We should understand the following before choosing colored contacts.
a. Water content
Refers to the ratio of quality of water in the lens and the the total mass of the lens. Water content determine the characteristics of the lens, water content can be divided into:
- Low water content <42%
- Middle water content 42% to 60%
- High water content > 60%.
The higher water content, the more flexible the lens are, it is easier to deform in hand. In contrast, the lower the water content, lens are easier to form in hand.
If water content is too high, the lens will reduce the moisture as it absorbs water from the eyes, causing discomfort to the eyes. If water content is too low, it will result in poor oxygen permeability, causing dryness to your eyes too, because oxygen is passing through the water content.
IDEAL water content should be between 50% - 60%, but it varies among people. Experts recommend contact lenses with high water content to those eyes are easily to get dry.
b. Diameter
It is the size of the lens. The bigger size of diameter, the more obvious the big eyes effect. Basically bigger diameter lens needs higher percentage of water content because water tends to be absorbed faster. You may notice that majority of the big eyes lenses (16mm) have 42% and above water content.
c. Base Curve
It is the center area of the curvature of the lens. Basic rule to select Base Curve is: it should not be tight. Experts advise common Base Curve are between 8.3 to 8.9. This helps it fit your cornea more comfortably since some corneas are "steeper" or "flatter" than others. The higher the base curve number the "flatter" the curvature of the cornea.
d. Center Thickness:
It is the thickness of center of contact lens. Experts remind those who have astigmatism, should select slightly thicker lens.
e. Oxygen Permeability:
It refers to the ability of oxygen permeate to eyes. Oxygen permeability varies from every type of lens, it depends on the material and thickness of lens. Generally the greater the diameter of the lens, the greater the coverage, oxygen permeability will be relatively poor.