UsefulNotes/Corrective Lenses
A page explaining the mechanics and necessities of vision correction


(permanent link) added: 2011-10-21 19:28:37 sponsor: ThreeferFAQMinorityChick (last reply: 2012-01-01 10:45:21)

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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.

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 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 will 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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[[folder: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 lens to correct. For some reason, astigmatism is the go-to impairment for nerdy characters who also happen to need vision correction.

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! [[/folder]]

[[folder:Types of Glasses and Vision Correction]]

Glasses

Glasses have been the usual method of correcting bad vision for centuries and is generally the cheapest way to do this job. After having an eye exam to determine the severity of one's visual impairment, the person will then go to pick out a set of frames, after which a set of lenses will be made according to the frame and the kind of vision the person has. After putting on the new glasses, you usually feel like everything has greater clarity and like you can see everything.

Wearing glasses tends to make people see their world through a single frame of any shape. When the wearer's eyes send in their two images, the brain combines the two signals to create the stereoscopic vision; in the process the central edges of the frames seem to disappear unless the wearer moves their eyes to one side or the other. Both lenses have to be in the glasses for them to correct the wearer's vision to their fullest potential. If, say, one of the lenses pops out but not the other, the lens that is still in corrects that eye's vision, but since the other lens is gone, then the image sent in by the uncorrected eye will be combined with that sent by the corrected eye to form an image with greater clarity than an image seen by uncorrected eyes, but is not as clear as an image that a glasses wearer sees with both eyes corrected.

For any pair of glasses, it is relatively easy to take care of them. You just got to remember to put them aside when you sleep and not do stupid things that can cause them to scratch. Plus, while it is considered inadvisable and liable to cause scratching to the lens, you can clean them and wipe them with any method that can do the job, like licking the lenses and wiping them with your shirt, without any risk to your health. It is considered most proper to clean your glasses by rinsing the lenses to remove any particles that could scratch the lenses and then wiping them with a fresh cloth or paper towel; worn shirts have particles on them that could scratch the lenses. Those who are particularly conscientious about this will buy a special solution and cloth specifically for the purpose of cleaning their glasses.

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. Modern lenses, including contact lenses, lack the abrupt transitions and the tell-tale lines.

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.

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. Someone who has these needs but doesn't wear contact lenses can get a pair of sunglasses made that can also correct vision, but these are pretty expensive. Therefore, some people who wear glasses will choose to get Transitions lenses that can darken when the light gets brighter. 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. YMMV as to whether these look endearingly dorky or not. Aviator sunglasses have large curved lenses designed to provide protection from light while reducing the wearer's field of vision as little as possible. Association with pilots and other people engaged in active pursuits contributed to their fashion cache, and they enjoyed a particular boom in popularity during the 1970s and early 80s.

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. A contact lens is a piece of flexible plastic shaped to fit onto one iris and, in some cases, correct the wearer's vision. There are also contacts that are tinted to make it look like the wearer's eyes are a different color. 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, if they have one of these. After the makeover, she will be shown to be so much more attractive without glasses and her life will improve. However, we rarely see the cleaning ritual that contact-wearers have to go through, which is descibed below.

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 commerically 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.

Removing Lenses: 1. 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. 2. Wash and rinse lens with solution in palm of non-dominant hand. 3. 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. Tap water and saliva are considered inadvisable for cleaning and using these to clean one's contact lenses can put one at risk for an eye infection. In contrast, a glasses-wearer can take their glasses off, lick them, wipe them with their shirt, and put them back on without a problem (aside from stares from people who are Squicked out).

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 itself 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 laserbeam 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 these complications, fears that the procedure might blind them if something goes wrong, and the fact that Lasik is an elective surgery that is not required, some decide to play it safe and stick with glasses and contacts.

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. 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 that one would use to correct the vision of one eye and would squint to hold it in place. 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.

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[[folder:Fun Facts]]

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.

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