A gas turbine engine has a row of circumferentially spaced rotor blades and a plurality of seal segments circumscribing the rotor blade tips and attached to a radially inward side of a casing of the engine. The invention also provides assays for the identification of compounds useful in the treatment or prevention of gastrointestinal and liver diseases, cancer disorders, hematological diseases, inflammatory diseases, respiratory diseases, neurological disorders, cardiovascular disorders, reproduction disorders and urological disorders. The arm portions may bend inward from the hinge portion towards a region defined between the temples and may bend outward and curve around a head of a wearer for a conformal fit with the head of the wearer.