NCLE Basic Exam Study Guide
1. "K" is the ____ of the two meridians - ANS-flatter
2. 4 refractive mediums - ANS--Cornea
3. -Aqueous
4. -Crystalline Lens
5. -Vitreous
6. 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. - ANS-loose
7. A lens with a steep CPC that vaults the corneal apex and touches the cornea at its
peripheries is considered a ____ fittinglens. This lens will not ride freely over the cornea
and will generally cause corneal edema and subsequent spectical blur. - ANS-tight
8. Back Surface Toric Lens - ANS--A contact lens that has two different and perpendicular
radii of curvature on its posterior surface only
9. -Has a spherical anterior surface
10. -Only functional when manifest cylinder is 1.5 times greater than corneal astigmatism
11. -Only used when the corneal toricity is so great that alignment in all meridians is not
possible
12. -Toric curves on the posterior surface are required when a spherical lens results in areas
of excessive clearance or bearing
13.
14. example: -2.00-4.00x180
15. 42.00@180/45.00@90
16.
17. Refractive Cyl: 4.00D
18. Corneal Cyl: 3.00D
19. Bitoric Lens - ANS-A contact lens that has two different and perpendicular radii of
curvatures on both the anterior and the posterior surfaces
20. Central Anterior Curves (CAC) - ANS--Radius of curvature of the anterior portion of the
lens
21. -Determines power of the finished lens
22. -Varies from lens to lens
23. -Must compute with the CPC to yield the pre-determined power
24. -Not relative to the fitting of the lens, only to its manufacture
25. -Does not have to relate to the surface power of the cornea
26. -Expressed in mm of radius of curvature
27. -Manufacturers have slide rules/charts available to relate the CAC to a required power
from a given CPC and thickness
, 28. Central Posterior Curve (CPC) - ANS--The Posterior radius of curvature designed to
conform to the apical zone of the cornea
29. -Must be highly polished and of definite optical quality
30. -Referred to in terms of the surface power of the cornea to which it is related
31. -Should be expressed in diopters, followed with its radius in mm enclosed in parenthesis.
32. -AKA base curve or radius
33. Complex formula for vertex distance - ANS-Fᴮ = ____Fᴬ____ *WVtx is less than RVtx
34. 1-(dFᴬ)
35.
36. Fᴮ = ____Fᴬ____ *WVtx is greater than RVtx
37. 1+(dFᴬ)
38.
39. Fᴬ = primary focal length of the RVtx
40. Fᴮ = focal length of the compensated power at the WVtx (eyewear or CL)
41. d = distance in meters that the lens has been moved
42.
43. *always round answer to the nearest 0.125D
44. Corneal Topography - Axial Map - ANS--Most widely understood map of the cornea for
many CL fitters
45. -Overall shape of the cornea
46. -Colors relate to steepness/flatness
47. -Sagittal reading measures the curvature of the cornea in diopters and is called the axial
power map
48. -Calculates curvature rather than power
49. Corneal Topography - Elevation Map - ANS--Shows the difference in the elevation of the
cornea
50. -Measured in microns
51. Corneal Topography - Irregularity Map - ANS--Similar to elevation maps
52. -Uses best fit toric surface as a reference
53. -Eliminates any toricity from the eye and displays the elevation differences
54. Corneal Topography - Keratometry Views - ANS--Represent the keratometric readings
along with the axes of the eye's presumed astigmatism
55. -Dioptric values define the findings from the center of the cornea to the periphery
56. -This view helps the practitioner to quickly determine if corneal astigmatism is
symmetrical
57. Corneal Topography - Numerical Views - ANS--Arranges individual keratometric findings
to depict curvature readings of the eye
58. -Extremely useful when fitting specialty contacts
59. -Corneal topographic software calculates the "average keratometric" value
60. Corneal Topography - Photokeratoscopic Views - ANS-Uses the placido rings which are
reflected onto the eye to subjectively determine the location and regularity of the rings
61. Corneal Topography - Profile Views - ANS--Graphically represent the individual axes of
the cornea to help depict the 3-D nature of the cornea
62. Corneal Topography - Refractive Power Map - ANS--Show spherical aberrations
1. "K" is the ____ of the two meridians - ANS-flatter
2. 4 refractive mediums - ANS--Cornea
3. -Aqueous
4. -Crystalline Lens
5. -Vitreous
6. 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. - ANS-loose
7. A lens with a steep CPC that vaults the corneal apex and touches the cornea at its
peripheries is considered a ____ fittinglens. This lens will not ride freely over the cornea
and will generally cause corneal edema and subsequent spectical blur. - ANS-tight
8. Back Surface Toric Lens - ANS--A contact lens that has two different and perpendicular
radii of curvature on its posterior surface only
9. -Has a spherical anterior surface
10. -Only functional when manifest cylinder is 1.5 times greater than corneal astigmatism
11. -Only used when the corneal toricity is so great that alignment in all meridians is not
possible
12. -Toric curves on the posterior surface are required when a spherical lens results in areas
of excessive clearance or bearing
13.
14. example: -2.00-4.00x180
15. 42.00@180/45.00@90
16.
17. Refractive Cyl: 4.00D
18. Corneal Cyl: 3.00D
19. Bitoric Lens - ANS-A contact lens that has two different and perpendicular radii of
curvatures on both the anterior and the posterior surfaces
20. Central Anterior Curves (CAC) - ANS--Radius of curvature of the anterior portion of the
lens
21. -Determines power of the finished lens
22. -Varies from lens to lens
23. -Must compute with the CPC to yield the pre-determined power
24. -Not relative to the fitting of the lens, only to its manufacture
25. -Does not have to relate to the surface power of the cornea
26. -Expressed in mm of radius of curvature
27. -Manufacturers have slide rules/charts available to relate the CAC to a required power
from a given CPC and thickness
, 28. Central Posterior Curve (CPC) - ANS--The Posterior radius of curvature designed to
conform to the apical zone of the cornea
29. -Must be highly polished and of definite optical quality
30. -Referred to in terms of the surface power of the cornea to which it is related
31. -Should be expressed in diopters, followed with its radius in mm enclosed in parenthesis.
32. -AKA base curve or radius
33. Complex formula for vertex distance - ANS-Fᴮ = ____Fᴬ____ *WVtx is less than RVtx
34. 1-(dFᴬ)
35.
36. Fᴮ = ____Fᴬ____ *WVtx is greater than RVtx
37. 1+(dFᴬ)
38.
39. Fᴬ = primary focal length of the RVtx
40. Fᴮ = focal length of the compensated power at the WVtx (eyewear or CL)
41. d = distance in meters that the lens has been moved
42.
43. *always round answer to the nearest 0.125D
44. Corneal Topography - Axial Map - ANS--Most widely understood map of the cornea for
many CL fitters
45. -Overall shape of the cornea
46. -Colors relate to steepness/flatness
47. -Sagittal reading measures the curvature of the cornea in diopters and is called the axial
power map
48. -Calculates curvature rather than power
49. Corneal Topography - Elevation Map - ANS--Shows the difference in the elevation of the
cornea
50. -Measured in microns
51. Corneal Topography - Irregularity Map - ANS--Similar to elevation maps
52. -Uses best fit toric surface as a reference
53. -Eliminates any toricity from the eye and displays the elevation differences
54. Corneal Topography - Keratometry Views - ANS--Represent the keratometric readings
along with the axes of the eye's presumed astigmatism
55. -Dioptric values define the findings from the center of the cornea to the periphery
56. -This view helps the practitioner to quickly determine if corneal astigmatism is
symmetrical
57. Corneal Topography - Numerical Views - ANS--Arranges individual keratometric findings
to depict curvature readings of the eye
58. -Extremely useful when fitting specialty contacts
59. -Corneal topographic software calculates the "average keratometric" value
60. Corneal Topography - Photokeratoscopic Views - ANS-Uses the placido rings which are
reflected onto the eye to subjectively determine the location and regularity of the rings
61. Corneal Topography - Profile Views - ANS--Graphically represent the individual axes of
the cornea to help depict the 3-D nature of the cornea
62. Corneal Topography - Refractive Power Map - ANS--Show spherical aberrations
