eschenbach low vision training program...low vision training module #6 the seven steps to dispensing...
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Eschenbach Low Vision Training Program
Edited by:Thomas Porter, ODAsst. Professor & DirectorLow Vision ServiceSt. Louis University, Dept. of Ophthalmology
© 2015 Eschenbach Optik of America, Inc. (Ver. 1)
Module 6: Telescopic Vision Aids, Part 1
© 2016 Eschenbach Optik of America, Inc. (Ver. 1)
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Low Vision Training Module #6
The Seven Steps to Dispensing Low Vision Aids®
1. Make sure the patient is under the current care of an eye doctor and has a current refraction
2. Identify the patient’s visual goals
3. Determine the magnification required
4. Demonstrate the impact of illumination
5. Select the appropriate vision aids for the goals identified
6. Train the patient in the use and care of the chosen vision aid
7. Schedule a follow-up visit
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Low Vision Training Module #6
Telescopic Vision Aids…
…can be used for any task at any distance
…can be used for spotting or extended viewing
…work primarily based on the principle of angular magnification
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Low Vision Training Module #6
• What they are
• How they work
• How to use them
• What types are available
• What are they made for
Agenda
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Low Vision Training Module #6
What is a telescope?
A telescope is a multiple element optical device that magnifies the image of a distant object
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Low Vision Training Module #6
How do Telescopes work?Barrel
Objective Lens / Entrance Pupil
Eyepiece
6 X 16
Power of TS
Diameter of Objective Lens
(mm)
EE
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Low Vision Training Module #6
There are two different design types in telescopic vision aids:
• Galilean telescopes
• Keplerian telescopesThese telescopes can be used in either of two ways:
• As a hand-held telescope
• As a mounted telescope
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Galilean Telescopes
Telescopic Vision Aids:Design types
Named after Galileo Galilei-Italian mathematician, physicist,
astronomer and astrologer
-invented his telescope design in 1609
Low Vision Training Module #6
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Low Vision Training Module #6
Minus eyepiece
Plus objective
Galilean Telescopes
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Low Vision Training Module #6
Galilean Telescopes:• Simple 2-lens design
• Bright
• Shorter barrel
• Lighter weight
• Easiest to fit
• Typically afocal
• Limited power range (< 5X)
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Keplerian Telescopes
Telescopic Vision Aids:Design types
Named after Johannes Kepler
-German mathematician, astronomer and astrologer
-invented his telescope design in 1611
Low Vision Training Module #6
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Low Vision Training Module #6
Plus objective
Plus eyepiece
Keplerian Telescopes
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Low Vision Training Module #6
Keplerian Telescopes
Plus objective
Plus eyepiece
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Low Vision Training Module #6
• Broad power range –up to 10X
Keplerian Telescopes:• Multi-element design
• Not as bright
• Longer barrel
• Heavier
• Challenging to fit
• Typically focusable
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E Exit Pupil
Plane of Exit Pupil
Why are Galilean telescopes easier to fit?
• They possess a virtual, internal exit pupil
Galilean
Telescopic Vision Aids:Design types
Low Vision Training Module #6
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E Exit Pupil
Plane of Exit Pupil
Why are Keplerian telescopes challenging to fit?
• They possess a real, external exit pupil
Galilean
Keplerian
Telescopic Vision Aids:Design types
Low Vision Training Module #6
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Hand-held telescopes‘monoculars’
Mounted telescopes
Telescopic Vision Aids:Design types
Low Vision Training Module #6
Types of Telescopes
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Focusable telescopes (sometimes semi-
focusable)
Fixed-focus or afocal telescopes
Telescopic Vision Aids:Design types
Low Vision Training Module #6
Types of Telescopes
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Clip-on Telescopes
Telescopic Vision Aids:Design types
Low Vision Training Module #6
Types of Telescopes
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Low Vision Training Module #6
Custommounted
telescopes
Types of Telescopes
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Binoculars & Opera Glasses
Telescopic Vision Aids:Design types
Low Vision Training Module #6
Types of Telescopes
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Low Vision Training Module #6
Rules for using telescopic vision aids properly:1. While stationary, locate a stationary
object to be viewed through the telescope
2. Focus the telescope on the object to be viewed
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Low Vision Training Module #6
1. Locate the object to be viewed through the telescope
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Low Vision Training Module #6
2. Point telescope at the object and focus the telescope on the object
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Once viewing a stationary object while stationary has been accomplished, the same 2 steps can be followed with:
1) moving object & stationary patient
2) moving object & moving patient
Telescopic Vision Aids:Training Tips
Low Vision Training Module #6
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Near applicationsUsing Monoculars in Reverse as a
Field Expander
Telescopic Vision Aids:Training Tips
Low Vision Training Module #6
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Low Vision Training Module #6
Tips for use of hand-held monoculars:• Pre-focus for candidate prior to trial
• Stabilize monocular against body or use finger ring
Tips for fitting mounted telescopic systems:• Use transilluminator to check pupil centration through objective lens
• Pre-focus for candidate prior to trial
• Incorporate refractive needs in solution
• Exit pupil: Galilean or Keplerian?
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Low Vision Training Module #6
Telescopic vision aids can be used to accomplish any task at any distance!
NearSpotting
NearExtended
Inter-mediateSpotting
Inter-mediate
Extended
DistanceSpotting
DistanceExtended
Hand-Held √
Stand √Spectacles √
Telescopes √ √ √ √ √ √
Video √ √ √
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Low Vision Training Module #6
Reading street signs
Hand – held telescopes for spotting tasks:
Reading bus numbers
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Shopping
Reading fast food menu boards
Telescopic Vision Aids:Tasks
Low Vision Training Module #6
Hand – held telescopes for spotting tasks:
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Low Vision Training Module #6
Watching television
Mounted telescopes for extended viewing tasks:
At the theater
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Low Vision Training Module #6
Advantages:• Ability to magnify
distant objects
• Focusability
Disadvantages:• Conspicuous
• Long working distances when used for near objects
• Loss of peripheral field
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Low Vision Training Module #6
Minus eyepiece
Plus objective
Reading Caps for Near applications
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Low Vision Training Module #6
(-) (+)
At eyepiece =
TS power² X 1m / f
At objective =
1m / f
Accommodative demand through telescope:
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Low Vision Training Module #6
(-) +
Equivalent Power (EP) for near =
TS power X Cap power (d)
+
Reading Cap
Use of reading caps for near
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Low Vision Training Module #6
Example:
A user puts a +8 D reading cap on a 2.2x Galilean telescope. What is the equivalent power of this combination for near? What is the focal length of this system?
EP = TS power X Cap power (diopters)
EP = 2.2 X 8 DSolution:
= 17.6 D
= 125mm or 5”f
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Low Vision Training Module #6
• What they are
• How they work
• How to use them
• What types are available
• What are they made for
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Low Vision Training Module #6
Questions?
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Low Vision Training Module #6
Thank You!