Glaucoma involves slowly progressive destruction of the uppermost layer of the retina, referred to as the nerve fibre layer. While the reasons for this disease are not yet known completely, increased pressure within the eye has been identified as a risk factor. Undetected progression of the disease can result in destruction of the optic nerve, ending in blindness.
There are three types of glaucoma:
- Open-angle glaucoma
Open-angle glaucoma usually occurs in older individuals. Accounting for 90% of all cases of glaucoma, it is the most common form of the disease. Drainage is blocked in the drainage angles of the eyes. While chamber fluid is unable to drain out of the anterior chamber of the eye evenly, it continues to be produced at a constant rate. As a result, the pressure within the eye slowly increases, even going unnoticed over a period of years. The constant mechanical pressure on the retina causes the slow death of the nerve fibres that lead to the optic nerve head. The glaucoma is then manifested by a hollowing of the optic nerve head due to neuronal death, along with gradual vision loss. This goes unnoticed by the patient, who does not become aware of the damage until the field of view has already become significantly restricted.
- Normal- or low-tension glaucoma
in patients with low-tension glaucoma, the nerve fibres also die slowly and gradually, although the pressure within the eye is within the normal range. In this case, it is assumed that low blood pressure prevents the sensory cells on the retina from getting an adequate supply of oxygen and nutrients. This deficiency causes the sensory cells to die and is responsible for the restricted field of view typical of glaucoma.
- Closed-angle glaucoma
In closed-angle glaucoma, the chamber angles at the sides of the anterior chamber are covered or blocked. This upsets the balance between chamber fluid production and drainage. The fluid is no longer able to drain off and collects in the anterior chamber. This leads to a sudden acute increase in the pressure in the eye. This sudden increase in pressure can cause pain, blurred vision and nausea and must be treated by an ophthalmologist immediately.
Possible examination methods: Tomography or mapping of the retinal surface (for instance, Heidelberg Retina Tomograph, HRT), optical coherence tomography (OCT) or 3-D mapping of the retinal structure (for example, SPECTRALIS), automated visual field testing (for example, Heidelberg Edge Perimeter, HEP)