The test reflects the conditions of the mucus and indirectly provides guidance on the osmolarity of tears. It got in atraumatically with a micropipette, without anesthesia, It is placed on a glass slide and allowed to dry at room temperature (20-22°C). The preparation is observed under phase contrast microscope 40-100 final magnifications. The test is based on a characteristic common to all mucous secretions, that is their capacity to crystallize in the form of ferns, when dried, because of evaporation.
ICP Dry eye analysis
The ferning test is an indirect qualitative index of the stability of the tear film with whom is possible to evaluate the balance between the muco-proteins and the salts dissolved in the tears. A drop of tears is dried on a glass slide at room temperature.
The classification of the tears sample is made with Rolando in 4 different degrees: 1° degree: it indicates a ferning distributed evenly on the whole dried drop; it is detectable in the 52% of subjects. 2° degree: it indicates crystallization with small gaps (defects); it is detectable in the 31% of subjects. 3° degree: it indicates a ferning with big defects; it is present in the 15% of subjects. 4° degree: it indicates a dried drop with scattered granules but without ferning, or with a hint of ferning; it is present in the 1% of subjects.
The 1° and the 2° degrees are present in the great majority of normal subjects, while in the 3° and the 4°
degrees is found more frequently in patients with dried keratoconjunctivitis. The problem of this test is that the classification can result difficult for the inexperienced because it must occur for comparison with reference patterns and so it will be necessary more detailed cytological knowledge. Furthermore, if the dehydration is too fast, the ferns are altered and is necessary to pay attention during the sample collection in order to not cause abrasions of the conjunctival mucosa with the with the tip of the suction pipette.
However, it is a test that, if made with others, can help to identifythe subjects with alteration the mucin layer that can be found for example in hypovitaminosis A, keratoconjunctivitis, chemical trauma and topical medications.