Ophthalmology Review Myron Yanoff, Weiye Li, Uriel Schechter, Vincent B Lam, Kelly A Williamson, An Vo, Nancy Crawford, Stephanie J Weiss
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Optics and RefractionCHAPTER 1

Uriel Schechter,
Clifford Goodrich
QUESTIONS
Identify the incorrect answer for all questions (unless instructed otherwise).
1. Visible light:
  1. Wavelengths represent about 1% of the electromagnetic spectrum.
  2. Has wavelengths about the size of bacteria.
  3. Has shorter wavelengths than ultraviolet light.
  4. Has shorter wavelengths than radiowaves.
  5. Has wavelengths about 400–700 nm.
2. Earth's atmosphere:
  1. Absorbs potentially harmful ultraviolet and infrared radiation.
  2. Contains oxygen, carbon dioxide, and water vapor as protective substances.
  3. Is held in place by gravity.
  4. Contains water vapor from the oceans.
  5. Contains ozone formed by the reaction between diatomic oxygen and ultraviolet radiation.
3. Rhodopsin:
  1. Functions as a light-powered transmembrane ion pump in many single-celled organisms.
  2. Is present in anaerobic bacteria.
  3. Undergoes cis-trans isomerization shortly after light stimulation.
  4. Responds best to light at 605 nm.
  5. Is the precursor to human cone color pigments.
4. Potential acuity measurement:
  1. May use interferometry.
  2. Requires clear lens areas.
  3. Requires the patient's understanding of the testing goals.
  4. Tends to overestimate visual acuity when the media are very dense.
  5. Tends to overestimate acuity in patients who have macular edema.2
5. Epithelial edema-induced halos:
  1. Occur when the cornea acts as a diffraction grating.
  2. Are white when white-light objects are viewed.
  3. Can be seen by patients who have contact lens overwear.
  4. Are colored when white objects are viewed.
  5. Are usually seen around bright lights at night.
6. Polarized light:
  1. Is totally reflected when incident on a surface at the Brewster angle.
  2. Is partial under most circumstances.
  3. Is vertical in most human surroundings.
  4. From the corneal surface may affect calculations of corneal shape.
  5. Oscillates in a single plane.
7. The ozone layer:
  1. Is found high in the atmosphere.
  2. Is depleted by halogenated organic molecules.
  3. Reacts with the solar winds to form the aurora borealis.
  4. Can be formed during lightning strikes.
  5. Filters out most harmful ultraviolet light rays.
8. Ultraviolet light:
  1. Constitutes 25% of the energy output of the sun.
  2. Contains ultraviolet (UV)-A, -B, and -C.
  3. Causes greater damage in older individuals.
  4. Is filtered from the retina by the crystalline lens.
  5. Obeys Planck's equation: The energy content of radiation is 1240/wavelength (nm).
9. Ultraviolet (UV) light:
  1. Is divided into UV-A, UV-B, and UV-C, with UV-A being the most harmful to the superficial layers of the skin.
  2. Can be harmful on a partly cloudy day.
  3. Is essential to vitamin D creation.
  4. Induces age spots, skin dryness, and wrinkling.
  5. Can cause basal and squamous cell carcinomas.
10. Damage to the eye from ultraviolet light:
  1. Is dependent on intensity and duration of exposure.
  2. May result in conjunctival tumors.
  3. Usually causes superficial punctate keratopathy about 2–3 hours after exposure.
  4. May produce spheroidal degeneration after long exposure.
  5. May produce pterygium after long exposure.
11. The crystalline lens:
  1. Is susceptible to cataract formation by ultraviolet (UV) light exposure.
  2. Is susceptible to cataract formation by infrared light exposure.
  3. Contains enzymes that are affected by exposure to UV-C light.3
  4. Is susceptible to presbyopia at a younger age at lower latitudes.
  5. Responds to UV light by the creation of free radicals and molecular bond breakage.
12. All sunglasses:
  1. Protect against light damage to the eye.
  2. Improve contrast sensitivity.
  3. Improve dark adaptation.
  4. Reduce glare sensitivity.
  5. Vary in how much ultraviolet (UV) light they block from entering through the pupil.
13. Photochromic lenses:
  1. Darken when they contact UV light.
  2. Take longer to darken than lighten.
  3. Are excellent UV absorbers when dark.
  4. May be of glass or plastic.
  5. Absorb about 80% of incident light when maximally darkened.
14. Ultraviolet-absorbing lenses:
  1. Include almost all dark lenses.
  2. Include clear plastic allyl diglycol carbonate (CR-39) lenses.
  3. Include polycarbonate lenses.
  4. Cannot be fabricated from glass materials.
  5. Of CR-39 are more effective than those made of CR+39.
15. Identify the incorrect statement.
  1. A photon of blue light carries more energy than a photon of red light.
  2. A photon's energy is proportional to its frequency.
  3. Stimulated emission produces incoherent light.
  4. Spontaneous emission is a random process.
  5. Stimulated emission is not a random process.
16. Identify the incorrect statement.
  1. Gas lasers are the most frequently used ophthalmic lasers.
  2. Population inversion is caused by lights external to the cavity or by an electric discharge.
  3. Once achieved, population inversion needs not to be maintained.
  4. Most high-energy states decay in a few nanoseconds by spontaneous emission.
  5. Population inversion occurs when electrons in high-energy states outnumber those in low-energy states.
17. Identify the incorrect statement.
  1. Pulsed lasers deliver more energy overtime than continuous lasers.
  2. “Laser” is an acronym for “light amplification by stimulated emission of radiation”.
  3. Continuous lasers allow more control over energy than pulsed lasers.
  4. Excimer and neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers are pulsed.4
  5. Excimer lasers emit a beam of light with a wavelength of less than 200 nm.
18. Identify the incorrect statement.
  1. The number of available laser wavelengths can be increased by harmonic generation and use of organic dyes.
  2. The argon ion produces wavelengths of blue–green and green wavelengths.
  3. Xanthophyll pigment is abundant in the human macula and highly absorbs green light.
  4. Lasers may use gases, liquids, or solids as exciting materials.
  5. Krypton red lasers operating at 647 nm are commonly available.
19. Identify the incorrect statement.
  1. Powerful lasers that are useful as weapons are commonly available.
  2. Laser photocoagulation involves tissue light absorption which generates heat.
  3. Laser photodisruption is a mechanical process that creates a small, but high-energy shock wave at its focus.
  4. Laser photoablation breaks chemical bonds essentially vaporizing tissue.
  5. The laser-specific wavelength determines which light–tissue interaction occurs.
20. Identify the incorrect statement.
  1. In retinal photocoagulation, laser light is absorbed by the pigment in the retinal pigment epithelium and choroid.
  2. In photocoagulation, the energy is uniformly distributed across the whole diameter of the aiming beam.
  3. A tenfold increase in exposure time roughly doubles laser lesion diameter.
  4. Assuming constant laser power and duration, a smaller spot size is more likely to cause complications than a larger spot size.
  5. Doubling power doubles the lesion size.
21. Identify the incorrect statement.
  1. As a rule, contact lenses that invert the fundus view roughly double the spot size.
  2. Whenever laser spot size is changed, power must be adjusted to maintain an equal burn intensity.
  3. Contact lenses giving direct fundus view (e.g. Goldmann three-mirror lens) do not change spot size.
  4. Smaller spot sizes are rarely necessary outside the posterior pole.
  5. Shorter duration burns are less likely to disrupt Bruch's membrane than longer duration burns, given the same power and size.
22. Identify the incorrect statement.
  1. The retina thins in the periphery, so less power is necessary in that area.5
  2. Treatment of the peripheral retina is often painful for the patient.
  3. A noncircular aiming beam has lower power density than a circular type.
  4. The laser beam is rarely parfocal with the slit-lamp's viewing optics.
  5. Treatment of the posterior pole requires brief exposure times.
23. Identify the incorrect statement.
  1. The neodymium-doped yttrium aluminum garnet laser is a photodisruptor.
  2. High-energy requirements of the Nd:YAG demand a pulsed energy system.
  3. Q-switching describes the method of changing a laser's frequency.
  4. Mode locking produces the shortest and most powerful pulses.
  5. Most clinical photodisruptors are Q-switched.
24. The neodymium-doped yttrium aluminum garnet laser:
  1. Produces visible red light.
  2. Rarely coincides with the aiming beam.
  3. Produces a cone of light.
  4. Is used in capsulectomy by focusing in the anterior vitreous and moving forward.
  5. Is more likely to damage silicone intraocular lenses optically than acrylic ones.
25. Identify the incorrect statement.
  1. The total chromatic aberration of the human eye is approximately 3 diopters.
  2. Maximum eye sensitivity occurs at about 560 nm.
  3. Retinal photoreceptors point toward the second nodal point of the eye.
  4. The cornea-aqueous interface is the site of the greatest change in refractive index within the eye.
  5. Depth of focus increases, as pupillary diameter decreases.
26. Identify the incorrect statement.
  1. The Snellen formula assumes that each element in a 20/20 (6/6) target subtends 5 minutes of arc.
  2. The high contrast of a Snellen acuity chart does not represent the contrast of everyday targets.
  3. The Bailey–Lovie acuity chart uses 10 letters of similar difficulty with 5 per line.
  4. The Bailey–Lovie acuity chart uses a uniform change in angular size for each line.
  5. The Snellen acuity chart does not have an orderly progression of target size changes from line to line.
27. Identify the incorrect statement.
  1. Contrast is the difference in luminance of objects against a background.6
  2. Contrast sensitivity decreases with age.
  3. Contrast sensitivity decreases with decreased luminance.
  4. Pupil size of 1 mm gives the maximal modulation transfer function for high spatial frequencies.
  5. Visual acuity of 20/20 (6/6) is equivalent to 30 cycles per degree.
28. Identify the incorrect statement.
  1. Vernier acuity testing involves cortical processing, and allowing a subject to detect targets that are smaller than the diffraction limit of the eye.
  2. Retinal photoreceptors are triggered by a minimum of 3 quanta of visible light.
  3. Professional tennis players cannot visually follow the ball to the racquet with accuracy.
  4. Babe Ruth was only able to see 20/200 (6/60) out of his left eye, but was able to see 20/15 (6/4.5) out of his right eye.
  5. More than three retinal ganglion cells are connected to each foveal cone.
29. Identify the incorrect statement.
  1. Myopia has a racial predilection.
  2. Prolonged near work may cause increased myopia.
  3. The majority of myopes have refractive errors exceeding 2 diopters.
  4. Approximately, 1–3% of the population has pathologic myopia.
  5. The majority of a typical medical school class is likely to be myopic.
30. Identify the incorrect statement.
  1. About half of all infants less than 2 years of age have more than 1 diopter of astigmatism.
  2. About 2% of adults have astigmatism more than 3 diopters.
  3. Most neonatal astigmatism persists into adulthood.
  4. Neonatal astigmatism changes at different ages in different populations around the world.
  5. Neonatal astigmatism may permit the infant with uncorrected myopia to have a better acuity by using accommodation.
31. Identify the incorrect statement.
  1. Presbyopia occurs earlier in persons who live closer to the equator because of ambient temperature effect.
  2. Presbyopes purchase two-third of spectacles in developed countries.
  3. The mean axial length of a full-term neonate measures 16–18 mm.
  4. Suturing together a monkey's eyelids leads to axial myopia.
  5. By age of 3 years, a human eye is about 20 mm in diameter.
32. A Jackson's cross cylinder test:
  1. Involves the principle of placing the circle of least confusion on the retina.
  2. Cannot determine the power of the astigmatic correction.
  3. Verifies the axis and power of the correcting cylindrical lens.7
  4. Uses a lens in which the principal powers are equal and opposite in sign.
  5. Has markings (red dots) on each end of the minus axis.
33. A red–green duochrome test:
  1. Is used for binocular balance.
  2. Makes use of the eye's chromatic aberration.
  3. Uses a pair of colored slides at 500 nm (green) and 670 nm (red).
  4. Should be performed prior to performing the Jackson's cross cylinder test.
  5. Is sensitive to 0.25 diopter.
34. A stenopeic slit:
  1. Acts as a line of pinholes.
  2. Can be used to screen for astigmatism.
  3. Is most useful in patients who have better than 20/40 (6/12) visual acuity.
  4. Is found in most trial lens sets.
  5. Is useful in patients who have scarred corneas.
35. Identify the incorrect statement.
  1. The optical center of a lens is the point where the prismatic displacement is zero.
  2. A low-Abbe number implies greater chromatic aberration by the lens.
  3. Polycarbonate lenses must be able to withstand the impact of dropping 16 g steel balls from the height of 10 feet.
  4. No IR lenses absorb infrared radiation without significantly decreasing transmission of visible light.
  5. Polycarbonate lenses are usually the material of choice for children's glasses.
36. Identify the incorrect statement.
  1. Pantoscopic tilt describes the positioning of a bifocal toward the nasal aspect of a prescription lens.
  2. Antireflective coatings are generally single layer of material equal in thickness to 0.25 of the wavelength of yellow light
  3. Antireflective coatings cannot be applied to glass lenses.
  4. Antiscratch properties can be added to lenses by heat treatment or dipping.
  5. Weak minus lenses are particularly susceptible to the creation of double imaging when viewed by others.
37. Identify the incorrect statement.
  1. Most patients are intolerant of a vertical prism imbalance of more than 0.5 diopter.
  2. Bicentral (slab-off) grinding is an inexpensive way of correcting induced vertical prism.
  3. A 3% size difference between the eyes is often sufficient for the creation of asthenopia.8
  4. A few laboratories can furnish iseikonic (“size”) lenses.
  5. A light shined through a 1 prism diopter lens deflects a ray of light 1 cm at a target distance of 1 meter.
38. Identify the incorrect statement.
  1. Flat top segments cause minimal image jump.
  2. Round top segments cause maximal image jump.
  3. In myopes, flat top segments minimize image displacement.
  4. In hyperopes, base-up prisms minimize image displacement.
  5. Franklin segments cause no image jump.
39. Progressive addition lenses:
  1. Are unable to use laboratory-applied coatings.
  2. Are available in glass and plastic.
  3. Are right and left eye specific.
  4. May disturb peripheral visual space.
  5. Require the patient to learn head turning.
40. Identify the incorrect statement.
  1. Hydrogel contact lenses have names ending in “filcon”.
  2. Nonhydrogel contact lenses have names ending in “focon”.
  3. Lenses with less than 10% water content are considered “low-water content” lenses by the US Food and Drug Administration.
  4. The Dk of contact lenses refers to the oxygen permeability of the lens.
  5. Central oxygen transmissibility of a contact lens depends on lens thickness.
41. Soft contact lenses fitted for extended wear:
  1. Contain essentially the same materials as soft lenses fitted for daily wear.
  2. Are associated with a 10–15 times greater incidence of microbial keratitis than daily wear lenses.
  3. May not contain the proper Dk/t necessary to maintain a healthy cornea.
  4. Are fit less frequently than rigid gas-permeable lenses for extended wear.
  5. Are approved by the US Food and Drug Administration for up to 7 days’ wear.
42. Soft contact lenses that:
  1. Fit too steeply will show minimal movement upon blinking.
  2. Fit too flatly will show excessive movement upon blinking.
  3. Are dry will exhibit poor keratometric mires.
  4. Fit too flatly may cause patient discomfort upon blinking.
  5. Fit steeply will decenter easily.
43. Corneal fluorescein staining with contact lens wear may be due to:
  1. Mechanical trauma.
  2. Metabolic interference.9
  3. Exposure keratitis.
  4. Chemical toxicity.
  5. Excessive lens permeability.
44. Corneal edema associated with contact lens wear:
  1. Appears as a central circular whitish gray opacity in patients wearing rigid gas-permeable lenses.
  2. Appears as posterior stroma striae or endothelial folds in patients wearing soft lenses.
  3. Usually occurs to some extent, patients who wear extended wear soft lenses.
  4. When appearing as stromal striae is usually oriented horizontally.
  5. Is usually caused by hypoxia.
45. Corneal microcysts:
  1. On slit-lamp examination distribute light similarly to the background.
  2. Are caused by disrupted cell growth resulting from hypoxia.
  3. May work through the corneal surface to cause fluorescein staining.
  4. Present after contact lenses are discontinued may increase for a few weeks.
  5. Are accumulations of dead cellular material.
46. Superior limbic keratoconjunctivitis:
  1. Is caused most often by extended wear of soft contact lenses in those who wear contact lenses.
  2. Is located in the posterior stroma.
  3. Is often quite painful.
  4. May be seen in individuals who do not wear contact lenses.
  5. Is usually not associated with epithelial defects.
47. Giant papillary conjunctivitis in contact lens wearers:
  1. Can be caused by mechanical irritation of the conjunctiva by the lens.
  2. Can be caused by an autoimmune reaction to the patient's mucoproteins on the lens.
  3. Includes papillae with a diameter of more than 0.5 mm.
  4. Consists of papillae containing lymphocytes and plasma cells.
  5. Does not significantly respond to mast cell stabilizers.
48. Identify the incorrect statement.
  1. A myope who wears contact lenses must accommodate more than one who wears glasses.
  2. A myope must converge more through glasses than contact lenses.
  3. A hyperope must converge less through glasses than contact lenses.
  4. Contact lenses induce a prismatic effect on convergence.
  5. A hyperope who wears contact lenses must accommodate less than one who wears glasses.
49. During retinoscopy:
  1. At neutralization, the far point of the patient's eye is focused at the peephole of the retinoscope.10
  2. A typical working distance is 75 cm.
  3. The far point of the uncorrected hyperope is behind the patient's retina.
  4. The closer to neutrality, the faster the reflex movement.
  5. The closer to neutrality, the brighter the reflex movement.
50. Identify the incorrect statement regarding keratometry.
  1. It assumes that the cornea is spherical or toric.
  2. Placido disc topography is primarily a qualitative assessment of the cornea.
  3. It measures only the anterior corneal power.
  4. It works well enough to permit accurate contact lens fittings.
  5. It compensates for the negative posterior corneal power by using a lower corneal refractive index.
51. A lensometer:
  1. Measures the focal length of the lens.
  2. Consists of a movable target, a powerful fixed lens, and a telescopic eyepiece.
  3. Maintains proportion among the power of the unknown lens, the target, and the fixed field lens.
  4. Can be used with progressive multifocal lenses.
  5. Has changed little in design since automation.
52. Indirect ophthalmoscope:
  1. Provides a real and inverted aerial image of the patient's illuminated fundus.
  2. When used with stronger lenses, it provides a larger field of retinal view.
  3. In examination of an emmetropic eye with a 20 diopter lens, it provides 2× magnification.
  4. Produces magnified images of small changes in retinal topography.
  5. Brings the patient's and the examiner's pupils into conjugate relationship.
ANSWERS
  1. C. Visible light has longer wavelengths than ultraviolet light.
  2. B. The earth's atmosphere contains ozone, carbon monoxide, and water vapor as protective substances.
  3. D. Rhodopsin responds best to light at 495 nm, but also responds to almost all visible light.
  4. D. When the media are very dense, interferometry may not be possible to find two clear areas to form an interference pattern on the retina.
  5. B. Haloes produced by epithelial edema are colored when white-light objects are viewed.
  6. C. Polarization of light is horizontal in most human surroundings.
  7. C. The ozone layer has no role in the creating the aurora borealis.11
  8. A. Ultraviolet light constitutes about 10% of the energy emitted by the sun.
  9. A. Damage to the superficial layers of the skin often referred to as “sunburn”, is caused mostly by ultraviolet (UV)-B.
  10. C. Ultraviolet light damage to the eye usually causes superficial punctate keratopathy about 8–12 hours after exposure.
  11. C. The crystalline lens enzymes are affected by exposure to ultraviolet (UV)-A and B light.
  12. A. Sunglasses ironically may increase the chance of light damage to the eye because the pupil dilates behind dark glasses and may actually allow more ultraviolet (UV) radiation to enter the eye.
  13. B. Photochromic lenses take longer to lighten than darken.
  14. D. Ultraviolet-absorbing lenses can be fabricated from glass materials.
  15. C. Stimulated emission produces coherent light.
  16. C. Once achieved, population inversion needs to be maintained.
  17. A. Continuous lasers deliver more energy overtime than pulsed lasers. The energy of pulsed lasers is concentrated into very brief time periods.
  18. C. Xanthophyll pigment is a common pigment in the macula; however, it does not absorb green light well.
  19. A. Regardless of their use in science fiction, lasers are not death rays.
  20. B. In most photocoagulators, the energy is concentrated in the center of the beam.
  21. E. Keeping power and size constant, a shorter duration burn delivers more power rapidly to the tissue, increasing the chance to disrupt Bruch's membrane.
  22. C. A noncircular aiming beam has a higher power density than a circular type.
  23. C. Q-switching is a method of producing shorter duration burns. Frequency doubling describes a method of changing a laser's frequency.
  24. A. Produces invisible infrared light.
  25. D. The air–tear interface is the site of the greatest change in refractive index within the eye.
  26. A. The Snellen formula assumes that each element in a 20/20 (6/6) target subtends 1 minutes of arc. The entire letter subtends 5 minutes of arc.
  27. D. Pupil size of 2.0–2.8 mm gives the maximal modulation transfer function for high spatial frequencies.
  28. B. Retinal photoreceptors can be triggered by a minimum of 1 quanta of visible light.
  29. C. The vast majority of myopes have refractive errors of 2 diopters or less.
  30. C. Most neonatal astigmatism has disappeared by adulthood.
  31. E. By age of 3 years, a human eye is about 23 mm in diameter. The eye at birth is about 18 mm in diameter.
  32. B. The Jackson's cross cylinder test determines the correct axis and power of the correcting lens by producing larger or smaller circles of least confusion.12
  33. A. The red–green duochrome test is used to refine the final sphere by making use of the chromatic aberration of the eye.
  34. C. The stenopeic slit is most useful to screen for a high degree of astigmatism in patients who have poor vision.
  35. C. Polycarbonate lenses must survive the impact of a 16 g steel ball traveling at a velocity of 16.4 ft/s, and dropped from a height of 4.2 feet (127 cm).
  36. A. Pantoscopic tilt refers to the tilting of the bottom of the lenses toward the patient eyes. The average patient's glasses have a pantoscopic tilt of 7–12°.
  37. B. Bicentral (slab-off) grinding can correct induced vertical prism but it is an expensive recourse.
  38. D. In hyperopes, base down prisms minimize image displacement.
  39. A. Laboratory-applied coatings can be used, but may make engraved markings difficult to find.
  40. C. Lenses with less than 50% of water content are considered “low-water content” lenses by the US Food and Drug Administration.
  41. D. Only a small percentage of patients are fitted for rigid gas-permeable lenses for extended wear; most are fitted with soft contact lenses.
  42. E. Soft contact lenses that fit flat may decenter easily. Soft contact lenses that fit steep usually will not decenter.
  43. E. Excessive lens permeability protects against corneal damage.
  44. D. Corneal edema associated with contact lens wear appears as posterior stromal striae usually oriented vertically.
  45. A. Corneal microcysts on slit-lamp examination display reversed illumination, i.e. the distribution of light within the microcysts is opposite to that of the background.
  46. B. Superior limbic keratoconjunctivitis secondary to contact lenses is located in the superior cornea.
  47. C. Giant papillary conjunctivitis in contact lens wearers includes papillae with a diameter of 0.4–0.9 mm. Normal micropapillae have a diameter of less than 0.3 mm.
  48. D. Contact lenses because they remain centered on the eye, do not induce a prismatic effect on convergence.
  49. B. During retinoscopy, a typical working distance is 66 cm (25”).
  50. B. Placido disc topography is a quantitative assessment. A keratoscope is an older hand-held device which uses a Placido disc for qualitative assessments.
  51. A. The lensometer does not measure the focal length of the lens, but measures the vertex power which is the reciprocal of the distance between the back surface of the lens and its secondary focal point, this distance being the “back focal length”.
  52. C. The indirect ophthalmoscope in examination of an emmetropic eye with a 20 diopter lens provides 3× magnification; whereas, a 30-diopter lens provides 2× magnification.