By Dr Ananya Mandal, MD
The normal eye is cased in the eyeball or the globe that lies in the orbit. This is filled with jelly like material called the vitreous humor. There are associated structures like:
Conjunctiva – the thin transparent cover in front of the eye.
The cornea that is transparent and allows light to pass.
Sclera - tough covering of the eyeball or the whites of the eyes.
The uvea middle layer covering of the eye ball with three parts including the pupil and the iris that act as light apertures, the ciliary body that regulates the pupillary opening and the choriod that is pigmented and nourishes the retina. The iris functions like the diaphragm of a camera. The iris contains muscles which control the size of the pupil and regulates the amount of light allowed to enter the eye.
The lens – the transparent crystalline non-cellular and hard lens that forms the image of the light onto the back of the eye or the retina. This lies behind the iris. It adjusts its shape and thickness to focus the image onto the retina.
The retina that forms the picture.
The optic nerve that carries the information to the brain and the brain “sees” the image.
The anterior chamber or front compartment of the eye that has the cornea in front and iris, pupil and the lens behind is filled with a watery fluid called the aqueous humor. This nourishes the cornea and the lens and provides them with oxygen and vital nutrients. The aqueous humor also functions to provide necessary pressure to help maintain the shape of the eye. This pressure is called the intraocular pressure (IOP).
Glaucoma describes a group of eye conditions that affect vision. It may affect both eyes and each eye may progress in a variable way. The primary feature of glaucoma is high IOP.
Glaucoma usually occurs if there is blockage in the drainage tubes (trabecular meshwork) within the eye. This prevents the flow and drainage of aqueous humour. This builds up pressure within the eye. High pressure within the eye leads to damage to the optic nerve and the nerve fibres from the retina. Glaucoma is the leading cause of blindness worldwide.
Types of glaucoma
There are four main types of glaucoma. These include:
Chronic open-angle glaucoma – this is the commonest type of glaucoma and develops very slowly.
Primary angle-closure glaucoma – this is a rare type and occurs slowly. This may also develop rapidly with a sudden, painful build-up of pressure in the eye.
Secondary glaucoma – This occurs after another trauma or disease condition. Secondary glaucoma may be seen after an eye injury or another eye condition such as uveitis.
Congenital glaucoma – This is rare and is seen at birth or develops shortly after birth.
Diagnosis of glaucoma
For diagnosis of glaucoma an instrument called the Tonometer is used to measure the pressure in the eye. Further tests are prescribed to check the visual field and the examination of the retina and optic nerve using ophthalmoscopy are prescribed.
Treatment of glaucoma
Glaucoma can be treated with eye drops containing medications. In some cases laser treatment or surgery is also used for treatment. If left untreated, glaucoma can cause visual impairment.
Prevention of glaucoma
Regular visits to the ophthalmologist for detection of early signs of glaucoma can help prevent worsening of glaucoma.
Epidemiology of glaucoma
Worldwide 12.5 million people are blind from glaucoma. In England around 480,000 people have chronic open-angle glaucoma. It is seen in about one in 50 people above 40 years old and one in 10 people above 75 years old among white Europeans. It is more common among people of black-African or black-Caribbean origins.
Acute angle-closure glaucoma may affect about one in 1,000 people in the white population. It is more common among those of Asian origin (1 in 100 population). There are over a million glaucoma-related hospital outpatient visits in England every year.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)