To demonstrate how the likelihood of making a correct diagnosis of dry eye disease varies according to the clinical test methods used.
The probability of a person having dry eye, given that they return a positive test, was calculated for a range of standard tests, using the Bayes-Price rule. Global specificity and sensitivity values for each test were estimated by employing the Beta distribution to combine all relevant data obtained from a literature review.
At an assumed prevalence of 11.6%, the single test with the highest probability of a correct diagnosis was corneal staining (probability = 0.28) and the lowest was the ocular surface disease index – OSDI (0.14). The best combination of symptoms with a single test of tear film homeostasis was the 5-item dry eye questionnaire (DEQ-5) + corneal staining (0.42) while OSDI + tear film break up time (TBUT) was the worst (0.23). The simultaneous observation of conjunctival and corneal staining was associated with a probability of 0.49. The probability of a correct diagnosis increased with the number of positive tests, up to a maximum of 0.90 when all of DEQ-5, conjunctival and corneal staining, osmolarity and TBUT were positive.
A significant risk of misdiagnosis is associated with using any single test for dry eye disease, or the minimum TFOS DEWS II criterion of symptoms plus any single test of tear film homeostasis. To minimize this risk, the maximum number of tests available should be performed and the results used to inform diagnosis. The simultaneous occurrence of conjunctival and corneal staining should be considered a key outcome and be specified in future guidelines.

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