NCLE Basic Exam Study Guide
Questions with 100% Correct
Answers
A ____ fitting lens is fitted flatter than K and will touch at the corneal apex with
excessive movement over the cornea. It is not uncommon for this lens to fall off the eye
or become easily decentered. Such a lens may cause abrasions at the corneal apex
and may also cause corneal edema. - Answer- loose
If the lens is too flat, the fitter will generally ____ the fit by going ____ . - Answer-
tighten, steeper
4 refractive mediums - Answer- -Cornea
-Aqueous
-Crystalline Lens
-Vitreous
Index of refraction of the cornea - Answer- 1.37(6) (Avg. dioptric power: 43D)
Index of refraction of the aqueous - Answer- 1.33
Index of refraction of the Crystalline lens - Answer- 1.42 (Avg. dioptric power: 17D)
Index of refraction of the vitreous - Answer- 1.33
Index of refraction of the tear film - Answer- 1.33
Index of refraction of the lens material - Answer- Varies depending on the material, but
generally close to 1.33
When measuring back vertex power, the lens should be read with the ____ surface
facing the examiner. - Answer- Anterior
The center of a GP CL is measured with a _____ - Answer- -Thickness gauge/lens
gauge/lens thickness gauge
-Measured in 10ths of mm
-Tolerance is +/-0.02 mm
, Central Posterior Curve (CPC) - Answer- -The Posterior radius of curvature designed to
conform to the apical zone of the cornea
-Must be highly polished and of definite optical quality
-Referred to in terms of the surface power of the cornea to which it is related
-Should be expressed in diopters, followed with its radius in mm enclosed in
parenthesis.
-AKA base curve or radius
Intermediate Posterior Curve (IPC) - Answer- -Section of curvature that lies between the
CPC and the peripheral posterior curve
-There may be one or more of these curvatures, which can be designated as IPC1,
IPC2, etc.
-Can be expressed in mm, but most often described in diopters
-Also notated by its width of curvature in mm
**example: IPC 37.00D (9-12 mm) width 0.2 mm
Peripheral Posterior Curve (PPC) - Answer- -Outermost curve of a lens
-Designed to yield a smooth transition from the IPC to the edge of the lens
-In combination with the IPC, it allows tear exchange beneath the lens
-Was once referred to as the secondary curve, bevel, or inner edge
-Also expressed in diopters, followed by a mm value and width
**example: PPC 26.00D (13.00 mm) width 0.4 mm
The lacrimal lens will have a refractive power ____ ____ to the dioptric value of the
steepness or flatness in relationship to the cornea. - Answer- proportionally equal
-Example: a lens fit 0.50D steeper than K will have a lacrimal lens of +0.50D
"K" is the ____ of the two meridians - Answer- flatter
Diffused Illumination - Answer- -Uses widest slit, longest aperture
-Light source positioned at an angle of 40º-50º
-Used to view overall areas, to observe the ocular adnexa, cornea, sclera, lids,
conjunctiva, lens surface, and CL fitting characteristics
Direct Illumination - Answer- -Most important/useful illumination
-Light source positioned at an angle of 40º-50º to oculars
-Light beam and oculars are focused in coincidence on area being evaluated
-The difference in the illumination is not the angle used, but where the beam is directed
or focused and the width
-Varying width and aperture creates different illuminations
Optic(al) Section - Answer- -Type of direct illumination that uses a narrow beam to
create a cross-section of the cornea
-Used to illuminate and observe individual layers of the cornea and tear film
-Used to evaluate corneal thickness, thinning, distortions, or depth of a foreign body
Questions with 100% Correct
Answers
A ____ fitting lens is fitted flatter than K and will touch at the corneal apex with
excessive movement over the cornea. It is not uncommon for this lens to fall off the eye
or become easily decentered. Such a lens may cause abrasions at the corneal apex
and may also cause corneal edema. - Answer- loose
If the lens is too flat, the fitter will generally ____ the fit by going ____ . - Answer-
tighten, steeper
4 refractive mediums - Answer- -Cornea
-Aqueous
-Crystalline Lens
-Vitreous
Index of refraction of the cornea - Answer- 1.37(6) (Avg. dioptric power: 43D)
Index of refraction of the aqueous - Answer- 1.33
Index of refraction of the Crystalline lens - Answer- 1.42 (Avg. dioptric power: 17D)
Index of refraction of the vitreous - Answer- 1.33
Index of refraction of the tear film - Answer- 1.33
Index of refraction of the lens material - Answer- Varies depending on the material, but
generally close to 1.33
When measuring back vertex power, the lens should be read with the ____ surface
facing the examiner. - Answer- Anterior
The center of a GP CL is measured with a _____ - Answer- -Thickness gauge/lens
gauge/lens thickness gauge
-Measured in 10ths of mm
-Tolerance is +/-0.02 mm
, Central Posterior Curve (CPC) - Answer- -The Posterior radius of curvature designed to
conform to the apical zone of the cornea
-Must be highly polished and of definite optical quality
-Referred to in terms of the surface power of the cornea to which it is related
-Should be expressed in diopters, followed with its radius in mm enclosed in
parenthesis.
-AKA base curve or radius
Intermediate Posterior Curve (IPC) - Answer- -Section of curvature that lies between the
CPC and the peripheral posterior curve
-There may be one or more of these curvatures, which can be designated as IPC1,
IPC2, etc.
-Can be expressed in mm, but most often described in diopters
-Also notated by its width of curvature in mm
**example: IPC 37.00D (9-12 mm) width 0.2 mm
Peripheral Posterior Curve (PPC) - Answer- -Outermost curve of a lens
-Designed to yield a smooth transition from the IPC to the edge of the lens
-In combination with the IPC, it allows tear exchange beneath the lens
-Was once referred to as the secondary curve, bevel, or inner edge
-Also expressed in diopters, followed by a mm value and width
**example: PPC 26.00D (13.00 mm) width 0.4 mm
The lacrimal lens will have a refractive power ____ ____ to the dioptric value of the
steepness or flatness in relationship to the cornea. - Answer- proportionally equal
-Example: a lens fit 0.50D steeper than K will have a lacrimal lens of +0.50D
"K" is the ____ of the two meridians - Answer- flatter
Diffused Illumination - Answer- -Uses widest slit, longest aperture
-Light source positioned at an angle of 40º-50º
-Used to view overall areas, to observe the ocular adnexa, cornea, sclera, lids,
conjunctiva, lens surface, and CL fitting characteristics
Direct Illumination - Answer- -Most important/useful illumination
-Light source positioned at an angle of 40º-50º to oculars
-Light beam and oculars are focused in coincidence on area being evaluated
-The difference in the illumination is not the angle used, but where the beam is directed
or focused and the width
-Varying width and aperture creates different illuminations
Optic(al) Section - Answer- -Type of direct illumination that uses a narrow beam to
create a cross-section of the cornea
-Used to illuminate and observe individual layers of the cornea and tear film
-Used to evaluate corneal thickness, thinning, distortions, or depth of a foreign body
