Types of Visual Impairment
An eye with normal vision
The light rays enter the eye through the cornea and the lens and gather into a sharp focal point on the retina. The nervous receptors then interpret the signals into electrical impulses and the information is carried by the optic nerve to the brain. The brain, in turn, changes the impulse into a comprehensible image which for us means „seeing“. Our eye works like a photo camera by making the image form in our brain.
Optical defect (ametrophy)
The eye with normal vision (emmetropia) has its cornea and lens in accordance with the eye’s axis length. Very often, though, that is not the case. In some cases the light that has reached the eye is not focusing exactly on the retina.
The eye is nearsighted if the faraway objects seem blurry. In that case the eye’s axis is too long and the light focuses in front of the retina. As a result you have a blurry vision.
A farsighted person has difficulties in seeing and reading objects that are close. A farsighted eye’s axis is too short and the light focuses behind the retina. That’s why it is not possible to see close objects clearly.
Astigmatism may occur also in a near- and farsighted eye. In case of astigmatism, the cornea does not have an ideally round form, it is rather in a shape of a rugby ball. That is why the light fails to come to a single focus on the retina to produce clear vision. Instead, multiple focus points occur, either in front of the retina or behind it (or both). The result being an overall out of focus vision.
Many people suffer from age related presbyopia – distant objects are clear but closer objects appear blurred. When they grow older, they need reading or bifocal glasses. During the natural aging process, the eye’s lens gradually loses the ability to focus quickly on objects that are close. Presbyopia is not caused by the eye’s axis length changes but the eye’s ability to focus objects at different distances. In order to correct age-related changes with a laser, you first need to consult your doctor.