History of contact lenses
Leonardo da Vinci is frequently credited with introducing the general principle of contact lenses in his 1508 Codex of the eye, Manual D, where he described a method of directly altering corneal power by submerging the eye in a bowl of water. Leonardo, however, did not suggest his idea be used for correcting vision—he was more interested in learning about the mechanisms of accommodation of the eye.
Rene Descartes proposed another idea in 1636, in which a glass tube filled with liquid is placed in direct contact with the cornea. The protruding end was to be composed of clear glass, shaped to correct vision; however the idea was impracticable, since it would make blinking impossible.
In 1801, while conducting experiments concerning the mechanisms of accommodation, scientist Thomas Young constructed a liquid-filled "eyecup" which could be considered a predecessor to the contact lens. On the eyecup's base, Young fitted a microscope eyepiece. However, like Leonardo's, Young's device was not intended to correct refraction errors.
Sir John Herschel, in a footnote of the 1845 edition of the Encyclopedia Metropolitana, posed two ideas for the visual correction: the first "a spherical capsule of glass filled with animal jelly", and "a mould of the cornea" which could be impressed on "some sort of transparent medium". Though Herschel reportedly never tested these ideas, they were both later advanced by several independent inventors such as Hungarian Dr. Dallos (1929), who perfected a method of making molds from living eyes. This enabled the manufacture of lenses that, for the first time, conformed to the actual shape of the eye.
It was not until 1887 that a German glassblower, F.E. Muller, produced the first eye covering to be seen through and tolerated. In the next year, the German physiologist Adolf Eugen Fick constructed and fitted the first successful contact lens. While working in Zurich, he described fabricating afocal scleral contact shells, which rested on the less sensitive rim of tissue around the cornea, and experimentally fitting them: initially on rabbits, then on himself, and lastly on a small group of volunteers. These lenses were made from heavy brown glass and were 18–21mm in diameter. Fick filled the empty space between cornea/callosity and glass with a dextrose solution. He published his work, "Contactbrille", in the journal Archiv für Augenheilkunde in March 1888.
Fick's lens was large, unwieldy, and could only be worn for a few hours at a time. August Muller in Kiel, Germany, corrected his own severe myopia with a more convenient glass-blown scleral contact lens of his own manufacture in 1888.
Also in 1887, Louis J. Girard invented a similar scleral form of contact lens.
Glass-blown scleral lenses remained the only form of contact lens until the 1930s when polymethyl methacrylate (PMMA or Perspex / Plexiglas) was developed, allowing plastic scleral lenses to be manufactured for the first time. In 1936, optometrist William Feinbloom introduced plastic lenses, making them lighter and more convenient. These lenses were a combination of glass and plastic.
In 1949, the first "corneal" lenses were developed. These were much smaller than the original scleral lenses, as they sat only on the cornea rather than across all of the visible ocular surface, and could be worn up to sixteen hours per day. PMMA corneal lenses became the first contact lenses to have mass appeal through the 1960s, as lens designs became more sophisticated with improving manufacturing (lathe) technology.
One important disadvantage of PMMA lenses is that no oxygen is transmitted through the lens to the conjunctiva and cornea, which can cause a number of adverse clinical effects. By the end of the 1970s, and through the 1980s and 1990s, a range of oxygen-permeable but rigid materials were developed to overcome this problem. Collectively, these polymers are referred to as "rigid gas permeable" or "RGP" materials or lenses. Although all the above lens types—sclerals, PMMA lenses and RGPs—could be correctly referred to as being "hard" or "rigid", the term hard is now used to refer to the original PMMA lenses which are still occasionally fitted and worn, whereas rigid is a generic term which can be used for all these lens types. That is, hard lenses (PMMA lenses) are a sub-set of rigid lenses. Occasionally, the term "gas permeable" is used to describe RGP lenses, but this is potentially misleading, as soft lenses are also gas permeable in that they allow oxygen to move through the lens to the ocular surface.
The principal breakthrough in soft lenses was made by the Czech chemist Otto Wichterle who published his work "Hydrophilic gels for biological use" in the journal Nature in 1959. This led to the launch of the first soft (hydrogel) lenses in some countries in the 1960s and the first approval of the "Soflens" material by the United States Food and Drug Administration (FDA) in 1971. These lenses were soon prescribed more often than rigid lenses, mainly due to the immediate comfort of soft lenses; by comparison, rigid lenses require a period of adaptation before full comfort is achieved. The polymers from which soft lenses are manufactured improved over the next 25 years, primarily in terms of increasing the oxygen permeability by varying the ingredients making up the polymers.
In 1999, an important development was the launch of the first silicone hydrogels onto the market. These new materials encapsulated the benefits of silicone—which has extremely high oxygen permeability—with the comfort and clinical performance of the conventional hydrogels which had been used for the previous 30 years. These lenses were initially advocated primarily for extended (overnight) wear although more recently, daily (no overnight) wear silicone hydrogels have been launched.
By. Wikipedia, the free encyclopedia
Usage of Contact Lenses
Before touching the contact lens or one's eyes, it is important to thoroughly wash & rinse hands with a soap that does not contain moisturizers or allergens such as fragrances. The soap should not be antibacterial due to risk of improper hand washing and the possibility of destroying the natural bacteria found on the eye. These bacteria keep pathogenic bacteria from colonizing the cornea. The technique for removing or inserting a contact lens varies slightly depending upon whether the lens is soft or rigid.
Insertion
Contact lenses are typically inserted into the eye by placing them on the index finger with the concave side upward and raising them to touch the cornea. The other hand may be employed to keep the eye open. Problems may arise particularly with disposable soft lenses; if the surface tension between the lens and the finger is too great the lens may turn itself inside out; alternatively it may fold itself in half. When the lens first contacts the eye, a brief period of irritation may ensue as the eye acclimatises to the lens and also (if a multi-use lens is not correctly cleansed) as dirt on the lens irritates the eye. Irrigation may help during this period, which generally should not exceed one minute.
Removal
A soft lens may be removed by holding the eyelids open and grasping the lens with opposing digits. This method can cause irritation, could risk damage to the eye and may in many cases be difficult, in part due to the blink reflex. If the lens is pushed off the cornea it will buckle up (due to the difference in curvature), making it easier to grasp.
Rigid contact lenses may be removed by pulling with one finger on the outer or lateral canthus , then blinking to cause the lens to lose adhesion. The other hand is typically cupped underneath the eye to catch the lens. There also exist small tools specifically for removing lenses, which resemble small plungers made of flexible plastic; the concave end is raised to the eye and touched to the lens, forming a seal stronger than that of the lens with the cornea and allowing the lens to be removed from the eye.
Care
While daily disposable lenses require no cleaning, other types require regular cleaning and disinfecting in order to retain clear vision and prevent discomfort and infections by various microorganisms including bacteria, fungi, and Achantamoeba, that form a biofilm on the lens surface. There are a number of products that can be used to perform these tasks:
1. Multipurpose solution - The most popular cleaning solution for contact lenses. Used for rinsing, disinfecting, cleaning and storing the lenses. Using this product eliminates the need for protein removal enzyme tablets in most cases. Some multipurpose solutions are not effective at disinfecting Acanthamoeba from the lens. In May 2007, one brand of multipurpose solution was recalled due to a cluster of Acanthamoeba infections.Newer generations of multipurpose solutions are effective against bacteria, fungi, and acanthamoeba and are designed to condition the lenses while soaking.
2. Saline solution - Used for rinsing the lens after cleaning and preparing it for insertion. Saline solutions do not disinfect the lenses.
3. Daily cleaner - Used to clean lenses on a daily basis. A few drops of cleaner are applied to the lens while it rests in the palm of the hand, then the lens is rubbed for about 20 seconds with a fingertip (check the cleaner's directions) on each side. Long fingernails can damage the lens, so care should be taken.
4. Hydrogen peroxide solution - Used for disinfecting the lenses, and available as 'two-step' or 'one-step' systems. If using a 'two-step' product, one must ensure that the lens taken out of the hydrogen peroxide is neutralized before it is worn, or else wear will be extremely painful. Saline must be used to rinse away the peroxide. If you get this solution in your eyes, it is highly recommended that you go to the Emergency Room and get your eye(s) irrigated.
5. Enzymatic cleaner - Used for cleaning protein deposits off lenses, usually weekly, if the daily cleaner is not sufficient. Typically, this cleaner is in tablet form. Protein deposits make use of contact lenses uncomfortable, and may lead to various eye problems.
Some products must only be used with certain types of contact lenses: it is important to check the product label to make sure that it can be used for a given type of lens. It is also important to follow the product's directions carefully to reduce risk of eye infection or eye irritation. In addition, one should remember to wash the contact cases or lens covers thoroughly with water and multipurpose solution or hydrogen peroxide to avoid formation of biofilms on its surfaces.
It is important to ensure that the product does not become contaminated with microorganisms : the tips of the containers for these solutions should never touch any surface, and the container should be kept closed when not in use. To counteract minor contamination of the product and kill microorganisms on the contact lens, some products may contain preservatives such as thiomersal, benzalkonium chloride, benzyl alcohol , and other compounds. In 1989, thiomersal was responsible for about 10% of problems related to contact lenses: because of this, many products no longer contain thimerosal. Preservative-free products usually have shorter shelf life. For example, non-aerosol preservative-free saline solutions can typically be used for only two weeks once opened. The introduction of silicone-hydrogel soft contact lens materials in 1999 made selection of the proper disinfecting solution more important. One study has noted several incompatibilities between these new lens materials and some solutions resulting in corneal staining.
By. Wikipedia, the free encyclopedia
Contact lenses and dry eyes
Contact lenses and dry eyes are usually only temporary and can time and again be minimized or eliminated by changing lens materials. Contact lens dry eyes can also be caused by wearing contact lense.
Cause of dry eyes
Dry eye syndrome (Keratoconjunctivitis sicca, also called keratitis sicca, sicca syndrome, xerophthalmia) or dry eyes is an eye disease caused by a lack of tear production and moisture which in turn decreases lubrication. Tears are vital to keep the eye moist and for general good eye health. If these tears are deficient or abnormal you may suffer from dry eyes when wearing contacts. There are many reason why your tears may be deficient or abnormal, some of the most common are:
1. Your contact lenses - eye contacts materials may absorb too much moisture. Cheap contact lenses can also cause discomfort
2. Environment – can cause dehydration of the eye. Air conditioning, cigarette smoke or a dry dusy environment are common culprits
3. Age – As we get older our tear production decreases. Hormone changes in women going through the menopause can also decrease tear production
4. Medicine – side-effects of some prescribed medication such as antihistamines
5. Illness – for example rheumatoid arthritis can cause dry eyes
6. Damage – eye injury can cause problems with blinking which can impair the natural production of tears
Symptoms of dry eye syndrome
Both eyes usually are affected and sufferers usually report dryness, burning and a gritty eye irritation that gets worse as the day goes on. Some may report a pressure behind the eye, redness and pain. If the eye surface is damaged by dry eyes, there may also be a sensitivity to bright light.
Treatments for dry eyes
Dry eye syndrome can not always be cured. Rubbing of the eyes will irritate them more and should be avoided. Routinely blinking more often and resting the eyes are basic steps one can adopt. If the environment is the case, then avoiding dry or dusty conditions could help.
Additional lubrication is the most important part of treatment for mild and moderate cases. Opticians possibly will prescribe artificial tears, lubricating eye drops that may lessen the dry, itchy-scratchy feeling and provide temporary relief.
You should not wear contact lenses whilst using eye ointment or eye drops. There are some drops available contact lens wearers that do not contain the preservative that can cause problems. Always take advice from an optician or doctor.
By contact-lenses.com
Tips to buy contact lenses
Contact lenses can make you different in sight. Follow this tips about contact lenses :
1. Choose contact lenses where the seal is not broken. If the seal is broken, the quality is not good.
2. When buy contact lens, don't forget to buy treatment package of contact lens, like contact lens case and cleaner for contact lenses. If you have sensitive eye, buy eye drop to avoid irritation of eye.
3. Choose contact lenses color which compatible with your skin color and hair color. If you have black hair color, it's will strange in sight to use a purple contact lenses color.So, choose the natural color like brown color or gray color.
4. Don't rub your eyes at random if you use contact lenses, cause the contact lenses can move.
5. Read expire of contact lenses to avoid eye irritation.
Contact lenses for cylinder eye
Many people say that someone who has cylinder eye can't use contact lenses which have minus size. That's true? someone who has cylinder eye still can use contact lenses with minus size, but their sight are not too good than someone who only have minus eyes. But, that is no problem, cause they will adapt by their sight .
Contact Lenses for first use
Treatment of contact lenses more difficult than glasses. we must clean frequently if use contact lenses. Although use contact lenses more difficult, many people like to use contact lenses, why?
For everyone who have high minus, they more like to use contact lenses than glasses, cause to avoid from swollen eye and tired eye.
First use of contact lenses make our sight be strange, all object become big size in our sight. But don't worry, it will be lose in several days and we will get normal in sight. If we feel strange in use, like contact lenses want to out from our eye, that means diameter or BC of contact lenses not compatible with our eyes, so before buy contact lenses, we have to know our size of eye.
Note: Many people compatible with freshlook contact lenses with diameter = 14.5 and BC = medium (8.5 - 8.7).
http://contact-lenses-survey.blogspot.com
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