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Joseph L Demer, Robert A Clark, Soh Youn Suh, JoAnn Giaconi, Kouros Nouri-Mahdavi, Simon K. Law, Laura Bonelli, Anne L Coleman, Joseph Caprioli; Globe Retraction During Adduction Tethering of the Optic Nerve (ON) Occurs in Primary Open Angle Glaucoma (POAG) With and Without Elevated Intraocular Pressure (IOP). Invest. Ophthalmol. Vis. Sci. 2019;60(9):6174.
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ON head deformation in adduction (Suh et al. IOVS58:5015-5021, 2017) due to ON traction has been proposed as a risk factor for optic neuropathy in POAG (Demer, et al., IOVS, 58: 4114-4125, 2017). We used MRI to determine if similar globe retraction by ON sheath traction occurs in patients who have POAG regardless of IOP elevation.
47 normal control subjects and 36 patients with POAG underwent,surface coil, axial & quasi-coronalorbital MRI in target-controlled central gaze & mean 30° ab- & adduction. All patients with POAG were under medical and/or surgical treatment to reduce IOP to clinical target pressures. Maximum IOP with or without treatment did not exceed 20 mmHg in patients in 26 patients the lower IOP group (POAG-LP, average mean deviation -8.2±1.2 dB, SEM), but did exceed 21 mmHg pre-treatment in 10 patients in the higher IOP group (POAG-HP, average mean deviation -6.6±1.3 dB). ON area centroids in 2 mm thick planes permitted computation of minimum paths as a straightness index. Globe dimensions were determined from cross sections, and translations by centroid displacement. Generalized estimating equation analysis corrected for possible interocular correlations among individuals.
For all 3 subject groups, the ON was significantly straighter in adduction than central gaze & abduction (P<0.0005), but in central gaze the ON was more redundant than normal in both POAG groups (P<0.05). For adduction, the ON had 102.0%±0.1% of minimum path length versus 104.0%±0.3% in central gaze for POAG-LP, and 102.0%±0.2% of minimum path length versus 103.8%±0.4% in central gaze for POAG-HP, compared with 101.7%±0.1% versus 102.9%±0.2% for controls. During adduction, globes retracted similarly at 0.68±0.08 mm in POAG-LP and 0.74±0.08 mm in POAG-HP, both significantly more than 0.08±0.06 mm in controls (P<10-6). Generalized linear regression showed the effect of POAG on globe retraction in adduction to be highly significant in models controlling for age, globe size, & gender.
Although globe tethering of the ON & sheath are normal in adduction, adduction is associated withsignificantlygreater globe retraction in POAG irrespective of IOP. Traction in adduction may cause neuropathic mechanical overloading of the ON head & peripapillary sclera, and contribute to glaucomatous damage at all levels of IOP.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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