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Osmolarity testing for dry eye

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Dr Jim Kokkinakis
BOptom FAAO ISCLS
The Eyepractice, Sydney

 

For the most part, optometrists treat dry eye as a symptomatic disease, yet research has shown that relying on symptoms alone may lead to misdiagnosing 40 per cent of patients.1

I liken dry eye management to piecing together a very large jigsaw puzzle. Like any puzzle, the more assumptions you can test by gathering data points along the way, the more complete the picture will begin to look.

Analysing my patients’ tears for their level of osmolarity gives me another data point that allows me to build a better picture of a patient’s ocular surface and their level of dry eye disease.

When we look at the other diagnostic tools for screening dry eye disease, the research indicates that measuring osmolarity is a superior predictor of dry eye.2,3 Tests like TBUT or corneal staining, although very useful, diagnose later-stage signs after the disease has progressed.

As the DEWS 2007 report pointed out, hyperosmolarity is a leading indicator for dry eye.4 The challenge in measuring osmolarity is that it cannot be seen, it can only be measured through a lab-on-chip device. Currently, the best and only way to test for hyperosmolarity in a practice setting is the TearLab system.

The osmolarity test indicates whether a patient’s tears have a higher than normal salt content; when the aqueous declines, the concentration of salt in the tear will increase. The higher the measurement, the ‘drier’ the eye.

This concentration level is measured in milliosmoles per litre (mOsmol/L), where a reading of > 308 mOsmol/L requires further investigation. A low reading with an inter-eye difference of +/-8 mOsmol/L is also deemed abnormal and also requires further investigation.

Knowing my patient’s osmolarity level helps me navigate through the different treatment options available, even to the point of deciding which artificial tear I will prescribe for a particular patient based on their osmolarity level. For example, patients with elevated osmolarity (> 308) are going to respond better to an artificial tear that has a lower osmolarity level such as Hylo-Fresh (AFT), Blink (AMO) or TheraTears (Akom).5-7

 

CASE REPORT 1

Dry eye symptoms with low osmolarity

MD, a 28-year-old female, presented with dry and irritated eyes. She had been suffering from these symptoms for 12 years and had seen many ophthalmologists and optometrists.

Our normal preliminary work-up includes tear film osmolarity, LipiView, OSDI questionnaire, eye-drop list, dry eye history, medication list and medical history.

Often symptoms that can mimic dry eye disease, such as recurrent corneal erosions, floppy eyelid syndrome, blepharitis, meibomian gland dysfunction, filamentary keratitis, Salzmann’s nodular degeneration and mucous fishing syndrome, can become quicker to isolate after first conducting an osmolarity test.8 Patients with these symptoms will measure a low osmolarity level, which allows me to narrow my diagnostic focus.

Her preliminary work-up results were:

TearLab: OD 285 mOsmol/L; OS 291 mOsmol/L (> 308 is suspicious of dry eye).

LipiView: R 65 microns; 62 microns (> 80 is considered normal). Blinking frequency and quality were normal.

Ocular surface disease index (OSDI): 24 (on a scale from 0 to 100). In our clinic, where we deal with the worst cases, a score > 60 is the norm; > 33 is considered significant.

Current eye-drops: Systane Ultra (four times per day); Visine Clear (twice a day).

This is not the typical dry eye profile. Very few eye clinics have the LipiView, so if we take these results away, it still will make the clinician aware that they are possibly not dealing with dry eye. Chronic dry eye, especially with such a long time-frame should have an elevated osmolarity.

These results immediately direct us to a different line of questioning.

Q: What bothers you more about your eyes, the irritation or the redness?
A: The redness

Q: When are your eyes at their worst, in the morning when you wake up or as the day progresses?
A: On waking irritation is worst.

Q: Describe the irritation in more detail.
A: Continually have a pus-like discharge with a mild to moderate grittiness.

The answers to these questions lead us away from the typical evaporative and aqueous-deficient dry eye. There is little doubt that we have an ocular surface disturbance, which is supported by the following observations:

• Significant palpebral papillary response

• Lid eversion revealed very floppy lids

• Significant conjunctival staining, especially inferiorly, which was suggestive of fishing syndrome

• A mild superficial punctate keratitis

The likely compounded diagnosis is:

• Floppy eyelid syndrome

• Fishing syndrome

• Rebound hyperaemia with corneal toxicity from the tetrahydrozoline hydrochloride decongestant and the benzalkonium chloride preservative in the Visine Clear eye-drops.

Treatment of this dilemma is a huge challenge but the following need mentioning.

Floppy eyelid syndrome can be managed conservatively with non-irritating ointments and lid-taping overnight. In resistant cases, lid surgery might help. This condition is often associated with both sleep apnoea and keratoconus.9

Fishing syndrome is a rebound mucous discharge that occurs from the continual irritation to the conjunctival surface from trying to digitally ‘fish out’ the overflow of mucous. Treatment can be successful with preservative-free topical steroids and the strict resistance of digitally removing the mucous.10

Rebound conjunctival hyperaemia and the often associated preservative toxicity can be treated again with a tapering dose of preservative-free topical steroid and strictly refraining from using the decongestants.

Ultimately, education, encouragement and patient compliance are paramount to long term success.

 

CASE REPORT 2

High osmolarity with no dry eye symptoms

A 62-year-old male returned for a routine eye examination. His previous eye examination had been with our clinic about three years prior. When asked if there were any eye issues that were bothering him, he admitted to intermittent reading blur.

Refraction revealed a reading add increase of about +0.25 D in each eye. Intermittent reading blur in this age bracket can be associated with evaporative dry eye, so we also performed a TearLab osmolarity measurement and a fluorescein assessment of the ocular surface.

The following measurements and observations were made:

TearLab: OD 325 mOsmol/L; OS 321 mOsmol/L. This elevated reading indicates some type of dry eye.

Fluorescein assessment: tear film was unstable with virtually every blink. Invasive tear break up time was two seconds, at best. Thumb expression of the meibomian glands revealed a stagnant and viscous meibum.

Treatment of this type of case is usually simple. We chose to supplement the tear film with a hypo-osmotic lubricant (Hylo-Fresh) four times per day for a month and combined this with daily hot compresses and lid massage.

At review three months later, the patient was not using any drops but had continued the compresses and massage once per day.

Subjectively, vision was perceived as normal and TearLab results were back into the normal range of < 300 mOsmol/L in each eye.

Although vital, osmolarity testing should not be used on its own. As with any diagnosis, it provides a data point that can be combined with other findings—such as corneal staining, symptoms, meibomian gland expression and so on—to help you piece together the dry-eye puzzle. The sum total of these findings will improve your disease diagnosis and help you to tailor a management plan that will add value to your patients’ visual outcomes and health.11

 

100 Osmolarity Case Study Figure -1

Tear Osmolarity data (mOsm/L) quantifies ocular surface health

 

1. Bron AJ, Tomlinson A, Foulks GN et al. Rethinking dry eye disease: a perspective on clinical implications. Ocul Surf 2014; 12 (2 Suppl): S1-31.

2. Farris RL. Tear osmolarity; a new gold standard? Adv Exp Med Biol 1994; 350: 495-503.

3. Tomlinson A, Khanal S, Ramaesh K et al. Tear film osmolarity: determination of a referent for dry eye diagnosis. Invest Ophthalmol Vis Sci 2006; 47: 10: 4309-4315.

4. The definition and classification of dry eye disease: report of the Definition and Classification Subcommittee of the International Dry Eye WorkShop. Ocul Surf 2007; 5: 2: 75-92.

5. Nelson JD, Farris RL. Sodium hyaluronate and polyvinyl alcohol artificial tear preparations. A comparison in patients with keratoconjunctivitis sicca. Arch Ophthalmol 1988; 106: 484-487.

6. Gilbard JP, Rossi SR, Heyda KG. Ophthalmic solutions, the ocular surface, and a unique therapeutic artificial tear formulation. Am J Ophthalmol 1989; 107: 4: 348-355.

7. Gilbard JP. Dry eye: pharmacological approaches, effects, and progress. CLAO J 1996; 22: 2: 141-145.

8. Lonsberry B, Karpecki PM. Can you spot these dry eye imposters? Review of Optom 2012 Oct.

9. Pihlblad MS, Schaefer DP. Eyelid laxity, obesity, and obstructive sleep apnea in keratoconus. Cornea 2013; 32: 9: 1232-1236.

10. Slagle WS, Slagle AM, Brough GH. Mucus fishing syndrome: case report and new treatment option. Optometry 2001; 72: 10: 634-640.

11. Sullivan BD, Whitmer D, Nichols KK et al. An objective approach to dry eye disease severity. Invest Ophthalmol Vis Sci 2010; 51: 12: 6125-6130.



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