A common reason for contact lens discomfort is poor fit.
There are several components of contact lens design that
can impact its fit, diameter of the lens and base curve.
The diameter of the contact lens is the entire width of
the lens and is measured in millimeters.
The base curve of the contact lens is the steepness of the
curve of the contact lens that fits against the cornea. A
contact lens design with a small base curve has a steeper
shape than one with a flatter base curve (an egg as
compared to an orange).
When a contact lens is fit correctly onto the cornea, the
lens should cover the entire cornea with only slight
movement with each blink.
Should the lens move excessively during wear, revealing
any portion of the cornea, dryness and/or irritation will
occur making the lens uncomfortable to wear as wearing
time increases. Should the contact lens move too little
during wear, the cornea can become irritated and the eye
can become red with blurred vision as the wearing time
increases.
A properly fit contact lens (correct diameter and base
curve) should have a comfortable wearing time up to 12
hours.
