Abstract
Purpose :
The clinically minimally important difference (MID) has not been defined for the commonly used 9-point ocular itching scale (0 – 4 with half-unit increments). Based on results from an allergic conjunctivitis (AC) field trial evaluating topical reproxolap compared to vehicle, the ocular itch score MID was calculated using a quality of life anchor-based approach and distributional statistics.
Methods :
In a double-masked, multi-center field trial, 60 patients with AC were randomized 1:1:1 to receive topical ocular solutions of either 0.25% reproxalap, 0.5% reproxalap, or vehicle four-times daily for one month during allergy season. Ocular itching scores (Ora Calibra™, 0-4 scale) were compared to the Allergic Conjunctivitis Quality of Life Questionnaire (ACQLQ), comprised of 15 sub-scales (0-6) to quantify how bothersome symptoms and signs are across a variety of parameters. Assessments were obtained at baseline (Day 2) and at the end of the trial (Day 28). Average MID across all sub-scales was calculated by subtracting improvement in itching score for subjects that did not improve on the bother scale from improvement in itch score for subjects that improved on the bother scale by one point (mean difference method). Baseline standard deviation (SD) and standard error of measurement (SEM) were used to confirm the anchor-based findings.
Results :
The MID was calculated to be 0.42 (95% CI 0.21, 0.64). Half of the baseline SD was 0.43, and the SEM was 0.48. The correlation of itch bother to ocular itch score was statistically significant (p<0.0001), with an r value of 0.8.
Conclusions :
Clinically meaningful change in the ocular itching scale was determined to be between 0.42 and 0.48 units, approximately the smallest unit of the itch score scale. The results provide clinically relevant context for the interpretation of AC clinical trials using the 9-point itching scale.
This is a 2021 ARVO Annual Meeting abstract.