What is the Normal Eye Power?
Normal eye power, often referred to as emmetropia, means a person can see clearly at a distance without needing corrective lenses. While 20/20 vision is considered "normal" and signifies clear vision at 20 feet, only about 35% of the population achieves this without glasses or contact lenses. A "perfect" eye has a sphere power (SPH) of 0.00 diopters and a cylinder power (CYL) of 0.00 diopters. When the cylinder power is zero, the axis value is irrelevant. An eye power of 0 indicates no need for lenses; however, "normal" vision encompasses a range beyond just 20/20. Near vision is also crucial, and "normal" near vision is often denoted as N6, with higher numbers indicating better near vision. It's important to note that vision changes naturally with age.
- 20/20 Vision: This is a common measure of visual acuity. It means you can see clearly at 20 feet what a person with normal vision can see at 20 feet. The number represents distance, and 20 is a standardized measure. A higher second number indicates poorer vision.
- Diopters (D): This unit measures the refractive power of a lens needed to correct vision. A 0.00 D SPH indicates no refractive error for distance vision. CYL refers to astigmatism correction.
- Near Vision (N): Near vision acuity is tested separately. N6 is generally considered normal near vision.
Variations in "Normal"
It's crucial to understand that "normal" vision is a range, not a single point. While 20/20 vision is a common benchmark, variations are normal, and many people have perfectly functional vision within a slightly broader range. Furthermore, visual acuity changes with age, with presbyopia (age-related near vision loss) being a natural part of aging.
