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(New page: {{Biopsy}} {{DiseaseDisorder infobox | Name = Anisometropia | ICD10 = {{ICD10|H|52|3|h|49}} | ICD9 = {{ICD9|367.31}} | }} '''Anisometropia''' is the condition in ...)
 
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{{Infobox medical condition (new)
{{DiseaseDisorder infobox |
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| name = Aniseikonia
Name = Anisometropia |
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ICD10 = {{ICD10|H|52|3|h|49}} |
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ICD9 = {{ICD9|367.31}} |
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| symptoms = objects different sizes in each eye
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| causes = [[Cataract surgery]], [[refractive surgery]]
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'''Anisometropia''' is the condition in which the two [[eye]]s have unequal [[refractive power]]; that is, are in different states of [[myopia]] (nearsightedness), [[hyperopia]] (farsightedness) or in the extreme, '''antimetropia''' (wherein one eye is myopic and the other is hyperopic), the unequal refractive states cause unequal rotations thus leading to [[diplopia]] and [[asthenopia]].
 
   
Anisometropia can adversely affect the development of [[binocular vision]] in infants and children if there is a large difference in clarity between the two eyes. The brain will often suppress the vision of the blurrier eye in a condition called [[amblyopia]], or lazy eye.
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'''Aniseikonia''' is an ocular condition where there is a significant difference in the [[magnification|perceived size]] of images. It can occur as an overall difference between the two eyes, or as a difference in a particular meridian.<ref name = Berens>{{Citation|last = Berens |first = Conrad | last2 = Loutfallah | first2 = Michael | year = 1938 | title = Aniseikonia: A Study of 836 Patients Examined with the Ophthalmo-Eikonometer | periodical = Trans Am Ophthalmol Soc. | series = | volume = 36 | pages = 234–67 | url = http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1315746&blobtype=pdf | pmc=1315746 | pmid=16693153}}</ref>
   
== Spectacle correction ==
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==Symptoms==
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When this [[magnification]] difference becomes excessive the effect can cause [[diplopia]], [[Suppression (eye)|suppression]], [[disorientation]], [[eyestrain]], [[headache]], and [[dizziness]] and [[balance disorder]]s.{{Citation needed|date=January 2015}}
For those with large degrees of anisometropia, spectacle correction may cause the person to experience a difference in image magnification between the two eyes which could also prevent the development of good binocular vision.
 
   
One study estimated that 6% of those between the ages of 6 and 18 have anisometropia<ref>Czepita D, Goslawski W, Mojsa A. "[Occurrence of anisometropia among students ranging from 6 to 18 years of age.]" ''Klin Oczna.'' 2005;107(4-6):297-9. Polish. PMID 16118943.</ref>
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==Causes==
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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 lens]]es 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.
   
The name is from four [[Greek language|Greek]] components: ''an-'' "not," ''iso-'' "same," ''metr-'' "measure," ''ops'' "eye."
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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 [[myopia|myopic]] (nearsighted) in one eye and [[hyperopia|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 [[corrective lens|glasses and contacts]].{{Citation needed|date=January 2015}}
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One cause of significant anisometropia and subsequent aniseikonia has been [[aphakia]]. Aphakic patients do not have a [[lens (anatomy)|crystalline lens]]. The crystalline lens is often removed because of opacities called [[cataract]]s. 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.{{Citation needed|date=January 2015}}
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==Diagnosis==
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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).{{Citation needed|date=January 2015}}
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==Treatment==
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Treatment is done by changing the optical magnification properties of the auxiliary optics ([[corrective lens]]es). 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. <!-- IS The following sentence RIGHT??? This makes sense because a contact lens can be thought of as a very thin spectacle lens with very little vertex distance. --> 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.{{Citation needed|date=January 2015}}
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Note however that before the optics can be designed, first the aniseikonia should be 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.{{Citation needed|date=January 2011}}<!-- Is the previous sentence accurate / up to date? -->
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==Etymology==
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Gr. "an" = "not", + "is(o)" = "equal," + "eikōn" = "image"{{Citation needed|date=January 2015}}
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==See also==
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*[[Adelbert Ames, Jr.]] (Dartmouth Eye Institute, research in the 1930s and 1940s on aniseikonia)
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*[[macropsia]], [[micropsia]]
   
 
==References==
 
==References==
<div class="references-small">
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{{reflist}}
<references/>
 
</div>
 
   
[[Category:Ophthalmology]]
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==Further reading==
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*{{Citation
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| last = Bannon
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| first = Robert E.
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| last2 = Neumueller
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| first2 = Julius
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| last3 = Boeder
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| first3 = Paul
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| last4 = Burian
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| first4 = Hermann M.
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| title = Aniseikonia and space perception: After 50 years
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| journal = American Journal of Optometry & Archives of American Academy of Optometry
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| volume = 47
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| issue = 6
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| pages = 423–441
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| origyear =
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|date=June 1970
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| doi=10.1097/00006324-197006000-00001
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}}
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*{{Citation
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| last = Bisno
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| first = David C.
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| title = Eyes in the Storm—President Hopkins' Dilemma: The Dartmouth Eye Institute
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| place = Norwich, Vermont
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| publisher = Norwich Book Press
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| year = 1994
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| pages = 288 }}
   
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== External links ==
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{{Medical resources
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| DiseasesDB = 29646
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| ICD10 = {{ICD10|H|52|3|h|49}}
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| ICD9 = {{ICD9|367.32}}
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| ICDO =
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| OMIM =
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| MedlinePlus =
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| eMedicineSubj =
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| eMedicineTopic =
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| MeshID = D000839
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}}
   
<!--
 
[[it:Anisometropia]]
 
[[pt:Anisometropia]]
 
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{{EnWP|Anisometropia}}
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<!-- The following is taken mostly from Optical Diagnostics' [http://www.opticaldiagnostics.com/products/ai/aniseikonia.html aniseikonia webpage] The site is commercial, trying to sell software. But the information is not false. Other references need to be found to support this information and it can be re-included into this article
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Aniseikonia is a binocular condition in which the two eyes perceive images of different size. These unequal images can be caused by a difference in:
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* optical magnification (i.e. different retinal image sizes)
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* retinal receptor distribution (i.e. a different sampling of the retinal images)
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* cortical processing (i.e. different processing of the sampled retinal images)
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Patients at risk of aniseikonia
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Aniseikonia is often associated with unequal refractive errors between the eyes (anisometropia). However, there are several other patient groups at risk. For example, research has shown that appr. 40% of the patients that underwent cataract surgery/surgeries and who had an intra-ocular lens(es) implanted, have complaints referable to aniseikonia. This also makes one wonder how much aniseikonia is induced with refractive surgery such as LASIK.
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Another group of patients at risk are patients who have a retinal condition or who underwent retinal surgery. For example with an epiretinal membrane (macular pucker) or after a retinal detachment surgery. The aniseikonia in these patients may be complicated because the aniseikonia is field-dependent (variable over the retina), but fortunately also these patients often can get more comfortable binocular vision by optically correcting the aniseikonia.
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Symptoms
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Most aniseikonic symptoms are quite general (a-specific), for example: headaches, asthenopia (ocular fatigue, burning, tearing, pain, pulling, etc.), light sensitivity, reading difficulty, nausea, and double images (diplopia). This is one of the reasons why aniseikonia is sometimes overseen by the treating eye care provider. Only, if the aniseikonia is severe, the patient could also actually see an image size difference by closing one eye at a time. However, symptoms usually occur already with much less aniseikonia.
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Clinically significant aniseikonia values
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Aniseikonia of 3% or more is generally considered clinically significant, but sensitive individuals may have symptoms with less aniseikonia.
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Testing for aniseikonia
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Testing for aniseikonia is important. In older books sometimes rules of thumb are given based on retinal images size differences alone. However, research has shown that even in anisometropia the retinal receptor distribution may be different between the eyes, making aniseikonia management based on calculated retinal image sizes inaccurate.
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Testing for aniseikonia can be done using a space eikonometric method (based on space distortions accompanying the aniseikonia) or a direct comparison method. The space eikonometric method is sometimes still used in research, but it is less suited for clinical purposes (and commercially unavailable). There are two commercially available aniseikonia tests: the New Aniseikonia Test1 (NAT, 1982) and the Aniseikonia Inspector2 (2003-2007). The first is a booklet and the second is software. The two tests are based on the same principle, but the Aniseikonia Inspector has several advanges due to the interactive possibilities when using a computer. Also, the Aniseikonia Inspector contains a module to calculate aniseikonia correcting prescriptions.
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Correcting aniseikonia
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Aniseikonia can be corrected by changing the optical magnification properties of the auxiliary optics (glasses, contact lenses). For example, if the curvature or thickness of a spectacle lens is changed (without changing its refractive power, so there will still be a good visual acuity), the optical magnification will change. Also, the distance between the spectacle lens and the eye (vertex distance) affects the optical magnification. Therefore, contact lenses will in general give a different aniseikonia than glasses. It might even be possible to correct aniseikonia by fitting a contact lens together with a spectacle lens, creating a weak telescope system. What solution is best depends on the amount of aniseikonia, type of aniseikonia (optical-induced or retinally-induced), the refraction, and the importance of cosmetics.
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-->
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{{Eye pathology}}
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[[Category:Disorders of ocular muscles, binocular movement, accommodation and refraction]]
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[[Category:Ophthalmology]]

Revision as of 19:00, March 19, 2020

Template:Infobox medical condition (new)

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.[1]

Symptoms

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

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.[citation needed]

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.[citation needed]

Diagnosis

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).[citation needed]

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.[citation needed]

Note however that before the optics can be designed, first the aniseikonia should be 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.[citation needed]

Etymology

Gr. "an" = "not", + "is(o)" = "equal," + "eikōn" = "image"[citation needed]

See also

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, doi:10.1097/00006324-197006000-00001 
  • Bisno, David C. (1994), Eyes in the Storm—President Hopkins' Dilemma: The Dartmouth Eye Institute, Norwich, Vermont: Norwich Book Press, pp. 288 

External links

Template:Medical resources



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