Functional slit lamp biomicroscopy for imaging bulbar conjunctival microvasculature in contact lens wearers

Purpose: To develop, test and validate functional slit lamp biomicroscopy (FSLB) for generating non-invasive bulbar conjunctival microvascular perfusion maps (nMPMs) and assessing morphometry and hemodynamics. Methods: FSLB was adapted from a traditional slit-lamp microscope by attaching a digital camera to image the bulbar conjunctiva to create nMPMs and measure venular blood flow hemodynamics. High definition images with a large field of view were obtained on the temporal bulbar conjunctiva for creating nMPMs. A high imaging rate of 60 frames per second and an similar to 210x high magnification were achieved using the camera inherited high speed setting and Movie Crop Function, for imaging hemodynamics. Custom software was developed to segment bulbar conjunctival nMPMs for further fractal analysis and quantitatively measure blood vessel diameter, blood flow velocity and flow rate. Six human subjects were imaged before and after 6 h of wearing contact lenses. Monofractal and multifractal analyses were performed to quantify fractality of the nMPMs. Results: The mean bulbar conjunctival vessel diameter was 18.8 +/- 2.7 mu m at baseline and increased to 19.6 +/- 2.4 mu m after 6 h of lens wear (P = 0.020). The blood flow velocity was increased from 0.60 +/- 0.12 mm/s to 0.88 +/- 0.21 mm/s (P = 0.001). The blood flow rate was also increased from 129.8 +/- 59.9 pl/s to 207.2 +/- 81.3 pl/s (P = 0.001). Bulbar conjunctival nMPMs showed the intricate details of the bulbar conjunctival microvascular network. At baseline, fractal dimension was 1.63 +/- 0.05 and 1.71 +/- 0.03 analyzed by monofractal and multifractal analyses, respectively. Significant increases in fractal dimensions were found after 6 h of lens wear (P < 0.05). Conclusions: Microvascular network's fractality, morphometry and hemodynamics of the human bulbar conjunctiva can be measured easily and reliably using FSLB. The alternations of the fractal dimensions, morphometry and hemodynamics during contact lens wear may indicate ocular microvascular responses to contact lens wear. (c) 2014 Elsevier Inc. All rights reserved.