If you cannot see far away, you are nearsighted. Refractive errors are extremely common vision conditions that affect how the eye focuses light, leading to blurred vision at certain distances. The eye acts like a camera, needing to precisely focus incoming light onto the light-sensitive tissue at the back of the eye, known as the retina. When the shape of the eye prevents light from focusing correctly, vision becomes blurry.
Nearsightedness: Clarifying the Terminology
If a person cannot see objects far away clearly, they are experiencing nearsightedness. This condition is formally called myopia, a term which has Greek origins translating to “close to the eyes.” The name is descriptive because a nearsighted individual can see near objects, such as a book or a phone, with perfect clarity. Distant objects, like road signs or a movie screen, appear blurred and indistinct.
How Myopia Changes the Eye’s Focus
Myopia occurs because the eye’s optical power is too strong for its length, causing light to focus prematurely inside the eye. Instead of converging precisely on the retina, light rays converge at a point in front of the retina. The primary cause of this premature focus is an eyeball that is too long from front to back, known as the axial length. An alternative cause can be a cornea or lens system that has too much curvature, effectively bending the light too strongly.
Understanding Farsightedness (Hyperopia) for Contrast
Farsightedness, or hyperopia, is the opposite of nearsightedness, meaning distant objects are often seen clearly while close-up objects are blurry. An individual with hyperopia may struggle to read fine print or see a computer screen without strain. This condition is caused by light focusing theoretically behind the retina. This posterior focus happens because the eye is too short, meaning the axial length is insufficient. Hyperopia can also occur if the cornea is too flat and lacks the necessary curvature to bend the light enough.
Corrective Measures for Refractive Errors
Corrective lenses are the most common solution for both nearsightedness and farsightedness, working by altering the path of light before it enters the eye. For myopia, a concave lens is used, which causes light rays to diverge and pushes the focal point backward onto the retina. Conversely, farsightedness requires a convex lens, which causes light rays to converge. This convergence adds the necessary focusing power to pull the focal point forward, placing the sharp image directly onto the retina. Corrective lenses are measured in diopters, with nearsightedness requiring a negative value and farsightedness requiring a positive value.