National Certification Organization
for Opticians
The National Contact Lens Examiners (NCLE) ABO
American Board of Opticianry
CLRE Contact Lens Registry Examination
Examination
180 minutes
Instructions:
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NCLE - CLRE Basic Contact Lens Exam Review
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The National Contact Lens Examiners NCLE ABO
American Board of Opticianry
CLRE Contact Lens Registry Examination
Read All Instructions Carefully and Answer All the
Questions Correctly Good Luck: -
Base curve
Radius of curvature on the back central surface of the contact
lens
Blend curve
the treatment given to the sharp junction between the
secondary and peripheral curve to eliminate sharp edges due
to abrupt changes in the curvature; it can be light, medium,
or heavy and it is typically equal to the average radii of the
secondary and peripheral curve.
Peripheral curve
Outermost curve on the back surface of the lens that is
designed to prevent the lens from pressing on the lumbar
area of the curve and enables it to move when the eye blinks.
Center Thickness (c.t.)
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The distance at the geometric center from the back surface to
the front surface
Diameter
Overall width of the lens from one end of the lens to the
other, at its widest point, and measured in mm.
Optical zone (o.z.)
Diameter on which the base curve extends on the back
surface of the lens.
Anterior optical zone
A curvature on the front surface that gives a lens its power,
also called lenticular cap
Back surface Toric lens design
Spherical front design but the back surface has Toric curves
at the major meridians, 90 degrees apart
Bitoric surface Toric lens design
Toric curves at the major meridians, 90 degrees apart, on
both the front and back surfaces of the lens
Front surface Toric lens design
Spherical back surface with Toric curves on the front surface
of the lens
“K”
The flattest meridian as determined by keratometry
Lenticular flange-a deliberate thickening or thinning of the
lens edge
Increase in edge thickness-aids
lens centering if the lens sits low in the cornea because it
raises the lens;known as a myoflange
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Decrease in edge thickness-good for high minus lenses to
limit lid interaction or to lower a high riding lens;known as
hyper flange
To increase edge thickness, order a flatter radius in relation
to the base curve
To decrease edge thickness, order a steeper radius in relation
to base curve
Lens edge- junction between the front and the back surface
of the lens
Anterior zone-touches the lid and it is designed to minimize
lid irritation
Posterior zone-small reverse curve on the back surface to
push the edge away from the surface of the eye; helps
maintain centration and allows movement of the lens during
blink.
Apex-where the two zones meet and should be sufficiently
rounded.
Lens power-
Measured as the difference between the radii of the front and
back surface
Prism ballast-
Larger addition of base down prism to the bottom of a lens
that helps orient position for specialty lenses such as
translating bifocal designs and Toric lenses.
Sagittal depth
Distance from a flat surface and the central back surface of
the lens
Spherical curves
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