Concordance between common dry eye diagnostic tests

Abstract

Aim: Large variations in results of diagnostic tests for mild to moderate dry eye are widely recognised. The purpose of this study was to assess if there was concordance between common dry eye diagnostic tests.

Methods: A total of 91 subjects were recruited to the study. The tear film and ocular surface were evaluated using the phenol red thread test (PRT), tear film break-up time (TBUT), biomicroscopic examination and impression cytological assessment of conjunctival goblet cells. Dry eye symptoms were assessed using McMonnies' dry eye questionnaire (MQ) and statistical correlations between all tests were assessed.

Results: This study cohort did not include severe aqueous deficient dry eye patients as determined by the PRT. A statistically significant difference was noted between PRT results and all other tests (p<or=0.001). Only Meibomian gland pathology, MQ, reduced goblet cell density and TBUT (<or=7 s) demonstrated correlation determined by McNemar's test.

Conclusion: A correlation was found only between tests assessing lipid/mucous deficiency (Meibomian gland evaluation, goblet cell density, TBUT and MQ).

Figure 1. PRT wetting data for all subjects tested

Fig. 1 represents the mean PRT data of both eyes for all subjects assessed (n=78). The overall mean PRT wetting length for the entire group was 23.5 ± 9 mm (range 2.5 to 40 mm) with the most common value being 32.5 mm. No subject was found to have a thread wetting length of ≤10 mm or below in both eyes.

Figure 2. Photomicrographs of representative impression cytology specimens stained with PAS

Photomicrographs of representative impression cytology specimens stained with PAS. Cells obtained from impression cytology sampling were stained directly on the nitrocellulose filter paper and photographed. A is a representative of a Grade 2 demonstrating a normal cytological picture with a high number of goblet cells present (indicated by arrows) (mag. × 200). B is representative of a normal cytological specimen post PAS staining: the presence of goblet cells embedded in the epithelial sheet represented by the pink colour against conjunctival epithelia, counterstained purple with haematoxylin with round shaped epithelial cells with dense staining round nuclei and abundant goblet cells stained bright pink (mag × 400). C is a representative of early loss of goblet cells in a subject with mild dry eye. A reduced number of goblet cells were visible post PAS staining (mag × 200). D represents a mild blepharitis with a high density of goblet cell secretions with snake-like strands of mucous secretions often associated with MGD (as indicated by the arrows) (mag × 200). E represents moderate-severe dry eye with distinct squamous metaplasia of the conjunctival epithelium and complete absence of goblet cells (mag × 400). F represents moderate-advanced squamous metaplasia from a subject with dry eye and ocular surface inflammation. The absence of goblet cells can also be noted (mag×200).