Clinical outcomes of low vision rehabilitation delivered by a mobile clinic

Abstract

Purpose: This prospective cohort study examined clinical outcomes of low vision rehabilitation (LVR) delivered by a mobile clinic.

Methods: Participants were recruited from those scheduled for mobile clinic LVR and met the United States definition of legal blindness. Participants completed the Massof Activity Inventory (AI) before LVR, 3 months post-LVR, and 1 year post-LVR. Change scores and measures of clinical effect (i.e. Cohen's effect size and minimum clinically important difference, MCID) were calculated for each time point and compared. Additional participant characteristics (age, acuity, contrast sensitivity, cause of visual impairment, training recommendations, and prior LVR experience) were also explored with respect to outcome measures.

Results: Of the 66 participants enroled in this study, 47% had no prior LVR experience. Significant differences were noted between baseline and 3-month person measures, and between baseline and 1-year person measures. There was no significant difference between 3-month and 1-year person measures, nor was there a significant difference in change score between these two time points. At 1 year post-LVR, overall visual ability effect size was 0.74. A clinically meaningful outcome was achieved in 56% of participants at 3 months and 71% at 1 year for overall visual ability. There was no significant difference in the proportion of participants achieving MCID at 3 months vs 1 year. Of participants who completed the 1-year post-LVR AI, 59% reported a subjective worsening of vision during the study period. This subgroup also tended to have smaller 1-year change scores.

Conclusions: Mobile clinic LVR is effective at expanding access to care and produces clinically meaningful outcomes comparable to those seen in other outpatient LVR delivery models.

Keywords: epidemiology; low vision.

Figure 1.

Enrolment flow chart.

Figure 2.

Primary cause of visual impairment. Other conditions included: congenital cataract (n = 2), retinopathy of prematurity (n = 2), neurological visual field loss (n = 2), chronic uveitis (n = 2), other unspecified congenital vision loss (n = 2), and cytomegalovirus retinitis (n = 1).

Figure 3.

Person measures at baseline, 3-month and 1-year time points. A three (time: baseline, 3 months, 1 year) by eight (overall goals and seven AI domains) within subject analysis of variance demonstrated significant improvements in person measures at each time point. Significant differences were identified between baseline and 3-month person measures (logits) for all AI domains (p < 0.0001). No significant differences were found between 3-month and 1-year person measures.

Figure 4.

Factor analysis plot of five sets of person measures. These findings support previous reports, reading loads most heavily onto one factor and mobility loads most heavily on the other.

Figure 5.

Minimum clinically important difference (MCID) at 3 months and 1 year. Percentages of participants who achieved the MCID based on Activity Inventory (AI) outcomes at 3 months (red bars) and 1 year (blue bars) are shown for overall visual ability (goals) as well as each AI domain (i.e. reading, visual information, visual motor, mobility, instrumental activities of daily living [IADL], inside the home, and outside the home). MCID was less frequently achieved at 3 months than at 1 year for all domains. In overall visual ability (goals), MCID was achieved in 56% of participants at 3 months and 71% of participants at 1 year.

Figure 6.

Cohen’s effect size comparison across prior studies. Cohen’s effect sizes measured in previous studies using visual function questionnaire data after Rasch analysis are shown above. Reported effect sizes range from 2.51 seen in LOVIT to 0.25 measured in Lamoureux 2006. The mobile clinic outcomes from this study were 1.12 at 3 months and 0.74 at 1 year.