Ancient scholar examining a stylized eye with misaligned elements, representing strabismus.

Unlocking Ancient Eye Care: Michael Psellus' Strabismus Definition Explained

Samir D’Costa in Health & Wellness August 2025 • 4 min read.

"Discover the insights of an 11th-century scholar on eye misalignment and its relevance to modern ophthalmology."

Strabismus, commonly known as eye misalignment or crossed eyes, has been recognized since the time of Hippocrates. The ancient Greeks not only identified this condition but also proposed early theories about its causes, including heredity. Over the centuries, physicians and scholars have sought to understand and treat strabismus, each building upon the knowledge of their predecessors.

Among these historical figures is Michael Constantine Psellus, an 11th-century Byzantine scholar. While not an oculist, Psellus contributed a unique definition of strabismus in his medical writings. His insights offer a glimpse into the medical understanding of his time and highlight the ongoing quest to unravel the complexities of vision disorders.

This article delves into the work of Michael Psellus, exploring his definition of strabismus within the context of ancient and Byzantine ophthalmology. We will examine his biography, his medical treatise, and the significance of his contribution to the history of understanding and addressing eye misalignment.

Psellus' Definition of Strabismus: A Glimpse into Ancient Eye Care

Ancient scholar examining a stylized eye with misaligned elements, representing strabismus.

Michael Constantine Psellus (1020-1105 AD) was a polymath of the Byzantine era, excelling in philosophy, politics, and science. His writings include a medical iambic poem where he defined various diseases and treatments. Within this work, he addressed strabismus, providing a definition that reflects the medical knowledge of his time.

Psellus defined strabismus as being "caused by a spasm of the bodies which move (the eye balls) and the oblique tendency of the muscles." This definition, though concise, demonstrates an understanding of the involvement of eye muscles in the condition. It suggests that an imbalance or dysfunction in these muscles leads to the misalignment of the eyes.

Here are the key components of Psellus' definition:

Spasm of the bodies which move the eye balls: This refers to involuntary contractions or dysfunction of the muscles responsible for eye movement.
Oblique tendency of the muscles: This highlights the misalignment caused by the affected muscles, pulling the eye in an abnormal direction.

Psellus's definition, though rooted in ancient medical understanding, touches on elements that are still relevant today. Modern ophthalmology recognizes that strabismus often arises from imbalances or abnormalities in the extraocular muscles. While our understanding of the mechanisms is far more detailed, the core concept of muscular involvement remains consistent.

The Enduring Legacy of Psellus' Definition

Michael Constantine Psellus may not have been an ophthalmologist, but his definition of strabismus offers a valuable insight into the history of medicine and the evolving understanding of eye disorders. His work demonstrates that even in ancient times, scholars recognized the role of muscles in eye alignment and sought to define the underlying causes of strabismus.

By examining Psellus' definition, we gain a greater appreciation for the progress of medical knowledge and the contributions of individuals throughout history. It reminds us that today's sophisticated understanding of strabismus is built upon centuries of observation, research, and intellectual curiosity.

Psellus' contribution is a reminder that progress in medicine is a collaborative effort across centuries. His work encourages continued exploration and innovative approaches to address vision-related challenges.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1080/09273972.2018.1467470, Alternate LINK

Title: Michael Constantine Psellus (1020–1105 Ad) And His Definition Of Strabismus

Subject: Ophthalmology

Journal: Strabismus

Publisher: Informa UK Limited

Authors: Gregory Tsoucalas, Theodoros Papaioannou, Marianna Karamanou

Published: 2018-07-03

Everything You Need To Know

How did Michael Psellus define strabismus?

Michael Constantine Psellus, an 11th-century Byzantine scholar, defined strabismus as being caused by a 'spasm of the bodies which move (the eye balls) and the oblique tendency of the muscles.' This definition highlights the role of eye muscles in eye misalignment. The 'spasm' indicates an involuntary contraction or dysfunction, while the 'oblique tendency' describes the resulting misalignment. This early understanding laid the groundwork for modern ophthalmology's understanding of the condition.

What is strabismus?

Strabismus, or eye misalignment, is when the eyes do not align properly. This condition has been recognized since the time of Hippocrates by ancient Greeks. It occurs when the eyes point in different directions. Causes can include imbalances or abnormalities in the extraocular muscles, which are the muscles that control eye movement. The impact can include visual impairment.

Why is Michael Psellus's definition of strabismus important?

Michael Psellus's work is significant because it provides a glimpse into the historical understanding of strabismus and how it was perceived in the 11th century. His definition, although based on the knowledge of his time, shows an early recognition of the role of eye muscles in misalignment. His insights bridge the gap between ancient and modern ophthalmology, showing how ideas have evolved over time. This historical context helps modern ophthalmologists understand the progression of ideas.

Who was Michael Psellus?

Michael Constantine Psellus was a Byzantine scholar who lived from 1020 to 1105 AD. His expertise was broad, including philosophy, politics, and science. Psellus wrote a medical iambic poem in which he defined various diseases and treatments. His writings included a definition of strabismus that reflected the medical understanding of his time and provided valuable insights into the history of medicine and the development of vision care.

How does the understanding of strabismus today compare to Michael Psellus's definition?

Modern ophthalmology recognizes that strabismus often arises from imbalances or abnormalities in the extraocular muscles, the same ones Michael Psellus referenced. While the specific mechanisms and causes are now understood in greater detail, the fundamental concept of muscular involvement in eye misalignment remains consistent with Psellus's definition. Today, treatments include glasses, eye exercises, and surgery, depending on the cause and severity of the strabismus.