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Lynn Shi, C Gustavo De Moraes, Denis Weng, Rashmi Rajshekhar, Robert Ritch, Donald Hood; Determinants of inter-eye asymmetry in circumpapillary retinal nerve fiber layer (cpRNFL) thickness in healthy and glaucoma patients. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3989.
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To investigate the causes of inter-eye asymmetry in cpRNFL thickness in glaucoma patients and healthy controls.
Both eyes of 63 glaucoma patients and 33 healthy patients had swept-source OCT wide-field cube scans (9x12 mm, DRI-OCT, Topcon, Inc.). At least one eye of the glaucoma patients had a 24-2 mean deviation better than -6D. For each patient, the inter-eye variability (IEV) in cpRNFL was defined as IEV = 1/n Σ ni=1 (xi,a-xi,b)2, where n is the number of circumpapillary values, a and b are right and left eyes. IEV was calculated for the (i) global cpRNFL (GB), (ii) superior (SQ) and (iii) inferior (IQ) quadrants. For each, linear regression models with the following parameters were tested: intraocular pressure (IOP), central corneal thickness (CCT), the angle (DFA) and distance (DFD) between the optic disc center and the fovea, disc area (DA), and the angles between the optic disc center and the superior (SBV) and inferior blood vessels (IBV).
On average, GB, SQ, and IQ IEV values of the 33 healthy patients (376±197, 296±219, 279±350) were smaller than that of the 63 glaucoma patients (932±672, 485±477, 1014±1087; all P<0.05). Among healthy patients, the 7 parameters explained 32%, 36%, and 32% of inter-eye asymmetry for GB, SQ, and IQ, respectively. For the healthy patients, the significant predictors were SBV and IBV for GB; IOP, SBV, and IBV for SQ; and only IBV for IQ. For the 17 (27%) of 63 glaucoma patients with unilateral disease, 3 had widespread and 14 had local loss. For the 46 (73%) patients with bilateral disease, a similar inter-eye pattern of damage was seen in 29 patients (Fig. 1), while 17 others had damage of different degrees (Fig. 2). The 7 parameters explained 10%, 11%, and 7% of inter-eye asymmetry for GB, SQ, and IQ, respectively. CCT was a significant predictor for SQ, while none of the tested parameters was a significant, independent predictor of inter-eye asymmetry for GB and IQ.
Qualitatively, eyes in patients tended to have damage in the same location. Quantitatively, for the healthy patients, blood vessel angles (SBV and IBV) played the largest role in inter-eye differences. In glaucoma patients, one healthy eye or different degrees of glaucomatous damage were major causes of inter-eye asymmetry in cpRNFL thickness.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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