Influence of Lighting Direction on the Visualization of Facial Volume Deficits: Frontal Flash versus Zenithal Continuous Lighting

Background: Accurate identification of facial volume deficits is essential for the precise placement of injectables. Standard frontal photography may inadequately capture subtle contour irregularities that depend on surface shadowing. The direction of lighting influences how shadows reveal underlying volume loss, yet its impact on the visualization of deficits has not been systematically compared. Objectives: This study aims to compare the efficacy of frontal flash lighting and zenithal (overhead) continuous lighting in visualizing and detecting facial volume deficits in standardized clinical photographs. Methods: Standardized photographs were obtained from 21 participants (16 females, 5 males; mean age 59.5 years, SD ±8.8) under two lighting conditions standard frontal flash and zenithal continuous illumination while maintaining all other acquisition parameters constant. An evaluator independently assessed each image, grading the severity of volume deficits across nine facial regions on a 4-point ordinal scale (0–3) and recording the presence or absence of a deficit in each region. The primary outcome was the per-region detection of facial volume deficits, compared between lighting conditions using the exact McNemar test; the aggregate global deficit score (sum of nine regions, range 0–27) was compared using the paired t-test with Cohen's d as the effect size. Results: Zenithal continuous lighting significantly enhanced the visualization of facial volume deficits compared to frontal flash. The mean global deficit score was higher under zenithal lighting (10.29 ± 4.56) than under frontal flash (6.81 ± 4.74), with a mean paired increase of 3.48 points (95% CI 2.28–4.68; paired t-test p < 0.001; Cohen's d = 1.24), with a higher score in 18 of 21 subjects (85.7%). The pooled per-region detection rate increased from 43.9% under frontal flash to 62.4% under zenithal lighting, achieving statistical significance in the temporal (p = 0.016), infraorbital (p = 0.008), and marionette (p = 0.039) regions, all favoring zenithal illumination. Zenithal lighting also increased the number of deficits identified (5.62 vs 3.95; p < 0.001) and evaluator diagnostic confidence (6.95 vs 5.29; p < 0.001) while reducing assessment time (37.4 vs 45.1 s; p < 0.001). The effect remained significant after adjustment for age, sex, and body mass index. Conclusions: Lighting direction significantly affects the visualization of facial volume deficits. Theat could function as an effective, low cost adjunct to enhance the identification of these deficits and guide the placement of injectables. Level of Evidence: This study constitutes a prospective, single arm diagnostic comparison in which each subject served as their own control (paired, within subject design), without a comparison group, randomization, or an independent reference standard. Under the levels-of-evidence framework for risk/prognostic and diagnostic studies used in facial plastic and aesthetic surgery, this corresponds to Level IV evidence.