DRY EYE DIAGNOSIS

Speaking during the first Cornea Day of the 26th Asia-Pacific Association of Cataract and Refractive Surgeons Annual Meeting, Peter Zloty MD, provided some perspective on current techniques and technology for identifying dry eye in clinical practice.

Discussing measurement of tear film osmolarity, Dr Zloty concluded that the commercially available point-of- care system (TearLab Osmolarity System, TearLab) could prove to be a useful tool to use in research studies, but that it should not be relied on as a stand-alone evaluation for diagnosing dry eye in daily patient care.

“Some individuals are saying that tear film osmolarity is necessary and the gold standard for accurately diagnosing dry eye syndrome, while others observe it as a snapshot observation,” said Dr Zloty, a cornea specialist in private practice in Alabama.

He noted that absolute values of tear film osmolarity that are diagnostic of dry eye are not yet determined, and unless the result is very hyperosmolar, the analysis may not be conclusive. Various studies investigating osmolarity cut points for differentiating between normal and dry eye have suggested numbers ranging from >305 up to 318 mOsmol/L, while in their seminal work, Tomlinson et al. reported that using ≥316 mOsmol/L as the diagnostic threshold provided 59 per cent sensitivity and 94 per cent specificity.

Dr Zloty suggested that a fundamental problem with using the point-of-care tear film osmolarity platform for diagnosing dry eye is that it only measures the dissolved ions in the aqueous matrix lying under the amphiphilic lipid layer of the tear film. Unlike the original laboratory- based method for determining tear film osmolarity that is based on freezing point depression, which is affected by all solutes in the solvent, the commercially available platform uses electrical conductivity, which is affected only by ions that are present.

“Measurement of tear film osmolarity with this device has nothing to do with the lipid layer of the tear film. That may explain the variability of studies evaluating its usefulness in diagnosing chronic ocular surface disease and why it will not necessarily detect patients with dry eye associated with lipid abnormalities,” Dr Zloty said.

He also cited a study presented at ARVO 2012 by Mudgil et al who reported that hyperosmolarity had no adverse effect on the stability of the tear film, and a published paper by Szalai et al who reported wide overlap in tear film osmolarity values comparing patients with Sjogrens syndrome and normal controls.

“However, Szalai et al found tear film breakup time had predictive value,” noted Dr Zloty, “and it may be that tear film breakup time is the most useful test for diagnosing dry eye.”

Discussing other diagnostic testing, Dr Zloty said that the Schirmer I test (without anaesthesia) is useful for identifying patients with aqueous deficient dry eye if the result is positive. However, individuals with pure aqueous deficient disease account for less than 20 per cent of the dry eye population.

Dr Zloty also reminded his colleagues that when performing a Schirmer test with anaesthesia, they should take care to standardise the materials and methods of their testing since meaningful interpretation of serial measurements depends on using a consistent technique.

All patients with dry eye-related complaints should be carefully examined for lid margin disease, especially if they are found to have adequate aqueous production, said Dr Zloty, noting evidence that evaluation of the lids is underperformed.

“According to one study, fewer than one out of 20 ophthalmologists assess the meibomian glands. I encourage everyone to look carefully at the lids, manipulate them and document the quantity and quality of the meibomian gland secretions,” he said.

Dr Zloty also categorised the Ocular Surface Disease Index (OSDI) and meibometry as diagnostic tools having value in research studies but with questionable utility in the office setting. For example, OSDI data may be useful for finding small differences between treatment groups in a clinical trial, he said.

As an alternative to administering the OSDI, Dr Zloty suggested simply querying patients with typical dry eye complaints if their symptoms are worse in the morning or at the end of the day as this information may provide a clue to underlying aetiology.

“The response to this question can help to identify whether a patient is suffering because of lid dysfunction, sleep apnoea that causes eye rubbing through the night, lagophthalmos, or classic keratoconjunctivitis sicca,” he said.

Dr Zloty concluded with a pearl for treatment of dry eye that he derived from a retrospective review published by Jonisch et al in 2010 – use of 0.01 per cent dexamethasone compounded in preservative-free artificial tears.

“This dilute corticosteroid preparation did not increase IOP, and it has tremendously augmented use of cyclosporine in my practice,” he said.