Measurement variability of the bulbar conjunctival microvasculature in healthy subjects using functional slit lamp biomicroscopy (FSLB)

Abstract

The goal was to determine the variability of the quantitative measurement of the bulbar conjunctival microvascular morphology and hemodynamics by testing the repeatability and variation during office hours. Functional slit-lamp biomicroscopy (FSLB) was used to image the bulbar conjunctival microvasculature, including the vessel diameter, blood flow velocity/rate and fractal dimensions of the microvascular network. The temporal side of the bulbar conjunctiva in 20 healthy subjects was imaged. The subject was imaged at 9AM to test the measurement repeatability by two independent graders. The intraclass correlation coefficient (ICC) and coefficient of repeatability (CoR) were calculated. These same subjects were then imaged every two hours from 9AM to 5PM to test the variation during office hours. Custom software was used to semi-automatically process all measurements. The CoR% and ICC values between two graders for measuring the vessel diameter were 4.87% and 0.989, respectively. For the axial blood flow velocity, the CoR% and ICC were 11.49% and 0.997, respectively. From 9AM to 5PM, There were no significant variations in the vessel diameter and hemodynamics (P > 0.05). Whereas, the fractal dimensions of the non-invasive microvascular perfusion maps (nMPMs) were significantly increased at 3PM and 5PM compared with the baseline obtained at 9AM (P < 0.05). FSLB appears to be capable of measuring vessel diameter, blood flow velocity and fractal dimension of the microvascular network in the bulbar conjunctiva. Slight variations over office hours were observed in the microvascular network, while the blood flow velocity remained stable.

Inter-visit variability of conjunctival microvascular hemodynamic measurements in healthy and diabetic retinopathy subjects

“…Previous studies have reported intra-visit variability of conjunctival microvascular hemodynamics in healthy subjects (Khansari et al, 2016b; Xu et al, 2015). However, to our knowledge, inter-visit variability of conjunctival microvascular hemodynamics has not been reported in NC subjects.…”

“…Previous studies have reported inter-visit variability of blood flow in native arteriovenous fistula in chronic hemodialysis subjects and retinal vascular oxygen saturation in healthy subjects (O'Connell et al, 2014; Valek et al, 2008). In the conjunctiva, intra-visit variability of hemodynamics has been established within one or multiple sessions during a single day (Duench et al, 2007; Khansari et al, 2016b; Xu et al, 2015). Nevertheless, to the best of our knowledge, inter-visit variability of conjunctival microvascular hemodynamics was not reported previously.…”

Altered Bulbar Conjunctival Microcirculation in Response to Contact Lens Wear

“…Our previous study established that the FSLB can capture red blood cell (RBC)/RBC cluster movement, which allows the blood flow velocity and vessel diameter to be measured. 22, 24, 26 In the present study, MCF with a magnification of 210×, a field of view of 0.9 × 0.7 mm 2 , and an image size of 640 × 480 pixels was utilized. Three to six different locations ~1mm away from the limbus (Fig.…”

“…22, 24, 26 The software semi-automatically processed the video clips to yield vessel diameters, lengths, vessel covering areas, and velocities for all measureable venules. Only conjunctival venules were analyzed in this study for blood flow velocity because the conjunctival pre-capillary arteriole blood flow velocity can be impacted by the pulse.…”

Automated Real-Time Conjunctival Microvasculature Image Stabilization

“…These systems assess the conjunctival hemodynamics by analyzing image sequences captured at high frame rates and magnifications. High magnification imaging is achieved with either additional optics [1, 5, 11, 12] or modification of the telephoto zoom via camera settings [14–16]. Nevertheless, these optical imaging systems have not incorporated image stabilization instrumentation to remove eye motion artifacts, a necessary step for quantification of conjunctival hemodynamics.…”