NCLE Basic Exam Study Guide 2024 Graded A+

Diffused Illumination – -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 – -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 – -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 – -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 – -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 – -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 – -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 – -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 – -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 – -Show spherical aberrations -More useful when assessing visual performance of post refractive patients Corneal Topography - Elevation Map – -Shows the difference in the elevation of the cornea -Measured in microns Corneal Topography - Irregularity Map – -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 - Photokeratoscopic Views - Uses the placido rings which are reflected onto the eye to subjectively determine the location and regularity of the rings Corneal Topography - Numerical Views – -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 - -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 - -Graphically represent the individual axes of the cornea to help depict the 3-D nature of the cornea Radiuscope - -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 - -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 - -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 - -Used to view lens edges, surface, blends, overall diameter, and optical zone diameter The optical zone diameter can be measured with what instruments? - -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... - -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... - -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 - +/-0.25D Tolerance for sphere powers over +/-10D - +/-0.50D Tolerance for cylinder powers less than 2D - +/-0.25D Tolerance for cylinder powers between 2D and 4D - +/-0.37D Tolerance for cylinder powers greater than 4D - +/-0.50D The axis should be within º - 5 The add power should be within +/- D - 0.25 The power of a given lens is usually expressed in vertex power. - Back (BVP) When measuring back vertex power, the lens should be read with the surface facing the examiner. - Anterior The center of a GP CL is measured with a - -Thickness gauge/lens gauge/lens thickness gauge -Measured in 10ths of mm -Tolerance is +/-0.02 mm Central Posterior Curve (CPC) - -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) - -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) - -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) - -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) - -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) - -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 - -Linear measurement of lens' chord length, passing through its geometrical center -Commonly called size or width -Expressed in mm Edge - -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 - -Should be read/expressed as BVP -Expressed in diopters Thickness - -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) - -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 - Optical Zone: 7.9mm