Contact lenses are a medical aid placed directly on the cornea of the eye, usually for therapeutic purposes, ie. correcting refractive errors of the eye, and sometimes for aesthetic purposes. The lens is a small and thin optical disc, made of different types of plastic.
The history of contact lenses
According to their function, contact lenses can be divided into:
Corrective contact lenses correct refractive errors of the eye. They work by focusing the rays of light directly to the retina.
• Spherical contact lenses are used for correction of nearsightedness and farsightedness.
Spherical lenses have only one diopter strength and freely rotate on the eye.
• Toric lenses are used to correct astigmatism.
They have two prescription strengths (one for the correction of nearsightedness or farsightedness, the second correction is for astigmatism). In order to work, these lenses should be stable on the eye and cannot be rotated.
Today there is a great variety of soft toric lens, so that most people with astigmatism can correct their visual error in this way as well .
• Multifocal contact lenses are used to correct presbyopia.
Today, people older than forty years can use contact lenses and enjoy various activities without glasses. This type of lens provides excellent near vision, as well as vision at the middle distance and distance. Every individual may not get used to this way of correction, and it takes a short time to adapt.
Consult your eye doctor about your options.
Cosmetic contact lenses are designed for changing eye color or enhancing the natural color.
But some experts have concluded that the wearing of decorative contact lenses can lead to problems, read more here.
Therapeutic contact lenses (soft lenses) are also used for treatment of various eye diseases that do not require correction of visual acuity. They are used as a bandage, protection of sick or injured cornea from the constant rubbing of the eyelids during blinking, and thus allow the cornea to heal. They can also be used for administering drugs to the eye.
According to the material, contact lenses can be divided into:
- Hard contact lenses
- RGP – rigid gas permeable
- Traditional soft contact lenses – made out of a hydrogel material
- A new generation of soft lenses – from silicone hydrogel material
Hard contact lenses are made of a PMMA (polymethyl methacrylate) material. This material does not leak oxygen and nowadays these lenses are becoming obsolete.
Semi-hard (gas permable) lenses are made in the eighties when new materials were developed (silicon, fluorsilicon) for hard lenses leaking large amounts of oxygen to the eye, which is extremely important for eye health. These lenses provide very sharp vision, they are long-term, correct various vision errors and are easy to handle. The disadvantages of these lenses are that it may be easy to decentre them in an eye or they can even fall out of the eye.
Soft lenses account for about 85% share in the use of lenses in the world. These lenses are characterized by short adjustment period, give a great comfort, do not move on the eye as RGP lenses and do not fall out. They are made of soft (hydrogel) material with different percentages of water (from 25% to 79%). As plastic itself does not leak oxygen, the water allows oxygen permeability to the eye.
Disadvantages: the material is porous, so there is an increased possibility of infection or irritation of the eye due to contamination by bacteria, dust or pools of proteins. Thus, soft contact lenses require strict hygiene and frequent replacement which reduce the likelihood of problems and provide eye health and satisfaction with wearing lenses.
Great progress in using materials for soft contact lenses occurred in 1999 with the appearance of silicone hydrogel material. Silicone hydrogel is a material that combines the best of the hydrogel material of soft lenses and silicone in hard gas permeable lenses.
The silicone component provides a high oxygen permeability (about 5 times more than traditional soft lenses), a hydrogel provides comfort and softness of soft lenses.
As silicone hydrogel lenses contain less water than traditional lenses, the dehydration or drying of the lens happen less often, which allows for longer and more comfortable wearing.
According to the frequency of replacement, lenses are divided into:
One day, two weeks, one month, three months, one year.
Most soft contact lenses can be worn only while awake. There are soft lenses that can be worn when sleeping up to 30 days.
These are contact lenses of silicone hydrogel material, which allow permeability of almost all the oxygen present in nature.
More about sleeping with contact lenses
Most people are good candidates for contact lenses. However, the eyes of each and every individual cannot be adapted to sleep with the lenses. You may be able to wear lenses overnight a few days, but not 30 days continuously.
For many years the leading soft lenses on the market were the ones replaced yearly. Today, these lenses are hardly used. The most commonly used replacement lenses are lenses with different time use.
To make wearing of soft lenses healthier and more comfortable, it is important to replace them often.
Even 40% of people wear worn out contact lenses
Daily lenses – disposable contact lenses :
• no maintenance
• suitable for people with allergies or similar problems, for those who wear lenses only occasionally, for sports or specific working conditions, travel…
More about one-day lenses
Replacement lenses – two-weekly, monthly, quarterly:
• Replacement soft contact lenses are packed by 3 or 6 pieces
• They are replaced with new lenses after the expiry of the stipulated wearing time
• The maintenance of these lenses is easy
• Deposits of proteins and lipids in a short time of wearing will not develop and cause problems.
Benefits of contact lenses compared to eyeglasses are:
• greater visual acuity, especially at higher diopters
• wider field of vision unlimited with the lens size and frames
• reduced or completely eliminated distortion of the image, sometimes present in glasses
• contact lenses should not blur when switching from cold to warm environment
• contact lenses are less bothered by damp, rainy weather
• contact lenses are ideal for practicing the sport, giving complete freedom of movement
• for many specific occupations contact lenses are the best solution
• some errors of the eye cannot be corrected by glasses with the same quality as contact lenses (keratoconus, aniseikonia)