By Marc Dinkin, MD
Synopsis: This study highlights measurable visual and structural changes in patients with mild traumatic brain injury (mTBI). Findings include convergence insufficiency, reduced contrast sensitivity, and occipital cortex changes, despite normal standard imaging and visual field tests. Machine learning discerned mTBI from controls with 72% accuracy, suggesting advanced diagnostics can uncover subtle abnormalities.
Source: Rasdall MA, Cho C, Stahl AN, et al. Primary visual pathway changes in individuals with chronic mild traumatic brain injury. JAMA Ophthalmol. 2024; Nov 27:e245076. doi: 10.1001/jamaophthalmol.2024.5076. [Online ahead of print].
Often we hear statements such as “Light bothers me,” “I can’t read for more than two minutes,” “I can see but my vision just seems wrong,” or “I’m seeing spots, blurs, and other things that aren’t there” from our patients who have experienced mild traumatic brain injury (mTBI). mTBI is defined by a Glasgow Coma Scale score > 13 and normal brain imaging; yet, on standard ophthalmic testing, including visual acuity, color plates, pupils, and formal visual fields, these patients pass with flying colors.
Meanwhile, structural assessments, such as fundus examination, ocular coherence tomography (OCT) scans of the optic nerve fibers and retina, and standard magnetic resonance imaging (MRI) of the brain, often remain normal as well. Patients may be told there is nothing wrong with them and are left confused and frustrated. Although it now is common knowledge that damage to the central nervous system following mTBI escapes the resolution of common MRI imaging and that examination techniques beyond assessment of raw visual function may be needed to reveal the underlying pathology, such techniques are not always used.
In a recent study published in JAMA Ophthalmology, Rasdall and colleagues address this practice gap in common assessment techniques of patients with mTBI by comparing results for a battery of testing between an mTBI cohort and control subjects. Comparing 28 patients with a history of mTBI vs. 28 age-matched controls, the authors found that mTBI patients had lower prism convergence testing (PCT) measurements, including the break point and recovery point, which are markers of convergence insufficiency. However, there were no significant differences in the ability of mTBI patients to accommodate, i.e., change the lens configuration to allow near focusing.
On afferent visual testing, four of the 28 mTBI patients showed reduced contrast sensitivity (CS), which resulted in an overall statistically significant difference in CS between the two groups, but there was no significant difference in Humphrey visual field results. Structural assessment of the mean peripapillary retinal nerve fiber layer (pRNFL) and optic nerve volume using OCT showed no differences and, surprisingly, visual evoked potentials demonstrated a higher binocular summation index in the mTBI group, which is a reflection of higher P100 amplitudes as compared with controls.
On MRI evaluation, four patients with mTBI demonstrated significant differences in brain volume in areas that varied based on the patient, including the lingual and fusiform gyri. Using diffusor tensor imaging, there was no difference in the optic radiation between the two groups.
However, in a subset of 18 mTBI patients and 18 controls, a machine learning model that incorporated all the optic radiation and occipital cortex metrics that were included was able to discern mTBI from control with an accuracy of 72%, with optic radiation fiber length and occipital gyri volumes playing an important role in the model’s success.
Finally, when the authors included their entire battery of testing into a z-score, they were able to identify 78% of mTBI patients as different from the mean control z-score.
Commentary
In this ambitious study of patients with mTBI, the authors demonstrated that we should be able to determine whether TBI has influenced visual function and associated structures using a specific set of examination maneuvers and tests. As expected, a major finding was convergence insufficiency, which has been reported in up to 38% of adults with mTBI and currently is being studied in a randomized clinical trial evaluating office-based therapy.1,2
I was surprised to see that accommodative insufficiency (AI) was not more common in the TBI group, since it has been reported in 24.1% of non-presbyopic TBI patients in one large study. In fact, in my own practice, I find that many mTBI patients with difficulty reading have been treated with convergence exercises without success because their chief issue actually is AI. Interestingly, although there were no differences in mean pRNFL, 31% of mTBI patients did demonstrate abnormal temporal thicknesses, a finding indicative of some damage to the maculopapillary bundle, which might account for the differences in CS seen in some of the mTBI patients.
Together, the OCT and CS findings suggest that there is a spectrum of traumatic optic neuropathy after TBI, with milder cases falling under the radar of typical visual testing. However, in light of the evidence for occipital cortex and optic radiation changes in the mTBI group (based on their effect on the machine learning algorithm’s ability to identify mTBI), it also is conceivable that any observed RNFL thinning was the consequence of retrograde trans-synaptic degeneration.3
This study stands as an enlightening demonstration of real and measurable differences in the visual function and structural pathways in our mTBI patients that could help us identify and quantify the effect of mTBI on vision if we just remember to look in the right places. Once diagnosed, clinical management of TBI-related visual complaints then can be tailored to the specific findings with the hope of helping our patients obtain a better visual quality of life.4
Marc Dinkin, MD, is Director of Neuro-Ophthalmology and Associate Professor, Departments of Ophthalmology and Neurology, Weill Cornell Medical College.
References
1. Alvarez TL, Scheiman M, Gohel S, et al. Effectiveness of treatment for concussion-related convergence insufficiency: The CONCUSS study protocol for a randomized clinical trial. PLoS One. 2024;19(11):e0314027.
2. Alvarez TL, Kim EH, Vicci VR, et al. Concurrent vision dysfunctions in convergence insufficiency with traumatic brain injury. Optom Vis Sci. 2012;89(12):1740-1751.
3. Dinkin M. Trans-synaptic retrograde degeneration in the human visual system: Slow, silent, and real. Curr Neurol Neurosci Rep. 2017;17(2):16.
4. Capo-Aponte JE, Urosevich TG, Temme LA, et al. Visual dysfunctions and symptoms during the subacute stage of blast-induced mild traumatic brain injury. Mil Med. 2012;177(7):804-813.
This study highlights measurable visual and structural changes in patients with mild traumatic brain injury (mTBI). Findings include convergence insufficiency, reduced contrast sensitivity, and occipital cortex changes, despite normal standard imaging and visual field tests. Machine learning discerned mTBI from controls with 72% accuracy, suggesting advanced diagnostics can uncover subtle abnormalities.
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