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Retinoscopy

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Retinoscopy

  1. 1. RETINOSCOPY By Dr. Mohamed A.A Etarshawi M.D Ophthalmology
  2. 2. HISTORY OF THE RETINOSCOPE • The observations that led to clinical < retinoscopy> were made in 1859 with a plane mirror ophthalmoscope lighted by a candle, when Sir William Bowman noted a linear shadow seen when examining an astigmatic eye. • By 1875, the optics were explained and the procedure was described as a “shadow test,” an allusion ‫إشارة‬ . ‫إلماع‬ to neutralization. H. Parent coined the term <retinoscopy> in 1881
  3. 3. HISTORY OF THE RETINOSCOPE • The earliest retinoscopes used a mirror to reflect a candle, which produced a “spot” of light. It was soon discovered that a linear streak of light could be produced with slit- shaped mirrors. • Early electric retinoscopes used spiral filament bulbs and a rotating slit. Jacob Copeland introduced a linear filament bulb that produced a sharp, bright line of light. The Copeland streak retinoscope set the standard for future retinoscopic developments.
  4. 4. OPTICS OF THE RETINOSCOPE • The streak retinoscope has supplanted ‫ل‬ّ ‫م‬ ‫ح‬ِ‫ّل‬ ‫ي‬َ‫ّلِح‬ ‫ل ه‬ّ ‫م‬‫ح‬َ‫ّلِح‬ ‫م‬َ‫ّلِح‬ the spot retinoscope in the modern eye clinic, and only the streak retinoscope is discussed in this chapter. • Although the various brands ‫ماركة‬ of streak retinoscopes differ in design, they all work similarly. Light is produced by a luminous filament within the base of the handle and emanates from a mirror in the head as a linear streak, with both orientation‫ج ه‬ُّ‫ه‬ ‫و‬َ‫ّلِح‬ ‫ت‬َ‫ّلِح‬ ; and vergence ‫إنحدار‬ ، ‫ميل‬ controlled by the retinoscopist.
  5. 5. HISTORY OF THE RETINOSCOPE • The streak of light passes through the patient's tear film, cornea, anterior chamber, lens, vitreous chamber, and retina. It is then reflected from the choroid and retinal pigment epithelium as a linear red reflex that passes back through the sensory retina, vitreous, lens, aqueous, cornea, and tear film, through the air between the patient and the examiner, and into the head of the retinoscope, through an aperture in the mirror.
  6. 6. OPTICS OF THE RETINOSCOPE • Finally exiting through the back of the retinoscope into the retinoscopist's own eye. • By observing qualities of the reflected light (the reflex) after it leaves the patient's eye, the retinoscopist can make determinations about the patient's refractive state.
  7. 7. streak retinoscope Diagrammatic cross-section of streak retinoscope
  8. 8. Diagrammatic cross-section of streak retinoscope. • Light from the filament passes through the lens to the mirror, where it is reflected toward the patient. The examiner views through the aperture behind the mirror. • The arrows represent the two controllable functions. The curved arrow indicates that the bulb may be rotated. The straight arrow indicates that the vergence of the light rays may be altered by changing the filament to lens distance. • The filament is shown at the focal length of the lens so that parallel light rays emerge.
  9. 9. OPTICS OF THE RETINOSCOPE • Explaining the optics and proper usage of the retinoscope can be a confusing business. To help simplify the text, we have chosen to use the feminine. ‫ن ث‬ّ ‫م‬‫مؤ‬ ‫ضمير‬ pronouns (e.g., “she” and “her”) when referring to the retinoscopist, and the masculine ones (e.g., “he,” “him,” and “his”) when referring to the patient.
  10. 10. OPTICS OF THE RETINOSCOPE • All streak retinoscopes are made of the same fundamental components: light source, condensing lens, mirror, and sleeve . • The light source is a light bulb with a fine, linear filament, which projects a fine, linear streak of light with the passage of an electric current. • The filament (therefore the streak), can be rotated 360 degrees by rotating the sleeve of the retinoscope. Currently, most retinoscopes use a halogen bulb, which projects a very bright streak.
  11. 11. OPTICS OF THE RETINOSCOPE • The condensing lens is a plus lens, which exerts positive vergence on the streak, which is emitted from the point-source filament in a highly diverging manner. • The position of the lens in relation to the light filament can be altered by raising or lowering the sleeve. • In this way, the vergence of the streak that is emitted from the retinoscope can be controlled by the retinoscopist, as described subsequently.
  12. 12. OPTICS OF THE RETINOSCOPE • The mirror bends light that originates in the handle and is initially projected upward toward the ceiling, to instead exit the retinoscope along an axis parallel to the floor so that it can be projected into the patient's eye. The mirror should not reflect 100% of visible light; rather, it must allow some light to pass through it. • Only in this way can the retinoscopist have a view into the patient's pupil that is coaxial ‫المحور‬ ‫متحد‬ to the path of the streak.
  13. 13. CONTROLLING THE PROPERTIES OF THE RETINOSCOPE • The basic idea behind the retinoscope is that the retinoscopist creates a streak of light, projects it into a patient's eye, bounces it ‫د‬ّ ‫يرت‬ off his retina, and makes deductions ‫استنتاج‬ concerning the patient's refractive status based on what the image of that streak looks like when it reaches the retinoscopist's eye. To aid her in this task, the retinoscopist has control over, and can easily vary, certain aspects of the system.
  14. 14. CONTROLLING THE PROPERTIES OF THE RETINOSCOPE Two things she can control have nothing to do with the intrinsic properties of the retinoscope she is holding: • The distance between the retinoscopist's eye and the patient's (W.D). • Which lenses she may be holding between the patient's eye and her own.
  15. 15. CONTROLLING THE PROPERTIES OF THE RETINOSCOPE • Optical effects of moving the retinoscope bulb to change the filament to lens distance; this type of retinoscope emits convergent light when the sleeve is moved up. Note the vergences of the emerging rays: • (left) concave mirror effect is produced when bulb is moved down; • (right) plane mirror effect is produced when bulb is moved up.
  16. 16. CONTROLLING THE PROPERTIES OF THE RETINOSCOPE Plane mirrorConcave mirror Movement of the light source
  17. 17. CONTROLLING THE PROPERTIES OF THE RETINOSCOPE However, two properties over which the retinoscopist has total control are completely intrinsic to the retinoscope she is holding. • 1-The first is the orientation of the streak as it leaves the retinoscope. Because the light source for the retinoscope is a fine filament, the light emanates from the retinoscope as a fine streak.
  18. 18. CONTROLLING THE PROPERTIES OF THE RETINOSCOPE • By rotating the light source, the retinoscopist can easily alter the orientation of the streak by more than 360 degrees. Merely by rotating the sleeve on the handle of the retinoscope, she can project a streak whose orientation is parallel to the floor, or perpendicular to it, or any meridian in between.
  19. 19. CONTROLLING THE PROPERTIES OF THE RETINOSCOPE • 2-The second property that can be controlled easily by the retinoscopist is the vergence of the incident streak. With the touch of a finger (or thumb), the retinoscopist can alter the streak so that it leaves the retinoscope as converging, diverging, or even parallel light. This feature gives the retinoscopist an incredible ‫يصدق‬ ‫ل‬ amount of power in evaluating a patient's refractive state. Unfortunately, it is probably the most underused feature of the retinoscope.
  20. 20. CONTROLLING THE PROPERTIES OF THE RETINOSCOPE • Changing the distance between the light filament and the condensing lens alters the vergence of the emitted streak. This can be accomplished by raising or lowering the sleeve in the handle of the retinoscope. • This is the most fundamental way in which different models of retinoscope will contrast, ‫يتغاير‬‫التختل ف‬ and it is obviously important for the retinoscopist to be familiar with the type of retinoscope with which she is working.
  21. 21. CONTROLLING THE PROPERTIES OF THE RETINOSCOPE • The condensing lens is fixed, and the light source can be raised or lowered by moving the sleeve up or down (Fig. 2). • When the sleeve is raised in these retinoscopes, the streak emanates as a diverging beam; when the sleeve is lowered, the streak emanates in a converging nature , and therefore we use the term “sleeve up” when the retinoscope emits diverging light and “sleeve down” when it emits converging light.
  22. 22. CONTROLLING THE PROPERTIES OF THE RETINOSCOPE By altering the vergence of the emitted streak, the retinoscopist is actually manipulating its focal point, the point where the emitted light comes to focus in a point in real or virtual space. When in maximum convergence (sleeve up), that focal point is a real image located 33 cm in front of the retinoscope. (You can test this by moving the palm of your hand in front of the retinoscope at a distance of 33 cm, then turning it on with the sleeve raised all the way up.
  23. 23. Figure 2 concave mirrorplane mirror Movement of the lens
  24. 24. CONTROLLING THE PROPERTIES OF THE RETINOSCOPE • Optical effects of moving the lens to change the filament to lens distance; this type of retinoscope emits convergent light when the sleeve is moved up. Note the vergences of the emerging rays: (left) plane mirror effect when lens is moved down; (right) concave mirror effect when lens is moved up. 2
  25. 25. DETERMINING THE VERGENCE OF THE RETINOSCOPE BEAM Lecture 1 To determine the vergence of a retinoscope at any sleeve adjustment, a simple trick called Foucault's Method (Fig. 4) can be used. The most instructive‫ي‬ّ ‫ف‬ِ‫ي‬‫قي‬ِ‫ي‬‫ث‬ْ‫ِق‬‫ت‬َ part of this exercise is shown in Figure 4A. Note that when a card is introduced at the edge of a converging beam, an opposite movement is produced on a screen located beyond the focal point.
  26. 26. Figure 4 against” motion with” motion with” motion Screen Rays converging beyond screen Diverging rays Rays converging at a focal point before screen
  27. 27. Foucault's method for determining vergence of rays emerging from a retinoscope • A card or your hand is introduced close to the retinoscope and moved at right angles to the emerging rays. Observe the shadow produced in the unfocused image on a screen or wall in a darkened room. • (A) Rays converging at a focal point before screen cause an “against” motion. • (B) Rays converging beyond screen cause a “with” motion. • (C) Diverging rays cause a “with” motion.
  28. 28. • Foucault's method for determining vergence of rays emerging from a retinoscope. A card or your hand is introduced close to the retinoscope and moved at right angles to the emerging rays. • Observe the shadow produced in the unfocused image on a screen or wall in a darkened room. • A. Rays converging at a focal point before screen cause an “against” motion. • B. Rays converging beyond screen cause a “with” motion. • C. Diverging rays cause a “with” motion.
  29. 29. Calibration of the Converging Beam Bring the sleeve all the way up and place it against a reflecting surface such as the wall. Move away from the wall and observe from the side (not through the peephole) until the streak is in sharp focus on the wall. You should note that when the retinoscope is moved beyond that distance, the streak will go out of focus because the filament light has converged and then diverged (seeFig. 4 A).
  30. 30. • Return to the point of sharp focus and measure to determine the focal point of the retinoscope: it should be about 33 cm, which corresponds to + 3.00 D. • Sit in the patient's examination chair and aim the retinoscope toward the distant wall while moving the sleeve up and down.
  31. 31. Calibration of the Parallel Beam • Watch where the finest focused image of the filament is observed. Note the relative position of the bottom of the sleeve with regard to the range of sleeve movement. • In that position, the retinoscope beam is as parallel as possible and it has no vergence and thus is focused at infinity.
  32. 32. NEUTRALIZATION RETINOSCOPY Neutralization is performed with the retinoscope held at a constant predetermined distance from the patient with the sleeve all the way down (light emitted in a diverging manner). The retinoscopist makes decisions about the patient's refractive error based on the appearance of the retinoscope reflex after it is reflected off the patient's fundus and back through the pupil(Fig. 16).
  33. 33. NEUTRALIZATION RETINOSCOPY • What the retinoscopist sees is not the image “on the retina” ,but rather the magnified image “of the retina.” • Therefore, discussion about neutralization must begin with discussion about the retinoscopic reflex at neutralization.
  34. 34. THE NEUTRALIZATION REFLEX • When performing neutralization the retinoscopist shines diverging light through the patient's pupil from a standard working distance (usually 66 cm). • This light is reflected off the patient's fundus, and in this way, the fundus acts as a new point source of light. This is called the illuminating system.
  35. 35. THE NEUTRALIZATION REFLEX • The light that originates from the luminous retina then passes through the patient's vitreous, lens, pupil, aqueous, and cornea, until it finally exits the patient's eye on its way back to the retinoscope. This is called the viewing system. • The retinoscopist must be able to differentiate between the illuminating and viewing systems because different techniques of retinoscopy can depend on varying the components of one but not the other.
  36. 36. THE NEUTRALIZATION REFLEX • 1-When diverging light is shone onto an emmetrope's retina, the retina becomes luminous and acts as a point source of light. The rays of light then escape his eye in a parallel fashion. If this concept is not intuitive, ‫ي‬ّ ‫ديه‬َ‫ب‬َ merely follow the standard light ray diagram backward. • 2-In similar fashion, light starting as a point on a myope's luminous retina is emitted as converging light, where more myopic individuals emit more highly converging light than less myopic ones.
  37. 37. THE NEUTRALIZATION REFLEX • 3-Similarly, light starting as a point on a hyperope's luminous retina is emitted as diverging light, and hyperopic patients emit more diverging light than less hyperopic ones. • The vergence of the rays emitted from the eye determines the qualities of the reflex seen by the retinoscopist. • A neutralization reflex occurs under the circumstance when the far point of the eye correlates ‫نظامية‬ ‫بصورة‬ ‫يربط‬ with the location of the peephole of the retinoscope
  38. 38. • If a retinoscopist were to examine an emmetropic eye at infinity, she could make assumptions ‫افتراض‬ on the diverging, converging, or parallel nature of the reflected light by sweeping the retinoscope streak back and forth across the patient's pupil. • However, it is not possible to perform retinoscopy from an infinite distance; it is customary to adapt a working distance of 66 cm, corresponding to + 1.50 D. • By introducing + 1.5 lens in front of the subject's eye, the far point of a plano prescription is relocated to 66 cm.
  39. 39. • In this circumstance, what the retinoscopist is truly evaluating is whether the :-retinoscope lies between the patient's eye and far point, lies at the far point, or lies beyond it. 1. If the patient is an emmetrope, the far point lies on the horizon, and therefore the retinoscope always must lie between the patient's eye and far point. 2. If the patient is a hyperope, the far point actually lies beyond the horizon, and the retinoscope also lies between the patient's eye and far point. FP FP
  40. 40. 3-Things are more interesting, however, when evaluating myopes in this way. Light is emitted from a myope in a converging manner so that the far point is somewhere in real space (finite) in front of the myope's eye. It is possible for the retinoscope to be placed A- between the patient and far point, B-exactly on the far point, or C-out beyond the far point.
  41. 41. THE NEUTRALIZATION REFLEX This relationship depends, of course, on both the location of the retinoscope (W.D), and the level of myopia (which determines the location of the far point). C
  42. 42. • If the retinoscope is placed between the eye and far point (as it is for all emmetropes and hyperopes, and some myopes) and turned so that the emitted streak is swept from side to side across the patient's pupil, the light reflex seen inside the pupil appears to sweep in the same direction as the light emitted from the retinoscope (seen on the patient's iris, lids, brow, and cheek). • This motion is called “with” motion because the light that is afferent to the retinoscope seems to move “with” the light that is efferent from the retinoscope
  43. 43. THE NEUTRALIZATION REFLEX • Fig. 17. The optical basis for neutralization < retinoscopy>. The location of far points produces the “with” and “against” motions for a retinoscope with a divergent beam when performing neutralization retinoscopy. “With” motion is seen under all circumstances except when the far point of the eye-corrective lens system is situated between the cornea and the peephole ‫ثقب‬ of the retinoscope. The far point of the illustrated eye is at the peephole and is thus neutralized.
  44. 44. Figure 17
  45. 45. Lecture 2 With” motion reflex in hyperopia
  46. 46. Fig. 18. “With” motion reflex in hyperopia A “with motion” reflex of light comes into the shadow projected in the optical system from the aperture of the retinoscope or the examiner's pupil. The rays from the filament to the retina are not shown. They form an unfocused horizontal filament image on the retina of the patient that acts as a new object with its image behind the retina. When the retinoscope is tilted slightly, the object (RETINA) moves down and the image (REFLEX) moves down and vise versa. This is seen as a “with motion” reflex.
  47. 47. Figure 19 against motion reflex of myopia • If the retinoscope is placed beyond the patient's far point and swept from side to side across the pupil, the light reflex (efferent) seen inside the pupil appears to sweep in the opposite direction as the streak emitted from the retinoscope (afferent ) Fig. 19 • This motion is called “against” motion because the light emitted from the eye (efferent) appears to move “against” the light that is emitted directly from the retinoscope (afferent (.
  48. 48. Fig. 19. Origin of the “against” movement in myopia
  49. 49. “On-off” phenomenon • When the retinoscope is placed exactly on the patient's far point, neither “with” nor “against” motion is seen. At this point, all the light emitted from the patient's eye enters the retinoscopist's eye simultaneously. • At exact neutrality, in a spherical eye with a small pupil, the retinoscopist may see no motion at all; rather, the patient's pupil seems to suddenly fill with light as the streak moves across it. • This is obtained in myopic eye exactly reciprocal to W.D in diopters. • This “on-off” phenomenon is important to recognize because it serves as the end point when performing the technique of neutralization.
  50. 50. Other qualities of the reflex • In addition to its direction of movement, other qualities of the reflected retinoscope streak can be evaluated. These qualities all give the retinoscopist clues as to how close to the far point the retinoscope is being held. The three most important qualities of the reflex are: 1. the speed at which it moves, 2. its brightness, 3. its width.
  51. 51. Other qualities of the reflex If one thinks of the reflex at the neutralization point as : • infinitely fast (so fast that it immediately fills the pupil without apparent motion), • infinitely ‫ ه‬ُ b ‫ل‬َ‫ّلِح‬ ‫د‬َّ ‫ح‬َ‫ّلِح‬ ‫ل‬ ; ‫ددود‬ُ b‫ح‬ْ‫ُد‬ ‫م‬َ‫ّلِح‬ ‫ر‬ُ b ‫ي‬ْ‫ُد‬‫غ‬َ‫ّلِح‬ bright, and • infinitely wide, it is easy to understand what the reflex should look like when the retinoscope is either near to, or far from, the neutralization point Fig. 20
  52. 52. qualities of the reflex • When the retinoscope is held near the patient's far point, the reflex should appear fairly fast, bright, and wide. • As the retinoscope is moved farther from the far point, the reflex appears to move slower and is dimmer and thinner. • The retinoscope can eventually be moved so far from the patient's far point that the reflex is slow, wide, and dim enough that it is quite difficult to recognize as a reflex at all.
  53. 53. Other qualities of the reflex • Fig. 20 .Neutralization retinoscopy diagram of changes in characteristics of reflex as in the zone surrounding the point of neutrality. • At neutrality, the reflex motion may be so fast that it cannot be detected. The end point or end zone should be approached from the “with” reflex side and the judgment of neutrality made erring ‫زل‬ِ‫ي‬ ‫ي‬َ . ‫يخطئ‬ toward the “with” reflex rather than the “against” reflex. • The neutral point lies within the neutralization zone where neutralization is best observed. (
  54. 54. Figure 20 Fig_ 20.htm
  55. 55. Optics of the Neutralization Reflex • Five features characterize the neutralization end point, the point at which neither a “with” nor “against” reflex can be identified. Three of these are considered to define the end point, but two others can also be observed. The three standard characteristics are : • Increases in speed, brightness, and width of the moving image. )1,2 3 ) • To these can be added : the “on-off phenomenon” (the intermittent disappearance of the observed reflex) and the scissors reflex) .4 5 (
  56. 56. Optics of the Neutralization Reflex 1-Speed of the “with” or “against” motion: • If the retinoscope mirror is tilted in a highly ametropic eye, the resultant reflex is (more rapid ) imaged at a far point that is much closer to the eye than the reflex of an almost emmetropic eye, the far point of which is located at a much greater distance. • With regard to the subject's pupil, movement of the image at the far point of the almost emmetropic eye will seem to have a greater angular velocity or speed.
  57. 57. Optics of the Neutralization Reflex • It should be stressed that the direction of movement of the fundus image is not influenced by the patient's ametropia ( illuminating system). • The “with” or “against” movement is a function of the observation (VIEWING) system, thus an “against” movement occurs only when the eye and external lens system have a far point lying between the patient's eye and the retinoscope peephole )High myopia)
  58. 58. Optics of the Neutralization Reflex 2-Brightness of the image: • As neutrality is approached, all of the rays emerging from the patient’s eye are focused at the peephole, where they provide the brightest image that the examiner observes. Illumination increases inversely to the square of image size. • At any other focal distance, some or all of the rays of light will not reach the peephole and the image becomes duller Fig. 21
  59. 59. 3-Width of reflex • In general, the width of the streak reflex and the apparent speed of the streak reflex as it moves across the pupil give an indication of how far you are from neutrality. • Young eyes that are not diseased and have not had surgery give the most defined reflexes. Corneal diseases, cataracts, IOLs, hazy posterior capsules, and cloudiness in the vitreous distort the reflexes and change the rules of appearance. • Sometimes width and speed do not give reliable clues and you must just rely on apparent with- motion to arrive at the best retinoscopic estimate.
  60. 60. A very wide (almost filling the pupil), slow moving streak reflex indicates that you are a long way from neutrality. For instance, the with or against reflex you would see at plano when streaking a (– or +5.00 hyperope.(
  61. 61. As we add plus sphere power the streak tends to narrow and speed up in its apparent motion. 3-Width of reflex
  62. 62. As we continue adding plus sphere power and approach‫تقريبا‬ neutrality, the streak widens again and speeds up even more. 3-Width of reflex
  63. 63. At neutrality the streak reflex widens more to completely fill the pupil. 3-Width of reflex
  64. 64. 3-Width of reflex In astigmatism :Streaking one meridian gives you against- motion, and streaking the meridian 90 degrees away gives you with- motion. • Streaking one meridian gives you with- motion (or against- motion) with a wide streak reflex, and streaking the meridian 90 degrees away gives you the same motion but with a narrower streak reflex.
  65. 65. 3-Width of reflex a wide streak reflex,narrower streak reflex
  66. 66. 3-Width of reflex • As we add plus sphere power, the reflex at 90 narrows and the reflex at 180 quickly widens and reaches neutrality.
  67. 67. Optics of the Neutralization Reflex 4-The on-off phenomenon: Although the retinoscopic reflex is bright and wide on either side of neutrality, the reflex may disappear completely when the retinoscope peephole is exactly conjugate to the eye- corrective lens system i.e far point of the examined eye. (see Fig. 21 (. • Fortunately, neither the patient's eye nor the examiner's eye and hand can maintain this exact position for long, but astute ‫ذكي‬ retinoscopist may notice the on-off phenomenon at neutrality.
  68. 68. Optics of the Neutralization Reflex • Fig. 21. The origin of the on-off phenomenon at neutrality. The far point of the eye is situated at the peephole of the retinoscope. Either all or none of the rays will pass through the peephole with the slightest shift in the subject's eye or the retinoscope or the retinoscopist's eye, causing the retinoscopist to see the contents of the pupil as either filled with light or black.
  69. 69. Fig. 21 the on-off phenomenon at neutrality Patient’s eye
  70. 70. Optics of the Neutralization Reflex Lecture 3 5-The scissors reflex: The refractive elements of the eye are not perfectly spherical. Thus, the center of the optical path may be slightly myopic when compared with that of the periphery. The amount of aberration may be small, but under circumstances of perfect neutralization and a widely dilated pupil, the center of the optical path may return a “with” motion while the periphery returns an “against” motion.
  71. 71. Optics of the Neutralization Reflex • This pattern of opposing central and peripheral retinoscopic movements is known as a scissors reflex. There is only a small dioptric distance over which the scissors reflex can be detected. The entire reflex returns to all “with” or all “against” motion within about 0.50 D on either side of neutralization). narrow zone)
  72. 72. Estimating Low Myopes via Neutralization Without Lenses • By now the reader should have determined that it is in fact quite possible to neutralize low myopes without the use of lenses. • The trick is to place the retinoscope directly on the patient's far point, sweep the retinoscope streak across the patient's pupil with the sleeve down, recognize the “on-off” phenomenon of the neutralization reflex, measure the distance from the patient's eye to the retinoscope in meters, take the reciprocal—thus converting from meters (distance) to diopters (vergence)—and the patient's refractive error has been determined.
  73. 73. Neutralization Without Lenses • For example, neutralization for a -2.00-D myope can be seen by placing the retinoscope 50 cm from the patient's eye, and for a -4.00-D myope by placing the retinoscope 25 cm from this patient's eye (without considering a certain W.D( • Neutralization for an emmetrope can only be done in this fashion by placing the retinoscope infinitely far from the patient's eye—theoretically possible, but not practically feasible. ‫ملمئم‬ . ‫ي‬ّ ‫م‬ ‫عمل‬
  74. 74. NEUTRALIZATION Without Lenses • Because the far points of hyperopes do not lie in real space (they lie beyond infinity), hyperopes cannot be neutralized in this way. • The aforementioned technique describes a way to estimate a low myope's refractive error without the use of lenses. • The key to this method is that the retinoscopist must change the distance that the retinoscope is held from the patient's eye when trying to find the far point.
  75. 75. Performing neutralization • When performing neutralization she does exactly the opposite—she holds the retinoscope at a constant specific working distance and uses lenses to bring the patient's far point to the retinoscope. • The first thing that a retinoscopist must do is choose a comfortable working distance. She wants to be as far from her patient as possible while still being close enough to comfortably manipulate lenses in front of his eye. Thus, the working distance usually is described as “arms length” away from the patient.
  76. 76. Performing neutralization • For the average retinoscopist, this distance works out to about 66 cm. Taller retinoscopists may prefer 75 cm, whereas shorter ones may use 50 cm. • It is not uncommon for retinoscopists to work closer than their usual working distance in difficult cases, such as small children, or adults with cataracts or small pupils. • The actual working distance does not matter as long the retinoscopist is aware of the distance and adjusts her calculations accordingly.
  77. 77. Performing neutralization of against” motion • The retinoscopist should be able to sit at her comfortable working distance while using lenses to bring the patient's far point to her. • The retinoscopist accomplishes this feat‫ل‬ٌ ‫عم‬ . ‫ل‬ٌ ‫عم‬ ‫ذ‬ّ ‫م‬‫ف‬َ‫ّلِح‬ by sweeping the retinoscope streak across the patient's pupil and evaluating the direction, speed, brightness, and width of the reflex. • If she observes “against” motion, the retinoscope must lie beyond the patient's far point, and the retinoscopist can move the far point toward the retinoscope by placing a minus lens in front of her patient's eye.
  78. 78. Performing neutralization of against” motion
  79. 79. Performing neutralization of against” motion • If the reflex is fast, bright, and wide, the retinoscope must have been near to the patient's far point, and a weak minus lens should be chosen. • However, if the reflex is slow, dim, and narrow, the retinoscope probably lies a greater distance from the far point, and a stronger minus lens should be chosen. • If “with” motion is observed after a minus lens is placed before the patient's eye, the patient's far point has been moved beyond the retinoscope because too strong of a minus lens was chosen. This lens should be removed and replaced with a weaker minus one.
  80. 80. Performing neutralization of “with” motion • Similar manipulations are performed if “with” motion is initially seen when neutralization is begun. In such cases, the far point must lie beyond the retinoscopist's comfortable working distance. • Again, how far away the far point lies can be estimated by judging the quality of the reflex. • A plus lens then is chosen to bring the far point forward toward the retinoscope.
  81. 81. Performing neutralization of “with” motion • Whenever possible, the retinoscopist should try to manipulate the far point in such a way that “with” motion is being observed. • A “with” reflex typically is sharper and easier to judge than an “against” reflex. Thus, if “against” motion is seen, neutralization will be easier to perform if a strong enough minus lens is placed to push the far point beyond the retinoscope, so that the retinoscopist can observe “with” motion.
  82. 82. minus lenses in front of younger patients can excite accommodation • Care must always be taken, however, when putting minus lenses in front of younger patients because they can easily “eat up” this minus by accommodating, thus leading the less careful retinoscopist down the wrong path. • It should also be noted that the neutralization end point is not exactly an end point—rather it is an end zone that measures about half a diopter in depth (see Fig. 20(
  83. 83. “zone of doubt” varies with pupil size and working distance • The true size of this “zone of doubt” varies with pupil size and working distance —it is narrowest with a small pupil and close working distance. • Best results are achieved when entering the zone of doubt from the plus side, by watching the “with” motion reflex get faster, brighter, and wider until the retinoscopist is convinced the neutralization reflex has been achieved. • If the zone of doubt is entered from the minus side (through “against” motion), there is a greater chance for error.
  84. 84. The neutralization reflex • Eventually, after just a few different lenses are placed before the patient's eye, the retinoscopist can observe the neutralization reflex. • At this point the goal is achieved, and the retinoscopist has managed to bring the patient's far point to the retinoscope (which is being held at the working distance). • The retinoscopist is now ready to write a spectacle correction )‫؛‬ prescription(.
  85. 85. CORRECTING THE PRESCRIPTION FOR THE WORKING DISTANCE LENS • However, the lenses currently in front of the patient's eye do not represent the correction needed to see clearly at infinite distance; rather, the lenses represent the correction needed to see clearly at 66 cm. • The patient will be quite dissatisfied ‫غير‬ ‫ض‬ٍ ‫را‬ if given a prescription for a pair of glasses that allows for clear vision only 66 cm away or closer.
  86. 86. CORRECTING THE PRESCRIPTION FOR THE WORKING DISTANCE LENS • The retinoscopist must always remember to modify the prescription for distance vision, a mathematical manipulation called correcting for the working distance. • The gross power is that which the retinoscopist is holding when retinoscopy is completed. • This corresponds to the power that brings light from the patient's luminous retina to focus at the working distanceِ‫ّل‬( on the peephole of the retinoscope(.
  87. 87. CORRECTING THE PRESCRIPTION FOR THE WORKING DISTANCE LENS • The net power is that which neutralizes the patient's refractive error for good distance vision—the power that focuses light from the luminous retina of the patient to a point at the horizon. )His far point must be at infinity after full correction).
  88. 88. CORRECTING THE PRESCRIPTION FOR THE WORKING DISTANCE LENS • The mathematical computation ‫سباب‬َ‫ّلِح‬ ‫ت‬ِ‫ّل‬‫ح‬ْ‫ُد‬ ‫ا‬ِ‫ّل‬ ; ‫حصباء‬ْ‫ُد‬ ‫إ‬ِ‫ّل‬ is simple. The retinoscopist merely subtracts the working distance (in diopters) from the gross to get the net power. • For example, when the working distance is 66 cm 1.50 +)= D) and the patient is neutralized with a • -2.5 D. lens, the gross power minus the working distance equals the net power, or: -2.5 - (+ 1.5) = - 4D. • The retinoscopist will give a prescription for a - 4D. lens. The previous discussion describes neutralization of spherical patients.
  89. 89. NEUTRALIZATION OF ASTIGMATIC EYES • In patients with astigmatism, the reflex seen in the pupil has one more quality in addition to speed, brightness, and width. The reflex in patients with astigmatism also appears to “break” as the light filament is rotated Fig. 22. The retinoscope reflex seen in the patient's pupil will not be continuous with the streak lying on the cornea, lids, forehead, and cheek; it will appear broken. • There will be, however, two meridians where the retinoscope reflex will be continuous with the streak—where it will not appear broken.
  90. 90. NEUTRALIZATION OF ASTIGMATIC EYES • These meridians correspond to the two axes of the patient's astigmatism. The retinoscopist merely needs to neutralize these two meridians separately and combine them to come up with the desired spectacle correction • This can be done using only spherical lenses (as is best when neutralizing children with loose lenses), spherical and plus cylindrical lenses (using a plus cylinder phoropter or loose lenses and trial frames), or spherical and minus cylindrical lenses (using a minus cylinder phoropter or loose lenses and trial frames).
  91. 91. NEUTRALIZATION OF ASTIGMATIC EYES • Let us further explore the methods of neutralizing astigmatic individuals in whom the less plus (or more minus) axis is neutralized first and the more plus (or less minus) axis is neutralized second. • When neutralizing the axes in this order, the retinoscopist can use either only spherical lenses, or spherical and plus cylindrical lenses.
  92. 92. Fig. 22.phenomenon Break The line between the streak in the pupil and outside the pupil is broken when the streak is off the correct axis. (
  93. 93. BREAK PHENOMENON • Astigmatism can also be detected by observation of the break phenomenon. It is useful in refining the axis of large astigmatic cylinders because one can observe a discontinuity, or “break,” between the enhanced intercept axis and that of the retinal reflex when the retinoscope filament beam is rotated somewhat away from the correct cylinder axis (see Fig. 22).
  94. 94. • Procedure for neutralizing an astigmatic eye • 1. The first step is to neutralize one of the meridians. You will be adding plus sphere power and streaking each of the primary meridians after each power change. • The meridian with the narrow, fast reflex will neutralize first. This meridian will be 90 degrees away from the meridian with the widest, slowest streak reflex. • In this example, the 180 degree( right one ) meridian will neutralize first.
  95. 95. As we add plus sphere power, the reflex at 90(left ) narrows and the reflex at 180 (right ) quickly widens and reaches neutral point. Procedure for neutralizing an astigmatic eye
  96. 96. • 2. The next step is to confirm/identify the axis of the astigmatism. We have a good idea of what the axis is from the neutralization process. There are several clues that we can use: A. The Thickness Phenomenon B. The Intensity Phenomenon C. The Break and Skew Phenomena D. Straddling the Axis Procedure for neutralizing an astigmatic eye
  97. 97. The Thickness Phenomenon: The streak reflex appears to be narrowest ( left ) when we are streaking the meridian of the correct axis. As you move away from the correct axis, the streak reflex becomes wider ( right ). Procedure for neutralizing an astigmatic eye
  98. 98. Procedure for neutralizing of an astigmatic eye • The Intensity Phenomenon The streak reflex appears brightest when you are streaking the meridian of the correct axis. As you move away from the correct axis, the streak reflex becomes more dim (less bright ).
  99. 99. The skew phenomenon: If we streak a meridian that is away from the meridian of the correct axis, the reflex will tend to travel along the correct meridian rather than follow the streak. This guides us back to the correct meridian. The skew phenomenonThe skew phenomenon Correct axis Procedure for neutralizing an astigmatic eye
  100. 100. • Straddling the Axis Assuming that there is regular astigmatism present, when one meridian has been neutralized, the meridian exactly 90 degrees away will have the strongest, most defined with- motion reflex. Procedure for neutralizing an astigmatic eye
  101. 101. • The axis can be confirmed by streaking the meridians 45 degrees to each side of what we believe to be the meridian of the correct axis.  In this case we believe that streaking the 90 degree meridian gives the most defined reflex.  We streak the 45 degree meridian and the streak reflex widens and degrades in sharpness.  The same thing happens when we streak the 135 degree meridian. This confirms 90 degrees as the correct meridian.  45 degrees 135 degrees Straddling the Axis Procedure for neutralizing an astigmatic eye
  102. 102. STRADDLING When the cylinder power is weak, straddling reveals an initial incorrect estimate of the axis location. The thinner image is called the “guide” because it guides us to adjust the plus-cylinder axis toward the thinner image. This step provides the initial detection of astigmatism, and the phoropter axis can be adjusted so that plus lenses can be dialed into place along the enhanced meridian.
  103. 103. Straddling • The straddling meridians are 45 degrees off the glass axis, at roughly 35 and 125 degrees. As you move back from the eye while comparing meridians, the reflex at 125 degrees remains narrow (A) at the same distance that the reflex at 35 degrees has become wide (B). This dissimilarity indicates axis error; the narrow reflex (A) is the guide toward which we must turn the glass axis.
  104. 104. Procedure for neutralizing an astigmatic eye • If the reflex in one of the straddle meridians is narrower than the reflex in the other straddle meridian, then we would adjust our estimated axis in the direction of the straddle meridian with the narrower reflex (guide). • We would retest 45 degrees to each side of the new axis to confirm that the reflex in each straddle meridian is equally wide.
  105. 105. 26
  106. 106. Spherical Lens Technique • The first step is for the retinoscopist to find the least plus axis. The retinoscope streak is swept back and forth across the pupil while it is rotated 360 degrees by rotating the light filament in the handle. • The retinoscopist then observes at which two meridians the retinoscope reflex does not appear broken—in cases of regular astigmatism, these two meridians should be 90 degrees apart.
  107. 107. Spherical Lens Technique • The retinoscopist then compares the reflex in one meridian to the reflex in the other, noting which meridian's streak exhibits more “against” (slower,, broader , dimmer) or less “with” (faster, thinner, brighter) qualities than the other. • The second meridian is neutralized first. If the reflex in one meridian shows “with” motion and in the other shows “against” motion, the meridian with the reflex that shows “with” is neutralized first
  108. 108. • The more minus meridian of the astigmatic person is then merely neutralized (second ) much as the spherical myope or hyperope described previously. • The axis of the streak is held along the meridian line and swept in a direction perpendicular to it i.e (if the 90-degree axis is being neutralized, the streak is oriented straight up and down and swept from side to side) perpendicular to 90 degrees. Spherical Lens Technique
  109. 109. Spherical Lens Technique • At first, it is not intuitive that the streak be held in the same orientation as the axis meridian because one is searching for the power of the astigmatism, and the power lies not along the axis, but perpendicular to it. • Here the retinoscopist must remember that the power is found not by holding the streak still (fixed ) , but rather by sweeping (moving ) it across the pupil. • The retinoscope streak is rotated 90 degrees, and the reflex is re-examined.
  110. 110. Spherical Lens Technique • The reflex should not appear broken in the new meridian—a broken reflex signifies that either the retinoscope streak is not exactly aligned along the patient's second axis or that the patient has irregular astigmatism. • If the reflex is not broken, it is neutralized with spherical lenses. If spherical lenses are to be used, the second meridian is neutralized in exactly the same manner as the first after removal of the lenses used before and starting a new steps to neutralize the other meridian also with spherical lenses .
  111. 111. Spherical Lens Technique • Once the neutralization reflex has been found in the second meridian, the retinoscopist again subtracts the working distance from the power in the 2 meridians and records the lens power needed to correct the patient for each particular axis. The difference in power of lenses between the 2 meridians is considered astigmatism.
  112. 112. Spherical Lens Technique • A simple conversion then needs to be performed before presenting the patient with the proper spectacle prescription, as follows: • Q: A patient is neutralized with the following lenses at a working distance of 66 cm: [+ 3.50 axis 90] and [+ 4.25 axis 180]. What is the eyeglasses prescription? A: Step 1: Subtract the working distance. In this case, the working distance is 66 cm, which is equal to 1.50 D: [+ 3.50 axis 90] - 1.50 = + 2.00 axis 90 [+ 4.25 axis 180] - 1.50 = + 2.75 axis 180 Step 2: Transpose from cross-cylinder notation to plus- cylinder notation: + 2.00 sphere + ([+ 2.75 - 2.00] axis 180) Objective prescription = +2.0 DS+ 0.75 DC x 180
  113. 113. Plus-Cylinder Technique • If the second meridian is to be neutralized with a plus-cylinder lens (as is done with a plus-cylinder phoropter or loose lenses and trial frames), the first spherical lens should be left in the phoropter or trial frames.Keeping the spherical lenses in place. The axis of the cylindrical lens is oriented in the direction of the axis of the streak for the second meridian.
  114. 114. Plus-Cylinder Technique • Because a cylinder lens is being used, no power is being added along the axis of the second meridian (which, of course, corresponds to the power of the first meridian). • When the neutralization reflex is found for the second meridian, the streak is rotated 90 degrees to ensure that the first meridian is still neutralized.
  115. 115. Plus-Cylinder Technique • The working distance is then subtracted from the spherical lens only, and the spectacle prescription is easily determined as follows: • Q: A patient is neutralized with the following lenses at a working distance of 66 cm: [+ 3.50 sphere] and [+ 0.75 axis 180]. What is the eyeglasses prescription? • A: Step 1: Subtract the working distance from the spherical lens only. In this case, the working distance is 66 cm, which is equal to 1.50 D: [+ 3.50 sphere] - 1.50 = + 2.00 sphere Step 2: Add the cylindrical lens to the new power of the spherical lens: + 2.00 sphere + [+ 0.75 axis 180] Objective prescription= 2.00 + DS + 0.75 DC x180
  116. 116. Minus-Cylinder Technique • Some clinicians prefer to work in minus cylinder, patients are neutralized in the same aforementioned manner, except that the more “with” or less “against” meridian is neutralized first with spherical lenses. • Then the less “with” or more “against” meridian is neutralized with a minus-cylinder in much the same way as the previous example used a plus-cylinder lens. • The transposition is done as follows:
  117. 117. Minus-Cylinder Technique • Q: A patient is neutralized with the following lenses at a working distance of 66 cm: [+ 4.25 sphere] and [-0.75 axis 90]. What is the eyeglasses prescription? A: Step 1: Subtract the working distance from the spherical lens only. In this case, the working distance is 66 cm, which is equal to 1.50 D: )+ 4.25 -1.50 (= + 2.75 sphere Step 2: Add the minus cylindrical lens to the new power of the spherical lens: • + 2.75 sphere + (-0.75 axis 90( 90 × 0.75 - 2.75 + =
  118. 118. The next step is to neutralize the astigmatism (with minus-cylinder power). Remember that one meridian has already been neutralized. The meridian 90 degrees away still has with-motion. We begin by streaking this meridian that has the brightest, narrowest with- reflex.
  119. 119. Since we are using a minus-cylinder lens, we will line up our cylinder axis perpendicular to the orientation of the streak. In other words, at 90 degrees in this example. We are streaking the 90 degree meridian, and the axis of the correcting minus-cylinder will be 90 degrees.
  120. 120. Once we have a neutral reflex, we have reached the endpoint. Neutrality can be assumed when any with- motion just disappears. This is preferable to relying on recognizing a neutral reflex, because the reflex may appear neutral over a wide range of power settings.
  121. 121. The final step is to subtract for our working distance. Lecture 6 • This is usually 1.50 D and it is subtracted from the sphere power only. Suppose our phoropter reads • -1.00-150x90 when we have finished neutralizing the astigmatic meridian. • We then would subtract 1.50 D sphere power for a final retinoscopic estimate of -2.50-1.50x90. • It is easiest to practice retinoscopy on younger adults, ages 20 to 50. They usually have clear media, relatively relaxed accommodation, and a definite refractometric endpoint with which to compare your retinoscopy.
  122. 122. RELIABILITY‫ي

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