Basics of Vision
Basic Anatomy of the EyeFocusing at different distances
Common Problems with the eyes and visual system
Basic anatomy of the eye
The human eye is composed of several tissue types that have been modified to allow for vision to occur. In general, the eye may be divided into refracting tissues (tissues that focus light), light sensitive tissues and supportive tissues.
Refracting tissues — Refracting tissues bend light that enters the eye to focus it on the light-sensitive nerve tissues at the back of the eye. If the refracting components of the eye are misaligned, improperly formed, or damaged, light will not be focused properly and blurry vision may result.
Cornea — The cornea is the clear structure at the front of the eye, and is responsible for approximately 70 percent of the eye’s ability to focus light. The cornea is composed of specialized tissue layers that adjust the amount of water inside of cells in order to remain transparent and allow for clear vision. The cornea is very sensitive to pain (think of how it feels when dust particles or a small eyelash get into your eye) because it has the highest density of nerves in the body. The cornea is also involved in keeping the surface of your eye moist with tears. Irregularities in the cornea may contribute to dry eye, a common medical problem that can be treated effectively.
Pupil — The pupil is the opening in the circular iris muscle, or the colored part of the eye, that appears black. Pupil size may impact your vision in brightly or poorly lighted environments and controls the amount of light that enters the eye, much like an aperture on a camera. Pupil size may be influenced by medications, illicit drugs, or a person’s emotional state. Abnormally shaped pupils may be a sign of trauma or developmental abnormalities and different sized pupils may occur as a result of nerve damage to the eye. Both of these situations should be evaluated by an eye doctor.
Lens and Ciliary Muscle — The lens is a transparent tissue of many cell layers. It is responsible for roughly 30 percent of the eye’s focusing power. The lens is unique in that it can vary the amount that it focuses light, much like the focusing system on a camera. This is accomplished through a series of fibers that connect the lens to the ciliary muscle, which stretches or relaxes to adjust the shape of the lens. With age, the lens tissues become less flexible, and the ability to variably focus light diminishes – this is termed presbyopia. When this occurs, additional power (usually supplied through corrective spectacle or contact lenses) is needed for the eye to view near objects, such as during reading tasks. Most people begin to benefit from reading glasses around the age of 40.
In addition to losing its focusing ability, the lens tends to become less transparent with age. This is usually first noticed as glare around bright lights or the need for brighter lighting when reading. When the lens becomes difficult to see through, a cataract has formed. Cataracts may occur naturally through aging, or may be a result of trauma to the eye, use of medications such as steroids, or ultraviolet light exposure. Cataracts are commonly treated by a surgical procedure that removes the natural lens of the eye and replaces it with an artificial lens tailored to meet an individual’s vision needs.
Aqueous and vitreous fluids – The eye is filled with two fluids that circulate nutrients to the tissues and help provide structure. The vitreous fluid is a viscous, gel-like substance that fills the posterior part of the eye. It has several attachment points to the retina that commonly pull away with age and may cause retinal detachment or bleeding in the eye, as well as flashes of light and so-called “floaters” that appear as moving spots in your vision. Whereas floaters are typically natural and harmless, any of these symptoms should be investigated by an eye doctor to rule out a retinal detachment.
The aqueous is a watery substance produced by specialized cells located just behind the lens of the eye. It is considered by some scientists to be an extension of the cerebrospinal fluid of the brain, and circulates regularly through the front of the eye. If a problem occurs with either the production or drainage of the aqueous fluid, the pressure inside the eye may rise dramatically, leading to permanent nerve damage in the eye and vision loss if prolonged. Glaucoma is an eye disease that is commonly (though not always) associated with increased pressure in the eye and is treated by lowering the pressure through medication or surgery.
Light-sensitive nerves
Retina – The retina is composed of several layers of specialized nerve cells designed to detect light and convert it into electrical signals to be conveyed to and interpreted by the brain, a process we call vision. The retina is a thin tissue prone to damage by excessive light exposure, trauma, disease, and certain medications. Because the retina receives and transmits the light signal entering the eye, damage to this tissue is almost always associated with a loss of vision.
Optic Nerve – The optic nerve is a bundle of nerve fibers that transmits the electrical signal from the retina to the brain. It may be damaged by disease, use of certain medications, or compressive lesions in the brain. Damage to the optic nerve is almost always associated with a loss of vision and frequently with abnormal responses of the pupil to light. This is why your pupil is carefully checked at each visit to an eye doctor.
Supportive Tissues
Conjunctiva – The conjunctiva is a thin, transparent membrane that covers most of the white part of the eye. If the conjunctiva becomes inflamed from infection, dryness, allergies, or trauma, it will appear red or pink. Many over the counter products, such as Visine, are available to treat the redness of an inflamed conjunctiva, though these products occasionally result in worse symptoms. If a red eye is persistent or associated with pain or loss of vision, a visit to the eye doctor is advised to rule out disease or infection.
Sclera – The sclera is the “white” of the eye, and provides shape and support to the globe while protecting it from injury. It is primarily composed of dense connective tissue.
Choroid – The choroid is a darkly pigmented tissue located in between the retina and sclera, and houses many of the blood vessels that provide nutrients to the eye.
Visual acuity
The most basic measure of vision is visual acuity, or the ability to distinguish characters, patterns, or objects of a certain size at a specified distance away from you. Eye doctors typically measure visual acuity by using either printed, projected, or electronic eye charts. In the United States, the standard is for the chart to be placed 20 ft (approximately 6 m) away from the patient, although it is common for eye doctors to use mirrors to simulate the same distance in a smaller room. Although many different eye charts are available, the most recognizable is the Snellen eye chart, named for the Dutch eye doctor who developed it in the 1800s. This chart is easily identified by its characteristic large “E” at the top, followed by rows of smaller-sized letters. The Snellen eye chart contains letters which, at a certain distance from a person’s eyes, span an angle of 5 arcmin, or 1/12 of a degree. Thus, each leg of the “E” is 1 arcmin (1/60 of a degree) thick, each white space between the legs is 1 arcmin thick, and the total angular height of the letter “E” is 5 arcmin.
Best-corrected visual acuity (a person’s best vision with the assistance of glasses or contact lenses) is used to set legal limits on driving and access to government assistance for visual disabilities. In most states, a person must achieve 20/40 (exactly 2x worse than 20/20 vision) best-corrected visual acuity in order to drive. 20/70 best-corrected vision is often the legal limit for “low vision” classification, and 20/200 or a total field of view of 20 degrees or less is the common limit for legal blindness.
It is important to recognize that visual acuity is only one way of measuring vision and cannot detect many vision abnormalities. Vision screenings, such as those used by school nurses, general medical practitioners and pediatricians, cannot substitute for a comprehensive vision exam by a licensed optometrist or ophthalmologist.
What does “20/20” vision mean?
The standard measure of “normal” visual acuity is the ability to recognize characters of a particular size on a chart at a distance of 20ft (or 6m). This measure reflects what an average person with healthy eyes should be able to see. Visual acuity measures are commonly represented as a fraction, with the distance at which the test was given in the numerator (normally 20ft), and the distance at which the character on the chart subtends 5 arcmin (1/12 of a degree) in the denominator. An easier way to think of this is that the numerator represents the distance the patient needs to stand away from the chart to see a certain size letter, and the denominator represents the distance a person with normal vision must stand from the chart to see the same letter.
Using the above analogy, a person with 20/15 acuity is able to see a letter at 20ft that a normal person cannot see until they are 15 feet away from the chart. In other words, this person has better than normal visual acuity, since they can see the same letter from further away! On the other hand, a person with 20/40 vision has to be 20ft away to see a letter that a normal person can see at 40 ft. Since this person needs to be closer than the average person to see the same letter, they have worse than normal visual acuity.
Focusing at different distances
Accommodation is the term used for the eye’s ability to focus. This occurs by reshaping the lens inside the eye to alter its power. When looking at an object far away, the focusing system is relaxed, and the fiber-like structures (called zonules) holding the lens in place are pulled taught, causing the lens to become thinner and less powerful. When the eye focuses on a near object, the fibrils supporting the lens become relaxed, allowing the lens to thicken and increasing its focusing power. This is accomplished by means of a muscle inside the eye called the ciliary muscle, which is attached to the fibrils supporting the lens and controls the tension they exert on it. The ciliary muscle may be affected by certain medications, both intentionally or unintentionally as a side effect.
Accommodative (or focusing) disorders are among the most common visual problems that lead to symptoms of visual discomfort or blur. Proper focusing requires input from muscles both inside and outside of the eye, as well as a healthy visual system. Proper focusing may be improved permanently in many cases by methods of visual training involving lenses and other equipment, or simply by wearing prescription lenses, often for near work.
Depth perception (Stereovision)
Depth perception , or stereovision, is one of the most advanced skills of the human brain, allowing input from each eye to be “summed” into a greater whole. This is akin to 1+1 = 3, in the sense that the brain is able to extract more information from two eyes working together well than is available simply from adding the visual information from each eye. Depth perception requires normal visual development at a very young age and may be influenced by a variety of factors, such as decreased vision in one or both eyes, imbalanced vision between the eyes, or subtle misalignment of one eye.
Color vision
Color vision is possible because of light-sensitive cells in the human retina that respond differently to different wavelengths of light. These cells, called “cones,” transmit information to other nerve cells in the eye that compare the degree by which different cells are stimulated by light to give the perception of color.
Not everyone experiences normal color vision. Approximately 8 percent of males and 1 out of every 200 females has a genetic color vision deficiency, usually resulting in confusion between red and green colors. Rarely, an individual will have difficulty perceiving different shades of blue. Genetic color vision deficiencies vary widely in their severity between individuals and even within families.
In addition to genetic causes, color vision may be affected by common medications (such as NSAIDs and Viagra) and diseases (such as diabetes, macular degeneration and multiple sclerosis).
Although largely ignored by some medical professionals, color vision deficits may have large functional impacts. Several studies have shown that colorblind individuals are significantly slower to respond to traffic signals while driving, and some fatal airline crashes have been attributed to inadequate color vision perception of pilots. For these reasons, many occupations require colorblind individuals to pass certain color vision tests in order to be licensed.
Common problems with the eye and visual system
Nearsightedness (or myopia) occurs when the refracting structures of the eye are too powerful relative to the shape of the eye, resulting in light being focused in front of, rather than directly on, the light-sensitive cells of the retina. This generally results in blurry vision of objects further away from the eye, and a clear image of objects close to the eye. Nearsightedness is the most common type of refractive error, affecting 30-40 percent of adults in the United States, and up to 80 percent of individuals in some Asian countries. Glasses, contact lenses, or laser refractive surgery may help the eye to focus light properly so clear vision is achieved at all distances.
Farsightedness (or hyperopia) occurs when the refracting structures of the eye are too weak relative to the shape of the eye, resulting in light being focused behind, rather than directly on, the light-sensitive cells of the retina. This generally results in blurry vision of objects at all distances from the eye, although young eyes may be able to exert focusing effort to increase the power of eye in order to see clearly. Farsightedness is associated with headaches and eyestrain, especially after looking at near objects for extended periods of time. Glasses, contact lenses, or laser refractive surgery may help the eye to focus light properly so clear vision is achieved at all distances.
Astigmatism is a term used to describe an abnormally shaped surface of the eye. The surface of the eye, or cornea, in astigmatism is not as spherical as a normal eye. This condition is quite common, affecting as many as 1 in 3 individuals in the United States. Astigmatism results in two images being presented to the retina, with resulting blur and distortion of viewed objects. It is corrected by special lenses termed cylindrical lenses, which can be incorporated into glasses or contact lenses. Alternatively, laser refractive surgery may correct for some amounts of astigmatism.
Difficulty with focusing, or accommodation, of the lens of the eye is one of the most common causes of eyestrain from the visual system. This condition is often accompanied by headaches, blur at distance or near and a general feeling of visual discomfort. Focusing problems may be caused by age-related stiffening of the lens of the eye (most commonly noticed in the mid-30s to mid-40s), drugs or medications such as caffeine or antihistamines, or trauma to the eye. Focusing problems may also occur due to a lack of regulation of the focusing mechanism, a common issue in childhood and in some adults. Effective therapy programs have been developed by many optometrists to improve regulation of the accommodative system and may prove effective for individuals suffering from a regulatory cause.
Double vision can be caused by a variety of conditions, including misalignment of the eyes, cataracts, astigmatism, or even life-threatening brain lesions. It is important to determine whether the double vision occurs with one eye or both eyes open, and whether it is only present in certain positions of gaze or after certain activities. Only a trained eye doctor is qualified to determine the cause of double vision; if you are experiencing this symptom, you are advised to seek appropriate professional care from an optometrist or ophthalmologist.
Diseases
Age-related macular degeneration, or AMD, is the leading cause of blindness in individuals over the age of 60 in the Western world. This disease comes in two forms, often referred to simply as “dry” and “wet” AMD, with the wet form being associated with fluid leakage from abnormal blood vessel growth into the retina. Only 10 percent of AMD sufferers have the wet form, but this type accounts for roughly 90 percent of blindness caused by AMD. In addition, some individuals with the dry form may develop the wet form of AMD as the disease progresses. Caucasians, smokers and those with a family history of the disease are at higher risk of developing AMD.
Currently, there are no approved drug therapies for the dry form of AMD, although in more advanced cases, nutritional therapy with antioxidants, zinc, omega-3s, and perhaps lutein and zeaxanthin may reduce the risk of vision loss and progression. Reducing exposure to bright outdoor light by using sunglasses may also be of some benefit. Medical therapy may be a future option, as several drugs are currently in FDA clinical trials.
Wet AMD often proves devastating to vision. A certain subset of wet AMD sufferers may benefit from treatment by laser or medications that inhibit harmful blood vessel growth in the eye, termed anti-VEGF drugs.
AMD of both forms tends to affect the most detail-sensitive central vision first, and may be devastating to quality of life and an individual’s ability to function well. For individuals who have already lost substantial vision to the disease, optometric low vision specialists may be able to increase quality of life by permitting enhanced vision through the use of magnifying lenses and devices. In addition, many states have low vision services specialists who are available to educate individuals with reduced vision on daily life adaptations.
Glaucoma is a devastating, chronic disease that leads to slowly progressive loss of vision – generally from the outside in – eventually leading to “tunnel vision.” This disease comes in several forms, but all affect the nerve fibers of the retina, resulting in death of the cells that transmit information to the brain. Most glaucoma is associated with an increase in the pressure of the aqueous fluid in the eye, which is measured at every comprehensive eye exam. Although there is no cure for glaucoma, treatment is available that centers on lowering the pressure inside of the eye through medications or laser surgery, or sometimes both. Individuals with glaucoma require regular eye exams to monitor the progression of the disease.
Cataract is the term used to describe an opacification of the lens of the eye, meaning the lens is no longer clear. Cataracts can occur normally as a result of advanced age, or abnormally from trauma, medication, or disease. Cataracts may result in yellow-tinged vision, difficulty with glare from bright lights (often noticed while driving at night), blurred vision, or even double vision.
Cataracts are typically treated once they begin to affect an individual’s functional vision, or their ability to perform daily tasks. Treatment involves a surgical procedure that removes the natural lens and replaces it with an artificial lens designed to allow for clear vision. Cataract removal is the most common surgical procedure performed in the United States and is considered relatively safe.
Eyestrain and visual headaches can occur from a variety of reasons. Most commonly, these symptoms result from an uncorrected refractive error (nearsightedness, farsightedness, or astigmatism), an inadequate focusing ability, or poor control of the eye muscles.
Dry eye is one of the most common disorders of the eye, affecting most women over the age of 50 as well as individuals of all ages. Dry eye is often caused by insufficient production of tears and is often the result of inflammation of the surface of the eye or the glands that produce tears. There are many effective treatments available for dry eye, including over-the-counter artificial tear eyedrops for mild dry eye, prescription medications that stimulate tear production or reduce inflammation in the eye, and surgical implants in the tear drainage system that permit tears to stay in the eye longer. If you suffer from dry eye, you are encouraged to consult the advice of an eye doctor on your condition. In some communities, dry eye specialists are available to diagnose and treat even the most severe cases.
Computer vision syndrome is a term used to describe visual discomfort, or eyestrain, associated with extended computer use, often in a workplace setting. Computer vision syndrome may be caused by glare from a computer screen, inadequate position of the computer from the eyes, the type of glasses or contacts worn (or lack of) during computer use, or misalignment or poor focusing of the eyes. Overall, eyestrain at computers is relatively common, and may be effectively reduced once the cause is identified. Many eye care practitioners, particularly optometrists, are skilled at identifying the causes of eyestrain at computers and may be able to assist with lenses, visual therapy, or advice on placement on the computer relative to the eyes and surrounding lighting.
In individuals over the age of 35 or 40, newly developed glasses called occupational progressive addition lenses may be prescribed for use at the computer or in the workplace. These glasses have been shown to help some individuals overcome limitations in other types of prescription glasses for a more comfortable viewing experience at the computer.
Vision Correction
Types of Glasses
Single vision glasses are glasses that contain only a single power in each lens. These glasses are the most inexpensive and simple type of glasses, and are most commonly prescribed for individuals under the age of 40 needing vision correction at distance. Reading glasses are also single vision glasses, however, when prescribed only for close work.
Bifocal glasses were invented by Benjamin Franklin, who discovered that he could combine the power of lens he needed to see at distance with the power he needed to see up close into a single frame. Bifocals have two distinct lens segments that allow two different powers for the same eye, depending on the direction of gaze. Most often, one power is for distance vision, while the other power is optimized for reading use. These types of glasses are available in a variety of forms and sizes, and although most commonly seen in individuals over the age of 40, may also be prescribed for younger persons and even children with focusing difficulties.
Trifocals are a variation of bifocal glasses that have an additional segment in the lens for seeing at intermediate distances.
Progressive Addition Lenses (PALs) are frequently called no-line bifocals, although the term is not a good description. PALs incorporate relatively new cutting technology to allow a lens to contain multiple powers ranging from distance to near prescriptions, and everything in between. These lenses permit a wider range of vision at varying distances than single vision lenses, bifocals, or even trifocals, as well as a enhanced look since the lens contains no bifocal “lines” that are visible to others. Individuals wearing PALs may find that they have to tilt their head forward or back when wearing their glasses in order to bring something into sharp focus.
PALs come in a variety of forms, some of which are better suited for certain jobs or uses than others, and require an exact fitting process tailored to the individual to allow for best vision through the lens. PALs have one big downside to them; in order to create this special lens design, places of poor vision occur outside of the middle area of the lens. This requires more head-turning when looking at objects in order to see them clearly, as well as distortion of objects in the periphery. In addition, PALs are among the most expensive lens options available to consumers.
Reading glasses are single vision glasses that are designed for best vision at a close distance. They give added plus lens power over an individual’s distance vision prescription. Reading glasses prescriptions are best determined by an optometrist (or ophthalmologist with sufficient refractive training). Although many drugstores sell over-the-counter reading glasses of various powers, these tend to be made of poor optical quality materials such as acrylic, and are mass-produced to best fit the “average” eye, meaning the optical center of the lenses may not correspond to your eyes. Most individuals find better success with custom-ordered prescription reading glasses obtained through an eye doctor’s or optician’s office.
Some individuals find reading through reading glasses very difficult. If this is the case, there is often an underlying binocular vision disorder, which may be treated with different lenses or vision training by an optometrist.
Computer glasses are glasses prescribed specifically for computer use. They often incorporate coatings that reduce the amount of glare from lights, and are sometimes tinted to further reduce glare. Most importantly, computer glasses are designed so that a wide area of the lens contains the power needed for optimal viewing at the distance your computer screen is located at.
Occupational Progressive Addition Lenses (OPLs) are relatively new lenses designed to allow the benefits of a progressive addition lens but with the widest usable area of the lens devoted to computer viewing. This lens design has been shown to relieve some of the symptoms of computer vision syndrome that are frequently experienced by bifocal or PAL wearers.
Prism glasses are specially prescribed glasses used to help relieve abinocular vision disorder or a loss of visual field. These lenses effectively shift an image in a particular direction to change the amount of movement needed by the eyes in order to view it.
Lens materials play an important role in glasses prescriptions. Lens materials are generally chosen to optimize the impact resistance, optical clarity (lack of distortion), thickness and scratch-resistance of a lens. In cases of specialty tinting, some lens materials may hold tints better than others.
Impact resistance of a lens is very important in children (18 years and under) and anyone involved in athletics, workplace activities, or hobbies where trauma to the eye is a possibility. The current standard of care is for children to only be prescribed dress eyewear made of either polycarbonate or Trivex materials, both of which are among the most impact-resistant materials available for prescription lenses. For occupational purposes, lenses and frames must meet a particular standard of impact resistance in order to be used. These lenses are marked with an “ANSI Z87.1” engraving certifying that they meet the appropriate standard. All athletes are encouraged to wear protective eyewear that meets the appropriate standard for their sports. Many of these lenses may be incorporated into modern-looking sport eyewear versus the traditional goggle-type protective frames. Protective eyewear may be purchased from your eye care professional, or non-prescription forms are available from many large distributors of home improvement products.
Contact lenses are an excellent alternative to glasses that allow crisp, clear vision without the hassles or looks of spectacle lenses. Contact lens technology has improved drastically even within the past 5 years, incorporating newer materials that are healthier for the eye and allow improved vision and comfort. Contact lenses are used for a variety of purposes, and can be successfully worn by nearly everyone with current materials and fitting techniques. The unique feature of contact lenses is that they are worn directly on the surface of the eye. Because they move along with the eye, contact lenses allow for a wider field of view than glasses and improved vision during athletic activities and for certain types of refractive conditions. Contacts come is a variety of forms, some of which are listed below.
All contact lenses, including those used for cosmetic purposes only, such as on Halloween or to alter eye color, are considered prescription medical devices by the FDA and should be fit and prescribed only by a licensed practitioner.
Rigid contact lenses were the first contact lenses to be used, and are made of hard plastic materials that reshape the eye to some extent. Rigid lenses carry the least risk of eye infection of all types of contacts and allow for healthier conditions by permitting tears to flow more freely underneath the lens. Rigid contact lenses may be more uncomfortable to wear than soft lenses and usually require 1-2 weeks of adaptation, although most people can successfully wear these lenses. Traditionally, individuals with astigmatism were forced to wear rigid contact lenses – now, newer soft lens technologies now allow for excellent correction of astigmatism. Because rigid contacts reshape the surface of the eye, some wearers of these lenses find that they do not see well with their glasses when they remove their contacts. The eye requires roughly 1-3 weeks to regain its original shape after rigid lenses are removed. This effect proves to be an advantage with orthokeratology lenses designed to be worn overnight.
Soft contact lenses are the most common type of contacts worn today. They are made from flexible materials that are more comfortable to wear than rigid contacts, and generally do not reshape the eye as rigid lenses do. Soft contacts may be used for all types of refractive error including astigmatism.
There are two general categories of materials used in soft contact lenses: traditional HEMA materials and silicone hydrogel materials. Silicone hydrogel lenses allow better oxygen penetration to the eye and are healthier to wear, but are not as durable and versatile as the older HEMA materials. Your eye doctor may recommend one material over the other depending on your individual circumstances.
Orthokeratology contact lenses are a new technology that allows freedom from contact lenses and glasses during the day. Specially designed rigid contacts are worn overnight to temporarily reshape the surface of the eye for good vision in people with nearsightedness, farsightedness and astigmatism. The effect generally lasts 24-48 hrs. Contact your eye care practitioner if you are interested in benefiting from this new technology.
Orthokeratology lenses are being explored as a possible method for reducing development of nearsightedness in children. Several clinical studies have linked the wearing of these lenses to a substantial decrease in the amount of nearsightedness developed in children at risk.
Multifocal contact lenses allow vision at distance and near in contacts. These specially designed lenses actually present multiple images to the eye, permitting the brain to “select” which image to pay attention to. These contacts require a period of time to adapt to this method of seeing, but can be very beneficial for individuals who need additional lenses to see up close but do not want to wear glasses.
Multifocal contact lenses are being explored as a possible method for reducing development of nearsightedness in children. Several clinical studies have linked the wearing of these lenses to a substantial decrease in the amount of nearsightedness developed in children at risk.
LASIK and Refractive Surgeries
LASIK and other forms of refractive surgery, such as PRK, are an excellent option for correcting nearsightedness, farsightedness, and astigmatism in some individuals. This procedure is performed by a trained ophthalmologist as an outpatient surgery, with relatively high levels of patient satisfaction. Individuals must fall within certain parameters of thickness of the front of the eye and amount of needed correction in order to successfully undergo refractive surgery.
Individuals wishing to undergo refractive surgery should be well educated about some very common effects of the procedure, however, including chronic dry eye, glare, haloes in vision, and occasionally poor visual outcomes. Contrary to popular belief, an individual is actually more likely to experience severe loss of vision and visual complications from LASIK and other forms of refractive surgery than from a lifetime of contact lens wear. For those who are exploring LASIK because they do not like the look of glasses, contact lenses should be first explored as a safer option. For patients who dislike the hassle of putting in and taking out contact lenses, newer contact lens technologies are available that allow one month of continuous wear of lenses (no more taking your contacts out when you go to sleep!). These options are safe and often have higher long-term success rates than refractive surgery.
See Orthokeratology
Vision Therapy
Vision therapy refers to a series of activities and exercises that enhance an individual’s ability to focus well, allow the eyes to work together more efficiently and accurately, and develop improved two-eyed vision. Vision therapy is designed to help people with symptoms of visual discomfort or blur that are not due to refractive error, or to aid an individual in seeing in 3D. Optometric specialists, more so than ophthalmologists, tend to develop expertise in vision therapy.
Children who have visual learning problems in school often benefit from vision therapy that trains them to more efficiently use their eyes to learn. If your child has difficulty reading, experiences double vision or visual headaches, or often loses their place or skips words while reading, a vision therapy consult may prove helpful.
Binocular Vision Disorders
Binocular vision disorders include any problem with the aiming or focusing abilities of the eyes that may cause visual discomfort, double vision, blurry vision, or a lack of ability to see depth (3D vision). Occasionally, medications, brain lesions, or trauma may cause problems with two-eyed vision. Some binocular vision disorders may be treated effectively with a proper lens prescription, or more permanently through visual therapy to train the eyes to overcome the problem. In both cases, an eye doctor should be consulted.
3D movies and television are gaining a lot of attention. These technologies are based upon the way that the human visual system interprets information by combining separate images from the two eyes. The two “flat” images are combined by higher brain centers into a single image that contains apparent depth and three-dimensionality. 3D entertainment is possible by presenting separate images to each eye. In order to fully enjoy these technologies, both of eyes must aim and focus together well. Many people discover that viewing 3D entertainment is either impossible or uncomfortable for them. If you are among those who have difficulty viewing 3D entertainment, a visit to an optometrist or vision therapist may be the answer to your problem.
Protecting Your Eyes
Protecting your eyes – Because the eyes are prone to many kinds of trauma, it is recommended that approved safety eyewear be worn during any type of activity where damage to the eyes may occur. Protective eyewear is often required for certain occupations, but is frequently neglected in equally important circumstances around the home such as doing yardwork and while using chemical cleaning agents. Protective eyewear should bear the ANSI Z86 engraving, meaning it is certified to withstand impact without breaking. Protecting your eyes also means using sunglasses when outdoors to avoid ultraviolet light exposure. UV light is thought to play a role in a number of eye diseases or deterioration such as cataracts, pingueculae, dry eye and perhaps even age-related macular degeneration. Children should be especially careful to wear sunglasses that block UV light, as studies show that a child’s eyes transmits much more ultraviolet light than an adult’s. Sunglasses should block 100 percent of UVA and UVB.
Ultraviolet (UV) light is light that is not visible to the human eye, yet is present in sunlight outdoors. Exposure to high levels of UV light is damaging to the cells and tissues of the eye, and is thought to play a role in a number of eye diseases such as macular degeneration and cataracts, or may even cause blindness in some situations.
It is very important to protect your eyes from UV light exposure, even in brief situations. Wearing a wide-brimmed hat or using sunglasses or eyewear that blocks 100 percent of UVA and UVB light and fits closely around the face are effective at limiting UV exposure.
Children are at even higher risk than adults for UV-related eye damage since their eyes are not fully developed and transmit more UV light than an adult eye. Children should be protected from the earliest ages, and sun eyewear for children should be impact-resistant (made of polycarbonate or Trivex material) in addition to blocking 100 percent of UV light.
The blue light hazard refers to the potential for damage to the eye from blue-colored light. Several well-done studies have shown that blue light exposure may increase the risk of developing certain chronic eye diseases later in life, such as macular degeneration. As the human eye ages, it naturally allows less blue light to reach the retina, but cataract surgery may disable this potentially protective effect. Some eye doctors encourage patients at risk for macular degeneration to wear special blue-blocking lenses (usually yellow or amber-brown in color) as a preventative measure, although the science to support this is not yet complete.
The human eye is prone to trauma from a variety of sources, and should be protected during occupational, athletic, or recreational activities that pose a hazard. Eye trauma may be prevented most easily by use of appropriate protective eyewear, especially eyewear meeting ANSI Z87.1 standards. Such eyewear is available over-the-counter from most drug or home improvement stores, or in prescription form from an eye doctor.
Vision and the Environment
Vision is a critical part of the human interaction with the environment. Over 70 percent of the human brain is involved with visual input or interpretation of visual information. A poorly functioning visual system may adversely affect other parts of human performance, including reading, athletics, working, and driving.
Focusing at different distances
Humans normally develop the ability to focus well at different distances at a young age as a response to a blurry image. Focusing at a near distance requires a much greater effort than focusing at distance, so most problems with focusing become evident during or after performing near tasks for an extended period of time. Occasionally, an individual will have trouble “releasing” their focusing effort when they look in the distance after doing tasks at near.
Focusing at near is accomplished by a muscle that indirectly releases tension on the lens inside the eye, causing it to thicken and become more powerful at focusing light. As the human lens ages, its ability to change shape diminishes until focusing at near distances is no longer possible. This process is usually first noticed around 40 years of age, and is generally complete by 60 years of age. Individuals over the age of 40 will typically benefit from a reading prescription to see more clearly and efficiently during near tasks.
Good vision is a key factor in the performance of any athlete. Most athletes have been shown to have superior abilities to see objects quickly and move their eyes to track a target in motion. Some level of visual ability can be trained athletes if not already present, and enhanced in athletes with already good vision.
Proper prescriptions are vital to athletic success. Most athletes find spectacle lenses cumbersome and restricting, so well-fit contact lenses are often worn by serious sports enthusiasts.
Sun protection is another factor in outdoor athletic events to block harmful UV rays and prevent glare that may hurt an athlete’s visual performance.
Computer Vision
Protecting Your Eyes
See Protecting Your Eyes Section
Your Best Vision
Most people rank their vision as the most critical of the 5 senses, yet many Americans have never had a comprehensive vision examination. The American Optometric Association has recommended that comprehensive eye exams be first given early in life to every infant between 6 months and 1 year of age. Receiving an eye exam early in life is critical, since any disruption to vision early in life may have permanent consequences, and vision is frequently the cause of poor school performance in otherwise intelligent children. It is important to recognize that only optometrists and ophthalmologists are fully trained to detect certain vision problems in infants and children; studies have shown that pediatricians, regular medical specialists, and nurses are far less likely to identify these problems. Once a comprehensive eye exam has been given, most specialists recommend continued eye exams at regular 1-2 year intervals, depending on the exam results.
Vision in the Workplace
Computer Vision
Vision Correction