Aniseikonia is an anomaly of binocular vision where the ocular images are unequal in size or shape. It becomes clinically significant when a patient has difficulty combining images of different sizes or shapes into a single perception. Aniseikonia can be static, where images are perceived as different sizes for fixed gaze positions, or dynamic, where different eye rotation is needed to fixate on the same point. It is classified as optical, retinal, or cortical depending on its underlying cause. Aniseikonia is commonly measured using computerized tests and managed using specialized contact lenses, occlusion therapies, or prism corrections.

2. INTRODUCTION
ANISEIKONIA(= UNEQUAL IMAGES)
ANOMALY OF BINOCULAR VISION , WHERE OCULAR IMAGES ARE UNEQUAL IN
SIZE OR SHAPE OR BOTH .
ANISEIKONIA CONSIDERED TO BE CLINICALLY SIGNIFICANT WHEN A PATIENT'S
VISUAL SYSTEM HAS DIFFICULTY COMBINING TWO IMAGES OF DIFFERENT SIZE
AND/OR SHAPE IN A SINGLE PERCEIVED IMAGE.

3. STATIC :
EYES GAZING IN A
CERTAIN DIRETION,
PERCEIVED IMAGES ARE
DIFFERENT IN SIZE.
DYNAMIC :
EYES HAVE TO ROTATE A
DIFFERENT AMOUNT TO
GAZE AT THE SAME POINT.
TYPES :

4. STATIC

5. DYNAMIC

6. OPTICAL
• Inherent
• Acquired anisometropia of high degree
RETINAL
• Displacement of retinal elements towards nodal point in
one eye
CORTICAL
• Asymmetrical simultaneous perception in spite of equal
size of two images
AETIOLOGY

7. OPTICAL :
Causes:
1.Secondary to anisometropia caused naturally
2.Secondary to refractive surgery
3.Pseudophakic IOL implantation
4. Aphakia
Aniseikonia is frequently associated with anisometropia.
Isometropic aniseikonia may exist if one eye is simply larger than the other, without a
refractive error difference and without a compensating redistribution of neural elements
however such a condition is rare.

8. Aniseikonia can be described by means of ANISEIKONIC ELLIPSE.
Overall
aniseikonia
describes the
minimum
aniseikonia.
Meridional
aniseikonia
describes the
direction
dependent part
(Usually
induced by
cylindrical glass
correction)

9. RETINAL :
1. Spacing of retinal elements
The retinal elements that receive the optical image
carry image size information
The density and distribution of retinal receptors would
therefore be expected to influence perceived image
size
If the spacing or density of these retinal elements
differs between the two eyes, the perceived image
sizes may also differ as a result of the differential
spacing of these retinal elements.
2.Compression,stretching or damage to retina can
cause light projected on retina by a perceived image to
appear larger(Macropsia) or smaller (Micropsia) , as a
variable number of photoreceptors are stimulated.

10. CAUSES:
1.Macular edema
2.Epiretinal membrane
3.Macular hole
4.Retinal detachment
5.Retinal tears
6.Retinoschisis

11. Retinal aniseikonia varies with field angles field-dependent aniseikonia. The
field angle is defined as the angle between the gaze direction and the direction of
a peripheral point
Schematic presentation of the ocular sources
determining aniseikonia and the visualization of a
visual field angle α (for simplicity the optical and
visual axis are assumed equal here).

12. If there are stretching or compression forces close
to the fovea, this would
have little effect on the receptor distribution far
away in the periphery. Therefore, a change in the
receptor distribution close to the fovea will be non-uniform.
Receptors are
compressed at the center while a little further
peripheral they are stretched to finally being
unaltered in a position even further out in the
periphery. The aniseikonia in this example would
be field-dependent with a larger effect for smaller
field angles

13. CORTICAL :
Distribution of cortical nerve fiber
Difference in the retinal image size may be obtained if there is alteration in the visual
system after the retina

14. CLINICAL TYPES
1.SYMMETRICAL
• Spherical
image may be magnified or minified equally in both meridia
• Cylindrical
image is magnified or minified symmetrical in one meridian

15. 2.ASYMMETRICAL :
i.Prismatic
Image difference increases progressively in one direction
ii.Pincushion
Image distortion increases progressively in both directions,
as seen with high plus correction in aphakia
iii.Barrel
Image distortion decreases progressively in both direction,
as seen with high minus correction
iv.Oblique
Image size remains the same but there occurs an oblique
distortion of shape
A– SphericalB– Cylindrical C– PrismaticD–
Pincushion
E – Barrel distortionF – Oblique distortion

16. CLINICAL FEATURES :
Clinical aniseikonia defined as the amount of aniseikonia that is necessary to
correct to eliminate the symptoms.
Occurs when image size difference between two eyes approaches 0.75%.
Symptoms are more common among those with meridional magnification
differences, more likely among patients with astigmatic anisometropia.
Oblique meridional aniseikonia causes rotatory deviation between fused images
of vertical lines in the two eyes : DECLINATION . It becomes clinically
troublesome when it approaches 0.3%

17. 1. Asthenopia symptoms
Occurs when the differences in image size of the two
images is between 0.75 to 5.0%
Headache , difficulty reading, photophobia, difficulty of
fixation,
vertigo, etc
2. Disturbances of binocular vision
Diplopia occur only if the difference exceeds 5%.
Escape attained by suppression of one eye at an early
stage.
3. Disturbances in depth perception and spatial
disorientations

18. MEASUREMENT:
1.ROUGH ESTIMATE:
RULE OF THUMB :
Based on Knapp's law, which deals with an image size difference
as projected onto the retina in anisometropia .
If the difference in image size associated with anisometropia is
primarily refractive in origin, the aniseikonia produced will be about
1.5% per diopter of anisometropia, but since anisometropia may
be partly axial, an estimate of 1.0% per D is useful clinically.

19. 2. SPACE EIKONOMETER
Formerly produced by the American Optical Company
Consist of size lens that could produce
magnification in two rotatable primary
meridians.
The display consisted of four vertical rods positioned at
the four corners at the center of the cube is another
vertical rod, with a cross consisting of two diagonal lines
intersecting at the middle
Performs its function not by actual measurement of the
ocular images but by measuring the rotations of the
observed field as affected by binocular clues alone.

20. SPACE EIKONOMETER

21. 3.STANDARD EIKONOMETER
Contains the following elements:
1.Device for securing the fixation of the eyes in the desired planes by fixing the head and
presenting the targets along the primary plane and the normal depressed plane for near
2.Devices which alter the size of the target without affecting the refraction and measure
discrepancies in percent
3. Projector which presents a target which has certain elements polarized so that each eye sees
some part of the target alone and some parts simultaneously
4. Polaroid filters before each eye to select the target elements for each eye

24.  The patient looks through red-green
glasses at the computer screen, which
gives a series of test images.
 For each test image the patient's task
is to identify which of the two I-shaped
bars is perceived as larger (a forced
choice procedure).
 Because of the red-green glasses,
one eye sees only the left I-bar and the
other eye sees only the right I-bar.
 If all images of a series have been
presented, the data can be plotted in a
'psychometric curve’.
 Using a maximum likelihood
mathematical method, the aniseikonia
value can be obtained from this data.
 .
ANISEIKONIA INSPECTOR VER 3

25. One of the advantages of this forced choice method compared to a method of adjustment (such as used in the
Basic Aniseikonia test and the 'New' Aniseikonia Test) is that the forced choice method also provides information
about the consistency/accuracy of the measurement. This is also very useful when the patient self-administers the
test and the results are analyzed elsewhere.

26. ANISEIKONIA VALUES
Represents how much the right eye should be magnified or minified to
cancel the aniseikonia.
Ex: -5% aniseikonia means the image in right eye is perceived as approx.
5% larger than left eye.
Thus, Aniseikonia can be corrected by
1. Minifying image in right eye by 5%
2. Magnifying image in left by 5%
3. Combination of both

27. SIMPLE TESTING FOR ANISEIKONIA
Size Lenses
Maddox Rod
Penlights
Prism Bar

28. SIZE LENSES
:
For subjective testing.
Size lenses are lenses without refractive power (the
image stays sharp), but with an optical magnification.
They may provide the patient with a sense of what it
would be like to have a certain aniseikonia correction.

30. Special Testing for Aniseikonia
1.The Leaf Room Effects
The leaf room is a cube with no size cues, perhaps
covered with patterned wallpaper, a leaf pattern.
This cubical “Leaf Room” doesn’t look square if you have
aniseikonia!
Can use the Leaf Room to simulate aniseikonia caused by
high monocular astigmatism, even in normal,
With planocylindrical magnifiers (size lenses) in front of
one eye only, as follows

31. This test, developed by Dr. Awaya of Japan, is very easy to administer and interpret.
The test uses a very clever direct comparative approach with the patient viewing pairs
of adjacent calibrated half-moon targets - one red and one green.
2.Awaya Aniseikonia Test

33. Management
OPTICAL:
i. Contact lens :
1.Iseikonic lenses- a correcting lens or device that generally acts by
altering magnification due to thickness of the lens and base curve w/o
altering its power.
2.Toric lenses- front or back surfaces are made toric or both
3.Doublet lenses- combination of two lenses, one is
telescopic and the other on microscopic lens.
4.Fused bifocal lenses.
ii. Aneiseikonic spectacle

34. 2.RETINAL :
aniseikonia cannot be fully corrected by optical means, because an optical
correction is approximately field independent. Nevertheless, a partial
correction often improves the vision comfort considerably.
If an optical correction is not possible or does not provide enough correction,
a partial occlusion may be tried. Some (field dependent) aniseikonia patients
have gained some relief by occluding part of the visual field (for example,
placing a (removable) dot in the center of one of the spectacle lenses or
(partially) shielding the periphery in one eye, creating kind of a tunnel vision
for one eye).
Instead of occluding part of the visual field, another approach could be to
occlude the whole visual field, but with a partial transparent foil.

35. THANK YOU