Don Nygord's Lensometer
An edited version of the original guide was published by Shooting Sports USA in May 2009 entitled, "Winning Vision", before the magazine transitioned into the online format. The following are some of my additional observations during the course of over a decade with hundreds of patients and some additional hints on getting a good eye exam to improve the sight picture. Your eyecare professionals may have taken good care of your needs but these additional tips will help further.
Many of my patients who came in for their shooter's exams may have brought in a copy of their most recent eyeglass prescriptions, some as recent as within a week. From my experience, much to my dismay, I have found that about half were incorrect. I simply show my patients through the phoroptor (instrument with all the lenses) what my results were as compared to the numbers written on their prescriptions. This may be from an Ophthalmologist or Optometrist and from private practices, HMO's, or commercial settings.
With our computerized society and all the data collections from various sources such as our credit card companies, cell phone service providers and so on, we cannot escape from being categorized. There is a dirty little secret I discovered in my industry a few years ago when my lab rep from one of the biggest vision plans dropped by. All doctors within this vision plan have a number attached to his/her profile, their "redo rate," some as high as 25%. That means 1 in 4 patients complained enough about their prescription eyeglasses that they had to be re-done. Realize that there may be a significant percentage who never complained.
During your eye exam, did your eyecare professional double check the distance vision with both eyes opened "after" doing the exam to each eye alone? Often, the eyes when checked binocularly may be different than when checked monocularly. Since we see with both eyes opened, this practice should always be done during the end of the refraction. Both the right and left eyes should be checked simultaneously with additional lenses to confirm what was found with each eye alone. It doesn't take long but this final verification tends to be omitted. The possible subsequent error to the Rx may account for frequent eyestrain.
There is a common practice of reducing the new eyeglass prescription which would lead to less than perfect vision. I'm from the "Old School" whereby one would do a diligent exam and prescribe what was found, as recommended by our Dean. However, I could never understand why some doctors frequently reduce the new prescriptions so that patients will "adjust easier" to their new eyeglasses. In reality, the patients are short-changed with a less than perfect Rx and they may need to come back sooner for another update. I have worked with some associates who changed the best Rx so consistently that it became ridiculous. I jokingly tell my patients who move away when seeking eyecare from another doctor, to find one who knows how to reload ammo, in which case, a more precise Rx may result.
Every doctor may have a certain preference to the sequence of tests. I believe that it would be most practical to start with the refraction first followed by the health tests such as the glaucoma test, visual field test, dilation and others when deemed necessary. There exists the possibilities of irritation to the eyes, fatigue and increased anxiety if the refraction is done at the end of the exam and thereby would affect the quality of the patient's responses. Although eye health tests are equally important, the refraction should not be treated as an after-thought.
Beware of the eyecare professionals who have never worn eyeglasses, and the younger doctors who do not need multifocal lenses. They may understand vision correction in theory but lack the practical experience in wearing corrective eyeglasses, in particularly multifocal lenses, to fully understand what most of us go through. Before a shooter's exam can be done well, the prescription must be accurate. These numbers will be the foundation to build upon the shooting Rx.
This upsets me when the patient is ignored. Listening, at times, appeared to be a lost art. Three doctors, 2 Optometrists and 1 Ophthalmologist, from a HMO were not able to solve a woman's vision complaint when she could not see well enough as a seamstress. No one bothered to acknowledge that she needed to see at 10" as they gave her a standard near Rx "for her age" focusing at 18". She was told there was no medical reason why she couldn't see. This is an example of why some of our shooters have a very difficult time describing their needs and getting an accurate correction for seeing their sights.
Computers are essential in our daily lives and in many fields including the optical/ophthalmic field. Many of you may have experienced automated instruments to determine your eye health and vision. Can you imagine a $15,000 - $60,000 computer telling the doctor which Rx you need to see best with, and the doctor listens? The computerized refraction printout may sway the doctor's final prescription, especially during a busy day. My patients have been very happy to "tell" me which lenses provide their best vision. My one-to-one interactions during the exam have been important as I developed a sixth sense of the responses and I would repeat the lens choices many times when needed to obtain the final Rx. With my way of checking eyes, my redo rate was miniscule, but bear in mind, patients changing their minds on their lens types, materials, tints and photochromic choices also count into our redo rate so it will never be 0%.
I was fascinated when I read Don Nygord's article on vision and the eyeglass prescription, coming from a person outside of the optical field. Don mentioned that lenses were rarely made correctly and he even had a lensometer to check and verify lenses. His Nikon lensometer was given to me as a souvenir and after evaluating it, I can say that it was highly sensitive to inaccuracy. The manager from one of my labs once said the most accurate and reliable lensometers are the manual ones. Computerized lensometers are the norm nowadays and although they work well, it's difficult to judge the blurriness of a lens when the Rx is off. With the manual lensometer, I can see the blurred cross hair images of the instrument. I once had a prolonged argument with a lab manager when I sent back a job which was off. He insisted that the lens was within tolerance using their "highly sophisticated computerized instruments," but I knew it wasn't. Unfortunately, there may be a fine line between quality control and profit margin.
Mistakes do happen. Transferring the Rx incorrectly from the exam record to the ordering screen of the lab website, typing + instead of -, lab technicians pulling out the wrong lens powers from their inventory, and making the lens with the astigmatism cylinder 90 degrees off axis are common. The final stage of quality control inspections by the lab sometimes is non-existent, but it is the responsibility at the doctor's office to perform the final inspections. I've seen firsthand where this was also non-existent. Unfortunately, many patients accept what they received and would never question the doctor or staff.
EXAM IN REAL SPACE: I no longer check the distance from the patient's eyes to the front sight and set that distance for the reading card before I proceed with the add determination. It may work out fine but I prefer to work outside in "real space."
I no longer consider the age of the shooter nor the length of their arms to determine their shooting Rx. It has become meaningless. Philip Hemphill (10-Time NRA National Police Shooting Champion-PPC and 2-Time NRA National Precision Pistol Champion) who responded to a past survey preferred +0.25 add when he was the age of 58, while John Bickar (holder of several NRA National Junior Pistol Records) needed a +1.50 add. Although not presbyopic even today, John has worn this type of shooting Rx since the age of 19. This type of add will prevent young shooters from peeking at the bullseye while they take their attention off from the front sight. When I examined Eric Pueppke (USAS Assistant National Pistol Team Coach, NRA/USAS/CMP Level 4 Advanced International Pistol Coach and National Pistol Coach Development Staff), I showed him these 2 extreme lens powers which did not work for him but another power was perfect, while his wife Char saw the best with her specific lens preference. Each of the four shooters saw best with an add power different from all of the rest.
Eric wrote, "... one comment I would like to make is that many shooters kind of take their vision for granted and don't realize that even though they see well, they don't see really well. We are all, of course, used to seeing the world the way we do, and I've run across so many shooters that thought they had great vision, only to find out that they actually don't! I have to date, found no one that gives the complete examination that you do, Norman. I still remember how you first corrected my vision with the glasses and then put in other shooter's lenses so I could "see the sights the way they do." This was a real "eye opener" (pun intended!!). All of the great position, shot process, and trigger control a shooter may develop will be greatly diminished if they have less than perfect vision."
EXAM USING PISTOL SIGHTS ONLY: I need to have the eyes relaxed as much as possible to determine the best possible shooting Rx. I prefer using actual pistol iron sights to get good patient feedback rather than an exam reading card. In my office, the shooting patient can look across the street and we use a round light fixture on the building as a bullseye target. Of interest, this was the old site of a drive-in where Spencer Tracy, Katharine Hepburn and Sidney Poitier appeared in the film, "Guess Who's Coming to Dinner." Every shooter will be able to identify his/her best lens for their preferred sight picture. Quoting Philip Hemphill, "My eye doctor here in Mississippi gets a little uneasy when I bring my guns into his office for sight picture correction. I have found that is the only way I can get a correct adjustment for vision. The lighting also affects the way I perceive the sights in his office."
BINOCULAR VS. MONOCULAR TESTING AND THE TRIAD: Typically when we check the eyes at near distances in the confined space of the exam room, we have both eyes opened with binocular testing. We then have what is known as the triad. When one looks close up at the reading card, both eyes must converge so that the line of sight of each eye comes to a single point. With convergence, the eyes also accommodate and the pupil size become smaller. In accommodation, the muscles inside the eye change causing the shape of the lens to change and thereby the focus. Even older shooters who wear multifocal lenses can still accommodate to a certain degree. For instance, a 60 year old shooter can accommodate 1.00 diopter. We also know that changes in pupil size can change the way we see.
These factors may affect our shooting prescription when doing near binocular testing while using a reading card. I've heard a number of times from shooters that even though the eye doctor used the measurement of the eye to the front sight, the shooting Rx was off. While doing monocular testing with iron sights, the line of sight of each eye would be parallel and the triad would no longer be a factor, thus a more consistent outcome would result.
DEPTH OF FIELD: I simulate the lighting conditions as close as possible to the shooting environment. When one needs to see outdoors to compete in daylight, we have large windows to allow plenty of light to the shooter's eyes, which will have a positive effect onto the pupil by making it smaller. With smaller pupils, we have an extended depth of field. At this point, the smaller pupil becomes advantageous for the sight picture appearance. This topic is further discussed in the following article.
SSUSA - Eye DominanceWhen we look at the front sight, the bullseye will be blurred, but how much blur would be preferable while the front sight is clear? We can have 20/25 blur or up to 20/100 or more blur. A very blurred bullseye at 50 yards may make it difficult to judge the sight picture and be frustrating. By checking the shooter's vision while he/she looks at the front sight in relationship to the rear sight and then the bullseye, the shooter will be able to "decide" on their lens preference without the loss of front sight clarity, or very minimal loss. Center hold, 6 O'clock hold, or sub-six hold may affect the shooter's decision. The preferable sight picture appearance chosen cannot be demonstrated by the use of a reading card. The shooting patient would be able to see the exact sight picture before getting their shooting glasses. No buyer's remorse.
As Jim O'Young discussed with Dr. Wong, "It's amazing that shooters may spend thousands of dollars for their equipment but totally ignore their vision. You can't hit what you can't see, and seeing depends on your eyes and the quality of your vision."
MODIFIED MONO-VISION WITH THE NON-SHOOTING EYE: Once the best lens is determined for the shooting eye, what do we do with the non-shooting eye? I don't believe any eye doctor who doesn't shoot will have any idea what to do (or care), however this is very important. A patient who came to see me for a second opinion about his shooting Rx told me his previous doctor asked him what to do with the opposite eye. Would the preference be the distance prescription or using the same add as the shooting lens? The answer is generally neither.
Shooters would like to see off to the distance without changing eyeglasses, especially important to see well enough to distinguish their target numbers and not cross-fire. However, having one lens for far and the other lens near may be difficult to adjust to and cause the feeling of disorientation. Trial lenses on a trial frame will demonstrate exactly if this will work or not. I have found that the full distance Rx for the non-shooting eye would not work, therefore a modification would be needed. Usually, by altering the power for the non-shooting eye by +0.25, to +0.50 at most, will allow this "modified mono-vision" technique to be workable. Very happy shooting patients! They now see the sight picture well with the shooting eye and see down-range well with the non-shooting eye, and comfortably.
For those who cannot keep both eyes opened for shooting without covering the non-shooting eye, one choice would be a flip-down occluder. Another choice would be a small piece of translucent scotch tape placed on the lens of the non-shooting eye so the sight picture would not be disturbed for the shooting eye. Closing the lids would not be recommended for Precision Shooting and similar types of competitions.
Progressive lenses are never recommended for seeing iron sights. Many shooters would be happy with single vision lenses, but if there is a need for better close-up vision to be able to score, load magazines, use an overlay and so on, then a simple standard bifocal has worked well. The position of the bifocal segment must be placed lower than normal to avoid interference with the sight picture. As the shooter becomes fatigued, so may the head position and stance. The exact final height position can easily be demonstrated with a small piece of scotch tape, with the top of the tape simulating the top of the bifocal segment. Usually, several repositioning attempts will be needed until the patient will know what height would be ideal. This is very important to get the shooter's feedback.
The final bifocal powers will then need to be adjusted after taking account of the different add powers for each eye on the major part of the lens. For instance, if a +2.25 add would be needed for the bifocal, the add for the shooting eye and the non-shooting eye must be subtracted to get the resultant bifocal powers for each lens.
[AR-15 and Rifles with Rear Aperture Sights]
By far the most popular rifles that my shooters bring in for their shooters' exam are their AR-15's using front iron sight posts with rear apertures, and no scopes. Vision with the AR-15 Rifle is more challenging because of the shorter sight radius. The only way to check vision is through the aperture onto the front sight post and view down range. Checking the eyes in the exam room does not work as well. Please take some time to review a past article "VISUAL DISTURBANCES THROUGH THE APERTURE," especially for older shooters.
SSUSA - Visual Disturbances Through the AperatureI have my shooters place their rifles on one of the steps of a 6 foot ladder at a comfortable height so that the rifles are absolutely still. Most of the time but not always, the shooters have their preference of the aperture size in place. At times, we do make a change to see if a different aperture size makes a difference to front post and bull clarity. Even with the extended depth of field by seeing through the aperture, many times the front post clarity is lacking. It doesn't take much of an add to make the post clear and to make the very distant target blurred. The goal would be to improve front sight post clarity without affecting target clarity. Patience would be needed because as the eye becomes accustomed to the lens add shown, the eye may fatigue and a slightly different power may be needed to be the best choice. It is not uncommon that it comes down to 2 final lens choices and then one lens becomes the eventual winner. The testing cannot be rushed. The first lens that seems to work best is usually not the final lens. We have some very astute serious shooters and the slightest change in their shooting lens would make a big difference during a match.
Wayland wrote, "The lens worked out great! My up-close vision had been getting worse & worse over the years, so I needed something that would bring the front sight into sharp focus when looking through the micrometer match rear sight on my rifle. Prior to the new lens, the front sight focus was inconsistent no matter how much I adjusted the iris on my rear sight, as I was struggling to get a good sight picture. The new lens solved the problem and allowed me to be more consistent, which as you know, leads to good scores. I have no doubt that the new lens helped me medal in the events that I did!!! Without it, I would've shot worse scores and ended up with lower medals or no medals at all." Wayland picked up his lens for the Champion Super Olympic shooting glasses a couple of days before leaving to the World Games in Virginia.
There is an after-market insert for the aperture which uses concentric diffraction rings to allow good simultaneous focus for the front sight and the bullseye. This may work well for some but others have come in to verify their vision because either the front post or bullseye were blurred. After a shooter's exam and a new shooting Rx, they saw well and were happy with the results. This is also not uncommon with multifocal intraocular lens implants used for cataract surgery and multifocal soft contact lenses which also incorporate diffraction rings. Ideally eyeglasses would not be needed afterwards but that has not always been the case.
VERTEX DISTANCE: As an important reminder when using Knobloch or Champion shooting glasses, keep in mind that the lens is situated farther than our normal day-to-day eyeglasses. Shooters having their prescription made for these types of shooting glasses may find that their vision wasn't what they had hoped for. The extended distance of the Knobloch and Champion lens position as compared to regular eyeglasses changes the power. A nearsighted minus lens becomes weaker when it is farther from the eye. A farsighted plus lens becomes stronger when farther from the eye. It is important to bring these frames and lens holders for the doctors to see and understand what is involved. A small prescription may be insignificant but there may a 0.25 to 0.50 diopter of error with higher prescriptions.
Please note some of the power changes in this article "VERTEX DISTANCE."
SSUSA - Vertex Distance, Optimum Vision Or Not?Best regards to our shooters who are the finest people in the world! Good vision and good shooting to all.
