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Blur is when the edges of an object appear to be not well defined. There are many sources of reduced visual acuity and failure to recognize characters, but blur and double vision are the only two addressed by EM.

Print may be too small to see without being blurry. This occurs when the angle of the print is smaller than the angle that can be seen with best-corrected visual acuity.

A normal healthy eye can experience blur by looking at images through lenses or mirrors that cannot be cleared by accommodation.

A common description of spherical (myopic or hyperopic) blur is that it looks like Gaussian blur. Note that spherical defocus can also cause double vision, not just blur.

A good normalized creates some blur or double vision challenge for distant objects, but objects that are slightly closer are clear. A good differential creates some blur or double vision challenge near the ergonomic working distance. They should be determined by calculating diopters and cm, but a normalized is typically 20/20 to 20/50, and a differential is typically 20/40 to 20/150.

Amount of blur Visual Acuity
none 20/5 to 20/15
tiny 20/15
little 20/20
some 20/25
a lot 20/50
a huge amount 20/300

Myopic vs Hyperopic Blur

Full Articles at Myopic defocus and Hyperopic defocus

Myopic blur is the type of blur normally experienced by people with uncompensated myopia. Hyperopic blur is the type normally experienced by people with uncompensated hyperopia. In order to induce blur, use a lens with the opposite diopter sign as the lens normally used for blur correction, so a plus lens will give myopic blur to an emmetrope. A weak negative lens will give myopic blur to a myope.

Diffusion blur

Diffusion such as frosted glass, causes myopia just as strong myopic lenses do in growing animals. This is also called form deprivation.

Directional blur

Text appears smeared in a direction. This is the defining symptom of astigmatism

Peripheral Blur

Peripheral blur is the blurring of the part of the image outside your center of focus. This happens normally when something to the side is at a different distance than the thing you're looking at. While wearing glasses this becomes more complex because the outside of your lenses are often stronger than the center of focus, and produce hyperopic blur (which may be a contributor to lens induced myopia).

Defocus as a stimulus

for accommodation

The lens in your eye is adjustable to try to compensate for moderate amounts of blur. As your eye experiences Defocus, the short term response is to move the lens in the direction needed to correct for that blur.

for eye length changes

The eye needs stimulus to make long term corrective changes. Studies have shown that inducing defocus can induce axial lengthening and shortening. [1] [2][3]

Blur Adaption

EM Blur Adaption

"Blur Adaption" unfortunately has two meanings. The meaning commonly meant by EM forum members is encountering so much blur that the visual system gives up. This is something like learned helplessness at the biological level.

Clinical Blur Adaption

When a doctor uses the term "Blur Adaption", they mean that a person has adapted to perform visual tasks despite their blur. A common symptom is that the visual cortex perceives less blur than there actually is. This can happen with EM blur adaption, resulting in perceived visual acuity increases without actual axial reduction.

See Also

External sources


  1. Zhou YY, Chun RKM, Wang JC, Zuo B, Li KK, Lam TC; et al. (2018). "Proteomic analysis of chick retina during early recovery from lens‑induced myopia". Mol Med Rep. 18 (1): 59–66. doi:10.3892/mmr.2018.8954. PMC 6059693. PMID 29749514.CS1 maint: multiple names: authors list (link)
  2. Tarutta, Elena (2016). "Long -term effects of optical defocus on eye growth and refractogenesis" (PDF). Pomeranian J Life Sci.
  3. Zhu, Xiaoying; McBrien, Neville A.; Smith, Earl L.; Troilo, David; Wallman, Josh (2013-04-01). "Eyes in Various Species Can Shorten to Compensate for Myopic Defocus". Investigative Ophthalmology & Visual Science. 54 (4): 2634–2644. doi:10.1167/iovs.12-10514. ISSN 1552-5783.