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Prescribing Bioptic Telescopes Qualify, Demonstrate, Indoctrinate, Recruit Henry A. Greene, OD, FAAO Reading is a solitary activity Most responsive to low vision aids high contrast controllable environment Reading is the most easily replaced visual activity talking books radio, TV sighted support Distance Vision is a Social Activity Seeing faces Interpersonal relations Non-verbal body language Making eye contact Avoidance of isolation Quality of life “Before I got the telescope, my world extended to the end of my arms. The telescope made my arms 4 times longer” “Visual Radius” Derived from Proximal Magnification Moving closer makes the retinal image larger The furthest distance at which one can discern facial features Under normal illumination Visual Acuity Correlate 2 feet = 20/200 1 foot = 20/400 The Telescope “Face” Test A good response to high contrast targets is not prognostic The face is a convenient low contrast target Seeing a face well through a TS at 8-10 feet is prognostic of magnification response Poor response associated with edematous maculas “Visual Radius” and “Social Range” “Social Range”- 3 to 15 feet Expand the “Visual Radius” sufficiently into the “Social Range” Telescopes extend the visual radius by the power of the device With a 4x telescope: 2 feet becomes 8 feet 6 inches becomes 24 inches TS Prescribing Paradigm Summary Identify the furthest distance that a face can be seen- “Visual Radius” Confirm a favorable response to telescope magnification- “Face Test” Extend the “Visual Radius” into the “Social Range” Establish realistic goals and expectations Magnification is not natural. Constraints of Magnification Working Distance Shallow Dept of Field Narrow Field of View Constraints on the patient Unnatural working distances Disorientation Inconvenience Fatigue What are bioptics? Eyeglasses with a miniature built-in telescope Allow use of normal and magnified vision by simply tilting the head- like “upside down bifocals” Do not interfere with walking Help you see things further away: Spotting- like the use of rear and side view mirrors Continuous tasks- TV, computer Best for midrange and beyond Not ideal for reading Basic Optical Concepts Galilean vs. Keplerian Larger objective lens: Larger, multi-element eyepiece: Brighter image Shallower depth of field wider FOV Longer eye-relief: Narrower FOV Characteristics of Bioptics Galilean Keplerian Size Small, Very Small Big, Bigger Shape Std. Tube Micro Std. Tube HLP, BTL Focusing Fixed, Manual Manual, AF Powers 1.8 – 8x 3 – 8x Fields 4x Narrow 5 deg Less Narrow 12.5 deg Optics vs. electronics Optics Electronics Image Resolution High Low to moderate Brightness Inside variable Outside good Inside good Outside poor FOV- 4x 12.5 deg 40 at 1x; 10 at 4x Power range Fixed Zoom Ease of Operation variable variable Mobility with aid Easy Variable to none Weight variable Variable to ugh! How much power? Enough magnification to achieve the goal Acuity demand: Average High Sporting ~20/40 goal ~20/30 goal events? More than 6x is tough to keep stable on the head More than 7x- time for binoculars How much Field? What is a degree? How much FOV is enough? It’s never enough- minimum ~ 5 deg Use comparisons- TV; rear view mirror It gets more natural Maximize for close distances Let the patient compare using handhelds 4x12 Keplerian vs. 3x Galilean User issues regarding bioptics Low Vision Device Use Among Veterans Watson, et.al., OVS, 74:5, May 1997 200 veterans, 740 devices, 130 spectacle TS Issues: Wider FOV Autofocus More power Brighter image Less noticeable 83% 79% 78% 49% 16% When to AF and when to not… Acuity between 20/70 and 20/200 Room and mid-range activities Dexterity issues Not for >20’ Tremors, Paresis Application issues Hands-free activities Courtesy CNN Which eye? Or both? Prescribe for the dominant eye if at all possible Binocular systems Suppression difficulties significantly undermine acceptance Challenging to keep aligned- Very stiff frame, Beecher Wider FOV, Acuity and CST summation, no suppression issues, lessens impact of scotomas Binocular Working distance fixed Monocular is easier What position? Types of mountings: Permanent (glued) vs. adjustable Minimum 3mm above eyepiece to top of lens Align the bottom of eyepiece to top of pupil The higher the eyepiece= the higher the TS angle the greater the head translation Lower and straighter position for midrange applications Use a head strap Use wide nosepads Carrier lens issues Use their habitual distance Rx Minimum 10mm between bottom of eyepiece and top of seg Single vision or multifocal Avoid progressives and trifocals Seg high but not too high Low but not too low Avoid polycarbonate lenses- hi index OK Tough to drill Qualify the Patient Not all patients are bioptic candidates Establish a prognosis for likely success The Clinical Evaluation Address Finances and Appearance This is not cheap-- “Is it worth it to you?” “It looks a little unusual-- will you wear it?” You’ll have to learn to use it Are you prepared to make the effort? Qualify the patient: Establish a telescope prognosis Hard Signs 1. VA between 20/70 and 20/300 (faces >2 feet) VA gain with 4x TS? Fluency 2. Response to low contrast target Faces at 10 feet through 4x12 TS 3. Better eye is dominant Soft Signs 1. Appropriate goals: mid-range and beyond 2. Motivation: appearance, enthusiasm 3. Dexterity Test and demonstrate with Handheld Telescopes first Handheld 4x12- prefocus! Determine the dominant eye Which eye do they take the TS to? Evaluate response to faces at ~10 ft Poor response undermines prognosis Needs brighter image Show: Narrow FOV- challenges in finding the target Shallow DOF- challenges in keeping clear Need to refocus- challenges in doing the activity Demonstrate Bioptics next Get them out of the exam chair Present the concept of the “Magnification Factor” Realistic experiences= realistic expectations With a 4x TS- What you see at 2’, you’ll see it at 8’ The “Eye Chart” is NOT the “real world” “Grocery Store,” CRT, Pictures on walls Sit in the “living room” (Waiting room) Outside- signs, flowers, faces Use your assistant Have family accompany Recruiting the Patient “We can teach them to ride the bike, but they have to do the pedaling.” The patient’s job: To want to improve their vision To make the effort to learn to use it To be frustrated To invest time and $ Training Techniques Sighting through eyepiece Translation Aiming and Switching Tracking Switching between carrier and eyepiece Localization Give them a tour of the device Moving targets Near localization and hand-eye coordination Finding the target