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

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.

Oculocardiac Reflex During Strabismus Surgery

We perfomed this study to evaluate the incidence of the oculocardiac reflex(OCR) and its difference relative to each extraocular muscles. In addition, preventive methods for oculocardiac reflex were also evaluated. From Febrary 1997 to January 1998, we examined the occurrence of the OCR of 65 patients who underwent strabismus surgery in 123 extraocular muscles under the general anesthesia. Those who showed severe OCR were prepared with retrobulbar injection of 1% lidocaine 2cc or 1% intravenous atropine and observed wheather OCR was prevented. The overall incidence of the OCR was 66.2% and there was no significant difference between the incidence in both eyes(p>0.999). The incidence in each of the extraocular muscles did not show statistically significance when the patients were prepared with preoperative intramuscular atropine(p=0.018). The incidence after intraoperative retrobulbar injection or intravenous atropine was decreased to 27.3% but was not statistically significant(p=0.34).