How to calculate my eye power ?
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Eye power, also known as refractive power, is calculated based on the refractive error of your eyes. This error can include myopia (nearsightedness), hyperopia (farsightedness), astigmatism, and presbyopia (age-related difficulty focusing on close objects).
Here’s how it’s calculated:
1. Visual Examination: An optometrist or ophthalmologist conducts a visual examination to assess your vision and identify any refractive errors.
2. Refraction Test: During a refraction test, you’ll look through a series of lenses while reading an eye chart. The doctor will ask which lenses make your vision clearer. This helps determine the amount of correction needed for your vision.
3. Retinoscopy: In this test, the doctor shines a light into your eye and observes the reflection off the retina while changing lenses. This provides an objective estimate of your refractive error.
4. Autorefraction: Some clinics use automated instruments to measure your refractive error quickly.
5. Keratometry: For astigmatism, the curvature of the cornea is measured using a keratometer.
6. Prescription: Based on the results of these tests, the doctor determines your prescription, which is measured in diopters (D) for each eye. For example +1.5 D means you have hypermetropia with 1.5 eye power. -2.5 D represents myopia with 2.5 eye power.This prescription indicates the strength of lenses needed to correct your vision to normal levels.
The prescription includes three main components:
– Sphere (Sph): Indicates the lens power needed to correct nearsightedness or farsightedness.
– Cylinder (Cyl): Indicates the lens power needed to correct astigmatism.
– Axis: Specifies the orientation of the cylinder for astigmatism correction.
Some other terms used:
O.S.
Oculus sinister denotes the left eye also prescribed as LT.
O.D.
oculus dextrus which represents the right eye also prescribed as RT.
Plus(+) sign before the numbers in your prescription indicates farsightedness or hypermetropia/ hyperopia.
(-) minus sign indicates near/shortsightedness or myopia.
Once your eye power prescription is determined, you can use it to get glasses, contact lenses, or undergo refractive surgery if suitable.