Micro Aberration Scatter Index (MASI) as an objective proxy for contrast sensitivity after keratorefractive surgery: a prospective observational study

PURPOSE: To evaluate the Micro Aberration Scatter Index (MASI) as an objective proxy for visual quality after keratorefractive surgery. METHODS: This prospective study included 200 eyes from 200 patients who underwent uneventful KLEx, PRK, or LASIK. Monocular testing was performed 30 days postoperatively. MASI was derived from pyramidal wavefront aberrometry (OSIRIS-T, CSO). Contrast sensitivity was measured at 3, 6, 12, and 18 cycles per degree (cpd) under photopic conditions using sine-wave grating charts. Uncorrected distance visual acuity (UDVA) was recorded in logMAR. Correlation, regression, and tertile subgroup analyses were performed. RESULTS: MASI values ranged from 13.1 to 79.5 (mean 34.0 ± 13.3). MASI showed significant inverse correlations with contrast sensitivity at all spatial frequencies (r = - 0.46 to - 0.62; all p < 0.001). Strongest relationship was at 18 cpd (r = - 0.62, R²=0.39). Linear regression showed each 10-point increase in MASI predicted a 0.18 unit decrease in contrast sensitivity at 18 cpd. MASI tertiles corresponded with differences in contrast sensitivity and uncorrected acuity. Stratification by MASI tertile revealed significant differences in visual performance: low MASI (mean 21 ± 4) had 18 cpd contrast sensitivity of1.30 ± 0.24 and mean UDVA of - 0.12 ± 0.09 logMAR; mid MASI (mean 31 ± 4) had 18 cpd contrast sensitivity of1.21 ± 0.31 and mean UDVA of - 0.13 ± 0.07 logMAR; high MASI (49 ± 9) had 18 cpd contrast sensitivity of0.86 ± 0.40 and UDVA of - 0.05 ± 0.14 logMAR (both p < 0.001). CONCLUSIONS: MASI shows early promise as a fast and clinically feasible index of optical quality. Within a single device and operator it correlated strongly with functional vision and distinguished subtle visual degradation not captured by high-contrast acuity alone. Because MASI is computed over the central 3 mm zone, its application to mesopic and night-vision symptoms should be regarded as hypothesis-generating, and inter-device, inter-operator, and multicenter reproducibility remain to be established.