A night window: raindrops sharp on the glass, distant city lights melted into soft round blurs.

How eyes focus

Myopia

Optical glossaryHow eyes focus

Nearsightedness: distance is blurred because light focuses in front of the retina. Corrected with minus lenses.

Nearsightedness brings distant light to a focus in front of the retina, farsightedness behind it. A minus or a plus lens moves the focus back onto the retina.

Illustrative · the shape of the principle, not measured data

In more depth

In a nearsighted eye the optics are too strong for the eye's length — usually because the eye is slightly long — so distant light comes to a focus in front of the retina. Close objects, whose light arrives spreading, still land in focus, which is why nearsighted people read comfortably without glasses.

A minus lens corrects it by spreading light before it enters the eye. Minus lenses are thinnest at the center and thicken toward the edge, so a stronger nearsighted prescription is where lens index and frame size make their biggest visible difference.

Related terms

Sphere (SPH)The main power of your prescription, in diopters. Minus corrects nearsightedness, plus corrects farsightedness; further from zero means stronger.HyperopiaFarsightedness: light would focus behind the retina, making near work effortful. Corrected with plus lenses.Refractive indexHow strongly a material bends light. Higher index means less material for the same power — a thinner lens.Frame measurementsThe code inside the temple arm (e.g. 51□19-145): lens width, bridge width, and temple length in millimeters. More than frame trivia — lens width drives edge thickness at stronger prescriptions, and together with the bridge it determines how far the lenses must shift to center on your pupils.

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