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Refractive Error

Refractive error is an error in the focusing of the eye that frequently results in reduced vision. The eye acts like a camera with light from an object travelling through the pupil and being focused by the cornea (front of the eye) and lens (inside the eye) onto a specific point on the retina at the back of the eye. A refractive error is present if the light does not come into focus on this specific point. This can be caused by factors including the length of the eyeball and the curvature of the cornea and the lens. 

There are three main types of refractive error: Myopia (shortsighted/nearsighted), Hypermetropia/Hyperopia (longsighted/farsighted) and Astigmatism. Presbyopia is a naturally occurring condition that occurs later in life, usually after the age of 45, and results in reduced near vision.

Myopia: Occurs when the light rays in the eye come into focus before they reach the retina. It is characterised by blurred distance vision that often becomes more clear as an object becomes nearer. Therefore it is commonly referred to as being nearsighted or shortsighted. Signs of myopia include blurred distance vision, squinting eyelids to focus on distant objects, eyestrain and holding objects such as books closer or moving closer to objects to see clearly.

Correction of myopia is achieved through the use of minus lenses in glasses to focus the light rays further back in the eye on the retina. At an appropriate age, contact lenses can be used as an alternative to glasses. Laser corrective surgery may also be considered at a later age once refractive changes stabilise and an Ophthalmologist deems it appropriate.

Hypermetropia or Hyperopia: Occurs when the light rays in the eye come into focus behind the retina. It is characterised by blurred near vision that becomes more clear as an object moves further away. Therefore it is commonly referred to as being longsighted or farsighted. Signs of hypermetropia include blurred vision, visual fatigue and eyestrain worsening as an object comes nearer. The most common complaint in children is headaches with prolonged near work.

Correction of hypermetropia is achieved through the use of plus lenses in glasses to focus the light rays further forward in the eye on the retina. At an appropriate age, contact lenses can be used as an alternative to glasses. Laser corrective surgery may also be considered at a later age once refractive changes stabilise and an Ophthalmologist deems it appropriate.

Astigmatism: Occurs when the cornea (surface of the eye) has an irregular shape and is more curved in one direction than the other. Rather than a symmetrical soccer ball shape, the eye can be thought of as more of a football shape in astigmatism. This results in blurred vision at all viewing distances as light is focused unevenly within the eye. Astigmatism often occurs in association with other refractive errors and the signs are similar with blurred vision at all distances and squinting to focus on objects.

Correction of astigmatism is achieved through the use of cylindrical shaped lenses in glasses to focus the light rays evenly on the retina. At an appropriate age, contact lenses can be used as an alternative to glasses. Laser corrective surgery may also be considered at a later age once refractive changes stabilise and an Ophthalmologist deems it appropriate.

Presbyopia: Occurs in all individuals, predominantly after the age of about 45. It results from natural ageing processes causing reduced ability of the lens in the eye to change shape in order to focus on small objects at close fixation. The main characteristic of presbyopia is blurred near vision and eyestrain with prolonged near visual work. Individuals may note having to hold objects such as newspapers further and further away over time to read clearly.

Correction of presbyopia is achieved through the use of plus lenses (reading glasses) to magnify small text and objects at near fixation. It can be expected that the power of reading glasses may need to be gradually increased over a 15-20 year period following the onset of presbyopia.

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Posted on

July 16, 2018