Glaucoma – Open Angle Glaucoma vs Angle Closure Glaucoma

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Glaucoma is a group of eye diseases in which the optic nerve is damaged leading to irreversible loss of vision. In most cases, this damage is due to an increased pressure within the eye. The eye produces a fluid called aqueous humor which is secreted by the ciliary body into the posterior chamber – a space between the iris and the lens. It then flows through the pupil into the anterior chamber between the iris and the cornea. From here, it drains through a sponge-like structure located at the base of the iris called the trabecular meshwork and leaves the eye. In a healthy eye, the rate of secretion balances the rate of drainage. In people with glaucoma, the drainage canal is partially or completely blocked. Fluid builds up in the chambers and this increases pressure within the eye. The pressure drives the lens back and presses on the vitreous body which in turn compresses and damages the blood vessels and nerve fibers running at the back of the eye. These damaged nerve fibers result in patches of vision loss, and if left untreated, may lead to total blindness. There are two main types of glaucoma: open-angle and angle-closure. Open-angle glaucoma , or chronic glaucoma, is caused by partial blockage of the drainage canal. The angle between the cornea and the iris is “open”, meaning the entrance to the drain is clear, but the flow of aqueous humor is somewhat slow. The pressure builds up gradually in the eye over a long period of time. Symptoms appear gradually, starting from peripheral vision loss, and may go on unnoticed until the central vision is affected. Progression of glaucoma can be stopped with medical treatments, but part of vision that is already lost can not be restored. This is why it’s very important to detect signs of glaucoma early with regular eye exams. Angle-closure glaucoma, or acute glaucoma, is caused by a sudden and complete blockage of aqueous humor drainage. The pressure within the eye rises rapidly and may lead to total vision loss quickly. Certain anatomical features of the eye such as narrow drainage angle, shallow anterior chamber, thin and droopy iris, make it easier to develop acute glaucoma. Typically, this happens when the pupil is dilated and the lens is stick to the back of the iris. This prevents the aqueous humor from flowing through the pupil into the anterior chamber. Accumulation of fluid in the posterior chamber presses on the iris causing it to bulge outward and block the drainage angle completely. Acute angle-closure glaucoma is a medical emergency and requires immediate attention.

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