Neuromechanisms of Convergence Insufficiency


As good as all of the presentations at the 50th annual COVD meeting were this year, a particularly exciting one was the joint presentation on Friday mid-afternoon by Drs. Tara Alvarez and Mitchell Scheiman. For those of you who aren’t already familiar with Dr. Alvarez and her neurobiological interest in convergence insufficiency, this TED talk provides nice background information.

In the financial world, “ROI” stands for Return on Investment. But in the realm of neurobiology, and in particular as related to cortical functionality, ROI is the acronym for Regions of Interest. ROIs in the brain may hold the key to a better understanding of the unification of space and time in the visual system. This is where fMRI comes into play, and the signature paper that brought the work of Dr. Alvarez at NJIT to the attention of the optometric world was published in Optometry and Vision Science in 2010: Vision Therapy in Adults with Convergence Insufficiency: Clinical and Functional Magnetic Resonance Imaging Measures. That has inspired others such as Dr. Tamara Oechslin and colleagues who won the VDR Article of the Year Award in 2017 for their paper on Imaging of Convergence Insufficiency Treatment Effects (ICITE) Pilot Study: Design and Methods.

The collaborative study that Drs. Alvarez and Scheiman reviewed in their lecture was The Convergence Insufficiency Neuro-mechanism in Adult Population Study (CINAPS) Randomized Clinical Trial: Design, Methods, and Clinical Data. The recruitment methodology and study design was laid out in detail in the hyperlinked article above in the journal Ophthalmic Epidemiology last year. The results of their study were published last month in Nature’s open access Scientific Reports: Underlying neurological mechanisms associated with symptomatic convergence insufficiency.

Drs. Alvarez and Scheiman presented the following conclusions:

  • OBVAT (Office-Based Vergence/Accommodative Therapy successfully remediated clinical signs and symptoms in 72% of young adults between the ages of 18 and 35. (Note that this is consistent with the success rate of 75% for OBVAT presented in the CITT for children ages 9-18, as you can re-visit in this DigiVision recording of Dr. Scheiman’s presentation to COVD in 2008).
  • In the Fast Fusional System:
    • Reaction time and peak velocity improved in disparity and accommodative vergence
    • Left FEF (Frontal Eye Field) significantly improved in CI post OBVAT but not in the sham treatment group
    • Left Thalamus significantly correlated to functional activity and peak velocity for BNC (Binocularly Normal Controls) and CI post OBVAT but not for the sham treatment group
  • In the Slow Fusional System:
    • Phoria adaptation significantly improved in magnitude and rate
    • Cuneus significantly improved in CI post OBVAT but not in the sham treatment group

As a neuro-refresher, the FEF (Frontal Eye Field) has afferent connections to the thalamus and occipital lobe, and efferent connections to cranial nerve III. The intimate interplay between FEF and thalamus influences attention, and the FEF/occipito-parietal connections facilitate visual-spatial awareness. (Take particular note of the FEF –> Thalamus –> SC –> premotor circuit –> eye muscle route.)

The cuneus is the wedge-shaped part of the occipital lobe beneath the parieto-occipital fissure where the parietal and occipital lobes meet, and above and also within the calcarine fissure located at the lower section of the occipital lobe. It is involved in processing visual information, and is part of both the dorsal and ventral visual streams.

Courtesy of Assoc Prof Frank Gaillard, Radiopaedia.org, rID: 47208

It is interesting to note that aside from its potential role in convergence, a reduction of cortical thickness of the cuneus has also been associated with the pathogenesis of trigeminal neuralgia. A more subtle form of trigeminal neuralgia, trigeminal dysphoria, has been postulated as a neuromechanism for discomfort in convergence insufficiency through the ophthalmic branch of the trigeminal nerve and its role in proprioception related to exophoria. Stay tuned, as much remains to be learned!

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