To characterize ocular surface features of patients with an unstable tear film caused primarily by a lipid tear abnormality resulting from noninflamed meibomian gland dysfunction.

Retrospective clinical data and results from rose bengal staining, modified meibography, and impression cytology were reviewed in 78 patients (142 eyes), all of whom had normal tear secretion and clearance verified by the fluorescein clearance test but an unstable tear film evidenced by tear breakup time ± SD of 3.4 ± 2.1 seconds (normal, <8 seconds).

Of 201 symptoms, 147 (73%) were presumably caused by an unstable tear film, 46 (23%) resulted from inflammation, and none were diurnally worsened. All patients had meibomian gland dysfunction characterized by poor or no meibum expression, orifice squamous metaplasia, or acinar atrophy. Rose bengal staining was negative in 95 eyes (67%), positive on nonexposure zones in 30 eyes (21%), and positive on exposure zones in 17 eyes (12%). Among 90 eyes receiving impression cytology, six (7%) were normal, 49 (54%) had pure “lytic” changes characterized by disrupted cell-cell junctions of normal small cells in the nonexposure zone, three (3%) had pure squamous metaplasia without mucous aggregates, two (2%) had squamous metaplasia with mucous aggregates (the latter being a frequent finding of aqueous tear deficiency), and 31 (34%) were mixed with lytic changes and squamous metaplasia.

Preferential distribution of rose bengal staining in the nonexposure zone and lytic cytologic changes without squamous metaplasia characterize lipid tear deficiency and help to differentiate it from aqueous tear deficiency in patients with an unstable tear film.