Table 1.

Study characteristics (participant recruitment, study sample size, country); population characteristics (age range/mean age, sex, grouping); prevalence data and measurement methods for DSI in the selected studies.

Source	Study characteristics	Sample population characteristics	Prevalence (%)	Measurement of DSI	Methodology: strengths and weaknesses
Lucas and Zelaya (20)	•Used data that was collected via the 2016 National Health interview Survey. •N = 33,208. •Country: United States.	•Age: 18–75 + years. •Male veterans and non- veterans.	•All percentages have a 95% confidence interval. •5.0% (3.4–6.9) DSI in veterans. •2.5% (2.2–2.9) in non-veterans. 18–44 years: 0.6% (0.4–0.9) •in non-veterans. 45–64 years: 5.1% (3.4–7.3) •in veterans and 3.2% (2.6–3.8) in non-veterans. 65–74 years: 6.8% (5.0–8.9) •in veterans and 5.1% (3.9–6.7) in non-veterans. •75 years and over: 10.6% (8.3–13.2) in veterans and 9.7% (6.8–13.3) in non-veterans.	•Self-reporting questionnaire. Questions asked to evaluate vision and hearing were: “Without the use of hearing aids or other listening devices, is your hearing excellent, good, a little trouble hearing, moderate trouble, a lot of trouble, or are you deaf?”, “Do you have any trouble seeing, even when wearing glasses or contact lenses?”, and “Are you blind or unable to see at all?”. •Categories for degree of hearing were obtained by combining “excellent” and “good” into on category, “a little trouble” and “moderate trouble” into another category, and “a lot of trouble” and “deaf” into another. •Participants who responded to the question about blindness were excluded as blindness could not be differentiated from other degrees of visual troubles, and only 142 respondents selected yes for this question, so could not be analysed separately. •DSI refers to combined V.I. and H.I. of any degree or loss.	Strengths: •Used national sample in the United States. •Large sample size. Weaknesses: •Focused on self- reporting, susceptible to bias. •Relied on subjective categorization of answer options.
Lew et al. (21)	•Used data from TBI evaluations carried out by Veterans Health Administration between October 2007 and June 2009. •N = 21,627. •Country: United States.	•Age: 18–65 years (M = 31.3, SD = 8.6). •93.9% male. •Subjects split into two groups: 12,521 patients with deployment- related TBI and 9,106 participants without TBI.	•35.% DSI in 10,431 patients with TBI and blast exposure. •30.3% DSI in 2,090 patients with TBI but no blast exposure. •24.6% DSI in 6,478 patients with blast exposure but no TBI. •22.7% DSI in 2,628 participants with no TBI and no blast exposure.	•Self-reporting of V.I. and H.I. using five-point Likert-type scale of rating “vision problems, blurring, trouble seeing, hearing difficulty” on a scale ranging from 0 (none) to 4 (very severe). Data was either treated as a quantitative scale or as a dichotomous categorical variable where those selecting “none” and “mild” were combined into one category.	Strengths: •Used national sample in the United States. •Large sample size. Weaknesses: •Focused on self- reporting, susceptible to bias.
Lew et al. (22)	•Used patient medical records of patients with TBI admitted to Department of Veterans Affairs Polytrauma Rehabilitation Centers (PRC) between December 2004 and March 2008. •N = 62. •Country: United States.	•DSI noted in 20 patients (32.3%).	•DSI noted in 20 patients (32.3%).	•Hearing component: Hughson Westlake procedure used to measure pure tone thresholds. Integrity of tympanic membrane and middle ear, as well as air and bone conduction also measured. •Vision component: Feinbloom chart was used to measure visual acuity and the ICD-9 was used to define V.I. •No definition of DSI provided by authors.	Strengths: •Used detailed medical records. •Detailed hearing and vison examinations. Weaknesses: •Small sample size. •No definitions of DSI.
Smith et al. (23)	•Used medical records of 1,472 patients seeking treatment at both optometry and audiology outpatient clinics at VA medical centre between June 2004 and May 2005. •N = 400. •Country: United States (Mountain Home, Tennessee).	•Patients divided into 4 age groups: <65 years (n = 505, range = 44–64), 65–74 years (n = 363), 75–84 years (n = 485), and >85 years (n = 199, range = 85–95 years). •100 patients were randomly selected from each age group.	•Significant increase in DSI prevalence with increasing age. 0% prevalence in <65 age group and 26% prevalence in >85 age group. •<65 years: 0% (PTA and HFPTA) •65–74 years: 1% (PTA) and 4% (HFPTA) •75–84 years: 9% (PTA) and 13% (HFPTA). •>85 years: 22% (PTA) and 26% (HFPTA). •Overall DSI prevalence 7.4% (HFPTA) and 5.0% (PTA).	•Hearing component: Measured using both HFPTA and traditional PTA, resulting in different prevalence figures for each. •Vision component: Snellen chart for distance visual acuity. •DSI definition: visual acuity of worse than 20/40 in the better eye and an unaided moderate hearing impairment or worse in the better ear (>40 dB).	Strengths: •Used detailed medical records. •Random patient selection. Weaknesses: •Small sample size. •Restricted to a specific geographical location in the United States.
Pogoda et al. (24)	•Used patient medical records veterans completing Veterans Affairs comprehensive TBI evaluation (CTBIE) between October 2007 and June 2009. •N = 13,746. •Country: United States.	•Age: 18–64 years (male patients had M = 31.4, SD = 8.7 years). •Sample split into two groups for comparison: 9,998 patients with mTBI history and 3,748 patients with no history of TBI	•Overall MSI rate of 13.9%. •MSI rate in patients with deployment-related mTBI (both blast and non-blast) was 17.4%.	•Self-reporting of V.I. and H.I. via the use of the Neurobehavioral Symptom Inventory (NSI-22, a 22-item patient self-report checklist). •Participants were asked to rate the degree of trouble in the last 30 days for “hearing difficulty”, “vision problems, blurring, trouble seeing”, and “feeling dizzy”, “loss of balance” and “poor coordination, clumsy” in reference to vestibular issues. These were rated on 5-point Likert scales ranging from 0 (none) to 4 (very severe). •Symptoms that were reported at least a 2 were categorised as moderate impairment. •MSI refers to combined reporting of V.I., H.I. and vestibular symptoms, with a score of 2 or greater for all three symptoms.	Strengths: •Used detailed medical records. •Large national sample Weaknesses: •Focused on self- reporting, susceptible to bias. •Relied on subjective categorization of answer options.