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PERIPHERAL FIELD DEFECT and low vision management

PERIPHERAL FIELD DEFECT and low vision management

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PERIPHERAL FIELD DEFECT and low vision management

  1. 1. PERIPHERAL FIELD DEFECTS AND LOW VISION MANAGEMENT • MANISHA DAHAL • 17th Batch, IOM
  2. 2. Presentation layout • Introduction to visual field • Common peripheral field defects • Difficulties with peripheral field defects • Peripheral visual field testing • Management
  3. 3. Visual field • The portion of space in which objects are visible during steady fixation of gaze in one direction.
  4. 4. Central field area from fixation point to a circle 30 ̊ away Peripheralfield: area beyond 30 ̊ to outer extent of field of vision
  5. 5. Types of visual field loss • Central visual field loss • Peripheral visual field loss • Hemianopic visual field loss
  6. 6. Peripheral Visual field loss • Retinitis pigmentosa • Glaucoma • Degenerative myopia • Rhegmatogenous Retinal detachment • Neurologic diseases-CNS tumours, MS,neurotoxic drugs • Vascular diseases-DM, Cerebrovascular accident, Aneurysms etc.
  7. 7. Common peripheral field defects 1. Constricted defect: Eg: Retinitis pigmentosa,Glaucoma 2. Sectoral defect: Eg: RD, Neurological disorders
  8. 8. Retinitis pigmentosa • Group of progressive bilateral disorders of retinal photoreceptor/RPE complex • Triad of  Night blindness  Visual field defect  Typical fundal appearance
  9. 9. • Progressive loss of visual fields is a hallmark of RP. • The visual field loss often begins as a donut like ring in mid-periphery. • As it progresses both centrally and peripherally, the resultant tunnel vision begins to affect the patient’s activities, driving and mobility.
  10. 10. • Pathologically in a patient with RP , the rod and cone outer segments are shortened and disorganized in the patient’s best field of vision • While in the area of visual loss; there is total loss of outer segments and a decrease in photoreceptors number.
  11. 11. Classification of peripheral visual field loss • The VF as determined by Goldmann’s perimetry monocularly is classified into seven grades by V4e indicator according to the reported classifications for patients with retinitis pigmentosa • Visual field loss graded from 0 to 6: • grade 0, normal visual field; • grade 1, some scattered scotomas in the midperiphery; • grade 2, ring scotoma; T Sugawara, AHagiwara,Hiramatsu, K Ogata, Y Mitamura and S Yamamoto Relationship between peripheral visual field loss and vision-related quality of life inpatients with retinitis pigmentosa Arch Ophthalmol 1997; 115: 53–59.
  12. 12. • grade 3, constricted visual field within the central 30 degree • grade 4, constricted visual field within the central 15 degree with isolated peripheral visual islands; • grade 5, constricted visual field within the central 15 degree without peripheral visual islands; • and grade 6, constricted visual field within the central 10 degree
  13. 13. Glaucoma • Is an optic neuropathy causing peripheral visual field loss progressing to central visual field loss. • Early glaucomatous visual field defects include paracentral scotomas, arcuate scotomas, nasal steps and temporal wedges.
  14. 14. Arrangement of nerve fibres in retina • From nasal half of retina come directly to optic disc as superior inferior radiating fibres • From macula pass straight to temporal part of disc as papillomacular bundle • Fibres from temporal retina arch above and below the macula and papillomacular bundle as superior and inferior arcuate fibres
  15. 15. NFL loss in glaucoma • Arcuate nerve fibers occupy the superior & inferior temporal portion of ONH & are most sensitive to glaucomatous damage. • Accounts for early loss in the corresponding regions of visual field • Macular fibers are most resistant to the glaucomatous damage & explain the retention of the central vision till end.
  16. 16. Visual field defects in glaucoma • Appear only after about 40% of axons have been damaged and field defects run parallel to the changes at the optic nerve head and continue to progress if IOP is not controlled.
  17. 17. • Progression of field defects: VF defects are initially observed in Bjerrum’s area(10-25 degree from fixation) & correlate with optic disc changes. Glaucomatous field loss takes the following sequence:
  18. 18. Early field defects 1. Isopter contraction : - mild generalised constriction of central as well as peripheral field. - earliest VF defect
  19. 19. 2. Baring of blind spot : • Exclusion of blind spot from the central field d/t inward curve of the outer boundary of 30◦ central field.
  20. 20. Nerve fibre bundle defects • Superior & inferior fibers are most vulnerable • Damage to the inferior and superior poles of the nerve results in loss of the arcuate nerve fiber bundles. • The resulting visual field defect types include:
  21. 21. 1. Paracentral scotoma : • earliest clinically significant field defect. • may appear below or above the blind spot b/w 10◦ to 20◦ of fixation point.
  22. 22. 2. Siedel’s scotoma : - paracentral scotoma joins the blind spot to form a sickle shaped scotoma
  23. 23. 3. Arcuate scotoma • scotoma that starts at or near the blind spot, arches around the point of fixation, and terminates abruptly at the nasal horizontal meridian .
  24. 24. 4. Ring or double arcuate scotoma • Develops when two arcuate scotomas join together.
  25. 25. 6. Nasal step • arcuate scotomas run in different arcs & meet to form a right-angled defect in the horizontal meridian.
  26. 26. Advanced glaucomatous defect • VF loss gradually spreads centrally as well as peripherally leaving behind a small island of central vision(tubular vision) & an accompanying temporal island are left. • With continued damage these islands of vision also diminish in size until central vision is totally extinguished. • Temporal island of vision is more resistant & is lost in the end leaving patient with no light perception.
  27. 27. Tunnel vision in advanced glaucoma
  28. 28. Degenerative myopia • Central ring shaped scotoma,as well as hemianopic and quadrantic defects. • The visual field defects is caused by a mechanical tension and distortion of the optic nerve fibers caused by an elongation of the axial length of the eye. Ohno-Matsui K, Shimada N, Yasuzumi K, et al. Long-term development of significant visual field defects in highly myopic eyes. Am J Ophthalmol 2011;152(2):256 –265.
  29. 29. • The degree and direction of myopic optic disc tilt affected the RNFL thickness profile. • The eyes with greater degree of horizontal optic disc tilt to the temporal side had more temporally located superior/inferior peaks of RNFL thickness and thicker temporal RNFL thickness than the eyes without optic disc tilt.
  30. 30. Diabetic Retinopathy • Laser panretinal photocoagulation for proliferative diabetic retinopathy is known to cause peripheral field constriction. • It is due to larger laser spot sizes • A calibrated spot size of 500 micrometer in patients was magnified approximately 5% by the Mainster lens used. • Furthermore, there is probably an unquantified increase in effective burn size due to lateral thermal spreading. Marianne Henricsson' and Anders Heij12, The effect of panretinal laser photocoagulation on visual acuity, visual fields and on subjective visual impairment in preproliferative and early proliferative diabetic retinopathy , Acta Ophthalmol
  31. 31. • Traumatic Brain Injury/Stroke Common form of visual field defect is homonymous hemianopia.
  32. 32. PROBLEMS DUE TO PERIPHERAL VISUAL FIELD LOSS • Mobility problems • Fear of growing to blind in future • Glare and photophobia • Tubular field of vision, bumping into objects
  33. 33. POSTURAL ABNORMALITIES • Head turn • Pronounced head and eye movements while travelling • A downward tilt
  34. 34. APPEARANCE • Nystagmus • Strabismus • Sunglasses worn inside the examination room(indicating severe photophobia /glare) • Soiled or missing buttons(possibly of difficulty in daily living skills • Fatigue appearance(indicator of serious systemic disorder, depression resulting from recent vision loss,or impact of other psychosocial factors.
  35. 35. MOBILITY • Tentative gait(abnormality in walking) • Postural stiffness • Maintainance of close proximity to walls or handrails • Reliance on tactile information by holding onto an individual or trailing a wall
  36. 36. PERIPHERAL VISUAL FIELD TESTING • Kinetic Vs Static (equal sensitivity) • Procedure – Confrontation (kinetic) – Tangent Screen (Kinetic) – Hand disc (Bernell Disc) Perimeter (kinetic) – Goldman (kinetic / static) – Automated (static)
  37. 37. Confrontation test • Best result are obtained when practitioner and assistant are involved in testing • The practitioner is seated in front of patient and attempts to hold the patient’s visual attention (bulbs,toys,favourite food,familiar face) while observing visual responses to incoming stimuli. • The assistant stands behind the patient and presents visually interesting objects in arcs delineating the principle quadrants.
  38. 38. • The patient is asked to name,point or look at the object when it first appears in his/her visual field • If it is not possible due to patient’s developmental level,observations of consistent changes in fixation will indicate the point of visual awareness of the incoming stimuli. • Standard precautions against the introduction of tactual and auditory cues should be taken
  39. 39. • Dynamic confrontation field • This method is performed by presenting a finger from one hand in one of the quadrant • The tester ask the patient to touch the finger • If there is defect then patient exhibits head movement and saccade to make contact with the finger.
  40. 40. • Penlight field testing • Requires 2 individual.One serving as fixation target and observer ,stands a few feet in front of patient • Other remains behind the patient and is responsible for bringing the penlight from behind the patient into each quadrant(nasal,temporal,superior and inferior) • The observer observes any response that patient may exhibit(head turn,eye turn)
  41. 41. • Functional field test • The patient serving as fixation target positions himself or herself 5 feet in front of the patient.The tester remains behind the patient • The tester walks slowly behind the patient,along one side until he or she is noticed.The tester then return to the original position and repeats the procedure • Variation in response time and position of the tester provides examiner with the gross indication of patient peripheral awareness.
  42. 42. MANAGEMENT OF PERIPHERAL FIELD DEFECTS Indirect • Maximize the visual acuity – Proper refraction, binocularity • Reduction of the effect of glare & photophobia – Filters (Amber / yellow colored filters) • Illumination – Most of time beneficial . – Can perform better • Referral to O & M trainers/ Rehabilitation specialist
  43. 43. Field enhancement techniques 1. Semi reflective mirror 2. Fresnel Prisms 3. Field expanding channel lens 4. Reverse Telescope 5. Amorphic or new horizontal lens 6. Image Minifiers 7. Concave lenses 8. Convex mirror • Direct
  44. 44. – Field expansion techniques – Field relocation technique • Field relocation only exchanges the position of the field loss relative to the environment. Eg.prisms, mirrors • Field expansion is actually the desired effect as it means that the simultaneously seen field is larger with the device than without it. Eg; Field expanding channel lens,Reverse Telescope,Amorphic or new horizontal lens,Image Minifiers,Concave lenses,Convex mirror Eli Peli , The Schepens Eye Research Institute, Harvard Medical School ,Field Expansion for Homonymous Hemianopia using Prism and Peripheral Diplopia, Vol 1, 1998, 74-77
  45. 45. • Semi reflective plano mirror is placed on the spectacle, in opposite side of field defect – eg: on nasal side for a bitemporal heminopsia • Mirror reflect the image of an object on the non seeing side to a more nasal functional retinal area 46 1. Semi reflective mirror
  46. 46. Semi reflective mirror contd.. Indications Hemianopia involving temporal field Avoided in Overall constriction 47
  47. 47. Available in – clip-on form or – can be permanently affixed to the spectacle frame – Plano – Convex – Semi-reflecting – Fully reflecting – Dichoric – Mirror position; behind lens or, – In front of lens 48
  48. 48. • Disadvantages – Bulky – Poor cosmesis – Confusion due to dual image – Image reversal 49
  49. 49. 2. Fresnel Prism • Press on prism • 1mm plastic sheet of polyvinyl chloride (PVC) • Applied in the back side of spectacle on carrier lens 50
  50. 50. Indications Overall constriction Upper or lower field altitudinal defect Homonymous hemianopia 51
  51. 51. • Prism placement – side of defect and base towards the defect – Eg: Bitemporal heminopsia • Prism placed base out in temporal part of the spectacle • By glancing into the prism – the patient can detect obstacles or targets in the non- seeing area with less eye movement than would be required without the prism 52
  52. 52. 53
  53. 53. Advantage of fresnel prism • Minimal weight • Minimal thickness • Minimal cost • Wide range of available powers(from 0.5 to 30 prism diopters)
  54. 54. DISADVANTAGES • Decrease in visual acuity • Decrease in contrast sensitivity • The prism will discolor over time • The prism may lose the surface tension over a period and fall off • Demonstrate greater distortion and chromatic abberation than an equal powered ground in prism.
  55. 55. Field relocation with binocular prism • Field relocation with overall binocular prism assumes that the eyes do not compensate for the prism (usually about 20 prism diopters) with a corresponding eye movement of about 10 degrees which will neutralize the effect of the prism. • There is also a corresponding field loss in the far periphery on the seeing side • The field loss caused by a binocular sector prism is in the center of the field. This field loss can be compensated by head movements and partially by eye movements This approach also provides only for field relocation Eli Peli , The Schepens Eye Research Institute, Harvard Medical School ,Field Expansion for Homonymous Hemianopia using Prism and Peripheral Diplopia, Vol 1, 1998, 74-77
  56. 56. • Furthermore, the effect of the prism takes place only after the patient changes his fixation towards the side of the hemianopic field. • Since the patient does not see objects in this part of his field, he is less likely to fixate into this field and intentional scanning is required. • The amount of prism typically used provides a very small shift of the field. A comparable access to the unseen part of the field could be achieved with a slightly larger eye movement than is necessary to shift into the field of the prism
  57. 57. • Monocularly fitted sector prisms expand the field, once the patient changed his fixation to within the field of the prism. • As long as the patient's eyes are at primary position of gaze or are directed away from the hemianopic field the monocular sector prism has no effect on the field of view. • The field expansion, achieved upon directing the gaze into the prism in the direction of the hemianopia, is accompanied by diplopia. • The central diplopia induced is very unpleasant to the patient
  58. 58. Field relocation with binocular sector mirrors • Binocular sector mirrors do provide view of a segment in the hemianopic field which can be large and positioned quite far into the periphery, but it is traded with an equal size scotoma on the seeing side.
  59. 59. • Monocularly placed sector mirrors provide an actual field expansion, since the part of the hemianopic field seen in the mirror in one eye is superimposed on the seeing part of the field of the other eye. • That means confusion as two different objects are perceived to be in the same direction. • The image reflected in a mirror is inverted right to left and is projected into the opposite direction of where it really is, making use of the device very difficult. • Similar effects, with similar difficulties, can be achieved over a larger field (and for monocular patients) using semi-reflective mirrors.
  60. 60. • The new method of field expansion involves a prism which is limited to the peripheral field (i.e., superior, inferior or both). • The peripheral prism is placed across the whole width of the lens spanning both sides of the pupil so that it is effective at all lateral positions of gaze.
  61. 61. • The prism expands the field via peripheral diplopia. Peripheral diplopia, however, is much more comfortable for the user than central diplopia since peripheral diplopia is a common feature of normal vision. • The field expansion effect of the prism is unaltered by eye and head movements over a wide range of such movements into either side. Eli Peli , The Schepens Eye Research Institute, Harvard Medical School ,Field Expansion for Homonymous Hemianopia using Prism and Peripheral Diplopia, Vol 1, 1998, 74-77
  62. 62. 3.Field Expanding channel lens • A pair of spectacle with each carrier lens having • Two 12 pd lateral prism and an inferior 8 pd lens – Central non-prismatic channel (distance/near prescription) • Apex towards the central non prismatic channel • Patients view object via channel while for O&M via prism for temporal, nasal & inferior awareness.
  63. 63. 3.Field Expanding channel lens • Channel width depends upon patient’s remaining central VF Field loss Channel size(mm) > 200 14 To 150 10 To 100 8 To 60 6
  64. 64. • Channel prisms provide no benefit at primary gaze. Inconsequential extension was provided by InWave prisms, although accessible with moderate gaze shifts. Higher-power prisms provide greater extension, with greater paracentral scotoma loss, but require uncomfortable gaze shifts. • Head turns, eye scans, are needed to see regions lost to the apical scotomas. Trifield prisms provide field expansion at all gaze positions. Eli Peli,Tunnel Vision Prismatic Field Expansion:Challenges and Requirements Acta Opththalmologica vol4 ,issue 6 ,nov 2015
  65. 65. 4. Reverse Telescope • Galilean or Keplerian telescope viewed through the objective lens causing minification. • Minification equal to power of telescope – Minification (MMIN) = 1/ magnification (M) • Eg: 3x telescope cause minification by 3x and reduce VA by three times. • Only for static view not successful for mobility (due to peripheral distortion, motion parallax)
  66. 66. 5. Amorphic or new Horizon lens • Use of +ve or – ve cylindrical lenses in combination, minification is limited only to the horizontal meridian • Resulting in horizontally compressed & vertically unchanged retinal image by a factor of lens power • Available powers: 1.2 x , 1.4x, 1.6 x, 1.8 x, 2x • Purpose: – to minimize the VA degradation as minification is limited to one meridian.
  67. 67. 6. Image Minifiers • Principle: – Reverse Galilean telescope that produces a 1/3rd image size reduction without producing excessive barrel distortion • Features: – Focusable, light weighted – Handheld. Clip on, spectacle mounted system
  68. 68. Minifiers Indications Overall constriction Avoided in Hemianopia 71
  69. 69. Field Enhancer Minifier
  70. 70. 7. Hand Held Concave Lenses • Concave lens held at specific distance from the eye • Act as a reverse telescope – Minification is provided by • Concave lens • Accommodation or add power to see the image clearly • Amount of Minification: Concave lens power (D) / Add/Acco.)(A)
  71. 71. t Nd a a When a is in radian, .t= d/2a. When, a. Is in degree .t= d/2 a. (/180) t  30d a The estimation of the power of negative lens field expander
  72. 72. -f N t Spectacle Magnification SM  1 1 - tF F = 1 - Min t where Min = 1/M = field expansion factor 1.M=-ft/fo=-acc/fo 2.Acc=1/(t-1/F)
  73. 73. A young emmetrope suffered from retinitis pigmentosa. His visual field was only 10 degrees in diameter and it was found that a minimum field of view of 30 degrees was needed for mobility. A nega- tive lens 35 mm in diameter is used in this case. The magnification M of the system ?
  74. 74. VF = 100 300 M = tan 100 tan 300  10 30 M = 0.333 d = 35mm t  30(0.035) 5 t = 0.21m F = 1 - Min t Min = 1 / 0.333 = 3 = 1 - 3 0.21 = -9.53D
  75. 75. GC Woo, B Ing & M-H Lee Determining the power of a negative lens field expander. Clinical and Experimental Optometry. 2001;84(3): 162-164.
  76. 76. 8. Convex mirror • Enhance FOV by minification • Used as side mirrors of vehicle, hall ways, doorways • Give wide field and help patient with constricted field to be aware of the surroundings
  77. 77. Summary of Devices Minifiers Mirror reflecting System Prism refracting system Indications Overall constriction Hemianopia involving temporal field Homonymous hemianopia Overall constriction Upper or lower field altitudinal defect Avoided in Hemianopia Overall constriction Effect on acuity ( markedly) Decreased Not affected Slightly decreased Effect on field ( markedly) Increased Objects from non- seeing field REFLECTED to appear superimposed on seeing field Objects from non- seeing field REFRACTED nearer to midline 80
  78. 78. Minifiers Mirror reflecting System Prism refracting system Binocular/ Monocular Monocular Fitted monocular but better if patient binocular Monocular/ Binocular Fitting characteristics Usually in upper part of lens Fitted on side of spectacle FURTHEST from defect, with reflecting surface TOWARDS defect Fitted on side of spectacle NEAREST to defect, prism base TOWARDS defect 81
  79. 79. Summary • It has become evident that not all PFD are sensitive to the same methods of field enhancement. • The differing results may be due to sudden field loss associated with strokes and brain injury versus more gradual field loss associated with RP and glaucoma. • Patients having gradual field loss may learn to be more efficient with their scanning ability and therefore have less need for prisms or mirrors • Thus ,greater understanding of pathologies causing visual field constriction and how they function in normal functioning of low vision patients is necessary to allow more specific treatment and improved rehabilitation
  80. 80. REFERENCES • Essential of low vision practice • Clinical procedure in optometry • Clinical optics • Kanski’s clinical ophthalmology • Internet

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