What do dry eye tests mean? (Part 7) Tear Volume (and how we measure it).
Probably the simplest test I do every day is – for me – one of the most important tests I consider in every dry eye evaluation. It has been around for over a century and involves a numbing drop and a tiny piece of filter paper placed along the edge of the eyelid for 5 minutes. It is called the Schirmer’s test and the reason I find it so useful is because it gives a reasonably accurate idea of the output of the “sprinkler system.” This helps to rapidly breakdown the source of dry eyes from one of two common pathways (that often intersect).
Simplistically, we can look at dry eye from the standpoint of tear quantity and tear quality. It can become very complicated when we look at what that means – but as dry eye doctors, we assess “Aqueous Tear Deficiency” or ATD and “Meibomian Gland Dysfunction” or MGD. ATD means not enough water and MGD means not enough (or not good enough) oil. This is important as treatments for one, generally are very different from the other. Since many patients have a degree of both, for simplicity’s sake, we might focus on the one that is the greater when the patient wants a stepwise approach (I like to advise tackling both simultaneously when clinically indicated and the patient is willing).
I have explained much of this in my earlier posts, and I always recommend that beginners go to the beginning of these posts to get updated. For regulars – or those in a hurry – I’ll point out that the “sprinklers” make the “good tears,” rich in water, salt, proteins, and oil (the “salad dressing”). The “emergency backup system” or “fire hose,” makes the salty tear water that floods the eye if it gets too dry, otherwise irritated, infected, damaged or if we emotionally cry. Numbing the eye helps to “turn off” this firehose reflex and allows the “sprinklers” a chance to do their job for the 5 quiet minutes we soak up that “salad dressing” tear.
Since most of this “good tear” (the “salad dressing” or “clear blood-like product”) is made of water, we can consider this the “Aqueous Tear” and too little leads to ATD. Fixing this nearly always involves drinking more water (to be fully hydrated). The obvious flip side is to also avoid too much “anti-water” (anything that encourages excess peeing – like caffeine, alcohol and many medications like antihistamines for allergies and sleep aides, decongestants for sinus congestion and cold pills, “water pills” for swelling and high blood pressure (check with your doctor prescribing these medicines to see if there are alternatives that would be safe for your health issues) – and the list goes on and on (bladder control pills, some mental health pills, high blood sugars as in less controlled diabetes, etc. etc.). After achieving a good water balance, the next step is reducing inflammation, as inflammation is particularly hard on the water producing cells involved with the Aqueous Tear production.
The number I like to see on this test is 15 millimeters or more – though patients under 30 years of age will often make 30mm or more, and the normal production levels tend to fall as we age. PRETTY MUCH EVERYONE SHOULD MAKE 10MMs OR MORE. This is because it takes about this much just to reasonably cover the surface of the eye (though more “open” eyes may need more - and less open eyes may get by with less). This helps understand how patients with excessively open eyes (like in Thyroid Eye Disease, or after “too good” a lid lift operation) can suffer even with “normal” tear amounts, as well as explaining why patients with droopy lids may tolerate relatively poor tear volume (and why a treatment for severely dry eyes can be the lateral tarsorrhaphy, where we surgically, partially close an eye for reducing exposure as added protection of the cornea). Punctal plugs may sometimes become indicated in this group (see my earlier posts on damming up the tears).
A common pitfall of this test is that it does require a careful attention to details to get a valid “number.” This involves making the surface sufficiently “numb,” (often harder to do when the surface has become overly sensitive from chronic dry eye damage and may require multiple drops), to turn off the “firehose” tear system. Then it is key to appropriately “dry” the gutter in the lower lid, to remove excess moisture (from the numbing drops and any patient-produced tears, so we can start from ground zero to measure only freshly made “sprinkler system” tears). Turning the room lights down also helps avoid glare-related reflex tearing and is better done early in this process. I start the “stopwatch” the moment I’ve finished drying this “gutter” (usually with a sterile QTip rolled gently along the floor of that “gutter”) and I’ve prepared the strips for placement at the start of the preparation for the test – so they are ready to go. A “Pro Tip” I learned, is to fold the outside edge of the strip for the right eye, so once placed and subsequently removed, it is easy to see which eye produced what result. Placement of the strips is along the outer (ear-side) edge of the lids so that the cornea is not directly impacted by these drying papers (avoiding extra stimulation of the firehose, as well as avoiding even minor damage to the cells on the cornea).
When the number is 6mm or less, it is sometimes not possible to effectively turn off the fire hose, as that has become the primary tear when the sprinklers are unable to produce enough tears. This is because the surface of the eye must stay moist to survive – when cells get dry, they die and drop off, exposing the underlying nerves and causing the pain these patients experience routinely. This is another “Achilles Heel” of the test – since we may get high numbers when we expect lower ones – but this can be inferred from other markers (like surface staining, tear salt levels and the microscopic evaluation of the tear layer along the lower lid if there is not too much conjunctivochalasis or CCH – as the “gasket effect” of that membrane can block the gutter-like reservoir in the lower lid from holding the normal volume of better tears and keeps the tear layer artificially high). It is also true that we will usually get similar numbers between the two eyes (unless one eye has had a unique problem, such as a single-eyed infection, injury, or surgery) – so if the two eyes have a similar history, we can usually expect a similar result on the test. When one is “abnormally high” when the other is “abnormally low” then it generally implies the higher one is artificially elevated by reflex tearing, and we go more by the lower one.
When the number is 10 or more (and we think this is a true reading), then we focus on the oil issues. Those patients should still stay well hydrated, since water levels can be quick to vary - and adding low volume to an otherwise poor tear oil is a recipe for ocular surface disasters. Making more and better oil generally requires eating good oil, doing good blinks, keeping that oil free flowing and keeping germs at bay, that would otherwise eat those oils and pollute those tears with byproducts of their digestion (What I call basic dry eye “Homework.”) Too much “germ poop” in the tears will lead to a vigorous immune response that can damage the tear glands and drive more ATD and MGD.
I’ve posted many times on our best tools for improving oils beyond this simple “Homework” – and this generally includes unclogging the oil (Meibomian) glands – with a heated expression - when the clogging is the typical, waxy plugs acquired early in this MGD disease (called evaporative dry eye). When they have been clogged for “too long” (which appears to vary by patient), there is a tendency to either develop “styes” (chalazia, as in an “acne pimple-like” cyst) or (more commonly) for the glands to silently wither and develop deeper levels of scarring that can “cut off” the glands. Scarring, if partial and mild, appears to respond to Intense Pulsed Light (IPL) and gentle, heated expressions. If the scars are more severe, then they often require probing (small, piano-wire-like tools used to “roto-rooter” the glands open). IPL also appears uniquely suited for stimulating the glands, reducing inflammation (by killing germs, mites and closing dilated blood vessels pouring the body’s “napalm, hand grenades and bazookas” into the tears, as a response to the irritation and damage caused by germ poop and dryness) and warming the glands to help in thinning the oils (though it doesn’t seem to keep the oil hot enough, long enough, to allow optimal expression – so I often advocate for following IPL treatments immediately, with an effective form of heated expressions).
Science is always looking for better tests - and a benchmark, century-old test is ripe for replacement by a “newer tool.” There is a test measuring “Lactoferrin levels” in tears, utilizing a tiny sample of tears, like the salt-level test. Lactoferrin is a common protein found uniquely in these “sprinkler system tears.” Low levels are more common in dry eyes and very low levels may indicate a higher risk of autoimmune dry eye (Sjogren’s being the usual one). It has been compared favorably to the Schirmer’s test and is now commercially available. Being relatively new, it remains to be seen how this will fit into the usual dry eye evaluation and cost remains an issue (the cost of a tiny piece of paper and a numbing drop is negligible and this newer test is not). I’ll keep you posted on this test as I develop some familiarity with it!
To schedule an appointment with Dr. Jaccoma, call Excellent Vision at either of these two dry eye offices:
(1) 155 Griffin Rd, Portsmouth, NH 03801 (603) 574-2020
(2) 3 Woodland Rd, STE 112 Stoneham, MA 02180 (near Boston) (781) 321-6463