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If you are under forty your prescription will probably consist of a “sphere,” a “cylinder,” and an “axis” for each eye.
The sphere measures how long-sighted or short-sighted you are. A plus (+) sphere indicates long sightedness or hypermetropia. A minus (-) sphere means you have myopia (short sight). The cylinder measures how much astigmatism you have (it can be + or -) and the axis is the orientation of this astigmatism between 0 and 180O.
Once we reach our forties we normally develop symptoms of presbyopia and need extra help for reading over and above any distance or general purpose prescription we may have. This characterised by having to hold close work further away to see it clearly.
Sometimes this reading prescription is written out in full (especially if you only need glasses for close work) but usually the extra power needed for reading is recorded as the “reading addition” or “Add”.
The reading addition is added to the sphere of your distance prescription to calculate your reading prescription.
Around the age of 55 we begin to notice that the middle distance cannot be seen clearly either through distance or reading glasses. At this stage many people require varifocals; however you may also be prescribed an intermediate addition for hobbies or specific tasks such as computer, piano or DIY.
There may also be other information on your prescription some of which we may need to make up your glasses. This information might include prism, vision, visual acuity, back vertex distance and dispensing advice. |