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Today, contact lenses are the preferred solution for many people because of the esthetic appearance, confidence and freedom that they offer. Their convenience and variety has made contact lenses increasingly popular.
Contact lenses are used to correct visual disorders, change the eye color or treat corneal diseases.
Contact lenses have come a long way from the glass-blown lenses of the 1800s which completely covered the pupil to our day's thin, high technology, plastic corneal lenses. Today, there is a great variety of lenses and lens materials available to modern lens wearers for different areas of use.
To select the correct contact lens for the eye, an ophthalmologist specialized in contact lenses examines the eyes. The type, diopter, base curve and diameter of the lens to be used are determined in the examination. To confirm suitability, lenses with the closest diopter values possible are placed. The movement, stability and position of the lens is checked.
Criteria for Well-Fitting Contact Lenses
Contact lenses are designed to stay on the cornea. Essentially, they remain in place by adhering to the lacrimal layer that covers the ocular surface and, to some degree, with pressure from the eyelids.
As the person blinks, eyelids slide over the contact lens surface, causing it to move slightly. This movement ensures that tears provide the necessary lubrication and helps to wash away any debris.
If the lens is too tight, it doesn't move at all. This may lead to sensitivity in the eye. The user may feel comfortable at first but visual acuity is poor. In the long term, complications may arise.
If the lens is too loose, it moves excessively. The lower eyelid feels the lens too much. Vision becomes blurred when the person blinks. The lens moves off-center. The edges of the lens may bend.
Physical Properties of Lenses
Back surface: The part of the lens that contacts the cornea.
Front surface: The part of the lens that has no contact with the cornea. It is curved to modify the refraction of light to correct the refractive error.
Base curve: For a contact lens to be comfortable, its back surface which contacts the eye should be compatible with the front surface of the cornea and have a similar curvature. The base curve is the back central optic radius. Since it is the curve that determines the fitting of the lens in the eye, it is one of the most important parameters. If the lens is too tight, the base curve should be increased; if too loose, it should be decreased.
A higher base curve is FLAT. A lower base curve is STEEP.
Diameter: It’s the distance, measured in millimeters at the center, from one edge of the contact lens to the other edge. The diameter affects the lens fit. This value is 13.5 / 14.5 mm for soft lenses and 7 / mm for rigid lenses.
Advantages of Contact Lenses