Tear film analysis and evaluation of optical quality: A review of the literature

Summary Dry eyeis a complex multifactorial disease of the ocular surface and tears. It is associated with ocular surface symptoms and is one of the most common causes for ophthalmologic consultation. Despite their frequent use in clinical practice, the usual tests to evaluate dry eyeand ocular surface disease–history of symptoms, tearbreak-up time (TBUT), Meibomian glandevaluation, corneal fluorescein staining, Schirmer test–have shown low reproducibility and reliability. In addition, subjective symptoms are often weakly or poorly correlated with objective signs. Since the tearfilm is the first system through which light must pass, the optical quality of the eye is highly dependent on the homogeneity of the tearfilm. Various investigative methods have been developed to evaluate both the structural and functional quality of the tearfilm, such as corneal topography, interferometry, tearmeniscus measurement, evaporation rate, tearosmolarity and even aberrometry. Some are easily accessible to clinicians, while others remain in the field of clinical research. All of these tests provide a better understanding of the pathophysiology of the tearfilm. This review hopes to provide an overview of the existing tests and their role in evaluating the significance of the tearfilm in visual function.