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LOW VISION AIDS



           Astha Jain
           Shashi Sharma
INTRODUCTION
DEFINITION (INDIA)
   According to the Person with Disabilities Act 1995, “A person with
    low vision means a person with impairment of visual functioning
    even after treatment of standard refractive correction but who uses
    or is potentially capable of using vision for the planning or execution
    of a task with appropriate assistive device.”
DEFINITION(WHO)
   WHO (ICD-10) definition
     “A person with low vision is one who suffers visual acuity between
      6/18 to 3/60 in the better eye after the best possible correction or a
      field of vision between 20 to 30 degrees.”
     Used for reporting and comparison of data



   The WHO working definition of Low Vision (Bangkok definition,
    1992)
     “A person with low vision is one who has impairment of visual
      functioning even after treatment, and/ or standard refractive correction,
      and has a visual acuity of less than 6/18 to light perception or a visual
      field of less than 10 degrees from the point of fixation, but who uses, or
      is potentially able to use, vision for the planning and/or execution of a
      task .”
     Defines population in need of low vision services
category   Corrected      WHO             working         Indian
           VA- better eye definition                      definition


0          6/6 – 6/18     Normal          Normal          Normal
1          <6/18 – 6/60   Visual          Low vision      Low vision
                          impairment
2          <6/60 – 3/60   Severe visual   Low vision      Blind
                          impairment


3          <3/60 – 1/60   Blind           Low vision      Blind
4          <1/60 - PL     Blind           Low vision      Blind
5          No PL          Blind           Total blindness Total blindness
VISUAL DISABILITY CHART
Category no.   Good eye        Worse eye       Percent
                                               blindness
1              6/9-6/18        6/24-6/36       20%
2              6/18-6/36       6/60-nil        40%
3              6/60-4/60       3/60-nil        75%
4              3/60-1/60       CF 1 ft- nil    100%
5              CF 1 ft – nil   CF 1 ft - nil   100%
6              6/6             nil             30%
FUNCTIONAL EFFECTS OF LOW VISION
   Loss of central vision (eg. macular degeneration, toxoplasma scar etc.)
     Difficulty reading
     Problems writing/ completing paperwork
     Inability to recognize distance objects and faces


   Loss of peripheral vision (eg. Retinitis pigmentosa, glaucoma etc. )
     Difficulty in mobility and navigation
     Difficulty reading if there is constricted central visual field
     Visual acuity may not be affected until very advanced disease


   Cloudy media (eg. Corneal scar, vitreous hemorrhage etc.)
       Blurred vision
       Reduced contrast
       Problems with glare
GOALS OF LOW VISION MANAGEMENT

   Increase functionality
      Make the most of the remaining vision


   Provide link to community resources and support services

   Education
STRATEGIES

   Be oriented towards activities of daily living

   Use appropriate technology

   Be cost effective

   Utilize appropriate educational and vocational adaption

   Focus on target groups
GLOBAL PREVALENCE OF LOW VISION
     True magnitude not known because :
        No uniform definition of low vision
        Incomplete surveys
        Low vision definition does not include standards of near vision,
         which is the main area dealt with low vision patients.

     Current Data *
           No. of visually impaired: 180 million
           No. of blind: 45 million
           Those with residual vision: 171 million
           Of these 171 million:
           Those with vision from PL to 3/60 : 36 million
           No. with vision from 3/60to 6/18: 135 million
           No. who can benefit from treatment: 103 million
           True low vision patients: 68 million
*Ramachandra Pararaiasegaram. Low vision care: the need to maximise visual potential. Community Eye Health. 2004; 17: 1-2
WHAT ARE LOW VISION AIDS AND HOW DO THEY
WORK ??


   Devices which help the people to use their sight to better advantage

   Can be optical devices like magnifiers or telescopes, or non optical
    devices like stands, lamps and large prints.

   Alter the environment perception through
     BBB – bigger brighter and blacker
     CCC – closer color and contrast
DISEASES WHERE LOW VISION AIDS ARE HELPFUL

   Retinitis pigmentosa
   Glaucoma
   Macular degeneration
   Corneal scar
   Albinism and aniridia
   Retinal detachment
   Diabetic retinopathy
   Chorioretinitis
   Optic atrophy
TYPES OF MAGNIFICATION
   Low vision aids make use of angular magnifications by increasing :

       Relative size

       Relative distance
   Angular : it is the apparent size of the object compared with true
    size of the object seen without the device.eg. Telescopic system




                         Angular magnification M = ω’/ ω
   Relative size: by making the object appear bigger (no
    accommodation required) eg. CCTV
   Relative distance: by bringing the object closer (requires good
    accommodation) eg. magnifiers
VISUAL ASSESSMENT
HISTORY
   Ocular history:
     To know cause of low vision
     To know the progression of disease



   Systemic diseases that may pose difficulty in using certain devices
    eg. arthritis, tremors

   Task analysis
VISUAL ACUITY
   Distance visual acuity:
    Lighthouse distance visual acuity test chart is preferred over the standard
    snellen’s chart as it has :

            Equal line difficulty

            geometric progression of optotype size from line to line

            5 letters on each line

            More lines at lower level of visual acuity

            Test distance of 2 meters can be used to cover visual acuity upto 20/400
   Near visual acuity:


       Text samples are better than single letter acuity charts

       Metric notations are used

       1M symbol subtends an angle of 5 minutes of arc at 1 meter and is
        roughly equal to the size of the newsprint

       Visual acuity is recorded as distance of reading material (in meters) over
        the letter size (in M units)

       Snellens equivalent can be calculated from the metric notations
OTHERS

   Contrast sensitivity

   Visual field analysis:
     Peripheral field: using Humphery or octopus perimetry
     Central field: using Amsler grid


   Glare :
     History
     Measuring visual acuity both with and without illumination in the chart


   Colour vision

   Look for dominant eye:
       by testing contrast sensitivity monocularly and binocularly
LOW VISION AIDS
OPTICAL


DISTANCE
        Hand held telescopes
        Mounted telescopes




NEAR
        Spectacles
                • Prismatic ½ eyes
                • Bifocals
        Magnifiers

                • Hand held vs. stand
                • Illuminated vs. non-illuminated
        Electronic Devices
NON-OPTICAL

   Glare reduction devices
   Contrast enhancement devices
   Computer software
   Accessory devices
     Talking watches, clocks, etc
     Writing guides
     Tactile markers
LOW VISION OPTICAL DEVICES
FOR NEAR
MAGNIFYING SPECTACLES

   High plus reading glasses to
    magnify the images

   Given as an add to the best distance refraction

   Reading distance is calculated by 100 divided by add

   Magnification is 1/4th the power of the lens.

   Used for near work

   Amount of add needed depends on the accommodation and the reading
    distance
   Reading add can be predicted using the Kestenbaum rule i.e the amount
    of add needed to read 1M print is the inverse of the visual acuity fraction

   However usually greater add is required than predicted as the patient also
    has reduced contrast sensitivity

   If the patient is monocular, the poorer eye may be occluded if it
    improves the functioning

   When binocular corrections are needed :
       Base in prisms are added to compensate for convergence angle.
       Optical center may be decentred


   Aspheric lenses may be used to reduce lenticular distortion
   Advantages :
     Hands are free
     Field of view larger when compared to telescope
     Greater reading speed
     Can be given in both monocular and binocular forms
     More portable
     Cosmetically acceptable


   Disadvantages:
     Higher the power, closer the reading distance
     Close reading distance causes fatigue and unacceptable posture
     Patients with eccentric fixation are unable to fix through these glasses
MAGNIFIERS
   Useful for near work

   Designed to be held close to the reading material to enlarge the image

   The eye lens distance should be minimum to achieve larger magnification

   Two types:
     Hand magnifier
     Stand magnifiers.
HAND MAGNIFIERS

   Available from + 4.0 to + 68.0 D.

   Available in three designs:
      Aspheric – reduces thickness and peripheral distortion
      Aplantic – flat and wide distortion free field and good clarity
      Biaspheric – eliminating aberrations from both surfaces


   Most patients accept upto 6x magnification
   Advantages
       The eye to lens distance can be varied
       Patient can maintain normal reading distance
       Work well with patients with eccentric viewing
       Some have light source which further enhances vision
       Easily available, over the counter



   Disadvantages:
     It occupies both hands
     Patients with tremors, arthritis etc have difficulty holding the magnifier
     Maintaining focus is a problem especially for elderly
     Field of vision is limited
STAND MAGNIFIERS

   The magnifiers are stand mounted

   The patient needs to place the stand magnifier on the reading material
    and move across the page to read

   Has a fixed focus

   Advantages :
       They are a choice for patients with tremors, arthritis and constricted
        visual fields.

   Disadvantage:
     Field of vision is reduced
     Too close reading posture is uncomfortable for the patient
     Blocks good lighting unless self illuminated
CLOSED CIRCUIT TELEVISION SYSTEM
   Closed circuit television system (CCTV) consists of a monitor, a
    camera and a platform to place the reading text

   It has control for brightness, contrast and change of polarity

   Magnification varies from 3X to 60X
LOW VISION OPTICAL DEVICES
FOR DISTANCE
TELESCOPES

   Work on the principle of angular magnification

   Telescopes with magnification power from 2x to 10x are prescribed

   They can be prescribed for near, intermediate and distant tasks

   Field of view decreases with magnification

   Types:
      Hand held monocular
      Clip on design
      Bioptic design: mounted on a pair of eyeglasses
   Principal
       Telescopes consist of two lenses (in practice two optical systems) mounted such
        that the focal point of the objective coincides with the focal point of the ocular.

       Objective lens is a converging lens


    Galilean telescope                        Keplerian telescope
    The eye piece is a negative lens and      Both eye piece and objective are
    the objective is a positive lens          positive lens
    Resultant image is virtual and erect      Resultant image is real and inverted.
                                              Prisms are incorporated to erect the
                                              image
    Loss of light reduces brightness of       Loss of light is more in this system
    the image
    Field quality is poor                     Field quality is relatively good
   Magnification of a telescope is given by the formula M = fo/fe

   Telescopes can be used to focus near objects by
     changing the distance between objective and ocular lens
     Increasing the power of the objective lens
GALILEAN TELESCOPE
            Objective
                        Eye piece




  a
                                    β   fo
                                        fe
KEPLERIAN TELESCOPE
       Objective             Eyepiece




                   fo   fe

   α                                    β
TELESCOPE FOR NEAR
   Advantages:
     Only possible device to enhance distant vision


   Disadvantage:
     Restriction of the field of view
     Appearance and apprehension
     Expensive and costly
     Depth perception is distorted
NON OPTICAL DEVICES
ILLUMINATION

   Positioning
         Light source should be to the side of better eye
         Moving light closer will yield higher illumination




   Higher levels of illumination is needed in patients with
         Lost cone functions (macular degeneration)
         Glaucoma

         Diabetic retinopathy

         Retinitis pigmentosa, Chorioretinitis




   Reduced illumination
         Albinism
         Aniridia
READING STAND

   Easy comfortable posture to the patient
WRITING GUIDE
   Black cards with rectangular cut outs horizontally along the card
   The patient can feel the empty cut out spaces and write
SIGNATURE GUIDE
TYPOSCOPE / READING GUIDE

   Masking device with a line cut out from an opaque, non reflecting
    black plastic or thick paper.
   Reduces glare and controls contrast.
NOTEX
   It is a rectangular piece of cardboard with steps on top right corner
    which helps in identifying the currency of the note

   1st cut indicates Rs. 500, 2nd cut indicates Rs.100, 3rd cut indicates
    Rs 50 and so on.
RELATIVE SIZE DEVICES

   Larger object subtends a larger visual angle at the eye and is thus
    easier to resolve
       Large print material
       Large type playing cards, computer keyboards
       Enlarged clocks, telephones, calendars
COMPUTER SOFTWARE
   Jaws screen reading software
   Connect out loud internet and email software
   Magic 8.0 screen magnification software and speech
GLARE REDUCING DEVICES

   Glare is described as unwanted light

   It is disabling in patients with cataracts, corneal opacities, albinism,
    retinitis pigmentosa


   Devices to prevent glare:
      Sunglasses
     Caps
     Umbrella
     Polaroid glasses
     NoIR filters
     Corning photochromic filters
     (CPF glasses)
CPF GLASEES
o   Attenuate 100% of UVB wavelengths.

o   Block 99% of UVA wavelengths.

o   The blue light portion of the visible spectrum is most likely to scatter
    in the eye, causing discomfort and hazy illusion.

o   Attenuate 98% of high-energy blue light, with exception of CPF
    450, which is 96% of high-energy blue light.

o   The number of the CPF glasses correspond to wavelength in
    nanometers above which light is transmitted
CPF® 550 (red)      Lens colour varies from        retinitis pigmentosa
                    orange-red when lightened      albinism
                    to brown when darkened.
CPF® 527 (orange)   Orange-amber lens darkens      retinitis pigmentosa
                    to brown in sunlight, giving   diabetic retinopathy
                    individuals better visual
                    function and reduced glare
CPF® 450 (yellow)   enhances contrast and helps    optic atrophy
                    control glare indoors          albinism
                                                   pseudophakia
CPF® 511 (yellow    Medium-range filter            macular degeneration
orange)             provides moderate blue light   glaucoma
                    filtering                      aphakia
                                                   pseudophakia
                                                   optic atrophy
                                                   developing cataracts
NOIR FILTERS

   Absorbs the short wavelengths of the visible spectrum that can
    scatter within the ocular media,

   Also absorbs ultraviolet light (to 4000 nm) and infrared light

   Manages overall visible light transmission (VLT) to allow the proper
    amount of light energy to reach the eyes.
   Includes a full range of lenses (spanning 90% to 1% VLT)

       2% dark amber: 100% UV, infrared and blue light protection, helpful on very
        bright days

       13% standard grey: good for postoperative cataract, glaucoma, diabetics and
        those who had corneal transplants

       20% medium plum: good in low light situations and can be worn indoors

       58% light grey: reduce indoor glare especially under fluorescent light

       65% yellow: retinitis pigmentosa and macular dgeneration
COLOR AND CONTRAST ENHANCEMENT

   Maximize contrast by using a light color against black or dark color

   Choose colors in the room or working area which have high contrast
PINHOLE GLASSES

   Multiple holes of approximately 1mm size are made in the glasses

   The distance between the holes should be atleast 3-3.5 mm or
    approximately the size of the pupil

   Used in patients with corneal opacities or conditions with irregular
    reflexes

   Not used in patients with central field defects as it reduces
    illumination and visual acuity
MOBILITY ASSISTING DEVICES

   Patients with low vision suffer a major problem of mobility
         Long canes
         Strong portable lights
FIELD EXPANDING DEVICES

   As the magnification increases, the field of view decreases

   Three methods of increasing the field:
         Compress the existing image to include more of available area
         Provide prisms that relocates the image from a non seeing to a seeing
          area
         Use a mirror to reflect an image from a non seeing area




   Reverse telescopes: they are usually not accepted due to minification

   Fresnel lenses with power of 10-15D with base in the direction of
    field loss
FUTURE
BIONIC EYE
   Designed for patients who are blind due to diseases like retinitis
    pigmentosa or AMD

   Can also be tried for those with severe vision loss

   Relies on patient having a healthy optic nerve and a developed visual
    cortex

   Cannot be used for people who were born blind

   The prosthesis consists of :
       A digital camera built into a pair of glasses
       A video processing microchip built into a hand held unit
       A radio transmitter on the glasses
       A receiver implanted above the ear
       A retinal implant with electrodes on a chip behind the retina
Camera captures an image


                           Send image to microchip


        Convert image to electrical impulse of light and dark pixels

                       Send image to radiotansmitter

                  Transmits pulses wirelessly to the receiver

     Sends impulses to the retinal implant by a hair thin implanted wire


The stimultaed electrodes generate electrical signals that travel to the visual cortex
   Requires training by the subject to actually see an object

   Subjects have to learn to interpret the array of white and dark dots as
    object

   It is still in clinical trial stage
Help when there is no cure
Thank you
Thank you

      Thank you

            Thank you
   Various forms are available
     1.  Powers usually available are +4.0, +5.0, +6.0, +10.0 , +12.0, +16.0,
         20.0 and +24.0
     2.  Binocular corrections are needed –Base in prisms are added to
         compensate for convergence angle.

    Optical quality of the lens should be an aspheric design to eliminate
     peripheral aberration and provide reasonable field.

    The reading glass should be prescribed as an addition over the distance
     correction.
GALLELIAN TELESCOPE
KREPLERIAN TELESCOPE
OPTICS OF LOW VISION AIDS


   Principle : Magnification = D/4
    on the assumption that the patient can sustain just enough
    accommodation to hold the matter at 25 cm.

   Modified formula : M = D + A-h AD/2.5 where
         A is the amplitude of accomodation
         h is the eye lens distance in meters.

   To increase magnification:
     Eyes should be kept close to the lens (reduce h)
     Object should be as close to the patient’s eye as his accomodation
      allows
Left: simulated with cataracts. Middle: CPF 511 lenses. Right:
normal eyes.
IMPACT OF OCULAR DISEASE ON THE PATIENT


   Visual disorder
    Anatomical changes in the visual organ caused by the disease of the eye

   Visual impairment
    Functional loss that results from the visual disorder

   Visual disability
    Refers to vision related changes in the skill and abilities of the patient

   Visual handicap
    Psychosocial and economic consequences of visual loss
   Legal Blindness
      Best corrected distance visual acuity not exceeding 6/60 in the
       better eye
      Visual field of 20 degrees or less at widest point in the better eye


   Low Vision
      Best corrected visual acuity between 6/60 to 6/18
      Significant field loss
      Impaired function


   All these definitions however do not consider
     Near vision
     Scotoma, hemianopia
     Visual performance like contrast
EYE DISORDERS AND LOW
VISION
RETINOPATHY OF PREMATURITY




       Retinopathy of prematurity requires bright light and
       near additions required for near work
ANIRIDIA




           Tinted glasses and cap
ALBINISM




 Typoscope
             Dark glasses
CORNEAL DAMAGE




 Multiple pin hole glasses   Hand magnifier
DIABETIC RETINOPATHY




     Diabetic Retinopathy with near glasses, hand magnifiers and
     a reading lamp
GALILEAN TELESCOPE
         Objective
                     Eye piece




a
                                 β   F
KEPLERIAN TELESCOPE
         Objective
                          Eye piece




  α                                   β
                      F
KEPLERIAN TELESCCOPE
TELESCOPE FOR NEAR

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low vision aids

  • 1. LOW VISION AIDS Astha Jain Shashi Sharma
  • 3. DEFINITION (INDIA)  According to the Person with Disabilities Act 1995, “A person with low vision means a person with impairment of visual functioning even after treatment of standard refractive correction but who uses or is potentially capable of using vision for the planning or execution of a task with appropriate assistive device.”
  • 4. DEFINITION(WHO)  WHO (ICD-10) definition  “A person with low vision is one who suffers visual acuity between 6/18 to 3/60 in the better eye after the best possible correction or a field of vision between 20 to 30 degrees.”  Used for reporting and comparison of data  The WHO working definition of Low Vision (Bangkok definition, 1992)  “A person with low vision is one who has impairment of visual functioning even after treatment, and/ or standard refractive correction, and has a visual acuity of less than 6/18 to light perception or a visual field of less than 10 degrees from the point of fixation, but who uses, or is potentially able to use, vision for the planning and/or execution of a task .”  Defines population in need of low vision services
  • 5. category Corrected WHO working Indian VA- better eye definition definition 0 6/6 – 6/18 Normal Normal Normal 1 <6/18 – 6/60 Visual Low vision Low vision impairment 2 <6/60 – 3/60 Severe visual Low vision Blind impairment 3 <3/60 – 1/60 Blind Low vision Blind 4 <1/60 - PL Blind Low vision Blind 5 No PL Blind Total blindness Total blindness
  • 6. VISUAL DISABILITY CHART Category no. Good eye Worse eye Percent blindness 1 6/9-6/18 6/24-6/36 20% 2 6/18-6/36 6/60-nil 40% 3 6/60-4/60 3/60-nil 75% 4 3/60-1/60 CF 1 ft- nil 100% 5 CF 1 ft – nil CF 1 ft - nil 100% 6 6/6 nil 30%
  • 7. FUNCTIONAL EFFECTS OF LOW VISION  Loss of central vision (eg. macular degeneration, toxoplasma scar etc.)  Difficulty reading  Problems writing/ completing paperwork  Inability to recognize distance objects and faces  Loss of peripheral vision (eg. Retinitis pigmentosa, glaucoma etc. )  Difficulty in mobility and navigation  Difficulty reading if there is constricted central visual field  Visual acuity may not be affected until very advanced disease  Cloudy media (eg. Corneal scar, vitreous hemorrhage etc.)  Blurred vision  Reduced contrast  Problems with glare
  • 8. GOALS OF LOW VISION MANAGEMENT  Increase functionality  Make the most of the remaining vision  Provide link to community resources and support services  Education
  • 9. STRATEGIES  Be oriented towards activities of daily living  Use appropriate technology  Be cost effective  Utilize appropriate educational and vocational adaption  Focus on target groups
  • 10. GLOBAL PREVALENCE OF LOW VISION  True magnitude not known because :  No uniform definition of low vision  Incomplete surveys  Low vision definition does not include standards of near vision, which is the main area dealt with low vision patients.  Current Data *  No. of visually impaired: 180 million  No. of blind: 45 million  Those with residual vision: 171 million  Of these 171 million:  Those with vision from PL to 3/60 : 36 million  No. with vision from 3/60to 6/18: 135 million  No. who can benefit from treatment: 103 million  True low vision patients: 68 million *Ramachandra Pararaiasegaram. Low vision care: the need to maximise visual potential. Community Eye Health. 2004; 17: 1-2
  • 11.
  • 12. WHAT ARE LOW VISION AIDS AND HOW DO THEY WORK ??  Devices which help the people to use their sight to better advantage  Can be optical devices like magnifiers or telescopes, or non optical devices like stands, lamps and large prints.  Alter the environment perception through  BBB – bigger brighter and blacker  CCC – closer color and contrast
  • 13. DISEASES WHERE LOW VISION AIDS ARE HELPFUL  Retinitis pigmentosa  Glaucoma  Macular degeneration  Corneal scar  Albinism and aniridia  Retinal detachment  Diabetic retinopathy  Chorioretinitis  Optic atrophy
  • 14. TYPES OF MAGNIFICATION  Low vision aids make use of angular magnifications by increasing :  Relative size  Relative distance
  • 15. Angular : it is the apparent size of the object compared with true size of the object seen without the device.eg. Telescopic system Angular magnification M = ω’/ ω
  • 16. Relative size: by making the object appear bigger (no accommodation required) eg. CCTV
  • 17. Relative distance: by bringing the object closer (requires good accommodation) eg. magnifiers
  • 19. HISTORY  Ocular history:  To know cause of low vision  To know the progression of disease  Systemic diseases that may pose difficulty in using certain devices eg. arthritis, tremors  Task analysis
  • 20. VISUAL ACUITY  Distance visual acuity: Lighthouse distance visual acuity test chart is preferred over the standard snellen’s chart as it has :  Equal line difficulty  geometric progression of optotype size from line to line  5 letters on each line  More lines at lower level of visual acuity  Test distance of 2 meters can be used to cover visual acuity upto 20/400
  • 21.
  • 22. Near visual acuity:  Text samples are better than single letter acuity charts  Metric notations are used  1M symbol subtends an angle of 5 minutes of arc at 1 meter and is roughly equal to the size of the newsprint  Visual acuity is recorded as distance of reading material (in meters) over the letter size (in M units)  Snellens equivalent can be calculated from the metric notations
  • 23.
  • 24. OTHERS  Contrast sensitivity  Visual field analysis:  Peripheral field: using Humphery or octopus perimetry  Central field: using Amsler grid  Glare :  History  Measuring visual acuity both with and without illumination in the chart  Colour vision  Look for dominant eye:  by testing contrast sensitivity monocularly and binocularly
  • 25. LOW VISION AIDS OPTICAL DISTANCE  Hand held telescopes  Mounted telescopes NEAR  Spectacles • Prismatic ½ eyes • Bifocals  Magnifiers • Hand held vs. stand • Illuminated vs. non-illuminated  Electronic Devices
  • 26. NON-OPTICAL  Glare reduction devices  Contrast enhancement devices  Computer software  Accessory devices  Talking watches, clocks, etc  Writing guides  Tactile markers
  • 27. LOW VISION OPTICAL DEVICES FOR NEAR
  • 28. MAGNIFYING SPECTACLES  High plus reading glasses to magnify the images  Given as an add to the best distance refraction  Reading distance is calculated by 100 divided by add  Magnification is 1/4th the power of the lens.  Used for near work  Amount of add needed depends on the accommodation and the reading distance
  • 29. Reading add can be predicted using the Kestenbaum rule i.e the amount of add needed to read 1M print is the inverse of the visual acuity fraction  However usually greater add is required than predicted as the patient also has reduced contrast sensitivity  If the patient is monocular, the poorer eye may be occluded if it improves the functioning  When binocular corrections are needed :  Base in prisms are added to compensate for convergence angle.  Optical center may be decentred  Aspheric lenses may be used to reduce lenticular distortion
  • 30. Advantages :  Hands are free  Field of view larger when compared to telescope  Greater reading speed  Can be given in both monocular and binocular forms  More portable  Cosmetically acceptable  Disadvantages:  Higher the power, closer the reading distance  Close reading distance causes fatigue and unacceptable posture  Patients with eccentric fixation are unable to fix through these glasses
  • 31. MAGNIFIERS  Useful for near work  Designed to be held close to the reading material to enlarge the image  The eye lens distance should be minimum to achieve larger magnification  Two types:  Hand magnifier  Stand magnifiers.
  • 32. HAND MAGNIFIERS  Available from + 4.0 to + 68.0 D.  Available in three designs:  Aspheric – reduces thickness and peripheral distortion  Aplantic – flat and wide distortion free field and good clarity  Biaspheric – eliminating aberrations from both surfaces  Most patients accept upto 6x magnification
  • 33. Advantages  The eye to lens distance can be varied  Patient can maintain normal reading distance  Work well with patients with eccentric viewing  Some have light source which further enhances vision  Easily available, over the counter  Disadvantages:  It occupies both hands  Patients with tremors, arthritis etc have difficulty holding the magnifier  Maintaining focus is a problem especially for elderly  Field of vision is limited
  • 34. STAND MAGNIFIERS  The magnifiers are stand mounted  The patient needs to place the stand magnifier on the reading material and move across the page to read  Has a fixed focus  Advantages :  They are a choice for patients with tremors, arthritis and constricted visual fields.  Disadvantage:  Field of vision is reduced  Too close reading posture is uncomfortable for the patient  Blocks good lighting unless self illuminated
  • 35. CLOSED CIRCUIT TELEVISION SYSTEM  Closed circuit television system (CCTV) consists of a monitor, a camera and a platform to place the reading text  It has control for brightness, contrast and change of polarity  Magnification varies from 3X to 60X
  • 36. LOW VISION OPTICAL DEVICES FOR DISTANCE
  • 37. TELESCOPES  Work on the principle of angular magnification  Telescopes with magnification power from 2x to 10x are prescribed  They can be prescribed for near, intermediate and distant tasks  Field of view decreases with magnification  Types:  Hand held monocular  Clip on design  Bioptic design: mounted on a pair of eyeglasses
  • 38. Principal  Telescopes consist of two lenses (in practice two optical systems) mounted such that the focal point of the objective coincides with the focal point of the ocular.  Objective lens is a converging lens Galilean telescope Keplerian telescope The eye piece is a negative lens and Both eye piece and objective are the objective is a positive lens positive lens Resultant image is virtual and erect Resultant image is real and inverted. Prisms are incorporated to erect the image Loss of light reduces brightness of Loss of light is more in this system the image Field quality is poor Field quality is relatively good
  • 39. Magnification of a telescope is given by the formula M = fo/fe  Telescopes can be used to focus near objects by  changing the distance between objective and ocular lens  Increasing the power of the objective lens
  • 40. GALILEAN TELESCOPE Objective Eye piece a β fo fe
  • 41. KEPLERIAN TELESCOPE Objective Eyepiece fo fe α β
  • 43. Advantages:  Only possible device to enhance distant vision  Disadvantage:  Restriction of the field of view  Appearance and apprehension  Expensive and costly  Depth perception is distorted
  • 45. ILLUMINATION  Positioning  Light source should be to the side of better eye  Moving light closer will yield higher illumination  Higher levels of illumination is needed in patients with  Lost cone functions (macular degeneration)  Glaucoma  Diabetic retinopathy  Retinitis pigmentosa, Chorioretinitis  Reduced illumination  Albinism  Aniridia
  • 46. READING STAND  Easy comfortable posture to the patient
  • 47. WRITING GUIDE  Black cards with rectangular cut outs horizontally along the card  The patient can feel the empty cut out spaces and write
  • 49. TYPOSCOPE / READING GUIDE  Masking device with a line cut out from an opaque, non reflecting black plastic or thick paper.  Reduces glare and controls contrast.
  • 50. NOTEX  It is a rectangular piece of cardboard with steps on top right corner which helps in identifying the currency of the note  1st cut indicates Rs. 500, 2nd cut indicates Rs.100, 3rd cut indicates Rs 50 and so on.
  • 51. RELATIVE SIZE DEVICES  Larger object subtends a larger visual angle at the eye and is thus easier to resolve  Large print material  Large type playing cards, computer keyboards  Enlarged clocks, telephones, calendars
  • 52. COMPUTER SOFTWARE  Jaws screen reading software  Connect out loud internet and email software  Magic 8.0 screen magnification software and speech
  • 53. GLARE REDUCING DEVICES  Glare is described as unwanted light  It is disabling in patients with cataracts, corneal opacities, albinism, retinitis pigmentosa  Devices to prevent glare:  Sunglasses  Caps  Umbrella  Polaroid glasses  NoIR filters  Corning photochromic filters (CPF glasses)
  • 54. CPF GLASEES o Attenuate 100% of UVB wavelengths. o Block 99% of UVA wavelengths. o The blue light portion of the visible spectrum is most likely to scatter in the eye, causing discomfort and hazy illusion. o Attenuate 98% of high-energy blue light, with exception of CPF 450, which is 96% of high-energy blue light. o The number of the CPF glasses correspond to wavelength in nanometers above which light is transmitted
  • 55. CPF® 550 (red) Lens colour varies from retinitis pigmentosa orange-red when lightened albinism to brown when darkened. CPF® 527 (orange) Orange-amber lens darkens retinitis pigmentosa to brown in sunlight, giving diabetic retinopathy individuals better visual function and reduced glare CPF® 450 (yellow) enhances contrast and helps optic atrophy control glare indoors albinism pseudophakia CPF® 511 (yellow Medium-range filter macular degeneration orange) provides moderate blue light glaucoma filtering aphakia pseudophakia optic atrophy developing cataracts
  • 56. NOIR FILTERS  Absorbs the short wavelengths of the visible spectrum that can scatter within the ocular media,  Also absorbs ultraviolet light (to 4000 nm) and infrared light  Manages overall visible light transmission (VLT) to allow the proper amount of light energy to reach the eyes.
  • 57. Includes a full range of lenses (spanning 90% to 1% VLT)  2% dark amber: 100% UV, infrared and blue light protection, helpful on very bright days  13% standard grey: good for postoperative cataract, glaucoma, diabetics and those who had corneal transplants  20% medium plum: good in low light situations and can be worn indoors  58% light grey: reduce indoor glare especially under fluorescent light  65% yellow: retinitis pigmentosa and macular dgeneration
  • 58. COLOR AND CONTRAST ENHANCEMENT  Maximize contrast by using a light color against black or dark color  Choose colors in the room or working area which have high contrast
  • 59. PINHOLE GLASSES  Multiple holes of approximately 1mm size are made in the glasses  The distance between the holes should be atleast 3-3.5 mm or approximately the size of the pupil  Used in patients with corneal opacities or conditions with irregular reflexes  Not used in patients with central field defects as it reduces illumination and visual acuity
  • 60. MOBILITY ASSISTING DEVICES  Patients with low vision suffer a major problem of mobility  Long canes  Strong portable lights
  • 61. FIELD EXPANDING DEVICES  As the magnification increases, the field of view decreases  Three methods of increasing the field:  Compress the existing image to include more of available area  Provide prisms that relocates the image from a non seeing to a seeing area  Use a mirror to reflect an image from a non seeing area  Reverse telescopes: they are usually not accepted due to minification  Fresnel lenses with power of 10-15D with base in the direction of field loss
  • 63. BIONIC EYE  Designed for patients who are blind due to diseases like retinitis pigmentosa or AMD  Can also be tried for those with severe vision loss  Relies on patient having a healthy optic nerve and a developed visual cortex  Cannot be used for people who were born blind  The prosthesis consists of :  A digital camera built into a pair of glasses  A video processing microchip built into a hand held unit  A radio transmitter on the glasses  A receiver implanted above the ear  A retinal implant with electrodes on a chip behind the retina
  • 64. Camera captures an image Send image to microchip Convert image to electrical impulse of light and dark pixels Send image to radiotansmitter Transmits pulses wirelessly to the receiver Sends impulses to the retinal implant by a hair thin implanted wire The stimultaed electrodes generate electrical signals that travel to the visual cortex
  • 65. Requires training by the subject to actually see an object  Subjects have to learn to interpret the array of white and dark dots as object  It is still in clinical trial stage
  • 66. Help when there is no cure
  • 68. Thank you Thank you Thank you
  • 69.
  • 70.
  • 71.
  • 72. Various forms are available 1. Powers usually available are +4.0, +5.0, +6.0, +10.0 , +12.0, +16.0, 20.0 and +24.0 2. Binocular corrections are needed –Base in prisms are added to compensate for convergence angle.  Optical quality of the lens should be an aspheric design to eliminate peripheral aberration and provide reasonable field.  The reading glass should be prescribed as an addition over the distance correction.
  • 75.
  • 76. OPTICS OF LOW VISION AIDS  Principle : Magnification = D/4 on the assumption that the patient can sustain just enough accommodation to hold the matter at 25 cm.  Modified formula : M = D + A-h AD/2.5 where A is the amplitude of accomodation h is the eye lens distance in meters.  To increase magnification:  Eyes should be kept close to the lens (reduce h)  Object should be as close to the patient’s eye as his accomodation allows
  • 77. Left: simulated with cataracts. Middle: CPF 511 lenses. Right: normal eyes.
  • 78. IMPACT OF OCULAR DISEASE ON THE PATIENT  Visual disorder Anatomical changes in the visual organ caused by the disease of the eye  Visual impairment Functional loss that results from the visual disorder  Visual disability Refers to vision related changes in the skill and abilities of the patient  Visual handicap Psychosocial and economic consequences of visual loss
  • 79. Legal Blindness  Best corrected distance visual acuity not exceeding 6/60 in the better eye  Visual field of 20 degrees or less at widest point in the better eye  Low Vision  Best corrected visual acuity between 6/60 to 6/18  Significant field loss  Impaired function  All these definitions however do not consider  Near vision  Scotoma, hemianopia  Visual performance like contrast
  • 80. EYE DISORDERS AND LOW VISION
  • 81. RETINOPATHY OF PREMATURITY Retinopathy of prematurity requires bright light and near additions required for near work
  • 82. ANIRIDIA Tinted glasses and cap
  • 83. ALBINISM Typoscope Dark glasses
  • 84. CORNEAL DAMAGE Multiple pin hole glasses Hand magnifier
  • 85. DIABETIC RETINOPATHY Diabetic Retinopathy with near glasses, hand magnifiers and a reading lamp
  • 86. GALILEAN TELESCOPE Objective Eye piece a β F
  • 87. KEPLERIAN TELESCOPE Objective Eye piece α β F

Notas del editor

  1. Central field:CME, toxoplasmosis, myopic degeneration, drug reaction, grid laser for macular edema, photocoagulation for CNVMPeripheral field:glaucoma, RP, Retinal dystrophy, PDR, Optic neuropathy, panretinal laser Cloudy media:corneal disorder, cataract, vitreous hage,keratoconus, herpes scar
  2. PrevalanceCommunity Eye Health. 2004; 17(49): 1–2. RamachandraPararajasegaram
  3. scar
  4. Cause and progression
  5. Left column metric notation . Vision is distance divided by this.Next column gives the snellens equivalenceRight column log units
  6. Left column metric notationRight is snellens equivalent and the amount of add required to read 1M line
  7. Superior monocular performance suggests interference from a poorer functioning dominant eye and supports use of monocular aids
  8. Formula of magnifivcTIION
  9. Magnifying glasses, standmagn.
  10. Images 7.5 7.6
  11. Availability
  12. Not only is this absorption of energy the most effective way to reduce glare, it also has the effect of enhancing contrast by highlighting visual distinction.
  13. Bloom portable light
  14. Reverse telescope door bellWhen the individual directs his eyes into the prism area, low contrast image from the missing field will come into view
  15. ??? Understand…American academy
  16. remove
  17. For visual acuity the commonly used threshold of 20/40 (0.5, 6/12) is accepted. For visual fields a binocular field of at least 120° horizontal and 40° vertical is suggested. .Contrast sensitivity screening is listed as desirable. India 6/18.