Dry eye disease is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance, and tear film instability with potential damage to the ocular surface [1
]. Based on data from the largest epidemiologic studies of dry eye to date, the Women’s Health Study [2
], and other studies [3
], it has been estimated that about 3.23 million American women 50 years and older have dry eye disease [5
]. A recent study estimated the prevalence of definite dry eye disease to be 10.1% in male subjects and 21.5% in female subjects in Japan [6
Among entities causing dry eye disease, Sjogren`s syndrome (SS) is a multifactorial autoimmune disorder, mainly affecting the salivary and lacrimal glands, which is influenced by genetic as well as environmental factors that are not yet completely understood. SS occurs worldwide and in people of all ages. The peak incidence has been reported to be in the fourth and fifth decades of life, with a female-to-male ratio of 9:1 [7
]. The incidence of primary SS reported in the literature varies from less than 1:1,000 to more than 1:100 [8
Dry eye is one of the pivotal events in SS [9
], the diagnosis of which requires an algorithm of multiple tests including Schirmer test, tear film break up time (BUT), and ocular surface evaluation with fluorescein, Rose Bengal, or Lisamine Green staining. The ocular surface dryness in SS has been linked to lacrimal hyposecretion and the accompanying inflammatory reactions of the ocular surface are believed to result in gradual ocular surface epithelial damage [9
]. The study of the conjunctiva at the cellular level by relatively invasive methods such as impression or brush cytology [10
] with incorporation of immunohistochemistry staining or flow cytometry [11
] for inflammatory markers revealed elevated conjunctival inflammation in SS patients. Among them, impression cytology examines the ocular surface epithelium with application of cellulose acetate filter material to the ocular surface to remove the superficial layers of the epithelium. The technique is easy to perform, and can be employed to observe the ocular surface epithelial cell changes over time. Impression cytology has been used for many ocular surface diseases including dry eye, atopic keratoconjunctivitis, ocular pemphigoid, and superior limbic keratoconjunctivitis (SLK) [12
]. Two studies using impression cytology samples by Nelson [16
] and Tseng et al. [17
] reported a grading system for squamous metaplasia based on cell size, N/C ratio, and goblet cell densities. Squamous metaplasia of the conjunctival epithelium has been reported as an integral part of many ocular surface diseases associated with dry eyes [18
]. The change in the extent of squamous metaplasia has been reported to be useful in the evaluation of treatment responses in dry eye syndromes [19
Although impression cytology is effective, safe and almost a non-invasive technique, it has limitations. It can evaluate only the superficial layer of the conjunctival epithelium. It is hard to evaluate the extent of inflammatory cell infiltration under or within the epithelium. It is also possible that there are cells that are not picked up by the cellulose acetate filter.
Confocal microscopy is a new emerging non-invasive technology to evaluate the tissue structure and cell phenotype in vivo, which is useful as a supplementary diagnostic tool for the assessment of the histopathological processes in many ocular surface diseases and anterior-segment disorders including the in vivo examination of the cornea, bulbar and palpebral conjunctiva, and the meibomian glands [23
In this study, we used confocal microscopy and impression cytology to evaluate the squamous metaplasia based on diagnostic parameters including the mean individual epithelial cell area (MIECA) and nucleocytoplasmic (N/C) ratio.
We evaluated and characterized the conjunctival findings in patients with SS using laser scanning confocal microscopy, and then compare the confocal microscopy parameters with the impression cytology findings. We also evaluated whether confocal microscopy examination could be an alternative for impression cytology in the assessment of squamous metaplasia in SS.