Allergic conjunctivitis is usually a clinical diagnosis. Laboratory tests are primarily supportive. They may help in differentiating intrinsic and extrinsic forms of the condition and thus, guide the treatment.

• Intradermal injections of individual allergens are administered to detect sensitivity^[1].
• It is a highly sensitive test^[2].
• The result is considered positive when the resulting wheal is at least 3 mm larger than the negative control. Systemic reactions are rare^[3].

In-vitro tests to detect IgE antibodies to specific allergens are widely used^[4] if skin testing is indicated but not advised such as^[5]:

• The patient cannot discontinue antihistaminic medications
• Ambiguous results (e.g., presence of dermatographism)
• To complement the results of previous skin testing.

• It involves instillation of an allergen on the conjunctiva of the affected eye and a control solution in the other^[6].
• More common in research settings to test novel treatments or to compare existing therapies^[5].
• Clinically helpful to identify local allergies in suspect patients but with negative or discordant skin prick testing and serum specific IgE^[7] . *Useful to assess the relationship between symptoms and exposure in polysensitized patients and the response to initiated therapy^[7].