A disease is an abnormal condition affecting a living organism. Diseases are generally understood to be medical conditions that involve a pathological process associated with a specific set of symptoms. Localized diseases affect specific parts of the body; disseminated diseases spread to other parts of the body; and systemic diseases affect the entire body.
Acute angle-closure glaucoma occurs when the flow of aqueous humour out of the eye is blocked and pressure inside the eye becomes too high very quickly. It is an emergency because if it is not treated quickly, it can lead to permanent loss of vision
Bacterial keratitis is an infection and inflammation of the cornea that cause pain, reduced vision, light sensitivity and tearing or discharge from the eye that can, in severe cases cause loss of vision
Allergic eye disease is common and takes a number of different forms but all are expressions of atopy, which may also manifest as atopic asthma, atopic dermatitis, or allergic rhinitis.
Major perturbations in this delicate homeostasis that favors net filtration out of the vascular space, or impaired return of fluid by lymphatics from the interstitial space, will result in edema.
Edema is defined as a palpable swelling caused by an increase in interstitial fluid volume. Edema, other than localized edema, does not become clinically apparent until the interstitial volume has increased by 2.5 to 3 liters.