Researchers at the Casey Eye Institute in Portland, OR, developed a classification system for blepharitis and dry eye based on a classification-tree model of a large group of subjects who were given a variety of objective physiologic tests.

The study evaluated 513 subjects. Some were healthy and some had blepharitis and dry eye. All were tested for tear volume, tear flow and tear turnover and were given the Schirmer test for dry eye. Investigators evaluated meibomian gland function by meibomian gland lipid expression for lipid volume and used lipid viscosity, evaporation and eyelid transillumination for meibomian gland drop-out. They subjected their data to cluster analysis and formulated a classification tree.

Cluster analysis most successfully grouped subjects by initially dividing them into two groups based on the presence or absence of gland drop-out and then by lipid viscosity and volume, Schirmer test results and evaporation. The analysis created nine categories. This division created an objective classification system that has clinical relevance. Normal subjects were distributed across several groups.

Using the classification tree developed in this study, blepharitis and dry eye can be classified with objective physiologic tests into clinically relevant groups that have common characteristics. The authors of the study believe that analysis establishes the central role of meibomian gland dysfunction in blepharitis and demonstrates the diverse characteristics of the normal population.