Refractive Errors

The correction of Refractive Errors involves the traditional diagnosis and treatment which the profession of Optometry has been mostly known for over many centuries. Here at Prime Vision-Care Centres, we pride ourselves on performing careful measurements to obtain the most accurate results to correct your vision to its best ability. Refractive Errors are the focussing weaknesses for which glasses and contact lenses are traditionally prescribed. As such the eye acts much like a camera, with the focussing components at the front of the eye, and the gathering of the light images at the back to send the results to the brain to tell us what we are seeing. There are four main types of Refractive Errors, and these can all occur by themselves or in combination with other types of Refractive Errors:

Hypermetropia: This is also known as “Long-Sightedness”. In this condition the length of the eyeball is too short for the focal length of the refractive structures of the eye. This results in blurred or strained vision at close range, even though the distance vision may be relatively clear. It is corrected with positive powered, or “convex” lenses, which bring the image to the correct focal position at the back of the eye.

Myopia: This is also known as “Short-Sightedness”. This the opposite of Hypermetropia, where the length of the eyeball is too long for the focal length of the refractive structures. This results in blurred vision at longer distances, even though the close range may be relatively clear. It is corrected with negative powered, or ves the “concave” lenses, which also bring the image to the correct focal position at the back of the eye.

Astigmatism: In this condition, the eyeball is irregular in shape, somewhat like a rugby ball, compared to a more spherical shaped soccer ball. This causes a warpage of the light’s focussing range at most distances, both near and far. This is corrected by a “cylindrical” shaped lens, which has different powers at different angles or “axes”. This also brings the image into correct focus at the back of the eyeball.

Presbyopia: This is a condition which eventually affects all human beings, if they live long enough. It involves the age-related hardening of the crystalline lens of the eye, behind the pupil, causing a lack of ability to focus at close distances compared to distance vision. This is also corrected by positive powered, or “convex” lenses (in a similar way to hypermetropia), to bring the images of close targets into focus at the back of the eye.