In reply
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.