The Nerve Fiber Analyzer (synonyms: GDx, GDX analysis, GDX Nerve Fiber Analyzer, GDX Optic Nerve Fiber Analysis, Retinal nerve fiber analysis, GDx) represents a diagnostic imaging technique in ophthalmology and is used to examine nerve fiber thickness at the retina (retina). The Nerve Fiber Analyzer is particularly important in the early detection of glaucoma, a disease associated with an increase in intraocular pressure.
The increase in intraocular pressure can be the result of either increased production or decreased outflow of aqueous humor. Furthermore, a distinction is made between acute glaucoma (sudden painful attack) and chronic glaucoma (frequently unnoticed increase in intraocular pressure). Untreated glaucoma can lead to visual field defects (reduced vision due to punctual defects in the visual field) in the long term, if it is not treated with a parasympathomimetic such as pilocarpine (improves aqueous humor outflow). The intraocular pressure is measured with the method of tonometry.
As a modern examination method, nerve fiber analysis offers the possibility of determining the thickness of the retinal nerve fibers as a computer-assisted procedure using laser technology. The importance of the Nerve Fiber Analyzer GDx continues to increase as:
- Nerve damage due to glaucoma can be detected much earlier than in perimetry (visual field determination), because visual field loss occurs only from a nerve fiber loss of about 25-30%.
- Papillary rim hemorrhage (bleeding in the area of the point where the individual nerve fibers of the eye join to form a common optic nerve) as a clear indication of glaucoma in the GDx be detected safely
- With this method also the distinction between on the one hand diffuse (distributed over a large area) and on the other hand locally circumscribed (limited to a small area) nerve fiber defects can be achieved.
Indications (areas of application)
- Follow-up inpatientswithglaucoma (glaucoma).
- Screening of people who are at high risk of developing glaucoma. People at particular risk are those with:
- Hypertension (high blood pressure)
- Increased intraocular pressure
- Genetic predisposition to glaucoma
- Myopia (nearsightedness) or hypermetropia (farsightedness).
- Diabetes mellitus (diabetes)
- Vasospasm (temporary and thus discontinuous occlusion of blood vessels in the eye due to increased sympathetic stimulation – stress response controlled by the autonomic nervous system – which may be associated with glaucoma development).
The procedure
The duration of the examination is only a few minutes. After the administration of atropine (pupil dilating eye drops), the patient sits facing the examiner and fixes flashing lines in the Nerve Fiber Analyzer. The thickness of the nerve fiber is then determined using a laser beam that is not visible to the patient. The measurement is displayed on a map, taking advantage of the birefringent characteristics of retinal fibers, allowing the fiber thickness to be mapped on the basis of color values in a two-dimensional image. Due to the physical properties, thick fibers appear lighter in the image than thin fibers. This is followed by a comparison with normal values stored in the computer.
The use of the Nerve Fiber Analyzer GDx is the first and only method in ophthalmology that allows the targeted measurement and assessment of the retinal nerve cell layer. Through the GDx, detection of glaucoma can be realized even before vision is impaired.