Contact Lenses
A contact lens (known as the contact lens or contact lens) lens is a corrective, cosmetic or therapeutic placed on the cornea of the eye. The modern contact lenses were invented by the Czech chemist Otto Wichterle, who also invented the first hydrogel used in their production.
Contact lenses have the same function as eyeglasses, but are distinguished by their small size and virtual invisibility. Many contact lenses are slightly tinted blue to better distinguish them in their storage case. The cosmetic contact lenses are specifically colored to change the appearance of the eye.
Approximately 125 million people worldwide wear contact lenses (2%), including 28 to 38 million in the United States and 13 million in Japan.
Users choose to wear contact lenses for various reasons. Many consider themselves more attractive by wearing contact lenses rather than glasses of view. Contact lenses are not affected by the weather, do not s'embrument and do not affect the field of vision. They are widely used by athletes. Finally, eye problems such as keratoconus and aniseikonia are better treated by wearing contact lenses.
Types of contact lenses
There are several types of contact lenses. Soft lenses and semi-rigid types are the most common lenses.
Soft lenses
Soft lenses are more common, because very adaptable, affordable, and easy to use for most people. Indeed, there are soft lenses daily, weekly, bi-monthly, monthly and yearly. Also, most cosmetic and therapeutic lenses are soft lenses.
The semi-rigid lenses and rigid
The semi-rigid lenses (oxygen permeable) lenses and rigid (or hard) is a type of lens but less satisfied with many carriers, especially those in need of tears, because of their high permeability oxygen.
Most semi-rigid lenses are more expensive than soft lenses, but the frequency of replacement is generally less regular. Indeed, some semi-rigid lenses can be used several years in a row.
There are significant disparities in the requirements of rigid lenses by country: they represent 20% of prescriptions in Japan, the Netherlands and Germany but only 5% of prescriptions in Scandinavia.
The lens function
Contact lenses can have functions corrective, cosmetic and / or treatment.
The corrective lenses
Contact lenses are corrective for most carriers. Indeed, for many people, there is a mismatch between the refractive power of the eye and the length of the eye that leads to an error of refraction. A contact lens neutralizes this lack and helps correct vision. The conditions for correction of vision with contact lenses include those closely (or short called hyperopia) and far (or long called myopia), but also astigmatism and presbyopia. Holders generally must remove their lenses every night or every two days, depending on the brand and style of contact. Some lenses "Night & Day" can be worn without interruption, they are designed to sleep with. Recently, there has been a renewed interest in orthokeratologie the correction of myopia by deliberate overnight to a flattening of the cornea, leaving the eye without contact lenses or eyeglasses correction during the day.
For persons with certain color deficiencies, a red-"X-Chrom" contact lens may be used. Although the lens does not restore perfect vision of color, it allows some color blind people to distinguish them.
ChromaGen lenses were used and these have proved to have limits on night vision while on the other hand, they produce significant improvements in color vision. Indeed, a previous study has shown very significant improvements in color vision. ChromaGen lenses have also shown very significant improvement of vision in addition to reading ability without the lenses. This system has been granted approval by the FDA in the United States.
Cosmetic lenses
The cosmetic contact lenses are designed to change the appearance of the eye. These lenses can sometimes correct the vision.
There are contact lenses in many colors. Indeed, all possible colors are adaptable lenses (blue, green, red, yellow, orange, etc). There are also fluorescent lenses (which glow in the dark) and lenses which can have eyes similar to those of various animals (especially cats and reptiles). The cosmetic contact lenses are used to reveal the eye of a fun, unusual or unnatural in appearance, especially in movies, where lenses can make eyes appear demonic, sunny, etc. ...
Another type of cosmetic lenses, scleral lenses, to cover the white of the eye. Because of their size, these lenses are difficult to insert and do not move very well in the eye. The user has a small space to see through, which may hamper the quality of his vision. As a result, these lenses generally can not be brought more than 3 hours because they can cause blurred vision. Similar lenses have more direct medical applications. For example, some lenses can give the enlarged iris appearance, or mask defects such as absence (aniridia) or damage (dyscoria) of the iris.
The therapeutic lens
Soft lenses are often used in the treatment and management of non-refractive disorders of the eye. By a bandage contact lens may protect the injured or diseased cornea of the friction of blinking eyelids thereby allowing healing. They are used in various treatment, including bullous keratopathy, dry eye, ulcers and erosion of the cornea, keratitis, edema of the cornea, Descemetocele the ectasis corneal ulcer Mooren, earlier dystrophy of the cornea, and neurotrophic keratoconjunctivitis. After the Lasik operation, you can use a certain type of lenses to improve the healing of the eye. Contact lenses containing drugs to the eye have also been developed.
Lenses night
Nowadays, some types of lenses (rigid and flexible) can be worn at night.
The rigid lenses, because of their materials, have greater permeability to oxygen and therefore virtually no indication against the port at night. These rigid lenses worn at night also helped the emergence of orthokeratologie is wearing rigid lenses with radii precise and, thanks to the elasticity cornea, can mold the cornea to reduce myopia by example. The results are variable and the lenses should be worn regularly to see results over a significant period.
Standard soft lenses are not designed to be worn when sleeping because they do not allow fresh air to the eye properly. In most cases, it is possible to sleep with these lenses. However, in cases of red eye or blurred vision on waking, it is better not repeat. If you forget, if you slept with the lenses, the eye can be dry and it is recommended to put a bit of sterile saline (not water) in the eye before removing the lenses.
Wearing night soft lenses developed more recently thanks to new materials with the appearance especially silicone hydrogel lenses that have a greater permeability to oxygen than standard soft lenses. Fluorescent soft lenses are used by a number of followers of club outings.
In all cases, the port at night need to take medical advice from an ophthalmologist.
Usage
Before touching contact lenses or eyes, it is important to wash and rinse your hands with soap that does not contain moisturizers or allergens such as perfumes. The soap used for washing hands before the use of lenses should not be antibacterial because of the risk of improper cleaning which entails the possibility of destroying the natural bacteria that are on the eyes. The technique for removing or inserting a contact lens varies slightly depending on whether it is flexible or rigid.
Insertion
Contact lenses are typically inserted in the eye by placing them on the index. The other hand can be used to keep your eyes peeled. But problems arise particularly with disposable soft contact lenses, if the surface tension between the lens and the finger is too large, the lens can be transformed itself. At the first contact with the eye, a brief period of irritation may ensue as the eye to adjust to the lens and sometimes, if a multi-use is not properly cleaned, dirt on the lens irritates the eyes. Irrigation of the eye to help during this period, which should generally not exceed one minute.
Withdrawal
A soft lens may be removed by holding the eyelids open with one hand and grasping the lens with another. This method may seem difficult, partly because of the blink reflex. If the lens is pushed off the cornea, it may loop (due to the difference in curvature), making it easier to grasp.
The rigid contact lenses may be removed by pulling with a finger on the outer face or side, and blinking for him to lose grip. The other hand is usually sucker under the eye to catch the lens. There are also small tools specifically designed to remove the lens, which resemble small plungers plastic flexible. The concave end is raised to the eye and touches the ice, forming a bond stronger than that of the lens with the cornea and the lens can be removed from the eye more easily.
Maintenance
To store contact lenses, there is often a case proposing solutions and a solution for disinfection and conservation. These are often put in the lens case filled with this solution. If disposable lenses require no cleaning, other types require regular cleaning and disinfection to maintain a clear vision and prevent discomfort and infections by various microorganisms such as bacteria, fungi, and Acanthamoeba, that form a biofilm on the surface of the lens. There are a number of products that can be used to perform these tasks:
* Multipurpose solution - The solution to cleaning the most widespread and popular contact lens. Used for rinsing, disinfecting, cleaning and storage of lenses. Using this product eliminates the need for protein removal enzyme tablets in most cases.
* Saline solution - Used for rinsing contact lenses after cleaning and preparation for their integration. The saline solution does not disinfect the lenses.
* Daily cleaner - Used to clean lenses on a daily basis.
* Hydrogen peroxide solution - used for disinfecting the lenses, and available in "two steps" or "one step".
* Enzymatic cleaner - Used for cleaning protein deposits from lenses, usually weekly, daily if the cleaning is not enough.
Read also Laser in-Situ Keratomileusis
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