Gas Permeable Contact Lenses – Lens Anatomy, Verification, and Selection Practice Test

These questions are part of the practice quiz. Start practicing

• Which statement about optic zone diameter and lens fit is true?
• The outermost curve that conforms to the flatter periphery is known as
• What is a downside of diagnostic GP fitting?
• When using a lens loupe/magnifier to identify the GP lens' overall diameter, is the diameter measured indirectly or directly?
• When selecting a GP lens, the most important aspect is the appropriate sagittal depth, which is influenced by:
• For high corneal cylinder nomograms start relative to K as:
• Nomograms for which corneal condition start steeper than K?
• In the SRx example, which option shows the cylinder axis (x) value?
• The optimum diameter should stabilize the lens along which meridians, and should allow for 1 mm of movement in which direction?
• The front optic zone diameter (OZD) is created by which factor?
• Which surface curvature determines the front optic zone diameter?
• What is the most common manufacturing method used for a GP lens?
• During lens verification, which aspect is prioritized to support patient comfort?
• Which of the following is a benefit of diagnostic GP fitting?
• What term describes the size of the GP lens from one edge to the opposite edge?
• What is the optically usable portion of the lens?
• Which statement best describes the purpose of base curve radius verification?
• Measuring corneal shape during pre-fit examination primarily helps with what aspect of lens design?
• What is the predicted final power when a GP lens is fit on K (on-K)?
• For steeper corneas (>45D), should you fit with smaller GP lenses or larger?
• Minus GP lenses position the lens in which direction?
• With the base curve expressed in radius (mm), a lower number corresponds to which curvature?
• Which parameter is primarily used to specify the refractive correction in a GP lens?
• In keratometry notation Ks 43/43.50 @ 090, what does the axis value specify?
• What is the average HVID used with GP lens fittings?
• A patient has an on-K GP lens. The GP trial power is -3.00 D, but the patient's prescription is -6.00 D. What is the over-refraction after vertex conversion?
• When the base curve is expressed in keratometry values (k's), a higher number indicates what?
• In GP lens terminology, what does BC stand for?
• For flatter corneas (<41D), should you fit with smaller GP lenses or larger?
• The base curve is the radius of curvature of which surface?
• Express the dioptric base curve in diopters when the radius (in millimeters) is given.
• Which scenario indicates toric lens over spherical?
• What term describes the distance across the GP lens from edge to edge?
• Which blending level allows for easy identification of the junction in a blended GP lens?
• How do we measure center/edge thickness of a GP lens?
• Increasing center thickness will cause decentration to become:
• Thicker edge profiles in GP lenses are most likely to influence which aspects?
• Decreasing the optic zone diameter leads to a flatter lens fit:
• What is a stated benefit of empirical GP fitting?
• How does increasing the base curve radius affect the dioptric value of the base curve?
• During GP lens verification, which parameter directly concerns the outer boundary of the lens?
• If a GP lens is fitted steeper than K and the tear layer is plus, this will require more of which power to neutralize?
• If we fit a GP lens flatter than the K, a minus/plus tear layer is formed (SAM FAP). What is the tear layer sign?
• In a diagnostic fitting set, the Dk value of lenses is typically:
• Aiming for about 0.5 mm wide band around the lens periphery is recommended.
• What does RA -0.50 x 180 represent?
• Which equation correctly represents the relationship between the optical zone, curve widths, and the overall diameter?
• Which statement describes the relationship between base curve radius and diopters?
• In the calculation example, what does OZ stand for in the equation OZ + 2(ICW) + 2(PCW) = OAD?
• In a tricurve GP lens, which region is the center and is the steepest?
• If we fit a GP lens flatter than K with a minus tear layer, this will require more plus or minus to neutralize? (SAM FAP)
• When the tear layer is minus, what adjustment is typically required to neutralize the final spherical power?
• If residual cylinder is less than -0.75 D OR less than 25% of overall spherical refractive error, using sphere is okay.
• A smaller GP lens tends to position the lens in which direction vertically on the cornea?
• The simplest fitting nomogram is based on which keratometry measure?
• If residual cylinder is 0.75 D OR greater AND at least 25% of the spherical refractive error, which lens type is recommended?
• If a GP lens is fitted steeper than the K, what tear layer sign is formed?
• Back optic zone diameter (OZD) is created by what?
• 0.1 mm radius of a base curve corresponds to how many diopters?
• What term describes the area between the innermost peripheral curves on each edge of a GP lens, which can be oval with toric designs?
• Which formula gives the radius of a GP lens when the base curve diopters are known?
• What is the mean Ks value if the readings are 43 and 43.50?
• In tear layer calculations for GP lenses, what constant is used in the tear layer formula tear layer power = (constant/diameter) - Ks?
• Which of the following is a stated benefit of empirical GP fitting?
• When measuring the power of a toric GP lens, all toric lenses will have ______ powers.
• If the tear layer power is +2.00 D, what adjustment is needed to neutralize this tear layer when determining the final spherical power?
• Increasing center thickness of a GP lens will cause the Dk to:
• Which statement best describes the palm test result for a good edge?
• What vision and comfort changes can occur with small GP lenses?
• Screening for GP lenses is virtually identical to SCLs. True or False?
• What is the power of the lenses included in a diagnostic fitting set?
• In keratometry-based base curve values, a lower value indicates the curve is
• Why is pupil diameter measurement important in GP lens fitting?
• Which of the following is NOT a corneal change typically looked for during the pre-fit examination of GP lenses?
• Which statement about the relationship between the base curve and the secondary curve in GP lens design?
• A WTR corneal astigmatism allows for better lens centration. Which option reflects this?
• Which option represents the average HVID used with GP lens fittings?
• What does OAD stand for in GP lens specifications?
• For moderate corneal cylinder, nomograms start relative to K as:
• Which of the following lists the three GP lens fit types?
• Which statement correctly describes the meaning of the difference between Ks readings with respect to astigmatism?
• Which two methods are used to measure the GP lens base curve?
• A 1D steeper K makes a tear lens of what power?
• A GP lens steeper than the keratometry readings yields a tear layer with which sign?
• In GP lenses, the direction of center thickness change associated with astigmatism is:
• In GP lens terminology, what does OZD stand for?
• Which fitting approach increases the first-fit success of GP lenses when used with empirical fitting?
• Back and bitoric lenses will have two base curves far from each other; front torics will have one base curve. Which lens type does this describe?
• For patient comfort, the two most important GP lens factors are:
• Which instrument is commonly used to evaluate the GP lens edge?
• Which corneal condition is explicitly listed as a good candidate for spherical GP lenses?
• How many curves are present in a tricurve GP lens?
• Which statement best describes a diagnostic GP fitting?
• How do we measure corneal shape during GP lens pre-fit assessment?
• Why is measuring corneal shape during the pre-fit examination important for GP lenses?
• For a tricurve GP lens, which curves would you expect to see?
• How do we find the spherical contact lens power of a GP lens?
• How do we verify the power of a GP lens?
• The smaller optic zone diameter results in the lens fit being:
• Which factor increases decentration in GP lenses?
• In a diagnostic fitting set, the center thickness (CT) of the lenses is:
• For spherical corneas, nomograms start relative to K as:
• What is the size of a large pupil?
• A radiusscope measures base curve by analyzing the distance between real and aerial images.
• Which instrument is used to verify the base curve radius of a GP lens?
• How are the peripheral widths typically measured?
• When the base curve is expressed in radius (mm), a higher number indicates what?
• In the pre-fit examination for gas-permeable lenses, how does palpebral aperture height influence the recommended lens size?
• The optic zone diameter should be larger than the pupil by about how many millimeters?
• The base curve corresponds to the radius of curvature of which surface?
• The curve that occurs between the base curve and the peripheral curve is called
• Which keratometry measurement defines the 'on K' nomogram?
• To position lower with minus lenses, the diameter should be:
• Plus GP lenses tend to position the lens:
• Why should the optic zone diameter be larger than the pupil by 1 mm?
• Which outcome is common to both empirical and diagnostic GP lens fittings?
• About a diagnostic fitting set, which statement is true?
• Lenses that will have two/multiple base curves very close to each other in the radiuscope are described as what?
• Using the formula OZ + 2(ICW) + 2(PCW) = OAD, if OAD = 9.2 mm, ICW = 0.3 mm, and PCW = 0.4 mm, what is OZ?
• Which corneal curvature category corresponds to fitting with a larger GP lens?
• True or False: Peripheral curve radii/widths are important for peripheral clearance because they help determine lens position and comfort.
• Front toric lenses will have how many base curves?
• A secondary/intermediate curve is flatter or steeper than the base curve?
• When evaluating surface quality, what should you look for on a GP lens?
• Which fitting approach dispenses GP lenses at a follow-up visit using information from the pre-fit examination?
• A larger GP lens tends to position the lens higher on the cornea.
• Topography is used in topographical fitting to create what?
• The central base curve should be steep enough to clear which anatomical landmark?
• If a tricurve GP is manufactured, what curves would you expect to see?
• The base curve radius will vary according to which two factors?
• For a tetracurve GP lens, which curves would you expect to see?
• What happens to Dk when center thickness increases?
• Which statement describes a good spherical GP lens candidate?
• More flexible materials will require a higher CT to prevent flexure. Which statement is correct?
• Minus lenses with plus carriers in GP lenses result in edges being:
• Which condition would most likely increase lens flexure?
• For a bicurve GP lens, which curves would you expect to see?
• Which of the following is an anatomic measurement category for GP lens pre-fit?
• For GP lenses with astigmatism, the center thickness is typically higher than standard. Which option reflects this?
• Which blending level makes junction identification particularly difficult?
• You fit a 7.34 mm GP lens on a patient with spherical Ks of 44.00 D. What is the power of your tear layer?
• What can edge thickness impact in GP lenses?
• For which level of corneal cylinder do nomograms typically start on K?
• If an edge is too blunt or too sharp, what is the likely outcome?
• What is the RA with SRx -2.50 -1.25 x 180 and Ks 45.00/45.75 @090?
• What are the two ways we can measure the base curve of a GP lens?
• Which term describes the widths of the curves surrounding the optical zone in GP lenses?
• The base curve of a GP lens is selected to optimize which fitting relationship?
• Which of the following is NOT listed as an aspect to identify during GP lens verification?
• Which blending level is the default if not specified in GP lens blending options?
• In Ks 43/43.50 @ 090, which meridian is steeper?
• Which statement is true about Dk and CT in diagnostic fitting sets?
• Besides the base curve radius, what else can we measure for lens verification?
• How is residual astigmatism calculated?
• Which statement best describes the relationship of plus/minus lens diameter to position?
• Which term denotes the diameter of the central optical zone on a GP lens?
• Which tools are used to measure HVID during the pre-fit evaluation?
• Which anatomic measurements should be recorded during the pre-fit GP lens examination?
• Which GP lens edge feature is described as ideal?
• What data are used to determine the base curve radius of a GP lens?
• The post-lens tear layer in gas-permeable lenses primarily eliminates which component of astigmatism?
• Why is it important to verify the base curve radius of a GP lens?
• For spherical GP candidacy, how does pupil size matter?
• If a bicurve GP is manufactured, what curves would you expect to see?
• What is the purpose of the tertiary/peripheral curve?
• What is the size of a small pupil?
• Increasing the optic zone diameter typically makes the lens fit:
• What is the correct setup when using a dial gauge to measure center/edge thickness?
• Which statement about GP base curve radius is true?
• Which fitting process involves placing diagnostic lenses on the eye and uses information from the pre-fit examination?
• What term describes the GP lens cornea-fitting relationship?
• If OAD = 9.6 mm, OZD = 7.8 mm, PCW = 0.4 mm, the ICW is:
• What is the typical average center thickness range for a GP lens?
• What is the mean keratometry reading derived from 43 and 43.50?
• Which statement about tear exchange in GP lenses is true?
• During pre-fit examination, which type of refractive information is extremely important for GP lenses?
• How can optical zone diameter be measured?
• The GP lens edge apex should be located relative to the posterior surface within which range?
• A 2D flatter K makes a tear lens of what power?
• What is the dioptric difference between the flat and steep keratometry readings in Ks 43/43.50 at 090?
• Which of the following is not part of the anatomic measurements collected in the pre-fit GP lens examination?
• For plus GP lenses, to position higher, the lens diameter should be:
• How is the overall diameter of a GP lens typically measured during verification?
• Which of the following is an accurate GP lens fit-type combination?
• Which instrument is used to verify the base curve radius of GP lenses?
• Which instruments can be used to evaluate the surface quality of a GP lens?
• To position higher with a plus GP lens, the diameter should be:
• Which statement correctly explains why full-time GP lens wearers may perform better than part-time wearers?
• Optical zone diameter can be determined by direct measurement or by calculation. Which formula describes the calculation?
• What potential problem can occur if the optic zone diameter is larger than the pupil by 1 mm?
• What is the standard optic zone diameter (OZD) labs select if you do not specify?
• Which corneal condition typically leads to nomograms starting flatter than K?
• Plus lenses with minus carriers in GP lenses affect edge thickness and seating how?
• Decreasing center thickness of a GP lens will cause lens flexure to:
• Which patient profile is listed as a good candidate for spherical GP lenses?
• What vision and comfort changes can occur with large GP lenses?
• How does a radiuscope determine the base curve radius?
• Measuring HVID during the pre-fit examination helps with what practical outcome?
• Why is taking an HVID measurement important during GP lens pre-fit examination?
• When the tear layer is plus, what adjustment is typically required to neutralize the final spherical power?
• Verification of a base curve radius should be performed before dispensing lenses.
• How many lenses are included in a diagnostic fitting set?
• During the palm test, which result indicates a good GP lens edge?
• What is the normal HVID measurement?
• In GP lens verification, which parameter defines the radius of the lens's base curve?