What type of lens corrects myopia?

Myopia is corrected with minus (concave, diverging) lenses. These lenses are thinnest at the center and thickest at the edges. They diverge incoming light rays so that the focal point moves back onto the retina instead of falling in front of it.

What is the difference between axial and refractive myopia?

Axial myopia occurs when the eye is too long for its optical power (the most common type). Refractive myopia occurs when the eye is normal length but has too much optical power, such as from a steep cornea or an increased lens index. Both result in light focusing in front of the retina.

What is the far point in myopia?

The far point is the farthest distance at which a myopic eye can see clearly without correction. It equals 1 divided by the myopia in diopters (in meters). For example, a -2.00 D myope has a far point at 50 cm. Objects beyond this distance appear blurry.

Myopia (Nearsightedness) for ABO

What Is Myopia?

Myopia (nearsightedness) is a refractive error where distant objects appear blurry while near objects remain clear. In a myopic eye, light from distant objects focuses in front of the retina rather than on it. This happens because the eye is optically too powerful for its length, or too long for its optical power.

Myopia is corrected with minus (concave) lenses that diverge light rays, effectively pushing the focal point back onto the retina.

Types of Myopia

Axial Myopia

Axial myopia is the most common form. The eye's axial length is too long for its refractive power. A normal eye is approximately 24 mm long; each additional millimeter of length adds roughly 3 diopters of myopia.

Refractive Myopia

Refractive myopia occurs when the eye is a normal length but has too much refractive power. This can result from:

A cornea that is too steep (high corneal power)
A crystalline lens with increased refractive index (as in nuclear sclerotic cataracts)
Anterior displacement of the lens

Classification by Amount

Classification	Range	Characteristics
Low myopia	Up to -3.00 D	Most common, stabilizes in early adulthood
Moderate myopia	-3.00 to -6.00 D	Higher risk of complications
High myopia	Above -6.00 D	Significant risk of retinal detachment, glaucoma, macular degeneration

The far point of a myopic eye is at a finite distance. For example, a -2.00 D myope has a far point at 1/2.00 = 0.50 meters (50 cm). Objects at or closer than this distance appear clear without correction. This is why myopia is called "nearsightedness."

Myopia Correction

Spectacle Lenses

Minus lenses are thinnest at the center and thickest at the edge. For higher prescriptions, opticians should consider:

Higher-index materials to reduce edge thickness
Aspheric designs to flatten the lens profile
Smaller frame sizes to minimize the thick edge area
Roll and polish the edge for cosmetic improvement

Contact Lenses

Contact lenses for myopia use the same minus power, but the effective power at the corneal plane differs from the spectacle prescription (vertex distance compensation applies above -4.00 D). Contact lenses also provide a wider field of corrected vision and eliminate spectacle magnification effects (minification).

Optical Effects of Minus Lenses

Minus lenses produce several optical effects that opticians should understand:

Minification: Objects appear smaller through minus lenses (about 2% per diopter at standard vertex distance)
Against motion: When moving the lens, objects appear to move in the same direction as the lens
Base-up prism below OC: Looking below the optical center of a minus lens induces base-up prism (important for bifocal vertical imbalance)
Ring scotoma: High-minus lenses create a ring of "missing" vision at the lens edge

When dispensing high-minus lenses, always discuss cosmetic options with the patient. High-index materials, aspheric designs, smaller frames, and anti-reflective coatings significantly improve the appearance and weight of thick minus lenses. These conversations build trust and demonstrate your expertise.

Confusing the optical effects of plus and minus lenses. Minus lenses MINIFY and show AGAINST motion. Plus lenses MAGNIFY and show WITH motion. This is a frequently tested distinction on the ABO exam.

Key Takeaways

Myopia focuses light in front of the retina; corrected with minus (concave) lenses
Axial myopia (long eye) is the most common form; ~3 D per mm of excess length
The far point equals 1/prescription (e.g., -4.00 D = 25 cm far point)
Minus lenses cause minification and against motion
High myopia (above -6.00 D) increases the risk of serious eye diseases