To the Editor Choi et al1 concluded that optic disc tilt, which they classified as a disc ovality (ratio between the longest and shortest disc diameters) greater than 1.30, appeared to be associated with bihemispheric retinal nerve fiber layer defects in patients with early glaucoma and that this association is a risk factor for glaucoma progression. To determine the disc dimensions, they traced the disc and peripapillary atrophy, which they refer to as beta zone peripapillary atrophy, with a mouse-driven cursor on the images. However, in looking at the color disc images of the 2 representative cases in their Figure 3, we believe there is a gray crescent in the optic nerve head2,3 of both discs, which the authors do not mention and apparently did not take into consideration in calculating the disc dimensions. In Figure 3A, the gray crescent is inferior from approximately the 4- to 8-o’clock positions and is encompassed by the faint white line of the scleral lip. In Figure 3B, the crescent is temporal from approximately the 12:30 to 5:30 positions. It can be appreciated by the change in curvature of the disc margin where it meets the crescent, especially in the inferior quadrant, and by faint segments of the scleral lip, especially near the 3-o’clock position, with apparent zones alpha and beta peripheral to the crescent. Using the mouse-driven method the authors describe, we presume the gray crescents were considered to be part of the peripapillary atrophy in calculating optic disc ovality. Because the gray crescent is located within the optic disc tissue, this would lead to inaccurate estimates of this measurement, upon which their observations and conclusions are based. Of course, the 2 cases that were selected as representative of the 136 eyes of 136 patients with glaucoma in their study may not be representative of the data set with regard to the presence of a gray crescent and might not materially alter their conclusions. Gray crescents in the optic disc are seen most commonly in persons of African heritage3 and less so in Asian populations.4 However, the authors may wish to review the remaining optic disc photographs for the presence of this finding to determine whether it affects their conclusions.
Allingham RR, Shields MB. Potential Effect of the Presence of Gray Crescent on Analysis of Optic Disc and Retinal Nerve Fiber Layer Defects. JAMA Ophthalmol. 2015;133(5):617–618. doi:10.1001/jamaophthalmol.2014.5329
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