The different types of contact lenses
There are two types of contact lenses: soft lenses and hard lenses.
Soft lenses:
Soft lenses are the most common, as they are adaptable and easy to use for most people.
Indeed, there are daily, weekly, bi-monthly, monthly and annual soft lenses.
Also, most cosmetic and therapeutic lenses are soft lenses.
Rigid lenses:
There are two types of rigid lenses (which replaced the old hard lenses): the first rigid lenses that have been around for a long time are made of PMMA and modern rigid lenses that are called oxygen permeable. Modern rigid lenses are a less common type of lens than soft lenses that are particularly suitable for people with dry eyes because of their high oxygen permeability.
Most rigid lenses are more expensive than soft lenses, but their replacement frequency is generally less regular. In fact, some rigid lenses can be used for one to two years.
Contact lenses can have corrective, cosmetic and therapeutic functions.
Corrective lenses:
Contact lenses correct in most cases hyperopia, myopia, but also astigmatism and presbyopia.
Wearers usually have to remove their lenses every night or every other day, depending on the brand and type of lenses. Some "Night & Day" lenses can be worn without interruptions, they are designed to be worn to sleep with.
For people with certain color deficiencies, a red tint - "X-Chrom" contact lens can be used. Although the lens does not restore perfect color vision, it does allow some color blind individuals to better distinguish colors.
ChromaGen lenses have been used and have been shown to have limitations on night vision while otherwise producing significant improvements in color vision. In fact, a previous study showed very significant improvements in color vision.
Cosmetic lenses:
Cosmetic contact lenses are designed to change the appearance of the eye. These lenses can also sometimes correct vision.
There are many colors of contact lenses. In fact, all possible colors are adaptable to the lenses (blue, green, red, yellow, orange, etc.).
In other cases, similar lenses have more direct medical applications.
For example, some lenses can make the iris appear enlarged, or mask defects such as the absence (aniridia) and damage (dyscoria) of the iris.
Therapeutic lenses:
Soft lenses are often used in the treatment of certain conditions of the front part of the eye: the cornea.
We are talking about bandage lenses: contact lenses can protect injured or sick corneas from the friction of blinking eyelids, thus allowing healing. They are used in a variety of treatments, including bullous keratopathy, dry eye, corneal ulcers and erosion, keratitis, corneal edema, Descemetocele, corneal ectasis, Mooren's ulcer, anterior corneal dystrophy, and neurotrophic keratoconjunctivitis.
After surgeries such as Lasik, a certain type of lens may be used to improve eye healing.
Contact lenses containing medications for the eyes were also developed.
Continuous wear lenses:
Nowadays, some types of lenses (soft and hard) can be worn day and night.
Standard soft lenses are not designed to be worn while sleeping because they do not allow the eye to oxygenate properly. In most cases, it is nevertheless possible to take a nap with these lenses. However, in the event of a red eye or blurred vision upon waking, it is best not to start again. In case of forgetfulness, if you have slept with your lenses in, the eye may be dry and it is then recommended to put a little sterile physiological serum (never water) in the eyes before removing the lenses.
The nighttime wearing of soft lenses has developed more recently thanks to new materials with the appearance in particular of silicone hydrogel lenses which have a greater permeability to oxygen than standard soft lenses.
However, the majority of ophthalmologists advise against continuous wear because it considerably increases the risk of infection and can lead to serious complications. These lenses (which can be removed every evening like traditional lenses) can be prescribed to patients who tend to occasionally forget to remove their lenses or in the case of people who feel discomfort with traditional lenses. In all cases, nighttime wear requires seeking medical advice from an ophthalmologist.
Side Effects:
Complications from contact lens wear affect approximately 4% of contact lens wearers each year.
Excessive contact lens wear, particularly at night, is associated with the most safety concerns.
Problems associated with contact lens wear can affect the eyelid, the conjunctiva, the different layers of the cornea, and even the tear film that covers the outer surface of the eye.
Studies conducted on the long-term side effects of contact lens wear, i.e. more than 5 years, for example by Zuguo conclude that "long-term contact lens wear appears to decrease the thickness of the entire cornea and increase corneal curvature and surface irregularities."
Long-term wear of rigid contact lenses is associated with a decrease in corneal keratocyte density and an increase in the number of epithelial Langerhans cells.
The most common complications affect the cornea:
- Can lead to corneal ulcers or abscesses often caused by poor hygiene, excessive wearing times (more than 10/12 hours per day) or failure to replace lenses monthly or by excessive dryness of the eye.
- A formidable peculiarity: amoebic keratitis which can lead to loss of the eye if the lenses are rinsed with tap water.
The poor tolerance that sometimes appears after a few years of wearing lenses is often the reason triggering the request for laser surgery for visual defects: refractive surgery.