Aim-A study was designed to investigate whether measurements of the optic nerve diameter (OND) and cross sectional area (ONCSA), as measured by B-scan ultrasonography, are altered in glaucoma. The reproducibility and test-retest variability of echographic estimates of retrobulbar optic nerve dimensions was also tested. Methods-One eye of 49 glaucoma patients and 90 control subjects underwent five repeated echographic measurements of the maximal interpial diameter and cross sectional area of the orbital optic nerve on two separate occasions. All measurements were taken by one experienced ultrasonographer. Conclusion-Echographic measurements of the orbital optic nerve are highly reproducible and not subject to clinically meaningful test-retest variability. Optic nerve interpial diameter and cross sectional area are reduced in glaucomatous eyes, reflecting nerve fibre loss. This technique may be useful in distinguishing between normal and glaucomatous eyes where optic disc morphometry is inconclusive or impossible as a result of opaque media. (Br J Ophthalmol 1998;82:43-47) Visual impairment related to glaucomatous damage can only be prevented if the disease process is identified and treated early in its course. Perimetry, morphometric evaluation of the optic nerve head, and the results of tonometry all contribute to the final diagnosis of glaucoma. However, several factors may restrict the role of these functional and morphological variables in the assessment of the glaucoma suspect. These include opaque media, optic disc anomalies, and the physical and mental limitations of the patient. Furthermore, the possibility of ocular hypertension and low tension glaucoma confounds the usefulness of intraocular pressure measurements. Therefore, an objective method of assessing the glaucoma suspect, independent of IOP and optic nerve head morphometry, would be a useful addition to the current array of investigations.
Results-MeanTo date, however, the diagnostic potential of orbital optic nerve measurements in glaucoma has been restricted by the poor resolving power of B-scan ultrasound in the retrobulbar region.1 We used a new generation B scanner to measure orbital optic nerve dimensions in eyes with glaucoma and ocular hypertension, and compared the results with those of control subjects. We also calculated the reproducibility and test-retest variability of our readings, and investigated the eVect of other ocular and nonocular variables on optic nerve measurements.
Patients and methodsThe inclusion criteria for control subjects in this study were: a visual acuity of 6/9 or better in either eye; a myopic refractive error not exceeding −8.00 dioptres 2 ; and no demonstrable intraocular pathology. Most control subjects were patients attending the accident and emergency department of the Birmingham and Midland Eye Centre (BMEC) with external eye disease, and some were enrolled from the clinic staV.Forty nine glaucoma subjects attending the visual function department of the BMEC for field analysis were recruited. Of...
