Friday, September 14, 2012

Other Glasses: Monocle


A monocle is a type of corrective lens used to correct or enhance the vision in only one eye. It consists of a circular lens, generally with a wire ring around the circumference that can be attached to a string. The other end of the string is then connected to the wearer's clothing to avoid losing the monocle. The antiquarian Philipp von Stosch wore a monocle in Rome in the 1720s, in order to closely examine engravings and antique engraved gems, but the monocle did not become an article of gentlemen's apparel until the nineteenth century. It was introduced by the dandy's quizzing glass of the 1790s, as a sense of high fashion.

Styles of monocle

There are three styles of monocle. The first style consists of a simple loop of metal with a lens which was slotted into the eye orbit. These were the first monocles worn in England and could be found from the 1830s onwards.

The second style, which was developed in the 1890s, was the most elaborate, consisting of a frame with a raised edge-like extension known as thegallery. The gallery was designed to help secure the monocle in place by raising it out of the eye orbit slightly, so that the eyelashes could not jar it. Monocles with galleries were often the most expensive. The very wealthy would have the frames custom-made to fit their own eye sockets. A sub-category of the galleried monocle was the "sprung gallery", where the gallery was replaced by an incomplete circle of flattened, ridged wire supported by three posts. The ends were pulled together, the monocle was placed in the eye orbit, and the ends released, causing the gallery to spring out and keep the monocle in place.

The third style of monocle was frameless. This consisted of a cut piece of glass, with a serrated edge to provide a grip and sometimes a hole drilled into one side for a cord. Often the frameless monocle had no cord and would be worn freely. This style was popular at the beginning of the 20th century as they could be cut to fit any shape eye orbit cheaply, without the cost of a customized frame.

It is a myth that monocles were uncomfortable to wear. If they were customised then they could be worn securely with no effort, though periodic adjustment is a fact of life for monocle wearers to keep the monocle from popping, as can be seen in films featuring Erich von Stroheim. Often only the rich could afford to have them custom-manufactured and the poor had to settle for poorly-fitted monocles that were less comfortable and less secure. The popular perception was (and still is) that a monocle could easily fall off with the wrong facial expression. This is true to an extent, as raising the eyebrow too far will allow the monocle to fall.


The quizzing glass should not be confused with a monocle since it is held to one's eye with a handle, in a similar fashion to a lorgnette, and not by A once-standard comedic device exploits this: an upper-class gentleman makes a shocked expression in response to some event, and his monocle falls into his drink, smashes into pieces on the floor, etc. In visual media, the monocle might also be illustrated, or visually captured mid-flight, with some slack to the string as the glass travels downward.

Other Glasses: Sunglasses

Sunglasses or sun glasses are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist, featuring lenses that are colored, polarized or darkened. In the early 20th century they were also known as sun cheaters (cheaters being an American slang term for glasses).


Most people find direct sunlight too bright for comfort during outdoor activities. Healthcare professionals recommend eye protection whenever the sun comes out to protect the eyes from ultraviolet radiation (UV) and blue light, which can cause several serious eye problems. Sunglasses have long been associated with celebrities and film actors primarily from a desire to mask their identity. Since the 1940s sunglasses have been popular as a fashion accessory, especially on the beach.

Lens

The color of the lens can vary depending on style, fashion, and purpose, but for general use, red, grey, green, or brown are recommended to avoid or minimize color distortion, which could affect safety when, for instance, driving a car or a school bus.
  • Gray and green lenses are considered neutral because they maintain true colors.
  • Brown lenses cause some color distortion, but also increase contrast.
  • Turquoise lenses are good for medium and high light conditions, because they are good at enhancing contrast, but do not cause significant color distortion.
  • Orange and yellow lenses increase both contrast and depth perception. They also increase color distortion. Yellow lenses are used by pilots, boaters, fishers, shooters, and hunters for their contrast enhancement and width perception properties.
  • Blue or purple lenses are mainly cosmetic.

With the introduction of office computing, ergonomists may recommend mildly tinted glasses for use by display operators, in order to increase contrast.

Frames

Frames are generally made of plastic, nylon, a metal or a metal alloy. Nylon frames are usually used in sports because they are lightweight and flexible. They are able to bend slightly and return to their original shape instead of breaking when pressure is applied to them. This flex can also help the glasses grip better on the wearer's face. Metal frames are usually more rigid than nylon frames, thus they can be more easily damaged when the wearer participates in sport activities, but this is not to say that they cannot be used for such activities. Because metal frames are more rigid, some models have spring loaded hinges to help them grip the wearer's face better. The end of the resting hook and the bridge over the nose can be textured or have rubber or plastic material to improve hold. The ends of the resting hook are usually curved so that they wrap around the ear; however, some models have straight resting hooks. Oakley, for example, has straight resting hooks on all their glasses, preferring to call them "earstems".

Some sports-optimized sunglasses have interchangeable lens options. Lenses can be easily removed and swapped for a different lens, usually of a different color. The purpose is to allow the wearer to easily change lenses when light conditions or activities change. The reasons are that the cost of a set of lenses is less than the cost of a separate pair of glasses, and carrying extra lenses is less bulky than carrying multiple pairs of glasses. It also allows easy replacement of a set of lenses if they are damaged. The most common type of sunglasses with interchangeable lenses has a single lens or shield that covers both eyes. Styles that use two lenses also exist, but are less common.

LASIK surgery

Some people might not felt comfortable wearing glasses and/or got sick and tired of putting contacts in his/her eyes every day. These people will evetually consider getting LASIK surgery. However, LASIK surgery has both good and bad sides which can affect their decision greatly.

The Good

1. The first reasons for Lasik Eye Surgery is the effectiveness of the surgery to correct eye conditions such as myopia (near-sightedness), hyperopia (far-sightedness) and astigmatism. Eye surgeries are not usually performed unless required as in the past before the time of Lasik Eye Surgery, where the majority of surgeries involve the removal of cataracts.
However, as eye surgeries improve to do more than just removing cataracts, patients are more open towards treatment for aesthetic purposes. They may not like wearing glasses, hence take the step for Lasik Eye Surgery once their glasses prescription stabilized, to make things more comfortable and look better.

2. Even though the name is Lasik Eye Surgery, the surgery is generally painless, and the surgery usually takes between 5 to 10 minutes, unlike other surgeries that may take hours to perform. A fast procedure like that makes it convenient for most people, erasing the fear of discomfort.

3. The technology used is highly computerised, hence the precision and accuracy in result is assured. The precision is required as there thickness of the cornea will be calculated to ensure that the laser ablation will work well to improve the patient’s sight.

4. The success of Lasik Eye Surgery is high, and most patients need only one single treatment for the desired result. However, there may be instances where an enhancement surgery may be required after many years when there are further changes to the cornea.

The Bad

1. Any surgery’s healing period and recovery will depend very much on the individual, and so it is the same also for Lasik Eye Surgery. A patient’s habits and lifestyle will definitely influence the rate of recovery, and also vary the results in each individual.

2. There are side effects to Lasik Eye Surgery, and it may actually worsen the vision of the patient, by causing glare, halos and night vision problems. However, it has to be noted that the side effects varies with individuals. Some may experience just a little bit of side effects, while others may experience them badly.

3. Also, while many people may not like the discomfort of dry eyes while wearing contact lenses, the dry-eyes condition may be worse than wearing contact lens in some individuals. Individuals experiencing dry-eyes will need to have a bottle of eye drops or fake tears around for comfort relief.

4. In some very rare conditions, the wish of a patient to correct vision by Lasik Eye Surgerymay be totally destroyed when the treatment cause vision to become worse. There may be many reasons for such rare circumstances, and the worsened conditions maybe not reversible, and cannot be corrected with regular glasses or contact lenses. In this situation, it can be really stressful as the patient actually will not be able to find an easy treatment for an important organ of the body, the eye.


The good and the bad of Lasik Eye Surgery is not meant to advertise for, or promote the technique, nor does it serve to scare patients with potential blindness. Going almost blind fromLasik Eye Surgery is extremely rare, although most cases just reported the need for a second surgery years later as there are, again, changes to the cornea which may have deteriorated the vision. In any circumstances, there is no reason to fear having Lasik Eye Surgery if both doctor and patient agree that it can bring the desired result. Lasik Eye Surgery is also a surgery not unlike any other, hence there will always be risks during the surgery with the intention of reaching the desired result.

Most importantly, patient should always refer to the doctor and ask questions if there are any doubts in mind. The trust between patient and doctor should be established early on in the relationship so that the patient will be comfortable enough to let the doctor perform surgery on the eyes. In any case at all, patient should always remember that Lasik Eye Surgery needs personalized attention, and what worked for a friend does not necessarily mean that it will work on everybody.

Eyeglasses vs. Contact Lenses


The popular question for people with sight problem is to use glasses or contact lenses

When choosing between contact lenses or eyeglasses there are several things you will want to consider. Lifestyle, time and aesthetics will all play a role in helping you determine which option is best for you. While glasses and contacts are both easy to maintain, affordable and correct astigmatism, below are some questions you may want to ask yourself when making your decision.

What kind of lifestyle do I have?

There’s no doubt that contact lenses are suitable for most people seeking vision correction. They’re often the perfect solution for anyone who spends the bulk of their time at home and in an office, classroom or store. But if your work or recreational activities result in regular encounters with eye irritants such as saltwater, sand, dust or debris, you may want to opt for eyeglasses.

Which is Most Comfortable for Me?


Some people feel that eyeglasses are bulky. Glasses can also become irritating on the bridge of the nose and behind the ears. This feeling of discomfort is more exaggerated if the wearer begins to sweat. If you might feel that glasses won’t provide you with optimal comfort, you may want to look at getting contact lenses.

Contacts also have some comfort issues. Allergy sufferers may discover that contact lenses feel “scratchy.” Contact lenses can also make the eyes feel dry and look red, which may in turn require the frequent use of eye drops. Ask your eye care professional for a sample pair of contacts to take home and test. If you find that contacts are irritating, you may want to go with glasses.

How Much Variety Do I Want?

Unless you have enough money to select several pairs of eyeglass frames, there’s little you can do to modify your look. Contact lenses, however, come in a variety of colors and tints. You can select contact lenses that are clear or simply enhance your natural eye color, or go with bolder shades like violet, emerald green and deep blue. Most vision centers will allow you to sample several shades to see which look is right for you.

How Comfortable Will I Be with Inserting My Contacts?

Let’s face it: some people are downright squeamish about inserting or removing contact lenses from their eyes. Contact lens insertion and removal does take practice, but it’s not for everyone. If you are thinking about getting contact lenses, have your eye care professional show you how to put them in and take them out and then decide if you will be able to accomplish this task on your own at home.

How Complicated Will Maintenance Be?
When it comes to eyeglasses, a dab of eyeglass cleaner and a lint-free wipe are usually all you’ll need to keep eyeglass lenses crystal clear. Contact lenses, however, require careful handling, daily cleaning, special cases, and sterile solutions. Since different types of contact lenses need different methods of cleaning and storage, it’s best to speak with your eye care professional about what cleaning procedures might be involved if you select contact lenses.

You Can Have the Best of Both Worlds

Most people don’t realize that they can have the best of both worlds by selecting contact lenses AND eyeglasses. Although you will need to have an eye exam specifically for glasses and another for contacts, you may want to wear glasses at school or in a more professional setting and then slip into your contact lenses for casual wear and social events. There are plenty of options available to you, so speak with your eye care provider about how to make the best possible eyewear decision.

How to take care of your glasses

Caring for your Glasses

When glasses are dry, avoid touching the lens surface
  • Do not to polish the lens
  • Do not rub the lens too hard with a dry cloth
  • When washing glasses in soapy water, ensure that the water is not too hot. This is particularly important when washing plastic framed glasses as their shape can become deformed with heat.
  • A dish soap or wishing up liquid is best and you should avoid hand soaps, as these can leave a residue from added moisturiser in them.
  • Never use any products containing ammonia to clean glasses as this can damage the lens.
  • Paper including tissues should not be used to clean glasses as the fibres can damage the lens.
  • If your glasses have a screw in them to hold the lens, ensure that it is in place securely, before washing glasses.
  • Take care not to chip the frame when washing glasses.

Cleaning your Glasses

Glasses should be cleaned with the cloth, which is usually included with the glasses. Fortnightly, you may wish to wash them in warm soapy water, rinse well and dry with a cleaning cloth. This should be done as follows:
  1. Rinse the glasses in warm water. Ideally, running water. 
  2. Then, using a mild soap, wash them in warm water. A dish-soap or wishing up liquid is best and you should avoid hand soaps, which can leave a residue. You may need to use a clean cloth, preferably cotton. Use circular motions to wipe off the soap as the glasses are rinsed under a running tap of warm water. 
  3. The glasses can then be dried gently with a cotton towel/chamois. The frame should also be dried. 
  4. If the nose pads need cleaning, try using a soft toothbrush but ensure that you do not scratch the lenses.

Alternatively, you may wish to place the glasses in soapy water and wrap a damp cloth around the front and back of the lens and wipe it using your fingers to push the cloth, from side to side gently. A cotton bud can be used to dry parts that are hard to reach.

After cleaning and drying your glasses, put them back on and inspect them for any stubborn marks or soap.

Frame and personalities

Eyeglasses can reflect personality, as there are thousands of styles that can accommodate any comfort level, size and face shape. Match your personality with eyeglass frames with helpful advice from and optometry office manager in this free video on prescription eyeglasses.

For Men

 

Video Transcript

All right, now I’m going to talk about you picking out frames that match your personality.
We carry over twelve hundred different frames at my location, with that many frames there is plenty to choose from, you’re not limited, you need to find something that you are comfortable with because if you’re not comfortable with your glasses you’re not going to want to wear them.
With all the different selection, we’ve talked about the semi-rimless, we’ve talked about things like a plastic frame such as this one over here and we’ve also talked about the rimless glasses.
What do you want your glasses to be, do you want them to disappear, do you want them, do you want people to notice your glasses, pick something, what do you want your vision and your style to be?
If you’re not comfortable wearing glasses and you don’t, don’t want to feel them, then the totally rimless and drill mount is going to be your best option.
If you just want them to disappear a bit, maybe not be so conspicuous then the semi-rimless is going to be your best option.
But let’s say you want, you want a little pizazz, you want to kind of be, you know bold, pick, you know, pick something again you know, kind of fits to, fits your personality, this frame in particular isn’t too, too flashy but there’s a little accent, you know something that will stick out a little bit, maybe just kind of show a little bit of a flair, so don’t feel you know limited and pigeonholed.
If you’re a more conservative guy you can go with you know the double bar if that’s what you’re comfortable with.
It’s all about going with what you’re comfortable with and picking something that suits you.
Don’t, don’t be pigeonholed by you know what a certain store or vendor might have, there’s lot of different options out there for you and I’m sure you can fit something, pick something that will fit your personality.

For Women



Video Transcript

One of the most important things when choosing out the glasses, if not the most important thing is picking out glasses that fit your personality.
What do you want your glasses to be, how are they going to describe you? You are going to be wearing them; most people are going to be wearing them all the time. 
Do you prefer things that are going to have color and be very bold or do you prefer the inconspicuous drill mount look to the glasses? 
There are lots of different options for you to choose and you need to determine what are your glasses going to do for you. 
So as women you have lots of different choices, lots of different colors, lots of different patterns to choose from. 
We have all these different colors of zyle frames, these plastic frames; we have blue, brown, orange, very thick, you know the thicker style frames. 
We have the less conspicuous but not totally rimless kind of a, I guess what I’m going to again call a more mature look, okay, so these frames are going to be a little bit bigger on you, so you also want to make sure that they are not going to be obtrusive okay.
You want them to fit, you know, your personality, if you like bright red, you should go with the bright red, you know, try the bright red frames, so people are very surprised with how bold colors actually turn out looking on them. 
So pick something that fits you, if you’re, you know ambitious, maybe you know for lack of a better word, maybe a little bit more funky, a little bit more trendy. 
Try something that kind of demonstrates that with your glasses and go with something that’s a little bit more bold. 
If you don’t want them to be noticed, if you want them to be a little less conspicuous try a rimless, you know try, try to go with something a little, a rimless or semi-rimless so that they will kind of blend in a little bit better, so your glasses describe you so make sure that you pick out something that is representative.

About the frame

Frame Material for Glasses

Frames can be made from many different types of metals and plastics. The drawbacks to plastic frames are that they break more easily than metal frames but they are ideal for people who are susceptible to allergies. Plastic frames may also get slightly weaker with sun exposure. Most frames for eye glasses are made of metal. This is because it shapes easily and does not corrode if it has the right kind of plating and becomes rust free. 

Plastic Zylonite Frames
Frames made of zylonite can be relatively cheap to buy and come in vibrant colours. The frames are usually very light in weight but can become less flexible overtime. Some people are allergic to zylonite frames but this is unlikely when high quality zylonite is used. Zylonite frames usually have an additional protective coating that prevents their colour from fading.

Plastic Propionate Frames
This is another lightweight plastic frame, which is hypoallergenic. 

Plastic Nylon Frames
Frames made from nylon are very common and have the benefit of being strong and light in weight. Many sports players choose nylon frames because they are highly resistant to hot and cold temperatures and are very flexible, yet also stiff. A wide variety of shapes can be made with nylon and therefore nylon frames come in many frame shapes. The main drawback to nylon frames is that colour of frames can be limited.

Titanium Frames
These frames have become increasingly popular and they are lightweight, strong and durable. Titanium is naturally grey but eyeglass frames can be coloured. Titanium may be mixed with another metal to create a frame made of an alloy. Nickel or copper may be combined with titanium to reduce the cost of the frame. Titanium also has the added benefit of being allergy free.
Beryllium Frames
These are relatively cheap frames and do not corrode nor tarnish. The frames are lightweight, strong and flexible. Further, beryllium frames can be made from a variety of colours. Beryllium frames are very easy to work with and opticians can easily bend them into the right shape because of their high flexibility. These frames are often favoured. 

Stainless Steel
Stainless steel frames have the benefit of being lightweight, low in toxicity and are quite strong yet do have an element of flexibility. For those who suffer from allergies, they are also hypoallergenic and at the same time, relatively cheap. 

Aluminium Frames
Like many metal frames, these are lightweight and very rarely corrode. These frames have a distinct look and are often used by high-end frame designers. The aluminium may be combined with silicon and iron, which makes the frame both strong and hard, as aluminium is naturally a soft metal.

Ticral Frames
These do not contain any nickel and are therefore hypoallergenic. They are exceptionally lightweight and cheaper than frames made purely of titanium. Ticral frames are also strong and long lasting and can come in a variety of colours. They can be made quite thick and can therefore look quite fashionable like plastic frames.

Flexon Frames
This is another material, which is often used to make frames for eye glasses. It is an alloy based on titanium and has the unique quality of returning to its original shape if it becomes damaged. This makes these frames particularly popular. Even if they are twisted or bent and crushed, they will still regain their shape. Further still, these frames are light in weight, hypoallergenic and do not corrode. An overall, ideal frame material.

Wood Frames
Designer bespoke frames may be made of wood but they are hand carved and expensive. These frames have a unique look and are not commonly worn.

Silver, gold, leather, semi-precious or precious stones can all be added decoratively, to plastic frames and metal frames. They create a fashionable or unique look. Frames may also be gold-plated, in a bespoke frame design.


The history of glasses

About 1,000 years ago, very few people had the need, or ability to read and write. Most of them were monks. As they grew older, reading and writing, in not very well lighted rooms, became very difficult (due to what we now call PRESBYOPIA). At that time, monks were able to make "Reading Stones".

The "Reading Stones" were a section of a spherical clear and polished natural Glass (quartz). Imagine a ping-pong ball made of transparent and polished glass: if you cut the ball in two equal sections, you have two reading stones or actually what we now call, PLANO-CONVEX magnifying lenses.

By trial and error, the monks realized that larger stones, ones with a larger spherical radius, would give less magnification than smaller stones, and the flat part of the stone did not have to be the middle of the sphere.

13th Century

The master-glassmakers of Venice began making spectacles at the end of the 13th century. The glasses were actually two magnifying lenses connected by hinge or pivot mechanism (with an inverted V shape), which could be made from wood, metal, or baleen and in later times copper wire.



These "Plus Lenses" glasses were only for correcting close distance vision (presbyopia and farsightedness). There are paintings of monks using these eyeglasses dating to the middle of the 13th century. Also, there is a church in Zaragoza, Spain that has statues of monks, one having a pair of early eyeglasses (circa 1,490).

15th and 16th Centuries

A significant development in the making of eyeglasses was the introduction of the concave lenses, solving the problem of nearsightedness (distance vision).
As in the previous post, eyeglasses for distance vision have what is called Minus Power Lenses: these lenses move the focal point from the front of the retina onto the retina itself.

17th Century

One of the major problems for the eyeglasses was how to keep them on. One solution was to have some string or ribbons attached to the lenses and loop them over the ears.

18th Century

Finally, the side temples were invented and have stayed with us for centuries! Temples with sliding extension were introduced in Europe.

Benjamin Franklin developed the bifocal eyeglasses. He needed eyeglasses for distance and close vision and he got tired of changing eyeglasses when he changed his vision from distance to close or vice versa. He had the lenses cut in halves, and mounted the distance vision half lens on the upper part and the close vision half lens on the lower part of the eyeglasses frames.

The Lorgnette became very popular with people who could not wear eyeglasses.


19th Century
Cylindrical lenses to correct Astigmatism were introduced.

The monocle (one lens) became very popular in Germany

At the end of the century, pinch-nose (Pince-Nez) eyeglasses were well established because of its convenience.

20th Century

Early in the century, eyeglasses frames began to be designed with fashion in mind.

By the 1945, a number of different Contact Lenses were available: By the 1970's, with greater improvement in the design of contact lenses (soft lenses),a large number of people started to use them.

And finally, eye surgery: Radial Keratotomy for Nearsightedness, and later, eye surgery using Laser and computers became well established for solving Farsightedness, Nearsightedness and Astigmatism (PKR and LASIK).

Some experimental techniques are being explored to correct Presbyopia.

About the lens

The strength of a lens is determined by the lens material and the angle of the curve that is ground into the lens. Lens strength is expressed as diopters (D), which indicates how much the light is bent. The higher the diopter, the stronger the lens. Also, a plus (+) or minus (-) sign before the diopter strength indicates the type of lens.

To make a lens, the first thing you need is a lens blank. Blanks are made in factories and shipped to individual labs to be made into eyeglasses. The raw lens material is poured into molds that form discs about 4 inches in diameter and between 1 and 1 1/2 inches thick. The bottom of the mold forms a spherical curve on the front face. A small segment with a stronger curve may be placed in the mold to form the segment for bifocals or progressive lenses.

How the Lens is Made

In the lab the patient's full prescription gives these exact details:
- The total power (in diopters) the finished lens must have.
- The strength and size of the segment (if needed).
- The power and orientation of any cylinder curves.
Details such as the location of the optical center and any induced prism that may be needed.

The lab technician selects a lens blank that has the correct segment (called an add) and a base curve that is close to the prescribed power. Then to make the power match the prescription exactly, another curve is ground on the back of the lens blank.
In most labs the equipment is designed to grind minus curves, so a strong, plus lens blank is usually selected.
If the base curve is too strong, then a minus curve is ground in the back of the lens, which reduces the total power of the lens.

For example, a very common lens blank is +6.00 diopters. If the prescription calls for a total of +2.00 diopters, a -4.00 diopter curve is ground on the back: (+6.00D) + (-4.00D) = +2.00D. (See the illustration below.) If it is needed, the cylinder curve is also ground at the same time.





If the prescription calls for a minus lens, the +6.00 diopter lens blank can still be used. To create a lens with the strength of -2.00 diopters, a -8.00 diopter curve is ground on the back: (+6.00D) + (-8.00D) = -2.00D.

Thursday, September 13, 2012

How glasses work?

One of the most common sights almost anywhere in the world is -- eyeglasses! Since we depend so much on the lenses inside those frames to improve our view of the world, you might wonder just what goes into creating them.

On the back of your eye is a complex layer of cells known as the retina. The retina reacts to light and conveys that information to the brain. The brain, in turn, translates all that activity into an image. Because the eye is a sphere, the surface of the retina is curved.

When you look at something, three things must happen:
- The image must be reduced in size to fit onto the retina.
- The scattered light must come together - that is, it must focus -- at the surface of the retina.
- The image must be curved to match the curve of the retina.

Out of Focus

Most vision problems occur when the eye cannot focus the image onto the retina. Here are a few of the most common problems:
  • Myopia (nearsightedness) occurs when a distant object looks blurred because the image comes into focus before it reaches the retina. Myopia can be corrected with a minus lens, which moves the focus farther back.
  • Hyperopia (farsightedness) occurs when a close object looks blurred because the image doesn't come into focus before it gets to the retina. Hyperopia, which can also occur as we age, can be corrected with a plus lensBifocal lenses, which have a small plus segment, can help a farsighted person read or do close work, such as sewing.
  • Astigmatism is caused by a distortion that results in a second focal point. It can be corrected with a cylinder curve.
In addition, lenses can be made to correct for double vision when the eyes do not work together ("crossed eyes"). The lenses do this by moving the image to match the wayward eye.
When light pass through the lens, it is always bent toward the thickest part of the lens. To make a minus lens (above), the thickest part, the base is on the outer edges and the thinnest part, the apex, is in the middle. This spreads the light away from the center of the lens and moves the focal point forward. The stronger the lens, the farther the focal point is from the lens.
To make a plus lens (below), the thickest part of the lens is in the middle and the thinnest part on the outer edges. The light is bent toward the center and the focal point moves back. The stronger the lens, the closer the focal point is to the lens.
Placing the correct type and power of lens in front of the eye will adjust the focal point to compensate for the eye's inability to focus the image on the retina.



And by putting those lens in the frame, the glasses are created.