Our eyes may be small but they are one of the most impressive systems in the body. The human eye is made up of many important parts which all work together to give us a clear view of the world around us.
Light enters the eye through the cornea, then through the pupil and the iris which can dilate and contract depending on the light intensity. The light then passes through the lens of the eye which both refines and helps to focus the light into the retina. The retina is located at the back of the eye. Here, the light is absorbed by photoreceptor nerve cells which change the light rays into electrical impulses. These impulses are sent up to the brain via optic nerve, where an image is interpreted.
Aging Vision (Presbyopia)
The aging of the eye is a natural process which normally starts to become noticeable around the age of 40. This common condition is called Presbyopia.
The lens of the eye starts to lose its natural elasticity, which reduces your ability to focus properly. Your vision may become increasingly harder to focus, especially when reading or working on a computer.
An optometrist /Ophthalmologist may prescribe reading glasses or may change your distance glasses to multifocal or bifocals in order to help you achieve clearer vision.
Astigmatism occurs when the shape of the cornea becomes steeper (or flatter) in one direction, similar to the shape of a rugby ball. As a result, when light rays are refracted through the lens of the eye, they do not converge properly and a blurred image on the retina is produced. It is common for people to have astigmatism in conjunction with either Myopia (short sightedness) or Hyperopia (long sightedness).
Astigmatism can be treated quite successfully with laser eye surgery or lens surgery.
Short Sightedness (Myopia)
People with short sightedness (myopia) typically have an eye that is slightly longer (front to back) or a cornea that is steeper than normal. This means that when the light passes from the cornea through the lens of the eye, the light rays converge incorrectly and the image becomes out of focus on the retina. In this case, clear sight is only possible at short distances and distant objects generally appear blurry.
Short sightedness can be treated with laser vision correction.
Long Sightedness (Hyperopia)
People with long sightedness (Hyperopia) have an eye that is slightly shorter or the curvature of the cornea is flatter than normal. Light rays that are refracted from the cornea through the lens of the eye converge incorrectly and the image becomes out of focus on the retina. People who are long sighted usually have problems viewing objects that are nearby. However long distance vision may also be affected. Long sightedness can be treated with laser eye surgery.
Other – Higher Order Aberration
Aberrations are differences from normal vision, which result in the blurring of an image. Long sightedness, short sightedness, presbyopia and astigmatism are considered first order aberrations and are responsible for 85% of the eye’s vision imperfections.
There are also other, higher order aberrations, which can cause poor quality vision. Approximately 80% of these occur on the corneal surface and 20% occur in the lens or in the vitreous body of the eye. Higher order aberrations generally cause difficulties seeing at night, at dusk and at dawn. This is because the rays of light do not meet as a single point, but instead are dispersed into two or more points. When the pupil dilates, your sight becomes significantly worse or you feel easily blinded.