Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

NCLE Basic Exam Study Guide Questions and Answers, Exams of Experimental Physics

A comprehensive study guide for the ncle (national contact lens examiners) basic exam. It covers a wide range of topics related to contact lens fitting and evaluation, including various illumination techniques, corneal topography, lens parameters, and optical principles. The guide provides detailed explanations and answers to key questions, making it a valuable resource for contact lens practitioners preparing for the ncle basic exam. The content covers essential knowledge and skills required for successful contact lens fitting and management, ensuring that readers are well-equipped to provide high-quality patient care. This study guide is designed to help students, optometrists, and other eye care professionals deepen their understanding of contact lens technology and enhance their clinical competence.

Typology: Exams

2024/2025

Available from 09/30/2024

LectDavid
LectDavid 🇬🇧

5

(2)

992 documents

1 / 12

Toggle sidebar

Related documents


Partial preview of the text

Download NCLE Basic Exam Study Guide Questions and Answers and more Exams Experimental Physics in PDF only on Docsity! 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