Speaker 1: Get technology with tech Stuff from dot Com. Hey there,
Speaker 1: and welcome to tech Stuff. I am your host, Jonathan Strickland.
Speaker 1: I'm an executive producer here at how Stuff Works and
Speaker 1: all of all things tech. Today, we are going to
Speaker 1: talk about the development of corrective lenses in general, and
Speaker 1: the contact lens in particular. Now, I used to wear
Speaker 1: contact lenses up until a few years ago when I
Speaker 1: got laser eye surgery. Long time listeners of tech Stuff
Speaker 1: probably have recollections of the episode we did where I
Speaker 1: talked about my laser eye surgery and I totally squicked
Speaker 1: Chris Pallette out. He was turning green by the end
Speaker 1: of that episode. It was awesome. Well, by the time
Speaker 1: I was wearing contact lenses, disposable contacts were readily available,
Speaker 1: but it took a long time to get from the
Speaker 1: earliest experiments to the point where you could buy a
Speaker 1: pack of one use contact lenses and where a fresh
Speaker 1: pair every single day. So we're gonna talk about how
Speaker 1: contact lenses work, how corrective lenses work, how vision works,
Speaker 1: how all of this was invented, and the changes that
Speaker 1: have happened since the earliest experiments with corrective lenses. Now,
Speaker 1: before we talk about contact lenses in the renaissance, because
Speaker 1: trust me, that's gonna happen. Let's talk first about how
Speaker 1: vision works. Now, we have to start with light. Vision
Speaker 1: is all about light and how our bodies direct light
Speaker 1: to the retina's. The retina is where are light sensing
Speaker 1: cells are. Those are the rods and cones. Those are
Speaker 1: specific specialized cells in our eyes. More on those in
Speaker 1: just a second. So imagine the retina is kind of
Speaker 1: like a solar cell in a solar panel. It's the
Speaker 1: part that takes light and converts it into an electrical impulse.
Speaker 1: Now in our case, it's not going to feed juice
Speaker 1: to a battery or run a light bulb or something. Instead,
Speaker 1: it's a signal that goes to the brain, which then
Speaker 1: interprets that electrical impulse as vision. The eyes are essentially
Speaker 1: part of the brain, but if we think of them
Speaker 1: as being separate, you could say the brain doesn't really
Speaker 1: deal with light at all. It just accepts those electrical impulses.
Speaker 1: The eyes handle all the light stuff on behalf of
Speaker 1: the brain. So the eye itself has several layers. The
Speaker 1: outermost layers are made of oil, water, and mucus. Yum yum. Now,
Speaker 1: Those layers keep the eye hydrated and they protect the
Speaker 1: eye from foreign bacteria. Collectively, those materials make up what
Speaker 1: is called the tier layer. Under the tier layer is
Speaker 1: the cornea and the sclera. The cornea itself has five layers.
Speaker 1: Outermost is the epithelium, then you have the bowman's layer,
Speaker 1: then the stroma, then decimays membrane, and innermost is the endothelium.
Speaker 1: The cornea's main purpose, besides providing some structure to the eye,
Speaker 1: is to focus the light coming into the eye towards
Speaker 1: the retina. The sclera is the white part of the eyeball.
Speaker 1: It's continuous with the cornea in the front of the
Speaker 1: eyeball through a junction called the limbus, and the sclare
Speaker 1: is really dense connective tissue. Behind the cornea, you have
Speaker 1: the interior chamber, which is filled with a fluid called
Speaker 1: the aqueous humor. This fluid helps nourish the cornea from
Speaker 1: the inside. So you've got fluids on either side of
Speaker 1: the cornea that keep it hydrated, the tier layer on
Speaker 1: one side and the aqueous humor on the other side. Next,
Speaker 1: if we keep going into the eye, which is kind
Speaker 1: of a gross way of saying that is the iris
Speaker 1: and the pupil. The iris is a layer of tissue
Speaker 1: that can adjust the size of the pupil, so I
Speaker 1: can dilate or constrict to allow either more light in
Speaker 1: or less light in. So if it's really bright, the
Speaker 1: iris can constrict and that limits the amount of light
Speaker 1: coming into the eye. And very low light, the iris
Speaker 1: can dilate the pupil and allow what little light there
Speaker 1: maybe to pass through the eye and give some low
Speaker 1: light vision. Behind the iris is a transparent lens which
Speaker 1: has four layers of its own, the capsule, subcapsular epithelium,
Speaker 1: the cortex, and the nucleus. The lens focuses lights so
Speaker 1: that passes through the next section of the eye, called
Speaker 1: the posterior chamber, through a jelly like substance called the
Speaker 1: vitreous humor before the light hits the retina. The retina
Speaker 1: has ten layers with those rod and cone cells I
Speaker 1: mentioned earlier. The rod cells are responsible for vision and
Speaker 1: low light situations, and the cone cells are responsible for
Speaker 1: color vision and for finer details. These cells, when stimulated
Speaker 1: by light, trigger chemical reactions that form a chemical called
Speaker 1: activated rhodopsin, which generates electrical impulses in the optic nerve,
Speaker 1: and that's where we no longer have to worry about light. Now.
Speaker 1: For vision to work, the lens in our eye has
Speaker 1: to be a will to focus the light properly on
Speaker 1: the surface of the retina. If the focal point for
Speaker 1: light is in front of or behind the retina, then
Speaker 1: we're gonna have problems with our visual focus. So if
Speaker 1: your eyeball is too long, the lens will focus the
Speaker 1: light in front of the retina instead of on the retina,
Speaker 1: and you will have what is called myopia, also known
Speaker 1: as near sightedness. This means you'll be able to see
Speaker 1: things in focus if they are relatively close to you,
Speaker 1: but the further away they get from you, the more
Speaker 1: out of focus it appears. If your eyeball is too short,
Speaker 1: then the lens will focus light on the point behind
Speaker 1: your retina, and you'll have hyperopia or far sightedness, meaning
Speaker 1: you can see things further away more clearly than things
Speaker 1: that are closer to you. Corrective lenses change the course
Speaker 1: of light as it passes through the lens before it
Speaker 1: has a chance to hit your eye. The lens you
Speaker 1: wear is making a correction to compensate for your near
Speaker 1: or far sightedness. There are also corrective lenses that can
Speaker 1: correct for other things like a stigmatism, and a stigmatism
Speaker 1: is an uneven curvature of the cornea, which in turn
Speaker 1: can distort vision. And I'll talk all about that a
Speaker 1: little bit later in this episode, but first I want
Speaker 1: to talk about some history of corrective lenses in general,
Speaker 1: because it's really fascinating. I knew a little bit about
Speaker 1: this before I started doing research, but the more research
Speaker 1: I did, the greater appreciation I had for the countless
Speaker 1: number of people who made contributions to our knowledge to
Speaker 1: make corrective lenses of possibility. So the concept of using
Speaker 1: magnification to augment eyesight dates back at least to ancient
Speaker 1: Egypt circa the fifth century before the Common Era. Egyptians
Speaker 1: figured out how to produce a type of magnifying glass,
Speaker 1: and there's some evidence to suggest that this was not
Speaker 1: a new idea even as early as the fifth century
Speaker 1: b c. E h. This knowledge eventually made its way
Speaker 1: to Rome. Seneca the Younger, who was interested in optics,
Speaker 1: lie mirrors, and other such matters, was said to have
Speaker 1: created some special glasses some lenses for the Emperor Nero
Speaker 1: to use to aid his eyesight, though the sources for
Speaker 1: this information may not be the most reliable. As it
Speaker 1: turns out, you get accounts from Rome that were written
Speaker 1: hundreds of years after the events they are describing, and
Speaker 1: it's not always reliable information. But generally the story is
Speaker 1: that Nero was using sunglasses made out of emerald to
Speaker 1: shield his eyes from light and to improve his eyesight somewhat.
Speaker 1: Whether or not that meant emerald as in the precious
Speaker 1: gemstone that we're familiar with, or some other substance has
Speaker 1: been an issue of debate, and frankly, it gets so
Speaker 1: wibbly wobbly that I'm willing to just leave it at that.
Speaker 1: There are other people we can talk about, however, such
Speaker 1: as the Islamic scientist Al Hasin, who advanced human understanding
Speaker 1: of optics and light. He was incredible. He also ended
Speaker 1: up establishing what would later on be adopted as essentially
Speaker 1: the scientific method, although it would be centuries before anyone
Speaker 1: else thought to do this. His works in the eleventh
Speaker 1: century found their way into medieval Europe and were translated
Speaker 1: into other languages, and he was the first recorded scientist
Speaker 1: to offer up a hypothesis on how vision works, and
Speaker 1: at least for the basics, he was pretty much spot
Speaker 1: on the origin of spectacles, as in glasses worn on
Speaker 1: the face in order to correct for vision, has been
Speaker 1: lost to the mists of time. Generally speaking, most experts
Speaker 1: believe that the invention dates to the late thirteenth century
Speaker 1: in Italy, but the history of this hinges and I
Speaker 1: used the term purposefully as a pun upon a single
Speaker 1: pair of Rivet type spectacles that was uncovered in Italy.
Speaker 1: It was discovered in the Veneto region of Italy, which
Speaker 1: is the area where place is like Venice or Padua
Speaker 1: to wed In, Padua or Verona. Those are all in
Speaker 1: that region. Now, there are other areas in Italy that
Speaker 1: sometimes claimed to be the birthplace of spectacles, but evidence
Speaker 1: supporting such claims is difficult to see. Ironically, I think
Speaker 1: there may be a lot of vision based puns in
Speaker 1: this episode. That warning probably arrives a little too late,
Speaker 1: but hey, hindsight is Scholarship on spectacles does date back
Speaker 1: to the late twelve hundreds. The English friar Roger Bacon.
Speaker 1: Fried Bacon wrote a piece titled Opus Magus sometime around
Speaker 1: twelve sixties six Common era. This piece was sort of
Speaker 1: a proposal. Bacon was trying to get support from the
Speaker 1: Pope to provide financial support for a more thorough examination
Speaker 1: on optics and the scientific principles of corrective lenses. Such
Speaker 1: support was not forthcoming, and as far as we know,
Speaker 1: Bacon left it that. Though he may have carried out
Speaker 1: some practical experiments as well using ground crystal, we just
Speaker 1: don't know for sure. There is a report that states
Speaker 1: that a priest named Nicholas Bullet used spectacles when he
Speaker 1: signed official papers, and there's a Venetian government document from
Speaker 1: twelve eighty four that lays out the rules of using
Speaker 1: crystal rather than white glass for the production of lenses
Speaker 1: in order to keep the quality high. By a Dominican
Speaker 1: friar from Italy named Giordano the Revolto wrote a sermon
Speaker 1: in which he referenced the creation of spectacles dating no
Speaker 1: more than twenty years earlier, which would put the creation
Speaker 1: of corrective lenses sometime around twelve eighty five. Whatever the
Speaker 1: actual origins, we know that corrective lenses in the form
Speaker 1: of spectacles preceded telescopes and contact lenses by a few centuries. Now,
Speaker 1: before I transition from glasses to contact lenses, well, let's
Speaker 1: talk for a second about how these lenses actually work.
Speaker 1: The physics remain the same, even though the forms are
Speaker 1: slightly different. First, a lens bends light. Light will bend
Speaker 1: towards the thickest part of a lens. So if you
Speaker 1: make a concave lens, also known as a minus lens,
Speaker 1: you're making one where the center of the lens is
Speaker 1: the thinnest part and the edges are the thicker parts
Speaker 1: of the lens that bends light away from the center.
Speaker 1: And it's tricky to talk about this without visual aids,
Speaker 1: but I'm gonna do my best. Now, imagine we're looking
Speaker 1: at a concave lens from the side. So from the side,
Speaker 1: it looks like it's thick on the on the outer edge,
Speaker 1: and then it bends inward on both sides, so we're
Speaker 1: looking at it kind of in silhouette. Now, imagine that
Speaker 1: parallel beams of light are coming from the left side
Speaker 1: of our view. We're gonna call this the front of
Speaker 1: the lens. When those beams of light hit this concave lens,
Speaker 1: they diverge, They start to point outward toward the various
Speaker 1: thick parts of the lens, the edges, and that continues
Speaker 1: on the right side of our view, which we're gonna
Speaker 1: call the of the lens. The beams of light hitting
Speaker 1: the upper half of our lens bent upward. The ones
Speaker 1: hitting halfway down our lens are bending downward. Now, if
Speaker 1: you were to look at these rays of light on
Speaker 1: the right side, the ones that are now bent going
Speaker 1: up or down, uh at a diagonal from the lens,
Speaker 1: and then you were to take those pathways and extend
Speaker 1: them back toward the left side, the front side of
Speaker 1: the lens, those beams would look like they have converged
Speaker 1: on a point in front of the concave lens. So
Speaker 1: you take those bent rays and you make them straight
Speaker 1: lines onto the front side, they're all going to converge
Speaker 1: at this one point. That's the focal point of the
Speaker 1: concave lens. It's actually in front of the lens, not
Speaker 1: behind it. The distance from the lens to that point
Speaker 1: is called the focal length. The stronger the lens is,
Speaker 1: the further the focal point will be, and therefore the
Speaker 1: greater the focal length will be. Now, with convex lens
Speaker 1: is it's quite different. Let's imagine again we're looking at
Speaker 1: a lens from the side. This time the lens bulges
Speaker 1: outward toward the middle, and it's thinner at its edges,
Speaker 1: the opposite of the concave lens. So parallel beams of
Speaker 1: light are coming from the left side the front of
Speaker 1: the lens. When they hit the lens, those beams are
Speaker 1: bent inward towards the center. The beams continue out through
Speaker 1: the back of the lens and they converge on a
Speaker 1: point behind the lens, and technically they keep going after converging,
Speaker 1: continuing in a straight line. But never mind that for now.
Speaker 1: That point of convergence is the focal point for the
Speaker 1: convex lens, so that focal point happens behind the lens,
Speaker 1: and the stronger the lens, the shorter the focal length is.
Speaker 1: In other words, the closer the focal point is to
Speaker 1: the lens itself. So a concave lens has the focal
Speaker 1: point in front the convex lens as the focal point behind.
Speaker 1: Using the right type of lens at the right strength
Speaker 1: can compensate for conditions like myopia or hyperopia. We measure
Speaker 1: the strength of a lens in a unit called diopters.
Speaker 1: It's a measurement of how much how much the light
Speaker 1: is actually bent within the lens itself. The higher the diopter,
Speaker 1: the stronger the lens, the more light is bent as
Speaker 1: it passes through, and we use plus or minus to
Speaker 1: indicate the type of lens convex versus concave in this case.
Speaker 1: I'll talk more about this a bit later when we
Speaker 1: talk about prescriptions, which were developed in the nineteenth century,
Speaker 1: but a basic understanding of how Lee's lenses could be
Speaker 1: fine tuned to correct vision dates back at least to
Speaker 1: sixteen o four Common Era, when Johannes Kepler described what
Speaker 1: the retina does and proved that a concave lens could
Speaker 1: correct myopia and a convex lens could correct hyperopia. All right, now,
Speaker 1: I'm ready to finally talk about contact lenses. But first
Speaker 1: let's take a quick break to thank our sponsor. All Right,
Speaker 1: I said I was gonna talk about contact lenses in
Speaker 1: the Renaissance. Let's do it. In the early sixteenth century
Speaker 1: the hundreds, there was a dude who is synonymous with
Speaker 1: the Renaissance, who made some observations that frequently are cited
Speaker 1: as the origins for contact lenses, and that dude was
Speaker 1: Maestro Leonardo da Vinci. He theorized that water had the
Speaker 1: ability to change the direction of light and therefore alter vision,
Speaker 1: and did some experiments with dunking people's faces and water
Speaker 1: and looking at things, and then said, hey, you know what,
Speaker 1: maybe if you used a water filled glass that you
Speaker 1: could dunk your eye into while it's you know, still
Speaker 1: in your head, you could bend light and perhaps even
Speaker 1: correct for failing vision. He wrote up his ideas in
Speaker 1: a fifteen o eight publication, and he titled it Codex
Speaker 1: of the Eye Manual d Because the dude wrote a lot.
Speaker 1: Da Vinci drew up a few sketches that illustrated his ideas. Now,
Speaker 1: the problem was that his solution lacked practicality, because you
Speaker 1: could fill up two glasses with water, and you could
Speaker 1: hold those two glasses up against your eyeballs, but obviously
Speaker 1: water would start to leak out. It just wasn't sustainable.
Speaker 1: Da Vinci apparently toyed with the idea of an invention
Speaker 1: that would include a funnel so that you could refill
Speaker 1: the glasses as they ran out of water, but again
Speaker 1: it wasn't really a practical solution. A bit More than
Speaker 1: a century later, the philosopher Rene Descartes, who, as Monty
Speaker 1: Python would explain, said I drink, therefore I am tried
Speaker 1: to build onto da Vinci's work. In sixteen thirty six,
Speaker 1: Descartes published a paper in which he proposed a lens
Speaker 1: that could be placed directly against the eye, a contact lens,
Speaker 1: in other words, to correct for vision. So this wasn't
Speaker 1: a corrective lens all by itself. It wasn't like the
Speaker 1: lens had been ground down so that it had the
Speaker 1: exact shape it needed. It actually was to be attached
Speaker 1: to a long tube that you would then fill with
Speaker 1: you guessed it water. The water would provide the light
Speaker 1: bending properties needed to correct for vision. But this would
Speaker 1: mean you'd end up looking like a character from a
Speaker 1: text avery cartoon, with the tubes bulging out from your eyes.
Speaker 1: And it would also mean you'd be completely unable to blink.
Speaker 1: And while people who wear contacts are willing to put
Speaker 1: up with some discomfort at times, it's asking a bit
Speaker 1: much even for them. To be fair, both da Vinci
Speaker 1: and Descartes were talking about ideas rather than practical solutions.
Speaker 1: They saw the potential for a solution further in the future,
Speaker 1: but it was one that they themselves could not attain,
Speaker 1: and it would take a couple more centuries to get there.
Speaker 1: Now why is that, Well, largely it was because our
Speaker 1: ability to create lenses that can conform to the shape
Speaker 1: of the eye was a relatively late development. In the
Speaker 1: nineteenth century, some folks toyed with the idea again. One
Speaker 1: of them was an English scientist named Thomas Young. Young
Speaker 1: thought Descartes was really onto something, so he built a
Speaker 1: prototype of a contact lens based off that tube lens
Speaker 1: description Descartes had proposed. He attached these water filled lenses
Speaker 1: to his eyes. He used wax to do it. This
Speaker 1: was in eighteen o one, so I assume he stopped
Speaker 1: screaming sometime in eighteen o two. I should point out
Speaker 1: I'm joking about the screaming. He was using a soft
Speaker 1: wax to create a seal. It wasn't hot wax or
Speaker 1: anything like that. I had to do the research to
Speaker 1: make absolutely sure. Thomas Young would go on to map
Speaker 1: the normal visual field for the average person, which would
Speaker 1: become one of the foundations for modern optometry. In eighty seven,
Speaker 1: Sir John Herschel, who is just plain old John Herschel.
Speaker 1: At that time he had not yet been knighted, wrote
Speaker 1: about grinding a lens so that would conform precisely to
Speaker 1: the shape of the eye. To do so, he suggested
Speaker 1: making a mold of a person's eye, using quote transparent
Speaker 1: animal jelly end quote. There are no records over whether
Speaker 1: he ever tried to make such a mold, but I
Speaker 1: will have nightmares for my natural life involving transparent animal
Speaker 1: jelly in my eyes. Thanks decades later, a Swiss physicist
Speaker 1: named A. E. Thick made a spherical glass structure to
Speaker 1: correct refractive errors for a person's eyes, and that same
Speaker 1: year Edward Kelt, who was a French optician, made fitted
Speaker 1: glass lenses, and a German medical student named August Mueller
Speaker 1: was using glass discs fitted against his own eyes to
Speaker 1: attempt to treat his myopia. These contacts were all rigid
Speaker 1: and were unpleasant to wear. For one thing, they fit
Speaker 1: around not just the cornea, but over the sclera, over
Speaker 1: the white outer layer of the eyeball. Covering the sclera
Speaker 1: deprives the cornea of oxygen. Glass is impermeable to oxygen.
Speaker 1: Oxygen cannot pass through it, so if you wore the lenses.
Speaker 1: You would not only tire out your eyes because the
Speaker 1: lenses were heavy, but it would become painful to wear
Speaker 1: them after a short while, like half an hour or so,
Speaker 1: so these were not an ideal alternative to spectacles. Most
Speaker 1: estimations say that very few people ever wore those early
Speaker 1: glass contact lenses, perhaps five people total, and you couldn't
Speaker 1: go for more than four hours tops, because those lenses
Speaker 1: were cutting off that sweet supply of oxygen that eyes need,
Speaker 1: and you would just be suffering intense amounts of pain.
Speaker 1: The first contact lenses made of plastic date from nineteen
Speaker 1: thirty eight when THEO. O. Brig and John Mullen introduced them.
Speaker 1: They used polymethyl methac relate, also known as p M
Speaker 1: m A. It had originally been used as a binder
Speaker 1: for paint, so clearly you should shove that into your eyes.
Speaker 1: These early contact lenses still had glass as well, so
Speaker 1: they were a hybrid of glass and plastic. It wouldn't
Speaker 1: be an till nineteen forty, when Heinrich Vulk started using
Speaker 1: all plastic lenses that this trend would begin to change.
Speaker 1: Even so, the lenses still covered the entire surface of
Speaker 1: the eyeball, not just the cornea. In ninety eight, an
Speaker 1: optical technician named Kevin Toohey was awarded a patent for
Speaker 1: his big discovery when he realized you could use smaller
Speaker 1: contacts that did not cover the whites of the eyes.
Speaker 1: This resulted in a slightly more comfortable contact lens that
Speaker 1: could be worn for longer periods of time. Towey actually
Speaker 1: discovered this totally by accident. He had been working on
Speaker 1: creating a full contact for the eye, one that would
Speaker 1: cover the sclera, and it was gonna be made of
Speaker 1: a new type of transparent plastic. But the part that
Speaker 1: would have covered the sclera broke off while he was
Speaker 1: trying to make it, and he thought, well, what would
Speaker 1: happen if I just used this part of a lens,
Speaker 1: the part that would fit over the cornea but not
Speaker 1: the sclera. Would it still work? So he tried it
Speaker 1: out and he discovered that it would stay in place
Speaker 1: even after he was blinking. So that was a revolutionary change.
Speaker 1: It meant that no longer did they have to build
Speaker 1: contact lenses that would go over the entire exposed part
Speaker 1: of the eyeball. It could just go over the cornea.
Speaker 1: Even so, these lenses were still hard lenses, and they
Speaker 1: were not the most comfortable thing to wear. They also
Speaker 1: had a small lip on them, which would make it
Speaker 1: easier to insert and remove the lens, but also meant
Speaker 1: that sometimes your eyelid might catch on it, or you
Speaker 1: might rub your eye in such a way that the
Speaker 1: lens would just pop out. And thus you have the
Speaker 1: birth of the classic physical comedy gag of a character
Speaker 1: suddenly exclaiming that he or she has lost a contact
Speaker 1: lens and that everyone must stop everything they are doing
Speaker 1: and help track it down. Kennedy Otto. Victorrell also made
Speaker 1: an incredible contribution to contact lenses. He created the first
Speaker 1: soft contact lens. He used a cross linked hydra of
Speaker 1: Fhilick material and I'm gonna try and say it, but
Speaker 1: this might take a few attempts he called it. Or
Speaker 1: actually the material itself is called hydroxy ethel methacrolate. Hey,
Speaker 1: I got the first try. It's easier. Name is hima
Speaker 1: h E m A. And he discovered this in nineteen
Speaker 1: fifty two. He noted that this material, which he was
Speaker 1: not making specifically for contact lenses, he was just working
Speaker 1: with plastics. He noted that it could retain moisture, it
Speaker 1: could absorb, and when it did absorb moisture, it became flexible,
Speaker 1: but it would also snap back to its original shape,
Speaker 1: so while you could bend it, if you let go,
Speaker 1: it would go back to the way it was supposed
Speaker 1: to be. And he figured this could be a good
Speaker 1: material for contact lenses, since even the plastic ones that
Speaker 1: have been made up to that point still at disadvantages.
Speaker 1: They were still impermeable to air. So he began working
Speaker 1: on this project for his employer, which at the time
Speaker 1: time was the Institute of macro Molecular Research in Czechoslovakia
Speaker 1: or what was then Czechoslovakia. But his bosses were not
Speaker 1: convinced that this was worthwhile research, so they told him
Speaker 1: to knock it off and get to work on other stuff. So,
Speaker 1: rather than abandoned this idea completely, he moved his work
Speaker 1: to his home and he used a jerry rigged system
Speaker 1: to start making these contact lenses. That system consisted of
Speaker 1: a gramophone, in other words, the predecessor to a record player.
Speaker 1: He used that to create a spinning motion and an erector,
Speaker 1: set a mechanical kit for kids to work with, and
Speaker 1: together he used these to make a spin casting machine. Now,
Speaker 1: spin casting is a technique that has been used for
Speaker 1: lots of different stuff, not just contact lenses. In this
Speaker 1: particular case, it was making a soft, breathable contact lens,
Speaker 1: but spin casting can be used for lots of different things.
Speaker 1: So what exactly is it. Well, let's stick with contact
Speaker 1: lenses for the explanation, and since that's the subject at hand,
Speaker 1: the conventional way to make contact lenses up to that
Speaker 1: point was to use a cast molding process and a press.
Speaker 1: So you would create a mold of the shape that
Speaker 1: you want your contact lens to be, and you would
Speaker 1: put some plastic in that, and then you would use
Speaker 1: a press to press down into the mold and form
Speaker 1: the plastic into the correct shape. But this method had disadvantages.
Speaker 1: When the press would withdraw, sometimes it would leave scars
Speaker 1: and aberrations upon the lens itself. And this is the
Speaker 1: inside of the lens, the part that would go against
Speaker 1: your eye, so it could potentially create damages that could
Speaker 1: in turn hurt your eyes. The edges of these contact
Speaker 1: lenses were also prone to defects and unevenness, so it
Speaker 1: can make the contact lens less accurate and more uncomfortable
Speaker 1: to wear. The spin cast method works differently. You put
Speaker 1: a small amount of liquefied plastic and you drip that
Speaker 1: into the old, and the mold then is spun in
Speaker 1: a circle. This creates the force necessary to draw out
Speaker 1: that plastic to spread it evenly over the mold. There's
Speaker 1: no press that makes physical contact with the lens, so
Speaker 1: there's nothing to leave behind those marks or scars or
Speaker 1: to create uneven edges. Now he secured a patent for
Speaker 1: his contact lens production method, and then Bauschan Loam swooped
Speaker 1: in to purchase the patent to put it into use.
Speaker 1: In nineteen seventy two, their soft contact lenses were ready
Speaker 1: for the market. In between his first experiments and Balsh
Speaker 1: and Loam's introduction of those contact lenses, the US Food
Speaker 1: and Drug Administration decided to classify soft contact lenses as
Speaker 1: a drug. Now, that might sound strange to you, because
Speaker 1: these are contact lenses you wear in your eyes. They're
Speaker 1: not something you ingest, they're not something you inject in yourself.
Speaker 1: You don't absorb them. But you have to remember there
Speaker 1: was a lot of development in the field at the time.
Speaker 1: Tons of companies and inventors were all rushing to experiment
Speaker 1: with different materials to create better contact lenses. The f
Speaker 1: d A wanted to create protections to put in place
Speaker 1: to make sure those materials passed numerous tests before they
Speaker 1: were ever marketed to consumers to make sure they were
Speaker 1: safe to use, because you wouldn't want to find out
Speaker 1: that your brand new contact lenses were actually toxic after
Speaker 1: they hit store shelves. Thus the necessity to classify them
Speaker 1: as a drug so they could pass all these numerous
Speaker 1: check marks before they could hit stores. Now more improvements
Speaker 1: have come along, mostly in the materials that we've used
Speaker 1: to create contact lenses. In Dr Michael bay Uh, He's,
Speaker 1: as far as I know, not related to the Hollywood
Speaker 1: director who makes things blow up, created a disposable contact lens.
Speaker 1: So until two, when you've got a pair of contact lenses,
Speaker 1: you're meant to use those indefinitely. You would only replace
Speaker 1: them if you had lost one or damaged one, or
Speaker 1: if your eyesight had changed and a new prescription was needed,
Speaker 1: but that also presented a hygienic issue. Contact lenses can
Speaker 1: develop what is called protein build up, and if you've
Speaker 1: ever seen a contact lens that has white or cloudy
Speaker 1: marks on it, that's likely protein build up, and if
Speaker 1: you were to put those lenses in your eyes, you
Speaker 1: might feel some discomfort, your vision might not be all
Speaker 1: that great. Worse, if your contact lenses get damaged, they
Speaker 1: could in turn scratch your corneas, which not only can hurt,
Speaker 1: but can make you sensitive to light or even lead
Speaker 1: to a corneal us ulcer, which can potentially damage your
Speaker 1: vision permanently. And lenses can also carry bacteria and germs,
Speaker 1: which can lead to infections like conjunctivitis and karatitis. So
Speaker 1: disposable contacts reduce those risks. Because you're not using the
Speaker 1: same pair of lenses indefinitely, there are fewer opportunities to
Speaker 1: shove gunk in your eyes. In other words, Also, if
Speaker 1: you ever have contact lenses that have protein build up,
Speaker 1: it's the one time where you're actually supposed to kind
Speaker 1: of scrub them with your solutions that you can clean
Speaker 1: them off, because just washing them in solution is not
Speaker 1: going to remove that protein build up. In general, you're
Speaker 1: not supposed to scrub contact lenses at all. They're very
Speaker 1: easily damaged, but that's one case where you are supposed
Speaker 1: to do it. Although I would argue at this stage,
Speaker 1: just go out and buy new context because you don't
Speaker 1: want to mess with that stuff. The first disposable content
Speaker 1: lenses were meant to be warned for a couple of
Speaker 1: weeks before you replace them. Dr Bay named them m
Speaker 1: I A lenses MIA not missing an action that m
Speaker 1: I A was the actual Those were the first initials
Speaker 1: of his name, his wife's name, and his daughter's name,
Speaker 1: So it's Michael Inga and Annette. In case you ever
Speaker 1: have pub trivia and you're asked, what did the initials
Speaker 1: M I A stand for? As far as contact lenses,
Speaker 1: Michael Inga and a net. His design was purchased by
Speaker 1: a company called Johnson and Johnson, famous company. They tweaked
Speaker 1: and rebranded the technology to create their own disposable contacts,
Speaker 1: and they launched that brand in nineteen eight seven under
Speaker 1: the name AC View in eight CIBA I assume that's
Speaker 1: how we pronounced the name of the company. C I
Speaker 1: B A created contact lenses using silicone hydrogels. Now, the
Speaker 1: big advantage of the hydrogel material was that it was
Speaker 1: particularly permeable to oxygen, so it can allow oxygen to
Speaker 1: pass through the contact lens and allow the cornea to
Speaker 1: get that sweet sweet oxygen. It craves so dearly. The
Speaker 1: first daily disposable lenses would debut in n Ron Hamilton's,
Speaker 1: who was an inventor in Scotland, gets credit for creating
Speaker 1: the first example, which he called the Premier Award Lens.
Speaker 1: Balsha and Loam would purchase Hamilton's company and rebranded the
Speaker 1: lens the Soft Lens One or the Soft Lens One Day.
Speaker 1: Hamilton's would go on to launch a different company called
Speaker 1: provis Now. There have been numerous improvements in materials and
Speaker 1: processes to contact lenses over the years, but the basic
Speaker 1: principles remained the same. Contact lenses bend light so that
Speaker 1: eyes can focus, which is a little reductive because there
Speaker 1: are contact lenses that are meant to protect eyes that
Speaker 1: have been damaged through injury or illness. There are some
Speaker 1: that are meant to treat diseases, not just a problem
Speaker 1: with vision, but actual diseases of the eye. There's also
Speaker 1: cosmetic contact lenses that don't have any corrective nature to
Speaker 1: them as well. But I'm going to focus pun intended
Speaker 1: un corrective contact lenses since that's such a common use
Speaker 1: for them, and that brings us to a couple of
Speaker 1: questions like, how does an optometrists determine what prescription you
Speaker 1: need when you go to get glasses or a contact?
Speaker 1: And where did that whole thing come from? Anyway, Well,
Speaker 1: in the next segment, I'll tell you, but first let's
Speaker 1: take another quick break to thank our sponsor. All right,
Speaker 1: So where did the concept of prescriptions come from? And
Speaker 1: how do I doctors determine what a person needs? So,
Speaker 1: like most innovations, the story is way more complicated than
Speaker 1: some really smart dude came up with it and changed everything.
Speaker 1: In reality, the journey to optometry was a long one
Speaker 1: and many different philosophers, physicians, and inventors contributed to our
Speaker 1: understanding of vision and optics. So, for example, Benjamin Franklin
Speaker 1: famously invented bifocal lenses for spectacles in seventeen eighty four.
Speaker 1: A decade later or so, John Dalton first described the
Speaker 1: condition of color blindness. As I mentioned earlier in this episode,
Speaker 1: Thomas Young mapped out the normal human visual field in
Speaker 1: eighteen o one. There was a physician an inventor named
Speaker 1: Herman von Helmholtz which might be the best name ever,
Speaker 1: who invented the opthalmoscope in eighteen fifty one. Now that's
Speaker 1: an instrument that gives the physician the ability to see
Speaker 1: into the interior of a living eye without you know,
Speaker 1: having to cut into it. So this would be the
Speaker 1: instrument that shines a light in your eye when the
Speaker 1: eye doctor is taking a look to make sure that
Speaker 1: everything look good. The use of that was while allowed
Speaker 1: doctors to slowly catalog what a healthy human eye should
Speaker 1: look like and what the various signs of diseases or
Speaker 1: conditions that can affect the eyes looks like. So it
Speaker 1: helped catalog all of that stuff because now they had
Speaker 1: a tool where they could actually see it in living people.
Speaker 1: Helmholtz did not stop there. In eighteen fifty six, he
Speaker 1: published an enormous work in three volumes. The English title
Speaker 1: for his work is Handbook of Physiological Optics. Six years later,
Speaker 1: in eighteen sixty two, there was a fellow named Herman
Speaker 1: Snellen who created a series of tests to help determine
Speaker 1: a person's visual acuity, including an eye chart. Probably seen
Speaker 1: examples of the kind of eye chart he created. Now,
Speaker 1: to be clear, pun intended. Many physicians were using ie
Speaker 1: charts at that point, but Snellen's became a standardized approach,
Speaker 1: which had a benefit of working across regions and making
Speaker 1: it easier to determine what type and strength of lens
Speaker 1: a patient would need in order to correct their vision.
Speaker 1: And this is kind of where we get to the
Speaker 1: concept of twenty twenty vision. If you have twenty twenty vision,
Speaker 1: it means you can see the same detail at a
Speaker 1: distance of twenty feet or six meters as someone who
Speaker 1: has what we consider to be normal vision. It also
Speaker 1: can be called six six vision for meters. Now, if
Speaker 1: you had twenty forty vision, it would mean that when
Speaker 1: you stand twenty feet away from an eye chart, that
Speaker 1: i chart would look to you as if it were
Speaker 1: forty feet away for someone with normal vision. In other words,
Speaker 1: you would see the same amount of clarity that a
Speaker 1: person with normal vision would see at forty feet, but
Speaker 1: you would be twenty feet away, so you would see
Speaker 1: things less clearly than the average person. If you had
Speaker 1: vision that was at twenty four hundred, that means your
Speaker 1: vision is pretty bad that you would see a chart
Speaker 1: at twenty ft away with the same amount of clarity
Speaker 1: as a normal person looking at that same chart, but
Speaker 1: there are four feet away, So you see how that
Speaker 1: scale quickly changes things. You can have better than normal vision.
Speaker 1: Of course, if you have twenty ten vision, it means
Speaker 1: that you can see the same level of detail at
Speaker 1: twenty feet that someone with normal vision would be able
Speaker 1: to make out from ten feet away, so they would
Speaker 1: have to be twice as close to the chart to
Speaker 1: see the same level of detail that you see. So
Speaker 1: that would mean you have a more keen eyesight than
Speaker 1: the average person. I technically had that shortly after I
Speaker 1: had laser eye surgery. My vision was somewhere around twelve,
Speaker 1: meaning that I could see better than the average person
Speaker 1: for these sort of eye charts. But don't get too
Speaker 1: excited about it. For one, eyesight does tend to deteriorate
Speaker 1: over time, so you're not guaranteed to have that amazing
Speaker 1: eye sight through the rest of your life. My eyesight
Speaker 1: slowly deteriorates even after I've had the laser surgery. Also,
Speaker 1: there are animals that visualuity that are closer to like
Speaker 1: twenty three, so let's not get too excited by this.
Speaker 1: Visual acuity is just one element of vision. By the way,
Speaker 1: there are other considerations such as peripheral awareness or eye
Speaker 1: coordination or depth perception, color vision, and the ability to
Speaker 1: focus on points near or far from your eyes. But
Speaker 1: the eye chart definitely helped move things towards a standard.
Speaker 1: In eighteen sixty four, FC. Donders, who actually worked with
Speaker 1: Snell and the guy who created the eye charts, published
Speaker 1: Anomalies of Accommodation and Refraction of the Eye. So in
Speaker 1: that work he laid out the principles that would become
Speaker 1: the basis for prescriptions. So let's take a quick moment
Speaker 1: to talk about the form prescriptions take and what that
Speaker 1: actually means. Now, a full prescription, one that someone with
Speaker 1: you know, eyesight where they might need bifocals, typically has
Speaker 1: four parts to it, and I'm going to use a
Speaker 1: hypothetical prescription in order to give an example. So let's
Speaker 1: say that you've got a shorthand prescription written out for
Speaker 1: you and it reads like this two point to five
Speaker 1: minus one point five zero times plus two point zero zero.
Speaker 1: Now that is not a math problem. Those pluses and
Speaker 1: minuses give you indications for the power of the various lenses.
Speaker 1: So let's take this piece by piece. That first number
Speaker 1: two point to five that represents the base strength or
Speaker 1: spherical strength and type of lens. Spherical lenses correct for
Speaker 1: myopia or hyperopia, so near sightedness and far sightedness. In
Speaker 1: our example, the two point to five gives us this information.
Speaker 1: It's two point to five diopters, remember the units that
Speaker 1: tell us how much the lens bends light. And because
Speaker 1: it lacks a negative sign, it means it's a plus
Speaker 1: type of lens, which means this is a prescription that
Speaker 1: is meant to correct for hyper opia or far sightedness.
Speaker 1: The next number, minus one point five zero refers to
Speaker 1: a cylindrical lens. These lenses would look kind of like
Speaker 1: a a pipe cut lengthwise and they fit within the
Speaker 1: overall glasses or contact lens, and they correct for a
Speaker 1: stigmatism and the axis of the lens matches the abnormality
Speaker 1: of the cornea, So that minus one point five zero
Speaker 1: tells us it's a minus lens at one point five
Speaker 1: oh diopters. Actually it's not quite that simple, but I'll
Speaker 1: get to that in a little bit. The third number
Speaker 1: one is the orientation of that cylindrical lens. It tells
Speaker 1: us the cylindrical lens is oriented at a D seven degrees.
Speaker 1: The fourth number two point zero zero is a bifocal
Speaker 1: segment at plus two diopters, and it's always going to
Speaker 1: be positive for bifocals. If you don't need bifocals, you
Speaker 1: wouldn't have a number like this trailing at the end
Speaker 1: of your prescription. What's more, you might see the letters
Speaker 1: O D or O S on the prescriptions, So what
Speaker 1: the heck did those mean? The O D means oculus dexter,
Speaker 1: and os is oculus sinister. That is Latin for right
Speaker 1: eye and left eye. So dexter and sinister mean right
Speaker 1: and left. So if you happen to be left handed
Speaker 1: like me, you're of a sinister persuasion. Insert evil laugh here.
Speaker 1: Oh wait uh. Prescriptions can become more complicated than the
Speaker 1: example I gave you. I should add there are other
Speaker 1: factors that could be included, and they account for things
Speaker 1: such as correction for eye alignment problems and other such issues. Also,
Speaker 1: eyeglass prescriptions and contact lens prescriptions are not always the
Speaker 1: same thing. Contact lens prescriptions need additional information such as
Speaker 1: what the curve of the back surface of the contact
Speaker 1: lens should be. That's the part that touches your eye.
Speaker 1: It also includes stuff like the diameter of the lens,
Speaker 1: and because eyeglasses are worn in front of the eyes
Speaker 1: at a sense of around twelve millimeters from your eye,
Speaker 1: and contact lenses are worn on the eyes, the power
Speaker 1: of the prescription tends to be different to produce the
Speaker 1: ideal result. In the Federal Trade Commission ruled that all
Speaker 1: eye doctors, both optometrists and ophthalmologists, must provide a copy
Speaker 1: of a patient's prescription upon the end of an eye exam.
Speaker 1: That way, the patient can choose the vendor he or
Speaker 1: she prefers when buying the actual glasses. Now I'm wrapping
Speaker 1: up here. There's a whole lot more I could talk about,
Speaker 1: including the way you take lens blanks and grind them
Speaker 1: down in order to make the proper lens, but that
Speaker 1: would almost require a second episode. And before I sign off,
Speaker 1: I think I should also explain what the differences between
Speaker 1: optometrists and ophthalmologists, and also what are opticians. So, an
Speaker 1: ophthalmologist is a medical or osteopathic doctor, someone who actually
Speaker 1: has a medical degree. They have extensive training in medicine
Speaker 1: and they specialize in eye and vision care. They have
Speaker 1: a license to practice medicine and surgery, so they treat
Speaker 1: eye diseases and conditions. They perform surgical procedures, and they
Speaker 1: can also prescribe and fit eyeglasses and contact lenses. They
Speaker 1: may also conduct research to gain further understanding into eye
Speaker 1: disorders and diseases. And there's some disagreement about whether or
Speaker 1: not an ophthalmologist or an optometrist is the best person
Speaker 1: to go when you are trying to get glasses or
Speaker 1: contact lenses, and the fights can get pretty nasty because
Speaker 1: they tend to involve ophthalmologists and optometrists calling each other things.
Speaker 1: So I'm not going to get into that here. But
Speaker 1: what is an optometrist. Well, that's a health care professional,
Speaker 1: but they are not a doctor, not a medical doctor
Speaker 1: at any rate. They must receive a Doctor of Optometry.
Speaker 1: That's an o d Degree, but it's not a medical degree.
Speaker 1: This is a four year degree from an optometry school,
Speaker 1: and that's after they've conducted at least three years of
Speaker 1: college education. So they do hold a doctorate, but they
Speaker 1: are not a medical doctor. Their licensed to conduct eye
Speaker 1: exams and prescribe glasses or contact lenses, and they can
Speaker 1: also generally prescribe some medications for certain types of eye diseases.
Speaker 1: And then you have opticians. Now these are technicians that
Speaker 1: are trained to design, to verify, and to fit eyeglass
Speaker 1: lenses and frames as well as contact lenses. They do
Speaker 1: not make prescriptions themselves, so they cannot prescribe the glasses,
Speaker 1: but they can take a prescription and make the glasses
Speaker 1: or contact lenses or fit them to you. They're allowed
Speaker 1: to do that. They are not licensed to diagnose or
Speaker 1: treat eye diseases or disorders. And there's also another weird
Speaker 1: difference between optometrists and ophthalmologists that I discovered as I
Speaker 1: was researching this episode, and that's how they write out prescriptions. Specifically,
Speaker 1: that second number I referenced, that's the difference. So remember
Speaker 1: our hypothetical prescription was two point to five minus one
Speaker 1: point five times one plus two point zero zero. Well,
Speaker 1: that minus one point five zero doesn't just tell us
Speaker 1: the lens power of the cylindrical lens that was meant
Speaker 1: to correct an a stigmatism. It also tells us that
Speaker 1: the person conducting that hypothetical I exam had to be
Speaker 1: an optometrist because it was a negative value. If it
Speaker 1: had read one point five zero instead of minus one
Speaker 1: point five zero, the actual effect in the finished glasses
Speaker 1: would be exactly the same. It would just mean that
Speaker 1: an ophthalmologist had written the prescription. Optometrists always have a
Speaker 1: negative value for cylindrical lens and ophthalmologists always have a
Speaker 1: positive value. Now this does change the value for that
Speaker 1: axis figure as well, so there is a slight other
Speaker 1: difference between an optometrist and an ophthalmologist prescription. But it
Speaker 1: really boils down to the fact that optometrists use negative
Speaker 1: cylindrical lens designation an ophthalmologists use positive cylindrical lens designation,
Speaker 1: even though they both do the exact same thing. So wacky, right,
Speaker 1: I learned something new today, well, guy, That wraps up
Speaker 1: this overview of where contact lenses came from and how
Speaker 1: we all got to the point of staring at these charts,
Speaker 1: and also answering the immortal question better like this or
Speaker 1: better like this A or B one or two? Man,
Speaker 1: I'm so glad I don't have to do that anymore.
Speaker 1: Laser eye surgery rules. If you guys have suggestions for
Speaker 1: future episodes of tech Stuff, please let me know. You
Speaker 1: can write me. My email address for the show is
Speaker 1: tech Stuff at how stuff works dot com, or you
Speaker 1: can drop me a line on Facebook. Or Twitter. The
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Speaker 1: Follow our Instagram account. You never know what Crystal is
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Speaker 1: sure you follow that and as always, make sure you
Speaker 1: join me one of these days for a live recording.
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