Evaluation of Toluidine blue (TB) 1% vital stain accuracy in diagnosing ocular surface squamous neoplasia (OSSN) compared to impression cytology.

: In a prospective study on ocular surface lesions, 1% TB staining was performed followed by impression cytology (IC). The positivity of TB staining in terms of distribution (diffuse, scatter and patchy), intensity (dark blue, light blue and mix) and the pattern of dye uptake by the lesion (stipple versus homogenous) were compared with the IC results regarding the presence of cellular atypia. Then the sensitivity, specificity and predictive values of TB staining were calculated.

88 eyes from 82 patients were enrolled. IC results demonstrated cellular atypia in 50 (56.8%) cases. Out of 45 (51.1%) TB positive cases, 43 (86.0%) had cellular atypia on IC (p˂ 0.001). Sensitivity and specificity of TB in identifying OSSN were 86% and 94.74%, respectively with the positive and negative predictive values of 95.56% and 83.72%. TB staining distribution was diffuse in 28 (45.9%), patchy in 29 (47.5%) and scattered in 4 (6.6%) cases. There was no correlation between color distribution and presence of atypia in IC (p=0.14). TB staining intensity was light blue in 21 (23.9%), dark blue in 24 (27.3%) and mixed in 15 (17.0%) cases. TB staining pattern showed 51 (82.3%) stippling and 11 (17.7%) homogenous dye uptakes. Dark blue or mixed staining and the stippled patterns were strongly correlated with dysplastic changes in IC (p˂0.001).

TB vital dye has a high sensitivity and specificity for diagnosing OSSN, especially when a dark blue or mixed intensity and a stippled pattern of staining are observed.