Graves' disease is a common form of hyperthyroidism in which the immune system attacks the thyroid gland, causing it to overproduce the hormone thyroxin. While excess thyroid hormone can cause physical and emotional changes throughout the body, the eyes can be particularly affected. Graves'-induced attacks by the immune system can lead to inflammation of the muscles behind the eye, causing structural changes to the eye and eyelids which may potentially lead to corneal damage and vision loss.
Proptosis and Corneal Exposure
Proptosis (sometimes called exophthalmos) is a condition in which the eye(s) abnormally protrude or bulge. The condition occurs when swelling in the area of the muscles behind the eye causes the eye itself to move forward. If inflammation continues for a year or more, scarring can occur, causing the muscles to freeze in a contracted and immovable state. Some muscles may be affected more than others and may scar at different rates, causing the eyes to go out of alignment. Misalignment can cause visual disturbances centrally or peripherally, commonly leading to double vision.
Proptosis interferes with the eyelid's normal protective function. This can cause a severe drying of the eye and the cornea, resulting in corneal exposure or exposure keratopathy--a condition in which there is abrasive damage to the cornea due to reduced tear film coverage on the eye itself.
Optic Nerve Compression
Inflammation causes the eye muscles to swell. As they continue to swell, they may begin to compress the optic nerve in the posterior orbit of the eye, potentially leading to a serious condition called compressive optic neuropathy. Already a tightly packed space, the orbit does not allow much room for swelling. If the inflammation is not relieved, compression can reduce nerve transmission behind the eye, leading to blurred or reduced vision or ulcers on the cornea. Chronic compression may stop corneal nerve transmission altogether, leading to blindness.
Other Frequent Symptoms
Some of the most frequent symptoms caused by inflammation related to Graves' disease include double vision (diplopia), exophthalmos or proptosis (bulging), general swelling and irritation of the eye (chemosis), corneal disease or damage and increased intraocular pressure (IOP). Upper and lower lid lag is particularly common. Excess thyroid hormone causes the lids to stay retracted such that when asked to look up or down, the eyelids will not shift normally with the eye, or may partly shift after some delay.
Other Less Frequent Symptoms
Less frequent symptoms related to inflammation caused by Graves' disease include infrequent blinking, a tremor of the eyelid while it is closed, pigmented eyelids, increased contraction of the pupil (hippus), decreased forehead wrinkling when turning gaze upward and difficulty turning the upper lid inside out.
