Examination of the ocular surface is very important for the diagnosis and treatment of dry eye syndrome. It is a multifactorial disease, defined as the loss of tear film homeostasis, accompanied by symptoms of ocular discomfort and inflammation, whose global prevalence is 5-50%, and which still poses several diagnostic and therapeutic challenges.
Thanks to recent advances in science and technology, diagnostic tests for eye diseases have advanced rapidly, which has also greatly improved the clinical approach to dry eye syndrome. Nevertheless, it can be difficult for the specialist to choose the most suitable test, ensure its repeatability and accurately interpret the results.
In this regard, a recent review analysed the latest advances in diagnostic tests for dry eye syndrome.
Tear analysis
Tears play an important role in maintaining the stability of the ocular surface microenvironment. Changes in the quality or quantity of tears can induce dry eye and play an important role in the treatment of dry eye syndrome. Therefore, the examination of tears is a very important indicator for the diagnosis of this condition.
- Schirmer's test: Used as a diagnostic test for dry eye syndrome since 1903, it is based on the physical tendency of a fluid to migrate along a strip of porous material by capillary action due to surface tension. It is a simple test to perform, but with low reliability.
- Lacrimal meniscus height assessment: tear meniscus assessment has been confirmed to have good reliability and accuracy. In addition, non-invasive diagnostic methods using optical coherence tomography (OCT) have been introduced that are advantageous for the patient and reliable in terms of outcome.
- Strip meniscometry: involves the use of a thin strip with a capillary absorber in the centre and two scale columns on either side to measure the volume of the tear meniscus. It has demonstrated good reliability and results consistent with the Schirmer test and the assessment of tear meniscus height.
- Ferning Test (or ferning test): is a simple method for assessing certain biochemical characteristics of the tear film layers, quickly and inexpensively.
- Measuring the osmotic pressure of tears: Tear osmotic pressure indicates the balance between tear secretion, evaporation, absorption and drainage. The tear osmolarity test is considered one of the most accurate methods for diagnosing dry eye syndrome. To date, techniques for measuring tear osmotic pressure involve the use of reliable and effective devices.
- Measurement of inflammatory biomarkers: two tests measuring metalloproteases and lactoferrin, respectively, are available. Indeed, there is strong evidence that inflammation is an important pillar in the pathophysiology of dry eye syndrome.
Tear film analysis
The most superficial layer of the tear film is the lipid layer, secreted by the Meibomian glands. When this layer is deficient, evaporative dry eye syndrome can occur.
- Breaking timeThe tear film break-up time is one of the most widely used methods of diagnosing dry eye syndrome in the last two decades. It is traditionally defined as 'the interval between the last complete blinking and the first appearance of a dry spot or break in the tear film'. To date, both invasive and non-invasive methods for measuring tear film break-up time are available.
- Tear film thickness measurement: Various technologies and new devices are available for assessing tear film thickness. One of the methods used is interferometry.
Examination of the eyelid margin and Meibomian Glands
Meibomian gland dysfunction (MGD) is among the main causes of dry eye syndrome (86%). The morphology and function of the Meibomian gland are routinely examined to diagnose MGD, through meibography. Assessing changes in the eyelids, eyelid margins and meibomian glands is crucial in the diagnosis of MGD. These changes can be assessed by observing the state of opening of the Meibomian glands, compressing the glands on the eyelid skin and observing difficulties in tear excretion. In addition, different imaging modalities can be used, including contact meibography, non-contact infrared meibography, keratography, in vivo confocal microscopy and OCT meibography.
Colouration of the ocular surface
Staining of ocular surface cells allows the barrier function and integrity of epithelial cells to be assessed as one of the indices for evaluating the severity of dry eye syndrome. Indeed, when the integrity of ocular surface cells is altered, these can be highlighted using specific dyes. The degree and area of staining correlate with the severity of the damage. Staining can, therefore, be used to assess barrier function and epithelial cell integrity. Sodium fluorescein staining is the most commonly used in clinical practice, although lissamine green and rose bengal staining can also be used.
Dry eye Analyser
This is an innovative device that integrates a wide variety of diagnostic tests for dry eye syndrome. This analyser can efficiently provide analyses including the measurement of tear film height, break-up time, tear film thickness, Meibomian glands and conjunctival hyperemia.
Confocal microscope
Confocal microscopy is a new technology that can help in the in vivo assessment of structural changes in various ocular surface diseases. The application of in vivo confocal microscopy (IVCM) in dry eye syndrome will, in the future, become a fundamental method for assessing morphological changes of the ocular surface. IVCM has already been applied in the examination of the cornea, conjunctiva, Meibomian glands and lacrimal glands.
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