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Aniseikonia, Anisometropia and Anisophoria: Commonly ignored vision problems

If you have trouble adapting to a new prescription or eyeglasses you may be suffering the effects of aniseikonia
Aniseikonia is a term used to describe and quantify the variance of ocular image sizes in a pair of eyes.

Causes of Aniseikonia
Aniseikonia arises most frequently when eyeglasses are prescribed and manufactured to correct an unequal refractive error between the two eyes. This difference is called anisometropia and often occurs after the patient undergoes cataract, retinal detachment or monovision refractive surgery. It is also a major reason that children refuse to wear their eyeglasses in the treatment of amblyopia (lazy eye). 

How do eyeglasses cause aniseikonia?
All spectacle lenses distort the image on the viewers retina. Lenses that correct near-sightedness cause the viewed object to appear smaller while lenses that correct far-signtedness cause the object to appear larger. Lenses that correct astigmatism cause a fattening or thinning of the object. Eyeglasses also distort the perceived position of an object due to the fact that they remain stationary while the eye moves behind them. Of course, if the prescription for each eye is about the same then both eyes receive the same distortion so that there are few adaptation problems. It is when there is a difference in the prescription that discrepancies in size and position occur with the associated dysfunction. Optometrists call ocular image size discrepancies sensory aniseikonia and position discrepancies motor aniseikonia or anisophoria.

Aniseikonia and Children
Children with anisometropia either with or without strabismus do much better when treated with an  iseikonic correcting system such as contact lenses or specially manufactured iseikonic spectacles. Regular eyeglasses often deepen suppression due to the creation of a differentially sized image. If your child won't keep his glasses on they may be doing more harm than good they 

Reading With Aniseikonia,

    
Effects of Aniseikonia
Double vision that increases with increased eccentricity of gaze (it gets worse if you look further off centre)
Impaired depth perception
Inability to fuse the images
Distortion of floor (may seem to be raised or lowered)
Suppression of the vision in one eye
Headaches and general vision malaise
Impaired  vision
Nausea and dizziness

Untreated aniseikonia in the aging population is considered a major cause of falls resulting in serious injury.

Diagnosis of Aniseikonia

Aniseikonia can be assessed using eikonometry and empirically by calculation. We use special trial size lenses to determine the necessary correction. Eyeglasses made to the required eikonometric specification are called iseikonic lenses.

Treatment, Now the good news! Aniseikonia  can be treated.

I have treated thousands of patients with aniseikonia successfully, in fact, most never new they had a problem because I designed eyeglasses to compensate optimally the first time.

I have even had success with many patients with lazy eye due to refractive amblyopia. Many of these patients saw  vision improvement from less than  20/100 to 20/30 in just 6 months  in ages from 6 to 60!

A number of strategies are considered based upon the measured values of sensory aniseikonia, motor aniseikonia and motor vergence limits and they include:
      Iseikonic spectacles (usually effective 95% of the time)
      Contact lenses (always an option, necessary with extreme cases, the other 5%)
      Refractive/cataract surgery  (I prefer to prescribe the amount necessary to ameliorate the problems)            
      Ortho-Keratalogy
      Combination of spectacles and surgery and /or contact lenses

How do iseikonic spectacle differ from regular spectacles?

Standard Design
Your eyeglass prescription contains information regarding the refractive power of each lens.The frame is chosen and along with the geometric position of the eyes (horizontal and vertical) is sent to the lab. The lab chooses the curvature and thickness according to either whats in stock or what looks best.  No consideration is paid to the induced distortions.

Iseikonic Design

The prescription for eyeglasses not only contains the refractive information but also the desired inter-ocular magnification. The challenge is to create a lens system that satisfies not only the refractive needs but also the inter-ocular image coordination.  This is done by manipulating the curvature and thickness of the lenses to, in essence, create magnification in the lower powered lens in a fashion similar to a Galilean telescope. Computer software (Lens Wizard)is used to  integrate the frame size, eye position (horizontal, vertical, and distance from lenses) and  refractive power and communicates exact specifications to the manufacturing laboratory.

Iseikonic lenses may sometimes be a little thicker, but you will be able to see properly and that is the reason most people wear eyeglasses. In extreme cases we can incorporate frames with a thicker eye-wire to hide the edge thickness and anti-reflection coatings can be applied to further improve appearance

What is the cost for iseikonic spectacles?

The manufacturing cost for iseikonic spectacles is about the same as for regular spectacles there is however a small additional professional fee to  take into account the additional time and expertise necessary to afford you the best in optometric care.
 
Iseikonic lens designs can be incorporated into almost any frame and tint. It may not be possible to use rimless frames due to cosmetic and mechanical limitations.

Typical Aniseikonia Case    

Prescription:    

	Standard design	Iseikonic design
Sensory magnification	2.5%	0%
Motor fusion magnification	4.3%	1.9%
Demand to fusion in near zone	2.7 cm/m	0.8cm/m
Iseikonic eye glasses, the thicker lens is the weaker