Comparison of Retinal Blood Flow Velocities in Normal Tension Glaucoma (NTG) and High Tension Glaucoma (HTG) using the Retinal Functional Imager (RFI)

Abstract

Purpose: : Numerous studies have attempted to evaluate ocular hemodynamics in HTG and NTG. We compared the retinal blood flow velocities between NTG and HTG patients using the RFI, which provides a novel non-invasive technique for measuring retinal blood flow velocity using high resolution direct imaging.

Methods: : Age-matched eyes with NTG (n=22) and HTG (n= 72) were evaluated using the RFI (Optical Imaging, Rehovot, Israel) at the New York Eye and Ear Infirmary. Glaucoma was defined by the presence of glaucomatous optic neuropathy and repeatable visual field abnormailities. All eyes had gonioscopically open angles and no secondary causes of glaucoma. Those patients with the above characteristics and a mean untreated intraocular pressure (IOP) consistently ≤21 mmHg on diurnal testing were labeled NTG. Those patients with untreated IOP >21 mmHg were diagnosed as having HTG. Blood flow velocity measurements in the central 35 degrees of the retinal circulation were obtained by averaging three or more RFI sessions from each eye by two operators

Results: : There were more women in the NTG group than in the HTG group (91% vs. 54%, p=0.002). Both groups had a similar mean age (62.3±11.5 vs. 62.7+15.4 yr, p=0.88), and the majority of patients in the NTG group were Caucasian (36%) compared to a Hispanic majority in the HTG group (53%) (p=0.003). Most patients were taking antiglaucoma medications (100% of NTG vs. 90% of HTG patients). The mean IOP in the NTG group was lower than that of the HTG group at the time of RFI analysis (15.5+4.6 vs. 12.0+2.8 mmHg p<0.001.) The NTG group had statistically significant higher average venous and arterial velocities than the HTG group (venous: 5.36+1.29 vs. 4.07+1.00 mm/sec, p=0.004, and arterial: 6.26+1.63 vs. 5.09+1.52 mm/sec, p=0.02).

Conclusions: : Unlike previous reports regarding the choroidal circulation, treated NTG eyes show faster retinal blood flow velocities than treated HTG eyes. Lower IOP values could be related with increased retinal blood flow velocities. Recent studies have proven that NTG eyes have narrower central retinal vessels than normals. The relationship between blood flow velocity and the caliber of retinal vessels between HTG and NTG warrant future investigation.

Keywords: imaging/image analysis: clinical • optic flow • blood supply