About Contact Lens
What are contact lenses?
Contact lenses can be used to correct vision disorders, change eye color or treat corneal diseases.
Contact lenses have evolved in the 1800s from blown glass lenses that completely cover the front of the pupil to thin plastic corneal lenses. Today, lens types and materials are varied with the usage options it provides.
An eye examination is performed by an ophthalmologist for the selection of contact lenses suitable for the patient’s eye structure. The lens type, diopter, base curve, and diameter to be used are determined in the examination. The same lens or a lens with the closest diopter possible is used to determine the fit. The movement, balance, and center of the lens are examined.
How to choose an appropriate contact lens?
Contact lenses are designed to be placed on the cornea. They are held in place mainly by sticking to the tear film that covers the front of the eye and a little by the pressure of the eyelids.
As the eye blinks, the eyelid slides over the surface of the contact lens, causing its front to move slightly. This action allows the tears to provide the necessary lubrication and helps to wash away the deposits.
The too tight lens will not move at all. It may cause eye sensitivity. At first, the user may be comfortable, but visual acuity is poor. It can cause complications in the long term.
The too loose lens moves excessively. The lower eyelid feels the lens a lot. After blinking, the image is blurred. The lens is off-center. Lens edges can be bent.
What should be considered when using contact lenses?
- The lens suitable for the eye is well centered and covers the cornea.
- The lens should move slightly to circulate the tear. It should be able to move 1 mm vertically in the push-up test and after the blink.
- The user should see clearly and comfortably and should not feel the lens.
- Vision should not change after blinking.
- The edge strip should not put pressure on the eye.
- Do not sleep with contact lenses. Do not enter the sea or pool.
- If you experience redness or stinging while using contact lenses, you should immediately remove the lens and consult a doctor.
Features of contact lenses
- Back surface: It is the part of the lens that comes into contact with the cornea.
- Front surface: It is the part of the lens that does not come into contact with the cornea. It is inclined to change the refraction of light to the extent of refractive error to correct the refractive error as necessary.
- Bace curve: For a lens to be comfortable, its posterior surface in contact with the eye and the anterior surface of the cornea must be compatible and have a similar curve. The bace curve is the radius of the optical area of the back surface. Fitting the lens to the eye is one of the most important parameters, as it has the curve. In cases where the used lens is too tight, the bace curve should be enlarged, otherwise, it should be reduced.
The larger bace curve is flat and is called FLAT. The smaller bace curve is curved and is called STEEP.
Diameter: It is the mm measurement taken from the outermost edge to the other edge in the center of the lens. Diameter affects the fit of the lens to the eye. For soft lenses, these values are between 13.5 / 14.5 mm, for hard lenses is 7 mm.
Prepared by the Dünyagöz Hospital Editorial Board.
*The content of this page is for informational purposes only. See your doctor for diagnosis and treatment.
Last Update Date: 10.03.2022
