perimetry

Perimetry is a diagnostic method used to map the functional extent of a patient’s visual field, measuring light sensitivity at multiple points around the central and peripheral retina. It helps identify scotomas (areas of visual loss) and other field defects that may result from retinal disease, optic neuropathies, or damage to the visual pathways.

Perimetry methods are broadly classified as static threshold perimetry and kinetic perimetry. Static threshold perimetry presents stationary light stimuli of varying brightness at fixed locations to determine threshold sensitivity, while kinetic perimetry uses moving stimuli of fixed brightness along the field border to delineate the field boundary. Automated systems (for example, Humphrey or Octopus) are common and typically use threshold strategies such as SITA.

Procedure and interpretation: The patient fixates a central point while stimuli are presented; responses indicate visibility. Reliability indices record fixation losses and erroneous responses (false positives/negatives). Results are shown as gray-scale or numerical sensitivity maps with patterns typical of glaucoma (arcuate defects, nasal steps), optic neuropathies, or chiasmal lesions.

Clinical applications: Perimetry is central to glaucoma management for detecting field loss and monitoring progression. It also aids evaluation of other ocular and neurologic disorders. Microperimetry maps macular sensitivity with fundus guidance. Common test patterns include 24-2, 30-2, and 10-2, chosen by suspected field extent.

Limitations: Results depend on fixation, attention, and test reliability; media opacities, cataracts, or poor cooperation can affect accuracy. Pediatric or cognitively impaired patients may require shorter tests or alternative methods. Perimetry is most informative when interpreted with structural tests and clinical findings.