When the eye is considered in focus and able to accurately view objects from 20ft away.
The standard metric used to determine if someone has achieved “normal” visual acuity. When your eye has a nominal performance of 20/20 vision, your vision is said to be in focus and accurately able to view items 20 feet away.
With 20/20 vision, the human eye is able to separate lines that are spaced 1.75mm apart at 20 feet away. When using the expression 20/40 vision, 20 would represent the distance in feet between you and the chart. The 40 means that the you can read the eye chart from 20 feet away as well as a normal person could read the same chart from 40 feet away. For example, a vision of 20/40 would be half as good as 20/20 vision. Keep in mind, 20/20 vision is not necessarily the best possible visual acuity you can have, but rather the standard for “normal” vision.
When the eye is not perfectly round, causing light to refract in more than one direction.
Like an odd-shaped, slightly-deflated basketball that just won’t bounce right, astigmatism is the product of an eye that is not perfectly round and causes light to bounce around abnormally inside the eye. The result of this light refracting in more than one direction is a lack of visual focus.
Astigmatism causes blurred vision and a lack of focus that can sometimes cause painful headaches, fatigue, and eyestrain. It is largely untreatable without the use of corrective lenses or refractive surgery – the latter of which is becoming more prevalent with the use of lasers.
Chalk this one up to genetics: there continues to be a cloud of mystery surrounding why astigmatism occurs at all, but it is a naturally-occurring phenomenon that should not be a cause for alarm or panic. In fact, it’s thought that most people have some form of an irregular eye shape that can lead to varying degrees of refractive error.
When a foggy buildup of protein covers the eye’s lens and allows less light to pass through.
Imagine your glass lenses are cloudy from an accumulation of dirt and smudges, obstructing your vision while you perform everyday tasks. That is essentially what happens with cataracts – a foggy, film-like buildup of protein covers the eye’s lens and worsens eyesight as less light is able to pass through.
Though common knowledge says that a cataract merely causes blurred vision, it can actually cause other eyebrow-raising symptoms, such as progressive nearsightedness (aka “second sight”), double vision, and an altered perception of color (think of that film as an Instagram filter).
There are four primary types of cataract causes:
Most common form of color blindness, involving confusion of red and green color hues.
This is a specific type of color blindness that involves confusing red, green, and sometimes yellow color hues. This is the most common type of color blindness.
Those who experience this type of color blindness can make out the general color scheme of reds and greens, but with a distortion of what they actually look like. Someone with deuteranopia can distinguish two or three different hues of green, versus seven different shades for someone with normal vision.
Deuteranopia is 10 times more likely to occur in males than females. This is because color blindness is a sex-linked trait attached to X chromosomes. Females have two X chromosomes so one of those chromosomes can compensate for any deficiencies in the other. On the other hand, males have only a single X chromosome without a "backup" x chromosome to make up for the faulty one
When the eye’s blood vessels deteriorate and fluid fills the retina, reducing overall vision.
The diabetic onset of retinal disease, retinopathy occurs when strength of the eye’s blood vessels deteriorates and causes fluid – blood or otherwise – to seep into the retina. In most cases, this fluid flows into the center of the eye and negatively impacts vision. Heightened levels of blood sugar can worsen this condition.
The obstruction of the retina and overflow of fluid to the center of the eye causes blurred vision as well as risks swelling the macula – the part of the eye that allows you to see the finer details of the world. (Think of it like transitioning from a 12 megapixel camera back to a six megapixel.) The disorder’s implications can be amplified if diabetes is left untreated.
The most common cause of diabetic retinopathy is unchecked diabetes. In most cases, retinopathy is left undiagnosed until dramatic changes in vision begin to occur, making it a much more difficult eye disease than most to catch early. Upon being diagnosed with diabetes, a follow-up appointment with an ophthalmologist is advised.
Seeing mirror images either horizontally or vertically, when focusing on a targeted object.
Sometimes referred to as "diplopia," double vision is the perception of mirror images and is often a sign of larger problems that stem from complications with the cornea, lens, and nerves of the eye, as well as the muscles that cause movement of the eye and lid.
Double vision may cause a sufferer to see dual images when focusing on a targeted object – either horizontally or vertically. It may also lead to droopy eyelids and cause a sharp pain when moving eyes in either direction. There are two types of double vision: binocular (“cross-eyed”), and monocular (double vision in only one of the eyes).
The misalignment of both eyes is what causes double vision. Corneal infections, cataracts, myasthenia (an autoimmune disease), unchecked diabetes, migraines, strokes, and aneurysm are among the most common causes and indicators of double vision.
Tiny dots that appear in your line of vision usually as a result of staring into bright spaces.
These are just what they sound like: tiny, difficult-to-distinguish dots that appear in your line of vision and often go away as quickly as they appear. Floaters most commonly occur upon staring at bright spaces, such as the sky on a bright day. Often, these spots are irksome but not dangerous. However, they should be noted in the case of rare eye conditions like retinal tears or detachment.
Aside from the presence of the dots themselves, long-term effects on vision are minimal to nonexistent. The dots themselves take shape in the form of squiggly lines or transparent strands. They sometimes manifest in interlaced shapes and can be scary, but not necessarily harmful. These dots move as your eyes try to focus on them.
A protein called collagen causes these dots to appear, with a substance called vitreous humor – located in the back nook of the eye – shrinking in a way that reduces the amount of light that can shine into the retina. This undetectable change occurs most prevalently in those between the ages of 50 and 75.
The buildup of pressure inside the eye which can pinch the optic nerve and damage vision.
The result of damage to the optic nerve, glaucoma is the buildup of pressure inside the eye. Glaucoma can occur slowly over time with no noticeable physical changes to the eye. However, in rare cases, glaucoma can develop quickly and cause severe, visible damage to the eye and require immediate medical attention.
The optive nerve acts as a sort of "image messenger" between the brain and optic nerve. Glaucoma can blocks this transmission and can cause pain, burning, itching, and fatigue. If left untreated, it can eventually lead to blindness.
When fluid in the frontal area of the optic nerve stops circulating normally, it builds to the point of having nowhere to go. Glaucoma is often passed through families, although it can also be caused by blunt trauma and chemical injuries. Glaucoma is likely to occur in those who are diabetic.
When the eye has difficulty focusing on close objects; also referred to as farsightedness.
The older brother of myopia, hyperopia is, put simply, farsightedness. One fifth of the U.S. population is farsighted, so hyperopia isn't necessarily classified as a disease. The disorder is one of many instances of irregularly-shaped corneas causing vision loss.
The symptoms of hyperopia are numerous but not dangerous – blurry vision (particularly when wandering around at night), difficult focusing on up-close objects, eyestrain, and headaches. The degree to which this impacts vision is likely to change over time, but is thought to either plateau early on in life, or accelerate upon hitting the prime middle-aged year of 40.
There is no known cause of hyperopia. It is a condition that often starts in youth – around age 9. In some cases, it needs no treatment at all, as the eyes can adjust at an early age and correct themselves. In children, watch for habits of eye-rubbing and an unwillingness to read when attempting to evaluate whether he/she may be farsighted.
The reduction of the eye’s ability to absorb, filter and protect from blue and ultraviolet light.
The macula is the yellow part of the retina that naturally protects the eye from an excess of blue and ultraviolet light by absorbing it. Macular degeneration can happen in two ways:
The symptoms are fairly similar for both types of macular degeneration: blind spots, a loss of central vision, and distorted vision in the form of moving lines. In a practical sense, pay attention to how often you need to use bright lights when working, as well as how well your eyes adjust to contrasting brightness levels (dimly-lit spaces, in particular).
Macular degeneration is age-related, meaning that the chances of it occurring increases as you age and tissue strength begins to dwindle. There is no certain cause of the condition, but be sure to pay attention to the aforementioned symptoms if you have high blood pressure or cholesterol, are obese, and are Caucasian.
Nearsightedness caused when light shining through the eye’s lens does not focus correctly.
Don’t let the language fool you – this is medical jargon for “nearsightedness.” Those suffering from myopia have difficulty seeing faraway objects (street signs, chalk boards, etc.), but can easily visualize ones that are nearby (books, phones, and more). The condition is fairly common: 32 million people in the United States who are older than 40 have some form of nearsightedness.
Beyond the obvious impairment of vision, myopia can cause eyestrain, fatigue, common headaches, and induce squinting, which can be damaging to long-term eye health. It also throws a wrench in everyday plans of driving, participating in the classroom, reading a prompter, and other all-too-real scenarios.
Myopia is a result of the light that shines through the eye’s lens does not focus correctly. Instead, it causes images to focus in the front of the eye and through the light-sensitive retina. There is no known cause of myopia, aside from the usual suspects of familial inheritance and age.
When the retinal tissue tears or detaches completely, causing blurred vision or blindness.
The retina itself is nerve tissue nestled toward the front end of the eye. It receives light and sends messages to the brain about what visual images are being perceived. When that thin tissue tears or detaches completely, it can cause blurred vision or even blindness. Surgical repairs are the only available treatment methods.
Floaters, which are in this case caused by vitreous gel shrinking and detaching itself from the retina, begin to appear in streaming flashes of lightning-like streaks. Eventually, these happen more frequently, and result in a loss of peripheral vision that culminates into a variety of other vision-loss problems.
Posterior vitreous detachment (the separation of the gel from the retina) occurs upon aging, and tears the retina like tape adhesive ripping apart skin. Diabetes, myopia, traumatic head injuries, and other eye conditions are all common warning signs of retinal detachment.
Caused by retinal cell damage and leads to progressive impairment and eventual blindness.
Retinitis pigmentosa is a progressive, degernative, and notoriously unpredictable disorder that can lead to major vision impairment and eventual blindness. The disorder affects the retina and is difficult to diagnose. It shows virtually no external effects on the eyes, and typically renders an individual as legally blind upon diagnosis.
Retinitis pigmentosa can cause blindness and severe loss of peripheral vision. It may also cause night blindness, extreme sensitivity to glares, and prolonged visual adjustments to contrasting shades of light (think: turning on and off a light switch). Currently, there is no cure for the disease, and treatment is scarce – though research suggests vitamin A supplements may delay blindness for nearly a decade.
Retinitis pigmentosa is an inherited condition that affects one in every 4,000 people in the United States. The disorder is a result of retinal cell damage, and is thought to develop rapidly among older adults. Symptoms appear early on in childhood.