People suffer from four types of refractive eye problems:
A refractive error occurs when light entering the eye is not precisely focused on the retina at the back of the eye, causing blurred vision. Normally, light rays passing through the cornea, pupil, and lens are focused directly on the retina, allowing you to perceive objects clearly.
Myopic patients experience vision that is clear for close objects, but blurred in the distance. This is caused by a cornea which is too steep for the length of the eye, causing light rays to focus in front of the retina.
Hypermetropic patients may see distant objects reasonably clearly, but have increasing difficulty with near objects. Conversely to myopia, this occurs due to a cornea which is relatively flat, causing light to focus behind the retina.
Astigmatism causes blurred vision at all distances. This is caused by an “egg” shaped cornea, where light rays are focused both behind and in front of the retina.
Presbyopic patients experience a decline in their ability to focus on near objects, due to a natural loss of elasticity of the lens. It is a common age-related condition, which is usually first noticed with reading deterioration or reliance on reading glasses, regardless of distance clarity.