What Is A Prescription?
Mr Glenn Carp provides an explanation of what prescriptions are and what the numbers mean in this 35 second video.
Mr Glenn Carp – “A prescription is essentially the patient’s refractive error. When the light enters the eye through the cornea and through the lens to reach the retina it needs to be focused on the retina. So any little refractive error in the pathway, whether it be in the lens or in the cornea in the front of the eye, will result in some de-focus in terms of the light reaching the retina. So your prescription essentially is just the correction factor to sharpen the light rays so that they do reach the target.”
Prescriptions Explained Further
To gain a prescription value Optometrists and Ophthalmologists measure the disorders of the eye, such as myopia, hyperopia, astigmatism, and presbyopia in units called dioptres. These show the amount of correction you need to see normally. One dioptre is the equivalent of a lens that can focus on an object one metre away. The more short-sighted, long-sighted, or astigmatic you are, the higher your prescription in dioptres. A typical prescription has three numbers such as -5.00 / -1.50 x 180.
The first number (-5.00) of a prescription identifies your degree of short-sightedness or long-sightedness. The minus sign in front of the number identifies you as short-sighted. A plus sign would show you were long-sighted.
The second number (-1.50) of a prescription identifies your degree of astigmatism. This is written with either a plus sign or a minus sign.
The third number (180) indicates the axis, the direction of your astigmatism. An axis of 180 degrees, for example, means the astigmatism is horizontal.
A prescription of -5.00 /-1.50 x 180 indicates that the patient is moderately short-sighted, with a moderate degree of astigmatism in a horizontal direction.
The table below illustrates the ranges from mild to severe short-sightedness and mild to severe long-sightedness:
|Mild short-sightedness||Myopia up to -3.00 dioptres|
|Low short-sightedness||Myopia up to -3.25 to 6.00 dioptres|
|Moderate short-sightedness||Myopia from -6.25 to -11.00 dioptres|
|Severe short-sightedness||Myopia from -11.25 to -23.50 dioptres|
|Low long-sightedness||Hyperopia from +0.75 to +2.50 dioptres|
|Moderate long-sightedness||Hyperopia from +2.75 to +6.00 dioptres|
|Severe long-sightedness||Hyperopia from +6.25 to +12.00 dioptres|
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