Technology overview

This briefing describes the regulated use of the technology for the indication specified, in the setting described, and with any other specific equipment referred to. It is the responsibility of healthcare professionals to check the regulatory status of any intended use of the technology in other indications and settings.

About the technology

CE marking

The TearLab osmolarity system is CE marked as an In Vitro Diagnostic Device (Class IIa). The CE mark was obtained in October 2008 and is held by the manufacturer, TearLab Corporation (USA).


The TearLab osmolarity system is a diagnostic device, which is used at the point of care to measure the osmolarity of human tears and help diagnose DED. The manufacturer also states that TearLab may be used to aid monitoring of treatment.

The TearLab osmolarity system consists of 3 components:

  • TearLab osmolarity system reader unit

  • TearLab osmolarity system pen

  • TearLab osmolarity test card with microchip, which is clipped into the top of the pen.

The system reader is a countertop unit that calculates and displays the osmolarity test result. It is powered by mains (230 V) supply and contains a liquid crystal display (LCD) screen, a simple key pad for operating the system, and docking ports to store system pens. System pens are powered by a rechargeable battery.

The single‑use polycarbonate microchip in the test card has a micro‑fluid channel that collects the tear fluid by passive capillary action. Gold electrodes, which allow measurement of tear osmolarity by electrical impedance, are embedded in the microchip within the pen. The composition and concentration of ions in tear fluid affects its electrical conductivity, so this can give a measurement of tear film osmolarity.

To do the test, a small sample of tear fluid (50 nanolitres) is collected by the test card on the top of the pen. The clinician places the tip of the test card next to the inferior lateral meniscus of the tear film, above the lower eyelid, to absorb the correct amount of fluid. It is recommended that tears should be collected at the outermost area of the eyelid to minimise the risk of injury to the cornea. Osmolarity may differ between the left and right eye, so the manufacturer recommends that both eyes are tested and the higher osmolarity reading should be considered as the relevant value. Separate test cards are needed for each eye. The pen confirms when the test card is correctly attached and when the tear fluid sample has been properly collected. Once the pen is docked, the system reader then calculates and displays the osmolarity measurement in mOsm/litre on the LCD screen.

The 2 reusable electronic check cards that come with the TearLab osmolarity system are used to ensure that the system and pen are functioning according to the original factory calibration. The manufacturer recommends that each pen should be tested with a check card before each day of patient testing, or if the pen has been dropped or mishandled, to verify that the system is working within manufactured calibration specifications. The system is calibrated at the factory, and is designed to stay calibrated during the life of the system (about 5 years). Normal and high osmolarity control solutions are used to verify the quantitative functioning of the osmolarity test cards. The manufacturer recommends testing each new batch of test cards with both levels of control solution, and to check test cards in storage monthly. Osmolarity control solutions are not included with the TearLab osmolarity system and must be bought separately. The manufacturer states that if either the control solution test or electronic check card results do not match the expected value range, the user should not test patients. The manufacturer suggests that osmolarity values above 308 mOsm/litre are generally indicative of DED. The DEWS (2007) report recommended a diagnostic cut‑off value of 316 mOsm/litre and higher for diagnosing DED.

Setting and intended use

The TearLab osmolarity system is intended to measure the osmolarity of tears to help diagnose DED, in conjunction with other tests and with clinical evaluation. TearLab Corporation recommends that the osmolarity test is done before any other tests, such as the fluorescein dye test, because they could stimulate the production of reflex tears (which differ from basal tears) and affect the value of the reading. Contact lenses do not have to be removed before the test.

In the NHS, TearLab is most likely to be used by optometrists or ophthalmologists and could be used in a primary or secondary care setting.

Current NHS options

No nationally accredited clinical guidelines or care pathways for the treatment of DED have been identified. Two separate guidelines developed by the Canadian Association of Optometrists (Prokopich et al. 2014) and the Sjogren Syndrome Foundation (Foulks et al. 2015) recommend that tear film osmolarity measurement is the most accurate single test for DED diagnosis. The NICE clinical knowledge summary on dry eye syndrome gives an overview of the evidence on diagnosing and managing DED. This is mainly based on the recommendations of the 2007 Report of the International Dry Eye Workshop (DEWS; sponsored by the Tear Film and Ocular Surface Society), but also from the Dry Eye Syndrome Preferred Practice Pattern (PPP), produced by the American Academy of Ophthalmology (2013). The NICE clinical knowledge summary on dry eye syndrome indicates that diagnosis can usually be made on medical history and presenting symptoms. The summary also states that special investigations such as slit lamp examination, Schirmer's test, and tear breakup time are not routinely done in primary care, and usually need referral, such as to an optometrist. Other tests include assessing corneal and conjunctival staining, tear film quality, meibomian gland function, and symptom questionnaires.

The following 2 tests are typically used by specialists to check for signs of DED (NHS website page on dry eyes):

  • Tear breakup time (TBUT) test (also known as the fluorescein dye test): eye drops containing a yellow‑orange dye are used so that the healthcare professional can see the tears more clearly. After the dye has been administered, a light is used to see how long it takes for a dry patch to appear. Patches beginning to appear in less than 10 seconds are typically taken as an indication of DED. In NHS practice, this test is usually conducted by an ophthalmologist or an optometrist.

  • Schirmer's test: small strips of blotting paper are hooked over the lower eyelid. After 5 minutes, the strips are removed and studied to determine how wet the paper is. If the tear fluid has travelled less than 10 mm from the eye surface along the absorbent paper in 5 minutes, this may indicate DED. In NHS practice, this test is usually conducted by an ophthalmologist or an optometrist.

NICE is not aware of any other CE‑marked devices that have a similar function to the TearLab osmolarity system. The Clifton osmometer can also be used to measure tear osmolarity, but this is only used in laboratory settings.

Costs and use of the technology

Information on the cost of using the technology has been sourced from the manufacturer.

The manufacturer states that the anticipated lifespan of the system (both the reader unit and the pen) is 20,000 tests. The manufacturer assumes an average of 4,000 tests per year in an NHS clinic and so each device has a lifespan of about 5 years. The cost of a TearLab system is £4370 (excluding VAT). The cost of the TearLab test cards (40 test cards) is £323 (excluding VAT). The manufacturer states that the average rate of use is 2 test cards per patient examination (1 test card per eye), which gives a cost per procedure of £16.58, including capital and consumable costs, excluding VAT. If the TearLab test is done in an ophthalmology outpatient setting, a consultation costs £124 and a follow‑up appointment costs £93 (Enhanced Tariff Option 2015/2016, NHS England March 2015). There are no service or maintenance costs, but it is recommended that each pen is tested daily before use to ensure that the system is properly calibrated and working within the manufacturer specifications.

Alternatively, DED can be diagnosed by a GP in a primary care setting. A 30 minute GP consultation costs £117 (Curtis 2014). The GP may also refer people to an optometrist or an ophthalmologist. An optometrist test costs £22 (based on the 2006 costings from Hernandez et al. [2008] inflated to 2014 prices, using the Hospital and Community Health Services index [Curtis 2014]). The national tariff for an ophthalmology outpatient consultation is £104 (NHS England 2013).

The assumed average length of time for each test is 1 minute.

No practical difficulties have been identified in using or adopting the technology.

Likely place in therapy

Because the current care pathway for DED is not clearly defined, the likely place for the TearLab osmolarity system is also uncertain. GPs may be able to diagnose DED based on symptoms and medical history, but may also refer people for further investigation. The manufacturer suggests that the TearLab osmolarity system may be used with other tests to diagnose DED and also for objective monitoring of treatment outcome in ophthalmology clinics by nurse practitioners or consultant ophthalmologists. The manufacturer also states that the TearLab osmolarity system may be used by community optometrists, working within a shared care pathway with local NHS hospitals.

Specialist commentator comments

Two specialist commentators noted that the DEWS (2007) definition of DED is now widely accepted because it refers to both aqueous and evaporative DED, and also acknowledges that inflammation is a significant factor in ocular surface damage.

One commentator highlighted that DED can significantly affect quality of life with symptoms leading to difficulty reading, using computers, watching TV, and driving. They noted that people with DED may report feelings of depression and anxiety, particularly before diagnosis.

One commentator explained that tear osmolarity has been used in DED research for many years, and stated that there is a significant amount of literature that recognises osmolarity as a reliable biomarker for DED. But the commentator noted that the main issue with using osmolarity as a marker for DED is whether it is the 'gold standard' single measurement. The same commentator stated that further large‑scale studies are needed to confirm the correlation with other clinical tests for DED and examine the longitudinal pattern of changes in tear osmolarity, which are thought to fluctuate more in people with than without DED.

One commentator explained that although there was no clear care pathway specifically for DED, there were several pathways by which people with general eye conditions may self‑refer or be referred by a GP to an optometrist. The same commentator considered that, in theory, only severe DED would be referred to a hospital eye service because mild to moderate DED can be managed by a community optometrist, but care pathways are not available for this in many areas. One specialist commentator noted that, according to their experience, GPs frequently use trial of treatment to aid diagnosis and rarely refer people to ophthalmology or optometry practices for diagnosis of DED. In contrast, another commentator suggested that GPs only tend to manage very mild DED and refer most other cases to specialist clinics because of a lack of training and access to relevant equipment. So even with training, the commentator indicated that it was unlikely a GP would rely on the TearLab osmolarity system as a diagnostic tool because of the risk of overlooking another eye condition and the cost of consumables needed to use the device. The same commentator noted that the TearLab osmolarity system is best placed in community‑ or hospital‑based eye clinics, to be used by ophthalmologists or ophthalmic nurse practitioners who can interpret findings in the context of history and other clinical findings. Two commentators concurred that measuring tear osmolarity was likely to be more popular in specialised eye clinics or research centres than in primary care settings unless equipment cost is low, because it would not significantly add to what can already be done in primary care. One of them noted that TearLab may be of more interest to GPs who have a special interest in ophthalmology. One commentator noted that although the TearLab system is reasonably priced compared with many ophthalmic instruments, the cost of consumables (2 test cards per person tested) could be significant unless discounts were available for bulk purchasing. The commentator highlighted that this would need to be taken into consideration when purchasing within the NHS to ensure the costs do not exceed NHS tariffs.

One specialist commentator noted that at present there is no single standard test that can clearly differentiate DED from other causes of ocular surface discomfort. Another commentator suggested that the most common tools for DED used by community optometrists were history, symptoms, TBUT and ocular surface integrity using fluorescein. They added that some practices had specific DED clinics that offered DED questionnaires, non‑invasive break‑up time tests, Schirmer's test, lissamine green, photography and meibomian gland dysfunction evaluations. According to the commentator, NHS ophthalmology clinics often use symptoms, TBUT ocular surface examination or integrity, and Schirmer's test to diagnose DED. The commentator suggested that Schirmer's test is not useful for diagnosing mild or predominantly evaporative DED, and noted that DED questionnaires are important research tools but are less commonly used in clinics because of time pressures. One commentator noted that if a series of tests for DED are being done, non‑invasive tests such as symptom questionnaires and slit lamp examinations should be carried out before the more invasive tests, such as the TearLab osmolarity test, TBUT or Schirmer's test.

One commentator stated that the TearLab osmolarity system is the only commercially available, reasonably priced method of measuring tear osmolarity in a clinical or research setting. According to the commentator's personal experience it is relatively easy to use after training and is minimally invasive, causing little discomfort to people being tested for DED. But the commentator noted that, although there are no published incidents of harm or side effects, it is theoretically possible to scratch the eye surface when collecting the tear sample; for example, if the user was untrained and the person being tested was unable to stay still. Another commentator highlighted that training, using the TearLab system often enough to maintain competence, and inter‑rater reliability (the degree of agreement among values obtained by different users) should be considered. One commentator expressed uncertainty about whether using the TearLab osmolarity system to collect tear samples in people with severe DED might lead to reflex tear secretion, and whether the TearLab system could be useful to distinguish between dry eye types such as evaporative and aqueous deficient DED.

Equality considerations

NICE is committed to promoting equality, eliminating unlawful discrimination and fostering good relations between people with particular protected characteristics and others. In producing guidance and advice, NICE aims to comply fully with all legal obligations to:

  • promote race and disability equality and equality of opportunity between men and women

  • eliminate unlawful discrimination on grounds of race, disability, age, sex, gender reassignment, marriage and civil partnership, pregnancy and maternity (including women post‑delivery), sexual orientation, and religion or belief (these are protected characteristics under the Equality Act 2010).

DED is a common condition, the prevalence of which increases with age, so the TearLab osmolarity system may be particularly beneficial in older adult populations. DED is 50% more common in women than in men, so women in particular may benefit from use of the TearLab osmolarity system. Age and sex are protected characteristics under the Equality Act 2010.