Optic disc height measurement with the Zeiss 4-mirror contact lens and 78 dioptre lens compared

Measurements of optic disc diameter with the Zeiss 4-mirror contact lens and 78 dioptre (D) lens, made by projecting a slit-beam of known height onto the image of the disc, were compared with planimetric measurements in 30 eyes. The 78 D lens measurements were significantly larger than both the Zeiss lens and planimetric measurements (p < 0.0001 and p = 0.0047 respectively). The measurements using the Zeiss lens and planimetry did not differ significantly. Compared with planimetry, for the 24 eyes within 3 D of emmetropia, the correlation was greater for the Zeiss (r = 0.8591) than for the 78 D lens (r = 0.7148). The Zeiss lens also showed better agreement and less scatter of results compared with the 78 D lens (standard error of the mean +/- 0.0373 mm for the Zeiss and +/- 0.0418 mm for the 78 D lens). The Zeiss contact lens measurements of optic disc diameter show stronger correlation and better agreement with planimetry than measurements using a 78 D lens.