Procedure
- If the patient wears glasses, they should be worn during the examination.
- Give the patient the Amsler grid and ask them to keep it at reading distance.
- Ask the patient to loosely cover one eye with one hand.
- Instruct the patient to fixate on the white dot in the middle of the chart.
- Ask if they see the intersections of the lines on the chart in focus.
- Ask if the lines run in a straight line.
- Repeat this for the other eye.
If there is a defect of the central visual field, the patient will indicate that they do not see the intersections of the lines in focus. This will also be the case if the patient has undiagnosed astigmatism. In order to distinguish between the two disorders, ask the patient to fixate on the edge of the chart. The grid pattern is now located in the peripheral visual field. In the case of a central visual field defect, the patient will see the line pattern as being in focus. The lines will remain blurred if the patient has astigmatism.
Peripheral And Central Scotoma
Peripheral Scotoma
A defect that is localised in the peripheral part of the visual field is referred to as a peripheral scotoma. Patients find this an inconvenience particularly when driving. The cause of the defect lies in the peripheral retina, the nerve fibres that conduct information from this part of the retina or the corresponding part of the visual cerebral cortex.
Central Scotoma
The defect lies in the central part of the visual field. Patients with this symptom often have problems reading or carrying out other activities that require focusing. Colour vision is generally also affected. The cause of the defect lies in the macula lutea, the nerve fibres that conduct information from this part of the retina or the corresponding part of the visual cerebral cortex.
By using specific examination and a perimeter chart, the diagnosed defect can be mapped and identified. Examinations carried out with the confrontation method, can only give an approximation of the defect.