Lack of association between glaucoma and macular choroidal thickness measured with enhanced depth-imaging optical coherence tomography.

The pathogenesis of glaucomatous optic neuropathy (GON) remains enigmatic despite being investigated for decades. Even more puzzling is the mechanism behind normal-tension glaucoma (NTG). Increased intraocular pressure (IOP) is the major risk factor for primary open-angle glaucoma (POAG) and the benefit of lowering IOP has been well documented.1,2 However, the concept of NTG, coupled with evidence that elevated IOP is not always associated with GON and that oftentimes GON progresses after lowering IOP, challenges the mechanical pathogenetic theory based on elevated IOP. This has led to the theory that, in addition to elevated IOP, other factors may play an important role in glaucoma pathogenesis. Particularly worthy of note is the vascular/hemodynamic theory that considers GON as an ischemic injury resulting from diminished blood supply after reduced ocular blood flow at the level of lamina cribrosa.3–5 There has been increasing interest in investigating the role of the choroid in the pathogenesis of GON. Previous studies have found an association between GON and impaired choroidal circulation or blood flow to the ONH.6–8 In addition, a limited number of studies, mostly histologic, have investigated the association between glaucoma and choroidal thickness with inconsistent findings.9–13 High-frequency ultrasonography has been used to measure choroidal thickness in chick and primate eyes.14,15 However, concerns regarding the related high-energy dispersion make this technique unsafe for use on the human ocular posterior segment. Laser Doppler interferometry is another technique that has allowed measurement of axial length both in chicks and in humans and of choroidal thickness in chicks to be made more accurately than ultrasonography,16–18 but reports on such measurements of choroidal thickness in humans are unavailable. Partial coherence interferometry can also measure choroidal thickness in humans and animals, but its use is limited because of substantial intrasubject variability.19 Optical frequency domain imaging (OFDI), also known as swept source OCT, has been shown to provide high-resolution images of the choroid,20 but choroidal thickness has yet to be measured with this technique. In addition, OFDI has not been available for clinical use. Thus, despite considerable improvements in ocular posterior segment imaging, in vivo assessment of the choroid has remained difficult even with the advent of spectral domain (SD) OCT because of significant signal strength (SS) attenuation beyond the retinal pigment epithelium (RPE).21,22 Enhanced depth-imaging (EDI) OCT is a new method that uses low SS and low resolution but increased depth on conventional SD-OCT to acquire detailed cross-sectional images of the choroid and to measure its thickness.23,24 Initial publications of EDI OCT measurements demonstrate the thickness of the choroid to be greatest either subfoveally or temporally with a significant reduction closer to the optic nerve.23 The choroid also appears to get thinner with increasing age and axial length.25 Spaide26 recently defined a new clinical entity called age-related choroidal atrophy; interestingly, glaucoma was present in 6 of 17 (35.3%) of the patients. The purpose of our study was twofold: to compare choroidal thickness measured with EDI OCT in normal eyes, eyes with NTG, and those with POAG, and to determine the effect of age, sex, ethnicity, axial length, IOP, and glaucoma severity on choroidal thickness.