NCLE Practice Question Guide 2024.

NCLE Practice Question Guide 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 center thickness - ANSWER the measurement in millimeters from the anterior to the posterior surface of the lens at its geometric center, this measurement varies significantly depending on the power of the lens anterior - ANSWER nearer the front, especially situated in the front of the body or nearer to the head posterior - ANSWER further back in position; of or nearer the rear or hind end, especially of the body or a part of it. lens power - ANSWER the difference between the radii of the anterior and posterior lens surface abrasion - ANSWER rubbing off of the superficial layer accommodation - ANSWER adjustment by the eye for seeing different distances, accomplished by changing the shape of the crystalline lens through action of the ciliary muscle