Neuroretinal rim assessment is an essential part of a glaucoma work-up, but it tends to be based on loose associations that lack specificity. Now Japanese researchers have developed a specific but significant formula for deciding if a patient’s rim areas indicate a risk for glaucoma. Those with a smaller neuroretinal rim area in the superior half disc, and a greater disc-fovea distance with greater superior and inferior half-rim areas, are more likely to develop various rick factors for glaucoma such as elevated IOP and thinner central corneal thicknesses (CCT).

The researchers looked into 3,762 Japanese residents who were 40 years and older. The subjects were given a detailed ocular examination, including sequential disc stereo photography. The researchers identified 2,474 normal eyes that met the inclusion criteria and analyzed their fundus photographs to measure the disc, rim and β-peripapillary atrophy (PPA) areas. Rims were divided into superior and inferior halves by a line connecting the fovea and disc center.

They found that the disc, the rim of the superior and inferior halves and β-PPA areas averaged 2.53mm²±0.50mm² (SD). After adjusting for other systemic and ocular factors such as age, disc and β-PPA areas, the researchers found the disc-fovea distance correlated positively while IOP and axial length correlated negatively with the rim areas of the superior and inferior halves, respectively. CCT and mean blood pressure correlated positively and male gender negatively, but only when measuring the rim of the superior half.