aniseikonia

　

WordNet

1. visual defect in which the shape and size of an ocular image differ in the two eyes

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/10/23 20:03:25」(JST)

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Aniseikonia
Classification and external resources
Specialty	ophthalmology
ICD-10	H52.3
ICD-9-CM	367.32
DiseasesDB	29646
MeSH	D000839

Aniseikonia is an ocular condition where there is a significant difference in the perceived size of images. It can occur as an overall difference between the two eyes, or as a difference in a particular meridian.

Etymology

Gr. "an" = "not", + "is(o)" = "equal," + "eikōn" = "image"

Causes

Retinal image size is determined by many factors. The size and position of the object being viewed affects the characteristics of the light entering the system. Corrective lenses affect these characteristics and are used commonly to correct refractive error. The optics of the eye including its refractive power and axial length also play a major role in retinal image size.

Aniseikonia can occur naturally or be induced by the correction of a refractive error, usually anisometropia (having significantly different refractive errors between each eye) or antimetropia (being myopic (nearsighted) in one eye and hyperopic (farsighted) in the other.) Meridional aniseikonia occurs when these refractive differences only occur in one meridian (see astigmatism). Refractive surgery can cause aniseikonia in much the same way that it is caused by glasses and contacts.

One cause of significant anisometropia and subsequent aniseikonia has been aphakia. Aphakic patients do not have a crystalline lens. The crystalline lens is often removed because of opacities called cataracts. The absence of this lens left the patient highly hyperopic (farsighted) in that eye. For some patients the removal was only performed on one eye, resulting in the anisometropia / aniseikonia. Today, this is rarely a problem because when the lens is removed in cataract surgery, an intraocular lens, or IOL is left in its place.

Demonstration

A way to demonstrate aniseikonia is to hold a near target (ex. pen or finger) approximately 6 inches directly in front of one eye. The person then closes one eye, and then the other. The person should notice that the target appears larger to the eye that it is directly in front of. When this object is viewed with both eyes, it is seen with a small amount of aniseikonia. The principles behind this demonstration are relative distance magnification (closer objects appear larger) and asymmetrical convergence (the target is not an equal distance from each eye).

Symptoms

When this magnification difference becomes excessive the effect can cause diplopia, suppression, disorientation, eyestrain, headache, and dizziness and balance disorders.

Treatment

Treatment is done by changing the optical magnification properties of the auxiliary optics (corrective lenses). The optical magnification properties of spectacle lenses can be adjusted by changing parameters like the base curve, vertex distance, and center thickness. Contact lenses may also provide a better optical magnification to reduce the difference in image size. The difference in magnification can also be eliminated by a combination of contact lenses and glasses (creating a weak telescope system). The optimum design solution will depend on different parameters like cost, cosmetic implications, and if the patient can tolerate wearing a contact lens.

Note however that before the optics can be designed, first the aniseikonia should be known=measured. When the image disparity is astigmatic (cylindrical) and not uniform, images can appear wider, taller, or diagonally different. When the disparity appears to vary across the visual field (field-dependent aniseikonia), as may be the case with an epiretinal membrane or retinal detachment, the aniseikonia cannot fully be corrected with traditional optical techniques like standard corrective lenses. However, partial correction often improves the patient's vision comfort significantly. Little is known yet about the possibilities of using surgical intervention to correct aniseikonia.

See also

• Adelbert Ames, Jr. (Dartmouth Eye Institute, research in the 1930s and 1940s on aniseikonia)
• macropsia, micropsia

References

Further reading

• Bannon, Robert E.; Neumueller, Julius; Boeder, Paul; Burian, Hermann M. (June 1970), "Aniseikonia and space perception: After 50 years", American Journal of Optometry & Archives of American Academy of Optometry, 47 (6): 423–441 
• Bisno, David C. (1994), Eyes in the Storm—President Hopkins' Dilemma: The Dartmouth Eye Institute, Norwich, Vermont: Norwich Book Press, p. 288 

External links

• Aniseikonia information at Optical Diagnostics

UpToDate Contents

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• 1. 小児における屈折異常 refractive errors in children
• 2. Amblyopia in children: Management and outcome

English Journal

• Intraocular lens exchange for high myopia in pseudophakic children.

• Kraus CL1, Trivedi RH2, Wilson ME2.
• Eye (London, England).Eye (Lond).2016 Sep;30(9):1199-203. doi: 10.1038/eye.2016.152. Epub 2016 Jul 15.
• PurposeThe purpose of this study was to examine the preoperative factors and postoperative outcomes following intraocular lens (IOL) exchange for high myopia in pseudophakic children.MethodsThe medical records of all patients undergoing IOL exchange for high myopia were retrospectively reviewed.Resu
• PMID 27419831

• Aniseikonia and Foveal Microstructure in Patients with Idiopathic Macular Hole.

• Okamoto F1, Sugiura Y2, Moriya Y2, Murakami T2, Okamoto Y2, Hiraoka T2, Oshika T2.
• Ophthalmology.Ophthalmology.2016 Sep;123(9):1926-32. doi: 10.1016/j.ophtha.2016.05.051. Epub 2016 Jul 9.
• PURPOSE: To quantify the severity of aniseikonia in patients undergoing vitrectomy for idiopathic macular hole (MH) and to examine any relationship between aniseikonia and the foveal microstructure.DESIGN: Prospective, consecutive, interventional case series.PARTICIPANTS: We included 56 eyes of 56 p
• PMID 27406114

• Evaluation of newly-developed aniseikonia testing method based on space eikonometry.

• Sasaki K1,2, Kobayashi K1, Usui C2, Hayashi T1,2, Kawashima M2, Tane Y2, Mizota A3.
• Clinical & experimental optometry.Clin Exp Optom.2016 Aug 23. doi: 10.1111/cxo.12427. [Epub ahead of print]
• BACKGROUND: We have developed a new aniseikonia testing method based on the space eikonometry (ATSE) principle. The purpose of this study was to compare aniseikonia obtained by the ATSE to that of the conventional new aniseikonia tests (NAT), which is commonly used in Japan.METHODS: Thirty normal su
• PMID 27553456

Japanese Journal

• 片眼特発性黄斑円孔症例の両眼視機能 : 片眼の中心窩の障害が立体視に及ぼす影響について

• 健康医療科学研究 = Journal of health and medical science : JHMS (5), 17-28, 2015
• NAID 40020649809

• 臨床報告 片眼特発性黄斑円孔症例の不等像視

• 臨床眼科 66(12), 1669-1675, 2012-11
• NAID 40019486204

• 測定距離の違いが不等像視に及ぼす影響

• 視覚の科学 = Japanese journal of visual science 33(3), 120-124, 2012-09-28
• NAID 10031121002

Related Links

• Aniseikonia | Define Aniseikonia at Dictionary.com

Aniseikonia definition, a defect of vision in which the images at the retinas are unequal in size. See more. Thesaurus Translate Reference Word of the Day Blog Slideshows Apps by Dictionary My Account Log Out Log In Dictionary ...

• Aniseikonia - Optical Diagnostics

If an aniseikonia test showed that a patient has 4% aniseikonia, this means that the image in the right eye (OD) needs to be magnified by 4% to cancel the aniseikonia. To see what the effect of a 4% aniseikonia correction is for the ...

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