MAXIMIZING THE OPPORTUNITIES FOR MAGNIFICATION
By David Lineaweaver, ABOC
Release Date: February 1, 2017
Expiration Date: November 28, 2021
- Identify the three max products, their capabilities and their intended use.
- Generally describe how these products achieve magnification.
- Identify customers that would benefit from each of these devices. For example, those with adds above 3.50, magnification for sports events/concerts or for very close tasks such as tying flies or working on small electronics.
This course is approved for one (1) hour of CE credit by the American Board of Opticianry (ABO). Technical Level III. Course STWJH649-3
David Lineaweaver, ABOC, CLVT, currently works as an ophthalmology health aid and technician at the Fort Harrison Mont., Veterans Administration Eye Clinic. Lineaweaver's approach to optics is practical, and that serves the low vision community especially well as a Certified Low Vision Therapist.
Magnification is a wonderful thing, and so is a comfortable working or viewing distance. Unfortunately, sometimes these two things are not maximized together in single-vision prescription, OTC reading glasses or multifocal ophthalmic lenses. Magnification and viewing/ working distance are inversely related in a single lens system. This is the category that all conventional eyeglass lenses fall into, whether single-vision or multifocal; as magnification increases, viewing/working distance decreases.
In addition, as we use lenses designed in flatter add forms, they magnify less at the same focal length. That magnification may have been the difference in an older adult for whether they could read the newspaper or the instructions on their medicine bottle.
However, there is a way around this “tradeoff”—telescopic lenses. You may balk at the idea of telescopic lenses for common everyday use, as the term may invoke images of heavy, complex devices that are costly, slide down the nose and are difficult to use. But let me present another side to telescopic glasses: introducing the max products from Eschenbach Optik—maxDetail, maxTV and maxEvent glasses.
These are lightweight, user-friendly glasses that provide hands-free magnification, with increased viewing distance, relative to their magnification (when compared to conventional eyeglass lenses). They also have an “open” feel, as they are not designed as “enclosed tubes” that the patient looks through. There are also clip-on devices available that attach to conventional prescription glasses, giving them “telescopic” capability.
This course reviews each of these devices, their intended use, capabilities and clinical applications. However, let’s first review some magnification and telescope fundamentals.
Magnification is an optical tool that can be used to improve vision. It is separate but connected to the focal length of lenses when it’s used to correct a refractive error or for presbyopia.
The general formula for “x” or “times” magnification for single lens systems is:
- +4.0 diopters = 1x
- There are other considerations when calculating magnification, but we’ll use this general formula as it works well for most applications.
- Focal length (cm) = 100/Diopter (for a single lens)
For example, to get 2x magnification for reading a book, you would need a +8.00 D lens (assuming there is no distance correction in addition). This lens would provide you an optimum viewing distance (focal length) of 12.5 cm (100/8=12.5 cm). That’s a pretty short working distance. Along with that short working distance, you are likely to need base-in prism, to compensate for the increased convergence demand, and you will no doubt experience a pronounced reduction in field of view.
Now that we’ve established what it would take to get 2x magnification in a single lens for reading, we can truly begin to appreciate what telescopic glasses have to offer.
All the max products are based on a single “x” power (as opposed to variable “x” power) two-lens Galilean telescope design. This means that the ocular lens (lens closest to the wearer) has minus power, and the objective lens (the lens furthest away from the wearer) has plus power. This telescoping device can be focused independently for each eye, similar to focusing a pair of binoculars. The spacing range between the ocular and objective lenses is crucial and is designed to: 1. Achieve the targeted focal length, 2. Provide for slight variations in viewing distances (through turning the diopter adjustment knob on the side of the glasses—that varies spacing distance between the ocular and objective lenses), and 3. Adjust for the wearer’s eyeglass Rx.
KNOW WHAT THE PRODUCT CAN AND CANNOT DO
Max glasses or clip-ons are designed for stationary viewing or working. They are not designed for walking, driving or participating in sports. They are not intended to function as safety glasses. Because of the magnifying ability of the lenses, they should be stored in the case, out of the sun because the high plus power can focus sunlight and potentially cause a fire.
Though not crucial to the presentation of these products, the formula for determining the x power of a telescope may be of interest to the reader. The power of the ocular lens (diopters) is divided by the power of the objective lens (diopters). That equals the x power of the telescope (Ocular (D)/Objective = x).
Since x or times power for telescopes is achieved differently than for single lens systems (eyeglass lenses), telescopes (and telescope glasses) are not bound to the magnification versus viewing distance dilemma. You literally can have the best of both worlds, i.e., increased magnification AND a comfortable viewing distance.
Since these devices are adjustable, and consumers can find the “power that they need,” they are not a substitute for routine eye exams. Additionally, low vision patients will benefit from a low vision evaluation. This typically involves seeing an optometrist that specializes in low vision and possibly a low vision therapist. An occupational therapist with vision rehabilitation training can also be helpful.
NEAR EQUIVALENT AND KESTENBAUM’S RULE
We’ll refer to near acuity in Snellen notation, with the assumption that it is the “near equivalent” of Snellen acuity; though near equivalent will be left off of the notation. There are other ways to denote near acuity, such as Jaeger or “M” scale, but I chose to use the Snellen notation, as it is the most familiar and relays the most meaning to the most people, i.e., patients as well as ECPs. Kestenbaum’s Rule: Kestenbaum’s Rule is used to predict the power needed for add power or magnifier power for reading. First, invert Snellen distance acuity. Then divide and the result is the predicted add power necessary (in addition to the distance correction) to read 1.0 M or 20/50 print, common book print size.
For example, a 62-year-old financial advisor expressed interest in a “versatile” pair of reading glasses. When probed about what he meant by versatile, he expressed a desire to have one pair of reading glasses that would: 1. Provide higher magnification than standard OTC readers, and 2. Allow for a comfortable viewing distance for all his office needs (viewing books, stock market page, computer screen and clock on the wall). Then he wanted to accomplish everything with one pair of glasses, to avoid the constant repositioning and reposturing that traditional multifocal lenses require for extended work in an active office setting.
The patient had the following prescription and corresponding acuities:
- OD: -1.00 sph 20/80
OS: -1.50 sph 20/80
Add: +3.75 20/40 ou
MaxDetail glasses were trialed, and he achieved 20/25 near acuity—much better than the short focal length of the +3.75 add, that resulted in 20/40 near acuity. With just brief instruction and a little practice, he was able to accomplish all of his office tasks comfortably and efficiently with maxDetail glasses. He actually reduced the font size on his computer back to the standard setting.
To increase the likelihood of success and avoid unnecessary frustration for the patient and the dispenser, it is important to know the general functional limits of the maxDetail glasses; 20/160 best corrected distance acuity. This limit is derived from Kestenbaum’s rule as follows: 160/20=+8.00D. Remember, +8.00 D equals 2x (for near), the power of the maxDetail glasses.
While it is possible to have success with the maxDetail, in patients with less than 20/160 distance acuities, the likelihood declines when you move away from the estimated 20/50 near acuity associated with a 20/160 distance vision.
These telescopic glasses are designed to enhance reading and near work vision by increasing magnification 2x beyond that of a typical conventional near correction, while maintaining a comfortable viewing or working distance of about 40 cm/16 inches. It also works well for viewing a computer screen.
MaxDetail glasses have two individually adjustable telescopes (one for the right eye and one for the left eye) built in to the front of the glasses. The diopter adjustment knob on each side of the glasses adjusts for the wearer’s prescription. There is no correction for astigmatism. It can also be used to slightly vary the focal length of the device outside of the targeted viewing distance of 40 cm/16 inches. This is similar to how one would adjust “focus” for various distances with binoculars. The diopter adjustment function is not to be confused with a variable magnification adjustment, i.e., you can’t turn the knob and get 3x or 4x magnification.
Specifications: The device is a Galilean style telescope of 2x power (only) made from clear PXM plastic, lens size is 32 mm; using a frosted frame and lens housing allows for an “open” feel for viewing without the unwanted reflections associated with clear polished plastic.
The standard working distance is 40 cm/16 inches. This is the same focal length as a +2.50 add that provides less than 1x magnification. There is a pre-set pupillary distance that generally works for PDs ranging from 60 to 68 mm and diopter adjustability that compensates for prescriptions of -3.00D to +3.00 D. The visual field/field of view is 20 degrees at a weight of 1.7 ounces or 49 grams.
Many people can benefit from using maxDetail from normally sighted patients with 20/20 vision to those visually impaired, whether congenital, from age or accident. Let’s look at an (unexpected) example.
Example: An 80-year-old male came in to our low vision clinic with complaints of not being able to read his medication bottles. The patient’s best acuity with their habitual FT bifocal (-0.75 sph OU, +3.00 add) is 20/60 distance each eye and 20/40 near. maxDetail glasses were trialed and the patient achieved 20/20 near.
However, he didn’t like the maxDetail as he was generally happier with the distance and near acuity using his current FT bifocal and only needed to read medication bottles occasionally. He was also not a reader. He preferred to listen to books on tape. It was later determined that a lighted 3x handheld magnifier worked for what this patient needed.
Unexpectedly, his 58-year-old son who accompanied his father to the clinic expressed an interest in the maxDetail glasses for tying flies for fly-fishing. He was not a patient at our clinic, relayed that he had no ocular pathology and had uncorrected 20/20 distance acuity, since bilateral cataract surgery two years ago. He used +2.25 OTC reading glasses for “all around” close work and used either a +3.25 OTC reading glass or a 2x lighted magnifying gooseneck lamp for tying flies. He really liked that the maxDetail was hands-free, and that the increased magnification was “where he looked” and not limited to a short working distance or the confines of the lamp magnifier lens. He reported back about a month later that the maxDetail was working very well for tying flies.
Focusing maxDetail: Focusing the maxDetail is easy. Simply look at a target object of approximately 40 cm or 16 inches away. Focus the right eye first or the eye that sees best. While keeping both eyes open, cover your left eye with your left hand. Take hold of the diopter adjustment knob with the fingers of your right hand. Turn the knob all the way in one direction and then back, until the target object comes into its sharpest focus. Refine the focus by small adjustments back and forth. Repeat this same process for the left (other) eye.
Once focused, advise patients to not make quick or “wide sweeping” head or eye movements with this device on as it makes adaptation longer and more difficult. It can also cause a sense of disorientation and nausea. You would want to use the same slow methodical approach to viewing or scanning that you typically would with binoculars.
Client selection: Try this device for customers with good acuity if they express a need that isn’t being met to their satisfaction (i.e., working with small circuit boards, tying flies for fly fishing, etc.). Perhaps a pair of +3.00D OTC readers does an adequate job, but the viewing distance is uncomfortably close, and the patient wishes for a little more clarity or definition.
For customers with less than good acuity, 20/40 or 20/50 near equivalent acuity with their standard prescription reading/multifocals or OTC readers, this device can also increase magnification. That may get them to see a little better than the visual threshold for reading standard book print. This means more comfort for sustained reading.
For people who normally read using large print books, not every book is available in large print. Nor does everyone read books, via an electronic device (iPad, Kindle, Android tablet) that can magnify letters and images. maxDetail could offer the hands-free freedom to hold books and a larger variety of standard print books, to people who were previously limited to books available only in large print.
For patients with 20/200 acuity, trial is possible to see if it gives them more visual function. The predicted magnification for these patients would be 3x, per Kestenbaums Rule, but a try is in order.
MaxDetail, as well as maxTV and maxEvent, can be used monocularly. A person may still benefit greatly from use of a max product, even if acuity in one eye only is improved. The person can also “occlude or block” one eye, if the “non-improved” eye is causing visual confusion. Sometimes improving acuity in one eye is successful.
MAXTV: MAGNIFICATION AT GREATER DISTANCES
MaxTV glasses are designed for viewing objects or activities from 10 feet (3 meters) to infinity, with 10 feet being its primary target focal length. MaxTV has the same individually adjustable telescopic lenses as the maxDetail, though the focal range is for distance. They are perfect for viewing TV, as their name implies. How many times have you heard the complaint: “I can see the picture on the TV, but I can’t see the print”? MaxTV glasses have the potential to resolve that problem in many instances. MaxTV also works well for theater performances (you now have a hands-free alternative to theater glasses) and sporting events.
Specifications: This is a Galilean telescope of 2.1x power, the lens material is Clear PMX Plastic and lens size is 32 mm. The frosted frame and lens housing allows for an “open” viewing, without unwanted reflections associated with clear polished plastic. The range of viewing distances is 10 feet (3 meters) to infinity with preset pupillary distances, which generally work for PDs ranging from 60 to 68 mm. The diopter adjustability to compensate for wearers’ Rx for each eye is -3.00 D to +3.00 D. The device delivers a visual field of 18 degrees and weighs 1.7 ounces or 49 grams.
Like the maxDetail, a wide range of patients would benefit from this device for distance viewing, ranging from those who have 20/20 acuity to low vision patients. To calculate predicted magnification needed for a distance telescopic device like maxTV, use the following formula: current distance acuity/desired distance acuity = X or times magnification needed.
For example, a patient who has 20/100 distance acuity and the goal is 20/50 acuity, would need 2x magnification. The maxTV glasses are noted as being 2.1x, but using 2x for calculation purposes will work fine. There are practical and functional limits to this calculation, as cost, weight, movement parallax, reduced field of view and overall difficulty to use increase as magnification increases. Therefore, there are trade-offs as magnification increases.
For example, it would not likely be a good choice to fit a 20/200 patient with a 10x device (+40D), with the hopes of getting a good functional 20/20. Think how hard it is to hold 10x binoculars in position and view a large area for an extended period of time. Now think about a hands-free 10x device resting on the bridge of your nose.
Predicting end acuity from the formula above can be very helpful for tasks such as viewing a chalkboard from the back of the class, watching TV (when the TV size and viewing distance is known). It is less helpful for things that aren’t typically measured in the visual sense, such as viewing a play or watching a sporting event. For these tasks, it is best to get an idea for how the magnification will benefit the patient by letting the patient try them. Go outside and let the patient compare distance objects or activity with and without maxTV glasses. This is a hands-on approach, much like looking at a book with OTC readers of different powers, to see what works.
MaxTV and maxEvent: MaxTV is focused the same as maxDetail, except viewing distance and target object should be at about 10 feet (3 meters). The device can also be adjusted with the diopter adjustment knobs to bring objects or activities of various distances into sharpest focus. The glasses have a mirror coating on objective lenses to reduce glare and eliminate the appearance of “magnified eyes” to others.
MaxEvent has a shortened distance/range between the objective and ocular lenses (compared to the maxTV) providing enhanced sharpness for viewing outdoor events. The target focal length is infinity. Remember the maxTV has a target focal length of 10 feet, but can be adjusted for viewing further away.
MaxEvent has a slightly expanded diopter compensation range of -2.75 D to +3.25D (compared to the maxTV) due to the reduced distance between the objective and ocular lenses. These glasses are focused in the same manner as maxTV. Patients can focus on a target at about 10 feet or choose a target further out to really get the sharpest image possible for far distance viewing. The device can also be slightly adjusted with the diopter adjustment knobs to bring objects or activities at various distances into focus. Remember, it is not necessary to verify an objective improvement in acuity. “Better vision” for watching a sporting event at 100 yards is not determined by acuity numbers; it is simply subjectively defined by the wearer as “seeing better” or “I can read the number on their jerseys” or “I can see the expression of the players’ faces.”
ADD A LITTLE COLOR
Although max products have clear lenses with the exception of maxEvent glasses, don’t let that limit your color options. Use slip-behind colored filters like the ones given by the doctor’s office after dilation. Standard dark gray is readily available, but with some looking yellow, brown and polarized options are available as well. A person may even desire to have multiple colored slip-behind filters for various lighting and glare conditions. Yellow has always been a staple for increased contrast for low vision patients. Again, this is a subjective benefit that a low vision visually impaired patient will identify by trial and error.
NOT A GOOD CANDIDATE
Who might not be a good candidate for max glasses? There is a variety and it is field, fit and prescription dependent; for example, people with severely restricted visual fields or typically acuity worse than 20/200. My experience, however, has been that the suitability is determined by the patient. People with spherical prescriptions far outside the diopter compensation range are generally not good candidates, though some find positive results. However, remember there is a little more power compensation range on the maxEvent. That also means those with a large amount of astigmatism in their prescription or PDs far outside the 60 to 68 mm range of the devices. Lastly, people who have prescribed prism in their prescription typically cannot use max glasses since there is no prism correction possible.
The good news is that people who are not good candidates for max glasses may be good candidates for a max clip-on to go over their prescription glasses. MaxDetail and maxTV clip-ons are currently available.
MaxDetail and maxTV clip-ons attach to prescription glasses, similar to how flip-up sun clips attach. There is a tab on top of the device; squeezing the tab will open the clamp. When the clamp is fully opened, it will spread four rubber-coated prongs (two prongs on each side) about 10 mm apart. MaxDetail and maxTV clip-ons have a “fixed” focus, as there is no need for diopter adjustment like the max glasses. However, this results in no ability to make slight focusing adjustment for different viewing distances.
The height of the device is adjustable and can be set in one of five positions. The position can be changed by removing one small Phillips head set-screw on each side and moving to the desired “set-height,” then reinstall the set screws. It is best to do this at a table, just in case you drop a screw. This allows for proper “line of sight” or visual axis alignment, helps with comfortable viewing and a maximum visual field. The whole telescoping lens assembly can also be flipped up, just like a flip-up sunglass can be flipped up when going indoors.
Some successes: A 70-year-old patient visited our low vision clinic hoping to be able to identify items on the overhead grocery aisle signs. She was otherwise happy with the performance of her trifocals and was able to read ingredients on cans in good lighting. A recent ocular health exam and refraction reported good health and the following prescription:
- OD: -5.50 +2.00 X180 Prism: 1.0 Base UP 20/60
OS: -4.75+1.75X 156 Prism: 1.0 Base down 20/70
Add: +3.00 20/30 OU
Max glasses were not an option due to the prescription and prism. We tried a maxTV clip-on over her current glasses. She was effectively able to flip down the maxTV to view overhead store signs and then flip it back up to navigate down the aisle. This greatly improved her efficiency for grocery shopping, and she was well pleased with the clip-on.
Pushing the boundaries: Another future possibility for the maxTV clip-on would be as a bioptic telescope device. This could be done by setting the maxTV device high to where the person views normally through their Rx lenses for distance and near, and tips his or her head downward to view through 2.1x magnification. This would allow increased clarity for quick spot-checking (road signs, menu item, signs at the grocery store, etc.). The maxTV clip, when set up as a bioptic could be used while driving. Currently, the maxTV clip-on is not set up to achieve the correct position or angle needed to function as a bioptic, but this could easily change with a slight redesign or modification to the mounting hardware. One objective could also be occluded, if a single bioptic was desired. Bioptic devices are not commonly used by “normally sighted” people, but why not? It could make the difference of identifying the small poorly contrasted sign of the street that you need to turn on in an unfamiliar area or “looping” the area several times until you happen to come across the correct street. This could also complement GPS use as well. Some states offer restricted driver’s licenses to low vision patients who use bioptics, but one should confer with his or her low vision care provider and their state DMV for particulars on that. The field of bioptic telescopes is broad and would be a topic for other courses.
Specifications: MaxDetail clip-on—visual field/field of view is 13 degrees, focus: 40 cm or 16 inches. The PD range is 62 to 67 mm and weighs 23 grams or 0.8 ounces. They attach like a flip-up sunglass clip with rubber-coated prongs that separate 10 mm to attach to both nasal sides of the eyeglass lens. There is a five-way adjustable height setting to ensure proper line of sight alignment. Max TV clip-on: visual field/field of view is 18 degrees, focus: 10 feet to infinity. They weigh 28.6 grams or 1.0 ounce and have a PD range of 60 to 68 mm. There is a five-way adjustable height setting to maximize alignment for line of sight.
Do you offer over-the-counter solutions that go beyond what conventional prescription glasses and OTC readers offer? Max products can improve vision in general for the visually impaired individual and for even some with good vision. The max product line can fill a niche between routine eyeglass offerings and low vision devices not typically addressed. Think of the additional patients served and potential revenue generated. This could max out your optical operation.