how many of the silicone hydrogel lens users who showed NSK were refitted into silicone hydrogel lenses from traditional hydrogel lenses prior to the research study period due to comparable problems while wearing hydrogel lenses.
Also, at the time of the research study, the only silicone hydrogel lenses approved for use in the U.K. were developed for regular monthly lens replacement, whereas there were a number of brand names of regular hydrogel lenses readily available for more frequent two-week replacement.
Today, several brand names of silicone hydrogel lenses are approved for use in the United States and Europe that are created for two-week and monthly replacement. There are even single-use silicone hydrogel lenses created for everyday disposal and replacement.
Allergic Response To Silicone Hydrogel Lenses
A number of blog sites and online forums contain problems among contact lens users that they have actually established allergy-like symptoms from wearing silicone hydrogel lenses.
The most typical grievances are soreness, discomfort, itchy eyes and higher lens awareness or dryness symptoms. Nevertheless, these symptoms can likewise be brought on by contact lens dryness or level of sensitivity to a brand-new contact lens option or care regimen.
Though silicone hydrogel lenses enable more oxygen to reach the surface of the eye, the added silicone can reduce the surface wettability of the lenses, potentially making it harder for them to stay moist on the eye. To fight this propensity, brand-new contact lens options have actually been developed that include unique wetting agents to keep silicone hydrogel lenses hydrated for all-day wear.
Though lens wettability might not be an issue for most wearers, individuals with marginal dry eyes may notice dryness pain from silicone hydrogel lenses that they didn’t experience with previous hydrogel lenses, and this dryness-related pain can be mistaken as symptomatic of an allergic reaction to silicone hydrogel lenses.
Since silicone hydrogel lenses allow more oxygen to reach the eye, some wearers may end up being more familiar with their lenses for another, more paradoxical reason.
Since of their increased oxygen transmissibility, silicone hydrogel lenses have most likely allowed many people to wear contacts for longer hours than they could have with regular hydrogel lenses.
A factor in why soft contact lenses are so comfortable for many users is due to the fact that the lowered oxygen supply to the front of the eye from using the lenses lowers the sensitivity of the corneal surface. When more oxygen is available by using highly oxygen-permeable silicone hydrogel lenses, it’s possible the cornea keeps its normal level of sensitivity, making the wearer more aware there is a lens on his or her eye.
In truth, in a study released in late 2010 in Investigative Ophthalmology & Visual Science, researchers discovered that when patients were fitted with silicone hydrogel lenses or refitted with silicone hydrogels to replace regular hydrogel contacts, the level of sensitivity of their cornea increased.
The research study also found modifications in corneal sensitivity among silicone hydrogel wearers when different lens care regular were used.
The findings of the research study led the researchers to conclude that the effect of soft contact lens wear on the performance of the sensory nerves on the front of the eye “appears to be more complicated than formerly thought.”
The research study authors suggested extra studies be carried out to investigate how ocular surface area sensitivity varies after longer-term silicone hydrogel lens wear and whether sensory aspects of the cornea and conjunctiva contribute to the end-of-day discomfort frequently reported by users of hydrogel and silicone hydrogel lenses alike.
When it comes to possible allergies to silicone hydrogel contact lenses, official proof of this is essentially nonexistent. Since this writing, it appears that no validated cases of allergic reactions to silicone hydrogel contacts have actually been reported to the Food and Drug Administration (FDA) in the United States or to the Medicines and Healthcare Products Regulatory Agency (MHRA) in the U.K., and no medical reports of such occurrences have been released in peer-reviewed medical journals in either nation.
Are Silicone Hydrogel Contact Lenses For You?
The majority of optometrists and ophthalmologists agree that the most obvious advantage of silicone hydrogel lenses is the reduction of hypoxia-related problems connected with soft lenses made of regular hydrogel products.
This likely has actually led to less contact lens-related red eyes, pain and severe keratitis issues from wearing contacts for prolonged time periods.
It’s also likely that due to their increased oxygen transmissibility, silicone hydrogel lenses have made it possible for many individuals to comfortably wear contacts for longer hours than they might have with regular hydrogel lenses.
Silicone hydrogel products also have enabled contact lens manufacturers to develop a wider range of lens styles while allowing a healthy amount of oxygen to reach the cornea for safe and comfortable day-to-day or continuous wear.
However, silicone hydrogel lenses have actually not solved contact lens pain problems entirely, and, in reality, some people might experience more lens awareness when wearing silicone hydrogel lenses than when wearing regular hydrogel lenses.
Some studies have actually revealed that silicone hydrogel lenses are more vulnerable to specific types of contact lens deposits than regular hydrogel lenses, and some contact lens solutions might be less reliable on silicone hydrogel lenses than they are on regular soft lenses.
Likewise, despite their increased oxygen permeability, silicone hydrogel lenses have been shown in some research studies to be connected with a higher risk of corneal inflammation and other complications in some patients, compared to regular hydrogel lenses. Reasons for these apparent problems stay uncertain.
Some experts likewise state that there is no hard evidence that the increase in oxygen supply to the eye when wearing silicone hydrogel lenses enhances end-of-day using comfort, compared with wearing regular hydrogel lenses.
Lastly, it’s also notable that presently the only soft contact lens that has been FDA-approved to be marketed as a contact lens for dry eyes is a regular hydrogel lens (Proclear; CooperVision), not a silicone hydrogel lens.
Due to the fact that there are pros and cons to every contact lens product or style, the best method to identify if silicone hydrogel lenses are the right choice for you is to go over all possible contact lens choices with your optometrist during your contact lens examination and consultation.