Instrument myopia, is a form of

myopia Near-sightedness, also known as myopia and short-sightedness, is an eye disease where light focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may include ...

that occurs when someone is looking into an optical instrument such as a

microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...

. The person focusses their eyes closer than needed for the image produced by the instrument.

Characteristics

Ordinarily, when someone looks at an object at, say, one meter from the

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

s, the eyes make reflex adjustments so the object appears single and clear.Duke-Elder, S. (1973). ''System of ophthalmology'' London: Henry Kimpton. That is, the eyes converge on the object, to bring its image in each eye onto the central part of each

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

, the

fovea Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure. Human anatomy *Fovea centralis of the retina * Fovea buccalis or Dimple * Fovea of the femoral head * Trochlear fovea of the fr ...

. This ensures that the person sees one object instead of two, and is referred to as

singleness of vision In legal definitions for interpersonal status, a single person refers to a person who is not in committed relationships, or is not part of a civil union. In common usage, the term 'single' is often used to refer to someone who is not involved in ...

binocular fusion In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an a ...

. The focussing of each eye, its accommodation, is adjusted so the retinal image of the object is as sharp as possible. This is done via contraction of the ciliary muscles controlling the shape of the crystalline lens of the eye. Although convergence and accommodation are separate processes, they normally operate synergistically. When someone looks into an optical instrument, such as a microscope, vision is far from ordinary. A microscope might force the person to use only one eye, it presents the person with a limited field of view, it presents a

magnified ''Magnified'' is the second album by the American alternative rock band Failure. Production Drummer Robert Gauss departed during the recording of the album; the remaining drum parts were played by John Dargahi and Greg Edwards. ''Magnified'' dif ...

view, and it allows the person to adjust the focus of the instrument for any viewing distance. Ideally, the person will choose a focus adjustment on the instrument that allows the eyes to have relaxed accommodation—that is to present the objects at a distance of about 6 meters, or optical infinity. However, most people tend to accommodate to nearer than 6 m. It is this too-close focussing of the eyes that is instrument myopia. Accommodating to a distance nearer than 6 meters makes the ciliary muscles work harder than they need to, leading to fatigue. Some binocular microscopes are designed so that the vergence of the eyes is correct for a 6-meter viewing distance. Accommodating to a closer distance will tend to converge the eyes, leading to double vision. According to Wesner and Miller (1986), instrument myopia is promoted when the viewing is with one eye, when the field of view is small, and when the

luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls withi ...

is low, concluding that these are consistent with accommodation's going towards a person's dark focus, which is about one meter from the eyes. Wesner and Miller also said it is possible that a person's knowledge that the viewed object is very close (on the microscope stage) contributes to instrument myopia. They said that instrument myopia is minimised by using a binocular microscope that forces the person's vergence angle to be small.

History

It is unknown by whom instrument myopia was first reported.

References

External links

*Articles by three ophthalmologists: http://www.eyeworld.org/article-instrument-and-microscope-myopia--what-s-all-the-focus-about {{DEFAULTSORT:Instrument myopia Eye Vision Disorders of ocular muscles, binocular movement, accommodation and refraction