Electronic Magnification CCTV

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Electronic Magnification (CCTV)
Mouse Unit EVS Max
Stand alone unit Telesensory
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Flipper port EVS
Videoeye Swing Arm
Max port Head Worn
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Electronic Magnification

• Advantages
• Can significantly increase size
• Controls for contrast and glare
• Portable depending on model
• Versatile
• Permits binocular use of eyes
• Preserves field of view

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Electronic Magnification

• Disadvantages
• Expensive
• 350 and up
• Cheaper models are not portable
• Can be difficult to wear and to position
• Higher cognitive demand
• Sometimes difficult to tolerate motion
• Perceived as high tech by older users

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Patients should always wear their eyeglasses when
using any magnifier

• Eyeglasses correct for refractive errors
• Hand held magnifier should be viewed through
  DISTANCE CORRECTION
  
• Stand magnifier should be viewed through READING
  ADD

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Telescopes

• Used to view objects at a distance
• Have different focusing ranges
• Afocal
• Focuses beyond 20 feet
• Reading cap
• Permits focusing distance of 16-18 inches

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Telescope Design
Objective lens
Ocular lens
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Exit pupil is the optical window the patient
views through
Exit pupil
Higher the magnification, the smaller the exit
pupil
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Telescopes Come in Two Basic Styles

• Galilean
• Used for most low vision
• Smaller and lighter weight
• Keplerian
• Astronomical telescope
• Has a larger exit pupil
• But weighs more

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Strength of Telescopes

• Label indicates power and field of view
• Example
• 6 x 30 telescope
• 6x power and a 30mm objective lens

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Challenges Using Telescopes

• Motion Parallax
• Movement is exaggerated through the telescope
• Creates a speed smear (described as bouncing)
  when used in dynamic situation
  
• Difficult to adjust to, reduces accuracy

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Challenges cont.

• Objects appear closer than they really are
• Generally the field of view is very small unless
  the magnifier is really bulky
  
• Lose light- images appear darker

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For maximum image brightness, the exit pupil
should match the patients pupil

• To determine the size of the exit pupil
• Divide the diameter of the objective lens by the
  power of the magnifier
  
• Example
• 6 x 30 magnifier
• 30 5 mm
• 6

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• Measure the width of the patients pupil using a
  metric ruler and compare
  
• If the exit pupil is smaller than the patients
  pupil, the image will be dark
  
• To correct-try a telescope with a larger exit
  pupil

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Clip-on Monocular

• For short term or periodic telescopic needs

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Bioptic (for continuous use)

• Used in combination with carrier lens
• Carrier is used for most activities-bioptic for
  detail
  
• Dip head to view through biotic
• Limited field, motion parallax

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Full Field Binocular

• Covers entire lens in frame
• often used to view sporting events /TV
• sportscopes
• Doesnt allow viewer to look around
• Can only use when stationary
• Heavy-can be hard on nose bridge and ears

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Clip on monocular
Head worn binocular
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Automatic Focusing Telescopes
Monocular
Binocular
from Ocutech
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Some persons can be fitted with a contact lens
system

• High minus power serves as the ocular lens
• Plus spectacle worn as the objective lens
• Provides a 50 degree visual field with 2x
  magnification

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Miscellaneous stuff.

• Monocular telescope powers
• 2.5x, 2.8x, 3x, 4x, 6x, 8x, 10x
• Spectacle powers
• 2x, 2.2x, 3x, 4x, 6x, 8x
• For monoculars, person should always wear glasses
  unless instructed not to
  
• Correct for astigmatism

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Telemicroscope

• Combination microscope and telescope
• Usually spectacle mounted
• Generally a microscope cap is placed on a
  telescope lens
  
• Gives advantage of microscope magnification at a
  longer focal distance

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Telemicroscope