We read with great interest the paper by Quigley et al.
1 investigating the change in anterior lamina cribrosa depth (LCD) before and after several intraocular pressure (IOP)-lowering procedures. They found that the LC can move either anteriorly or posteriorly with IOP decrease, and this change was greater with lower IOP.
Quantitative assessment of LCD depends on the reference plane from which the measurements are made, and it is significantly influenced by choroidal thickness (CT) when a Bruch's membrane opening (BMO) reference plane is used.
2,3
In the study by Quigley et al.,
1 the anterior LCD was assessed by reference to the position of BMO. The authors discuss in depth the variety of LC behaviors when IOP decreases and the factors related to LC position, but they did not mention the influence of CT on LCD measurements.
In eyes with a thick peripapillary choroid, the LCD would be overestimated even if the anterior surface of the LC remains at its original position without any deformation, and by contrast, it would be underestimated in eyes with a thin choroid. Supporting that, Vianna et al.
2 reported a significant choroidal thinning in most patients in whom anterior movement of the lamina occurred with BMO reference plane; they concluded that LCD should be measured from an anterior sclera reference plane to reduce the influence of CT changes.
CT is known to be variable among individuals, and it is influenced by several factors, including sex, race, age-related changes, diurnal variations, and blood pressure and IOP fluctuations.
4,5 Most relevant is that a significant thickening of peripapillary choroid has been reported after trabeculectomy using manual measurements by optical coherence tomography (OCT).
6,7
We performed a longitudinal prospective study to automatically measure the CT changes before and after deep sclerectomy (DS) in 39 patients with primary open-angle glaucoma (mean age: 72 ± 9.8 years; mean deviation: −11.7 ± 8.5 dB). The peripapillary CT (pCT) was assessed from a circumferential 3.4-mm-diameter section centered at the center of the optic nerve head, and the mean from the measurements at four peripapillary locations was calculated by swept-source OCT (DRI Triton, Topcon, Japan). All scans were performed between 8 and 10 AM before surgery, 1 week postoperatively, and 2 months after surgery by a single masked operator (VdJ). A significant choroidal thickening was found in the mean pCT 1 week and 2 months after surgery (P = 0.000 and P = 0.036, respectively) and in all four locations 1 week after surgery (P < 0.003) (Rebolleda G, et al., unpublished observations, 2017).
In the study by Quigley et al.,
1 a choroidal thickening following IOP decrease would increase the LCD measured from the BMO plane. However, the authors did not include CT measurements in their paper; therefore, we cannot know whether their results would have been modified based on this factor.