First Contact (Lens)

got laser eye surgery. Long time listeners of tech Stuff probably have recollections of the episode we did where I talked about my laser eye surgery and I totally squicked Chris Pallette out. He was turning green by the end of that episode. It was awesome. Well, by the time I was wearing contact lenses, disposable contacts were readily available, but it took a long time to get from the earliest experiments to the point where you could buy a pack of one use contact lenses and where a fresh

pair every single day. So we're gonna talk about how contact lenses work, how corrective lenses work, how vision works, how all of this was invented, and the changes that have happened since the earliest experiments with corrective lenses. Now, before we talk about contact lenses in the renaissance, because trust me, that's gonna happen. Let's talk first about how vision works. Now, we have to start with light. Vision is all about light and how our bodies direct light

to the retina's. The retina is where are light sensing cells are. Those are the rods and cones. Those are specific specialized cells in our eyes. More on those in just a second. So imagine the retina is kind of like a solar cell in a solar panel. It's the part that takes light and converts it into an electrical impulse. Now in our case, it's not going to feed juice to a battery or run a light bulb or something. Instead, it's a signal that goes to the brain, which then

interprets that electrical impulse as vision. The eyes are essentially part of the brain, but if we think of them as being separate, you could say the brain doesn't really deal with light at all. It just accepts those electrical impulses. The eyes handle all the light stuff on behalf of the brain. So the eye itself has several layers. The outermost layers are made of oil, water, and mucus. Yum yum. Now, Those layers keep the eye hydrated and they protect the

eye from foreign bacteria. Collectively, those materials make up what is called the tier layer. Under the tier layer is the cornea and the sclera. The cornea itself has five layers. Outermost is the epithelium, then you have the bowman's layer, then the stroma, then decimays membrane, and innermost is the endothelium. The cornea's main purpose, besides providing some structure to the eye, is to focus the light coming into the eye towards the retina. The sclera is the white part of the eyeball.

It's continuous with the cornea in the front of the eyeball through a junction called the limbus, and the sclare is really dense connective tissue. Behind the cornea, you have the interior chamber, which is filled with a fluid called the aqueous humor. This fluid helps nourish the cornea from the inside. So you've got fluids on either side of the cornea that keep it hydrated, the tier layer on

one side and the aqueous humor on the other side. Next, if we keep going into the eye, which is kind of a gross way of saying that is the iris and the pupil. The iris is a layer of tissue that can adjust the size of the pupil, so I can dilate or constrict to allow either more light in or less light in. So if it's really bright, the iris can constrict and that limits the amount of light

coming into the eye. And very low light, the iris can dilate the pupil and allow what little light there maybe to pass through the eye and give some low light vision. Behind the iris is a transparent lens which has four layers of its own, the capsule, subcapsular epithelium, the cortex, and the nucleus. The lens focuses lights so that passes through the next section of the eye, called the posterior chamber, through a jelly like substance called the

vitreous humor before the light hits the retina. The retina has ten layers with those rod and cone cells I mentioned earlier. The rod cells are responsible for vision and low light situations, and the cone cells are responsible for color vision and for finer details. These cells, when stimulated by light, trigger chemical reactions that form a chemical called activated rhodopsin, which generates electrical impulses in the optic nerve, and that's where we no longer have to worry about light. Now.

For vision to work, the lens in our eye has to be a will to focus the light properly on the surface of the retina. If the focal point for light is in front of or behind the retina, then we're gonna have problems with our visual focus. So if your eyeball is too long, the lens will focus the light in front of the retina instead of on the retina, and you will have what is called myopia, also known

as near sightedness. This means you'll be able to see things in focus if they are relatively close to you, but the further away they get from you, the more out of focus it appears. If your eyeball is too short, then the lens will focus light on the point behind your retina, and you'll have hyperopia or far sightedness, meaning you can see things further away more clearly than things that are closer to you. Corrective lenses change the course of light as it passes through the lens before it

has a chance to hit your eye. The lens you wear is making a correction to compensate for your near or far sightedness. There are also corrective lenses that can correct for other things like a stigmatism, and a stigmatism is an uneven curvature of the cornea, which in turn can distort vision. And I'll talk all about that a little bit later in this episode, but first I want to talk about some history of corrective lenses in general,

because it's really fascinating. I knew a little bit about this before I started doing research, but the more research I did, the greater appreciation I had for the countless number of people who made contributions to our knowledge to make corrective lenses of possibility. So the concept of using magnification to augment eyesight dates back at least to ancient

Egypt circa the fifth century before the Common Era. Egyptians figured out how to produce a type of magnifying glass, and there's some evidence to suggest that this was not a new idea even as early as the fifth century b c. E h. This knowledge eventually made its way to Rome. Seneca the Younger, who was interested in optics, lie mirrors, and other such matters, was said to have created some special glasses some lenses for the Emperor Nero to use to aid his eyesight, though the sources for

this information may not be the most reliable. As it turns out, you get accounts from Rome that were written hundreds of years after the events they are describing, and it's not always reliable information. But generally the story is that Nero was using sunglasses made out of emerald to shield his eyes from light and to improve his eyesight somewhat.

Whether or not that meant emerald as in the precious gemstone that we're familiar with, or some other substance has been an issue of debate, and frankly, it gets so wibbly wobbly that I'm willing to just leave it at that. There are other people we can talk about, however, such as the Islamic scientist Al Hasin, who advanced human understanding

of optics and light. He was incredible. He also ended up establishing what would later on be adopted as essentially the scientific method, although it would be centuries before anyone

else thought to do this. His works in the eleventh century found their way into medieval Europe and were translated into other languages, and he was the first recorded scientist to offer up a hypothesis on how vision works, and at least for the basics, he was pretty much spot on the origin of spectacles, as in glasses worn on the face in order to correct for vision, has been

lost to the mists of time. Generally speaking, most experts believe that the invention dates to the late thirteenth century in Italy, but the history of this hinges and I used the term purposefully as a pun upon a single pair of Rivet type spectacles that was uncovered in Italy. It was discovered in the Veneto region of Italy, which is the area where place is like Venice or Padua to wed In, Padua or Verona. Those are all in

that region. Now, there are other areas in Italy that sometimes claimed to be the birthplace of spectacles, but evidence supporting such claims is difficult to see. Ironically, I think there may be a lot of vision based puns in this episode. That warning probably arrives a little too late, but hey, hindsight is Scholarship on spectacles does date back to the late twelve hundreds. The English friar Roger Bacon. Fried Bacon wrote a piece titled Opus Magus sometime around

twelve sixties six Common era. This piece was sort of a proposal. Bacon was trying to get support from the Pope to provide financial support for a more thorough examination on optics and the scientific principles of corrective lenses. Such support was not forthcoming, and as far as we know, Bacon left it that. Though he may have carried out some practical experiments as well using ground crystal, we just

don't know for sure. There is a report that states that a priest named Nicholas Bullet used spectacles when he signed official papers, and there's a Venetian government document from twelve eighty four that lays out the rules of using crystal rather than white glass for the production of lenses

in order to keep the quality high. By a Dominican friar from Italy named Giordano the Revolto wrote a sermon in which he referenced the creation of spectacles dating no more than twenty years earlier, which would put the creation of corrective lenses sometime around twelve eighty five. Whatever the actual origins, we know that corrective lenses in the form

of spectacles preceded telescopes and contact lenses by a few centuries. Now, before I transition from glasses to contact lenses, well, let's talk for a second about how these lenses actually work. The physics remain the same, even though the forms are slightly different. First, a lens bends light. Light will bend

towards the thickest part of a lens. So if you make a concave lens, also known as a minus lens, you're making one where the center of the lens is the thinnest part and the edges are the thicker parts of the lens that bends light away from the center. And it's tricky to talk about this without visual aids, but I'm gonna do my best. Now, imagine we're looking

at a concave lens from the side. So from the side, it looks like it's thick on the on the outer edge, and then it bends inward on both sides, so we're looking at it kind of in silhouette. Now, imagine that parallel beams of light are coming from the left side of our view. We're gonna call this the front of

the lens. When those beams of light hit this concave lens, they diverge, They start to point outward toward the various thick parts of the lens, the edges, and that continues on the right side of our view, which we're gonna call the of the lens. The beams of light hitting the upper half of our lens bent upward. The ones

hitting halfway down our lens are bending downward. Now, if you were to look at these rays of light on the right side, the ones that are now bent going up or down, uh at a diagonal from the lens, and then you were to take those pathways and extend them back toward the left side, the front side of the lens, those beams would look like they have converged

on a point in front of the concave lens. So you take those bent rays and you make them straight lines onto the front side, they're all going to converge at this one point. That's the focal point of the concave lens. It's actually in front of the lens, not behind it. The distance from the lens to that point is called the focal length. The stronger the lens is, the further the focal point will be, and therefore the greater the focal length will be. Now, with convex lens

is it's quite different. Let's imagine again we're looking at a lens from the side. This time the lens bulges outward toward the middle, and it's thinner at its edges, the opposite of the concave lens. So parallel beams of light are coming from the left side the front of the lens. When they hit the lens, those beams are

bent inward towards the center. The beams continue out through the back of the lens and they converge on a point behind the lens, and technically they keep going after converging, continuing in a straight line. But never mind that for now. That point of convergence is the focal point for the convex lens, so that focal point happens behind the lens, and the stronger the lens, the shorter the focal length is. In other words, the closer the focal point is to

the lens itself. So a concave lens has the focal point in front the convex lens as the focal point behind. Using the right type of lens at the right strength can compensate for conditions like myopia or hyperopia. We measure the strength of a lens in a unit called diopters. It's a measurement of how much how much the light

is actually bent within the lens itself. The higher the diopter, the stronger the lens, the more light is bent as it passes through, and we use plus or minus to indicate the type of lens convex versus concave in this case.

I'll talk more about this a bit later when we talk about prescriptions, which were developed in the nineteenth century, but a basic understanding of how Lee's lenses could be fine tuned to correct vision dates back at least to sixteen o four Common Era, when Johannes Kepler described what the retina does and proved that a concave lens could correct myopia and a convex lens could correct hyperopia. All right, now, I'm ready to finally talk about contact lenses. But first

let's take a quick break to thank our sponsor. All Right, I said I was gonna talk about contact lenses in the Renaissance. Let's do it. In the early sixteenth century the hundreds, there was a dude who is synonymous with the Renaissance, who made some observations that frequently are cited as the origins for contact lenses, and that dude was

Maestro Leonardo da Vinci. He theorized that water had the ability to change the direction of light and therefore alter vision, and did some experiments with dunking people's faces and water and looking at things, and then said, hey, you know what, maybe if you used a water filled glass that you could dunk your eye into while it's you know, still in your head, you could bend light and perhaps even

correct for failing vision. He wrote up his ideas in a fifteen o eight publication, and he titled it Codex of the Eye Manual d Because the dude wrote a lot. Da Vinci drew up a few sketches that illustrated his ideas. Now, the problem was that his solution lacked practicality, because you could fill up two glasses with water, and you could hold those two glasses up against your eyeballs, but obviously water would start to leak out. It just wasn't sustainable.

Da Vinci apparently toyed with the idea of an invention that would include a funnel so that you could refill the glasses as they ran out of water, but again it wasn't really a practical solution. A bit More than a century later, the philosopher Rene Descartes, who, as Monty Python would explain, said I drink, therefore I am tried

to build onto da Vinci's work. In sixteen thirty six, Descartes published a paper in which he proposed a lens that could be placed directly against the eye, a contact lens, in other words, to correct for vision. So this wasn't a corrective lens all by itself. It wasn't like the lens had been ground down so that it had the exact shape it needed. It actually was to be attached to a long tube that you would then fill with you guessed it water. The water would provide the light

bending properties needed to correct for vision. But this would mean you'd end up looking like a character from a text avery cartoon, with the tubes bulging out from your eyes. And it would also mean you'd be completely unable to blink. And while people who wear contacts are willing to put up with some discomfort at times, it's asking a bit much even for them. To be fair, both da Vinci and Descartes were talking about ideas rather than practical solutions.

They saw the potential for a solution further in the future, but it was one that they themselves could not attain, and it would take a couple more centuries to get there. Now why is that, Well, largely it was because our ability to create lenses that can conform to the shape of the eye was a relatively late development. In the nineteenth century, some folks toyed with the idea again. One

of them was an English scientist named Thomas Young. Young thought Descartes was really onto something, so he built a prototype of a contact lens based off that tube lens description Descartes had proposed. He attached these water filled lenses to his eyes. He used wax to do it. This was in eighteen o one, so I assume he stopped screaming sometime in eighteen o two. I should point out I'm joking about the screaming. He was using a soft wax to create a seal. It wasn't hot wax or

anything like that. I had to do the research to make absolutely sure. Thomas Young would go on to map the normal visual field for the average person, which would become one of the foundations for modern optometry. In eighty seven, Sir John Herschel, who is just plain old John Herschel. At that time he had not yet been knighted, wrote about grinding a lens so that would conform precisely to the shape of the eye. To do so, he suggested making a mold of a person's eye, using quote transparent

animal jelly end quote. There are no records over whether he ever tried to make such a mold, but I will have nightmares for my natural life involving transparent animal

jelly in my eyes. Thanks decades later, a Swiss physicist named A. E. Thick made a spherical glass structure to correct refractive errors for a person's eyes, and that same year Edward Kelt, who was a French optician, made fitted glass lenses, and a German medical student named August Mueller was using glass discs fitted against his own eyes to attempt to treat his myopia. These contacts were all rigid

and were unpleasant to wear. For one thing, they fit around not just the cornea, but over the sclera, over the white outer layer of the eyeball. Covering the sclera deprives the cornea of oxygen. Glass is impermeable to oxygen. Oxygen cannot pass through it, so if you wore the lenses. You would not only tire out your eyes because the lenses were heavy, but it would become painful to wear them after a short while, like half an hour or so,

so these were not an ideal alternative to spectacles. Most estimations say that very few people ever wore those early glass contact lenses, perhaps five people total, and you couldn't go for more than four hours tops, because those lenses were cutting off that sweet supply of oxygen that eyes need, and you would just be suffering intense amounts of pain. The first contact lenses made of plastic date from nineteen thirty eight when THEO. O. Brig and John Mullen introduced them.

They used polymethyl methac relate, also known as p M m A. It had originally been used as a binder for paint, so clearly you should shove that into your eyes. These early contact lenses still had glass as well, so they were a hybrid of glass and plastic. It wouldn't be an till nineteen forty, when Heinrich Vulk started using all plastic lenses that this trend would begin to change. Even so, the lenses still covered the entire surface of

the eyeball, not just the cornea. In ninety eight, an optical technician named Kevin Toohey was awarded a patent for his big discovery when he realized you could use smaller contacts that did not cover the whites of the eyes. This resulted in a slightly more comfortable contact lens that could be worn for longer periods of time. Towey actually

discovered this totally by accident. He had been working on creating a full contact for the eye, one that would cover the sclera, and it was gonna be made of a new type of transparent plastic. But the part that would have covered the sclera broke off while he was trying to make it, and he thought, well, what would happen if I just used this part of a lens, the part that would fit over the cornea but not

the sclera. Would it still work? So he tried it out and he discovered that it would stay in place even after he was blinking. So that was a revolutionary change. It meant that no longer did they have to build contact lenses that would go over the entire exposed part of the eyeball. It could just go over the cornea. Even so, these lenses were still hard lenses, and they

were not the most comfortable thing to wear. They also had a small lip on them, which would make it easier to insert and remove the lens, but also meant that sometimes your eyelid might catch on it, or you might rub your eye in such a way that the lens would just pop out. And thus you have the birth of the classic physical comedy gag of a character suddenly exclaiming that he or she has lost a contact lens and that everyone must stop everything they are doing

and help track it down. Kennedy Otto. Victorrell also made an incredible contribution to contact lenses. He created the first soft contact lens. He used a cross linked hydra of Fhilick material and I'm gonna try and say it, but this might take a few attempts he called it. Or actually the material itself is called hydroxy ethel methacrolate. Hey, I got the first try. It's easier. Name is hima h E m A. And he discovered this in nineteen

fifty two. He noted that this material, which he was not making specifically for contact lenses, he was just working with plastics. He noted that it could retain moisture, it could absorb, and when it did absorb moisture, it became flexible, but it would also snap back to its original shape, so while you could bend it, if you let go, it would go back to the way it was supposed

to be. And he figured this could be a good material for contact lenses, since even the plastic ones that have been made up to that point still at disadvantages. They were still impermeable to air. So he began working on this project for his employer, which at the time time was the Institute of macro Molecular Research in Czechoslovakia or what was then Czechoslovakia. But his bosses were not convinced that this was worthwhile research, so they told him

to knock it off and get to work on other stuff. So, rather than abandoned this idea completely, he moved his work to his home and he used a jerry rigged system to start making these contact lenses. That system consisted of a gramophone, in other words, the predecessor to a record player. He used that to create a spinning motion and an erector, set a mechanical kit for kids to work with, and

together he used these to make a spin casting machine. Now, spin casting is a technique that has been used for lots of different stuff, not just contact lenses. In this particular case, it was making a soft, breathable contact lens, but spin casting can be used for lots of different things.

So what exactly is it. Well, let's stick with contact lenses for the explanation, and since that's the subject at hand, the conventional way to make contact lenses up to that point was to use a cast molding process and a press. So you would create a mold of the shape that you want your contact lens to be, and you would put some plastic in that, and then you would use a press to press down into the mold and form the plastic into the correct shape. But this method had disadvantages.

When the press would withdraw, sometimes it would leave scars and aberrations upon the lens itself. And this is the inside of the lens, the part that would go against your eye, so it could potentially create damages that could in turn hurt your eyes. The edges of these contact lenses were also prone to defects and unevenness, so it can make the contact lens less accurate and more uncomfortable

to wear. The spin cast method works differently. You put a small amount of liquefied plastic and you drip that into the old, and the mold then is spun in a circle. This creates the force necessary to draw out that plastic to spread it evenly over the mold. There's no press that makes physical contact with the lens, so there's nothing to leave behind those marks or scars or

to create uneven edges. Now he secured a patent for his contact lens production method, and then Bauschan Loam swooped in to purchase the patent to put it into use. In nineteen seventy two, their soft contact lenses were ready for the market. In between his first experiments and Balsh and Loam's introduction of those contact lenses, the US Food and Drug Administration decided to classify soft contact lenses as a drug. Now, that might sound strange to you, because

these are contact lenses you wear in your eyes. They're not something you ingest, they're not something you inject in yourself. You don't absorb them. But you have to remember there was a lot of development in the field at the time. Tons of companies and inventors were all rushing to experiment

with different materials to create better contact lenses. The f d A wanted to create protections to put in place to make sure those materials passed numerous tests before they were ever marketed to consumers to make sure they were safe to use, because you wouldn't want to find out that your brand new contact lenses were actually toxic after they hit store shelves. Thus the necessity to classify them as a drug so they could pass all these numerous

check marks before they could hit stores. Now more improvements have come along, mostly in the materials that we've used to create contact lenses. In Dr Michael bay Uh, He's, as far as I know, not related to the Hollywood director who makes things blow up, created a disposable contact lens. So until two, when you've got a pair of contact lenses,

you're meant to use those indefinitely. You would only replace them if you had lost one or damaged one, or if your eyesight had changed and a new prescription was needed, but that also presented a hygienic issue. Contact lenses can develop what is called protein build up, and if you've ever seen a contact lens that has white or cloudy marks on it, that's likely protein build up, and if you were to put those lenses in your eyes, you might feel some discomfort, your vision might not be all

that great. Worse, if your contact lenses get damaged, they could in turn scratch your corneas, which not only can hurt, but can make you sensitive to light or even lead to a corneal us ulcer, which can potentially damage your vision permanently. And lenses can also carry bacteria and germs, which can lead to infections like conjunctivitis and karatitis. So disposable contacts reduce those risks. Because you're not using the same pair of lenses indefinitely, there are fewer opportunities to

shove gunk in your eyes. In other words, Also, if you ever have contact lenses that have protein build up, it's the one time where you're actually supposed to kind of scrub them with your solutions that you can clean them off, because just washing them in solution is not going to remove that protein build up. In general, you're not supposed to scrub contact lenses at all. They're very easily damaged, but that's one case where you are supposed

to do it. Although I would argue at this stage, just go out and buy new context because you don't want to mess with that stuff. The first disposable content lenses were meant to be warned for a couple of weeks before you replace them. Dr Bay named them m I A lenses MIA not missing an action that m I A was the actual Those were the first initials of his name, his wife's name, and his daughter's name,

So it's Michael Inga and Annette. In case you ever have pub trivia and you're asked, what did the initials M I A stand for? As far as contact lenses, Michael Inga and a net. His design was purchased by a company called Johnson and Johnson, famous company. They tweaked and rebranded the technology to create their own disposable contacts, and they launched that brand in nineteen eight seven under the name AC View in eight CIBA I assume that's how we pronounced the name of the company. C I

B A created contact lenses using silicone hydrogels. Now, the big advantage of the hydrogel material was that it was particularly permeable to oxygen, so it can allow oxygen to pass through the contact lens and allow the cornea to get that sweet sweet oxygen. It craves so dearly. The first daily disposable lenses would debut in n Ron Hamilton's, who was an inventor in Scotland, gets credit for creating the first example, which he called the Premier Award Lens.

Balsha and Loam would purchase Hamilton's company and rebranded the lens the Soft Lens One or the Soft Lens One Day. Hamilton's would go on to launch a different company called provis Now. There have been numerous improvements in materials and processes to contact lenses over the years, but the basic principles remained the same. Contact lenses bend light so that eyes can focus, which is a little reductive because there are contact lenses that are meant to protect eyes that

have been damaged through injury or illness. There are some that are meant to treat diseases, not just a problem with vision, but actual diseases of the eye. There's also cosmetic contact lenses that don't have any corrective nature to

them as well. But I'm going to focus pun intended un corrective contact lenses since that's such a common use for them, and that brings us to a couple of questions like, how does an optometrists determine what prescription you need when you go to get glasses or a contact? And where did that whole thing come from? Anyway, Well, in the next segment, I'll tell you, but first let's take another quick break to thank our sponsor. All right, So where did the concept of prescriptions come from? And

how do I doctors determine what a person needs? So, like most innovations, the story is way more complicated than some really smart dude came up with it and changed everything. In reality, the journey to optometry was a long one and many different philosophers, physicians, and inventors contributed to our understanding of vision and optics. So, for example, Benjamin Franklin famously invented bifocal lenses for spectacles in seventeen eighty four.

A decade later or so, John Dalton first described the condition of color blindness. As I mentioned earlier in this episode, Thomas Young mapped out the normal human visual field in eighteen o one. There was a physician an inventor named Herman von Helmholtz which might be the best name ever, who invented the opthalmoscope in eighteen fifty one. Now that's an instrument that gives the physician the ability to see into the interior of a living eye without you know,

having to cut into it. So this would be the instrument that shines a light in your eye when the eye doctor is taking a look to make sure that everything look good. The use of that was while allowed doctors to slowly catalog what a healthy human eye should look like and what the various signs of diseases or conditions that can affect the eyes looks like. So it helped catalog all of that stuff because now they had a tool where they could actually see it in living people.

Helmholtz did not stop there. In eighteen fifty six, he published an enormous work in three volumes. The English title for his work is Handbook of Physiological Optics. Six years later, in eighteen sixty two, there was a fellow named Herman Snellen who created a series of tests to help determine a person's visual acuity, including an eye chart. Probably seen examples of the kind of eye chart he created. Now,

to be clear, pun intended. Many physicians were using ie charts at that point, but Snellen's became a standardized approach, which had a benefit of working across regions and making it easier to determine what type and strength of lens a patient would need in order to correct their vision. And this is kind of where we get to the concept of twenty twenty vision. If you have twenty twenty vision, it means you can see the same detail at a distance of twenty feet or six meters as someone who

has what we consider to be normal vision. It also can be called six six vision for meters. Now, if you had twenty forty vision, it would mean that when you stand twenty feet away from an eye chart, that i chart would look to you as if it were forty feet away for someone with normal vision. In other words, you would see the same amount of clarity that a person with normal vision would see at forty feet, but you would be twenty feet away, so you would see

things less clearly than the average person. If you had vision that was at twenty four hundred, that means your vision is pretty bad that you would see a chart at twenty ft away with the same amount of clarity as a normal person looking at that same chart, but there are four feet away, So you see how that scale quickly changes things. You can have better than normal vision.

Of course, if you have twenty ten vision, it means that you can see the same level of detail at twenty feet that someone with normal vision would be able to make out from ten feet away, so they would have to be twice as close to the chart to see the same level of detail that you see. So that would mean you have a more keen eyesight than the average person. I technically had that shortly after I

had laser eye surgery. My vision was somewhere around twelve, meaning that I could see better than the average person for these sort of eye charts. But don't get too excited about it. For one, eyesight does tend to deteriorate over time, so you're not guaranteed to have that amazing eye sight through the rest of your life. My eyesight

slowly deteriorates even after I've had the laser surgery. Also, there are animals that visualuity that are closer to like twenty three, so let's not get too excited by this. Visual acuity is just one element of vision. By the way, there are other considerations such as peripheral awareness or eye coordination or depth perception, color vision, and the ability to focus on points near or far from your eyes. But the eye chart definitely helped move things towards a standard.

In eighteen sixty four, FC. Donders, who actually worked with Snell and the guy who created the eye charts, published Anomalies of Accommodation and Refraction of the Eye. So in that work he laid out the principles that would become the basis for prescriptions. So let's take a quick moment to talk about the form prescriptions take and what that

actually means. Now, a full prescription, one that someone with you know, eyesight where they might need bifocals, typically has four parts to it, and I'm going to use a hypothetical prescription in order to give an example. So let's say that you've got a shorthand prescription written out for you and it reads like this two point to five minus one point five zero times plus two point zero zero.

Now that is not a math problem. Those pluses and minuses give you indications for the power of the various lenses. So let's take this piece by piece. That first number two point to five that represents the base strength or spherical strength and type of lens. Spherical lenses correct for myopia or hyperopia, so near sightedness and far sightedness. In our example, the two point to five gives us this information. It's two point to five diopters, remember the units that

tell us how much the lens bends light. And because it lacks a negative sign, it means it's a plus type of lens, which means this is a prescription that is meant to correct for hyper opia or far sightedness. The next number, minus one point five zero refers to

a cylindrical lens. These lenses would look kind of like a a pipe cut lengthwise and they fit within the overall glasses or contact lens, and they correct for a stigmatism and the axis of the lens matches the abnormality of the cornea, So that minus one point five zero tells us it's a minus lens at one point five oh diopters. Actually it's not quite that simple, but I'll get to that in a little bit. The third number

one is the orientation of that cylindrical lens. It tells us the cylindrical lens is oriented at a D seven degrees. The fourth number two point zero zero is a bifocal segment at plus two diopters, and it's always going to be positive for bifocals. If you don't need bifocals, you wouldn't have a number like this trailing at the end of your prescription. What's more, you might see the letters O D or O S on the prescriptions, So what the heck did those mean? The O D means oculus dexter,

and os is oculus sinister. That is Latin for right eye and left eye. So dexter and sinister mean right and left. So if you happen to be left handed like me, you're of a sinister persuasion. Insert evil laugh here. Oh wait uh. Prescriptions can become more complicated than the example I gave you. I should add there are other factors that could be included, and they account for things

such as correction for eye alignment problems and other such issues. Also, eyeglass prescriptions and contact lens prescriptions are not always the same thing. Contact lens prescriptions need additional information such as what the curve of the back surface of the contact lens should be. That's the part that touches your eye.

It also includes stuff like the diameter of the lens, and because eyeglasses are worn in front of the eyes at a sense of around twelve millimeters from your eye, and contact lenses are worn on the eyes, the power of the prescription tends to be different to produce the ideal result. In the Federal Trade Commission ruled that all eye doctors, both optometrists and ophthalmologists, must provide a copy of a patient's prescription upon the end of an eye exam.

That way, the patient can choose the vendor he or she prefers when buying the actual glasses. Now I'm wrapping up here. There's a whole lot more I could talk about, including the way you take lens blanks and grind them down in order to make the proper lens, but that would almost require a second episode. And before I sign off, I think I should also explain what the differences between

optometrists and ophthalmologists, and also what are opticians. So, an ophthalmologist is a medical or osteopathic doctor, someone who actually has a medical degree. They have extensive training in medicine and they specialize in eye and vision care. They have a license to practice medicine and surgery, so they treat eye diseases and conditions. They perform surgical procedures, and they

can also prescribe and fit eyeglasses and contact lenses. They may also conduct research to gain further understanding into eye disorders and diseases. And there's some disagreement about whether or not an ophthalmologist or an optometrist is the best person to go when you are trying to get glasses or contact lenses, and the fights can get pretty nasty because they tend to involve ophthalmologists and optometrists calling each other things. So I'm not going to get into that here. But

what is an optometrist. Well, that's a health care professional, but they are not a doctor, not a medical doctor at any rate. They must receive a Doctor of Optometry. That's an o d Degree, but it's not a medical degree. This is a four year degree from an optometry school, and that's after they've conducted at least three years of college education. So they do hold a doctorate, but they

are not a medical doctor. Their licensed to conduct eye exams and prescribe glasses or contact lenses, and they can also generally prescribe some medications for certain types of eye diseases. And then you have opticians. Now these are technicians that are trained to design, to verify, and to fit eyeglass lenses and frames as well as contact lenses. They do not make prescriptions themselves, so they cannot prescribe the glasses, but they can take a prescription and make the glasses

or contact lenses or fit them to you. They're allowed to do that. They are not licensed to diagnose or treat eye diseases or disorders. And there's also another weird difference between optometrists and ophthalmologists that I discovered as I was researching this episode, and that's how they write out prescriptions. Specifically, that second number I referenced, that's the difference. So remember our hypothetical prescription was two point to five minus one

point five times one plus two point zero zero. Well, that minus one point five zero doesn't just tell us the lens power of the cylindrical lens that was meant to correct an a stigmatism. It also tells us that the person conducting that hypothetical I exam had to be an optometrist because it was a negative value. If it had read one point five zero instead of minus one point five zero, the actual effect in the finished glasses would be exactly the same. It would just mean that

an ophthalmologist had written the prescription. Optometrists always have a negative value for cylindrical lens and ophthalmologists always have a positive value. Now this does change the value for that axis figure as well, so there is a slight other difference between an optometrist and an ophthalmologist prescription. But it really boils down to the fact that optometrists use negative cylindrical lens designation an ophthalmologists use positive cylindrical lens designation,

even though they both do the exact same thing. So wacky, right, I learned something new today, well, guy, That wraps up this overview of where contact lenses came from and how we all got to the point of staring at these charts, and also answering the immortal question better like this or better like this A or B one or two? Man, I'm so glad I don't have to do that anymore. Laser eye surgery rules. If you guys have suggestions for future episodes of tech Stuff, please let me know. You

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