Entopic phenomenon


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  • Bennett & Rabbetts (Clinical Visual Optics) Figure 22.8. (a) The Emsley-Fincham test for distinguishing a lenticular halo. The stenopaeic slit is passed across the pupil, isolating differently orientated groups of lens fibres responsible for the sections of the halo shown in (b).
  • Tunnacliffe Fig. 7.58 a & b (a) Shadow cast by an opacity close to the retina. Note there will probably be a detectable shadow on the retina. Such shadows are usually only seen when looking at a bright surface. (b) An opacity further forwards may not cast its shadow on the retina. (c) A lenticular opacity (cataract) may be made visible by placing a pinhole at the anterior focal point of the eye and looking at a bright surface.
  • Bennett & Rabbetts (Clinical Visual Optics) Figure 22.3. The use of parallax to locate the site of an opacity. The circles on the right represent the entoptic field and the apparent relative position of a central opacity as seen by the subject. (a) Opacity behind pupil, pinhole central. (b) Effect on (a) of downward movement of pinhole. (c) Opposite effect of pinhole shift when opacity is in front of pupil.
  • Ring shaped floater (probably vitreous detachment)
  • Light source to view Purkinje Tree
  • LED light stimulus
  • Blue Arc’s extending outward from LED
  • Entopic phenomenon

    1. 1. Entopic Phenomenon in Eye Gauri S. Shrestha, M.Optom, FIACLE LecturerB.P. Koirala Lions Centre for Ophthalmic Studies
    2. 2. What Does ‘Entopic Phenomenon’Mean? This is any sensation that comes from INSIDE the eye  Ent-Optic: ‘inside the optics’ Visual sensation can also be raised from shadows of opacities within the eye  Eg mechanical pressure on the globe Entoptic phenomena are produced when something other than light stimulates the retina These sensation not directly due to the formation of an optical image by the refracting system of the eye gs101lg@hotmail.com
    3. 3. What Is An Example? Can be seen especially when looking at a bright blue sky What Does It Look Like?  Small, rapid pin-point sparks of light darting about in the central vision. We all have the potential to see this phenomenon, but most of us ignore it. gs101lg@hotmail.com
    4. 4. Entopic Phenomenon gs101lg@hotmail.com
    5. 5. What Causes It? Some people think these sparks are floaters. They actually represent white blood cells moving through the blood capillaries of the retina.  Red blood cells are not seen  Compact and close to the retina This is a normal finding, and actually may indicate normal retinal function gs101lg@hotmail.com
    6. 6. Patients and Entopic Phenomenon Some people become suddenly aware of this phenomenon.  Sudden awareness can lead to the idea that there is a problem with the eyes, when actually there is not Sparkles that can be seen illuminating in the central vision  Most visible when we look at something bright then close our eyes or immediately look at something dark. gs101lg@hotmail.com
    7. 7. Causes of Entoptic Phenomena Refractive Effects  Xanthophyll Effects  Tear film  Maxwells spot  Corneal corrugation  Haidingers brush Diffraction Effects  Pressure Phosphenes  Corneal haloes  Corneal corona  Digital Pressure  Ciliary corona  Eye Movement  Asterism  Moore’s Lightning Shadows Streaks  Ocular opacities  Electrical Phosphenes  Purkinje tree  Blue field  Battery stimulation entoptoscope  Blue arcs of the gs101lg@hotmail.com retina
    8. 8. Refractive effect Small surface changes across the cornea can redirect light outside the retinal image. Tear film When the eye blinks, a horizontal ridge of tears is left momentarily where the lids came together Some observers report a “shadow” effect seen as a horizontal striation Mucous strands can do the same thing, but they last longer and move around with the blink gs101lg@hotmail.com
    9. 9. Refractive effect Corneal corrugations Squeezing the lids tightly shut gives transient ridges on the cornea that can give “shadow” streaks, monocular diplopia, and even decreased visual acuity, which in extreme cases can last longer than an hour gs101lg@hotmail.com
    10. 10. Diffraction effects: Corneal Halos The stroma of the cornea is composed of collagen fibrils between 19-34 nm in thickness. The interfibrillar separation is much smaller than the wavelength of light  light scattered by one fibril can’t constructively interfere with another fibril.  No diffraction pattern is formed.  In addition, there is destructive interference between scattered and non-scattered light,  further reduce the effects of the scatter gs101lg@hotmail.com
    11. 11. Epithelium Endotheliumgs101lg@hotmail.com
    12. 12. Diffraction effects : Corneal Corona With corneal edema, the regularity of the collagen fibrils is disrupted and the normal beneficial destructive interference no longer occurs  With severe edema and water droplets or water clefts in the epithelium, even more scattering occurs. With monochromatic light, an Airy-disc like appearance is seen. With white light, a white center will be surrounded by chromatic rings or red- yellow, purple, etc. This is called the gs101lg@hotmail.com corneal corona.
    13. 13. Ciliary corona Spread of light around an isolated bright source of light eg street lamp Diffraction of particles with in the eye No color fringe is seen Only central disc is perceived Diameter of disc depends upon the source brightness Normal phenomenon gs101lg@hotmail.com
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    15. 15. Diffraction effects: Corneal Colored Halos Corneal edema can be caused by increased intraocular pressure that forces water into the cornea producing water clefts, which act as diffractive particles.  e.g., patients may report colored haloes around small bright lights during episodes of acute glaucoma. Swimming in chlorinated pools and overwear of contact lenses may give a similar effect. gs101lg@hotmail.com
    16. 16. Diffraction effects : Lenticular Halo The lens also has regularly-arranged fibers. With the exception of the zonular area and the anterior cellular area, its fibers are laid out in a radial fashion. The axial part of the lens is uniform, so no halo is seen with small pupil diameters (< 3mm). Under low light conditions or when dilated, the effects of the peripheral zones become apparent and a halo is seen. gs101lg@hotmail.com
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    18. 18. Emsley-Fincham test A lenticular halo is normal! Since the corneal and lenticular halos look similar and the corneal halo is not normal, they must be differentiated via the Emsley-Fincham test.  Move a stenopaeic slit across the pupil.  The corneal halo is reduced in brightness a bit no matter where the slit.  The lenticular halo changes in shape as the slit moves! gs101lg@hotmail.com
    19. 19. Distinguishing a Lenticular Halo gs101lg@hotmail.com
    20. 20. Asterisms Small bright objects against a dark background usually have spikes surrounding their geometric images. An example of this is bright stars where the effect is so prominent that artists frequently depict stars with spikes. This effect is assumed to be due to diffraction off the suture lines of the crystalline lens. gs101lg@hotmail.com
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    22. 22. Shadows The passage of light through the ocular media may be affected by localized heterogeneities in refractive index that scatter light, or by opacities that absorb or scatter light. gs101lg@hotmail.com
    23. 23. Shadows 1. Ocular opacities 2. Purkinje tree 3. Blue field entoptoscope gs101lg@hotmail.com
    24. 24. Shadows Unless an opacity is nearly the same size as the pupil or close to the retina, it won’t cast a significant shadow.  Objects in a room lit by a single window won’t have strong shadows, except for those near the walls. We use a small light source to make the shadows denser and more defined. gs101lg@hotmail.com
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    26. 26. Shadows and Parallax By using parallax, the location of an opacity can be localized.  If the opacity is behind the exit pupil, against motion is seen.  If the opacity is in front of the exit pupil, with motion is seen.  The farther away from the exit pupil, the more motion seen. gs101lg@hotmail.com
    27. 27. Locating the Site of Opacities gs101lg@hotmail.com
    28. 28. Ocular opacities Visualization of striae, folds, vacuoles, cysts and corneal nerves, lens vacuoles vitreous opacities, mucous, oil globules, lens sutures, Muscae volitantes Entoptic image of eye lashes and corneal opacity shows with movement Lenticular and vitreous opacity downward movement• Corneal scars, lens opacities, intraocular foreign bodies, vitreal floaters and blood cells would all be expected to cast shadows.• The effect is strongest for opacities nearest to the retina because objects near the retina project an umbra rather than just a penumbra onto the retina. gs101lg@hotmail.com
    29. 29. Opacities may not be noticed at all by the patient if completely opaque. •An example is asteroid hyalosis, which are calcium deposits in the vitreous.•To the doctor looking in, they look very bright and may make a good view of the fundus difficult due to glare; but because they are opaque, from the retinal side they are dark and the patient may be unaware of them. gs101lg@hotmail.com
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    32. 32. Muscae Volitantes Cellular debris, probably from the embryonic hyaloid vascular system. Cast shadows and refracts light into bright circular spots and other shapes such as wavy filaments or cobwebs. Most commonly seen when viewing a bright background like a bright sky or white wall. They move on eye movement. Become more noticeable with age as the vitreous liquifies. gs101lg@hotmail.com
    33. 33. Vitreous Opacities Most vitreous opacities are harmless. A sudden onset of floaters may be serious, especially if accompanied by photopsia (flashes of light). The sudden appearance of a “film, haze or cloud” of opacities may be caused by bleeding into the vitreous or vitreous detachment. Vitreous opacities may be removed by vitrectomy. gs101lg@hotmail.com
    34. 34. Purkinje Tree Because the branching retinal blood vessels are in front of the photoreceptors, they can cast a shadow that resembles a tree. They are normally not seen, but a small bright light can reveal them as a branched pattern stopping short of the avascular zone around the fovea gs101lg@hotmail.com
    35. 35. Purkinje Tree Since stable images on the retina quickly fade (the Troxler effect), the Purkinje tree is best seen if the light source is constantly moved over a large angle. Patients sometimes comment on the Purkinje tree when they are examined with bright lights, such as the slit lamp or BIO. gs101lg@hotmail.com
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    38. 38. Purkinje tree gs101lg@hotmail.com
    39. 39. Blood Cells and the Blue-Field Entoptoscope When looking at a bright blue background such as the sky, a person may see bright spots moving along curved lines and their flow may even seem to pulse with the heartbeat. These are thought to be white blood cells, which interrupt the columns of red blood cells in the smaller retinal blood vessels.  The white blood cells allow blue light to pass, whereas red blood cells absorb blue light. gs101lg@hotmail.com
    40. 40. Blood Cells and the Blue-Field Entoptoscope This entoptic image has been incorporated into a machine known as a blue field entoptoscope to serve as a gross subjective assessment of the vascular function of the retina. gs101lg@hotmail.com
    41. 41. Xanthophyll effects  Maxwells spot  Haidingers brush gs101lg@hotmail.com
    42. 42. Maxwell’s Spot If a blue filter is quickly placed in front of your eye as you view a bright, uniform white background, a dark disk appears in the macular area. This is due to a Xanthophyll pigment (zeaxanthin) in the macula. This acts like a yellow filter, which excludes more of the blue light than the surrounding retina does so that a relatively dark spot appears in the part of the visual field that corresponds to the macula. gs101lg@hotmail.com
    43. 43. Maxwell’s Spot Maxwell’s spot is used in vision therapy to “tag” where the patient is fixating. Maxwell’s spot can also be used to measure the density of macular pigment. The darker Maxwell’s spot, the denser the pigment. e.g., cigarette smoking reduces the amount of macular pigment, which makes a person more susceptible to UV damage and to ARMD. gs101lg@hotmail.com
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    45. 45. Haidinger’s Brushes Propellar like figure seen in polarized light near the fixation point Uniformly illuminated white screen is viewed through a rotating polarizer and blue filter= yellow brushes appear. Haidinger’s brush is due to birefringence induced by Xanthophyll, which is radially polarizing.  A competing theory is that radially oriented receptor cell axons form a birefringent layer in the macula. gs101lg@hotmail.com
    46. 46. Haidinger’s brushes Some structure in eye behaves as radial analyzer of blue filter-yellow macular pigment (Xanthophyll) radial analyzer Vertical vibration falls on analyzer and horizontal vibration on plane of transmission perpendicular to plane of incidence Vertical element transmit more blue light- so blue brush is seen gs101lg@hotmail.com
    47. 47. Haidinger’s Brushes Dichroism=the effect of absorption of light polarized in one direction and transmission in the plane at right angles The figure fades rapidly due to visual adaptation, so it must be kept in view by rotating the Polaroid filter so that the hourglass also appears to rotate and exposes new retina. gs101lg@hotmail.com
    48. 48. Haidinger’s Brushes The effect is less pronounced or absent in macular edema. This can occur even before ophthalmoscopic signs of macular edema. gs101lg@hotmail.com
    49. 49. Haidinger’s Brushes Because Haidingers brush corresponds to the macula, it is sometimes used as a gross subjective test of macular function and sometimes as a training technique in amblyopia to improve fixation. Haidinger’s brush can determine whether amblyopic patients fixate with their foveas or not (eccentric fixation) since the fovea always corresponds to the center of the hourglass and the center of rotation. gs101lg@hotmail.com
    50. 50. Pressure Phosphenes  1. Digital Pressure  2. Eye Movement Phosphenes  3. Moore’s Lightning Streaks gs101lg@hotmail.com
    51. 51. Digital Pressure Phosphenes Phosphenes of all kinds are weak stimuli and therefore have to be viewed in the dark. If pressure is applied in the dark to the side of the eyeball through the closed lid, a circular bright spot will be seen The pressure directly activates retinal cells. gs101lg@hotmail.com
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    53. 53. gs101lg@hotmail.com
    54. 54. Pressure Phosphenes Pressure phosphenes are now being used to monitor patient’s intraocular pressure at home with a device called the Proview. The patient applies pressure through the eyelid until a pressure phosphene is seen. The pressure needed to produce the phosphene is read off the instrument. gs101lg@hotmail.com
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    57. 57. Pressure Phosphenes Mechanical traction on the retina also can cause phosphenes. Patients will complain of photopsia -- flashes of light.  This is why a complaint of flashes of light must be treated with utmost concern. Retinal detachments are ocular emergencies.  Vitreous liquifaction and detachment can also cause photopsia. gs101lg@hotmail.com
    58. 58. Eye Movement Phosphenes If you close your eyes and move them all the way to the left or right, then try to move them even further, you’ll see a bright half-ring shaped light with a dark center on the opposite side of the field. This is due to the extreme contraction of the rectus muscle deforming the globe a bit and mechanically stimulating the photoreceptors under the muscle’s insertion site. gs101lg@hotmail.com
    59. 59. Moore’s Lightning Streaks When the vitreous liquefies with age (syneresis), the points of remaining adherence between vitreous and retina may tug on the retina, especially during eye movements. This produces pressure phosphenes, which appear as lightning streaks at points in the visual field that correspond to the locations of adherence. gs101lg@hotmail.com
    60. 60. Moore’s Lightning Streaks These may be benign, but the clinician should check carefully for the possibility of retinal tears and detachments because they are more likely to occur in patients who experience these events. gs101lg@hotmail.com
    61. 61. Electrical phosphenes  1. Battery stimulation  2. Blue arcs of the retina gs101lg@hotmail.com
    62. 62. Electrical and X-ray phosphenes Battery stimulation If a low-voltage battery (<10 V) is placed in the mouth between tongue and upper lip in the dark, a faint glow will be seen over the visual field.  Do not try this with high voltage battery X-rays stimulation of the retina (typically higher doses) can also produce phosphenes. gs101lg@hotmail.com
    63. 63. Blue Arcs of the Retina gs101lg@hotmail.com
    64. 64. Blue Arcs of the Retina If a red patch of light (such as a very small red LED light) is viewed in a dark room monocularly, blue arcs will be seen emerging from the light source and heading towards the blind spot.  This is sometimes seen when looking at the red LEDs on a digital clock in a darkened room.  The effect is subtle, but is a little easier to see if one fixates slightly to the side of the red light. The arcs follow the course of the ganglion cell axons in the nerve fiber layer gs101lg@hotmail.com
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    69. 69. Blue Arcs of the Retina Some people explain the effect as due to an electrical “short circuit” between the axons from ganglion cells under the red stimulus and ganglion cells encountered along the path of those axons. Others claim it is due to the electrical signals in the ganglion cells in the fiber bundles stimulated by the red light abnormally causing the photoreceptors below them to respond. gs101lg@hotmail.com
    70. 70. Thanks gs101lg@hotmail.com
    71. 71. Orientation and location of obstructionThe erect retinal shadow of An axial opacity behind the a pin, placed between the exit pupil casting a shadow on pinhole and the eye, the retina in the centre of the appears inverted illuminated retinal area Downward movement of pin Downward movement of hole casts image in opposite pinhole casts image on the side gs101lg@hotmail.com same side
    72. 72. Entoptic shadow Intense light transilluminate the sclera gs101lg@hotmail.com