Eye Tracking Applications: Strabismus Screening

Eye Tracking Applications: Strabismus Screening

In our last blog, we discussed the application of eye-tracking technology to the medical field through stroke rehabilitation. We continue in today’s series with an article on how eye tracking relates to the diagnosis of strabismus. Read on to learn more, check out our publications page to investigate more possible applications, and integrate a Gazepoint research-grade eye tracker into your next study.

What Is Strabismus?

Strabismus, more commonly referred to as crossed eyes or “wall-eyed,” refers to a condition in which someone’s eyes do not both look at the same place at the same time. One eye may turn in, out, up, or down. This deviation may be constant, or it may only occur when the individual in question is tired, sick, or doing a lot of close-up work such as reading. It typically develops in toddlers by the time they are 3 years old – an estimated 5% of all children have a type of strabismus – but it can also develop in older children and adults.


There are a few possible causes of strabismus. When we direct our eyes to look at a certain object, a signal begins in our brain and travels through nerves to reach the muscles that direct the movement of our eyes. Problems relating to strabismus can occur anywhere along this path. Often, strabismus is a result of poor muscle control surrounding that eye. However, it can also be caused by issues within the nerves transmitting the signal or issues within the control center of the brain.


Strabismus can cause double vision, poor depth perception, and reduced vision development in the deviating eye. While some believe that a child diagnosed with strabismus will “grow out of it,” treatment is required for improvement, and many cases show that it can be cured completely if diagnosed when the patient is still young.

Strabismus Treatment

The correction of strabismus can include prescription glasses, vision therapy, prisms, or surgery. Treatment often leads to positive results when implemented early.

How Eye Tracking Can Help

Eye-tracking technology can benefit those with strabismus by simplifying the screening process. Current practices are often time-consuming and subjective and scale poorly to large populations like young children in schools. Eye tracking can provide a solution that is fast, objective, non-invasive, and easy to use.

Current Screening Procedures

There are a few ways patients are currently screened for strabismus, all of which must be performed by a health professional such as an optometrist or ophthalmologist. Many diagnoses are made through a comprehensive eye exam that measures an individual’s visual acuity, tests their eye alignment and focus, and allows a professional to examine the internal and external structures of the eye. There are also specific tests used to diagnose strabismus.

Cover/Uncover Test

One of the least technical options for diagnosing strabismus is the cover/uncover test. The patient covers one eye for a few seconds at a time while a professional looks for movements in the uncovered eye. The eye that deviates when both are uncovered often realigns with the object the patient is focusing on when the fixated eye is covered. There is a similar test where each eye is alternately covered and uncovered in quick succession that can offer clues as to a misalignment in the patient’s gaze.

Hirschberg Test

The Hirschberg test involves a pen light and an examination of the patient’s retinal reflex. When the pen light is pointed at the patient’s eye, the light reflects off their corneas, and the reflection should fall very close to their pupils and be symmetrical in both eyes. If the reflection falls elsewhere on one eye, it’s indicative of strabismus, and the unusual position of the reflection can indicate what kind of tropia, or misalignment, the individual is experiencing.

Krimsky Test

The Krimsky test is essentially a modified version of the Hirschberg test. It involves elements of placing prisms in front of the patient’s eyes, or, in some cases, just their fixating eye. A professional can approximate the deviation in the patient’s gaze by adjusting the prisms to center the corneal reflection in the patient’s deviated eye. However, this test can be inaccurate.

Brückner Test

In a Brückner test, a health professional uses an ophthalmoscope – a dedicated tool used to inspect a patient’s retina and other structures of the eye – to produce a red reflex in the patient’s eyes. This procedure is meant to diagnose strabismus, but it does not offer a measurement of the deviation. The deviated eye will have a lighter and brighter reflex than the fixated eye, and this simple comparison is why the Brückner test is often used by primary care doctors to screen patients for strabismus.

Screening for Strabismus With Eye-Tracking Technology

As you can see, the existing procedures for screening strabismus take time, expertise, and in some cases, specialized equipment. When it comes to screening large populations, such as school children, quickly and effectively, these tests fall short.

Eye tracking offers a solution, and several studies have already been published in pursuit of this ideal. One paper pitched a series of computer games, used in conjunction with eye-tracking technology, to measure for deviations in an individual’s gaze, and several scientists have already begun studying the possibility. The benefits of using eye-tracking hardware and software for the purpose of strabismus screening are clear:

  • Faster, more accurate, and more exacting results
  • Portable and easy to use equipment
  • Reduced time requirements and improved efficiency

With a more effective screening procedure, health professionals can diagnose strabismus earlier in a patient’s life, quickly implement a treatment plan, and possibly reduce the overall number of patients with strabismus.

Explore the Possibilities With Gazepoint

Are you interested in investigating the use of eye tracking in medical diagnosis or another field of study? Gazepoint offers research-grade equipment at a consumer price point. Explore all our bundled options, and place your order today to get started.

To learn more about all the possible applications, explore our blog and read through our publications page. If you have published a study using Gazepoint technology, please contact a member of our team so we can add it to the list and share your results!

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