TO SEE WHAT THE FALCON SEES!

By David Lineaweaver, ABOC-AC

Release Date: April 4, 2022

Expiration Date: April 4, 2023

Learning Objectives:

Upon completion of this program, the participant should be able to:

Explain how a bioptic telescope functions as a low vision aide.
Describe the difference in Galilean versus Keplerian Telescope bioptics.
Recognize the benefits of autofocusing bioptics to produce more functional vision for low vision patients.

Credit Statement:

ABO 1 hour, Technical Level III STWJHI017-3

Have you ever wondered what it would be like to have the eyesight of a falcon? The peregrine falcon’s vision is so sharp, it spots small prey from more than a mile away! Birds of prey have a flicker fusion frequency (FFF) of more than 100 hertz, compared to humans who have a FFF of 60 hertz. This allows them to maintain sharp vision in a 180 mile per hour hunting dive! The peregrine falcon has two foveae per eye (one for distance and one for near) with about 33 percent more cones than humans. The peregrine falcon also sees in the ultra-violet (UV) range, which is very helpful for hunting since rodents like voles and moles leave trails of urine that emit UV light.

The Ocutech Falcon Bioptic Telescope for low vision won’t give you the ability to spot a mouse a mile away or perfect vision in a 180 mile per hour dive! Sorry if that was on your wish list. But it will improve functional vision in a more natural way for many visually impaired patients (Fig. 1).

Who could benefit from a bioptic? Bioptics are most often used by those with low vision and the legally blind. The term “low vision” is generally accepted as 20/70 or worse best-corrected acuity in the better-seeing eye. Legal blindness is rigidly defined as best-corrected visual acuity of 20/200 in the better-seeing eye or a visual field of 20 degrees diameter or less in the eye with the most extensive visual field. With that being said, the value and benefit of a bioptic or any low vision device is not determined by acuity alone but by the functional benefits it offers—increased independence, improved ability to accomplish daily tasks and overall patient satisfaction.

Ocutech, the manufacturer of VES-Falcon, developed a four question survey to help determine if a bioptic may be helpful to you. If you answer “Yes” to all of them, you’ll likely be a good candidate for a bioptic:

1. Is your vision loss due to macular degeneration or a similar disorder that causes a loss of central vision?
2. Is vision in the better eye with your best eyeglass prescription (if used) 20/300 or better?
3. Can you read the headlines in the newspaper? 4. Can you watch TV or recognize people’s faces from further than 2 feet away?

What is a bioptic telescope? A bioptic is a telescope typically mounted in the superior (upper) portion of single vision distance or multifocal eyewear (the eyeglass prescription is called the “carrier lens”). This position allows the wearer to use their prescription glasses for everyday tasks, looking straight ahead for “normal” distance viewing, and looking down and maybe tilting the head back slightly to view near objects or print through multifocal. When a magnified distance view is needed (verifying street names, words on a sign, etc.), the wearer can tip their head down to align their eye to look through the bioptic’s eyepiece for brief “spot checking” distant objects or people. This is like holding binoculars up to the distance portion of prescription eyewear to get a magnified view, but a bioptic allows it to be hands free.

Basic telescope design: Since a bioptic employs a telescope, a brief discussion of basic telescope optical design is in order. The bioptic telescope can be of Keplerian or Galilean design. The Galilean telescope has a plus objective lens (lens closest to object being viewed) and a minus eyepiece (lens closest to the viewer). The objective lens and eyepiece of a Galilean telescope are precisely spaced apart to cause the (real) focal point of the objective lens and the (virtual) focal point of the eyepiece to coincide posterior to the eyepiece, with the image erect.

The Keplerian telescope has a plus objective lens and a plus eyepiece. A Keplerian telescope’s objective lens and eyepiece are precisely spaced apart to cause the focal points to coincide at a point inside the telescope tube, posterior to the objective lens and anterior to the eyepiece. This will produce an inverted image, so an image erecting system incorporating prisms is required.

“X” magnification of a telescope is determined by dividing the dioptric power of the eyepiece by the dioptric power of the objective lens. This number will always be positive, so the minus sign of the Galilean eyepiece can be ignored. For example, a Galilean telescope with a +20 D objective lens and a -40.00 D eyepiece will render 2x magnification, as will a Keplerian telescope with +40 D objective and +20 D eyepiece.

The exit pupil of a telescope is its functional “viewing window” and is defined by the formula: Exit pupil = Clear Aperture of Objective lens diameter (in mm)/magnification of the telescope

Clear aperture refers to the functional diameter of the objective lens that is not covered or obstructed by lens mounts or telescope housing. Theoretically, the larger the exit pupil, the larger the viewing window. However, there is little practical need for an exit pupil larger than 5 mm, due to the 2 mm average undilated pupil diameter.

The closer the exit pupil of the telescope to the viewer’s eye, the wider the effective field of view. Therefore, a Keplerian telescope will always offer a wider field of view than a Galilean telescope of the same power. This is because the exit pupil is formed outside the eyepiece of a Keplerian telescope, closer to the viewer’s eye. The exit pupil of the Galilean telescope is inside the telescope and furthest from the viewer’s eye. This is like the difference between putting your eye up to a hole in your fence to look in your neighbor’s yard versus looking through that same hole 2 feet away. But don’t spy on your neighbor! This is the reason most bioptic telescopes are Keplerian for powers greater than 3x magnification.

Focus: People use the term “focus” to refer to making an object, viewed through a fixeddistance telescope clearer, through ocular lens adjustment. The term focus also describes a telescope’s ability to adjust to focus objects (more) clearly at different distances. Both uses of the term can be correct, so it’s important to know the context of the discussion.

Bioptic Design: Some bioptic devices fit close to the eye through a hole in the prescription lens. Many contemporary bioptic products are designed to fit in front of the front curve of the prescription or carrier lens. Some also use a telescope for each eye. However, this can be problematic for binocular alignment (especially when eccentric viewing is involved), so employing just one telescope (especially in powers 3x and higher) is the norm. When one telescope is used, the prescribing low vision optometrist will determine if the telescope will be most effective over the better-seeing eye or the dominant eye. In the best-case scenario, the betterseeing eye and the dominant eye will be the same, but that’s not always the case. Some Galilean bioptic and all Keplerian bioptic can also be manually focused for near viewing.

How do you get a bioptic telescope? Bioptics are prescribed by optometrists, typically specializing in the treatment of low vision. Bioptics come in various “single” magnification levels (usually 3x through 7x). Currently, there is no bioptic with variable progressive magnification or “zoom” capability. The prescribing low vision OD will determine what to prescribe based on eye dominance, distance visual acuity, visual field, and patient needs and goals. As a rule of thumb, the low vision OD often divides the denominator of the patient’s best-corrected distance vision in the eye to be fitted with the bioptic (“X” magnification formula mentioned above).

Keep in mind: The goal is functional magnification with as much field of view as possible. Trying to achieve the absolute best acuity with the bioptic can lead to a smaller field of view that is more difficult to use. For example, it is determined that a bioptic is to fit over the better-seeing eye (which also happens to be the dominant eye), which sees 20/100. The low vision OD further determines that 20/40 acuity through the bioptic would work well for the patient: 100/40=2.5, rounded up would be 3x. A 5x bioptic can bring acuity to 20/20, but it is unnecessary as 20/40 provides adequate vision. To put it in “distance” perspective, a patient who can read a road sign at 80 feet with his “every day” distance correction would be able to read that same sign at 20 feet when viewing through a 4x bioptic.

On the other hand, when more magnification is prescribed than is needed, there is an unnecessary reduction in the field of view (FOV) and an increase in “image jump.” Finding the right balance is the primary consideration of the prescribing doctor.

The optical components of the Falcon have an anti-reflective coating to reduce reflection and maximize visible light transmission (VLT) for better lens clarity. Prescription and carrier lenses, used in Falcon frames, are also available with an anti-reflective coating.

How does the VES-Falcon Autofocus Bioptic work? The Ocutech Falcon uses Time of Flight (ToF) technology to determine the distance to the object viewed. The Falcon sends out a beam of infra-red light (exact wavelength is proprietary) that reflects off the viewed object and returns to the Falcon sensor. The distance is determined by the amount of time it takes that particular wavelength of infrared (IR) light to return to the sensor. Once the distance is determined, a lookup table is indexed, and then a motor controller moves the focusing lens to the appropriate position to view the object clearly. Focus is based on the center 1-degree area of the object viewed. Lookup tables are based on focus curves for each telescope power. Distance (infinity) focus becomes farther away with each telescope magnification increase. Each Falcon is calibrated at the factory to eliminate any variation due to assembly. The Falcon employs a proprietary code to keep images clear and smooth during movement. The potential effects of temperature variations are also mitigated by proprietary means. The sensor can get “swamped” with very bright light. Special bandpass filters counter this by filtering out all wavelengths except the one that is used in ToF measurement. Time of Flight Technology is very sophisticated and largely proprietary. However, the reader can get an idea of its function when considering a laser range finder, commonly used for determining distance in golf and hunting.

What’s unique about the VES-Falcon Bioptic Telescope? (Fig. 2) The Falcon utilizes a Keplerian telescope (plus eyepiece and objective lenses) maximized for the field of view (FOV). The Falcon offers a magnified view for spot-checking distant objects in 3x, 4x and 5.5x options, like other bioptics. However, it is the only bioptic (used over one eye) that smoothly and automatically focuses from infinity to intermediate ranges to near, based on where the wearer is looking without the user manually focusing the device! As mentioned earlier, improved functionality is critical in low vision devices. A bioptic that auto focuses provides a smoother and more natural vision. Eliminating manual adjustment to focus at various distances is an enormous improvement over old bioptic technologies with tiresome and inconvenient manual focusing adjustments. For example, imagine the difference between auto focus bioptic versus a manual focus bioptic for a student who is frequently changing focal distance from a book to the chalkboard, to the teacher or a student next to them. Add to this that manual adjustment for a moving object is essentially impossible! The Falcon allows the eye to view varying distances (more) clearly, naturally and seamlessly, like the pre-presbyopic eye!

The Falcon requires single vision distance or flat-top bifocal lenses, as trifocal or progressive lenses do not allow sufficient room for each viewing distance when mounted in a Falcon-approved frame. Prescription or carrier lenses for the Falcon can be fabricated in CR-39, Polycarbonate Trivex or hi-index plastic materials.

All optical components of the Falcon utilize an anti-reflective coating to minimize internal and surface reflections for maximum visible light transmission and enhanced lens clarity. Prescription and carrier lenses, used in Falcon frames, are available with an anti-reflective coating as well.

Specifications of the Falcon:

The 3x model has a 15-degree FOV and focuses to 13” (.3m).
The 4x model has a 12.5-degree FOV and focuses to 13” (.3m).
The 5.5x model has a 9.5-degree FOV and focuses to 15” (.38m).
Focusable eyepiece adjusts to prescriptions of +/8D. Custom eyepiece corrections are available for high spherical and cylinder prescriptions; recommended for cylinder over 3D.
Weight 3.2 oz. (90g).
Rechargeable battery that lasts for 8 hours.
Snap-on filter cap available (provides tint to the monocular telescope).
Slip-behind sun filters available in red, grey, brown and blue-blocker yellow (provides tint to both prescription lenses).
Intended for those with 20/300 vision or better.

How would a low vision patient use bioptic in daily life? Let’s take 32 year old nurse and student Janet as a case study. She is a licensed practical nurse who works in an intensive care unit while working on a bachelor’s degree in nursing to become a registered nurse. Working as a nurse is fast paced and requires quick and accurate determination of vital signs and medication dosing (seeing decimal points is critical). Her college work involves computer work, seeing the chalkboard from the back of the classroom and hands-on practicum with patients. Janet has Stargardt’s Disease, impeding her central vision and glaucoma, constricting her visual fields (OD worse than OS). Her best-corrected distance acuity is 20/150 OU. Her distance prescription is OD -3.00+3.75X 180 and OS -2.50+4.25X 165. Janet being left eye dominant and left-handed meant that her left eye was chosen for the bioptic. Due to high astigmatism, a custom prescription was fabricated for the eyepiece and fit over the left eye.

As a strong visual learner, Janet rejected audio devices in the past, and she rejected CCTVs (closed-circuit televisions), as she views these larger devices as incompatible with her on-the-go lifestyle. She was trialed with 3x, 4x and 5.5x Falcon bioptic to determine the optimal balance between visual acuity and visual field. While the 3x and 4x worked well for general purposes, they did not provide the level of clarity needed for accurately determining vital signs and medication dosage and rates read-outs displayed on monitors. She also had difficulty seeing accurately drawing up medication in syringes. Despite a reduction in the functional visual field, these difficulties were alleviated with the 5.5x (rendering an acuity of 20/25 to 20/30). She quickly gained a renewed confidence in her ability to accurately and rapidly determine vital biomedical data and draw up medication using the 5.5x Falcon. The Falcon did not interfere with the use of her single vision distance glasses (did not need a multifocal) for common everyday tasks. She did have some trouble “getting lost” or keeping her place while viewing writing on the chalkboard for her college work. However, she developed a smooth systematic technique for effectively viewing and scanning the chalkboard over time with the help of a low vision therapist. Currently, her state does not allow driving with bioptics, but she is hopeful to do some limited driving in the future.

Low vision specialists may prescribe the Falcon Bioptic Telescope to aid low vision patients while driving. Note: The manufacturer of the Falcon Bioptic telescope (Ocutech) makes no claims nor accepts any responsibility if the product is used while driving.

For the visually impaired driver, the challenge is that there isn’t adequate time to react by the time they are close enough to a sign. The bioptic telescope allows them to respond quicker because they see the sign sooner (Fig. 3). Drivers use their regular eyeglass lenses most of the time while driving but look through the telescope short periods of time similar to the quick visual check of rear and side-view mirrors. Each state’s motor vehicle agency has its own rules and regulations regarding bioptic driving. Low vision specialists prescribing the Falcon should consult their states’ DMV regulations and requirements for obtaining a bioptic driver’s license. Decisions regarding driving with bioptics rest solely with the licensing agency, the prescriber and the user.

TAKING FLIGHT!

Ocutech Falcon is the only autofocusing bioptic telescope. Don’t be surprised if low vision patients have a very emotional response to experiencing clear, uninterrupted handsfree distance to near vision the first time they put on their glasses fit with the Falcon Bioptic Telescope. While the Falcon is primarily used by people with impaired vision, it can benefit “normally-sighted” people (even people with 20/20 vision) by enhancing clarity for spotchecking distant objects, in vocational settings or for hobbies. It will be interesting to see what new heights the Falcon will reach in the future!