How Do Ophthalmic Antihistamines Work?

Ophthalmic antihistamines relieve eye allergy symptoms by blocking the release of histamine by mast cells, a type of immune cell. Mast cells release histamine when they detect foreign substances in the body. Histamine causes swelling and inflammation. The blood vessels in your eyes swell and your eyes get red, teary and itchy.

Mast cells are part of the front-line immune system defense against antigens. Mast cells are present in mucous and epithelial tissue that line the surface of all organs. In the eyes, mast cells are abundant in the conjunctiva, the clear mucous membrane that forms a protective layer over the eyes and the inner surfaces of the eyelids.

In addition to histamine, mast cells also release other inflammatory proteins such as cytokines and chemokines which activate other types of immune cells such as eosinophils which further promote inflammation. Blocking the activity of histamines, therefore, is effective in controlling inflammation.

Ophthalmic antihistamines bind to certain proteins at the inflammation site known as H1-receptors to prevent allergic response. Ophthalmic antihistamines work in the following ways:

Block the release of histamine by mast cells

• Inhibit the activation of eosinophils
• Inhibit the movement of mast cell and eosinophil to the inflammation site
• Reduce the permeability of blood vessels and prevent leakage of inflammatory substances into the inflammation site

Ophthalmic antihistamines are solutions administered in the eyes to relieve symptoms of allergic conjunctivitis. Allergic conjunctivitis is inflammation of the conjunctiva caused by a reaction to allergens such as pollen, dust, dander and mold spores.

Side effects of ophthalmic antihistamines may include the following:

Ocular side effects:

• Irritation and foreign body sensation
• Pain, burning or stinging
• Redness (erythema)
• Itching (pruritus)
• Tearing and/or discharge
• Eye swelling
• Eyelid redness and edema
• Hyperemia (dilation of blood vessels)
• Blurred vision
• Reduced visual acuity
• Folliculosis (collection of lymphocytes in the conjunctiva)
• Corneal inflammation (keratitis)
• Dilation of pupils (mydriasis)
• Eyelid disorder
• Light sensitivity
• Dry eyes
• Systemic side effects:
• Headache
• Influenza symptoms
• Non-ocular infection
• Drowsiness
• Inflammation of nasal passage (rhinitis)
• Inflammation of the pharynx (pharyngitis)
• Inflammation of both nasal passage and pharynx (nasopharyngitis)
• Inflammation of the sinus (sinusitis)
• Hypersensitivity reactions such as:
  • Itching
  • Body rash
  • Swelling of the face
  • Swelling of lips, tongue and/or throat
  • Allergic dermatitis
• Taste disorder
• Asthma
• Conjunctivitis
• Shortness of breath (dyspnea)
• Fatigue
• Lack of energy (asthenia)
• Cold syndrome
• Nausea

The information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Generic and brand names of some ophthalmic antihistamines include:

• Alcaftadine ophthalmic (Lastacaft)
• Azelastine hydrochloride ophthalmic
• Bepotastine besilate (Bepreve)
• Cetirizine hydrochloride ophthalmic (Zerviate)
• Epinastine hydrochloride (Elestat)
• Ketotifen fumarate ophthalmic (Alaway, Zaditor)
• Olopatadine hydrochloride ophthalmic (Pataday)