Targeted perimetry for mapping the shape of glaucomatous arcuate scotomata.

Purpose: Recent work has shown potential benefits for perimetry with dense spacing. To investigate the impact of normal inhomogeneity of perimetric sensitivity on perimetry with dense spacing, suprathreshold perimetry was used near the optic disc where shadows of blood vessels affect sensitivity in healthy eyes.

Methods: Three groups of participants were tested: 58 healthy older controls, 29 healthy younger controls and 18 patients with glaucoma. A Compass perimeter was operated with the Open Perimetry Interface, using custom software with three components: the first found the centre of the blind spot and assessed the general height, the second performed 'circle perimetry' with suprathreshold testing at 75 locations on three circles around the disc (radius 6°, 8° and 10°) and the third conducted adaptive 'high-density perimetry' to map scotomata. Suprathreshold contrasts were set to a chosen offset above mean normal contrast threshold, adjusted by the general height.

Results: Circle perimetry at different offsets in controls found that an offset of 5 dB was needed to keep the false positive rate below 5%. Test-retest measurements in controls found limits of agreement for general height were ±2.5 dB, and that reproducible defects on circle perimetry were at locations consistent with shadows of blood vessels. Circle perimetry and high-density perimetry with a small offset of 1 dB led to the appearance of artefactual arcuate defects in controls. Circle perimetry with an offset of 5 dB in 26 eyes of 18 patients with glaucoma found scotomata in 22 sectors of 16 eyes in 13 patients. High-density perimetry was performed with a 5 dB offset for 15 sectors in 12 of these eyes and confirmed arcuate defects in all cases.

Conclusions: Targeted perimetry identified arcuate perimetric defects but required an offset of 5 dB to have reasonable specificity. Suggestions are made for improving the performance of targeted perimetry.