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

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NCLE Basic Exam Study Guide Questions

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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

Corneal Topography - Photokeratoscopic Views -Answer✅ Uses the placido rings which are reflected onto the eye to subjectively determine the location and regularity of the rings Corneal Topography - Elevation Map -Answer✅ -Shows the difference in the elevation of the cornea -Measured in microns Corneal Topography - Irregularity Map -Answer✅ -Similar to elevation maps -Uses best fit toric surface as a reference -Eliminates any toricity from the eye and displays the elevation differences Corneal Topography - Numerical Views -Answer✅ -Arranges individual keratometric findings to depict curvature readings of the eye -Extremely useful when fitting specialty contacts -Corneal topographic software calculates the "average keratometric" value Corneal Topography - Keratometry Views -Answer✅ -Represent the keratometric readings along with the axes of the eye's presumed astigmatism -Dioptric values define the findings from the center of the cornea to the periphery -This view helps the practitioner to quickly determine if corneal astigmatism is symmetrical Corneal Topography - Profile Views -Answer✅ -Graphically represent the individual axes of the cornea to help depict the 3-D nature of the cornea Radiuscope -Answer✅ -AKA optic spherometer -Used to verify base curves, including both spherical and toric curves -Also used to detect warped CLs -Tolerance for BC is +/-0.025 mm Lensometer -Answer✅ -AKA vertometer, lensmeter, focimeter

-Used to verify power of the lens, optics evaluation, cylinder power, axis location, and prism -When documenting power, the user should identify whether the reading is in front vertex vs. back vertex V-Channel; Hand Measuring Magnifier; or Shadowscope -Answer✅ -Used to measure the overall diameter of a GP lens -Measurement should be taken across the middle part of the lens -Tolerance is +/-0.05 mm in all meridians Shadowscope -Answer✅ -Used to view lens edges, surface, blends, overall diameter, and optical zone diameter The optical zone diameter can be measured with what instruments? - Answer✅ -Hand Measuring Magnifier or Shadowscope -Tolerance is +/-0.10 mm for a mild blend -Tolerance is +/-0.20 for a medium/heavy blend The blend on a GP lens should be... -Answer✅ -Light Blend: 0.10 mm -Medium Blend: 0.20 mm -Heavy Blend: 0.30 mm -Light blends are easier to see than heavy blends Peripheral curve width is measured... -Answer✅ -Using a hand measuring magnifier or a shadowscope -Tolerance is +/-0.05 mm for a light blend; +/-0.10 mm for a heavy blend Tolerance for sphere powers up to +/-10D -Answer✅ +/-0.25D Tolerance for sphere powers over +/-10D -Answer✅ +/-0.50D

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. 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

-HINT: Peripheral and intermediate curves are on BOTH sides of the lens Find the Optical Zone: PPC: 0.4mm IPC1: 0.2mm IPC2: 0.2mm Lens Diameter: 9.5mm -Answer✅ Optical Zone: 7.9mm 0.8mm x 2 = 1.6mm 9.5mm - 1.6mm = 7.9mm Lacrimal Lens -Answer✅ -AKA tear lens -Layer of tears between the back surface of the lens and the front surface of the cornea -If a lens is fit directly on the cornea, the lacrimal lens on zero -If a lens is fit steeper than the cornea, then a plus lacrimal lens is created and must be compensated for: steeper add minus (SAM) -If a lens is fit flatter than the cornea, then a minus lacrimal lens is created and must be compensated for: flatter add plus (FAP) -Will take on the properties of a lens when in contact between the cornea and contact lens 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. -Answer✅ tight 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. Index of refraction of the Crystalline lens -Answer✅ 1.42 (Avg. dioptric power: 17D) Index of refraction of the vitreous -Answer✅ 1. Index of refraction of the tear film -Answer✅ 1. Index of refraction of the lens material -Answer✅ Varies depending on the material, but generally close to 1. 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 Sagittal Value -Answer✅ The distance from the geometrical center of a lens on its posterior surface, perpendicular to its corneal 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- 4.00x 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/ 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