July 2017
Volume 58, Issue 9
Open Access
Letters to the Editor  |   July 2017
Biomechanical Responses of Lamina Cribrosa to Intraocular Pressure Change Assessed by Optical Coherence Tomography in Glaucoma Eyes
Author Affiliations & Notes
  • Gema Rebolleda
    Department of Ophthalmology, Hospital Universitario Ramón y Cajal, Madrid, Spain.
  • Laura Díez-Álvarez
    Department of Ophthalmology, Hospital Universitario Ramón y Cajal, Madrid, Spain.
  • Victoria de Juan
    Department of Ophthalmology, Hospital Universitario Ramón y Cajal, Madrid, Spain.
  • Francisco J. Muñoz-Negrete
    Department of Ophthalmology, Hospital Universitario Ramón y Cajal, Madrid, Spain.
Investigative Ophthalmology & Visual Science July 2017, Vol.58, 3376. doi:10.1167/iovs.17-22262
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      Gema Rebolleda, Laura Díez-Álvarez, Victoria de Juan, Francisco J. Muñoz-Negrete; Biomechanical Responses of Lamina Cribrosa to Intraocular Pressure Change Assessed by Optical Coherence Tomography in Glaucoma Eyes. Invest. Ophthalmol. Vis. Sci. 2017;58(9):3376. doi: 10.1167/iovs.17-22262.

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      © ARVO (1962-2015); The Authors (2016-present)

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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. 
References
Quigley H, Arora K, Idrees S, et al. Biomechanical responses of lamina cribrosa to intraocular pressure change assessed by optical coherence tomography in glaucoma eyes. Invest Ophthalmol Vis Sci. 2017; 58: 2566–2577.
Vianna JR, Lanoe VR, Quach J, et al. Serial changes in lamina cribrosa depth and neuroretinal parameters in glaucoma: impact of choroidal thickness [published online ahead of print April 28, 2017]. Ophthalmology. doi:10.1016/j.ophtha.2017.03.048.
Lee SH, Yu DA, Kim TW, Lee EJ, Girard MJ, Mari JM. Reduction of the lamina cribrosa curvature after trabeculectomy in glaucoma. Invest Ophthalmol Vis Sci. 2016; 57: 5006–5014.
Rhodes LA, Huisingh C, Johnstone J, et al. Peripapillary choroidal thickness variation with age and race in normal eyes. Invest Ophthalmol Vis Sci. 2015; 56: 1872–1879.
Tan CS, Ouyang Y, Ruiz H, Sadda SR. Diurnal variation of choroidal thickness in normal, healthy subjects measured by spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci. 2012; 53: 261–266.
Kara N, Baz O, Altan C, Satana B, Kurt T, Demirok A. Changes in choroidal thickness, axial length, and ocular perfusion pressure accompanying successful glaucoma filtration surgery. Eye. 2013; 27: 940–945.
Saeedi O, Pillar A, Jefferys J, et al. Change in choroidal thickness and axial length with change in intraocular pressure after trabeculectomy. Br J Ophthalmol. 2014; 98: 976–979.
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