Useful Notes: Corrective Lenses
Glasses and other types of lenses worn for vision correction or UV protection are ubiquitous enough in Real Life and in media that there is a whole index dedicated to the different tropes involving their usage. A lot of times though, the way some of these tropes have been used have led to a lot of misconceptions about the way glasses work in real life. Despite popular misconceptions, wearing glasses or contacts does not always equal better vision. A person with vision less adequate than 20/20 can't get just any pair of glasses and be good to go. He or she will have to see an optometrist, who will give them an eye exam to discern whether the person is nearsighted or farsighted and just how severely their vision is impaired. Then the person will get new glasses with lenses made based on their level of visual impairment (This also applies to contacts). The lenses are shaped in a certain way to refract light in such a way that the person with bad uncorrected vision will be able to have optimal vision as long as he or she has them on. We say "optimal" rather than "perfect" because some people have vision that is so bad that even with correction, they cannot attain 20/20 vision. Those whose vision cannot be corrected to better than 20/200 in their better eye, or whose visual field is 20 degrees or less in their better eye are considered legally blind. Therefore, it is inaccurate to say that someone is "legally blind without their glasses" to describe their severely bad vision. Also, not everyone who wears corrective lenses is "blind without them." Someone with a weaker prescription will most likely not be bumping into walls or mistaking lampposts for people should their lenses be lost or broken. A pair or glasses or contacts can do wonders, but only for the person they were designed for. Because of the fact that a pair of corrective lenses refracts light to correct a certain type of bad vision, it is generally considered inadvisable to try on a pair that belongs to someone else. This is played for laughs in The Big Bang Theory, when Priya makes Leonard wear contact lenses, resulting in him falling over stuff. In fact, unnecessarily wearing glasses with prescription lenses can even be harmful, as with Elton John, who wore glasses (that unfortunately had prescription lenses) in his youth because he thought they looked good, but years of wearing unnecessary corrective lenses ruined his eyes to the point where he actually needs]] real glasses. However, once a person is discovered to have bad vision, simply giving them a set of corrective lenses will not solve their problems for the rest of their life. Those who need vision correction are advised to update their prescription every two years. Once they reach a certain age, they are then advised to update their prescriptions once a year. This is because as one ages, their vision fluctuates in such a way that the set of glasses that gave them perfect vision at the age of 18 may need to be replaced by the time they turn 21. No matter how careful you are with your glasses, they will not suit your changing eyes forever. If you are really unable to get a new pair of glasses with an updated prescription, wearing an old pair of glasses actually does more good for your eyes than going without any form of correction. Going without any kind of correction or wearing older lenses long-term can actually exacerbate the deterioration of one's vision; regularly updating your prescription lenses and wearing them is the best way to maintain your vision and slow its age-related deterioration. As we mentioned before, there are multiple ways in which a person can have bad vision. People whose vision is impaired to the point where it has to be corrected range from the child who needs glasses to see what's written on the board in school to the teenager who wears contacts to the middle-aged man who needs glasses to be able to read to the senior citizen with years of experience working out the tricky experience of wearing bifocals.
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Types of Correctable Bad Vision
Hyperopia/Far-sightedness If you are far-sighted, you can only clearly see things that are farther away from yourself. Henry Beemis from The Twilight Zone is obviously far-sighted because when his glasses break, it renders him unable to read and that wouldn't be the case if he was near-sighted. (If he was near-sighted, reading would be one of the only things he could do from there on out.) Far-sighted vision requires convex lenses, the same type used in magnifying glasses, for correction. Myopia/Near-sightedness If you are near-sighted , then you are only able to see things that are in close proximity to yourself with clarity. People with uncorrected near-sightedness will often cope with their type of bad vision by sitting at an unusually close distance from the television and holding books too close to their faces. Stereotypically, a child is revealed to need glasses through a noted inability to read the board clearly because they are too far away to because it is more common to be near-sighted rather than far-sighted if you are young. Glasses that are designed for near-sighted people will have concave lenses. Myopia (near-sightedness) is a more common birth defect than hyperopia (far-sightedness). Astigmatism Another way vision can be impaired, in addition to near-sightedness and far-sightedness, is astigmatism, a condition where your lenses are technically fine, but the shape of your cornea makes it so that the correctly focused light lands incorrectly on your retina. This manifests in symptoms similar to near-sighted and far-sighted individuals, but requires a cylindrical or toric lens to correct. For some reason, astigmatism is the go-to impairment for nerdy characters who also happen to need vision correction. Prescriptions for lenses to correct for astigmatism will consist of both a power (amount of refraction) and an angle which the correction is applied on. Presbyopia As well as Crack! Oh My Back!, aging can also bring presbyopia, in which the lens of the eye loses flexibility and cannot focus. This is associated with middle age (usual onset around age 45). This leads to specific, aging-related glasses and behaviours with glasses. Some people (who do not need glasses for distance vision) may wear distictive half-glasses or reading glasses for close work. Other people (who are nearsighted) may simply take off their distance glasses to read. Often people who use glasses for presbyopia are shown putting the glasses on their heads (often men), or wearing them on a chain round the neck (usually women). The glasses themselves can have bifocal or trifocal lenses. Other When people's eyes deteriorate as they age, they become more and more far-sighted. This is why younger people with glasses generally are myopic and why hyperopic glasses for older people can just be bought off-the-shelf. Far-sightedness in youth is generally pretty rare. However, myopia and hyperopia are not mutually exclusive. Some people are simultaneously near- and far-sighted and thus require bifocals. Similarly, one can have astigmatism as well as hyperopia or myopia, or all three! These different types of bad vision can shift with time independently of each other, so someone going in for an eye exam to update their prescription may find that while they have the same degree of myopia, the axis of their astigmatism has shifted, requiring new lenses.
Types of Glasses and Vision Correction
Glasses Glasses have been the usual method of correcting bad vision for centuries, and are generally the cheapest and most convenient method. First you have an eye exam, to determine the nature and extent of your uncorrected impairment; then, you might go and pick out a set of frames from the available options (usually displayed on racks along the walls of an optometrist's office), or maybe keep the frames you've got already if this isn't your first pair of glasses and you liked the last one well enough; finally, once the proper lenses for your prescription and frame have been manufactured, you'll come back to the optometrist and get them adjusted for proper fit. If you've never worn glasses before, but really needed them, this is the point at which you experience a brief epiphany on the subject of "holy crap so that's what things actually look like". Your optometrist will concern himself with the quality of your lenses, but he probably won't stop you from picking a lousy set of frames; he is selling them, after all. It's a bit oversimplifying things to say that quality and durability are inversely proportional to price and the presence of designer labels, but the rule serves a useful purpose nonetheless; while there is a certain undeniable appeal to a pair of rimless gunmetal-gray frames made of space-age composites that masses a quarter of a gram and looks like something Steve Jobs would've worn, keep in mind that this is something you are going to be wearing on your face for more or less all of the time you spend awake, and that, unless you lead an extremely sedentary lifestyle and basically never exert yourself at all, sturdiness is at least occasionally going to be a quality you'll need your glasses to exhibit. Rimless glasses in particular have trouble with durability, because the complete lack of rims puts much more stress on the lens material and consequently tends to shorten its useful life; if that's where your interests lie, consider "rimway" frames, which compromise with an arch around the upper half of the lens to bear stresses which would otherwise impact the lens itself, but leave the lower edge bare. Sometimes people who don't wear glasses wonder whether people who do wear glasses are annoyed by having the frames around the edges of their visual field. The answer is "no, not really"; after you've worn glasses for a while, you don't really notice the frames, any more than you notice your nose. Depending on the shape and size of the frames, your glasses will do more or less to correct your peripheral vision, but even in the best case, the lenses will refract light coming in through the edges; this doesn't help, but eventually you work out the degree to which you can (and can't) trust what you perceive around the edges of the visual field. Your glasses have one lens per eye for a reason. If you lose one, your brain, which is expecting to combine two corrected images into one relatively continuous visual field, instead receives a corrected image from one eye, and an uncorrected image from the other. If your prescription is modest, this probably won't be too much of a problem; if you're at 20/80 or higher, you're likely to have an easier time navigating the world if you just take your glasses off entirely until you can get the lens replaced; the alternative is to squint a lot and develop a crushing headache. (This is but one of many reasons why most glasses wearers keep a spare pair somewhere reasonably handy.) Glasses aren't that hard to take care of, especially newer ones. Older lenses made of soft soda-lime glass will with relative ease pick up scratches deep enough to substantially impair their clarity, while modern lenses are quite tough by comparison — plastic lenses are almost certainly either CR-39 resin, which originated as a material for casting B-17 fuel tanks, or polycarbonate, which is used in bulletproof "glass"; glass lenses are almost certainly borosilicate, found in labs around the world as "Pyrex" and myriad other trade names, and favored there over ordinary soda-lime glass for its improved thermal stability and hardness. These are not delicate materials; while, ideally, you'd clean the lenses with Windex-type spray and a soft microfiber or chamois cloth kept expressly for the purpose, in practice you're just as likely to yank them off your face, scrub at them with your shirt tail, and stick them back on, no harm done. Frames are even easier; about all that's really required there is to take them off before you go to sleep, so you don't wake up to find yourself lying on top of their uselessly twisted remains. Multifocals Multifocals are most often used to correct presbyopia. Earlier versions of this technology had visible lines in the lenses; aside from producing areas of abrupt focal change (which could be disorienting to the wearer), the lines themselves were a visible marker of the wearer's age. Newer lenses can be made without the tell-tale lines; such lenses are known as "progressive bifocals" or just "progressive lenses", and have both benefits and drawbacks compared to the older style — generally, progressive lenses are a little more comfortable and useful once you've become familiar with them, but standard bifocals make for a somewhat easier transition from standard single-focus lenses, because the areas of differing focus are sharply delineated and easy to distinguish. Unlike regular glasses, which only have lenses in a simple convex or concave shape to correct either hyperopia or myopia, multifocals combine the corrective elements of convex and concave shapes in the same lens, but in different areas. A common design for a bifocal lens is a concave lens for seeing at distances with a convex area for reading. Trifocals will have another area for seeing at arm's distance. Because multifocal lenses provide different kinds of vision correction based on which area of the lens the wearer is looking through, the wearer will have to work out getting used to looking through a certain area of their glasses according to what they're doing. This is really difficult at first, especially after years of taking it for granted that you could look in any direction and also have vision good enough for looking at whatever you want to see; on the other hand, as with most things, using multifocals gets easier with practice, and if you need them but don't use them then your vision will actually get worse, faster, than if you do. Sunglasses People with all kinds of vision can wear sunglasses, a pair of glasses with lenses that are tinted to filter UV rays and protect the eyes. Obviously, off-the-rack sunglasses are generally cheaper because they can be mass-produced without taking vision correction needs into account, and a contact lens wearer can of course wear any style of sunglasses she pleases, without compatibility concerns. Prescription sunglasses are available; they're essentially the same as ordinary glasses, but with an added permanent tint applied to the lenses. These cost the same as an ordinary pair of glasses or a little more, though, and are strictly special-purpose wear; a popular alternative is the use of "Transitions" lenses, which tint dark brown when placed in direct sunlight, and return to transparency once removed. These make effective automatic sunglasses, but only in direct sunlight; the photochromic coating responds to ultraviolet light, which renders it of strictly limited use if the light falling on your eyes has already passed through UV-filtering glass, such as that from which all modern vehicle windshields are made. For a period of time beginning around 30 to 40 years ago and lasting about a decade, a solution for people who needed both corrective glasses and sunglasses involved a pair of thin plastic shaded "lenses" resembling the older pince-nez which could be attached to regular glasses. Often the small plastic clip that attached these to the central glasses frame was also hinged, so that the sunshades could be flipped up when indoors instead of being totally removed. As Transitional lens technology improved, these fell out of favour; they are still manufactured, and occasionally found available for sale, but almost never used. (Interestingly, the "shaded clip-ons" have started to make a comeback for a specific application: 3D glasses for 3D movies in a theater or on a passive-3D TV set.) Another version leaves off the clip, but adds tiny magnets to the outside "corners" of the sunglass frame and matching metal studs to the eyeglass frame. You can't flip these up when not in use, but they stay put a little better than clip-ons, and they don't risk scratching the wearer's prescription lenses. On the other hand, unlike clip-ons, they're also designed to mate specifically with a single model of frame and no others, and are considerably more expensive and less disposable. There are also large-framed plastic sunglasses made to fit over another pair of (prescription) glasses. It is a considerable understatement to say that these are not stylish or aesthetically pleasing, but they may be more convenient for tasks like driving as they are easy to slip on and off quickly. Another variation is "moonglasses", made for low-light conditions. Instead of protecting from UV (though some do that too), they cut down on glare (such as the headlights from the oncoming lane when driving) and make it easier to see in a dark place with lights. Sunglasses could do this, but they would make it even darker and defeat the purpose. They are usually bright yellow. Contact Lenses People who don't like the way glasses look on them, or else for more practical reasons, decide to wear contact lenses. As anyone who regularly wears contacts can tell you, contacts are more expensive than glasses. Contact lenses used to be made of glass or rigid plastic, shaped individually to fit the cornea of their wearers' eyes. This caused problems for early contact lens wearers, because the cornea lacks blood vessels and its cells are oxygenated by direct gas exchange with the surrounding air; older lens materials prevented this gas exchange with potentially unfortunate results, while modern contact lenses are made from flexible, breathable plastic which avoids this drawback. Contact lenses can be made to correct the wearer's vision, change the appearance of the wearer's eyes (changed color or monster/animal eyes), or both. It is common in media to have someone who wears glasses as part of their Hollywood Homely look (usually a girl or woman) switch to contacts as part of a makeover; afterward, she will be shown to be much more attractive without glasses, and her life will improve accordingly. However, such media rarely bothers to portray either the rather involved cleaning ritual that contact-wearers have to go through, which is described below, or the process of getting accommodated to wearing contact lenses in the first place, which in comparison to that for glasses is both protracted and fraught with difficulty. (All of which, too, neatly sidesteps the fact that lots of folks find glasses appealing in their own right.) Putting on Lenses: 1. Wash and dry hands. 2. Open lens case. Identify lens. Clear lenses are nearly impossible to see, so most manufacturers tint them a very light blue. 3. Put a finger on the lens and it will cup to the finger. Water tension holds it on. Lift it out of the solution. 4. Carefully take lens with your other hand and rinse it with a commercially made and sterile solution. 5. Return lens to index or middle finger of dominant hand. With non-dominant hand, pull up eyelid to open eye. 6. Place lens in eye and blink to properly seat lens. (If you're new to wearing contacts, you will need to repeat steps 4 through 6 in front of the bathroom mirror until you're absolutely sick of it. Oh, and be careful how you blink! If you do it wrong, you'll dislodge the things, and have to start all over again. And it's really weird at first, having these thin slices of plastic stuck to your eyeballs, and you will want to blink them away, so as soon as you stop paying attention to not doing it...) Removing Lenses: 1. Wash and dry hands. 2.Pull up on eyelid with non-dominant hand. Roll eye upward. Lens should dislodge. Pinch lens carefully on either side with dominant hand and remove. 3. Wash and rinse lens with solution in palm of non-dominant hand. 4. Place lens in case and add fresh solution. Close case lid tightly. You've got to go through all that to protect your ocular health when wearing contacts. A glasses-wearer can take their glasses off, lick them, wipe them with their shirt, and put them back on without a problem; this is because glasses' lenses aren't in direct contact with the eyeball, a trait contact lenses do not share. (It's even in the name!) Tap water and (especially) saliva are far from sterile; your eyes produce tears precisely in order that occasional exposure to contaminants won't necessarily result in an eye infection, but tears can't get between your cornea and the lens which stays stuck to it for hours at a time, which makes a contaminated lens an excellent vector for infection. Surgery Some people end up deciding to surgically correct their bad vision with Lasik, such as "Weird Al" Yankovic, who wore glasses because of having vision that was especially bad. The surgery is relatively straightforward in a theoretical sense; the cornea is incised almost all the way around with a laser, then reattached with fine stitches so that its curvature more closely approximates the ideal spherical section. In practice, though, it involves having to keep your eye open as a laser does its job while you are awake. Sometimes, the patient is given a mild sedative and anaesthetic eye drops before the procedure, but you're still awake with your eye open while a laser beam is directly pointing right in your eye. Not to mention that the doctor has told you, with good reason, to not move your eye while the laser is doing its work. After the surgery, the patient is given a course of antibiotics and eye drops, as well as further instructions to reduce the risk of complications. Said complications include dry eye and damage to the cornea. Given the potential for complications, fears that the procedure might blind them if something goes wrong, and the fact that Lasik is an elective surgery, many people decide to play it safe and stick with glasses or contacts; while neither of those options approaches the convenience of just having good eyesight, all but the most severe impairments can be corrected to an acceptable degree without needing to go to the extent of having your corneas lasered off and sewn back on. Historical Forms of Spectacles Pince-nez are a very early form of spectacles (16th or 17th century) that were most popular circa 1880 through 1920. US Presidents Teddy Roosevelt and Woodrow Wilson wore them. The pads between the lenses literally pinched the bridge of the wearer's nose by means of springs to keep them in place, hence the name. In contrast, a modern pair of glasses may have pads in the same places that a pince-nez might have them, but they aren't nearly so tight, and the addition of arms reaching back to hook over the wearer's ears makes modern glasses much more stable as well. Those who were more self-conscious of their appearance might wear a "lorgnette," a pair of framed lenses on a handle, rather like some forms of carnival mask. The handle, in turn, is often attached to a chain or cord of some kind. People using these often only bring them to their faces for close inspection of something; it's as if the polite interactions with one's peers are thought to be impossible with the "mask" of spectacles as a barrier. They were almost always used by upper-class women, generally in Europe and North America during the 19th century. A monocle is a single lens, held in place by squinting, that one would use to correct the vision of one eye. Given the current social acceptability of glasses and the availability of contact lenses, historical forms of spectacles mainly appear in works as part of a setting meant to seem antiquated, as in the Harry Potter series, or as part of an Anachronism Stew setting, such as that of A Series of Unfortunate Events. Modern cataract surgery involves replacing the now-opaque lens of the patient's eye with a prescription lens. But before the 1940s, a cataract patient would instead have their lens removed and get to wear special cataract glasses from then out. These glasses had extra-heavy magnifying lenses, to the point where if you'd only had one cataract removed the glasses wouldn't balance on your face. You also had no peripheral vision to speak of, because the focus point was dead-center on the eye. Given that most cataract patients are older, the old "'borrow' Grandma's glasses to fry ants" stunt may have involved grabbing her cataract glasses, instead of reading glasses or bifocals.
In addition to the usages of concave and convex lenses for vision correction mentioned above, the old fry-ants-on-the-sidewalk trick cannot be done with concave lenses - the sort of lenses that most children have - as concave lenses will create a sort of halo around the shadow of the lens. This can be done, however, with convex lenses as they are essentially just magnifying glasses. As mentioned above, "Weird Al" Yankovic used to need glasses pretty badly, but doesn't anymore due to having gotten Lasik surgery. Because his glasses became a trademark of his, he has gotten You Don't Look Like You reactions from fans and has been asked to wear glasses for live performances.