Physical signs associated with thyroid eye disease may vary, depending on the tissues involved, the extent of the inflammation, and the amount of swelling that develops in response to the production and secretion of glycosaminoglycans. At a superficial level, thyroid eye disease may involve a thin transparent layer of tissue called the conjunctiva that covers the outer surface of the eyeball and the inner surfaces of the eyelids. Inflammation of the conjunctiva may lead to dilation of blood vessels with increased blood flow through this layer of tissue. This may lead to reddening of the visible portion of the eyeball called conjunctival injection. At a deeper level, swelling of tissues may block the normal flow of fluid in the blood vessels and lymphatic vessels that drain the conjunctiva, eyelids, and soft tissues that surround the eye sockets. This blockage may cause a backup of fluid that may lead swelling of these tissues. Swelling of the conjunctiva may be visible as a boggy thickening of the visible portion of the eyeball called chemosis. Swelling of the eyelids called lid edema may lead to problems with closure of the eyelids that may leave the surface of the eyeball exposed. This may lead to drying and inflammation of the cornea of the eyeball called exposure keratitis. Swelling of the soft tissues that surround the eye sockets may be visible as puffiness of the cheeks and brow called periorbital edema.
The most significant physical signs associated with thyroid eye disease usually reflect involvement of the tissues that surround the eyeballs deep within the eye sockets. The eyeballs are held in place by thin muscles attached to the back of the eye sockets called the extraocular muscles. There are six extraocular muscles present in each eye socket. One end of each extraocular muscle is directly attached to the globe of the eyeball. The other end is attached to a ring at the back of the eye socket surrounding the optic nerve. In the normal state, the extraocular muscles work together to direct the movement of the eyeballs, contracting in different combinations to maintain steady lines of sight. As a group, they are surrounded by fat and soft tissue that fill the space of each eye socket.
Problems that may arise in the setting of active thyroid eye disease stem from the fact that each eye socket represents an enclosed space bounded by four walls of bone and a thick layer of connective tissue that holds each eyeball in place. This enclosed space is only meant to hold a certain volume of tissue. Swelling of the extraocular muscles and soft tissue that may occur as in the setting of active thyroid eye disease may increase the volume of tissue in this enclosed space. This may in turn increase the overall pressure exerted on the eyeballs, optic nerves, and extraocular muscles. Increased pressure exerted on the eyeballs may cause them to protrude outward beyond the normal front edges of the sockets. This may lead to visible bulging of the eyes called proptosis. Increased pressure exerted on the extraocular muscles may lead to entrapment that limits their motion. This can lead to restriction of normal movement that may disrupt lines of sight. Significant disruption may lead to problems with double vision, contributing to a condition called diplopia. Increased pressure exerted on the optic nerves may disrupt the signals that are transmitted from the retina of each eyeball to the vision center of the brain. Over time, compression of the optic nerves may lead to problems with perception of certain colors, blurring of vision, and progressive loss of vision.