The oil layer
Meibum from the eyelid glands spreads over the tears with each blink into a layer nanometers thick. It greatly slows evaporation and gives the tear surface a smooth optical finish. Meibomian gland dysfunction thins or removes it, and the tears evaporate in seconds. This is the layer that fails in most dry eye, and it is restored by treating the glands rather than by adding drops.
The water layer
The lacrimal gland, above the outer corner of the eye, produces the watery bulk of the tears continuously, with reflex surges in response to irritation. It carries oxygen, salts, proteins and antimicrobial factors to the cornea. Production falls with age, with Sjogren's syndrome and other autoimmune conditions, with some medications and after some surgeries. Low production is aqueous deficient dry eye, measured by Schirmer testing, and it is treated with lubricants, punctal plugs to retain what is made, anti-inflammatories to protect the gland, and serum tears in severe cases.
The mucin layer
Goblet cells in the conjunctiva secrete mucins that coat the cornea and let the watery tears spread over it evenly instead of beading up. Chronic inflammation, vitamin A deficiency, chemical injury and some conjunctival diseases reduce goblet cells, and the tear film then breaks up in patches however much tear there is. Treating the inflammation and the surface restores wettability over time.
How dysfunction is measured
Tear break-up time shows overall stability. Interferometry measures the oil layer's thickness. Meibography shows the glands that make it. Schirmer testing and meniscus height measure the water layer. Surface staining with dyes shows where wetting has failed. Osmolarity and MMP-9 testing show the concentration and inflammation that result. The dry eye evaluation runs these together to say which layer, or layers, need treatment.
Why the tear film matters for vision
The tear film is the first optical surface light meets, and together with the cornea beneath it, it forms the eye's most powerful focusing surface. When it is unstable, vision blurs and clears with each blink. An unstable film also distorts the measurements that laser and lens surgery depend on, which is why the film is stabilized before those procedures.
Is this right for your eyes?
Nothing on this page is a diagnosis. Whether this is what is affecting your vision is decided by a full examination at one of our 4 offices: Pasadena, Huntington Beach, Woodland Hills and Beverly Hills.
About this content: This page was written with the assistance of AI tools and reviewed for medical accuracy by Dr. Bavand Youssefzadeh, DO. It is general information, not medical advice, and does not replace an eye examination. Individual results vary. Read our medical disclaimer.
