Anisometropia is a condition where there is unequal refraction between a person's eyes, with a difference greater than 1 diopter clinically significant. It can be absolute, where the total refraction differs between eyes, or relative, when the eyes have different axial lengths but similar refractive power. Causes include trauma, keratoplasty, asymmetric aging, or aphakia from cataract surgery. Diagnosis involves retinoscopy and tests of binocular vision. Anisometropia is managed optically with spectacle correction or contact lenses, or surgically with refractive corneal surgery, lens removal and implantation, or phakic intraocular lenses.

1. Anisometropia
By Getachew Kassahun
Gondar, Ethiopia.
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2. Definition
• Anisometropia is a condition where there is unequal
refraction between a person’s eyes. Most people’s eyes
have a similar level of refraction, with a difference
between the eyes of less than 1.0 diopters (D).
• Difference of 0.25 D between the eyes is considered as
anisometropia but not clinically significant.
• 1D difference of power in the eyes causes 2% retinal
image size difference and this amount of anisometropia
is clinically significant.
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3. Types of Anisometropia
• There are two broad categories of anisometropia:
absolute anisometropia and relative anisometropia.
• Absolute anisometropia is then divided further.
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4. Relative anisometropia
• This is when the total refraction of the two eyes is the
same (or at least similar enough not to qualify as
anisometropic), but there is a difference in axial length
between the eyes. Put in simpler terms, it is when the
eyes are similar in refractive power but of different
sizes. This means both eyes put out a clear image, but
the images are of different sizes.
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5. Absolute anisometropia
• Occurs when the total refraction of the two eyes differs enough to be a
problem.
This condition is then further categorized, depending on how each eye
refracts.
• Simple anisometropia: One eye is emmetrope, while the other is myopic
or hypermetropic.
• Compound anisometropia: Both eyes are myopic or hypermetropic (also
called ametropic).
• Mixed anisometropia: One eye is myopic; the other is hypermetropic.
Also called Antimetropia
• Compound astigmatic anisometropia: Both eyes are astigmatic, but to an
unequal degree.
• Simple astigmatic anisometropia: One eye is either myopic or 5

6. Simple Anisometropia
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7. Compound anisometropia
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8. Mixed anisometropia( Antimetropia)
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9. Simple astigmatic anisometropia
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10. Compound astigmatic anisometropia
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11. Causes of anisometropia
Anisometropia can be caused by one of the following
• Trauma to the eye
• Keratoplasty in one eye
• Asymmetric age changes
• Uniocular aphakia after removal of cataracteous lens
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12. Aphakia
• Aphakia occurs with the lens of the eye (the focusing
mechanism) is removed and not replaced with an artificial lens
(this is called pseudophakia if an artificial intraocular lens is
implanted).
• Aphakia may be intentional (for example with a baby that has a
dense cataract). The resulting difference in glasses correction
may be quite large as the lens of the eye contributes a refractive
power of about +16 diopters
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13. Status of binocular vision
There are three binocular vision status conditions:-
1. Binocular single vision present in small degree of
anisometropia(<3D)
2. Uniocular vision when refractive error in one eye is
very high
3. Alternate vision occurs when one eye is emmetropic
or moderately hypermetropic and the other myopic.
The hypermetropic eye used for distance vision and
the myopic one for near vision.
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14. Symptoms
• Eye strain
• Headache
• Nausea
• Tiredness
• Diplopia
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15. Diagnosis
1. Retinoscopic examination
2. Testing for binocular single vision status
 FRIEND test
 Worth’s four dots test
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16. FRIEND test
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17. Cont.…
• The patient wears red/green goggle, red on the right
and green on left eye. And
• Sits at 6m distance from the letters.
• He /she is asked to read the letters.
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18. Interpretation of the results
A. If the patient reads FRIEND there
is binocular single vision.
B. Patient having Uniocular vision
will read FIN or RED.
C. If the patient has alternate vision
he will read FIN at one time and
RED at other time. 18

19. Worth’s four dots test
• The patient wears red/green goggle
and
• sits at 6m from four lights one red
two green and one white.
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20. Interpretation of the results
1. Normal binocular single vision :- if the patient
sees all the 4 lights in the absence of manifest
squint
2. In ARC the patient sees 4 lights in the presence
of manifest squint
3. If patient sees only two red lights – LEFT
suppression
4. If the patient sees only three green lights –
RIGHT suppression
5. If alternately sees red and green –alternate
vision
6. If the patient sees five lights (2 red and 3 green ),20

21. Management
• Anisometropia can be managed optically or surgically
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22. Optical correction
1. Spectacle correction :- prescribed in anisometropia up to 4D.
Because difference of >4D will not be tolerated by the patient
due to spectacle magnification difference b/n the two eyes.
• This results anisokonia _un equal retinal image in the two
retinas.
2. Contact lens for high degree anisometropia
3. Anisometropic spectacle
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23. Surgical management
• Refractive corneal surgery. Used to improve the cornea’s
refraction of light, this surgery can correct unilateral myopia,
hypermetropia, and astigmatism.
• Removal of the crystalline lens. Removing the crystalline lens can
actually improve overall vision in some conditions. The sight in
that eye can then be adjusted with special glasses or further
surgeries.
• Intraocular lens implantation. Intraocular lens implantation (IOL)
is a relatively common surgery for those with a cataract or
astigmatism in their eye that is seriously impacting their life.
• Phakic IOL. This intraocular lens implantation is similar to the
above surgery, but it does not remove the crystalline lens. Instead,
the intraocular lens is placed in the eye with the natural lens. The
two will then work together to improve vision. 23

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