J Korean Ophthalmol Soc.  1999 Jan;40(1):182-191.

The Difference of the Optic Disc Size Calculated Using a Modified Formula of an Ellipse from Those Obtained with Twelve Radii

• Cho JS
• Lee YJ
• Uhm KB

Abstract

The aim of this study was to compare optic disc size obtained using the two methods Color polaroid photographs of optic disc of 130 normal subjects and 174 patients with glaucoma were evaluated by means of computeraided morphometry. In the first method, the optic disc size were calculated by applying the modified formula of an ellipse, where area=pi/4xthe horizontal diameterxthe vertical diameter. In the second method, we obtained optic disc size [] using the twelve radii that were measured every 30 degrees. Magnification effects of the eye and camera were corrected in the two methods. The measurements of the optic disc area(2.49mm2), cup area(1.01mm2) and neuroretinal rim area (1.49mm2) by the first method were significantly(P<0.003, Wilcoxon signed -rank test) different from the measurements by the second method(2.48mm2, 1.03mm2, 1.45mm2, respectively) (the average difference; 0.05+/-0.05mm2, 0.05+/-0.05mm2, 0.07+/-0.06mm2,respectively). The mean error for the neuroretinal rim area was 4.2+/-3.3% in the normal group and 7.5+/-8.5% in the glaucoma group(P=0.005). It increased with decreasing neuroretinal rim area and increasing visual field defects. Thus the magnification corrected measurements of the horizontal and vertical diameters and the modified formula of an ellipse can be used for a quick approximate estimation of the optic disc size, but cannot replace more accurate method of optic disc measurements using twelve radii.

Keyword

Computer-aided morphometry; Glaucoma; Neuroretinal rim area; Optic disc

MeSH Terms

Glaucoma
Humans
Visual Fields