Comitant strabismus etiology: extraocular muscle integrity and central nervous system involvement—a narrative review

Abstract

Strabismus is not a condition in itself but the consequence of an underlying problem. Eye misalignment can be caused by disease, injury, and/or abnormalities in any of the structures and processes involved in visual perception and oculomotor control, from the extraocular muscles and their innervations to the oculomotor and visual processing areas in the brain. A small percentage of all strabismus cases are the consequence of well-described genetic syndromes, acquired insult, or disease affecting the extraocular muscles (EOMs) or their innervations. We will refer to them as strabismus of peripheral origin since their etiology lies in the peripheral nervous system. However, in most strabismus cases, that is comitant, non-restrictive, non-paralytic strabismus, the EOMs and their innervations function properly. These cases are not related to specific syndromes and their precise causes remain poorly understood. They are generally believed to be caused by deficits in the central neural pathways involved in visual perception and oculomotor control. Therefore, we will refer to them as central strabismus. The goal of this narrative review is to discuss the possible causes behind this particular type of eye misalignment and to raise awareness among eyecare professionals about the important role the central nervous system plays in strabismus etiology, and the subsequent implications regarding its treatment. A non-systematic search was conducted using PubMed, Medline, Cochrane, and Google Scholar databases with the keywords “origins,” “causes,” and “etiology” combined with “strabismus.” A snowball approach was also used to find relevant references. In the following article, we will first describe EOM integrity in central strabismus; next, we will address numerous reasons that support the idea of central nervous system (CNS) involvement in the origin of the deviation, followed by listing several possible central causes of the ocular misalignment. Finally, we will discuss the implications CNS etiology has on strabismus treatment.

Non-Surgical Strabismus Treatment

“…When visual acuity is poor or one eye is blind, deviation can occur due to a lack of stimulus for fusion [8]. The cause of strabismus can be diseases affecting the eye or nervous system (for example, tumors), and injuries in any structures and processes that are involved in the process of visual perception and oculomotor control [3].…”

“…The cause of strabismus can be diseases affecting the eye or nervous system (for example, tumors), and injuries in any structures and processes that are involved in the process of visual perception and oculomotor control [3]. A small percentage of strabismus is the result of genetic syndromes, acquired stroke, or disease affecting the extraocular muscles or their innervation [3,8].…”

An overview of neuro-ophthalmic disorders at Jenna Ophthalmic Center, Baghdad, Iraq (2021-2022)

“…Proptosis may also be caused by malignancies affecting the optic nerve and meninges [ 11 , 12 ]. Ocular motor nerve palsies are significant etiological factors contributing to the development of strabismus (commonly known as squint) and diplopia (double vision) [ 13 ].…”

Distribution and appearance of myosin, dystrophin, and collagen IV in strabismus-affected extraocular muscle tissue compared with control tissue

“…Conversely, noncomitant strabismus is usually the result of a limitation in eye movement that is associated with a paralytic or mechanical etiology. 4 Surgical treatment is believed to improve the quality of life of patients with some types of strabismus, 5 , 6 but does not achieve a long-lasting effect in all cases, similar to other therapeutic measures. 7 , 8 The development of new methods to treat strabismus thus remains an urgent need.…”