Abstract:
To evaluate the impact of optic disc diameter (ODD) on retinal nerve fiber layer thickness (RNFLT) for a given cup to disc ratio (CDR) as measured by optical coherence tomography (OCT.)
415 eyes of 210 consecutive patients received optic disc measurements using OCT. Parameters measured included cup–to–disc ratio (CDR), ODD, and RNFLT for each eye. Patients were first divided into groups based on CDR, then subdivided into three groups based on ODD: Small (less than 1.5 mm), medium (greater than 1.5mm and less than 2.2 mm) and large (greater than 2.2 mm.)
Patients with CDR greater than .4 and less than .5: Patients with small ODD had an RNFLT of 83.11 +/– 7.78, medium ODD had an RNFLT of 93.65 +/– 18.53, and large ODD had an RNFLT of 100.28 +/– 10.74.
Patients with CDR greater than .5 and less than .6: Patients with small ODD had an RNFLT of 81.22 +/– 12.68, medium ODD had an RNFLT of 94.85 +/– 12.70, and large ODD had an RNFLT of 106.62 +/– 45.63.
Patients with CDR greater than .6 and less than .7: Patients with small ODD had an RNFLT of 70.92 +/– 16.03, medium ODD had an RNFLT of 88.50 +/– 15.25, and large ODD had an RNFLT of 95.31 +/– 13.87.
Patients with CDR greater than .7 and less than .8: Patients with small ODD had an RNFLT of 67.83 +/– 4.38, medium ODD had an RNFLT of 78.63 +/– 14.06, and large ODD had an RNFLT of 89.54 +/– 22.49.
Patients with CDR greater than .8 and less than .9: Patients with small ODD had an RNFLT of 67.41 +/– 4.61, medium ODD had an RNFLT of 65.16 +/– 16.34, and large ODD had an RNFLT of 64.65 +/– 23.35
Patients with CDR greater than .9: Patients with small ODD had an RNFLT of 92.85, medium ODD had an RNFLT of 63.33 +/– 50.40, and large ODD had an RNFLT of 69.90 +/– 21.68.
For patients with CDR ranging from .4 to .8, there is a positive correlation between optic disc diameter and retinal nerve fiber thickness. This suggests that for a fixed CDR, increased ODD corresponds to thicker RNFLT. This relationship was not established for patients with CDR greater than .8. The severity of glaucomatous damage in these patients warrants a larger study population to discern if a subtle impact of ODD is present in this subgroup as well.