Utility
Why Test Tears
In 1899, Schirmer began using paper strips, along with stains developed in 1888, to assess dry eye. This technology indicated how much water was available, and indicated if water drops (like saline) could provide benefits. In the Twentieth century, doctors and scientists have determined that dry eye is more complicated than water. The preocular tear film contains very important biochemical disease markers.
Protein sufficient tears are critical to good eye health Since they provide the same functions for the cornea that blood provides for the body, and because there are no blood vessels in the cornea, the tears must deliver:
1) all the nutrition for corneal metabolism,
2) all the local infection protection,
3) all the oxygen for epithelial respiration, and
4) all the growth and repair chemicals to keep your eye healthy.
It is well known that both the primary and auxiliary lacrimal glands are lined with acinar secretory cells. These cells generate all the locally secreted biochemicals necessary for:
1) hydration: water, dissolved oxygen, electrolytes, etc.,
2) infection protection: lysozyme, lactoferrin, s-IgA, etc.,
3) wound healing: Epidennal Growth Factor (EGF), TGF-b, etc,
4) nutrition: proteins, sugars, enzymes, etc.,
5) anti-inflammatories, lactoferrin, etc.
Studies have shown that locally secreted proteins, lactoferrin, lysozyme, tear albumin, and s-IgA, maintain the same concentrations in both basal and reflex tears. However, like serum, tear biochemicals change when ocular problems occur. The quantity of these changes is frequently related to the severity of the problem.
Secretory function can be decreased by lack of neurologic response (decrease in on I off signal), (acute) inflammation, lacrimal degeneration, Sjogren’s, suppression by medications, and other causes (see: NEI Dry Eye Report). Lactoferrin (LFN) is an ideal marker for assessing epithehial acinar cell secretory functionality.
Inununoglobulin E (IgE) from the conjunctival plasma cells is the primary responder in allergic Type 1
(anaphylactic) inflaniniation. These allergic responses can be cumulative, thus elevating a subacute response to
an acute response. Thus having a quantitative IgE test is essential to managing the acute or sub-acute
(potential) inflammatory rcsponse.
Bilateral Responses:
Most doctors test both eyes to obtain additional insight to differentiate local responses from systemic responses.
- Aqueous Deficient dry eye systemic responses include Sjogren’s Syndrome, diabetes, arthritis, and suppression by concomitant medications, etc. Common local responses include: neurologic, inflammation, unilateral degeneration, etc.
- Allergic systemic responses include vernal and other anaphylactic conditions. Bilateral elevation of IgE may suggest the patient should be referred to an allergist for further treatment. Common local responses include GPC, SAC, mild allergic, etc.
Now 100 years later, new, accurate technology permits eye doctors to have biochemical data, just like the general practitioner has serum data. The Touch Tear MicroAssay SystemTM is an inexpensive, (cost = 25% of reimbursement) quick test requiring only 0.5 uL (1/100t of a drop) of patient sample.
It is fully reimbursed by Medicare and most insurance companies. Thus this useful data not only pays for itself, but if you see 3 dry eye or inflammation patients per week, it is also a net contributor to the practice.