When refractive differences become too great

How can the difference in refractive power between two eyes affect a patient’s everyday life? And how can you, as an optometrist, make a difference? In this article we explain anisometropia, aniseikonia and optical anisophoria – and what you should keep in mind in daily practice.

What happens in anisometropia?

When we speak of anisometropia, we mean a difference in refractive power between the eyes. This can amount to several dioptres. Some individuals can live with this difference, but it may result in two specific problems:

• Aniseikonia – the images on the retinas differ in size.

• Optical anisophoria – prismatic effects indused by the corrective lenses.

The result may be that the patient experiences blur, headaches or difficulty using both eyes together.

Aniseikonia – when the images do not match

When the difference exceeds approximately 2 D, the risk of aniseikonia is significant. In such cases you, as the optometrist, should consider compensation. There are several ways to determine the most suitable solution for your patient.

1. Get support with the calculation

   By adjusting the magnification through aniseikonic lens design, the difference can be minimised. This does not always resolve the entire problem, but in most cases it provides a significant improvement.

   If required, Multilens can calculate a solution that minimises the difference in magnification or minification. You will receive a recommendation for suitable compensation based on the refraction and what is technically feasible.

2. Evaluate with trial lenses

   With ML Grand trial lenses you can practically test magnification by three or six per cent on the eye with the lowest plus or highest minus. The patient can directly experience the difference — and you can then order the corresponding compensation. A one diopter difference corresponds to approximately one per cent magnification with ML Grand.

3. Specific tests

   With tests such as Awaya or Aniseikonia Inspector, you can obtain the values needed to determine the correct compensation.

Optical anisophoria – prismatic differences

In addition to unequal image size, the spectacle lenses can produce prismatic effects that create imbalance between the eyes.

A simple Pen test can quickly reveal whether optical anisophoria is present.

Points to consider:

• Progressive lenses with short corridors usually provide less prismatic difference.

• In cases of diplopia in the near zone of multifocal lenses, slab-off may be required — but most commonly the aniseikonia itself is compensated in other ways.

Multilens offers a guarantee of exchange on these corrections, allowing you to start with the simplest solution confidently.

Your role as an optometrist

The patient often only describes that “something does not feel right”. For you, the key is to recognise the pattern: when the difference in refractive power becomes too large, the issue is no longer merely about sphere and cylinder, but about how the brain can fuse two disparate images.

By asking the right questions, performing the right tests and suggesting the right solution, you can make a decisive difference in your patient’s quality of life.