ABSTRACT
This chapter discusses the basic principles and the use of the Amsler grid. It presents the step-by-step process for undertaking practical procedures of the uniocular test by the Amsler grid and provides information on pearl. The disturbance in the ganglion cells (GC) position results in distortion of the perceived image – when GCs are disproportionately separated when compared with their V1 position (i.e. in retinal oedema), the image will appear pinched. Similarly, contraction of the spaces between them (i.e. in retinal fibrosis) causes straight lines to appear bent or curved. This phenomenon of metamorphopsia is assessed using the Amsler grids. Alignment aids are provided on some of the charts for patients with significant central scotomas, and both monochrome and coloured charts are available. It is a screening test, and, in most cases, the chart used is a box grid of black lines on a white background with a black central target.
