Click each question to find the answer or the definition of the optical term.
Click each question to find the answer or the definition of the optical term.
Simply, once per year for everyone. But when our patient’s ask us this question, the answer is tailored for the patient’s specific age group:
First, it is important to verify exactly what the screening included at school. Most are simply a test to see where the child can read on the eye chart. The typical failure criteria is vision worse than 20/30. This means that if your child can see 20/30, he or she is passed. Ask your eye doctor to demonstrate to you exactly what 20/30 vision looks like through trial lenses. Guaranteed, you would not be happy with 20/30 vision if that was the best you could see. Also, simple 20/20 vision does not mean perfect eyes. The visual system should be thought of as a complex optical instrument, not only including the eyes, but the visual pathways through the brain to the sight center and how the information is processed. There is also a complex mechanism which controls eye movement and alignment. Just because a person can read “the bottom line” on the eye chart does not necessarily mean the eyes are working as smoothly and efficiently as possible. Also, screenings only test for nearsightedness. A person who is farsighted will be tested as having 20/20 vision, but may have terrible eyestrain when reading. We tell parents this, “The school nurse and her volunteers work as hard as possible to identify those children who may have vision problems. However, their time and equipment is limited. A Comprehensive Eye Examination with a trained doctor of Optometry is a simple, inexpensive way to be 100% certain that your child is seeing as best as possible.”
There are many tests which must be completed to ensure a comprehensive exam was completed, but remember to listen to how you feel when its over. Did the doctor take time to ask about your life and health? Was the doctor a good communicator and compassionate? Did the doctor educate you about your eyes so you will be better able to take care of them? Does your doctor focus on prevention of eye diseases as well as treatment and rehabilitation? Make sure that the doctor had a good, long look inside your eye. The process takes several minutes, and even though most of us don’t like the bright light in our eyes, it is necessary to complete a thorough examination. Sure, technology continues to accelerate each year and optometrists are equipped with more tools than ever before, but the foundation of eyecare remains the caring human being behind the instrument, your optometrist.
Actually, not every eye exam performed by an eye doctor will indicate if a patient has an underlying systemic health condition such as high blood pressure, diabetes, Multiple Sclerosis, leukemia or other blood dyscrasia, cancer, arthritis, etc. A thorough eye examination demands time and care, and must include not only the determination of glasses prescription, but intense examination of the ocular health of the eye that must include dilation of the patient’s pupils with drops. A Comprehensive Eye Examination should always include a refraction to determine spectacle prescription, a detailed case history, biomicroscopy to examine the health of the outside of the eye at the microscopic level, ocular neurological testing, visual field (peripheral vision) testing, glaucoma testing and dilation of he pupils.
We are able to detect systemic disease because the eye is comprised of the same tissues that make up the rest of the body. For example, the retina and optic nerve is made of the same nervous tissue that is found in the Central (brain) and Autonomic (peripheral) Nervous System. Consequently, Multiple sclerosis, a neurological condition which effects the nervous system, will also frequently effects vision and the appearance of the optic nerve.
Another example is diabetes. Diabetes is devastating to the vascular system in the body. The eye, kidneys and feet have the most fragile blood vessels, therefore these blood vessels here are typically effected first in the disease process. The eye is unique because the blood vessels actual lay on top of the retina. Therefore when your optometrist looks inside of your eye, they are seeing blood vessels with no overlying tissue to obscure their view. Nowhere else can a doctor see a blood vessel like this without cutting the patient open! Again, this internal evaluation of the eye can not be completely performed without dilating the pupils.
Arthritis can be seen in the eye because the fibrous connective tissue that makes up the sclera is the same connective tissue which cushions our joints. Inflammations of the connective tissue (arthritis) therefore can effect the joints (arthritis) and the sclera (scleritis).
There are many factors that can cause the front of the eye to be inadequately lubricated. Normally when you blink, the tears are distributed across the cornea (the clear tissue which covers the colored part of your eye) to bathe and nourish it. This keeps the cornea comfortable and healthy, allowing old cells to slough off and new cells to grow. The first factor linked to dry eye is aging. As you age, the glands that produce the tears (the Lacrimal and Meibomian glands, along with Goblet cells) decrease in function. Second, many medications, including birth control pills, anti-histamines, and high blood pressure medications, can cause dry eyes. Next, seasonal allergies can dry the eyes out as well. Also, anyone who smokes cigarettes or who is exposed to second-hand smoke may suffer from dry eyes. Contact lenses can cause dry eyes by increasing lubricating demands on the tears as they absorb water, and/or disturb the natural tear flow across the eye. Excessive computer use is another culprit, as most people blink less frequently when staring at their screen. Individuals who consume alcohol and caffeine tend to be dehydrated regularly and this decreases the amount of tears produced. Finally, some systemic diseases cause dry eyes as well, like Sjogrens Syndrome. If you think your eyes are dry, you should consult with your optometrist, as there are several types of treatments that range from using artificial tear lubricating drops, to a procedure called punctal occlusion where the drainage holes (punctas) where tears leave the eye are plugged with tiny implants. The doctors of Vision Clinics perform all types of treatment for dry eyes.
Yes, there is a group of symptoms referred to as Computer Vision Syndrome. This condition includes eye fatigue, blurred vision, increased effort while focusing, dry eyes, transient ghosting/doubling of images, light sensitivity, possible increase in nearsightedness, and even head, neck, and backaches. These symptoms occur largely because the eyes were not designed to stare at, and perform “visual acrobatics,” with a computer monitor all day. Also, most computer workstations are not designed to be “user friendly.”
Since using a computer requires that you look at the monitor, selecting the easiest one on the eyes is important. The best type of monitor has a large, flat LCD screen. Older monochromatic monitors have flicker, poor contrast, and glare, causing considerable strain on the visual system. They also are usually reverse contrast screens, where the letters are white, green or amber on a black background. This makes reflections easily seen. Reflections are seen at different depths in the screen and cause excessive focusing and refocusing of the eyes. The mirror-like images of the overhead lights behind you, or even your own white shirt can cause the eyes to keep changing their depth of focus. Repositioning the monitor or purchasing a polarized screen cover can also eliminate reflections on your monitor screen.
Dry eyes are quite common among computer users. As our concentration is focused on the ever-changing computer image, our blink frequency decreases. The average person blinks 12 times per minute, however, studies have shown an individual using a computer may blink as little as only four time per minute. This situation is only made worse with the poor lighting in many offices, contact lens wear, smoking, or medication side effects. We recommend to our patients who use computers to use an artificial tear drop (not a “red-out” formula) at least four times during the day.
Take a 2-minute “visual break” every 20 minutes by looking at objects that are at least 20 feet away. This rests the eyes focusing mechanisms and muscles. Do some light stretching of your arms, neck and legs. This is essential for increasing overall performance of the visual system for a full day.
Consider the following suggestions to help arrange your monitor (VDT) and keyboard to allow you to work productively and comfortably: 1) the monitor should be 20 to 30 inches from your eyes, 2) the top of the VDT just below horizontal eye level, 3) the VDT should be tilted away from you at a 10 to 20 degree angle, 4) the VDT and keyboard should be in line, 5) place document holders just to the side of the VDT to minimize eye movements and constant changes in depth of focus, 6) keep your screen clean of dust and fingerprints.
Consider these suggestions regarding VDTs and lighting, to improve your visual efficiency when using your VDT: 1) match the level of brightness of surroundings to that of the VDT screen, 2) keep contrast between the characters and the background high, 3) minimize glare on the screen by using dimmer-switches and anti-reflective and anti-glare coated screens, 4) position your VDT perpendicular to windows or other bright light sources to reduce glare.
Human eyes were made for most efficient operation at far distances, but if you use the suggestions made here, you will be able to use your VDT more productively, comfortably and efficiently.
A stye (or hordeolum) is an infection that occurs within the eyelids. A stye usually begins as a subtle irritation of the eyelid, or a foreign body sensation on the eye. Close inspection will usually reveal a small red spot on the eyelid. As the infection continues, the stye will become a painful, red lump, causing the eyelid to become swollen. Eventually, the swollen nodule may form a pustule, and drain. If the stye does not resolve, the nodule may harden as the infective debris solidifies. A stye results from blockage of one or more of the small oil producing glands (meibomian glands) that are found in the upper and lower eyelids. These blockages trap the oil produced by the glands and cause a lump on the eyelid that is usually about the size of a pea. Bacteria that exist normally on the eyelid also become trapped in the gland, and begin the infective process. Treatment of styes involves persistent hot compress application. Antibiotic drops, ointments, or other topical applications are typically ineffective due to the infection occurring in the deeper tissues of the eyelids. If the stye does not resolve with heat, oral antibiotics, steroid injection at the site of the swelling, or surgical incision and drainage may be performed. The progression of treatment depends on the severity of the symptoms, the frequency with which the stye reoccurs, and the size of the lump. Any lump should be evaluated by a doctor of optometry or ophthalmologist before any treatment is initiated.
Floaters are many times described as little black colored shapes ranging from strands to squiggles and clumps. Fortunately, floaters are not usually a serious symptom of any eye disease. However, if you notice showers of floaters that suddenly appear along with flashes of light or decreased vision, you may be experiencing a retinal detachment and should seek immediate care. “Normal” floaters are tiny solid particles suspended in the fluid that fills the eye (the vitreous humor). These tiny objects make shadows on the retina, and the brain interprets them as dark objects floating out in front of your face. These floaters are more noticeable when viewed against a white wall, a uniformly blue sky, or when reading. You can have floaters at any age, but they tend to increase as we grow older. There is nothing that can be done about uncomplicated floaters, and are simply annoying to most people. If the floater is associated with a retinal detachment, immediate treatment is imperative. An eye doctor should be immediately consulted, and an examination of your retina should be done through dilated pupils to determine the floaters origin.
The top five sports with greatest percentage of eye injury among children under 14 are as follows: baseball (21%), basketball (16%), soccer (14%), football (13%), and hockey (10%). For athletes ages 15 to 24, basketball is the highest risk sport for eye injury (32%). Even when wearing contact lenses while playing sports, eye safety must be considered. Contacts may allow better clarity of vision, but safety glasses should still be worn. For instance, a soccer ball is too large to harm the eyeball directly, but a racquetball fits into the eye socket easily. Yet, even while playing soccer you are at risk to receive an eye injury with an elbow or scratch to the eye. When safety glasses/sport goggles are chosen, polycarbonate lenses are required for their impact-resistance.
UV light comes from many sources including the sun, tanning lamps, welding equipment, and computer monitors. There are three different types of UV light called UVA, UVB, and UVC. UVA radiation accumulates over time, is painless, and causes irreversible damage (cataracts). UVB causes acute damage that can be severe and painful, but usually temporary (sun burn). UVC is absorbed by the ozone layer currently and does not reach earth. Short-term exposure (minutes) to UV radiation can produce photokeratitis, also called welders flash, snowblindness, and sunburn of the eyes. Long-term exposure (years) results in cataracts, retinal problems, eyelid cancer, and premature wrinkling of skin around the eyes (crows feet). Simple precautions include: 1) use an spf-15 lotion when outdoors, 2) get UV coatings on all eyewear including spectacle lenses and contacts, 3) wear sunglasses even on overcast days because UV light passes through clouds, 4) wear a hat with a brim, 5) never stare directly at the sun.
There are several materials of which spectacle lenses can be made. There is glass, plastic, polycarbonate and high-index materials. Glass is the material that has the truest optical properties and is least likely to scratch. However, glass is easily shattered, heavy and thick, so for these reasons it is usually not the material of choice. Plastic is lighter and thinner than glass, and is more shatter-resistant, but scratches more easily. With a scratch-resistant coating applied, the plastic lens is nearly as scratch-resistant as glass. Polycarbonate material is even lighter and thinner than plastic, and is 10 times more impact-resistant. Additionally, polycarbonate material has inherent UV protecting properties. It is recommended for children, sports, safety, and patients who may rely on only one eye (to provide as much protection for the good eye). High-index material is the lightest and thinnest material yet. With any given prescription, lenses made of high-index material can be made thinner because it bends light more quickly and thus focuses light with less material needed. As everyones needs are different, and there are numerous choices, this is something to discuss with a knowledgeable eye-care professional.
The doctors in our office are frequently asked to give a “contact lens prescription” after doing an eye examination for glasses or even after placing a “trial” contact lens on a prospective contact lens wearer’s eye. When the patient’s request is refused, they understandably become upset. During the routine examination, doctors perform certain tests which give more information about what contact lens might be worn. Additional things to be considered are:
If the doctor feels that the patient is a good candidate for contact lenses, a “trial lens” must be placed on the eye. EVERY LENS IS A “TRIAL LENS” UNTIL AFTER SEVERAL WEEKS (OR LONGER) OF WEAR AND THE DOCTOR AND PATIENT ARE SATISFIED ABOUT THE LENSES SUITABILITY.
A lens that looks satisfactory at the initial dispensing, may tighten while being worn and cause discomfort of blurred vision. The materials from which the lens is made may be incompatible with the patient’s eye tissue or tear layer. This cannot be determined at the time of the original fitting.
Therefore, a doctor is not able to give a contact lens prescription based solely on the preliminary findings of the examination. The doctors at Vision Clinics, Ltd. insist that thepatient enter into Contact Lens Management. This is a prescribed period, usually lasting several weeks, in which the contact lens fit, vision obtained, and their effects on the eyes health is closely monitored.
Photochromic lenses are spectacle lenses that change from light to dark. The darkening process requires direct exposure to ultraviolet light (UV) to stimulate the chemical within the lens, creating the darkening. When you are in the car, the windows are coated to eliminate UV light. It is important to know this when you are considering purchasing this type of lens. If sun protection is important to you while driving your car, consider a pair of polarized sunglass lens.
Possibly.There are several reasons that reading “cheaters” purchased at the drugstore can contribute to eye problems. First, they always have the same prescription in each lens, and most people require a different power in each eye. Therefore one eye will be over- or under-corrected, leading to focusing disorders. Second, drugstore glasses never include correction for astigmatism, which nearly everyone has. Astigmatism blurs both distance and near vision. Even small amounts of astigmatism, when left uncorrected, can cause eyestrain and fatigue. Next, drugstore “readers” can be harmful because they are not properly fitted. This includes how the lenses are centered in front of the eyes. Every prescription lens has an optical center. This point on the lens must sit directly in front of the center of the pupil. If this alignment is off even by a millimeter, it can cause prismatic effects and distortion, all contributing to eyestrain and fatigue. That is why it is important to have spectacles fit by trained professionals. Remember that drugstore readers carry no guarantee as to the optical quality of the lens material and its shatter-resistance. Of most importance however, is the importance of examining the health of the eyes, especially during the years when near vision starts to decrease. Many serious eye diseases are age-related. If you are experiencing blurry vision, youll want a full eye examination by a competent eye doctor to be sure that a more serious problem is not occurring.
Yes. Some sunglasses at drugstores have a decal that claims 100% UV (ultra-violet) protection. In reality, they have 100% of the FDA minimum recommended UV protection, which amounts to only 70% UV protection. This is deceptive, but legal, unfortunately. The problem lies in the fact that UV light is known to contribute to cataract formation and macular degeneration, and therefore it is important to block 100% of these harmful rays. We should buy sunglasses is to protect our eyes 100%. Of course, fashion is important today as well, but saving a few dollars on drugstore sunglasses may cost you serious vision problems in the long run. Drugstore sunglasses typically lack in optical quality. Cheap lenses cause distortion, possibly decreasing the clarity of your vision, or at least causing eyestrain. If you have ever worn cheap sunglasses and had to remove them and rub your eyes, chances are youve experienced poor quality-induced distortion. Patients will claim they are too careless with their sunglasses to invest in a nice pair. We tell our patients that if they invest in a quality pair of sunglasses, they are much more durable, and when they appreciate the quality, they will happily take care of them. Think of your sunglasses as a vision-saving device, and not just a fashion accessory.
This mode of wearing contact lenses is unhealthy for several reasons. First, the cornea only gets oxygen from the air; there is no blood supply or other circulation. While wearing contact lenses, the corneas oxygen exposure is significantly reduced. “Overwear” starves the cornea of oxygen and goes into a state of oxygen deprivation called hypoxia. This signals blood vessels from the white part of the eye (sclera) to grow into the cornea. This neovascularization, or new blood vessel growth, is an attempt to provide an alternative method of nurishing the corneal tissue. Unfortunately, these blood vessels are not transparent and blindness can occur if one of the blood vessels grow across the center of the pupil. Next, dirt and deposits on the lenses build rapidly. When the lenses are not removed to be cleaned, rinsed and disinfected, the protein and lipid coating thickens to an unacceptable level. The health of the cornea is further is jeopardized as oxygen is now diminished, and the dirty contact lens promotes bacterial growth. Sleeping in contact lenses puts the wearer at a 15-25% greater risk of corneal infections and ulcers; a sight-threatening outcome. In no instance do the doctors of Vision Clinics recommend extended contact lens wear; even when a contact lens is approved by the FDA for extended wear.
Yes. You have several options to consider besides using reading glasses over your contacts when your near vision starts to decrease. In actuality, bifocal contacts have been available since 1985. Bifocal contact lenses are available in soft and rigid materials, and can be fitted for patients with nearsightedness, farsightedness, and astigmatism. True bifocal contact lenses fully correct both eyes for distance and near vision simultaneously. This is most like your natural vision. Bifocal contact lenses are a long-term solution to all levels of presbyopia (loss of near vision after age 40). Just recently, a two-week (daily wear) disposable soft bifocal contact lens was released and we have already fitted many of our patients. Contact lens technology is rapidly advancing, and the doctors of Vision Clinics use all of the most current lenses available, as well as the ones weve fit on patients for years.
Yes. There are two alternatives. The first is to simply purchase a pair of reading glasses for over your contact lenses. When you look up from your reading, you will however have to remove the glasses to see far away because reading glasses are only focused for near. Many patients will select a bifocal spectacle lens (either with the line or blended), to allow them to look up from their reading and still be able to see clearly into the distance without removing their glasses. The next option you have is to be fitted into “Monovision” contact lenses. Here, standard contact lenses, many times identical to the lenses you are currently wearing, are fitted to correct one eye for distance vision, and the other eye for near vision. In actuality, as strange as this sounds, there is an 80 to 90% success rate with the adaptation to this system. We do caution our patients that there may be a compromise in their vision, and they should test their acceptance “slowly,” but again, the vast majority of patients are thrilled with their vision.
The answer to this question depends on many factors. The term “disposable” means that you replace the lenses on a planned schedule instead of keeping one pair for an entire year. Just saying that you wear disposable contact lenses means nothing in terms of the proper care that is required. Many other variables need to be known before advice on proper lens care can be given. For example, there are many types of disposable contact lenses, including 1-day disposables, 2-week disposables, and 1, 2 and 3-month disposables. Lenses worn for one day and then discarded do not need to be cleaned at all. Daily-wear lenses worn for 1 month or less can usually be cleaned with a multi-purpose solution only. This is a single bottle that is used for cleaning, rinsing, and disinfecting. When contact lenses are prescribed for wear of longer than one month, an additional protein remover is usually needed. This can be in the form of enzyme tablets, or a second liquid drop that is added to your storage case. It might need to be used daily or once a week. There are many factors that determine this. Examples are the number of days per week and hours per day the lenses are worn, your work and home environments, if you smoke cigarettes, the cleanliness of your hands, the number of years you have worn contacts, and the quality of your tears. Some people have sensitive eyes and need to use solutions that are preservative-free. As you can see, this is an important discussion that we have with every patient. One final point that should be made clear is that all 2-week disposable lenses must be cleaned, rinsed and disinfected nightly upon removal. Some patients are misinformed that they need not be clean at all. This misinformation can lead to serious eye infections and corneal ulcers.
Refractive surgery is the newest and most exciting topic related to vision. Refractive surgery is the actual correction of refractive error (the need for glasses or contact lenses) through permanent surgical techniques. There are numerous surgical procedures being done, but essentially they fall into four categories: 1. Incisional surgery where a scalpel or similar instrument is used to cut into the cornea for reshaping. (Example: Radial Keratotomy (RK) and Automated Lamellar Keratomileusis (ALK)) 2. Laser light application to the cornea which cause shape modification of the tissue. (Example: PhotoRefractive Keratectomy (PRK)) 3. A combination of incision and laser correction for both near and farsightedness (Example: Laser In-Situ Keratomileusis (LASIK)) 4. Intraocular surgical implant of corrective lenses (Example: Clear lens extraction, Phakic lens implant, and Corneal Rings). Each individual surgical procedure has its risks and benefits, and each individual patient should be personally evaluated to determine which treatment they are best suited for. Seeing a doctor of Optometry for evaluation allows the patient an unbiased assessment of which procedure is indicated. The doctors of Vision Clinics, Ltd. co-manage with three refractive surgeons in the greater Cleveland area. Between these three surgens, all four procedures are represented; but no one surgeon does all four. Therefore, referral to the proper surgeon insures the most appropriate procedure will be done. Our co-management relationship also allows the use of our records to assist the surgeon in the preparation of the surgical correction, and all postoperative care is done at one of our convenient Vision Clinics, Ltd. offices. While current eye examination data is required, a consultation at no charge can be done by the doctors of Vision Clinics, Ltd.
This is obviously one of the most important questions that can be asked about refractive surgery. Fortunately, most LASIK procedures are performed with no problems of any kind. It is important however, that anyone having surgery, especially on their eyes, be aware of the possible complications, however rare they may be.
Astigmatism is an optical condition of the eye where the light is not focused on the back of the eye as a point, but as a line. In other words, there is more than one point of focus. This requires a correction that has a ‘cylinder’ and ‘axis’ in it along with the ‘sphere’. Most people have some degree of astigmatism. The important thing to remember is that it is not unusual and that it is not a disease. However, there are diseases of the cornea, such as keratoconus, that can cause large amounts of astigmatism.
When one or both eyes do not correct to 20/20 vision with glasses or contact lenses. 90% of the time, amblyopia is due to the eyes not developing properly and could have been prevented by wearing glasses prior to four years of age. Patching the good eye and forcing the bad one to see is the first part of therapy for amblyopia, after which the eyes must be trained to work together as a team. Dr. Kammer sometimes prescribes contact lenses for this condition, even in very young children. A blurred lens is placed in front of the ‘good’ eye, forcing the weaker eye, which is also corrected with a contact lens, to work. Patching is effectively accomplished, and no patch is required.
The photoreceptors in the retina responsible for color image perception.
The small, flexible lens within the eye, that allows variable focusing power of the eye.
A measurement of power in optics. One ‘1’ diopter of plus power bends light so that it converges (focuses) on a point 1 meter away. 2 diopters of plus power focuses the light 1/2 meter away, and is therefore stronger (bends the light more). 3 diopters of plus power focuses the light 1/3 meter away, 4 diopters 1/4 meter, 5 diopters 1/5 meter and so on.
See Hyperopia
Hyperopia, or farsightedness, occurs when the curvature of the cornea, which causes light to come to a focus within the eye, is not steeply curved enough, compared to the length of the eyeball. The image entering the eye focuses behind the retina. Consequently, objects farther away will appear clearer than those at near. Young farsighted patients can usually see both distant and near objects, depending on the severity of their farsightedness. Unfortunately, their eyes have to work extra hard to see clear and this usually causes problems with the ability of their eyes to work together, leading to headaches, eye strain, reading problems, etc. School screenings typically will not detect farsightedness.
An instrument that measures the prescription of an ophthalmic lens.
Myopia, or nearsighted, occurs when the curvature of the cornea, which causes light to come to a focus within the eye, is too steep compared to the length of the eye. Patients that are nearsighted can usually find some point in front of them where their vision is clear. Consequently, near objects appear clearer than those farther away.
See Myopia
Stands for Oculus Dexter which is Latin for ‘Right Eye’.
Stands for Oculus Sinister which is Latin for ‘Left Eye’
An eye doctor who first receives a medical degree. A residency at a hospital depending on his specialty follows an internship. Areas of specialty might be ‘cornea’, ‘retina’, ‘cataract’, etc. An ophthalmologist specializes in treating medical conditions related to the eyes.
An eye care professional that is trained in optics, lenses, and the fitting of glasses.
‘Pupillary Distance,’ or the distance between the pupils. This is an important measurement because the ‘optical center’ of an ophthalmic lens should be set directly in front of the pupil.
An ocular condition in which the crystalline lens in the eye is no longer flexible enough to change shape. Consequently, the focus of light when objects are held at intermediate or reading distances is not clear. Beginning near the age of 40, a multifocal lens (bifocal, trifocal or no-line) is prescribed.
In an eye doctors office, a refraction is the testing performed to determine a patients spectacle correction. This is usually accomplished with the aid of a phoropter, which has many lenses in it, and by asking the patient which series of lenses allows them to see better. An objective refraction can also be done where the doctor can determine the patients spectacle prescription without asking any questions. While this is not as precise as the subjective refraction described above, it is certainly accurate enough for a child or individual who cannot respond to subjective testing.
The lining on the inside surface of the eye, similar to the film in a camera. This lining contains the photoreceptors (See Rods and Cones), which convert light into the electrical signal our brain reads as vision.
The photoreceptors in the retina responsible for black and white image perception.
The “white part” of the eye.
The 20/20 Vision notation system is a crude method of describing the clarity of vision. It is based on the prediction as to what a person with “normal” vision should be able to see from a distance of 20 feet. Therefore, a person with 20/20 vision is said to have “normal” clarity of vision. If a person has 20/40 vision for instance, a person with 20/20 vision could move back to 40 feet and still see what the 20/40 vision person would see at 20 feet. Legal driving in most states is 20/40 vision. * This really is too simplistic of a measure of vision because so many other factors need to be considered in vision such as how the eyes function as a team, ocular alignment, color vision, depth perception and ocular health.
This is used in conjunction with coatings, tints, photogrey, and glass sunglass lenses. It is a measure of the amount of light that is allowed to pass through the lens into the eye. If a lens has 100% transmission, then the lens is perfectly clear. If it allows 50% transmission then 1/2 of the light passes through into the eye and 50% is absorbed or reflected away. Sunglasses are defined as being 30% or less transmission of light. Boaters and skiers should have 15% transmission sunglasses.