Human eyes can differentiate between several thousand colors, assess the speed of a flying tennis ball and recognize letters as well as images in less than a fraction of a second. However, all of this works perfectly only if your eyes are absolutely healthy. Millions of people suffer from visual impairments. They have to wear eyeglasses. A vision test performed by your eye care professional will tell you if you are nearsighted, farsighted or suffering from any age-related vision impairments.
Myopia, hyperopia or presbyopia - eye experts use plenty of Latin vocabulary to describe visual challenges. As a patient, do not let the language confuse you, because all of these medical terms simply refer to a wide variety of vision impairments.
In plain English, myopia is called nearsightedness, hyperopia farsightedness and presbyopia refers to age-related vision impairments. More than half of the population struggles with one or the other imperfection when it comes to visual acuity. A vision test determines the actual condition instantly. As a result, appropriate eyeglass lenses can be prescribed and perfect vision restored.
Rays of light that reach the eye from a distance are bundled by the retina, which results in the creation of a distorted image. The near sighted eye, i.e. the one affected by myopia, is either too long or the refraction rate of the lens is too high. As a result, objects in the distance cannot be recognized clearly.
We recommend visiting your eye care professional once a year for a brief vision exam. If you are one of the many people who go through life without needing glasses for many years and suddenly realize that you cannot make out road signs anymore while driving, you should definitely make an appointment for an eye exam.
How does myopia develop?
In most cases, an excessively long eyeball is the cause of myopia. Even a discrepancy as small as 1 millimeter can result in near sightedness with a severity of about -3 diopters. Given that the human eye’s accommodation can only enlarge the refractory rate, the eye cannot compensate for near sightedness without a visual aid.
The root causes of myopia remain a mystery. The only fact that has been established to date is that genetic factors do play a pertinent role. This is one of the reasons why a higher percentage of people of Chinese heritage suffer from myopia than people with a European background. Genetic myopia starts in school age children and usually varies from -2 to -4 diopters. The process usually comes to a slow halt during puberty or in young adults.
How do eye care professionals perform eye exams?
Eye care professionals check the acuity of your vision. They use tools such as a measuring device, into which they insert a variety of eyeglasses or an instrument called a phoropter.
In just a few simple steps, the examiner can test an array of lenses placed in front of your eyes. The patient can easily determine which of these lenses improves his or her vision and which ones do not. Computer supported measuring processes are now also available.
In eyes affected by this condition, incoming light rays are bundled behind the retina and create a distorted image. The farsighted eye, i.e., the eye affected by hyperopia is too short and the refraction rate of the lens is not sufficient. This condition can cause the following problems:
Make an appointment for an exam with your eye care professional if you have repeated headaches after reading or doing close-up work, for instance on a computer. Younger eyes can actually compensate hyperopia with the assistance of the eye lens’s accommodation strength. Many younger people affected by this dysfunction do not even notice it until they are older. However, if you notice any such symptoms, take them seriously and have your eyes checked.
How does hyperopia develop?
The eyeball of patients suffering from hyperopia is either too short or the refraction rate of the lens is insufficient. As a result, light rays are bundled only once they are behind the retina. People with normal vision have eyes that stay completely relaxed when zooming in on objects that are nearby.
The refraction rate of the lens has to be increased in farsighted eyes to provide sharp close range vision. This can be achieved only if the ciliary muscle is tightened, which causes the lens to bend more. This added muscle tension can cause the above described ailments. Many people do not even complain when this added strain causes migraines, which is why many of them continue to suffer until their hyperopia is finally diagnosed.
How spectacle lenses correct hyperopia
After a vision test (see details above) at the eye care professional, glasses with convex lenses are prescribed to ensure that the light beams coming from objects in the distance are bundled on the retina without the eye having to struggle to compensate for this vision problem through its accommodation strength.
As the lenses of our eyes change with age, we may eventually find ourselves confronted with an age-related vision problem. Starting at around age 45 the lens begins to lose its capacity to adjust to the close-up vision tasks it is required to handle. This is evident in the following symptoms:
See your eye care professional as soon as you notice your first vision problems, for instance if you suddenly find reading very tiring.
How does presbyopia develop?
The root cause of this vision problem has been determined: As we age, the content of water in the eye’s lens diminishes, while the insoluble protein content increases. As a result, the lens becomes stiffer and loses its elasticity. Consequently, it can no longer bend as much as it needs to for the human eye to be able to see clearly up close.
Presbyopia begins to develop around the age of 45. In the early stages, only minimal corrections of about +0.75 diopters are required. As the years pass, the accommodation strength continues to decline. The process is usually complete after the age of 60 and the impairment remains at the same level.
How spectacle lenses correct presbyopia
Once the patient’s visual acuity has been determined, this visual impairment can be compensated with a variety of lens options. Patients, who were previously blessed with normal vision, will need reading glasses with concave lenses. Depending on the close up strength, these glasses have to be taken off during some close-up work, for instance while working on a computer.
The situation of people who were previously nearsighted or farsighted is a little more complicated. Nearsighted patients need reading glasses with weaker diffusion lenses. Farsighted patients are prescribed stronger concave lenses and reading glasses. Because most users do not like having to constantly switch between eyeglasses, most people who are farsighted will opt for varifocal lenses.
In addition to covering both long- and short-range vision issues, they also have a corrective zone that allows users to see comfortably at medium-range distances. Varifocal lenses Varifocal lenses provide seamless transitions from near to far. In fact, they emulate our natural vision patterns. Modern glasses are so easy to get used to that the familiarization periods are now amazingly brief.
This visual impairment is caused by an irregular curvature of the cornea and in rare cases, irregularities in the lens. Those affected by this condition see distorted and blurred images. Almost all people have very mild forms of astigmatism, because a precise standard does not exist in nature.
Experts believe that the condition is caused by excessive lid tension, which makes the eye surface take on a slightly elliptic form. As a result, the refraction of the incoming light is increased. Objects are seen in blurry and distorted patterns and a dot-shaped light source looks like a line.
In most cases, astigmatism occurs in conjunction with myopia or hyperopia. Experts distinguish between two types of astigmatism: Patients with regular astigmatism have only two different refraction levels. Those suffering from irregular astigmatism have corneas that are shaped so irregularly that the incoming light is not bundled in a single, but in multiple points.
How eyeglass lenses correct these conditions
Patients who have regular astigmatism are prescribed cylinder lenses. They refract the light in different directions. Pertinent prescriptions not only stipulate details about the myopia or hyperopia, but also the degree levels for the cylinder lens.
Important: Children who have these vision problems should start wearing glasses made for their specific needs as early as possible. Otherwise, the patient might suffer from headaches, double and distorted vision as an adult because the brain has learned to correctly interpret the objects depicted incorrectly on the retina. As a result, it has to be retrained.
The only correction for irregular astigmatism is available in the form of special contact lenses. They allow the tear film between the cornea and the contact lens to compensate for the irregularities.