The term ‘‘aniseikonia” comes from the Greek words ‘‘an” (not) ‘‘is” (equal) & ‘‘eikon” (icon or image) so aniseikonia is a binocular condition in which the apparent sizes of the images seen with the two eyes are unequal. Whenever refractive ametropias in the two eyes of a person are different (i.e., when there is an anisometropia), the corrected retinal images of the two eyes, and consequently the two visual images, differ in size. This condition has been termed aniseikonia Optical aniseikonia Retinal aniseikonia Cortical aniseikonia

1. ANISEIKONIA
Md.Azizul Islam
Associate Optometrist (Oculoplasty Dept:)
Ispahani Islamia Eye Institute & Hospital
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2.  The term ‘‘aniseikonia” comes from the Greek words ‘‘an” (not)
‘‘is” (equal) & ‘‘eikon” (icon or image) so aniseikonia is a
binocular condition in which the apparent sizes of the images
seen with the two eyes are unequal.
 Whenever refractive ametropias in the two eyes of a person are
different (i.e., when there is an anisometropia), the corrected
retinal images of the two eyes, and consequently the two visual
images, differ in size.
 This condition has been termed aniseikonia
Aniseikonia
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3. We know that,
 It is a condition where the different ocular image size is present between
two eyes.
 Aniseikonia of > 3% is significant.
 Each 0.25D difference between the two eyes causes 0.5% difference in size
between the two retinal images.
 A difference of 5% of the image size can be tolerated well (i.e. 2.5D
difference of refraction between two eyes). If it is more, the effort of
fusion may give rise the symptom of eye-stain, or diplopia.
 It is thought that >0.75% is clinically significant and can produce
symptoms.
 1-3% Aniseikonia is thought to produce definite symptoms and binocular
fusion difficulties.
Aniseikonia
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4. Aniseikonia
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5. Symptoms :
Asthenopia, Headaches, Diplopia,
Photophobia, Reading Difficulty,
Nausea, Motility difficulty, Difficulty
in fixation, Nervousness, Vertigo,
Dizziness, General, Fatigue,
Distortion of space perception.
(when the difference in image size of
the two images between 0.75 to 5%).
Signs :
Aphakia, Anisometropia,
Astigmatism, Low Stereopsis,
Strabismus, Amblyopia etc.
Clinical Features / Symptoms
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6. 1. Optical aniseikonia: May occur due to either inherent or acquired
anisometropia of high degree.
2. Retinal aniseikonia : May develop due to: displacement of retinal
elements towards the nodal point in one eye due to stretching or
oedema of the retina.
3. Cortical aniseikonia: Implies asymmetrical simultaneous
perception in spite of equal size of images formed on the two retinae.
Etiological Types of Aniseikonia
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7.  1. Symmetrical aniseikonia:
a. Spherical: Image may be magnified or minified equally in both meridian.
b. Cylindrical: Image is magnified or minified symmetrically in one
meridian.
2. Asymmetrical aniseikonia:
a. Prismatic: In it image difference increases progressively in one direction.
b. Pincushion: In it image distortion increases progressively in both
directions, as seen with high plus correction in aphakia.
c. Barrel distortion: In it image distortion decreases progressively in both
directions, as seen with high minus correction.
d. Oblique distortion: In it the size of image is same, but there occurs an
oblique distortion of shape.
Clinical types of aniseikonia
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8. Normal Image
A
B C
D
EF
Clinical types of aniseikonia
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9. The following tests can determine aniseikonia:
1. Eikonometer: An instrument used to measure the aniseikonic
condition.
2. Alternate cover test:
Here the horizontal target is used to perform the test. a patient is
instructed to look at the target. here, occlude should not be placed on
the eye for more than 1 sec.
3 . Turville test: Vertical aniseikonia is diagnosed in this test.
4. Maddox rod and two-point light sources: To determine the
presence and measurement of vertical aniseikonia
Determination of Aniseikonia
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10. Eikonometer
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11.  Have the patient wear the appropriate spectacle correction and fixate a distance
square target that is alone in the visual field.
 Occlude each eye alternately and ask the patient to compare the horizontal size of the
target seen with each eye. The cover paddle should be moved quickly between eyes and
held for about 1 second in front of each eye to facilitate comparison of the two images.
 If there is a difference in perceived size, repeat the test with a size lens in front of the
eye with the smaller perceived image. Change the size lens until the image seen with
each eye appears to be the same size as the cover paddle is alternated.
 The process is repeated for the vertical dimensions.
 The results are recorded, indicating the magnification needed in each meridian to
equalize the perceived images of the two eyes.
Alternate Cover Test
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12. The Turville test can be used for detecting and measuring aniseikonia in the
vertical meridian using the slide with two horizontal lines that Morgan
developed.
 Position the septum so that the patient sees the right half of the target
with the right eye and the left half of the target with the left while wearing
the appropriate spectacle correction.
 Have the patient compare the vertical separation of the two lines on the
right target with the separation of the two lines on the left target. A
difference in the perceived vertical separation of the lines on the right side
suggests vertical aniseikonia.
 Aniseikonia can be measured using a size lens in front of the eye with the
smallest separation and changing the size lens to equalize the perceived
vertical separation of the lines on both sides.
 This measure of the vertical aniseikonia should be recorded.
Turville Test
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13. Testing with a Maddox rod and two light sources is performed as follows:
 Two small light sources are placed about 60 cm away from the patient, with a horizontal
separation of about 20 cm. The patient wears the appropriate spectacle correction and
views the lights through a Maddox rod in front of only one eye, with the axis at 180
degrees. One eye sees the two light sources, and the other (behind the Maddox rod) sees
two vertical luminous lines.
 Have the patient compare the relative separation of the lights with the relative
separation of the luminous streaks. A difference in the separation suggests aniseikonia.
Prism can be used to align the light and line on one side if a lateral heterophoria makes
the judgment difficult by causing a displacement of the streaks from the light sources.
 A size lens in front of the eye that perceives the smallest separation (of the lights or
streaks) can be used to measure aniseikonia. Change the power of the size lens to
equalize the separation between the lights and the streaks.
 The test can be repeated with the light sources separated vertically and the Maddox rod
at axis 90 degrees placed in front of only one eye to determine the presence and
measurement of vertical aniseikonia.
 The size lens that produces the same distance between the lights and
the luminous streaks is recorded as a measure of aniseikonia.
Maddox Rod And Two-point Light Sources
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14.  Proper Retinoscopic refraction along with Cycloplegic Refraction.
Iseikonic lenses should be prescribed.
 Vertex distance is also an essential factor for Aniseikonia. the
change in vertex distance achieves magnification. lens material
index of refraction (crown 1.523, high index 1.66, polycarbonate
1.586, other plastic 1.49).
 The base curve is also an essential factor. To change base curve,
magnification is needed.
 Doublet lenses- combination of two lenses, one is telescopic and
the other on microscopic lens.
Management of Aniseikonia
 Optical: IOL in Aphakia. contact lenses. Refractive surgery.
 Retinal Anisokonia : corrected by treating the causative disease.
 Cortical Anisokonia : Difficult to treat .
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15. References
 Retinally-induced aniseikonia. Binocular Vision &
Strabismus Quarterly 2007
 Optics & Refraction By A K Khurana .
 https://hoool.com/aniseikonia.
 Clinical Optics By A R. Elkington .
 Picture: Me ,Google.
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16. THANKS-ALL