PART 3: LENS FORM AND ANALYSIS PRACTICE TEST - KEY d 1. c 2. To determine the power of a thin lens in air, it is necessary to consider: a. front curve and index of refraction b. back curve and index of refraction c. index of refraction only d. front curve, back curve and index of refraction A standard lens measure is calibrated for an index of refraction of: a. 1.490 b. 1.523 c. 1.530 d. 1.580 a 3. A +1.75 diopter lens fabricated with a +6.00 base curve will require a back curve of: Hint: +6.00 + Back Curve = +1.75 a. -4.25 D b. +4.25 D c. -7.75 D d. +7.75 D c 4. Toric transposition is used to determine: a. lens diameter b. lens thickness c. lens power in the principal meridians d. lens material d 5. A patient presents you with a prescription reading +2.75-1.00 x 180 in each eye. The refractive anomaly indicated by this Rx is: a. simple myopic astigmatism b. simple hyperopic astigmatism c. mixed astigmatism d. compound hyperopic astigmatism a 6. Corrected curve lenses are designed to: a. increase the useful area of the lens b. accommodate for larger eye sizes c. decenter more accurately d. always contain plus cylinders b 7. The following lenses are all made with the same radius of curvature on the front surface. Which of these materials will yield the greatest front surface power? Hint: Highest index of refraction. 1
a. crown glass b. flint glass c. CR-39 d. polycarbonate a 8. Rx: +2.50-0.50 x 180 +2.50 sphere PD = 67 During final inspection, it was determined that the optical centers of the lenses were placed 63mm apart. How much total prism will this produce, and in which direction is the base? Determine lens power at 180 degrees (Spheres are the same power in all directions). Apply Prentice s Rule. (2.50 x 4)/10 a. 1.0 prism diopter base in b. 1.0 prism diopter base out c. 0.5 prism diopter base in d. 0.5 prism diopter base out d 9. If the Rx -3.00 +0.50 x 90 is decentered 2 mm too much, how much prism will be created and in which direction is the base? Determine lens power at 180 degrees. Transposed, Rx reads -2.50-0.50 x 180. Apply Prentice s Rule (2.50x2)/10 = 0.5 a. 1.00 prism diopter base in b. 1.00 prism diopter base out c. 0.50 prism diopter base in d. 0.50 prism diopter base out d 10. Rx: +2.00-4.00 x 45 How much prism will be created if the optical center of this lens is received 5mm too wide? Determine lens power at 180 degrees. +2.00-2.00 (1/2 of cyl power since oriented at 45 degrees) = 0 or Plano Apply Prentice s Rule. (0x5)/10 = 0 a. 1.0 prism diopter b. 2.0 prism diopters c. 3.0 prism diopters d. none b 11. As a corrected curve lens increases in minus power, the base curve tends to become gradually: 2
b 12. As the radius of curvature of a spherical surface increases in length, its curve becomes gradually: a 13. As a corrected curve lens increases in plus power, the base curve tends to become gradually. a 14. As the radius of curvature of a spherical surface decreases in length, its curve becomes gradually: b 15. Rx: Plano 2.00 x 180 Which of the following refractive conditions if this lens designed to correct? a. simple hyperopic astigmatism b. simple myopic astigmatism c. compound hyperopic astigmatism d. compound myopic astigmatism c 16. Rx: +0.50-0.75 x 10 Which of the following conditions is this lens designed to correct? a. compound hyperopic astigmatism b. compound myopic astigmatism c. mixed astigmatism d. antimetropia c 17. Compound ophthalmic lenses usually consist of: a. spherical surfaces only b. cylindrical surfaces only c. both cylindrical and spherical surfaces d. all of the above a 18. The power of a cylinder along its axis contains: 3
a. no cylinder power b. the full power of the cylinder c. half the cylinder power d. three quarters of the cylinder power b 19. When the surfaces of a 1.530 index glass lens are measured with a lens clock, the front curve reads +6.00 and the back curve reads -5.50 D. The focal length of that lens is: hint: +6.00+-5.50 = 0.5 (total power) so, f=1/d or 2 = 1/0.5 a. 1 meter b. 2 meters c, 3 meters d. 4 meters a 20. The power of a compound lens in any given meridian will vary as the axis of the cylinder changes. Which of the following lenses contain no power in the ninety degree meridian? Hint: Transpose the following answers. a. -2.50 +2.50 x 180 Plano 2.50 x 90 b. -2.50 +2.50 x 90 c. -2.50 +2.50 x 45 d. -2.50 +2.50 x 135 b 21. When a plus lens is moved closer to the eye, its effective power: a. increases b. decreases c. remains the same d. creates prism b 22. When a high powered minus lens is moved closer to the eye, the compensated power must: a. be increased b. be decreased c. remain the same d. change the cylinder axis b 23. A +10.00 diopter lens is fit at a 14mm vertex distance. A new frame is selected which positions the back surface of the lens 9mm from the cornea. The power of the new lens needed to compensate for the change in vertex distance is: a. +11.00 b. +10.50 c. +10.00 d. +9.50 4
c 24. It is important to consider the vertex distance in spectacle lenses when the power exceeds: a. +/- 3.00 D b. +/- 4.00 D c. +/- 7.00 D d. +/- 9.00 D d 25. When a lens shape contains one convex surface and one concave surface, it is called a lens. a. biconvex b. biconcave c. plano concave d. meniscus c 26. The amount of power contained in any given prism is correctly expressed as: a. degrees of prism b. angle of deviation c. diopters of prism d. compensated power 5