Our eyes are incredibly strong. When someone’s eyes aren’t lining up, there is usually a coordination issue, not a strength problem. Here is Dr. Press’s words on the subject from his blog, The Vision Help Blog.
By Leonard J. Press, O.D., FAAO, FCOVD
Thanks to our colleague, Dr. Doug Major, for pointing out this superb article on strabismus that appeared earlier this year in Greafe’s Archive for Clinical and Experimental Ophthalmology: Comitant strabismus etiology: extraocular muscle integrity and central nervous system involvement—a narrative review. It’s basically an update and extension of the concept that our colleague Dr. Bob Sanet brought to light many years ago, which is the dissenting opinion within ophthalmology that strabismus is not primarily an eye muscle problem. It goes way back to an address that Dr. A.D. Ruedemann, Chairman of the Section on Ophthalmology of the American Medical Association, presented on June 12,1956. In that address he stated, regarding strabismus: “The anatomical changes that we see in the eye muscles are minimal and only in rare instances are they of any importance in the total picture. Most of these patients have learned to coordinate their eyes incorrectly and they are just as deficient in their incorrectness as they should have been in the correct method of using them and unless the correct method is taught to them, one cannot effect a cure”.
Let’s cut to the chase (no pun intended), and get right to the key messages in this new article:
Here is a notable statement at the outset of the paper:
“Strabismus can present itself in multiple forms, what some authors have called “strabismus polymorphy”. This suggests that the eye turn is a consequence of a vast number of conditions of multiple possible origins, influenced by either genetic or environmental factors, or a combination of both. Strabismus is not a single entity nor a condition in itself. The eye misalignment is a manifestation/sign of an underlying problem involving one or multiple components of the visual and oculomotor systems along the peripheral-central axis (see Fig. 1), from the extraocular muscles (EOMs) themselves, their pulleys and their innervations, to all brain areas involved in visual perception and oculomotor control: midbrain fusion centres, the lateral geniculate nucleus (LGN) and striate and extrastriate areas.”
The authors of this new paper note that 75–95% of all strabismus cases are concomitant, non-restrictive, non-paralytic, or developmental. They are not related to specific syndromes, and their genetic associations remain poorly understood. They highlight that most cases or strabismus are generally believed to be caused by deficits in the central neural pathways involved in visual perception and oculomotor control. Although several possible mechanisms have been hypothesized, the specific central origins of strabismus remain elusive. Here are some additional salient points excerpted from the paper:
- Strabismus is associated with neurodevelopmental and neurologic disorders such as cerebral palsy, Down’s syndrome, neurodevelopment delay, intellectual disability, and white matter damage of immaturity.
- Acquired brain injury (ABI), which is any type of brain injury occurring after birth, often leads to eye movement and binocular coordination disorders, including strabismus. ABI are predominantly caused by stroke, brain tumor, infection, cerebral hypoxia, or after impact or sudden shake to the head. Lesions can occur at the level of the cranial nerves innervating the EOMs (periphery) or in the brainstem and brain areas involved in oculomotor control (center).
- The higher-than-average prevalence of strabismus in the presence of CNS defects indicates that in many cases, the cause of strabismus lies in the brain. Moreover, these studies depict the relationship between strabismus and obvious, well-defined neurological alterations. More subtle, covert neurological deficits could be the cause of strabismus in a much larger proportion of cases.
- The concept of strabismic control is another important point indicating central origin and central relevance in strabismus. It is widely recognized that strabismus control plays a significant role in the outcomes of EOM surgery, especially in intermittent exotropia.
- People, whether with strabismus or without, have a certain amount of sensorimotor knowledge related to their eyes and their position in space.
- Some people with strabismus are capable of altering the magnitude of the eye turn, they can do “something” to decrease the deviation, and “something” to increase it even though they are often unable to describe how they do it. In line with strabismus control, in many cases, the deviation worsens when the person is sick, tired, distracted, or absorbed in a highly attention-demanding task. All these unequivocally point to cerebral involvement in eye misalignment pathogenesis.
- Central strabismus can be the consequence of anatomical and/or functional abnormalities found in any of the brain areas and pathways involved in vision and oculomotor control, including the oculomotor and proprioceptive nuclei in the brainstem, the medial reticular formation, the pontine reticular formation, the superior colliculus, the thalamus, the cerebellum, the corpus callosum, and the occipital lobe, and the extraestriate areas involved in visual processing in the parietal and frontal lobes, the parietal eye field, and the frontal and supplementary eye fields.
Here are some key statements from the paper regarding treatment:
- Classical and contemporary standard treatment for strabismus, i.e., EOMs surgery, acts exclusively at a peripheral level. EOM surgery consists of mechanically weakening or strengthening the muscles to correct the eye misalignment.
- However, in most strabismus cases, there is little or no evidence of abnormalities in the EOMs. In addition, the presence of co-existing CNS abnormalities suggests that the CNS plays a role in strabismus pathogenesis. Not being able to address the concomitant CNS abnormalities in strabismus could be the cause of surgical treatment varying and sometimes unsuccessful results, often with high recurrence and reoperation rates, all despite being a common and frequently implemented procedure worldwide.
- By surgically rearranging EOM position, no steps are taken to enhance control, nor to improve oculomotor and perceptual abilities. If anything, awareness of eye position could be increasingly limited due to the destruction of proprioceptive afferents. Considering that multiple causes, along the periphery-center axis, can be behind the ocular deviation, different treatment strategies tailored to the precise strabismus causes might be needed.
- Some cases benefiting from surgery, others from patch therapy, glasses prescription, vision therapy, and in some cases, the deviation can resolve spontaneously.
- A multidisciplinary approach between ophthalmologists, optometrists, and maybe in the future neurologists. can incorporating treatment directed at improving oculomotor control, enhancing fusion, proprioception, and interhemispheric connectivity.
- Different treatment methods focusing on distinct points of the peripheral-central axis might allow for a more customized approach and yield better results. With some strabismus cases responding better to periphery-acting treatment (surgery), while other cases showing better outcome with treatment acting at CNS level (non-surgical).
This article is a wonderful addition to the literature showing an idealized synergy between ophthalmology and optometry in combing the best approaches of each field toward maximizing patient outcomes in strabismus.