Myopia, commonly known as nearsightedness, is a highly prevalent refractive error where people struggle to see distant objects clearly while near vision remains intact. This condition is estimated to affect a significant portion of the global population. When someone experiences this distance blur, the underlying problem is a focusing error that requires an optical correction. The primary solution for managing this vision condition is a specific type of lens that alters the path of light entering the eye.
How Myopia Affects Focus
Myopia develops when the eye’s shape causes light to focus incorrectly, resulting in a blurred image of distant objects. In a properly functioning eye, light rays bend as they pass through the cornea and the lens, converging directly onto the retina at the back of the eye, creating a sharp image. In a myopic eye, the eyeball is typically either too long or the cornea and lens are too steeply curved. This excess focusing power causes the light rays to converge and meet their focal point in front of the retina. The goal of correction is to precisely shift this premature focal point backward so that it lands exactly where it should.
The Concave Lens Correction
The direct answer to correcting this premature focus is the use of a concave lens, also referred to as a minus power lens or a diverging lens. This lens type is designed to compensate for the eye’s excessive focusing power. Physically, a concave lens is thinner in the center and gradually becomes thicker toward the edges, creating an inward-curving profile.
When light passes through this shape, the lens works by slightly spreading, or “diverging,” the incoming light rays before they enter the eye. This pre-divergence effectively reduces the overall focusing strength, pushing the final point of focus further back. The power of the corrective lens is calculated to ensure the light is spread just enough to land the focal point directly onto the retina.
The strength of the correction is measured in units called diopters (D) and is always indicated by a minus sign (-) on a prescription. A higher negative number, such as -6.00 D, signifies a greater degree of myopia and requires a lens that diverges light more significantly than a lower number, like -3.00 D. The concave lens effectively neutralizes the excess convergence power of the myopic eye, providing clear distance vision.
Lens Delivery Methods
The concave lens correction is delivered primarily through two main forms: eyeglasses and contact lenses. Traditional eyeglasses are the most common option, holding the concave lens in a frame in front of the eye. For individuals with higher degrees of myopia, the edges of the concave lens can become noticeably thicker. To address this cosmetic concern, lens manufacturers recommend using high-index materials, which allow the lens to be made significantly thinner and lighter.
Contact lenses offer the same concave correction but sit directly on the cornea, eliminating the visual distortions that can occur with glasses. Because contacts sit closer to the eye, their power calculation may be slightly different from that of a spectacle lens to achieve the same corrective effect.
Beyond standard correction, specialized lenses are used for myopia management, particularly in children whose vision is still progressing. These advanced lenses are designed to slow the eye’s elongation, which is the root cause of myopia progression. Options include Orthokeratology (Ortho-K) lenses, which are rigid lenses worn overnight to temporarily reshape the cornea. Soft multifocal contact lenses and certain eyeglass lenses use a technology called peripheral defocus. These lenses have a clear central zone for distance vision, surrounded by rings or segments that intentionally shift the light in the peripheral vision to focus slightly in front of the retina.