What is normal vision?
In order to better understand how refractive errors affect our vision, it is important
to understand how normal vision happens. For people with normal vision, the following
sequence takes place:
Light enters the eye through the cornea, the clear, dome-shaped surface that covers
the front of the eye.
From the cornea, the light passes through the pupil. The amount of light passing through
is regulated by the iris, the colored part of the eye.
From there, the light then hits the lens, the transparent structure inside the eye
that focuses light rays onto the retina.
Next, it passes through the vitreous humor. This is the clear, jelly-like substance
that fills the center of the eye and helps to keep the eye round in shape.
Finally, it reaches the retina. This is the light-sensitive nerve layer that lines
the back of the eye, where the image is inverted.
The optic nerve is then responsible for sending this information to the brain. The
brain interprets the impulses it receives into images.
What are refractive errors?
Refractive errors happen when the shape of the eye prevents light from focusing directly
on the retina. The following are the most common refractive errors. These errors affect
vision and may need corrective lenses or surgery for correction or improvement:
Astigmatism is a condition in which an abnormal curvature of the cornea can cause
two focal points to fall in two different locations. This makes objects up close and
at a distance appear blurry. Astigmatism may cause eye strain and may be combined
with nearsightedness or farsightedness. Eyeglasses, contact lenses, or corrective
surgery may help to correct or improve the condition.
Commonly known as farsightedness, hyperopia is the most common refractive error in
which an image of a distant object becomes focused behind the retina. This happens
either because the eyeball axis is too short, or because the refractive power of the
eye is too weak. This condition makes close objects appear out of focus. It may cause
headaches and/or eye strain.
Eyeglasses or contact lenses may help to correct or improve hyperopia by adjusting
the focusing power to the retina. Corrective surgery may also help by changing the
shape of the cornea to a more spherical, round shape instead of an oval shape.
Commonly known as nearsightedness, myopia is the opposite of hyperopia. It is a condition
in which an image of a distant object becomes focused in front the retina. This happens
either because the eyeball axis is too long, or because the refractive power of the
eye is too strong. This condition makes distant objects appear out of focus and may
cause headaches and/or eye strain.
Eyeglasses or contact lenses may help to correct or improve myopia by adjusting the
focusing power to the retina. Corrective surgery may also help by changing the shape
of the cornea to a more spherical, round shape instead of an oblong shape.
Another type of farsightedness, presbyopia is caused when the center of the eye lens
hardens. This makes it unable to accommodate near vision. This condition eventually
affects almost everyone, beginning as early as the age of 35. It even affects those
with myopia. Eyeglasses or contact lenses may be prescribed to correct or improve