What is glaucoma?
Glaucoma is an eye disease characterized by a gradual loss of nerve cells in the eye, often, but not always as a result of high pressure in the eye; a bad blood perfusion of the optic nerve may also play a role.
Untreated glaucoma may lead to blindness
The dead nerve cells of the eye cannot be replaced which means that the resulting vision loss is irreversible! Hence the importance of early detection and treatment of glaucoma before major loss of vision has occurred.
Glaucoma is an insidious and treacherous disease
People with glaucoma rarely notice any symptom until the disease is well advanced. There are two reasons for that: first, glaucoma does not cause any subjective complaint, such as eye pain or strain, and second, your visual acuity will be preserved until late in the disease process. You won’t be bothered by hazy vision and you will be able to discriminate the smallest details (reading vision) for a long period of time.
The damage caused by glaucoma starts as a slow but progressive shrinkage of the visual field outside the central zone of vision. The visual field is defined as the entire image our eye perceives when fixating a specific point in space. The fixation point and the small area surrounding it constitute the central visual field, an area that is spared until late in the disease process which explains why as a glaucoma patient you will retain reading vision for a long time. Glaucomatous damage will first occur in areas outside the central visual field and will progress very slowly, so slowly that you will not notice it. Moreover, defects in the visual field are not perceived as missing areas or black spots in the visual field, because our brain uses information from neighbouring healthy areas to fill in the defects. This compensation strategy will only fail in advanced disease when the brain no longer receives enough information from the eye to compensate for the large and profound defects in the visual field. At that point the eye has already lost a substantial amount of the visual field.
The photos show the image seen by a left eye. Below each photo is the corresponding visual field obtained by the ophthalmologist (see perimetry) . Visual field defects are shown as black areas. The normal visual field always displays a black spot, the so called blind spot which corresponds to the area where the optic nerve leaves the eye. This area is devoid of retinal tissue and hence there is no image formation at that spot. We are not aware of this blind spot because the brain fills in the defect as explained above. Likewise, the glaucoma patient will not notice visual field defects as the same compensation mechanism will operate. Therefore the patient with early glaucoma will not see the children crossing the road at his right ( middle photo) when he looks at the traffic in front of him (the 4 yellow dots indicate the point of fixation). He will not be aware of his visual field deficit. Even in more advanced gllaucoma the brain is still capable of producing an acceptable image, although the patient will miss a lot of detail without realizing it (right photo).
In the advanced stages of the disese, the the brain is no longer able to compensate for the loss of information and only then will the patient become aware of his serious handicap (lower photo).
In end stage disease the central visual field will also disappear leading to blindness. Glaucoma is a bilateral disease but the damage is often asymmetrical, more advanced in one eye than in the other.
Blindness from glaucoma is a preventable disease.
Your eye doctor has a wide range of therapeutic options to preserve your visual function and to stop further deterioration. This is why it is so crucial to detect glaucoma in an early stage before the advent of significant visual loss. A comprehensive examination by a qualified eye doctor is a must as it is the only reliable way to diagnose glaucoma.