Mild Traumatic Brain Injury (mTBI) Cohort Inclusion Criteria:
1. are aged 18 - 40;
2. have suffered a mTBI according to VA/Department of Defense (DoD) criteria with documented evidence of alteration of consciousness (AOC) \< 24 hours or loss of consciousness (LOC) less than 30 minutes;
3. were injured between 1 month and 15 years ago;
4. received a Glasgow coma scale (GCS) score of between 13 and 15 upon emergency department (ED) admission, if available;
5. experienced less than 24 hours of post-traumatic amnesia (PTA), if any;
6. have ongoing post-concussive symptoms as evidenced by a score of 18 or greater or a score of 2 or greater on question 6 (vision problems, blurring, trouble seeing) on the Neurobehavioral Symptom Inventory (NSI);
7. have ongoing vision-related symptoms as evidenced by a score of 31 or higher on the Brain Injury Vision Symptom Survey (BIVSS);
8. have PTCI as evidenced by obtaining a score of 21 or higher on the convergence insufficiency symptom survey (CISS), a specific measure of convergence insufficiency;
9. are fluent in English; and
10. have been on stable doses of any vision-altering medications for the past 2 months.
11. Stereopsis of 500 sec arc using Randot Stereo Test.
12. Exophoria at near 4 prism-diopter (PD) or greater than magnitude at distance
13. Near point of convergence (NPC) \> 5 cm
14. Convergence amplitude at near \< 15PD break or the Sheard criterion not met
Control Inclusion Criteria:
1. are aged 18 - 40;
2. CISS score of 20 or lower;
3. near point of convergence (NPC) \< 6cm; and
4. positive fusional range \>15 prism diopters.
5. Stereopsis of 500 sec arc using Randot Stereo Test.
Exclusion Criteria:
1. prior history of other neurological diseases, so as to reduce the risk of confounding effects on vision;
2. history of psychosis, as there are known visual performance findings associated with psychosis;
3. history of current or recent (within two years) substance/alcohol dependence, to reduce confounding effects on visual function
4. recent medical hospitalization (within three weeks), to reduce risk of rehospitalization during the study;
5. any condition that would prevent the participant from completing the protocol;
6. appointment of a legal representative, to avoid coercion of a vulnerable population;
7. any ongoing litigation related to TBI, to prevent interference with legal proceedings;
8. membership in an identified vulnerable population, including minors and prisoners, so as to prevent coercion.
9. Previous vergence therapy, orthoptics, home-based therapy, etc.
10. Amblyopia or constant strabismus or strabismus surgery.
11. High refractive error: Myopia ≥ 6.0PD sphere; Hyperopia ≥ 5.0PD sphere; Astigmatism ≥ 4.0PD; Anisometropia \>1.5PD difference between eyes; Prior refractive surgery.
12. Manifest or latent nystagmus evident clinically.
13. Systemic diseases that affect accommodation, vergence, or ocular motility (i.e. multiple sclerosis, Graves' thyroid disease, myasthenia gravis, diabetes, chemotherapy or Parkinson disease).
