NCLE Basic Exam Study Guide Questions and Answers Rated A+, Exams of Advanced Education

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NCLE Basic Exam Study Guide Questions and Answers Rated A+ 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 -Shows corneal-lens relationship Parallelepiped -Answer✅ -Type of direct illumination -Uses a 0.5-3.0 mm beam and a 40º-50º angle to create a 3-D cube -Used to assess width, depth, and height of an object within the cornea -Useful in observing scars, infiltrates, staining, and the corneal-lens relationship Indirect Illumination -Answer✅ -Light source is moved out-of-click, the beam is 2-3 mm wide and is positioned next to the area being studied -Illuminated area is translucent or opaque, allowing for observation adjacent to illumination -Used to observe foreign bodies, corneal nerves, and opacities -Oscillation of light accentuates details Retroillumination -Answer✅ -Light source is out-of-click, moved to the side of the area being observed -Using a 1-3 mm beam, the light is reflected off the iris and used to back-light the area studied -Useful in examining corneal scars, debris, microcysts, scratches on the lens, sub-epithelial changes, corneal vascularization, diffuse edema, and surface deposits Sclerotic Scatter -Answer✅ -Uses a focused parellelepiped placed out-of-click directed at the limbus -Oculars are not used -The light is dispersed at the limbus, reflected through the cornea, creating a circumcorneal halo -Used to observe edema, stromal folds, lens deposits, bubbles under the lens, lens defects, and scratches Corneal Topography - Axial Map -Answer✅ -Most widely understood map of the cornea for many CL fitters -Overall shape of the cornea -Colors relate to steepness/flatness -Sagittal reading measures the curvature of the cornea in diopters and is called the axial power map -Calculates curvature rather than power Corneal Topography - Tangential Map -Answer✅ -More sensitive map of the cornea -Calculates corneal curvature based on the tangent to normal -Found to be more beneficial in identifying corneal pathology -Not used as frequently to fit CLs Corneal Topography - Refractive Power Map -Answer✅ -Show spherical aberrations -More useful when assessing visual performance of post refractive patients Tolerance for cylinder powers less than 2D -Answer✅ +/-0.25D Tolerance for cylinder powers between 2D and 4D -Answer✅ +/-0.37D Tolerance for cylinder powers greater than 4D -Answer✅ +/-0.50D The axis should be within º -Answer✅ 5 The add power should be within +/- D -Answer✅ 0.25 The power of a given lens is usually expressed in vertex power. -Answer✅ Back (BVP) 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 Central Anterior Curves (CAC) -Answer✅ -Radius of curvature of the anterior portion of the lens -Determines power of the finished lens -Varies from lens to lens -Must compute with the CPC to yield the pre-determined power -Not relative to the fitting of the lens, only to its manufacture -Does not have to relate to the surface power of the cornea -Expressed in mm of radius of curvature -Manufacturers have slide rules/charts available to relate the CAC to a required power from a given CPC and thickness Intermediate Anterior Curvature (IAC) -Answer✅ -The curvature on the anterior lens surface between the central anterior curve and the peripheral anterior curve -Present in high plus lenses with a lenticular flange to increase edge thickness or in high minus lenses to reduce edge thickness -Expressed in mm of radius of curvature Peripheral Anterior Curve (PAC) -Answer✅ -Lies between the IAC and the edge of the lens -Expressed in mm -Generation and polishing are considered part of the edging process of manufacture -Previously called the front bevel Diameter -Answer✅ -Linear measurement of lens' chord length, passing through its geometrical center -Commonly called size or width -Expressed in mm Edge -Answer✅ -Junction of the PAC and PPC -Blended and polished with a high speed buffing wheel or is cut or ground in any number of specific manners -The edging process is considered part of the generation and polishing of the peripheral curves -Should only be refered to as the edge, rather than bevel or secondary curve Power -Answer✅ -Should be read/expressed as BVP -Expressed in diopters Thickness -Answer✅ -Measured at geometrical center -Variable: depends on power, CPC, index of refraction of plastic being used, and diameter -A lens is generally ordered with a specific diameter and CPC. If so, the manufacturer will select a CAC that will yield minimal central thickness -If a lenticular type lens is used, the flange thickness is measured at the junction of the CAC and IAC -Measured in hundredths of millimeters Optical Zone (OZ) -Answer✅ -Area on the posterior lens surface -The linear diameter of the CPC -Determined by subtracting TWICE the widths of the PPC and various IPC from the overall diameter Bitoric Lens -Answer✅ A contact lens that has two different and perpendicular radii of curvatures on both the anterior and the posterior surfaces Front Surface Toric Lens -Answer✅ -A contact lens that has two different and perpendicular radii of curvature on its anterior surface only -Has a spherical posterior surface -Must be stabilized by truncation and/or prism ballast -Used when a spherical GP lens results in unacceptable residual astigmatism -When corneal astigmatism is less than refractive astigmatism, a special anterior surface may be needed Back Surface Toric Lens -Answer✅ -A contact lens that has two different and perpendicular radii of curvature on its posterior surface only -Has a spherical anterior surface -Only functional when manifest cylinder is 1.5 times greater than corneal astigmatism -Only used when the corneal toricity is so great that alignment in all meridians is not possible -Toric curves on the posterior surface are required when a spherical lens results in areas of excessive clearance or bearing example: -2.00-4.00x180 42.00@180/45.00@90 Refractive Cyl: 4.00D Corneal Cyl: 3.00D Delta K (∆K) -Answer✅ -Difference in the powers in the two principal meridians on the cornea -True corneal astigmatism is when ∆K equals the manifest cylinder, both in power and in axis If corneal astigmatism falls between 0 and 1.75D, you would start by going than K. - Answer✅ +0.50 steeper example: flattest meridian is 42.50. Going steeper by +0.50 brings it to 43.00, which would be the starting BC When moving a plus lens closer to the eye, it will effective power. -Answer✅ Decrease When moving a plus lens further from the eye, it will effective power. -Answer✅ Increase When moving a minus lens closer to the eye, it will effective power. -Answer✅ Increase When moving a minus lens further from the eye, it will effective power. -Answer✅ Decrease Vertex distance should be compensated for if power is over . -Answer✅ +/-7.00D for glasses +/-4.00D for contacts Simple formula for vertex distance -Answer✅ per mm of change = D²/1000 D= dioptric power If corneal astigmatism falls between 1.87 and 2.87D, you would start by going than K. - Answer✅ 0.75D steeper Complex formula for vertex distance -Answer✅ Fᴮ = Fᴬ *WVtx is less than RVtx 1-(dFᴬ) Fᴮ = Fᴬ *WVtx is greater than RVtx 1+(dFᴬ) Fᴬ = primary focal length of the RVtx Fᴮ = focal length of the compensated power at the WVtx (eyewear or CL) d = distance in meters that the lens has been moved *always round answer to the nearest 0.125D If corneal astigmatism is 3D and above, you would consider using a lens -Answer✅ Bitoric What diameter would you choose if Ks fall between 39.00-41.87? -Answer✅ 9.5mm What diameter would you choose if Ks fall between 42.00-45.87 -Answer✅ 9.0mm What diameter would you choose if Ks fall between 46.00-47.50 -Answer✅ 8.8mm If the diameter is kept constant and the BC is changed, the sagittal depth of the lens changes: Steeper BC = sag = fit Flatter BC = sag = fit -Answer✅ Steeper BC = Larger sag = Steeper fit Flatter BC = Smaller sag = Flatter fit