70 Multiple Choice Questions (MCQS) - optics and refraction.doc
- 1. Each question below contains suggested responses. Select the one best response to each Question Questions: 1-4. Object is 1 meter in front of a -2.00 D lens, which is 2/3 meter in front of a +3.00 lens 1. The intermediate image formed by the concave lens is (A) real, inverted, and minified (B) virtual, upright, and magnified (C) virtual, upright, and minified (D) real, upright, and magnified (E) virtual, inverted, and magnified 2. The intermediate image formed by the concave lens is located (A) 1/3 m in front of the lens (B) 1/2 m in front of the lens (C) 2/3 m in front of the lens (D) 1/3 m behind the lens (E) 1/2 m behind the lens 3. The final image formed by the convex lens is (A) virtual and upright (B) formed at the lens (C) real and upright (D) virtual and inverted (E) real and inverted 4. The final image formed by the convex lens is located (A) at infinity (B) 1/2 m in front of the lens (C) 1/3 m behind the lens (D) 1/2 m behind the lens (E) 2 m behind the lens 5. You wish to correct an exotropia of 14∆ with distance fixation in a bilaterally aphakic patient wearing +20 D spectacle lenses OU. How much and in which direction should you decenter each lens to achieve the desired prismatic correction? (A) 7 mm in (B) 3.5 mm in (C) 7 mm out (D) 3.5 mm out (E) 2.8 mm out 6. A patient wearing +3.00 +3.00 x 180° OD and -2.00 +4.00 x 90° OS complains of vertical diplopia reading 8 mm below the optical centers. The net spectacle-induced vertical prism in the reading position is (A) 3.2∆ base up right eye (B) 6.4∆ base up left eye (C) 6.4∆ base down left eye (D) 3.2∆ "" base up left eye (E) 1.6∆ base down left eye 1
- 2. 7. The entrance pupil of the human eye is (A) the image of the pupil as formed by the crystalline lens and vitreous humor (B) located at the anterior focal point of the eye when fully accommodated (C) the image of the pupil as formed by the v cornea and aqueous humor (D) 50 percent larger than and 2 mm in front of the actual pupil in most eyes (E) located at the posterior focal point of the emmetropic eye 8. You must recalibrate your visual acuity test letters to accommodate a 3 m testing distance. How tall should the recalibrated 20/100 letters be in millimeters? (A) 4.36 (B) 13.7 (C) 18.9 (D) 21.8 (E) 37.8 9. A patient with -3D refractive errors OD has a combined horizontal and vertical strabismus in primary position requiring a 4∆ base down prism OD and 12∆ base out prism OS for correction. How might you prescribe the prisms to distribute the weight equally between the two lenses? (A) 4∆ base down OD, 12∆ base out OS (B) 6∆ base out OD, 2∆ base up OS (C) 6∆ base at 18° OD (D) 6∆ base down and out at 18° OD, 6∆ base up and out at 18° OS (E) 7∆ base down and out at 25° OD, 7∆ base up and out at 25° OS Questions: 10-11. Object is located 2 meters in front of a +2.50 D lens, which is located 1.5 meters in front of a +2.00 D lens. 10. The vergence of light from the object exiting the posterior surface of lens 2 is (A) -1 D (B) -0.5 D (C) 0 D (D) +1D (E) +3 D 11. If the object is moved 1.5 m closer to lens 1, its final image moves (A) 1 m further away from lens 2 (B) 1.5 m further away from lens 2 (C) 0.5 m closer to lens 2 (D) 0.75 m closer to lens 2 (E) to infinity 12. The back vertex power of a thick, biconvex, spherical lens in air is (A) measured by placing the anterior surface of the lens against the nose cone of a manual lensmeter (B) always greater than the effective lens power (C) the reciprocal of the distance from the secondary principal plane to the posterior vertex point (D) equal to its front vertex power (E) measured as the reciprocal of the distance from the posterior nodal point to the posterior focal point 2
- 3. 13. A young myopic patient has an uncorrected far point of 25 cm and an amplitude of accommodation of 8 D. Wearing -2 0 lenses, OU, his near point of accommodation is (A) 5 cm (B) 10 cm (C) 12.5 cm (D) 16.7 cm (E) 50 cm 14. If the two spherocylindrical lenses below are added together, the resultant lens measures +4 -3 x 180° +2 +3 x 90° (A) +3 +9 x 90° (B) +3 +6 x 180° (C) +9 -6 x 180° (D) +9 -6 x 90° (E) +3 -6 x 90° 15. An object is placed in front of a convex spherical mirror with radius of curvature r. Its image is (A) real, upright, and magnified (B) virtual, upright, and magnified (C) real, inverted, and minified (D) real, inverted, and magnified (E) virtual, upright, and minified 16. Part way through the process of performing cycloplegic streak retinoscopy on the right eye of a 4-year-old child, +2.00 +2.00 x 90° is dialed into the Phoroptor. You find "with" movement sweeping the 180° meridian and "against" movement sweeping the 90° meridian. Assuming a working distance of 67 cm, which of the following final prescriptions is plausible? (A) -2.00 +3.00 x 90° (B) +0.50 +2.00 x 90° (C) +4.00 -2.00 x 180° (D) +1.00 +3.00 x 90° 17. In the process of refracting a patient from scratch using a Phoroptor, you determine an initial spherical correction and find no cylinder power in the 90°/180° meridians using a 0.25 D Jackson cross cylinder. The patient's visual acuity is 20/30. Your next step is to (A) refine the axis (B) look for cylinder power in the 45°/135° meridians (C) substitute a 1.00 D Jackson cross cylinder and look for cylinder power at 90°/180° (D) write the prescription (E) refine the sphere 18. Image jump and displacement are at their worst when bifocal spectacles with top segments are prescribed for patients. (A) round, emmetropic (B) flat, hyperopic (C) round, hyperopic (D) flat, myopic (E) round, myopic 3
- 4. 19. If a + 15 D spectacle lens at a vertex distance of 13 mm corrects an aphakic eye for distance viewing, what power contact lens will be necessary to correct the eye? (A) 18.90 D (B) 18.60 D (C) 17.30 D (D) 16.20 D (E) 13.8 D 20. When determining image location in a mirror system by ray tracing methods, the chief ray (A) passes through the focal point (B) strikes the mirror at right angles to its surface (C) is incident to the mirror parallel to the optical axis (D) is one of two rays available to determine object location (E) is always drawn from the tip of the object 21. Refer to the figure below. Regarding reflection and refraction of light at an optical interface, light is traveling from medium 1(n1) to medium 2 (n2). Note: n1 > n2 (A) the critical angle, θc for total internal reflection is sin-1 (n2/ n1) (B) if n1 = n2 all the light will be reflected (C) θi = θt only if n1 = n2 (D) as n1 approaches n2, θi approaches θr (E) light travels faster in medium n1 than in medium n2 22. An object is placed 1 m in front of a -2 D lens. The lateral or transverse magnification of the virtual image formed by the lens is (A) 1x (B) 3x (C) -3x (D) 0.33x (E) -0.33x 23. A submarine with an advanced, visible-wavelength laser antimissile weapon system and a not-so-advanced enemy missile tracking system (a recruit who looks out a window on the ship near the laser gun) is patrolling the ocean when an airborne enemy missile is sighted. To strike the missile, the laser must be directed (A) in front of the missile if it is approaching the submarine (B) behind the missile if it is approaching the submarine (C) directly at the missile whenever it is within range (D) directly at the missile, but only when it is precisely overhead (E) at the surface of the ocean at the critical angle for total internal reflection 24. Light streaming through a window highlights dust floating in the air. Assume the average dust particle is 0.1 mm in diameter and that an observer can see dust particles from 5 m away. Using the reduced schematic eye, the retinal image size of the average dust particle is (A) 0.34 mm (B) 0.28 mm (C) 0.028 mm (D) 0.34 μm (E) 0.28 μm 4
- 5. 25. A spherocylindrical lens +2.00 = +4.00 x 135° focuses light from infinity. The circle of least confusion is (A) located at the focal point of the sodium yellow wavelength (B) located midway linearly between the anterior and posterior focal lines (C) 25 mm posterior to the lens (D) 3 m posterior to the lens (E) located at the point that corresponds to the spherical equivalent of the lens 26. In recording strabismic deviations in degrees instead of prism diopters, 30∆ corresponds to (A) 86.6° (B) 57.7° (C) 23.4° (D) 16.7 ° (E) 8.66° 27. The anterior surface of a cornea with a radius of curvature of 7.7 mm and a refractive index of 1.376 has a reflecting power of (A) -260 D (B) -130 D (C) -48.8 D (D) -40 D (E) -15.7 D 28. The posterior surface of a cornea with a radius of curvature of 6.8 mm and a refractive index of 1.376 has a refracting power of (A) 5.76 D (B) 202 D (C) -55.3 D (D) -5.88 D (E) -4.76 D Question (29-35): An object is located 25 cm in front of lens 1 (+2 D), which located 50 cm in front of lens 2 (+1 D), which is located 50 cm in front of a lens 3 (unknown power), which is 50 cm in front of the image. 29. The vergence of light from the object as it exits lens 1 is (A) -4 D (B) -2 D (C) 0 D (D) 2 D (E) 6 D 30. Where is the intermediate image (if one exists) formed by lens 1 with respect to lens 1? (A) There is no intermediate image (B) At optical infinity (C) 2 m in front of lens 1 (D) 50 cm in front of lens 1 (E) 50 cm behind lens 1 31. The intermediate image formed by lens 1 (if one exists) is best described by which of the following? (A) There is no intermediate image (B) Real image at plus infinity (to the right of the lens) 5
- 6. (C) Virtual image at minus infinity (to the left of the lens) (D) Real and inverted (E) Virtual and upright 32. The vergence of light from the object exiting lens 2 is (A) -1 D (B) -0.33 D (C) 0 D (D) +1.33 D (E) +3 D 33. Where is the intermediate image formed by lens 2 with respect to lens 2? (A) 3 m in front of lens 2 (B) 1 m in front of lens 2 (C) at plus infinity (real image) or minus infinity (virtual image) (D) 33 cm behind lens 2 (E) 75 cm behind lens 2 3-34. The vergence of light from the object midway between lens 2 and lens 3 is (A) -0.8 D (B) -0.31 D (C) 0D (D) +2 D (E) +12.5 D 35. What power must be assigned to lens 3 for the final image to form as indicated? (A) +3 D (B) +2.8 D (C) +2 D (D) -2 D (E) No lens will work 36. A unilaterally aphakic patient comes to you for fitting of rigid contact lenses. The only contact lenses in your office are +3 D trial lenses. A lens with a 7.7 mm base curve, 9.5 mm diameter, and 8 mm optical zone is found to perform optimally from a mechanically fitting standpoint. Over this trial lens, a refraction of + I 4.5 D sphere at a vertex distance of 10 mm gives distance vision of 20/20+. What contact lens power would you specify when ordering the contact lens? (A)+17.5D (B) + 18 D (C) +18.5 D (D) + 19 D (E) +20 D 37. All the statements below regarding soft contact lenses are true EXCEPT (A) a lens whose diameter is too small will exhibit poor centration and excessive movement (B) a lens whose diameter is too large will produce fluctuations in visual acuity on blinking and will move poorly (C) lens power can be determined by transposing a manifest refraction to minus cylinder format and dropping the cylindrical component (D) the degree of hydration varies from 25 to 80 percent (E) large-molecule fluorescein preparations can be used without risk of staining the 6
- 7. lens 38. An aphakic optical engineer loses both of his +20 D contact lenses. He pulls from his dresser drawer a 50 mm diameter crown glass plus lens with a focal length of 125 mm. How far must he hold the lens from his eye to see objects in the distance clearly? (A) The lens will not work at any distance (B) 37 mm (C) 50 mm (D) 60 mm (E) 75 mm 39. A myopic boy with a cycloplegic refractive error of -5 D is given a +4 D lens and asked to hold it in a way that allows him to see clearly in the distance. Where must he hold it? (A) There is no distance at which it will work (B) 1 m behind him, optically speaking (C) 20 cm in front of him (D) 45 cm in front of him (E) 1 m away 40. A low-vision patient attempts to read newspaper print at a distance of 25 cm. He holds a 10 D lens 10 cm from the print. The angular magnification provided by this lens is (A) 1x (B) 2.5x (C) 5x (D) 6x (E) 10x 41. All the following may be used to test macular function in patients with dense cataracts EXCEPT (A) a strobe light (B) a laser interferometer (C) a Guyton-Minkowski potential acuity meter (D) a dark-room pinhole acuity test (E) a transilluminator light that is moved rapidly across closed eyelids to evoke an entopic image of the retinal vessels 42. Which of the following statements regarding light is FALSE? (A) If a HeNe aiming beam and an Nd:YAG beam focus at precisely the same point in air, the HeNe beam will focus anterior to the Nd:YAG beam inside the eye (B) If the pulse duration of an N d: Y A G laser is cut in half while the energy setting is kept the same, the power delivered with each pulse doubles (C) The xanthophyll pigment of the macula is more efficient at absorbing krypton red light than argon blue-green light (D) Irradiance (watts/meter2) is a radiometric measure of the amount of light incident on a surface per unit area (E) Illuminance (lux, or footcandles) is a photometric measure of the amount of light incident on a surface per unit area Question (43-45): While performing cycloplegic streak retinoscopy with a lens rack on a 3-year- old, you obtain the power cross: +3 D @ 90°, -2 D @ 180°. The power cross does not account for your working distance of 67 cm. 7
- 8. 43. What is the correct spectacle prescription? (A) +1.50 -5.00 x 180° (B) -3.50 +1.50 x 180° (C) -2.00 +5.00 x 180 ° (D) +1.50 -5.00 x 180° (E) + 1.50 -5.00 x 90° 44. What is the spherical equivalent refraction for this spectacle lens? (A) +0.50 D (B) + 1.00 D (C) 0 D (equivalent to a Jackson cross cylinder) (D) 1.00 D (E) -2.00 D 45. Which of the following statements is TRUE concerning this patient? (A) The eye behind the spectacle lens has to move more in the horizontal direction than in the vertical direction to sweep through the same visual angle in space (B) The child has with-the-rule astigmatism (C) It is not necessary to prescribe glasses because most children do well with uncorrected astigmatism (D) The child has mixed astigmatism (E) The child's myopic far line is located 1 m in front of the eye 46. An eye with a near point of accommodation of 12.5 cm has an amplitude of accommodation of 5 D. What is its spherical refractive error? (A) -5 D (B) -4 D (C) -3.5 D (D) -3 D (E) +3 D 47. Six weeks after phacoemulsification with intraocular lens implantation through a superiorly located 5.5-mm limbal wound closed with interrupted sutures, the following refraction is measured: +2.25 -6.75 x 75°. At what clock position would you look for a suture to cut? (A) You would not want to cut sutures in this case (B) 11 o'clock (C) 11:30 o'clock (D) 12 o'clock (E) 1 o'clock 48. What horizontal deviation is produced by looking 10 mm to the right of the optical centers of the following prescription lenses? OD +3.00 +1.00 x 90° (power cross: +3 D @ 90°, +4 D @ 180°) OS -4.00 +2.00 x 180° (power cross: -2 D @ 90°, -4 D @ 180°) (A) There is no induced ocular misalignment (B) 3∆ esodeviation (C) 8∆ esodeviation (D) 3∆ exodeviation (E) 8∆ exodeviation 49. If a human optic nerve head is 1.75 mm in vertical height, what is the height of its image as formed on the inside of a perimeter with a radius of curvature of 33 cm? (A) 3.4 mm (B) 6.1 mm 8
- 9. (C) 17 mm (D) 27 mm (E) 34 mm DIRECTIONS: Each question below contains four suggested responses of which one or more is correct. Select: A if 1, 2, and 3 are correct B if 1 and 3 are correct C if 2 and 4 are correct D if 4 is correct E if 1, 2, 3, and 4are correct 50. Equivalent methods for describing the power cross: +2 D @ 90°, +3 D @ 180° include (1) +2 + I x 180° (2) +3 -1 x 180° (3) +2 x 90° combined with +3 x 180° (4) +2 +1 x 90° 51. The image of an object placed at the center of rotation of a concave spherical mirror is (1) real (2) inverted (3) located at the same axial position as the object (4) the same size as the object 52. True statements about laser light include which of the following? (I) Argon green light emanating from a fiberoptic bundle is spatially coherent (2) Temporal coherence is a measure of the ability of two separated portions of a wavefront to interfere with each other (3) The typical beam divergence of most gas lasers is around 30°, or π/6 radians (4) Devices that test retinal potential acuity behind cataracts by forming interference fringes on the retina depend on a light source that is spatially coherent 53. Correct spherocylinder notations for this power cross: +2 D @ 135°, +3 D @ 45° include (1) +3 +2 x 45° (2) +3.-2 x 45° (3) +2 -1 x 135° (4) +2 +1 x 135° 3-54. Following cataract surgery, a patient who was 3.5 D myopic OU is now emmetropic in one eye. You are concerned about inducing vertical diplopia if you prescribe bifocal spectacles. Reasonable approaches to this potential problem include (1) prescribing the bifocals and seeing if the patient can adapt to them (2) prescribing slab off prism (3) encouraging the patient to forgo glasses and try monovision (4) prescribing a contact lens for the myopic eye and over-the-counter reading glasses 55. A 15-year-old boy wearing -3D spectacles OV reads the 20/15 line OU. Uncorrected, he reads the 20/25 line OU. His amplitude of accommodation is 12 D. True statements include (1) his near point of accommodation is 1/3 m (2) he is probably "overminused" (3) his range of accommodation in the uncorrected state is 1/3 m to infinity (4) his far point of accommodation in the uncorrected state determines his refractive error 9
- 10. 56. Using a Prince rule, you find that a patient's near point of accommodation is 10 cm and his far point of accommodation is 20 cm. True statements include (1) this patient is probably in his early 40s (2) this patient should be able to see clearly in the distance wearing -7 D spectacle lenses (3) the patient's near point of accommodation wearing the correct prescription lenses is 20 cm (4) the range of accommodation in the spectacle-corrected state is 10 cm 57. In a centered multiple-element optical system immersed in water, (1) a ray of light directed into the optical system through the anterior focal point exits the system parallel to the optical axis (2) the anterior principal point and the anterior nodal point are the same (3) a ray of light directed through the anterior nodal point will appear to emerge from the posterior nodal point displaced, but with the same inclination to the optical axis (4) the posterior principal point is the same as the posterior nodal point 58. In an optical system: a +5 D lens is placed 15 cm in front of a -20 D lens (1) produces inverted images of objects located at optical infinity (2) is an example of a simple astronomical telescope (3) has a net power of -15 D for distant objects, using thin lens optics (4) has an optical power of 4x 59. True statements regarding prism and cover test measurements of strabismus include which of the following? (1) Highly myopic patients have smaller actual deviations than they measure through their spectacles (2) Highly hyperopic, esotropic patients tend to be overcorrected if operated upon based on measurements obtained through spectacles (3) The actual deviation is greater than the measured deviation if a strabismus is measured with plastic prisms stacked in the same direction (4) Prisms should not be stacked in orthogonal directions (horizontally and vertically) over the same eye 60. True statements regarding pinhole apertures include (1) an eye with a pupil that is miotic from the use of pilocarpine will measure an artificially close near point of accommodation (2) the ideal diameter of a pinhole for screening patients for refractive errors in the -5 D to +5 range is 1.2 mm (3) patients with small, uncorrected refractive errors often squint to achieve a pinhole effect (4) if a pinhole aperture is too small, visual acuity will be limited by lateral chromatic aberration 61. Correct statements regarding Purkinje-Sanson images include (1) the first image is the brightest and is located posterior to the cornea (2) the first, third, and fourth images can be used to determine the tilt and decentration of intraocular lenses (3) eye movements may be tracked by determining the locations of the first and fourth Images (4) the fourth image is virtual and forms just behind the posterior surface of the lens 10
- 11. 62. True statements regarding magnification and ophthalmoscopes include which of the following? (1) The lateral magnification obtained using a direct ophthalmoscope is approximately 15x (2) The lateral magnification obtained using an indirect ophthalmoscope with a +20 D condensing lens is approximately 3x viewing the aerial image from 25 cm (3) The lateral magnification obtained using an indirect ophthalmoscope with a +30 D condensing lens is approximately 2x viewing the aerial image from 25 cm (4) The axial magnification obtained using an indirect ophthalmoscope with a +20 D condensing lens is 1 x viewing the aerial image from 25 cm 63. Monocular distortion from cylindrical spectacle lenses can be reduced by (1) switching to contact lenses (2) decreasing vertex distance (3) grinding the cylinder correction on the posterior lens surface (4) rotating the cylinder axis toward 90° or 180° 64. A young college student comes to you for a contact lens fitting. With his current spectacle prescription of -3 D sphere OU, he sees 20/15 OU. You place him in -3 D rigid, gas- permeable contact lenses OU. The lenses move and center well, but his visual acuity drops to 20/25 OU. With a manifest overrefraction of -1.25 +2.50 x 90° OU, he improves to 20/15 OU. True statements regarding this situation include (1) he probably has lenticular astigmatism (2) he probably has with-the-rule corneal astIgmatism (3) simple daily-wear, soft contact lenses should give a good optical result (4) bitoric, rigid, gas-permeable lenses cannot correct this patient's refractive error 65. Proper positioning of ophthalmic prisms is described by which of the following? (1) glass prisms are calibrated to be held in the Prentice position (2) Plastic prisms should be held with the visual axis perpendicular to the posterior surface of the prism (3) If a plastic prism is held in any position other than the calibrated position, it will produce (or correct) a deviation that is larger than the measured deviation (4) The primary deviation is measured by holding prisms over the fixating eye 3-66. True statements regarding the contrast sensitivity function include (1) it is an approximation to the modulation transfer function used to characterize linear optical systems (2) it is obtained ideally with single Landolt C optotypes of various sizes and contrasts (3) the peak of the normal human contrast sensitivity function is at 3 to 10 cycles per degree (4) cataract increases contrast sensitivity at all spatial frequencies 67. Early in the performance of streak retinoscopy at 67 cm, before any lenses have been dialed into the Phoroptor, you notice "with" motion in all meridians. The "with" motion sweeping the 180° meridian appears to move faster and have a broader reflex than that in other meridians. True statements include (1) your next step is to add minus sphere (dial up) in a plus cylinder Phoroptor (2) a -1.5 D lens "pushes" both far lines beyond optical infinity if they are not already there (3) this patient cannot have mixed astigmatism (4) this patient may have compound myopic astigmatism 11
- 12. 68. At the point of neutrality during streak retinoscopy (1) the reflex moves very slowly (2) moving away from the patient just a little produces "against" motion in all meridians (3) the refraction is complete . (4) the retina and the peephole of the retinoscope are conjugate points 69. Front surface toric contact lenses must be kept from rotating on the cornea if they are to correct residual (lenticular) astigmatism. Effective means for preventing lens rotation include which of the following? (1) Incorporating 1.5∆ of base down prism ballast (2) Truncating the lens by 0.5 to 1.0 mm (3) Choosing a toric posterior surface if there is a high degree of corneal astigmatism (4) Choosing a lenticular cut and a peripheral carrier with a minus design 70. The rate of oxygen flow to the cornea through a contact lens is (1) directly proportional to lens thickness (2) directly proportional to the surface area of the contact lens (3) indirectly proportional to the difference between the partial pressure of oxygen in the atmosphere and that at the corneal surface (Pair - P cornea) (4) directly proportional to the product of the solubility coefficient of oxygen in the lens material, D, and the diffusion coefficient of oxygen in the lens material, K. 12