PurposeEvaluating anti-scarring therapies require objective assessment of scarring, and knowledge of normal fornix anatomy. Measurement of conjunctival scarring has focused on inferior fornix shortening, although the superior fornix is often overlooked. There are data on normal fornix depth (FD) in South Asians, but there are no studies investigating normal conjunctival FD in white Caucasians. We designed a fornix depth measurer (FDM) for objective measurement of upper and lower conjunctival FD. The purpose of this study was to evaluate intra- and inter-observer variability, and to establish a reference for normal conjunctival FD in an ethnically white Caucasian population.Patients and methodsProspective cross-sectional study evaluating conjunctival FD in 252 clinically normal white Caucasian participants aged 20-80. Paired observers evaluated inter- and intra-observer variability. Data was analyzed using Bland-Altman plots and analysis of variance.ResultsFor white Caucasian subjects, mean upper and lower conjunctival fornix depths were 15.6 mm (95% confidence interval (CI), 12.5-18.8) and 10.9 mm (95% CI, 8.0-13.7), respectively. Females have smaller FDs (upper FD 15.3 mm±1.6 females, 16.2 mm±1.4 males, P<0.001; lower FD 10.6 mm±1.3 females, 11.3 mm±1.4 males, P<0.001). There was a progressive decline in FD with age (upper fornix depth 16.3 mm±1.2 at age 20-29, and 15.0 mm±1.8 at age 80+ (P=0.04)). There was 94-100% intra-observer and inter-observer agreement for upper and lower fornix measurements.ConclusionsUsing a slightly different custom-designed FDM, central conjunctival fornix depth in white Caucasian eyes appears to be similar to data previously reported in South Asian eyes. Fornix depth measurements were repeatable and reproducible.