Document Type
Dissertation
Date of Award
12-31-2020
Degree Name
Doctor of Philosophy in Biomedical Engineering - (Ph.D.)
Department
Biomedical Engineering
First Advisor
Tara L. Alvarez
Second Advisor
Xiaobo Li
Third Advisor
Bharat Biswal
Fourth Advisor
Catherine E. Myers
Fifth Advisor
Suril Gohel
Sixth Advisor
Chang Yaramothu
Seventh Advisor
Xin Di
Abstract
Convergence insufficiency (CI) is a binocular vision dysfunction in which the person has difficulty maintaining a sustained fixation on an object in the near field of view. This condition is present in about 5% of the general population and with a greater prevalence in patients with traumatic brain injury or attentional deficit hyperactivity disorder. One therapeutic intervention for CI is Office-Based Vergence and Accommodative therapy (OBVAT) which is successful in about 75% of the pediatric and young adult population. The neural mechanism by which OBVAT leads to a sustained reduction in visual symptoms is not fully understood. Vergence eye movements have been modeled as two component control system, the Dual Mode system. One input to the vergence system is the disparity signal that stimulates the biomechanics of the oculomotor system. According to the Dual Mode model, one portion of the disparity vergence system is preprogrammed and the other is feedback back controlled for the fine tuning in eyes position, this is referred to as the fast fusional vergence system. In addition, through slow adaptation the phoria level can be modified to optimize a person's current visual position which is called the slow fusional vergence system. Electrophysiology studies performed in monkeys support that specific cortical and subcortical areas are involved in the control of vergence eye movements. However, more knowledge needs to be acquired to fully understand how vergence eye movements are controlled in humans.
This body of research investigates in the human living brain the function of specific brain areas while stimulating the fast and slow vergence systems using functional magnetic resonance imaging (fMRI). First, the test-retest reliability of these experiments is assessed. A group of Binocularly Normal Control (BNC) participants is recruited and asked to perform these tasks while a fMRI scan is acquired. Fast vergence task is reliable within the hypothesized regions involved in vergence eye movements, while the slow vergence task is reliable in some regions. As part of a randomized clinical trial, the neural basis of OBVAT is investigated and compared to office-based placebo therapy (OBPT) in BNC and CI participants. The longitudinal analysis shows significant differences in functional activation within the left frontal eye field for the fast-fusional system response task while a trend is observed during the slow fusional system within the right cuneus. When the relation between brain activation and behavior measured in the lab is analyzed, the fast-fusional task resulted in a cluster within the thalamus that is significantly correlated to the peak velocity of vergence step responses for participants that received the OBVAT but not for OBPT group. For the slow fusional system, no significant correlation is observed between the behavior and functional activation. This research shows the neural mechanistic differences between CI and BNC and the neural basis of OBVAT compared to OBPT. These results have broad clinical implication for the design of new therapeutic interventions for patients with CI.
Recommended Citation
Morales Carrasco, Cristian, "A longitudinal investigation of functional activity changes from vision therapy: a study of binocularly normal controls and patients with convergence insufficiency" (2020). Dissertations. 1907.
https://digitalcommons.njit.edu/dissertations/1907
