How Vision Works. The function of the eye is similar to a camera. A camera creates images by focusing on an object and allowing specific amounts of light to pass through a hole to create a visual impression on film. The eye functions in much the same way. Common eye problems include Astigmatism, Farsightedness, Nearsightedness and Presbyopia.
Hyperopia or farsightedness is very common, affecting up to 62% of people over the age of 40. Hyperopia occurs when the eyeball is too short or the cornea is too flat. When rays of light enter a hyperopic (short) eyeball, they are focused behind the retina instead of directly on the retina where light must be directed for normal vision. Because of this, the focusing apparatus in the eye must work constantly to make up for the problem and focus images. Symptoms of farsightedness can include eyestrain, blurred vision, or headache (especially when reading or at the end of the day). Symptoms can increase over time.
Young people with hyperopia (30 to 45 years) may not have any problems seeing things in the distance, but may strain their eyes unnecessarily to maintain focus on close-up objects. This ability to see things 'far away,' but not near, is how the term 'farsightedness' came into being.
Middle-aged hyperopes (45 to 55 years) al... Read More
Astigmatism occurs in nearly 30% of the non-Asian population. In an eye with astigmatism, the front of the cornea is not equally curved; it is slightly oval in shape, like a football. Light rays entering the eye bend unequally, resulting in a distorted image. Astigmatism usually occurs in conjunction with myopia (nearsightedness) or hyperopia (farsightedness), and is a complicating factor for refractive surgery.
Astigmatism can be corrected with eyeglasses, contact lenses or refractive surgery.
The best way to understand function of the eye is to compare it to a camera. A camera creates images by focusing on an object and allowing specific amounts of light to pass through a hole to create a visual impression on film. The eye functions in much the same way.
When light enters the eye, it passes through the cornea (camera lens) where 2/3 of focus is achieved. The light then passes through the pupil where the iris (aperture) adjusts the amount of light that is allowed to enter. The remaining 1/3 of focus is then achieved when the light passes through the lens (camera lens).
The shape of the lens can adjust (either thinner or thicker) by tensing or relaxing the muscles of the eye. The focused light finally reaches the retina (film) where it is converted by the rods and cones into a signal that can travel to the brain (film development). Once the image reaches the brain, you have sight.
What causes vision problems?
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Myopia or nearsightedness is very common, affecting 26% of the non-Asian population. (Myopia occurs at a much higher rate in the Asian population.) It is a condition in which people have difficulties seeing objects in the distance, but may have no problems focusing on objects that are up close. This ability to see 'near' but not far is why this condition is more commonly called 'nearsightedness.'
Myopia occurs when the eyeball is too long or the cornea is too steep. When rays of light enter a myopic (long) eyeball, they are focused in front of the retina instead of directly on the retina where light must be directed for normal vision. Symptoms of nearsightedness can include eyestrain, blurred vision or headaches.
Myopia or nearsightedness requires a concave corrective lens (glasses or contact lenses), which is written as a 'negative number' in your prescription. Surgically, nearsightedness is corrected by... Read More
People often confuse farsightedness with another condition called presbyopia, which occurs as a normal result of aging. Presbyopia affects most of those over the age of 40 and all over the age of 51, as the aging process affects the eyes' natural ability to bring near objects into focus.
Presbyopia occurs when the lens inside the eye loses flexibility, preventing accurate focusing on objects that are up close. People with this condition may experience eye fatigue when reading in poor lighting or at the end of the day, trouble changing the focus from distance to near, or the need to constantly reposition reading material in an attempt to find the right focus.
This condition affects people with good vision or myopia (nearsightedness), but is more problematic for those who are hyperopic (farsighted). Prior to becoming presbyopic, hyperopes were able to naturally accommodate to bring things into focus at any distance. Suddenly, after ... Read More