Dry Eye Diagnostics Guide
Tear Osmolarity Testing with ScoutPro
If you have dry eye or ongoing eye irritation, a tear osmolarity test gives your doctor an objective number that helps explain your symptoms and guide treatment. ScoutPro is a quick, in-office osmolarity test, and it is one of the most useful first steps in understanding the health of your eye surface.
Key Takeaways
- Tear osmolarity measures how much salt is in your tears, reported in milliosmoles per liter (mOsm/L).
- A high salt level, called hyperosmolarity, can irritate and damage the surface of the eye and drive dry eye symptoms.
- Results are generally normal below 308 mOsm/L, with less than 8 difference between your two eyes.
- Osmolarity gives an objective number, which is useful because symptoms do not always match how severe dry eye is.
- Tracking it over time helps your doctor see how your eyes respond to treatment, similar to following cholesterol or blood sugar.
- It is especially valuable before cataract or LASIK surgery, since a healthy eye surface supports better measurements and outcomes.
- ScoutPro is a handheld system that gives an osmolarity result in seconds from a tiny tear sample.
Quick Answer: Why should I get a tear osmolarity test?
A tear osmolarity test measures the salt concentration in your tears and helps your doctor confirm dry eye, gauge how severe it is, and track whether treatment is working. It is quick, done in the office, and especially important if you have ongoing irritation or are preparing for cataract or refractive surgery. ScoutPro provides this measurement from a very small tear sample within seconds.
What Is Tear Osmolarity?
Tear osmolarity is a measure of how much salt is dissolved in your tears. A healthy tear film has a balanced salt level. When tears evaporate too quickly or you do not make enough of them, the salt becomes more concentrated. That concentrated, salty state is called hyperosmolarity, and it is hard on the delicate surface of the eye.
Over time, an overly salty tear film can damage the cells on the cornea, the clear front window of the eye, and trigger inflammation. This is one of the core drivers of dry eye, and it can cause dryness, a gritty or foreign-body feeling, blurry or fluctuating vision, and general irritation.
Source: Patient Guide to Tear Osmolarity Testing (Bausch + Lomb, 2025) and the tear osmolarity literature, including the TFOS DEWS II Report (2017).
Normal vs Abnormal Results
Osmolarity is measured in milliosmoles per liter (mOsm/L). Both eyes are tested, because the difference between them also matters.
| Result | Reading | What It Suggests |
|---|---|---|
| Normal | Below 308 mOsm/L, and less than 8 difference between the two eyes | The salt level is generally not high enough to damage the cornea or cause inflammation. |
| Abnormal | Above 308 mOsm/L, or more than 8 difference between the two eyes | A higher or less stable salt level (hyperosmolarity) that can irritate and damage the eye surface. |
If your osmolarity is normal but you still have symptoms, it is worth looking at other causes such as allergies, eyelid problems like blepharitis, or infection. A normal number does not rule out every cause of discomfort, which is why the full picture matters.
Why Osmolarity Matters for Dry Eye
Dry eye can be tricky to pin down, because how your eyes feel does not always match how severe the problem is. Some people have strong symptoms with mild findings, and others have surface damage with few complaints. Osmolarity gives your doctor an objective number to work from instead of relying on symptoms alone.
Just as important, that number can be tracked over time. Repeating the test lets your doctor see whether a treatment is actually lowering your osmolarity and improving the health of your eye surface, much like following cholesterol or blood sugar to judge how a plan is working.
What Is ScoutPro?
ScoutPro is a handheld tear osmolarity system from Bausch + Lomb. Your eye doctor uses it to collect a very small tear sample, about 50 nanoliters, which is small enough to test even very dry eyes. The pen reads the salt concentration and shows a result in mOsm/L within seconds, so you and your doctor can discuss it during the same visit.
Seconds
Fast In-Office Result
The measurement appears on the handheld pen within seconds of collecting the sample.
50 nL
Tiny Tear Sample
It needs only about 50 nanoliters of tears, so it works even on very dry eyes.
2 Eyes
Objective & Trackable
Both eyes are tested for an objective number your doctor can follow over time.
Why It Matters Before Eye Surgery
A healthy eye surface is not just about comfort. Before cataract or refractive surgery such as LASIK, the surface of your eye affects the measurements used to plan the procedure and choose a lens. If the tear film is unstable, those measurements can be less reliable, which can affect the result.
That is why many surgeons check the ocular surface before surgery. Research has found that a large share of patients heading into cataract surgery have ocular surface issues, often without obvious symptoms, and that an unhealthy, hyperosmolar tear film is linked to less predictable outcomes. Identifying and treating this ahead of time helps set up the best possible result.
Based on published cataract surgery research and ASCRS preoperative ocular surface guidance.
Who Should Consider Osmolarity Testing?
Tear osmolarity testing can help in many situations. It is worth asking your eye doctor about if any of the following apply to you.
- Ongoing dry, gritty, burning, or irritated eyes
- Blurry or fluctuating vision that comes and goes
- Watery eyes that feel dry, a common sign of an unstable tear film
- Contact lens discomfort that is getting worse
- Dry eye that is not improving with drops or other treatment
- Preparing for cataract or refractive surgery such as LASIK
- Following an existing dry eye treatment plan to see if it is working
What to Expect During the Test
Osmolarity testing is quick and comfortable, with no needles and no dilation required for the test itself.
- Your eye doctor or technician gently touches a small tip to the edge of your lower eyelid to collect a tiny tear sample.
- The sample is very small, about 50 nanoliters, so it works even if your eyes feel dry.
- Both eyes are tested, since the difference between them is part of the result.
- The ScoutPro pen reads the salt concentration and shows a number in mOsm/L within seconds.
- Your doctor reviews the result with you and explains what it means for your treatment plan.
Dry Eye Rescue Tip
Ask whether your eye doctor offers tear osmolarity testing, especially if your dry eye is not improving or you are planning surgery. An objective number at your first visit, and again later, makes it much easier to see whether your treatment is truly working.
Find a Doctor Who Offers Osmolarity Testing
Use the Dry Eye Rescue Doctor Locator to find an eye doctor near you who can evaluate your dry eye and check your tear osmolarity. You can also take the DryEye Q assessment to prepare for your visit.
Disclaimer
This page is for educational purposes only and does not replace medical advice or an eye exam. Tear osmolarity testing is performed by a licensed eye care professional. ScoutPro and Bausch + Lomb are trademarks of Bausch + Lomb Incorporated. For official product information, visit getscoutpro.com.
Frequently Asked Questions
What is tear osmolarity?
Tear osmolarity is a measure of how much salt is in your tears, reported in milliosmoles per liter (mOsm/L). A high level, called hyperosmolarity, can irritate and damage the surface of the eye and is a key part of dry eye.
What is a normal tear osmolarity result?
Results are generally considered normal below 308 mOsm/L, with a difference of less than 8 between your two eyes. Higher readings, or a larger gap between the eyes, are considered abnormal.
Why should I get a tear osmolarity test?
It gives your doctor an objective number to confirm dry eye, judge how severe it is, and track whether treatment is working. Symptoms alone do not always reflect how severe dry eye really is, so the test adds important information.
What is ScoutPro?
ScoutPro is a handheld tear osmolarity system from Bausch + Lomb. Your eye doctor uses it to measure osmolarity from a very small tear sample, about 50 nanoliters, and it shows a result in mOsm/L within seconds.
Does the test hurt?
No. The test is quick and comfortable. A small tip gently collects a tiny tear sample from the edge of the lower eyelid, with no needles involved.
Why is osmolarity testing done before cataract or LASIK surgery?
A healthy eye surface supports more reliable measurements used to plan surgery. An unstable, hyperosmolar tear film is linked to less predictable results, so checking and treating it beforehand helps set up the best outcome.
My osmolarity is normal but my eyes still bother me. Why?
A normal osmolarity does not rule out every cause of discomfort. Allergies, eyelid conditions like blepharitis, and infections can also cause symptoms. Your eye doctor can help find the underlying cause.
Where can I get a tear osmolarity test?
Use the Dry Eye Rescue Doctor Locator at locator.dryeyerescue.com to find an eye doctor near you who can evaluate your dry eye and check your tear osmolarity.
Get a Clear Picture of Your Dry Eye
A tear osmolarity test gives you and your doctor an objective starting point. Find a provider who offers osmolarity testing, then build a treatment plan you can actually track.
