What Is a Contact Lens? Who Can Use Contact Lenses?
Contact lenses are lenses placed directly on the eye to correct visual problems.
They are used to correct refractive errors such as myopia, hyperopia and astigmatism. In keratoconus, vision is reduced and even glasses cannot improve it sufficiently.
In these patients vision can be improved with gas-permeable rigid lenses, piggy-back lenses or hybrid lenses. Cosmetic lenses are also made to change the colour of the eye.
For people who do sport, and especially for those with a high prescription, contact lenses offer a major advantage because they provide a wider field of vision and show objects at their normal size.
What Should We Pay Attention to When Buying Contact Lenses?
Because contact lenses are placed directly on the eye, they must only be prescribed by an ophthalmologist, who will assess whether the eye is suitable for lens wear. The contact lens must be compatible with the eye.
A lens that does not move enough on the surface of the eye causes erosions and redness due to impaired nourishment of the cornea. A lens that moves too much on the eye causes irritation, a foreign-body sensation and redness.
Tear deficiency, allergy and the working environment are important factors that affect lens wear.
How Is a Contact Lens Examination Performed?
Before any contact lens is prescribed, the patient’s glasses prescription must always be re-checked. A change in glasses prescription is one of the most common causes of dissatisfaction with contact lenses.
A trial lens close to the patient’s prescription is placed on the eye and kept in place for a while. After that the fit of the lens is assessed.
If the fit is good, the prescription is rechecked through the lens and the contact lens is ordered. Buying contact lenses based on a glasses prescription alone, without an examination, can have serious consequences — up to and including loss of the eye.
What Types of Contact Lenses Are Available?
Different contact lenses are produced for different needs. Which type is suitable for a particular patient must be decided by the doctor.
01 MONTHLY LENSES
These lenses must be removed every evening for at least 8 hours and discarded after one month. Although extended-wear monthly lenses do exist, even those should be removed for one night a week. For people leading a normal daily life it is healthier to use monthly contact lenses that are removed at night.
02 YEARLY LENSES
Lenses that are removed every evening for at least 8 hours and discarded after one year.
03 GAS-PERMEABLE RIGID CONTACT LENSES
Used in conditions in which the cornea is irregular — such as keratoconus — and in patients with high astigmatism.
04 SOFT LENSES
More suitable for patients whose astigmatism is below a certain level, for those working in dusty environments and for people who do sport.
05 SOFT TORIC LENSES
Provide better vision for patients with astigmatism of 0.75 or above.
06 BIFOCAL LENSES
Lenses that allow both near and distance vision. Recommended for people who are active in working life, or for those already using lenses for distance who later develop a need for reading glasses.
07 PIGGY-BACK LENSES
A combination of soft and gas-permeable rigid lenses used together. Used in patients who need a gas-permeable rigid lens but are unable to tolerate one alone for various reasons.
08 HYBRID LENSES
Lenses with a gas-permeable rigid centre and a soft periphery. Used for the same indications as piggy-back lenses.
09 COLOURED LENSES
Contact lenses used to change the colour of the eye.
10 PROSTHETIC LENSES
Used for aesthetic purposes in cases where the cornea has become opaque (white) following a previous disease.
11 CHROMAGEN LENSES
Used in patients with colour blindness, helping them to perceive colours close to true.
Prepared by the Editorial Board of Eye Foundation Hospitals.
