Glaucoma

D.F Garway-Heath, Consultant Ophthalmologist, Glaucoma Research Unit
Moorfields Eye Hospital, London

Glaucoma is the name given to a group of conditions in which the optic nerve is damaged at the back of the eye. The optic nerve damage causes patchy loss of vision that varies in severity from patient to patient. Without treatment, the loss of vision usually gets worse over the course of many months or several years.

The loss of vision in glaucoma is permanent, but with early treatment, the damage to vision can be minimised.

Glaucoma of some type is found in about 2% of the population over the age of 40. It can also affect children and young adults, although much less frequently. It is estimated that about 2.2 million people have raised pressure within their eyes or suffer from glaucoma in the UK alone with more than 70 million people affected across the world. In the developed world about half of those with glaucoma have the chronic form of the condition and in this group half remain undetected. People of African-Caribbean origin have about four times the risk of chronic glaucoma as whites.

All blood relations of chronic glaucoma patients must be regarded as at increased risk of glaucoma and those over the age of 35 should be sought and tested appropriately. If there are other risk factors in addition to the family history of the condition e.g. being of African Caribbean origin then testing from an even earlier age is recommended.

The treatment of glaucoma has undergone considerable change in recent years with new, more potent drugs available which have fewer side effects than the earlier medications. Surgical techniques have also improved and it is estimated that over 95% of those diagnosed with early glaucoma in the UK will retain useful sight for life.

Tragically, glaucoma is a chronic condition which usually affects both eyes, but produces few symptoms until the sufferer becomes aware of serious restriction in the field of vision or even loss of central vision in the worse eye, which is why early detection through screening during a routine eye examination is so important.

How the eye works
An introduction to the eye
Structure and function of the eye

The eye is shaped like a ball. Its tough white outer coat is called the sclera and its surface is covered by a thin skin (the conjunctiva). The outer coat is clear at the front of the eye. This area is called the cornea.

Figure 1.

Behind the cornea is the iris - the coloured part of the eye - with the pupil forming a hole in its centre (Figure 1) . The space between the cornea and the iris is filled with a clear fluid, called 'aqueous humour', which maintains the pressure in the eye (the intraocular pressure). The pressure is determined by a balance between the fluid entering and leaving the eye.

Aqueous humour is produced behind the iris by the ciliary body. It flows through the pupil and drains away at the angle between the cornea and iris (the drainage angle) (Figure 2).

Figure 2

The lens of the eye is suspended behind the pupil by fine ligaments from the ciliary body. The cornea and lens focus a picture of your surroundings on the retina, which is the light sensitive film that coats the inside of the eye. The picture of your surroundings is sent from the retina to the brain by nerve fibres, which derive from nerve cells in the retina. The optic nerve is formed by about one million of these nerve fibres collected together. The optic nerve starts at the back of the eye at the 'optic nerve head', which is also called the 'optic disc'.

Figure 3a

Figure 3b

The nerve fibres leave the eye through pores (holes) in the lamina cribrosa, a sieve-like structure in the optic nerve head. Blood vessels enter and leave the eye through the same structure. The nerve fibres form a rim around the edge of the optic nerve head (neuro-retinal rim), leaving a central depression (without nerve fibres) called the optic cup (Figure 3a and 3b).

Glaucoma causes nerve fibres to die and this results in loss of vision. As nerve fibres die, the neuro-retinal rim of the optic nerve head thins and the optic cup enlarges. This is called glaucomatous cupping (Figure 4).

Figure 4

The loss of nerve fibres is usually patchy. This patchy loss of nerve fibres gives rise to patchy loss of vision, in which some parts of the picture of your surroundings are less distinct than other parts. This loss of vision can be picked up with the visual field test.

Figure 5

The visual field test demonstrates the completeness of the field of vision. The normal visual field test shows that the field of vision is complete, except for a small patch called the 'blind spot' (Figure 5). The 'blind spot' is where the optic nerve enters the eye. The centre of the field of vision, where the lines cross, is the vision you use for reading vision and recognising people.

Figure 6

The visual field test from an eye with glaucoma demonstrates patches of damaged (indistinct or lost) vision in areas away from the reading vision (Figure 6). Repeating the visual field test, at intervals of months or years, enables the eye doctor to tell if the glaucoma is stable or getting worse (progressing).

Glaucoma is responsible wholly or in part for 13% of those on the blind register in England and Wales. It is the leading cause of preventable blindness in the UK.

D.F Garway-Heath, Consultant Ophthalmologist, Glaucoma Research Unit
Moorfields Eye Hospital, London

VOLUNTEERS REQUIRED

Volunteers with healthy eyes are required to take part in projects running at the Glaucoma Research Unit at Moorfields Eye Hospital NHS Trust.

Founded in 1804, Moorfields Eye Hospital in London is one of the leading centres for eye health in the world. Research projects undertaken by Moorfields are frequently carried out in conjunction with the Institute of Ophthalmology, the research facility based next to the main hospital. The Trust and the Institute have joint research strategies that focus on major causes of blindness.

The Glaucoma Research Unit is involved in clinical research into new and potentially important instruments that are used to detect and monitor glaucoma. Glaucoma is one of the leading causes of blindness in the developed world. In the UK, 1 in 50 people over 40 have this condition, and it becomes more frequent with greater age. Although glaucoma is not curable, blindness is preventable if it is diagnosed and treated early enough. Part of the research carried out at the Glaucoma Research Unit involves the evaluation of instruments that make measurements of the pressure of the eye, that image the optic nerve head at the back of the eye and that test the function of the optic nerve, all of which are altered in glaucoma. It is necessary to assess subjects that have healthy eyes in order to obtain the limits of normality.

If you are interested in taking part in one of the projects that are currently taking place at the GRU, or would like further information, please contact Aachal Kotecha at Moorfields Eye Hospital on 0207 566 2059/ 2117, or email Aachal.Kotecha@moorfields.nhs.uk

All studies will have the approval of the Local Research Ethics Committee and are undertaken at the main hospital in London.