How Eyes Work

Have you ever heard the adage that we don’t see with our eyes, “we see with our brain”? Well, it’s true. The eyes are responsible for transmitting images to the brain, by focusing on an object and understanding what the object is. Our eyes are considered by many as the most precious of senses.It is the shape and size of your eye that determines whether our eyes are able to focus on an object, or if corrective ophthalmic lenses are necessary. When your eye focuses on an object, an image is formed. The brain then processes the object, projecting a virtual image. Optical scientists rely on our knowledge of eye sight, the brain and how it processes images to design the best possible lenses to correct an individual’s blurry vision. The Human Vision System is a complex system consisting of two sets of lenses (the cornea and crystalline lens), two sensing devices (retina), and the brain.

How Eyes Work (continued...)

The Cornea is in the front of the eye and is responsible for focusing on an image. The Crystalline Lens is found in the anterior chamber of the eye, which not only focuses on an image, but adjusts your eyes to see objects far away, or within a short distance as well as close up. Consider when you wake up from a nap and try to focus on an image. Your eyes may have to blink once or twice to actually see a clear image.

The cornea and crystalline lens of the eye both carry a curved shaped, making our eyes appear round. When the cornea and crystalline lens of the eye are of normal size and shape, we see images clearly. If, however, a person’s cornea is too curved or not curved enough, they have a Refractive Error.

Simply stated, a refractive error means that there is an error in getting the eye to focus clearly on an image.

How Eyes Work (continued...)

Ophthalmic Lenses are needed to focus on an object and perceive it clearly. Refractive Errors include Myopia, Hyperopia and Astigmia.

If you are Myopic, Hyperopic or Astigmatic, you will need an ophthalmic lens to assist your eyes to see clearly. If your eyes also need help focusing on images close up, you have a condition known as Presbyopia. This means that your crystalline lens, due to the natural aging process, can no longer focus and adjust your focus as it used to. In this case, additional magnification is needed to focus up close.

This additional magnification can be obtained through reading glasses, bifocals, or progressive addition lenses. (Please see “Eyes Over 40” for more information).

How Eyes Work (continued...)

Our eyes are considered by many as the most precious of senses. We only get one set, and it is vital that we care for and protect them. No matter what refractive error one may have, clear, uncompromised vision is possible with a great lens. Improvements in science and technology allow lens engineers to recreate vision through lens designs. When it comes to your vision, if you need corrective lenses, insist on the best…insist on Shamir lenses.

Vision Conditions

The miracle of sight is one we hold dear. Maintaining healthy eyes is in everyone’s best interest. If our vision begins to fail, science and medicine play a large role in recreating vision through various optical technologies.

The following guide of Vision Conditions is to help you gain a better understanding of your own visual condition, so that you can better prepare to find the best optical solution to fit your needs. Let’s start with an overview of three main categories, Refractive Errors, Conditions of the Eye, and Diseases of the Eye.

Refractive Errors

If you have 20/20 vision at both distance and near, you have Emmetropia. An Emmetropic Eye has the ability to focus distant light rays to a point focus on the retina. In addition to this, the Emmetropic eye can accommodate and focus near point objects for reading without the aid of ophthalmic lenses.

Vision Conditions (continued...)

Refractive errors, simply put, are errors in the refraction of light through the eye. That is, the eye’s inability to properly transmit and refract light to focus on the retina, in the back of the eye. There are three types of Refractive Errors: Myopia, Hyperopia and Astigmia.

Myopia

Myopia, sometimes referred to as “nearsightedness”, is a refractive error where light does not reach the retina. Light comes to a focus before the retina, in the vitreous humor, the gel-like substance inside the globe of the eye. Because the light rays do not focus on the retina, the image formed in the brain is blurred. There are three types of Myopia which include Corneal Myopia (cornea is too steep), Axial Myopia (length of the eye is too long), or Lenticular Myopia (the lens system inside the eye is too strong). The myopic eye refracts light too much…it needs minus (concave) lenses for correction.

Vision Conditions (continued...)

The far point of the myopic eye, its own unique focal length, is inside optical infinity (inside twenty feet). If an eye has a low amount of myopia, its far point could be out to 10, even 15 feet. If an eye has a large amount of myopia, its far point could be as little as 10 centimeters. In either case, ophthalmic lenses are used for its correction. Myopic eyes have a tendency to increase slightly over the years, and rarely remain stable over one’s lifetime. It is important to visit your eye doctor on a regular basis to be sure that you manage your myopia and eliminate eyestrain with current lenses.

Hyperopia

Hyperopia, sometimes referred to as “farsightedness”, is also a refractive error of the eye. In this case, light rays come to a focus behind the retina. The cause of Hyperopia could be that the cornea is too flat (Corneal Hyperopia), or the globe of the eye is too short (Axial Hyperopia).

Vision Conditions (continued...)

The far point of the hyperopic eye can vary too. In theory, it is beyond optical infinity/20 feet. Some Hyperopes can see fine in the distance, but cannot see close up. Others need corrective lenses all of the time. Plus (convex) lenses are used for the correction of Hyperopia, to redirect the focus of light so that it reaches the retina. One particular type of Hyperopia, Latent Hyperopia, is difficult to detect without the use of cycloplegics, eye drops to relax the muscle inside of the eye to stop accommodation. Children with Latent Hyperopia over-use their accommodative system, which masks their refractive error. It is crucial that children see the eye doctor prior to entering the first grade, and then again before the third grade. Consult your local eye care provider for more information.

Vision Conditions (continued...)

Astigmia

Astigmia is the plural for Astigmatism, of which there are five types:
1. Simple Myopic Astigmatism
2. Simple Hyperopic Astigmatism
3. Compound Myopic Astigmatism
4. Compound Hyperopic Astigmatism
5. Mixed Astigmatism

In each type, light rays do not make a point focus before or beyond the retina, but have two major meridians of focus, usually 90 degrees apart. If you do not have Astigmatism, your eyes are spherical. If you have Astigmatism, your eyes are aspherical. A spherical eye (myopic or hyperopic) requires a spherical lens (concave or convex) to correct its refractive error. An aspherical eye needs a lens that corrects for the error in refraction differently in the major meridians. A way to imagine this is to compare the shapes with a basketball and a football.

Vision Conditions (continued...)

If you could measure the curvature in a basketball, it would be the same all the way around, in all meridians. If you could measure curvatures in a football, they would vary…a flatter side and a steeper side. Similarly, the astigmatic eye has some areas with flatter curvature, and some with steeper curves. A simple convex or concave lens will not correct this refractive error…it requires an ophthalmic lens that has two major meridians of curvature, each to offset that of the eye. These lenses are toroidal in nature, and called “cylinder lenses”. The five types of astigmatism are classifications of where the major meridian light rays focus: on/in front of the retina, on/beyond the retina, both in front of the retina, at separate points, both beyond the retina, at separate points, or one in front of the retina, and one behind.

Myopia or Hyperopia can be combined with Astigmatism, in which case a spherocylinder lens is used for its correction. This lens design, known as “cylinder lenses” is commonly used for the correction of Astigmatism.

Glossary of Opthalmic Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A
accommodation (uh-kah-muh-DAY-shun). The autotic adjustment of optical power by the eye in order to maintain a clear image (focus) as objects are moved closer.

age-related macular degeneration (AMD, ARMD) (MAK-yu-lur). A condition that includes deterioration of the macula and resulting in loss of sharp central vision. Most common cause of decreased vision after age 60.

astigmatism (uh-STIG-muh-tiz-um). A Refractive Error of the eye in which refractive power is not uniform in all directions (meridians). Light rays entering the eye are refracted unequally through different meridians, which prevents formation of a sharp image focus on the retina.  Correctable with a cylindrical lens.

Glossary of Opthalmic Terms (continued...)

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B
bifocals. A lens having two separate and distinct points of focus (focal lengths) which incorporate two different powers in each lens, usually for near and distance corrections.

binocular vision. Focusing and fusing of the separate images seen by each eye into one single binocular image.

blind spot. Sightless area within the visual field of a normal eye, where the optic disc attaches the optic nerve to the eye.  Caused by absence of light sensitive photoreceptors where the optic nerve enters the eye.

Glossary of Opthalmic Terms (continued...)

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C
cataract. Clouding of the crystalline lens, which may prevent a clear image from forming on the retina. If visual loss becomes significant, surgical removal is required. Types of cataracts include traumatic, congenital and age-related. 

central vision.An eye's best vision; used for reading and discriminating fine detail and color. 

color blindness. Decreased ability to determine differences between colors, especially shades of red and green. Usually hereditary.

cornea (KOR-nee-uh). Transparent membrane in the front of the eye that covers the iris, pupil, and anterior chamber and provides most of an eye's optical power.

Glossary of Opthalmic Terms (continued...)

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crystalline lens. The natural lens inside of the eye. Transparent, biconvex intraocular tissue that converges light to helps bring rays of light to the retina.

D
diopter (D) (di-AHP-tur). Unit of measurement for lens power.  It is the reciprocal of the focal length in Meters.

diplopia, double vision. A visualization of two images from one object; images may be horizontal, vertical or oblique.

E
emmetropia (em-uh-TROH-pee-uh). Absence of Refractive Error.  Sometimes called “Normal 20/20 Vision.”  Images at 20 feet focus sharply on the retina. 

Glossary of Opthalmic Terms (continued...)

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F
fovea (FOH-vee-uh). Central area in the macula that produces the sharpest focus. Contains a high concentration of cones which aid in clear central vision.

G
glaucoma (glaw-KOH-muh). A disease of the eye characterized by increased intraocular pressure. A common cause of preventable vision loss. May be treated by prescription drugs or surgery.

Glossary of Opthalmic Terms (continued...)

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H
hyperopia (hi-pur-OH-pee-uh), farsightedness. Focusing defect in which an eye is underpowered. Light rays coming from a distant object strike the retina before coming to sharp focus,  causing blurred vision. Corrected with plus (convex) lenses.

I
iris. Pigmented tissue lying behind the cornea that gives color to the eye (e.g., blue eyes) Controls light by contracting and constricting the opening (pupil).

Glossary of Opthalmic Terms (continued...)

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L
lens, crystalline lens. The natural lens inside the eye. Transparent, biconvex intraocular tissue that helps refract  rays of light to a point focus on the retina.
low vision. Term usually used to indicate vision of less than 20/200.  May require additional optical aids, especially for near point tasks.

M
myopia (mi-OH-pee-uh), nearsightedness. A Refractive Error in which the eye over focuses light. Rays of light traveling  from a distant object are brought to focus in front of the retina. Requires a minus (concave) lens to correct.

Glossary of Opthalmic Terms (continued...)

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O
ophthalmologist (ahf-thal-MAH-loh-jist). Physician (MD) specializing in diagnosis and treatment of refractive, medical and surgical problems related to eye

optician (ahp-TISH-un). Professional who makes and adjusts optical aids, e.g., eyeglass lenses, from refraction prescriptions supplied by an ophthalmologist or optometrist.

optometrist (ahp-TAHM-uh-trist). Doctor of optometry (OD) specializing in vision problems, treating vision conditions with spectacles, contact lenses, low vision aids and vision therapy, and prescribing medications for certain eye diseases.

Glossary of Opthalmic Terms (continued...)

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orthoptics. Optical specialty dealing with the diagnosis and treatment of defective eye coordination, binocular vision, and functional amblyopia by non-medical and non-surgical methods, e.g., glasses, prisms, exercises.

P
peripheral vision. Side vision; vision, caused by stimuli falling on retinal areas distant from the macula, toward the sides of the globe.

photophobia (foh-toh-FOH-bee-uh). Extreme sensitivity to, and discomfort from, light. May be associated with excessive tearing.

presbyopia (prez-bee-OH-pee-uh). Refractive condition in which there is a diminished power of accommodation arising from loss of elasticity of the crystalline lens, as occurs with aging. Usually becomes significant after age 40.

Glossary of Opthalmic Terms (continued...)

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progressive addition lens (PAL), progressive-power lens.. Ophthalmic lens that utilizes a steepening of curves to incorporate corrections for distance vision through intermediate range, to near vision (usually in lower part of lens), with smooth transitions and no bifocal demarcation line.

pupil. An opening in the center of the iris, of variable sizes, that regulates the amount of light that enters the eye.

R
refraction. A test to determine the refractive state of the eye, and the best corrective lenses required to aid in clear vision.  A series of lenses in graded powers are offered to determine which provide sharpest, clearest vision.

Glossary of Opthalmic Terms (continued...)

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

refractive error. An error in refraction of the eye.  An optical defect in an unaccommodating eye in which parallel light rays do not focus sharply on the retina.

retina (RET-ih-nuh). Light sensitive with photoreceptors in the eye that converts images from the eye's optical system into electrical impulses that are sent to the brain where the image is formed.

T
trifocal (TRI-foh-kul).  An ophthalmic lens that incorporates three lenses of different powers. The main portion is usually focused for distance (20 ft.), the center segment for about 2 ft., and the lower segment for near (40 cm, or 16 inches).

Glossary of Opthalmic Terms (continued...)

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

20/20. “Normal” vision. Upper number is the standard distance (20 feet) between an eye being tested and the eye chart; lower number indicates that a tested eye can see the same small standard-sized letters or symbols as an emmetropic eye at 20 feet.

V
visual acuity. Assessment of the eye's ability to distinguish object details and shape, using the smallest identifiable object that can be seen at a specified distance (usually 20 ft. or 16 in.) and letter height (8.87mm).

visual field.  The area visible to an eye that is fixating straight ahead.

Eyes Over 40

Have you ever heard the old saying, “Your arms are getting too short…?”

Perhaps you have Presbyopia. Presbyopia is not a refractive error, but rather, a condition of the eye. Specifically, Presbyopia is a natural break down of the ciliary muscle and accommodative system. As our body slows its production of collagen, the elasticity in the lens inside of the eye, the crystalline lens, loses its ability to flex.

Here is how it works

When we view something at near, many things are happening in the eye-brain visual system automatically. The eyes turn downward and inward (convergence) and the lens inside the eye focuses on the reading material, or near image. This is known as accommodation. Our ability to accommodate for near tasks gets more and more difficult as we age.

Eyes Over 40 (continued...)

While medicine has made great advancements in the ability to slow the aging process of the body, the aging process of the eye cannot be controlled.

Accommodation is the body’s response to blurry near vision by adding magnification at near. The accommodative system counteracts blurry images up close while using the eye-brain visual system to add magnification (convex lens power) to aid in near vision. After a while, as the lens loses elasticity, accommodation becomes increasingly difficult. This leads to asthenopia, or uncomfortable vision/tired eyes.

Thanks to technology, science and engineering can replace the magnification abilities of the lens with an ophthalmic lens. An ophthalmic lens can converge the light rays at varying focal lengths just as the eyes’ natural system.

Eyes Over 40 (continued...)

If you have Presbyopia, you are in a very popular group… baby boomer’s and beyond… The good news is, technology has kept up with your visual needs and can supply advanced lens system to aid in your correction of Presbyopia. Whether in an office, or relaxing on a ship, there is an optical solution to your visual needs.

Protecting Your Eyes

It goes without saying that the eyes are the most precious among senses.  The miracle of vision is one we hold dear.  Loss of sight from trauma is a tragedy we would all like to avoid.  The good news is that 90 percent of all workplace eye injuries are preventable with the use of proper safety eyewear.

Despite this good news, nearly one million Americans have already lost some degree of vision due to an eye injury.  According to the Bureau of Labor Statistics, over 365,000 work-related eye injuries still occur each year.  Another alarming fact is that, while work-related eye injuries have decreased over the years, eye injuries at home are on the rise.  According to Prevent Blindness of America, the incidence of home-related eye injuries is increasing, and there is a belief that many more occur, which are never reported.  This directly correlates to increased availability and affordability to power tools, lawn tools as well as household chemicals. 

Protecting Your Eyes (continued...)

Yet, the distributors and retailers of these products do not as readily make available or promote safety eyewear.

Consumer studies show more people buy protective gloves for gardening and household chores than protective eyewear.  Beyond awareness with such an array of products and technologies, how do you know what is best for you?  The following guide will enable you to best determine the protective eyewear suited to your needs.

Protecting Your Eyes (continued...)

Lenses:

1. Polycarbonate:  Polycarbonate is a material that will sustain high velocity impact.  Environments that have a potential for high velocity projectiles such as wood-working, lawn mowing, and drilling lend to the risk of eye injuries.

2. Trivex:  Trivex is a plastic-type material that has the same impact resistance as polycarbonate, with improved optics.

3. Glass:  Although not as impact resistant as polycarbonate and trivex, glass is more resistant to chemicals and heat.  For example, a welder or those working with solvents.

Protecting Your Eyes (continued...)

Frames:

To be effective, safety frames must be part of a lens package.  As previously mentioned, the proper material depends on the occupation or hobby. Safety frames are available in plastics or metals.

If you think you may need safety eyewear for your tasks or hobbies, you probably do. Remember, when in doubt, medical science has yet to create a false eye that can see.

The above information is for reference only, please be sure to consult with your eye care professional.

How To Choose Your Lenses

Your selection of eyewear is an important decision as it encompasses both function and style.  Think of your eyewear as similar to a watch; it is a fashion statement that also provides necessary information.  Your prescription lenses provide visual information to your brain, through your ability to see clearly and comfortably.  Properly chosen prescription lenses also protect the inner systems of your eye from damaging UV radiation.  Meanwhile, your eyeglass frames make a dramatic impact on the appearance of your face.  This is an opportunity for your personal style to shine through.

With the array of lens and frame choices as well as available technologies, selecting eyewear can be an overwhelming task.  The following guidelines will assist you in evaluating your needs along with your eyecare professional.

How To Choose Your Lenses (continued...)

Lenses:

Ophthalmic lenses are carefully designed to recreate natural vision.  There are different designs available for specific visual tasks and needs.  For example, if you are a Presbyope and need adjusted power for nearpoint tasks, you will likely want a multifocal lens.  The Progressive Addition Lens (PAL) provides the most natural vision with the best cosmetic appearance, as there is not a visible line, resulting in image jump.  Shamir Insight’s Genesis premium PAL provides wide areas of clear vision.  Many occupational and hobby environments, particularly computer use, require a lens specifically designed for small spaces.  Shamir Insight’s Office Lens is an occupational/hobby lens created for just such tasks.  Additionally, premium PALs and small environment lenses provide an ultraviolet radiation filter, critical to the health of your eyes.

How To Choose Your Lenses (continued...)

Frames

When selecting frames, it is important to choose a design that suits your prescription.  Your eyecare professional can assist you in this important category.  In addition, your frames should be cosmetically appealing.  When considering cosmetics, you will want to incorporate your individual coloring, face shape, and personal style.  What is the best frame for you cosmetically?  It is all about color and facial features.  In regard to face shape, it is all about balance.  An Oval face is a balanced shape, and may wear any frame design, so long as the prescription allows.  Other face shapes are categorized as follows:

How To Choose Your Lenses (continued...)

All of the face shapes can be grouped into three main categories:  Oval, Wide and Narrow.  The frame design can dramatically alter the appearance of a face shape to give the illusion of an oval.  This fashion technique/optical makeover is accomplished with the placement of the endpiece, where the sides meet the front of the frame.  If you wish to give a narrow face a wider look, then the end-pieces should be midline to the frame front.  If your goal is to make a wide face look slimmer, than a high endpiece attachment is needed.

Looks

Once you identify your prescription needs, lens options and frame considerations, you are ready to combine the best of everything to create a look that reflects your personality and style.  Optical makeovers are a great way to combine function and fashion that is your very own.  Different occasions require different looks. 

How To Choose Your Lenses (continued...)

You would not wear a business suit to the beach, nor would you wear cut-off shorts to a board meeting.  Today’s eyewear fashions include business classic, evening elegance, casual and sporty designs.  Color trends continue to gain popularity, as well as streamlined rimless that are light-weight, and seem to disappear on your face.  A wardrobe of eyewear, suited to various aspects of your lifestyle, is not only convenient; it shows the many faces of you!

What Are Occupational Lenses?

An occupational lens is a design in prescription eyewear that allows the wearer to view all working distances, side to side, up and down, within a conventional working distance, or small environment.  A working distance typical to many occupations will fall somewhere between ten to thirteen feet, respectively.

Our working and lifestyle environments require that we have clear vision at working distances of 1.5, 2.5 and out to 10 feet.  And, this vision must be clear in all areas of the lens, at all viewing angles.

The Problem:

The problem is, presbyopes (bifocal/progressive addition lens wearers) have had limited options for mid and near range visual requirements.  The solution to this unique visual requirement based on occupational/visual needs is a variable occupational lens. It is the best optical solution.

What Are Occupational Lenses? (continued...)

According to USA Today...

More than 100 million people use computers (a statistic from 1998…it is likely much higher today…)

Ergonomics play a large role in our ability to work comfortably, without causing neck and back strain at the end of the day.   For best comfort, we should be plane with our computer station, or balanced, in essence.  This requires that we are able to sit up straight in a chair, view our computer monitor below our line of sight, at a comfortable viewing angle.  All the while, we need to be able to relax our wrists and forearms while typing, and maintain focus on the ever-changing computer monitor pixels with varying contrasts.

Quite a challenge!

What Are Occupational Lenses? (continued...)

The Solution:  Occupational Lenses

Different than a progressive addition lens, this variable design begins with the full reading prescription at the bottom of the lens, and weakens, for mid-range vision, as the eyes rotate upward.  Almost like an upside down progressive – taking away power vs. adding power.

In the middle of the lens, the entire design is devoted to intermediate vision.  The Shamir Office Occupational Lens is the only design to take this approach. Then, the other portion of the prescribed reading power is reduced as it reaches the upper part of the lens.  This unique design approach brings quality optics from 10 – 12 feet distance, tapering in to normal reading distances, around 16 inches, or 40 centimeters.  If your lens is working for you, you can give your neck and back a break.

What Are Occupational Lenses? (continued...)

You will not need to tilt your head in order to find the best optical zone in the lens…it is designed to match visual requirement with ergonomics. 

Comfortable vision and good working ergonomics are too important to leave to chance.  Choosing an occupational lens, specifically designed for small environments with adapting optics is the best optical solution for clear vision at varying focal ranges.  Choose the Shamir Office occupational lens… your eyes and back will thank you!

How Lenses Are Made

Ophthalmic Lenses are designed to refract light so that it reaches the retina. It is necessary for light rays to focus on each retina, in the back of our eyes, in order for us to see. When the eye’s own optical system cannot refract light onto the retina, ophthalmic lenses are needed.

The main job of the ophthalmic lens is to manipulate light. Lenses are used for many reasons. The main reasons they are prescribed is for safety, vision and comfort. Different materials are used for specific purposes and visual needs. The following list is an example of what ophthalmic lenses do:

• Refract light rays to reach the retina
• Reflect uncomfortable or dangerous light rays
• Reflect annoying glare and reflections
• Absorb light for comfort or safety
• Transmit light for better vision
• Block dangerous light and blinding glare

How Lenses Are Made (continued...)

The design and production of lenses is a complex art and science. Glass and Plastic-type lenses, with the exception of polycarbonate, are made from a molding process. First, the lens designer calculates the best curvatures necessary for superior optical quality. Then, a computerized program attached to a digital file and lathe cuts the inside/top surface of the mold. This could be a single curvature for single vision lenses, or multiple curves for an aspheric lens or a progressive addition lens. Then, the back of the mold is attached and liquid plastic (monomers and polymers) are added. After the annealing and cooling process is complete, the lens is ready to be surfaced. Surfacing a lens means cutting curves into the back side to create the prescribed numbers, or spectacle Rx. In simple spherical curves, a steeper curve yields a stronger prescription and a flatter curve yield a weaker prescription. Once polished, the finished lens is ready to be edged for the shape of the frame or eyewire. Many coatings and filters can be added to the lens to manipulate light in different ways.

How Lenses Are Made (continued...)

A vacuum-sealed process is necessary for coatings to adhere properly. Examples of coatings are ultra violet filters, tints, anti-reflective coatings, mirrors and more.

The most common reason lenses are prescribed is for vision. Three factors determine the prescription in a lens. They are the material (index of refraction), thickness, and curvature. In theory, lenses are considered as being prisms attached, base to base or apex to apex. A convex lens (prisms base to base) magnifies images, and is used for the correction of Hyperopia or Presbyopia. A concave lens (apex to apex) minifies images, and is used for the correction of Myopia. Cylinder (toric) lenses are also used for the correction of astigmatism, and have different powers in different zones of the lens. Technology and science have improved the way lenses are made and it keeps getting better. Shamir Insight’s team of optical scientists are dedicated to improving lens designs to deliver the best possible vision ever, recreating perfect vision.