Myopia, Hyperopia, astigmatism and Presbyopia
In order for our eyes to be able to see, light rays must be bent or refracted by the cornea and the lens so they can focus on the retina, the layer of light-sensitive cells lining the back of the eye.
The retina receives the picture formed by these light rays and sends the image to the brain through the optic nerve.
A refractive error means that due to its shape, your eye doesn’t refract the light properly, so the image you see is blurred. Although refractive errors are called eye disorders, they are not diseases. In a normal eye, the cornea and lens focus light rays on the retina.
The cornea is the clear front window of the eye. A normal cornea is round and smooth, like a basketball. If you have astigmatism, the cornea curves more in one direction than in the other, like a football. Astigmatism distorts or blurs vision for both near and far objects. It’s almost like looking into a fun-house mirror in which you appear too tall, too wide or too thin. It is possible to have astigmatism in combination with myopia or hyperopia.
When you are young, the lens in your eye is soft and flexible. The lens of the eye changes its shape easily, allowing you to focus on objects both close and far away. After the age of 40, the lens becomes more rigid. Because the lens can’t change shape as easily as it once did, it is more difficult to read at close range.
This normal condition is called presbyopia. You can also have presbyopia in combination with myopia, hyperopia or astigmatism. In astigmatism, the cornea is uneven. Images focus in front of and beyond the retina, causing both close and distant objects to appear blurry.
Retina Lens Cornea Light rays Light is focused in front of and behind the retina
How are refractive errors corrected ?
Eyeglasses or contact lenses are the most common methods of correcting refractive errors.
They work by refocusing light rays on the retina, compensating for the shape of your eye. Refractive surgery is also an option to correct or improve your vision. These surgical procedures are used to adjust your eye’s focusing ability by reshaping the cornea, or front surface of your eye. There is not adequate scientific evidence to suggest that eye exercises, vitamins or pills can prevent or cure refractive errors.
Wearing eyeglasses is an easy method to correct refractive errors. They can also help protect your eyes from harmful light rays, such as ultraviolet (UV) light rays. A special lens coating that screens out UV light is available. Glasses or goggles made of protective lens material (polycarbonate) should be used for sports and all hazardous activities. All children and adults who have one poorly seeing eye should wear protective polycarbonate lenses at all times to protect their “good” eye.
Bifocals are eyeglasses used to correct presbyopia. They have a correction for reading on the bottom half of the lens and another for seeing at a distance on the top. Trifocals are lenses with three different lens corrections in one set of eyeglasses. If you don’t need correction for seeing at a distance, you can receive a prescription for reading glasses or buy them over the counter to correct presbyopia.
No exercise or medication can reverse presbyopia. You will probably need to change your prescription from time to time between the ages of 40 and 60 because your lens will continue to lose flexibility.
There is now a wide variety of contact lenses available. The type best suited for you depends on your refractive error and your lifestyle. If you want to wear contact lenses, discuss the various options with your ophthalmologist.