NCLE Practice questions with correct answers

base curve - Answer refers to the radius of curvature of the central posterior surface of the lens. It may be expressed in diopters of surface power (D) or in millimeters (mm) of radius or curvature. optical zone - Answer the chord diameter over which the base curve extends on the posterior surface of the contact lens, described in millimeters secondary or intermediate curves - Answer lies between the base curve and the peripheral curve on the posterior lens surface, usually 0.70mm to 1.50mm flatter than the base curve radius, this allows the lens to better align the flatter portion of the cornea adjacent to the optical zone peripheral curve - Answer the outermost curve on the posterior lens surface, its function is to clear the flatter periphery of the cornea and to prevent lens impingement in the limbal areas as the lens moves with blinking blend curve - Answer the treatment given to the sharp junctions created by the difference in the radii of curvature between the base curve, the secondary curve, and the peripheral curve, rarely required at the base curve/secondary curve junction. lens diameter - Answer refers to the overall width of the lens from one edge to the other, it is measured in millimeters. Normal ranges are from 7.00mm to 10.50mm in rigid lenses and from 12.50mm to 16.00mm in soft contacts