Ultrasonography of the optic disc cup in discs of various sizes.
OBJECTIVE
The aim of the study was to evaluate the sensitivity of modern, eye-medicated B-scanners in detecting optic disc cups and to correlate the echographic measurements with an optical assessment. A secondary aim was to correlate the rim-to-rim diameter of the optic disc and the width of the retrobulbar optic nerve on standardised A-scan.


METHODS
A prospective study was conducted on 25 emmetropic subjects (50 eyes) with discs and cups of various sizes. They were examined optically by one observer using a high-magnification slit lamp and the 90 D Volk lens. Another observer measured the B-scan dimensions of the disc cups and the retrobulbar optic nerve. Data from the two observers were compared at the end of the study.


RESULTS
High resolution B-scan detected optic disc cups of 0.5 mm or larger in all cases. A statistically significant correlation was obtained between echographic measurements and both vertical optical cup disc diameters and cup disc (C:D) ratios (p < 0.0001). Large C:D ratios (0.6 or larger) but small rim-to-rim disc diameter were reported as 'small' on echography. No correlation was found between the measurement of retrobulbar nerve and the diameter of the vertical optical disc diameter.


CONCLUSIONS
Modern, eye-dedicated ultrasonographic scanners are capable of detecting optic disc cups of 0.5 mm or larger. As there is a normal variation in optic disc rim-to-rim diameter, and this cannot be measured using ultrasound, we suggest the reporting of a C:D ratio on the ultrasonography to be potentially misleading. Large disc cups are, however, easily seen and many are likely to be 'pathological'.
Winder
S
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Eye Clinic, Aberdeen Royal Infirmary, Foresterhill, UK.
Atta
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HR
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005901:Glaucoma / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009898:Optic Disk / Q000000981:diagnostic imaging*; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D016037:Single-Blind Method; D014463:Ultrasonography