Eschenbach Low Vision Training Program Module 6: Telescopic Vision Aids, Part 1 Edited by: Thomas Porter, OD Asst. Professor & Director Low Vision Service St. Louis University, Dept. of Ophthalmology 2016 2015 Eschenbach Optik Optik of America, of Inc. Inc. (Ver. (Ver. 1) 1)
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
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
Agenda What they are How they work How to use them What types are available What are they made for
What is a telescope? A telescope is a multiple element optical device that magnifies the image of a distant object
How do Telescopes work? Power of TS Barrel E 6 X 16 E Eyepiece Diameter of Objective Lens (mm) Objective Lens / Entrance Pupil
There are two different design types in telescopic vision aids: Galilean telescopes Keplerian telescopes These telescopes can be used in either of two ways: As a hand-held telescope As a mounted telescope
Telescopic Vision Aids: Design types Galilean Telescopes Named after Galileo Galilei -Italian mathematician, physicist, astronomer and astrologer -invented his telescope design in 1609
Galilean Telescopes Minus eyepiece Plus objective
Galilean Telescopes: Simple 2-lens design Bright Shorter barrel Lighter weight Easiest to fit Typically afocal Limited power range (< 5X)
Telescopic Vision Aids: Design types Keplerian Telescopes Named after Johannes Kepler -German mathematician, astronomer and astrologer -invented his telescope design in 1611
Keplerian Telescopes Plus eyepiece Plus objective
Keplerian Telescopes Plus eyepiece Plus objective
Keplerian Telescopes: Multi-element design Not as bright Longer barrel Heavier Challenging to fit Typically focusable Broad power range up to 10X
Telescopic Vision Aids: Design types Galilean E Exit Pupil Why are Galilean telescopes easier to fit? They possess a virtual, internal exit pupil Plane of Exit Pupil
Telescopic Vision Aids: Design types Galilean Keplerian E Exit Pupil Why are Keplerian telescopes challenging to fit? They possess a real, external exit pupil Plane of Exit Pupil
Telescopic Vision Aids: Design types Low Vision Training Module #6 Types of Telescopes Hand-held telescopes monoculars Mounted telescopes
Telescopic Vision Aids: Design types Low Vision Training Module #6 Types of Telescopes Focusable telescopes (sometimes semifocusable) Fixed-focus or afocal telescopes
Low Vision Training Module #6 Types of Telescopes Clip-on Telescopes Telescopic Vision Aids: Design types
Low Vision Training Module #6 Types of Telescopes Custom mounted telescopes
Telescopic Vision Aids: Design types Low Vision Training Module #6 Types of Telescopes Binoculars & Opera Glasses
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
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 Low Vision Training Module #6
Telescopic Vision Aids: Training Tips 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 Using Near applications Monoculars in Reverse as a Field Expander
Tips for use of handheld 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?
Telescopic vision aids can be used to accomplish any task at any distance! Near Spotting Near Extended Spotting Intermediate Intermediate Extended Distance Spotting Distance Extended Hand-Held Stand Spectacles Telescopes Video
Hand held telescopes for spotting tasks: Reading street signs Reading bus numbers
Telescopic Vision Aids: Tasks Hand held telescopes for spotting tasks: Shopping Reading fast food menu boards
Mounted telescopes for extended viewing tasks: Watching television At the theater
Advantages: Disadvantages: Ability to magnify distant objects Focusability Conspicuous Loss of peripheral field Long working distances when used for near objects
Reading Caps for Near applications Minus eyepiece Plus objective
Accommodative demand through telescope: (-) (+) At eyepiece = TS power² X 1m / f At objective = 1m / f
Use of reading caps for near Reading Cap (-) + + Equivalent Power (EP) for near = TS power X Cap power (d)
EP = TS power X Example: Cap power (diopters) 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? Solution: EP = 2.2 X 8 D = 17.6 D f = 125mm or 5
What they are How they work How to use them What types are available What are they made for
Questions?
Thank You!