Archive for the ‘Eye Facts’ Category
When Shakespeare’s King Lear calls on “cataracts” to spout during his “Blow winds, and crack your cheeks!” speech, he’s not asking for cloudy vision.
In Shakespeare’s day, a “cataract” also meant a huge waterfall.
This is fitting, because the clouds of white foam arising from a waterfall are metaphorically like the cloudy vision caused by a cataract.
Roughly half of everyone who lives to age 80 will eventually get cataracts in one or both eyes.
Live to age 95, like the great San Francisco poet and City Lights bookstore owner Lawrence Ferlinghetti, born March 14, 1919, and you’ll have close to a 100-percent chance of getting cataracts. But that’s a small price to pay for such awesome longevity.
What exactly is a cataract? To answer that question, let’s begin by looking at the eye.
A cataract is a clouding of the eye’s lens. On the picture, do you see where the lens is in the eye? Yes, right behind the pupil.
Light enters the eye through the pupil. As the picture shows, the lens focuses light onto the retina, which is a layer of light-sensitive cells at the back of the eye.
The lens must be clear to focus light onto the retina. If the lens has become cloudy with a cataract, the image you see will be blurry.
People say that having a cataract is like looking through a dirty car windshield.
Now let’s look at how cataracts form.
The eye’s lens is composed of two substances. The first is water.
The second is protein.
As we age, some of the protein that constitutes the eye’s lens (along with water) can clump together, causing the clouding of the lens.
Although most cataracts are simply a product of aging, there are other causes of cataracts, too.
Diabetics can develop cataracts.
So can steroid users.
Cataracts can develop after an eye injury, sometimes years later.
Sometimes babies can be born with cataracts.
Cataracts can develop after exposure to radiation.
Other factors that could cause cataracts include those common bugaboos smoking and drinking.
Here are the symptoms of cataracts, in case you think you might have one.
Cloudy or blurry vision.
Colors look faded.
Glare from headlights, lamps or sunlight bother you more than it used to. You may also see halos around lights.
Other symptoms could include double vision or multiple images in one eye.
Frequent changes in your prescription for eyeglasses or contact lenses could also be a sign of cataracts. If you notice any of these symptoms, or if you are age 60 or older, ask your eye doctor to check your eyes for cataracts, as well as for age-related macular degeneration, glaucoma, or any other vision issues during your next eye exam, which should be soon.
If you do have a cataract, and it’s interfering with your normal, everyday activities, such as driving, reading, or watching TV, your cloudy lens can be surgically removed and replaced with a clear, artificial lens.
If you need cataract surgery in both eyes, usually the doctor will do each eye a month or two apart.
However, surgery should be avoided unless it’s absolutely necessary for your vision, or if a cataract interferes with getting another eye issue treated, such as age-related macular degeneration or diabetic retinopathy.
Nevertheless, cataract removal is one of the most common operations performed in the United States, and about 90 percent of people who have cataracts removed have improved vision.
Now if you don’t have cataracts and you want to forestall getting them, there are some precautions you can take, according to research done by staffers of the Mayo Clinic.
Get regular eye exams, at least once every two years, or more frequently if you notice changes in your vision.
Quit smoking and drinking alcohol.
Yeah, we know. We selected the picture. More power to her.
We like this old joke, “If I’d known I was going to live this long, I’d have taken better care of myself.” But in reality, most smokers and drinkers won’t live to 100.
Wear sunglasses and clear glasses with 100% Ultraviolet (UV) protection.
Maintain a healthy weight.
Eat plenty of fresh fruits and vegetables.
The latter finding is buttressed by research performed at the University of Oxford, the results of which were published in 2011 in the American Journal of Clinical Nutrition.
The study found that the risk of getting cataracts was greatest for high meat eaters (those who ate more than 3.5 ounces of meat each day). It decreased from each dietary group to the next, in this order: moderate meat eaters, low meat eaters, fish eaters (people who eat fish but no other meat), vegetarians, and vegans. In fact, the risk for vegans was roughly 40 percent lower than for the high meat eaters.
As addressed in this Zenni blog post on Nutrition and Vision, dark green leafy vegetables such as spinach and kale, both of which contain the antioxidant-carotenoids lutein and zeaxanthin, are associated with significantly lower risks of cataracts.
So, quit smoking, decrease or eliminate drinking alcohol, decrease or eliminate eating meat, increase eating fruits and veggies, and you might live long enough to have your first cataract as a 95th birthday present – among other goodies!
Tuesday, April, 1 2014 by Matthew Surrence
Did you ever see the classic Mel Brooks comedy “Young Frankenstein”?
If not, watch it as soon as possible. It’s hilarious!
Go ahead, we’ll wait.
OK, you’ve watched the movie. Were we wrong? I mean, the “Puttin’ on the Ritz” dance? It doesn’t get any funnier than that.
Now that you’ve seen this comedy classic, let’s talk about one character in particular: Igor, played by Marty Feldman.
There’s a reason his name is not pronounced “EE-gore” but “EYE-gore,” and it’s not just because Dr. Frankenstein’s name is pronounced “FRONK-en-steen”.
It’s that when Feldman is onscreen, you can’t take your eyes off his eyes, which do not point in the same direction. The actor had a condition called exotropia. Exotropia? What’s that? A space colony? No. Good try, though.
Exotropia is a form of strabismus.
“OK wise guy,” we hear you saying. “What are exotropia and strabismus?”
We thought you’d never ask.
Let’s start with strabismus.
Strabismus is a condition in which the eyes are not aligned with each other because not all of the eyes’ muscles are working together. Here’s how it works: There are six muscles in each eye that control the eye’s movements. These are called “extra-ocular muscles”.
They enable your eyes to rotate in all directions, which is necessary for you to be able to properly express sarcasm.
But sometimes, these six extra-ocular muscles are not perfectly coordinated with each other, meaning you’ve got a slacker in the bunch. If this is the case, your two eyes don’t look at the same thing at the same time. Just like Marty Feldman’s Igor.
Exotropia, as we said, is a form of strabismus. The prefix “Exo” means “to exit” or to “move out”. Try it when you want to get rid of (and befuddle) a bad roommate:
“It’s exotropia time, loser!”
Exotropia is the type of strabismus Marty Feldman had, as a result of a botched operation in his youth, causing his eyes to turn outward (exo). A more common way to refer to this is “walleyed”.
The other form of strabismus, in which one or both eyes turn inward, is called esotropia. This is more commonly referred to as being “cross-eyed”.
If this guy wasn’t just playing around to freak you out, and really is cross-eyed, he is one of about four percent of all people who have strabismus. Strabismus hampers the ability of the brain to fuse the two images that the eyes see into one 3-D image, which creates depth perception. Along with a lack of depth perception, a person with strabismus may also experience double vision.
In the optical world, double vision is known as diplopia. If you have diplopia, you may see two images, or one blurry one.
Fortunately, eyeglasses with a prism embedded in the lenses can correct this. However, diplopia can also be caused by having one blind eye or an eye with minimal vision. Unfortunately, this can’t be corrected by a prism alone; eye surgery on the extra-ocular muscles may be necessary, too.
But let’s say you have vision in both eyes, and you need only a mild nearsighted or farsighted prescription (and possibly an astigmatism correction). In this instance, if you have diplopia, it would most likely occur toward the end of the day, when your eyes are tired and you start noticing a little double vision. This could be happening if you’re working on a computer all day, or focusing on printed text (especially small print) all day, and you find you’re experiencing eyestrain. In this case, a prism in your lenses would be all you would need to correct your diplopia.
Here is a prism and its effect:
You may find that, after looking at this picture, you have an uncontrollable urge to listen to Pink Floyd’s “Dark Side of the Moon.”
This is an urge that should never be ignored.
But first, let’s talk a little bit about prisms. As we know, and as the picture indicates, a prism is a clear glass or plastic pyramid, which causes the white light that enters it to exit in the rainbow color spectrum. We learned about this as kids with the mnemonic (memory device) “Roy G. Biv” (Red, Orange, Yellow, Green, Blue, Indigo, Violet). However, people who wear glasses with prism corrections don’t see the world in rainbow colors. Wouldn’t it be nice if we did!
In addition to dividing white light into its constituent parts, a prism also changes the direction of the light that passes through it. Therefore, when you put a prism correction in a pair of ophthalmic lenses, it displaces the image that the eyes’ double vision puts in the wrong place, restoring it to where it should be to provide one 3-D image.
But what about the rainbow effect?
Here’s what happens with that. Prism corrections in eyeglass lenses have two prisms per lens, each one meeting the other at the base (the bottom of the triangle) or the apex (the peak or point of the triangle).
When light passes from one prism to another, it is restored to the white light that entered the first prism. Basically, light enters the first prism as white light and exits as a rainbow; it enters the second prism as a rainbow and leaves as white light. But when light leaves a prism, the direction of the light changes.
Just as with nearsighted or farsighted corrections, prism corrections are either plus or minus. When they are plus, the two prisms meet base to base. When they are minus, they meet apex to apex.
If your eye doctor put a prism correction on your prescription, you will see a little triangle indicating a prism. This is written as the Greek letter delta, which we all know from “Animal House.”
You will also see indications for the direction of the base. It will be either Base Up (BU), Base Down (BD), Base In (BI) or Base Out (BO). There will also be a number, somewhere between 0.50 and 5.00, indicating the amount of image displacement needed on one lens or both lenes to correct for double vision. This is written in diopters, which is the unit of measurement of the optical power of a lens.
A corrective prism on your lenses will be so thin you won’t even be able to tell it’s there. But your brain will, unconsciously. With a prism correction, the image the eye takes in is shifted for either the problematic eye or for both eyes. Your brain processes this information and fuses the images together.
Let’s say that only the right eye is the problem. For good binocular vision (which means both eyes acting together), let’s also say the prism correction needed is Base Up, 3.0 diopters. But instead of putting the whole prism correction in the right lens, an eye doctor will often split the difference, and make the right lens Base Up 1.5 and the left lens Base Down 1.5, equalizing the correction so the two lenses maintain the same thinness.
With this prism correction, it makes it appear to the brain that your eyes are working in concert. This directs the brain to fuse into one the two images the eyes see, pulling the disparate images together and creating the 3-D image that allows for depth perception.
Deep, Bluto. Now pass the keg. Hmm … kegs and toga parties … could that be the cause of the double vision?
Wednesday, January, 15 2014 by Matthew Surrence
Moving sidewalks. Check. Robot vacuum cleaners. Check. Talking alarm clocks. Check. Speedy push-button cooking. Check. Live video chats. Check. Personal jetpacks. Check. Flying cars. Check.
All of these futuristic conveniences were depicted in “The Jetsons” when it debuted 50 years ago. At that time they didn’t exist. Now they do.
What? Even the flying car? Yes, even the flying car, which exists as a hybrid car / airplane that’s about three years away from the market. Don’t believe me? Google it (after you’ve finished reading this blog).
We still don’t have George Jetson’s nine-hour work week (sigh). And you’d pretty much have to go to an airport to ride on a moving sidewalk.
But all of these things have, in one way or another, come to pass, not to mention some little ol’ things “The Jetsons” didn’t foresee, such as the personal computer and the internet.
All of these devices have changed our lives for the better. (OK, maybe not the talking alarm clock.) But other inventions, such as eyeglasses, despite some improvements and refinements, have stubbornly remained pretty much the way they were in the 20th century.
That’s about to change, with new generations of eyeglasses being developed or currently available that provide these amazing functions:
Giving limited vision to the blind. Check. Correcting colorblindness. Check. Automatically changing the focus of your single-vision eyeglasses from distance to near. Check. Downloadable glasses made in a 3-D printer. Check. Eye exams done on your smartphone. Check.
Plus the biggest change of all, which has gotten the most ink: Google Glass, a pair of glasses that are not actually eyeglasses, but a computer that’s worn on your face, just like a pair of glasses.
You’ve doubtless heard about Google Glass, its innovations as well as its drawbacks. Even though it won’t be released for purchase to the general public until next year, it’s already getting some angry pushback from people disturbed by the invasion-of-privacy implications of Glass wearers being able surreptitiously to video-record or photograph them, who have coined the term “Glassholes.”
Google’s competitors, including Sony, Nokia, Microsoft and Apple, among others, are rushing to improve on a product that isn’t even available for purchase yet.
(Some software developers were allowed to buy and test prototype Google Glasses at $1,500 a pop.)
But other companies are creating specific-purpose computing eyewear. Recon Instruments, for example, is developing smart glasses for skiers, who will be able to see their speed, elevation and distance, among other data, right inside their ski goggles.
Another futuristic type of glasses is being developed by 2AI Labs. Their O2Amps are designed to detect changes in the blood flow to the face of the person the wearer is looking at. The blood flow indicates their emotional state, as well as possible bruising or other trauma below the skin.
Doctors and nurses would find this application useful, as would law-enforcement personnel, poker players and the spouse whose partner has come home suspiciously late.
However, none of these glasses are prescription eyeglasses that will correct or improve your vision. Google Glass and all of these other smart glasses will have to be worn over prescription eyeglasses or be configured to include the wearer’s prescription.
No, for innovations in prescription eyewear, the main focus, as it were, is on glasses that replace progressives or bifocals. Some people just can’t get used to having their distance and reading prescriptions (bifocals) or their distance, computer and reading prescriptions (progressives) in one lens.
These multifocal glasses will be right for them. They have lenses that go from distance to computer to reading vision all at the touch of a button, slider or dial, like the focus knob on a pair of binoculars.
Here’s how it works.
A pair of glasses is outfitted with outer and inner lenses. The outer lens has distance vision, and the inner lens contains liquid. One company uses a slider on the bridge of the eyeglasses that activates the inner, liquid-containing lens.
By adjusting this slider, you can adjust the eyeglasses’ correction to the type of vision you need: distance, intermediate or near vision. It changes the shape of the lens not unlike the way a makeup or shaving mirror can be rotated for a magnified image.
Another company is also using two lenses per eye. But instead of a slider, it is embedding a processor chip in the glasses to change the focus automatically when the wearer’s head tilts, or when the wearer touches a button on the frame.
Do you want to save money and share your glasses with your mate? With these glasses, eyeglasses wearers can program two different prescriptions, so a family member can wear them when the other person is asleep or wearing a different pair of glasses.
At more than $1,000 per pair, it is unlikely that these glasses will catch on with the eyeglasses-wearing public, which is just getting hip to buying their eyeglasses at steep discounts from online retailers.
Not only that, but some domestic squabbles might ensue if both parties want to wear the glasses at the same time. At least the high price should serve as a deterrent to an eyeglasses tug-of-war.
However, along with the exorbitant cost, there’s another problem with auto-focusing eyeglasses: Along with their nearsighted or farsighted correction, most eyeglasses wearers also have an astigmatism, which makes everything blurry if it’s not corrected. This is something auto-focus eyeglasses cannot do.
People with astigmatism may not benefit from eyeglasses 2.0, but those with colorblindness may.
EnChroma glasses use a coating on the eyeglass lenses to make red and green objects pop. But you’re looking at spending more than $500 for a pair.
The Oxy-Iso version of the O2Amps also decreases the red / green deficiency that plagues the colorblind.
Some people with more intense blindness than colorblindness, that is, people whose vision has been diminished by macular degeneration, could regain some sight with eyeglasses that are being developed by English researchers at Oxford and Cambridge.
These glasses use light-embedded lenses that create outlines of objects facing the wearer. The glasses contain tiny cameras and computers that can read the expressions of people the wearer is looking at, sending a green or red signal to the wearer that’s invisible to the other person, indicating whether that person’s expression is positive or negative.
But there’s no telling whether the expression of a poker-faced person could be read with these glasses, unlike the blood-flow-detecting pair.
How would you like to make your glasses at home?
You’ve probably heard about people making guns with 3-D printers. Well, a Dutch company is working on developing eyeglasses with prescription lenses that can be made in a 3-D printer. The lenses will need no subsequent polishing, grinding or tinting.
Some new-fangled eyeglasses are mostly for fun. If you were in high school or college in the late 1960s, you may recall light boxes.
Kids would hook their record players up to these light boxes, which looked a bit like speakers, but they contained little colored bulbs.
The bulbs would light up and the light boxes would change color, depending on the rhythm and melody of the music that was being played. All over America, kids would crank up the Grateful Dead, fire up a doobie, stare at the light box and murmur, “Far out!”
Now a startup is creating eyeglasses that will function the same way as a light box, only on your face.
The glasses, called DropShades, light up and change colors based on the music that’s being played where the glasses are being worn. Presumably the glasses, which feature slats rather than full lenses, would turn bright, racy colors during a rock concert but display sedate pastels when the wearer is listening to elevator music.
Along these same lines, there’s a new kind of glasses being developed for those who want to be a character in a Beatles song, specifically the Girl (or Boy) with Kaleidoscope Eyes, a.k.a. “Lucy in the Sky with Diamonds”.
Now you can be that person, with a trippy pair of eyeglasses made by a company called Future Eyes. These glasses don’t correct your vision. They mess it up, giving you the vision of an insect. That’s useful if you want to dodge a flyswatter, or simply space out. They’re not so great for driving.
Eyeglasses like these are mostly for artistic types, to help them see the world in a new way, to inspire their creative vision.
But one of the most promising innovations is not in eyeglasses, but in eye exams. A company called EyeNetra has created a smartphone app that enables you to do your own eye exam when you attach its eye examining device to your smartphone.
Finally, since the internet shrunk the four corners of the globe to a village, people all over the world can now communicate with each other for business and pleasure.
In addition, people of various backgrounds who immigrate to countries with diverse populations, such as the U.S., need to be able to understand and be understood by people who do not speak the language or languages in which they are fluent.
In this regard, Microsoft is boldly going where no man (or woman) has gone before. The company is working on a nonfiction version of the “Star Trek”-inspired universal translator, which will instantly translate the speaker’s language to the wearer’s.
That’s how to live long and prosper!
Wednesday, January, 8 2014 by Matthew Surrence
It’s great being over 40.
No, 40 is not really the new 20. That’s because at 40 you really begin to come into your own, personally and professionally, unlike when you’re 20. It’s in your 40s when you start to figure out who you really are. Sure, you’ve made some mistakes. Who hasn’t? But now that you’re over 40 you find you’re actually learning from your mistakes, rather than making the same ones over and over again.
But just at the point you start to hit your stride, you also start noticing that physically, certain things don’t work as well as they used to.
Like your eyes, for example.
It used to be that when you were younger, whether you were nearsighted, farsighted or had perfect vision, your eyes could adjust to see things both far away and up close, whether you were looking through prescription eyeglasses or not. But now that you’ve entered your fifth decade, a curious thing happens. You notice you’re not able to see things up close as well as you used to.
Reading an instructional manual? No way.
The directions on a pill bottle? Fuggedaboutit.
Now you find yourself constantly moving what you’re trying to read back and forth, back and forth, as you attempt to find the exact position where you can see it clearly. You do this so much you start to feel like a trombone player.
You don’t want to admit it, but you know it’s true. It’s time to start thinking about multifocal glasses. Or at least reading glasses.
But what should you get? If you already wear glasses to correct nearsighted or farsighted vision, the first thing that probably pops into your mind is bifocals. But what enters your mind right after that is grandma, rocking and knitting and watching “Matlock.”
That’s not me, you say to yourself. I don’t want people looking at me, seeing that line on my glasses and thinking, “Out to pasture.” You’ve heard there are such things as no-line bifocals, or multifocal glasses, called progressives, but you’re not sure about them. You’ve heard that some people have a hard time finding their visual sweet spot.
So you consider separate pairs of glasses, for distance, computer, and reading vision. But if you wear corrective lenses already, you might not want to have to worry about using multiple pairs of glasses. “Glasses strewn all over the house?” Uh-uh. “Reading glasses on a chain?” Even more emphatically: Uh-uh. Once again the dreaded image comes to mind: Grandma.
Don’t worry. You’re not your grandma. You’re years away from the early bird special at Denny’s. All you need is a little help with your presbyopia.
My what? OK, we’ll explain. When you’re young and your eye muscles are elastic, they easily expand and contract to allow the lens of your eye to change shape to enable you to see objects clearly at various distances.
This process is called accommodation.
But after your eye muscles do this for about 40 years, they get a little tired and stiff, just like your other muscles. Consequently, no longer can your eye muscles so easily expand and contract to enable the accommodation process.
This condition is called presbyopia.
If you have it, and once you hit your 40s there’s no way around it, you’re going to need some kind of reading magnification power. So let’s look at the various options to see which is right for you.
Again, if you already are wearing corrective eyeglasses, multifocal lenses will most likely be your best option. So let’s start with bifocals.
The invention of bifocals is credited to Benjamin Franklin, who ingeniously took one pair of glasses with a distance-vision prescription and another pair of glasses with a near-vision prescription. He cut each lens in half horizontally. Then he put the two pairs of glasses together, with the distance-vision lens half on the top and the near-vision lens half on the bottom. Voila: bifocals.
Bifocals come in various styles. At Zenni Optical we offer the most popular bifocal lens style, the flat-top 28 bifocal (FT 28). This means that, unlike some bifocals with a round, near-vision (reading-vision) segment lens, the flat-top bifocal is in the shape of a D turned on its side, with the flat part of the D facing up and the curved portion at the bottom. Because of this, it’s also known as a D segment lens. The 28 comes from the width of the bifocal lens, roughly 28 millimeters across.
It’s important to know that, at Zenni Optical, the bifocal segment lens starts two millimeters below the center horizontal line of the lens. So if you select a lens with a height of 30 millimeters (the minimum lens height necessary to accommodate a multifocal prescription at Zenni), the bifocal segment lens will go from the bottom to 13 millimeters up from the bottom. That’s half of the lens height, 15 millimeters, minus two. If you select a lens with a height of 36 millimeters, your bifocal lens will start at 16 millimeters up from the bottom. That’s 18 (half of 36) millimeters minus two.
People who like bifocals prefer having their distance and near vision clearly separated by a visible line. They don’t care, or are less concerned about, what this implies about their age. However, people who don’t like the way bifocals correct their vision complain about the phenomenon known as “image jump”, which refers to the abrupt switch from distance to near vision, which can be disorienting.
Presbyopes who want a smoother blend between distance and near vision tend to prefer multifocal lenses with no visible line separating the larger distance portion and the smaller near segment. These invisible line bifocals (or, more accurately, multifocals) are called progressives.
That’s because the vision “progresses” from distance to near vision with no image jump. In addition, in between the portion of the lens with distance vision and the portion with near vision, there is a portion of the lens that provides intermediate or computer vision.
Let’s look at these no-line multifocal lenses a little more closely. Progressives could also be called no-line trifocals, because there are three fields of vision in the lens with no visible line separating them. This is great for disguising your need to wear “old people’s glasses” but it comes at a cost. Literally, since progressive eyeglasses are, as a rule, more expensive than single-vision or bifocal glasses. But there’s also an aspect to pay attention to in terms of the amount of vision correction on the lens.
The reading-segment lens of bifocals is, as we noted, roughly 28 millimeters across. But with progressives, the reading segment lens is about half that, roughly 14 millimeters across. In addition, there is no vision correction on either side of the reading portion of the lens.
To get a sense of how a progressive lens is configured, think of a mushroom.
Here’s a good mushroom image:
Imagine the cap is the distance-vision section of the lens. Think of the mushroom’s stem as the intermediate and reading portion of the lens, around 14 millimeters wide. People who prefer the wider reading segment provided by bifocal lenses often feel that the progressive lens doesn’t provide a wide-enough near-vision reading corridor.
At ZenniOptical.com we offer a few ways to customize a pair of progressive glasses for your preference when you order glasses online. For example, we ask questions to help us create the right progressive correction for your needs.
The first question we ask is, “What is your primary use for these glasses?” The choices are “General / Office” (the most common) and “Sports, Outdoors or Driving”. If you select General / Office, your lenses will have expanded distance and reading portions and a narrow intermediate (computer) section. If you select Sports, Outdoors or Driving, the lens is optimized for outdoor use. It has an increased distance and intermediate section but a smaller reading section.
The next question we ask is, “Where will you wear the glasses on your nose?” You have three choices: high on my nose, middle of my nose or low on my nose.
If you choose “high on my nose” the progressive section of the lens will begin at the exact horizontal midpoint on the lens. Again, with a lens height of 30 millimeters, the intermediate (computer) vision section will be at 15 millimeters up from the bottom. However, if you select either middle or low, the intermediate (computer) vision section will be at 17 millimeters up from the bottom, meaning two millimeters about the center horizontal line.
This is the opposite of bifocals, where the correction starts two millimeters below the center horizontal line.
Progressives won’t work for everyone, though. Some people respond adversely to the lack of a visible line separating the three focal fields, to the point of feeling dizzy or nauseous while wearing progressives. For most first-time progressive eyeglasses wearers, this goes away in a few minutes or a few days.
For some people, however, the discomfort they feel wearing progressives never goes away. Moreover, wearing a pair of multifocal glasses, bifocals or progressives, can be dangerous for some people, according to research published by Investigative Ophthalmology & Visual Science. This study found that people wearing either bifocal or progressive glasses are more than twice as likely to fall when wearing multifocal glasses than they are while wearing single-vision glasses. This increases if the wearer is walking downstairs.
People who feel they might have a hard time maintaining their balance while wearing multifocal glasses, or who have tried and dislike bifocals and progressives, would very likely do better with separate pairs of single-vision glasses for distance, computer and reading vision.
Single-vision distance glasses are used for seeing distances roughly two feet away or more. Single-vision intermediate (computer) glasses are used for seeing distances between one-and-a-half and two feet away, basically how far away a person usually is from a computer screen. Single-vision near (reading) glasses are used for seeing objects six inches to one-and-a-half feet away, roughly where you would hold a book you are reading.
For single-vision distance glasses, all that is needed are the plus or minus numbers in the Sphere (abbreviated SPH), Cylinder (CYL) and AXIS sections of a prescription. Ignore the plus number (it will be the same for both eyes) in the NV-ADD (Near-Vision reading ADDition) section of your prescription till you are ordering intermediate and reading glasses.
For single-vision reading glasses, it’s a little more complicated, although it just requires a bit of grade-school arithmetic. Take the plus number in the NV-ADD section of your prescription and add it to the numbers in the SPH section. For example, if you have -1.00 in your SPHs, and +2.00 in the NV-ADD, when you add these two numbers together, you end up with +1.00 in the SPH section. That gives you near single-vision.
Remember, if you are ordering single-vision reading glasses, you will need to lower your distance vision pupillary distance (PD). Your PD is the measurement, in millimeters, between the middle of one pupil to the center of the other.
If you have a single PD number, which would be one number between 50 and 75, subtract three. For example, let’s say your distance vision PD is 63. Lower this by three, to 60, for single-vision reading glasses.
However, you may have a dual PD, which is the measurement from the center of each pupil to the center of the bridge of your nose. In this case, you would have two numbers, each somewhere between the mid-20s to the mid-30s. These two numbers should add up to the single PD number. For example, if you had a dual PD of 31.5 in the right eye and 31.5 in the left, your PD would add up to 63. Therefore, to get your near-vision dual PD for single-vision reading glasses, you would lower each eye’s PD by one-and-a-half, since combining two of that number adds up to three. That would be 60, just as it is if you have a single PD.
For single-vision intermediate (computer) glasses, if you take your NV-ADD number and divide it in half (+2.00 divided by 2=+1.00), then add that to your -1.00 SPHs (+1.00 + -1.00=0.00), you get your intermediate (computer) single-vision. You don’t have to change the PD at all, but you could lower it by one or two millimeters, if you have a high PD (over 66).
If you want to use a pair of bifocals to reconfigure your prescription to get computer vision in the top part of your lens and reading vision in the bottom, do the same thing you would do for single vision computer glasses.
Divide the NV-ADD in half and add this half number to the SPHs. But this time, leave the remainder in the NV-ADD section. That’s how you would get computer vision in the top part of the lens and reading vision on the bottom.
It’s as simple as that.
Tuesday, December, 17 2013 by Matthew Surrence
Have you seen the movie Gravity? Did you see it in 3-D?
If so, you probably found yourself marveling at the amazing technological effect of seeing Sandra Bullock and George Clooney tumble through a very realistic depiction of the depths of outer space.
But you probably never find yourself marveling at the even more amazing technological effect of seeing everything in the world in 3-D – achieved by simply having two eyes, as well as a brain that blends the images your eyes see.
Very simply, this is depth perception, meaning the ability to see things in three dimensions – length, width, and depth – and to perceive how near or far away people and objects are.
One way humans perceive depth is by having eyes that are spaced a little bit apart. This is contrary to certain animals that tend to be prey, and have evolved so that their eyes are on either side of their head to enable them to spot predators. (Predator animals, on the other hand, or paw, usually have eyes positioned closely together, like humans, to enable them to spot, chase, and swoop down upon prey.)
Like those clunky 3-D glasses you wore while watching Gravity, human eyes spaced a little bit apart see two slightly different images, based on each eye’s position on your face. These two slightly different images are called binocular visual cues. They’re called binocular because the images are seen by two eyes.
Here’s a fun way to test your binocular vision. Take a look at the picture of the baseball below:
Now hold up one finger about six inches away from your face, in front of the picture of the baseball. If you focus your eyes on the baseball, you will see two somewhat transparent images of your finger, on either side of the baseball.
Now focus your eyes on your finger. You will see two somewhat transparent images of the baseball, on either side of your finger. That’s depth perception.
Here’s another way to test your depth perception, and to see whether one of your eyes is dominant.
Hold your finger in front of the baseball, just like before. Focus on the baseball and close your left eye. Your finger should appear to the left of the baseball. Now open your left eye and close your right eye. Your finger will seem to jump to the right of the baseball.
Once again, as in the previous test, if this is what you see, you have binocular – also known as stereo – vision. However, you may have faulty depth perception if you experience any of these things:
- You can see your finger better on one side than the other.
The view of your finger is larger with one eye than with the other.
- One eye’s finger image appears right over the baseball, while the other one is far to the left or right.
- You can only see one finger image.
If you do experience any of these things, it would be a good idea to get your eyes checked by an ophthalmologist or an optometrist.
But what if you have sight in only one eye? Do you still have depth perception, even if you don’t have binocular (stereo) vision?
Yes! Here is a way to test your one good eye for depth perception.
Let’s say you are doing this indoors. You will need stationary objects in three different distances from you: one object close to you, one a little farther away, and one still farther away from that one.
Let’s try this with three objects you may find indoors: a chair (close to you), a filing cabinet (a little farther away), and a table (farther away).
You can do this outside, too. Try it with, say, a bush (close to you), a tree (a little farther away), and a house (farther away).
Of course you don’t have to use these three indoor and outdoor objects, in these three positions. You can use them in different positions, or you can use three other objects, as long as the one farthest away is large enough so you can see it well.
Focus on the object in the mid-distance range – the table if you are inside, the tree if you are outside, if you are using those objects. Then walk from side to side.
As you focus on the midrange object, perhaps the filing cabinet or tree, you will see the object closer to you (the chair or the bush) move to the opposite direction from where you are walking. You will also see the object farther away (the table or the house) appear to move in the same direction that you are moving.
If you can see this with one eye (if you are sighted in both eyes you can close one eye while you do this), you have depth perception!
Another way either one or both eyes can perceive depth is by perspective – which means how objects appear based on the position of your eyes in relation to the object.
Here’s a very common way we perceive perspective. When we’re standing on the ground and looking straight down at parallel lines, they appear parallel:
If you click the below link it will take you another tab. Click the red “add perspective” ball, and you’ll see the lines converge (and be sure to come back when you are done). It’s like when you look at railroad tracks off in the distance as they approach the horizon. They appear to meet at what is called the “vanishing point”:
Just like the way perspective can trick the eye into seeing parallel lines that appear impossibly to meet, artists can use perspective tricks to create other optical illusions. Look at this one, created by the German psychiatrist Franz Muller-Lyer in 1889:
The two parallel lines are the exact same length. You can prove it with your ruler. But the line on the top appears longer, because our brains perceive the inverted angles as lengthening the line.
What causes this? Theorists have advanced various explanations, none proven. If you are interested in exploring this further, you can read the explanations at the link below, and test their validity yourself:
Your perspective affects not just your view of distance, but the appearance of colors and hues you perceive as well. Check out this picture:
The gray bar across the middle of the picture appears lighter on the left and darker on the right. But that’s only because of the contrast between the gray bar and the different shades of gray in the background. The background is darker on the left and lighter on the right. Despite its appearance, the gray bar is actually the same color on the right and left.
In addition to appearing to vary shades of a color, sometimes our visual perspective can cause us to see colors that are not actually there. This is because our brains can perceive color in relation to other colors that are present. Take a look at this optical illusion, follow the simple instructions, and notice if you see green grass:
These optical illusions are all results of perspective – what you perceive as true is determined by your perspective, a principle that can apply not only in vision but in many other aspects of life, as well!
As you ponder this, here are some other fun optical illusions to look at and share with your family and friends, to get their perspective, too!
Tuesday, December, 10 2013 by Matthew Surrence