Friday, December 1, 2023
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Ocular examination is usually sufficient for making differential diagnosis of ocular allergy in chronic and severe cases such as AKC and VKC. In the milder and earlier forms of ocular allergies, however, it may be more difficult to distinguish between the diseases. Thus, the addition of in-vitro and in-vivo diagnostic tests is essential in making more specific diagnoses. In addition to conventional tests (i.e. total/specific serum IgE measurements, eosinophil counts, patch tests), methods have been developed to more specifically assess ocular allergic inflammation (i.e. conjunctival provocation tests, mediator/IgE measurement in tears, tear film evaluation, microbial tests, conjunctival cytodiagnosis, and confocal imagining).[32]
Conjunctival provocation tests have been extensively used to determine the etiological agent of allergic conjunctivitis, to assess nonspecific hyperreactivity, and to evaluate sensitivity to therapeutics. Modified use of this technique has recently enabled investigators to detect nonspecific conjunctival hyperreactivity in patients with or without a history of allergy, suggesting that there is a mechanism of conjunctival hyperreactivity independent of allergic inflammation.[33]
Differential cytokine levels in tear samples have been implicated as good indicators of pathophysiological mechanisms occurring in allergic conjunctivitis.[32] Small tear volumes have been tested using conventional enzyme-linked immunosorbent assay, causing limitations in the number of conducted assays. The use of multiplex bead immunoassays, however, significantly reduces the amount of sample needed and allows simultaneous measurement of several cytokines per sample. Using this technology, it has recently been found that subgroups of allergic conjunctivitis (i.e. SAC, VKC, AKC) have unique cytokine production profiles. These profiles can help clarify mechanisms involved in ocular allergic diseases and may serve as targets for development of therapeutics.[30**] Multiplex bead immunoassays have the potential to serve as good supplemental diagnostic methods to more conventional methods.
A novel application of confocal microscopy has been used as a noninvasive method to assess conjunctival inflammation in humans. With the use of this relatively new technology, investigators have been able to assess the number of rolling and arresting leukocytes in the ocular vessels of patients with various ocular disorders. It was concluded that the number of rolling and arrested leukocytes was proportional to the severity of the ocular disease.[34*] Utilizing noncontact confocal microscopy, investigators have successfully observed differences in tear film composition between normal patients, those with nonspecific or allergic conjunctivitis, and patients with dry eye.[35*] These forms of confocal microscopy serve as excellent tools to noninvasively assess, classify, and diagnose ocular inflammatory diseases with maximal resolution and high image quality.
