الفهرس 
? Anatomy and Physiology of the Tear FilmOnly 14 pages are availabe for public view
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Abstract
The tear film overlays the ocular surface and provides the interface between the eye and the external environment. The tear film is essential for the nutrition and protection of the ocular surface and for clear vision as the tear film is the first refractive surface of the eye.
Dry eye is a disorder of the tear film which occurs due to tear deficiency or excessive tear evaporation. Dry eye is a common condition reported by patients who seek ophthalmologic care. Dry eye is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance and tears film instability, with potential damage to the ocular surface. It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface.
Cigarette smoke is an essential source of intake of heavy metals and toxic elements. These toxic compounds have multiple adverse physiologic effects with profound pathological disturbances in different organs, including the eye. Epidemiological data link cigarette smoking as a risk factor for many ophthalmological disorders including age related macular degeneration, cataract, thyroid ophthalmopathy, conjunctival intraepithelial neoplasia, and development of dry eyes.
300 Egyptian subjects living in Cairo who attended the Ophthalmology Department of Ain Shams University Hospital were enrolled in the study. Two study groups were established: group #1 = 150 current smokers, group #2 = 150 non-smokers. All subjects were between 30 – 50 years old. Subjects were excluded if they had an active ocular surface disease. Full ophthalmological examination was performed together with Schirmer test and TBUT test to all the cases.