Eschenbach Low Vision Training Program...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

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)

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

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

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

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

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

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

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

Low Vision Training Module #6

Minus eyepiece

Plus objective

Galilean Telescopes

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)

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

Low Vision Training Module #6

Plus objective

Plus eyepiece

Keplerian Telescopes

Low Vision Training Module #6

Keplerian Telescopes

Plus objective

Plus eyepiece

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

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

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

Hand-held telescopes‘monoculars’

Mounted telescopes

Telescopic Vision Aids:Design types

Low Vision Training Module #6

Types of Telescopes

Focusable telescopes (sometimes semi-

focusable)

Fixed-focus or afocal telescopes

Telescopic Vision Aids:Design types

Low Vision Training Module #6

Types of Telescopes

Clip-on Telescopes

Telescopic Vision Aids:Design types

Low Vision Training Module #6

Types of Telescopes

Low Vision Training Module #6

Custommounted

telescopes

Types of Telescopes

Binoculars & Opera Glasses

Telescopic Vision Aids:Design types

Low Vision Training Module #6

Types of Telescopes

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

Low Vision Training Module #6

1. Locate the object to be viewed through the telescope

Low Vision Training Module #6

2. Point telescope at the object and focus the telescope on the object

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

Near applicationsUsing Monoculars in Reverse as a

Field Expander

Telescopic Vision Aids:Training Tips

Low Vision Training Module #6

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?

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 √ √ √

Low Vision Training Module #6

Reading street signs

Hand – held telescopes for spotting tasks:

Reading bus numbers

Shopping

Reading fast food menu boards

Telescopic Vision Aids:Tasks

Low Vision Training Module #6

Hand – held telescopes for spotting tasks:

Low Vision Training Module #6

Watching television

Mounted telescopes for extended viewing tasks:

At the theater

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

Low Vision Training Module #6

Minus eyepiece

Plus objective

Reading Caps for Near applications

Low Vision Training Module #6

(-) (+)

At eyepiece =

TS power² X 1m / f

At objective =

1m / f

Accommodative demand through telescope:

Low Vision Training Module #6

(-) +

Equivalent Power (EP) for near =

TS power X Cap power (d)

+

Reading Cap

Use of reading caps for near

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

Low Vision Training Module #6

• What they are

• How they work

• How to use them

• What types are available

• What are they made for

Low Vision Training Module #6

Questions?

Low Vision Training Module #6

Thank You!