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Many factors contribute to definition of dry eye disease
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Dry eye disease, or DED, is a common disorder among Asians. The reported prevalence of DED or severe dry eye symptoms among adults in various Asian population-based studies ranges from 7.7% up to 33.7%. The large variation in prevalence rates is due to the lack of a well-defined, concise and widely accepted definition of DED.
In 2007, DED was defined by the International Dry Eye WorkShop as “a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance and tear file instability. It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface.” Since then, a myriad of diagnostic and treatment options have been introduced targeting the hyperosmolar and inflammatory components of the disease. However, there is a lack of common consensus on the best diagnostic and treatment options for daily clinical practice. The complexity behind this seemingly simple eye problem has yet to be resolved.
To further complicate matters, there is lack of correlation between signs and symptoms, leading to the implication of the role of corneal nerves; in addition, primary aqueous-deficient DED rarely exists alone. DED and meibomian gland dysfunction (MGD) often co-exist, and the pathophysiological mechanisms of DED and MGD have been described as interacting in a double vicious cycle.
In 2011, the International Workshop on Meibomian Gland Dysfunction defined MGD as “a chronic, diffuse abnormality of the meibomian glands, commonly characterized by terminal duct obstruction and/or qualitative/quantitative changes in the glandular secretion. It may result in alteration of the tear film, symptoms of eye irritation, clinically apparent inflammation, and ocular surface disease.” Thus, dry eye becomes an interplay of various entwining matrices of interactions among environmental, age-related, hormonal and immune factors; among lacrimal glands, eyelids and ocular surfaces; among tear film stability, evaporation and osmolarity; among qualitative and quantitative alterations in aqueous and various meibomian secretions; and among inflammation and proliferation of bacterial flora and Demodex. Because DED is such a common condition that is encountered day-in and day-out in all ophthalmic practices, an evidence-based while cost-effective guide for the diagnosis and treatment of DED and MGD is desperately needed.
Another area that is more debatable in recent years is the choice of refractive surgery for patients with DED. It is well known that DED contact lens-intolerant patients are at risk of troubling dry eye symptoms after LASIK. Therefore, small incision lenticule extraction (SMILE) has been proposed to replace LASIK for correction of refractive error with an aim to reduce postoperative DED. A recent meta-analysis showed that SMILE resulted in longer tear breakup time and better ocular surface disease index scores than LASIK at 6 months postoperatively. Another meta-analysis showed that the LASIK group developed more severe dry eye symptoms than the SMILE group. Whether these benefits to post-refractive surgery DED can be sustained in the long term requires further evaluation.
References:
Baudouin C, et al. Br J Ophthalmol. 2016;doi:10.1136/bjophthalmol-2015-307415.
Lam DK, et al. Hong Kong J Ophthalmol. 2011;15(2):58-62.
Lin PY, et al. Ophthalmology. 2003;doi:10.1016/S0161-6420(03)00262-8.
Nichols KK, et al. Invest Ophthalmol Vis Sci. 2011;doi:10.1167/iovs.10-6997a.
The definition and classification of dry eye disease: report of the Definition and Classification Subcommittee of the International Dry Eye WorkShop (2007). Ocul Surf. 2007;doi:10.1016/S1542-0124(12)70081-2.
For more information:
Dennis S.C. Lam, MD, FRCOphth, can be reached at State Key Laboratory in Ophthalmology, Sun Yat-Yen University, 54 South Xianlie Road, Guangzhou 510060, People’s Republic of China; email: dennislam.gm@gmail.com.
Disclosure: The authors report no relevant financial disclosures.