HRT-3 Moorfields reference plane: effect on rim area repeatability and identification of progression

To assess the effect of the Moorfields Reference Plane on Heidelberg Retina Tomograph (HRT) rim area repeatability and its effect on progression rates using an event analysis.

The HRT reference plane (RP) defines structures above as "rim" and below as "cup." The Moorfields RP applies the Standard RP (located 50 microm posterior to the temporal disc margin) at baseline and maintains the distance between the Standard RP and the reference ring (located in the image periphery) for follow-up images. The Moorfields RP was applied to an HRT test-retest dataset, and rim area repeatability coefficients were calculated. Repeatability coefficients were compared between the Moorfields, Standard and 320 (located 320 microm posterior to the reference ring) RPs. The Moorfields RP was applied to HRT images from 198 ocular hypertensives, acquired over 6 years. HRT progression required rim area baseline/follow-up differences exceeding the repeatability coefficient in two or more sectors, with confirmation in at least one of two consecutive images. Field progression was assessed using Advanced Glaucoma Intervention Study criteria.

The Moorfields RP improved rim area repeatability compared with the Standard RP; repeatability was similar between the Moorfields and the 320 RP. The frequency of identified progression using Moorfields RP was 40% compared with 28% for the 320 RP. There was a greater percentage with concurrent field progression -15.1% (Moorfields RP) compared with 12.1% (320 RP).

Although rim area repeatability was similar using the 320 RP and the Moorfields RP, the latter resulted in greater rates of detection of change.