Methods for Measuring Tear Secretion
Schirmer I Test
This test evaluates the basal secretion of tears. A strip of filter paper measuring 5 mm × 35 mm is folded at one end by 5 mm and placed in the outer one-third of the lower conjunctival sac, with the remaining portion suspended over the skin surface. The eyes are gently closed, and the length of the filter paper moistened by tears is measured after 5 minutes. When surface anesthetics are applied beforehand, the test primarily reflects accessory lacrimal gland function, with a result shorter than 5 mm considered abnormal. Without the application of anesthetics, the test evaluates the main lacrimal gland function, with a result shorter than 10 mm regarded as abnormal.
Figure 1 Methods for measuring tear secretion
Schirmer II Test
This test assesses reflex tear secretion by performing the Schirmer I test after nasal stimulation. It can help differentiate Sjögren's Syndrome from non-Sjögren's aqueous tear deficiency. In Sjögren's Syndrome, both Schirmer I and Schirmer II results are reduced, whereas in non-Sjögren's cases, Schirmer I results may be less than 5 mm, but Schirmer II results are generally normal.
Tear Hyposecretion
Tear hyposecretion, also known as lacrimal hyposecretion, refers to abnormal tear production leading to tear film deficiencies. This weakens the protective function of the tear film on the ocular surface, potentially resulting in dry eye and even corneal damage, which can impair vision.
The causes of tear hyposecretion are diverse and can be categorized into congenital and acquired. Acquired cases, with Sjögren's Syndrome being the most common, predominate.
Congenital Tear Hyposecretion
Congenital absence of tears, such as alacrima, may be observed in Riley-Day Syndrome (familial dysautonomia). Patients may initially present without symptoms but gradually develop classic signs of dry eye, corneal hypoesthesia, and conjunctival or corneal scarring.
Sjögren's Syndrome
Sjögren's Syndrome, also known as Sicca Syndrome, is an autoimmune disease of unknown etiology that affects multiple systems. Primary Sjögren's Syndrome is more common in women. Secondary Sjögren's Syndrome encompasses other autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, scleroderma, and polymyositis. Key symptoms include dryness and a gritty sensation in the eyes, along with oral dryness. Fluorescein staining reveals diffuse punctate epithelial damage on the corneal surface. In severe cases of keratoconjunctival dryness, complications such as eyelid-ball adhesion, neovascularization, and visual impairment may occur.
Other Conditions Leading to Tear Hyposecretion
These include lacrimal gland inflammation, trauma, infections causing lacrimal duct obstruction, and reduced reflex tear secretion.
Treatment primarily focuses on symptomatic relief, with a localized approach. The application of artificial tears alleviates symptoms, while severe cases may require occlusion of the upper and lower puncta to minimize tear loss.
Tear Hypersecretion
Tear hypersecretion, or lacrimal hypersecretion, can be classified into primary and secondary causes. Primary tear hypersecretion is relatively rare and typically arises from intrinsic lacrimal gland conditions such as dacryoadenitis, lacrimal gland cysts, or tumors, necessitating differentiation from lacrimal duct obstruction. Secondary causes are more diverse and include physical or chemical irritation, emotional states, medication use, and ocular diseases.
A particular form of paradoxical tear secretion, known as "crocodile tears," is characterized by tearing during eating. It occurs mainly after facial nerve paralysis, where misdirected nerve regeneration leads to abnormal tear production.
Patients often experience episodic tearing, which may cause discomfort. Excessive tears can saturate the lower eyelids, resulting in conditions such as blepharitis, eczema, or lower eyelid ectropion.
Treatment generally targets the underlying cause. In cases where excessive tearing significantly affects daily life, interventions such as destroying the lacrimal gland and its ducts or interrupting the pterygopalatine ganglion can be considered to reduce tear secretion.