We thank Khanifar and colleagues for their letter regarding our article.1 Their comments are very timely and much appreciated given the recent emergence of high-resolution SD-OCT technologies, particularly for measuring the retinal ganglion cell layer.2,3 It is exciting and important that our ongoing investigations of visual function and OCT in MS now incorporate SD-OCT and will benefit from use of these new methods with respect to (1) greater resolution of images (10 μm vs 5 μm axial resolution, as pointed out by Khanifar and colleagues); (2) higher degrees of interrater and test-retest reliability of measurements in the eyes of persons with MS, as shown by 2 recent studies by our collaborative group4,5; and (3) reduced operator dependency of scan placement. Unlike TD-OCT, for which a single brand is available (OCT-3/Stratus OCT), there are already several manufacturers of SD-OCT. Several MS clinical trials have incorporated TD-OCT measures of retinal nerve fiber layer thickness and macular thickness and volume as exploratory outcomes; these trials will require continued evaluation of TD-OCT measurements, while careful consideration of differences between high-resolution and current technologies and their costs will have to be weighed for future MS trials.
Laura J. Balcer, Elliot M. Frohman, Peter A. Calabresi, Steven L. Galetta. Evaluating Retinal Abnormalities in Patients With Multiple Sclerosis—Reply. Arch Neurol. 2010;67(8):1035–1036. doi:10.1001/archneurol.2010.181