Definition and Diagnosis
Definition and Diagnosis
In 2016, the Japan Dry Eye Society revised and released its “Definition and Diagnostic Criteria of Dry Eye,” updating the most recent version established in 2006.
In 2016, the Dry Eye Society committee responsible for investigating the dry eye definition and its diagnostic criteria updated the contents, which were originally established in 1995 and revised in 2006. It may be useful to review the chronology of events leading up to the current version, which follows a decade after its predecessor. The 2006 diagnostic criteria depended on the fulfillment of three criteria: (1) tear abnormalities, (2) keratoconjunctival epithelial disorders, and 3) subjective symptoms. However, research over the past 20+ years has demonstrated that even in the absence of keratoconjunctival epithelial disorders, patients with unstable tear film exhibit dry eye with symptoms equal to those of severe aqueous deficient dry eye.
Historically, these patients were described as having “short break-up time (sBUT)-type dry eye,” and were excluded from the 2006 diagnostic criteria. Instead, they were described as having “suspected dry eye,” as they fulfilled two of the diagnostic criteria (tear abnormalities and subjective symptoms). sBUT-type gradually proliferated, as evidenced by epidemiological research such as the Osaka Study. In the international arena, researchers such as Steve Pflugfelder and Scheffer Tseng have pointed to tear film instability as the key determinant in dry eye onset.
In recent years, dry eye has been linked to issues such as depression, post-traumatic syndrome, sleep disorders, unhappiness, and stress disorders. Dry eye accompanying general eye-related malaise was commonly considered a more minor illness than Sjögren’s Syndrome and other severe forms of aqueous deficient dry eye. In actuality, the symptoms suggest that the disease is not minor at all, and we now know that it is also related to sBUT-type dry eye.
Moreover, we also know that dry eye may induce deterioration of visual function and that this mechanism is related to tear film instability. In other words, we have learned that the essential anomaly of dry eye is due more to tear film instability than to lacrimal hyposecretion indicated by Schirmer’s test or keratoconjunctival epithelial disorder determined by vital staining. These developments generated a need to revise the definition and diagnostic criteria pertaining to dry eye.
BUT of 5 seconds or less combined with subjective dry eye symptoms yields a definitive dry eye diagnosis. However, even if subjective dry eye symptoms are present, there can be no definitive diagnosis if Schirmer's test I is less than 5mm and BUT exceeds 5 seconds (a rare situation). Moreover, requirements for a definitive diagnosis also fail without subjective dry eye symptoms. There are currently wide-ranging discussions on dry eye symptoms; as many patients with BUT measuring 5 seconds or less have no subjective symptoms, some dry eye cases include not only tear film instability, but also corneal paresthesia (namely, corneal imperception) and—conversely—the mechanism of corneal hypersensitivity (namely, neuropathic pain). Great strides are expected in these areas in the future. It is notable that the decision to revise the dry eye diagnostic criteria extends past Japan to embrace other Asian nations. As the Asia Dry Eye Society’s diagnostic criteria published in the journal Ocular Surface in 2017 mirrored those of Japan, one might conclude that Asian nations accept Japan’s approach. As tear-film-oriented therapy (TFOT) demonstrates, whether derived from the decreased aqueous layer in tears, the abnormal lipid component in meibomian gland dysfunction (MGD), or membrane-type mucin abnormalities, tear film instability itself is the focal point of dry eye cases, and treatment should be directed toward the ocular surface component deficiency which induces tear film instability. In recent years, the classification of tear film breakup patterns established by Dr. Norihiko Yokoi of the Kyoto Prefectural University of Medicine has allowed us to differentiate dry eye subtypes, enabling major advancements in diagnosis and treatment.
The primary mechanism of dry eye lies in tear film instability. The ocular surface is comprised of the tear film and the surface epithelium, and when an abnormality occurs on the tear film layers and/or the surface epithelium, tear film stability deteriorates. TFOD (tear-film-oriented diagnosis) detects ocular surface component deficiencies which cause tear film stability deterioration and can suggest a dry eye treatment which maximizes tear film stability through component replenishment.
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