Utilization of a self-refracting system on the streets to improve vision in an urban unhoused population

To evaluate the effectiveness of the USee self-refracting eyewear kit in an urban unhoused population and identify predictors of instances in which the USee does not improve vision.

In this retrospective cross-sectional study, 110 patients (220 eyes) experiencing homelessness in Phoenix, Arizona, were evaluated before refractive correction (control) and after USee refraction. Visual acuity (VA) testing and USee refraction were performed in mobile outreach settings. Mixed-effects models were used to determine VA outcomes. USee failure was defined as USee-corrected visual acuity (USeeVA) worse than 20/40 or any worsening of USeeVA compared to uncorrected visual acuity (UCVA). Predictors of USee failure were evaluated using receiver-operating characteristic curves (AUC-ROC). Thresholds were determined using Youden's Index and Liu's method. The primary outcome was the change in binocular VA. Secondary outcomes included the rate of achieving 20/40 vision or better and determining what factors predicted USee device failure.

Mean binocular VA improved from 20/64 to 20/31. The proportion of patients achieving 20/40 vision or better increased from 40% to 81%. Pinhole VA alone (AUC: 0.74), cylinder alone (AUC: 0.67), and their combination (AUC: 0.81) predicted USee failure. A pinhole VA worse than 20/60 had sensitivity 0.667, specificity 0.819 (positive likelihood ratio, LR⁺: 3.69, negative likelihood ratio, LR⁻: 0.41). A cylinder threshold less than - 0.5 diopters (D) had sensitivity 0.346, specificity 0.511 (LR⁺: 0.71, LR⁻: 1.28).

The USee device improves vision in low-resource, transient populations. Screening using pinhole VA and cylinder may help optimize patient selection for USee-based refractive correction.